Materials

21 pages, 13257 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Laser Beam Processing on the Properties of WC-Co Coatings Deposited on Steel

by Norbert Radek, Janusz Konstanty, Jacek Pietraszek, Łukasz J. Orman, Marcin Szczepaniak and Damian Przestacki

Materials 2021, 14(3), 538; https://doi.org/10.3390/ma14030538 - 23 Jan 2021

Cited by 35 | Viewed by 2061

Abstract

The main objective of the present work is to determine the effects of laser processing on properties of WC-Co electro-spark deposited (ESD) coatings on steel substrates. Tungsten carbide coatings have been applied to steel substrates using a manual electrode feeder, model EIL-8A. The [...] Read more.

The main objective of the present work is to determine the effects of laser processing on properties of WC-Co electro-spark deposited (ESD) coatings on steel substrates. Tungsten carbide coatings have been applied to steel substrates using a manual electrode feeder, model EIL-8A. The laser beam processing (LBP) of electro-spark coatings was performed using an Nd:YAG fiber laser. The microstructure and properties of laser treated/melted coatings were evaluated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), surface geometric structure (SGS) and roughness measurements and adhesion, microhardness, residual stresses, corrosion resistance and application tests. The obtained experimental data were subjected to statistical analysis and multidimensional numerical and visual exploratory techniques. It has been shown conclusively that the laser-treated ESD WC-Co coatings are characterized by lower microhardness, higher resistance to corrosion, increased roughness and better adhesion to the substrate. LBP homogenizes the chemical composition, refines the microstructure and heals microcracks and pores of ESD coatings. The laser treated ESD WC-Co coatings can be used in frictional sliding nodes (e.g., on the front seal rings used in pumps) and as protective layers. Full article

(This article belongs to the Special Issue Laser Treatment for Surface Layers)

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16 pages, 3807 KiB

Open AccessEditor’s ChoiceArticle

Sulfur Detection in Soil by Laser Induced Breakdown Spectroscopy Assisted by Multivariate Analysis

by Odhisea Gazeli, Dimitrios Stefas and Stelios Couris

Materials 2021, 14(3), 541; https://doi.org/10.3390/ma14030541 - 23 Jan 2021

Cited by 13 | Viewed by 2493

Abstract

Laser-induced breakdown spectroscopy (LIBS) is used for the detection and determination of sulfur content in some organic soil samples. The most suitable sulfur spectral lines for such tasks were found to occur in the vacuum ultraviolet (VUV) spectral region and they were used [...] Read more.

Laser-induced breakdown spectroscopy (LIBS) is used for the detection and determination of sulfur content in some organic soil samples. The most suitable sulfur spectral lines for such tasks were found to occur in the vacuum ultraviolet (VUV) spectral region and they were used for the construction of calibration curves. For the analysis, both univariate and multivariate statistical models were employed. The results obtained by the different analysis techniques are evaluated and compared. The present study demonstrates both the applicability and efficiency of LIBS for fast sulfur detection in soil matrices when aided by multivariate analysis methods improving the accuracy and extending the potential use of LIBS in such applications. Full article

(This article belongs to the Special Issue Materials Light Life)

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26 pages, 6372 KiB

Open AccessEditor’s ChoiceArticle

Warsaw Glacial Quartz Sand with Different Grain-Size Characteristics and Its Shear Wave Velocity from Various Interpretation Methods of BET

by Katarzyna Gabryś, Emil Soból, Wojciech Sas, Raimondas Šadzevičius and Rytis Skominas

Materials 2021, 14(3), 544; https://doi.org/10.3390/ma14030544 - 23 Jan 2021

Cited by 6 | Viewed by 1860

Abstract

After obtaining the value of shear wave velocity (V_S) from the bender elements test (BET), the shear modulus of soils at small strains (G_max) can be estimated. Shear wave velocity is an important parameter in the design [...] Read more.

After obtaining the value of shear wave velocity (V_S) from the bender elements test (BET), the shear modulus of soils at small strains (G_max) can be estimated. Shear wave velocity is an important parameter in the design of geo-structures subjected to static and dynamic loading. While bender elements are increasingly used in both academic and commercial laboratory test systems, there remains a lack of agreement when interpreting the shear wave travel time from these tests. Based on the test data of 12 Warsaw glacial quartz samples of sand, primarily two different approaches were examined for determining V_S. They are both related to the observation of the source and received BE signal, namely, the first time of arrival and the peak-to-peak method. These methods were performed through visual analysis of BET data by the authors, so that subjective travel time estimates were produced. Subsequently, automated analysis methods from the GDS Bender Element Analysis Tool (BEAT) were applied. Here, three techniques in the time-domain (TD) were selected, namely, the peak-to-peak, the zero-crossing, and the cross-correlation function. Additionally, a cross-power spectrum calculation of the signals was completed, viewed as a frequency-domain (FD) method. Final comparisons between subjective observational analyses and automated interpretations of BET results showed good agreement. There is compatibility especially between the two methods: the first time of arrival and the cross-correlation, which the authors considered the best interpreting techniques for their soils. Moreover, the laboratory tests were performed on compact, medium, and well-grained sand samples with different curvature coefficient and mean grain size. Investigation of the influence of the grain-size characteristics of quartz sand on shear wave velocity demonstrated that V_S is larger for higher values of the uniformity coefficient, while it is rather independent of the curvature coefficient and the mean grain size. Full article

(This article belongs to the Special Issue Testing of Materials and Elements in Civil Engineering)

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10 pages, 40221 KiB

Open AccessEditor’s ChoiceArticle

High-Temperature Oxidation Properties and Microstructural Evolution of Nanostructure Fe-Cr-Al ODS Alloys

by Zhengyuan Li, Lijia Chen, Haoyu Zhang and Siyu Liu

Materials 2021, 14(3), 526; https://doi.org/10.3390/ma14030526 - 22 Jan 2021

Cited by 4 | Viewed by 1901

Abstract

The oxidation behavior and microstructural evolution of the nanostructure of Fe-Cr-Al oxide dispersion strengthened (ODS) alloys prepared by spark plasma sintering were investigated by high-temperature oxidation experiments in air at 1200 °C for 100 h. The formation of Al₂O₃ scale [...] Read more.

The oxidation behavior and microstructural evolution of the nanostructure of Fe-Cr-Al oxide dispersion strengthened (ODS) alloys prepared by spark plasma sintering were investigated by high-temperature oxidation experiments in air at 1200 °C for 100 h. The formation of Al₂O₃ scale was observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) line scans. The oxidation rate of Fe-Cr-Al ODS alloys is lower than that of conventional Fe-Cr-Al alloys, and the oxide layer formed on the Fe-Cr-Al alloy appeared loose and cracked, whereas the oxide layer formed on the Fe-Cr-Al ODS alloys was adherent and flat. This is due to the high density of dispersed nano-oxides hindering the diffusion of Al element and the formation of vacancies caused by them. In addition, the nano-oxides could also adhere to the oxide layer. Besides, the microstructure of the Fe-Cr-Al ODS alloy had excellent stability during high-temperature oxidation. Full article

(This article belongs to the Special Issue High Temperature Corrosion of the Structural Materials and Degradation of Coatings in Harsh Conditions)

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16 pages, 5251 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Preliminary Evaluation of Cement Mortars Containing Waste Silt Optimized with the Design of Experiments Method

by Abbas Solouki, Giovanni Viscomi, Piergiorgio Tataranni and Cesare Sangiorgi

Materials 2021, 14(3), 528; https://doi.org/10.3390/ma14030528 - 22 Jan 2021

Cited by 9 | Viewed by 2173

Abstract

Every year, up to 3 billion tons of non-renewable natural aggregates are demanded by the construction sector and approximately 623 million tons of waste (mining and quarrying) was produced in 2018. Global efforts have been made to reduce the number of virgin aggregates [...] Read more.

Every year, up to 3 billion tons of non-renewable natural aggregates are demanded by the construction sector and approximately 623 million tons of waste (mining and quarrying) was produced in 2018. Global efforts have been made to reduce the number of virgin aggregates used for construction and infrastructure sectors. According to the revised waste framework directive in Europe, recycling at least 70% of construction and demolition waste materials by 2020 was obligatory for all member states. Nonetheless, quarries must work at full capacity to keep up with the demands, which has made quarry/mining waste management an important aspect during the past decades. Amongst the various recycling methods, quarry waste can be included in cement mortar mixtures. Thus, the current research focuses on producing cement mortars by partially substituting natural sand with the waste silt obtained from the limestone aggregate production in S.A.P.A.B.A. s.r.l. (Italy). A Design of Experiments (DOE) method is proposed to define the optimum mix design, aiming to include waste silt in cement mortar mixtures without affecting the final performance. Three cement mortar beams were produced and tested for each of the 49 randomized mixtures defined by the DOE method. The obtained results validate the design approach and suggest the possibility of substituting up to 20% of natural sand with waste silt in cement mortar mixtures. Full article

(This article belongs to the Collection Concrete and Building Materials)

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13 pages, 7349 KiB

Open AccessEditor’s ChoiceArticle

Multi-Stage Cold Forging Process for Manufacturing a High-Strength One-Body Input Shaft

by A Ra Jo, Myeong Sik Jeong, Sang Kon Lee, Young Hoon Moon and Sun Kwang Hwang

Materials 2021, 14(3), 532; https://doi.org/10.3390/ma14030532 - 22 Jan 2021

Cited by 15 | Viewed by 7743

Abstract

A multi-stage cold forging process was developed and complemented with finite element analysis (FEA) to manufacture a high-strength one-body input shaft with a long length body and no separate parts. FEA showed that the one-body input shaft was manufactured without any defects or [...] Read more.

A multi-stage cold forging process was developed and complemented with finite element analysis (FEA) to manufacture a high-strength one-body input shaft with a long length body and no separate parts. FEA showed that the one-body input shaft was manufactured without any defects or fractures. Experiments, such as tensile, hardness, torsion, and fatigue tests, and microstructural characterization, were performed to compare the properties of the input shaft produced by the proposed method with those produced using the machining process. The ultimate tensile strength showed a 50% increase and the torque showed a 100 Nm increase, confirming that the input shaft manufactured using the proposed process is superior to that processed using the machining process. Thus, this study provides a proof-of-concept for the design and development of a multi-stage cold forging process to manufacture a one-body input shaft with improved mechanical properties and material recovery rate. Full article

(This article belongs to the Special Issue Metal Forming: Fundamentals, Simulation and Applications)

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13 pages, 3355 KiB

Open AccessEditor’s ChoiceArticle

Nylon 6 Nanofiber Web-Based Signal Transmission Line Treated with PEDOT:PSS and DMSO Treatment

by Sungeun Shin, Eugene Lee and Gilsoo Cho

Materials 2021, 14(3), 498; https://doi.org/10.3390/ma14030498 - 21 Jan 2021

Cited by 3 | Viewed by 1870

Abstract

Highly conductive nylon 6 nanofiber webs, incorporating poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and dimethyl sulfoxide (DMSO), were prepared for textile-based signal transmission lines. To improve the electrical performance of the textiles, they were optimized by the number of coating cycles and the solvent treatment step. The [...] Read more.

Highly conductive nylon 6 nanofiber webs, incorporating poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and dimethyl sulfoxide (DMSO), were prepared for textile-based signal transmission lines. To improve the electrical performance of the textiles, they were optimized by the number of coating cycles and the solvent treatment step. The nanofiber web coated four times with PEDOT:PSS showed a six-times reduction in sheet resistance compared to that of once. In addition, the sample treated with both adding and dipping of DMSO showed a significant decrease of 83 times in sheet resistance compared to the sample without treatment of DMSO. Using samples with excellent electrical conductivity, the waveforms of the signal in the time domain were analyzed and shown to have an amplitude and phase almost identical to that of the conventional copper wire. As a result of the S21 characteristic curve, selected textiles were available up to the 15 MHz frequency bandwidth. In the FE-SEM image, it was observed that the surface of the coated sample was generally covered with PEDOT:PSS, which was distinguished from the untreated sample. These results demonstrate that the nanofiber web treated with the optimized conditions of PEDOT:PSS and DMSO can be applied as promising textile-based signal transmission lines for smart clothing. Full article

(This article belongs to the Special Issue Smart Textile Materials and Fabric-Based Wearable Devices)

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18 pages, 12367 KiB

Open AccessEditor’s ChoiceArticle

Ultrasonic Deposition of Carbon Nanotubes on Polycrystalline Cubic Boron Nitride Composites

by Manuela Pacella, Sina Saremi-Yarahmadi and Luciano Lamberti

Materials 2021, 14(3), 516; https://doi.org/10.3390/ma14030516 - 21 Jan 2021

Cited by 2 | Viewed by 2076

Abstract

Polycrystalline cubic boron nitride (PcBN) are super-hard materials with high hardness and excellent abrasive resistance, widely used in cutting tools for precision machining of automotive and aerospace parts; however, their brittle properties make them prone to premature failure. Coatings are often applied to [...] Read more.

Polycrystalline cubic boron nitride (PcBN) are super-hard materials with high hardness and excellent abrasive resistance, widely used in cutting tools for precision machining of automotive and aerospace parts; however, their brittle properties make them prone to premature failure. Coatings are often applied to PcBN to extend their range of applicability and durability. Conventional coating methods are limited to the thickness range of a few hundred nanometres, poor adhesion to the substrate, and limited stability under ambient conditions. To further the properties of PcBN composites, in this paper, we explore the use of ultrasonic bonding to apply thick coatings (30–80 μm) on PcBN cutting tools. For the first time, a multi-walled carbon nanotube (MWCNT) powder is preplaced on a PcBN substrate to allow an unconventional coating technique to take place. The effects of ultrasonic bonding parameters on the change of mechanical properties of the coated tools are investigated through scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), micro-hardness analyses, and white light interferometry. The structure of the carbon nanotubes is investigated through transmission electron microscopy (pre coating) and cross-section of the bonded MWCNTs is studied via focused ion beam milling and SEM to evaluate the bonding between the multi-walled nanotubes. Optimum processing windows (i.e., bonding speed, energy, and pressure) are discovered for coating MWCNTs on PcBN. Focus ion beam milling analyses revealed a relationship between consolidation parameters and porosity of MW(pCNT) bonds. The proposed method paves the way for the novel design of functional coatings with attunable properties (i.e., thickness and hardness) and therefore improved productivity in the machining of aerospace and automotive parts. Full article

(This article belongs to the Special Issue In Situ TEM and AFM for Investigation of Materials)

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21 pages, 6745 KiB

Open AccessEditor’s ChoiceArticle

A Mechanical Analysis of Chemically Stimulated Linear Shape Memory Polymer Actuation

by Hakan Dumlu, Axel Marquardt, Elias M. Zirdehi, Fathollah Varnik, Yucen Shen, Klaus Neuking and Gunther Eggeler

Materials 2021, 14(3), 481; https://doi.org/10.3390/ma14030481 - 20 Jan 2021

Cited by 9 | Viewed by 2222

Abstract

In the present work, we study the role of programming strain (50% and 100%), end loads (0, 0.5, 1.0, and 1.5 MPa), and chemical environments (acetone, ethanol, and water) on the exploitable stroke of linear shape memory polymer (SMP) actuators made from ESTANE [...] Read more.

In the present work, we study the role of programming strain (50% and 100%), end loads (0, 0.5, 1.0, and 1.5 MPa), and chemical environments (acetone, ethanol, and water) on the exploitable stroke of linear shape memory polymer (SMP) actuators made from ESTANE ETE 75DT3 (SMP-E). Dynamic mechanical thermal analysis (DMTA) shows how the uptake of solvents results in a decrease in the glass temperature of the molecular switch component of SMP-E. A novel in situ technique allows studying chemically triggered shape recovery as a function of time. It is found that the velocity of actuation decreases in the order acetone > ethanol > water, while the exploitable strokes show the inverse tendency and increases in the order water > ethanol > acetone. The results are interpreted on the basis of the underlying chemical (how solvents affect thermophysical properties) and micromechanical processes (the phenomenological spring dashpot model of Lethersich type rationalizes the behavior). The study provides initial data which can be used for micromechanical modeling of chemically triggered actuation of SMPs. The results are discussed in the light of underlying chemical and mechanical elementary processes, and areas in need of further work are highlighted. Full article

(This article belongs to the Special Issue Strong Coupling of Thermo-Chemical and Thermo-Mechanical States in Applied Materials)

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19 pages, 2015 KiB

Open AccessEditor’s ChoiceArticle

Insight into Thermal Stress Distribution and Required Reinforcement Reducing Early-Age Cracking in Mass Foundation Slabs

by Barbara Klemczak and Aneta Żmij

Materials 2021, 14(3), 477; https://doi.org/10.3390/ma14030477 - 20 Jan 2021

Cited by 11 | Viewed by 3575

Abstract

The heat released during cement hydration results in temperature-induced non-uniform volume changes in concrete structures. As a consequence, tensile thermal stresses of significant values may occur. The level of these stresses can be lowered by using various technological measures during the construction process [...] Read more.

The heat released during cement hydration results in temperature-induced non-uniform volume changes in concrete structures. As a consequence, tensile thermal stresses of significant values may occur. The level of these stresses can be lowered by using various technological measures during the construction process and a proper concrete mix composition. Nevertheless, the application of an appropriate reinforcement is a reliable method for controlling the width and spacing of possible cracks. The rules for calculating this reinforcement are not precisely detailed in the standards devoted to concrete structures. Additionally, the correct calculation of the reinforcement requires the identification of the tensile stress distribution in a mass slab. The presented study provides insight into stress distribution and relevant reinforcement for controlling early-age cracks of thermal origin. The existing standards and guidelines are discussed and clarified. The possible paths for calculating the reinforcement are proposed through the example of mass foundation slabs with different levels of external restraints. The results indicate a significant impact of the calculation method as well as the restraint conditions of the slab on the area of required reinforcement. Full article

(This article belongs to the Special Issue Masonry Structures and Reinforced Concrete Structures)

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9 pages, 2028 KiB

Open AccessEditor’s ChoiceArticle

Carbon Monoxide Oxidation over Gold Nanoparticles Deposited onto Alumina Film Grown on Mo(110) Substrate: An Effect of Charge Tunneling through the Oxide Film

by Tamerlan Magkoev

Materials 2021, 14(3), 485; https://doi.org/10.3390/ma14030485 - 20 Jan 2021

Cited by 1 | Viewed by 1348

Abstract

Formation of gold nanosized particles supported by aluminum oxide film grown on Mo(110) substrate and oxidation of carbon monoxide molecules on their surface have been in-situ studied in ultra-high vacuum by means of Auger electron spectroscopy (AES), reflection-absorption infrared spectroscopy (RAIRS), low energy [...] Read more.

Formation of gold nanosized particles supported by aluminum oxide film grown on Mo(110) substrate and oxidation of carbon monoxide molecules on their surface have been in-situ studied in ultra-high vacuum by means of Auger electron spectroscopy (AES), reflection-absorption infrared spectroscopy (RAIRS), low energy electron diffraction (LEED), atomic force microscopy (AFM), temperature-programmed desorption (TPD), and work function measurements. The main focus was to follow how the thickness of the alumina film influences the efficiency of CO oxidation in an attempt to find out evidence of the possible effect of electron tunneling between the metal substrate and the Au particle through the oxide interlayer. Providing the largest degree of surface identity of the studied metal/oxide system at different thicknesses of the alumina film (two, four, six, and eight monolayers), it was found that the CO oxidation efficiency, defined as CO₂ to CO TPD peaks intensity ratio, exponentially decays with the oxide film thickness growth. Taking into account the known fact that the CO oxidation efficiency depends on the amount of excess charge acquired by Au particle, the latter suggests that electron tunneling adds efficiency to the oxidation process, although not significantly. Full article

(This article belongs to the Special Issue Adsorption of Solid and Gaseous Surface)

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12 pages, 4041 KiB

Open AccessEditor’s ChoiceArticle

Acousto-Optic Cells with Phased-Array Transducers and Their Application in Systems of Optical Information Processing

by Vladimir Balakshy, Maxim Kupreychik, Sergey Mantsevich and Vladimir Molchanov

Materials 2021, 14(2), 451; https://doi.org/10.3390/ma14020451 - 18 Jan 2021

Cited by 11 | Viewed by 2702

Abstract

This paper presents the results of theoretical and experimental studies of anisotropic acousto-optic interaction in a spatially periodical acoustic field created by a phased-array transducer with antiphase excitation of adjacent sections. In this case, contrary to the nonsectioned transducer, light diffraction is absent [...] Read more.

This paper presents the results of theoretical and experimental studies of anisotropic acousto-optic interaction in a spatially periodical acoustic field created by a phased-array transducer with antiphase excitation of adjacent sections. In this case, contrary to the nonsectioned transducer, light diffraction is absent when the optical beam falls on the phased-array cell at the Bragg angle. However, the diffraction takes place at some other angles (called “optimal” here), which are situated on the opposite sides to the Bragg angle. Our calculations show that the diffraction efficiency can reach 100% at these optimal angles in spite of a noticeable acousto-optic phase mismatch. This kind of acousto-optic interaction possesses a number of interesting regularities which can be useful for designing acousto-optic devices of a new type. Our experiments were performed with a paratellurite (TeO₂) cell in which a shear acoustic mode was excited at a 9

^{\circ}

angle to the crystal plane (001). The piezoelectric transducer had to nine antiphase sections. The efficiency of electric to acoustic power conversion was 99% at the maximum frequency response, and the ultrasound excitation band extended from 70 to 160 MHz. The experiments have confirmed basic results of the theoretical analysis. Full article

(This article belongs to the Special Issue Acousto-Optical Spectral Technologies)

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24 pages, 5466 KiB

Open AccessEditor’s ChoiceArticle

Multi-Scale Analyses and Modeling of Metallic Nano-Layers

by Zara Moleinia and David F. Bahr

Materials 2021, 14(2), 450; https://doi.org/10.3390/ma14020450 - 18 Jan 2021

Cited by 2 | Viewed by 1635

Abstract

The current work centers on multi-scale approaches to simulate and predict metallic nano-layers’ thermomechanical responses in crystal plasticity large deformation finite element platforms. The study is divided into two major scales: nano- and homogenized levels where Cu/Nb nano-layers are designated as case studies. [...] Read more.

The current work centers on multi-scale approaches to simulate and predict metallic nano-layers’ thermomechanical responses in crystal plasticity large deformation finite element platforms. The study is divided into two major scales: nano- and homogenized levels where Cu/Nb nano-layers are designated as case studies. At the nano-scale, a size-dependent constitutive model based on entropic kinetics is developed. A deep-learning adaptive boosting technique named single layer calibration is established to acquire associated constitutive parameters through a single process applicable to a broad range of setups entirely different from those of the calibration. The model is validated through experimental data with solid agreement followed by the behavioral predictions of multiple cases regarding size, loading pattern, layer type, and geometrical combination effects for which the performances are discussed. At the homogenized scale, founded on statistical analyses of microcanonical ensembles, a homogenized crystal plasticity-based constitutive model is developed with the aim of expediting while retaining the accuracy of computational processes. Accordingly, effective constitutive functionals are realized where the associated constants are obtained via metaheuristic genetic algorithms. The model is favorably verified with nano-scale data while accelerating the computational processes by several orders of magnitude. Ultimately, a temperature-dependent homogenized constitutive model is developed where the effective constitutive functionals along with the associated constants are determined. The model is validated by experimental data with which multiple demonstrations of temperature effects are assessed and analyzed. Full article

(This article belongs to the Section Materials Simulation and Design)

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14 pages, 5626 KiB

Open AccessEditor’s ChoiceArticle

A Numerical Study of Geometry’s Impact on the Thermal and Mechanical Properties of Periodic Surface Structures

by Elzbieta Gawronska and Robert Dyja

Materials 2021, 14(2), 427; https://doi.org/10.3390/ma14020427 - 16 Jan 2021

Cited by 15 | Viewed by 2430

Abstract

The paper focuses on thermal and mechanical analysis of Periodic Surface Structure (PSS). PSS is a continuous surface with a specific topology that is mathematically formulated by geometric factors. Cubic P-surface (“primitive”), D-surface (“diamond”), and G-surface (“gyroid”) structures were simulated under load and [...] Read more.

The paper focuses on thermal and mechanical analysis of Periodic Surface Structure (PSS). PSS is a continuous surface with a specific topology that is mathematically formulated by geometric factors. Cubic P-surface (“primitive”), D-surface (“diamond”), and G-surface (“gyroid”) structures were simulated under load and heat transport using a numerical approach. We conducted our study by solving the stress and heat equations using the Finite Element Method (FEM). We achieved results using our software module, which generates PSS and simulates stress and temperature distribution. The stress model defined by dependence between stress and strain, gained from an experiment, and correlation of strain and displacement, gained from geometric conditions, was used in numerical experiments. The influence of geometric factors on the thermal and mechanical behavior of PSS was qualitatively determined. We showed decreasing effective stress values with an increased number of cells in the cubic domain for concerned PSS. It is important, because the increase in the number of cells does not increase the structure’s volume. Full article

(This article belongs to the Special Issue Manufacturing and Mechanics of Materials)

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12 pages, 3722 KiB

Open AccessEditor’s ChoiceArticle

Temperature-Dependent Stimulated Emission Cross-Section in Nd³⁺:YLF Crystal

by Giorgio Turri, Scott Webster, Michael Bass and Alessandra Toncelli

Materials 2021, 14(2), 431; https://doi.org/10.3390/ma14020431 - 16 Jan 2021

Cited by 8 | Viewed by 2358

Abstract

Spectroscopic properties of neodymium-doped yttrium lithium fluoride were measured at different temperatures from 35 K to 350 K in specimens with 1 at% Nd³⁺ concentration. The absorption spectrum was measured at room temperature from 400 to 900 nm. The decay dynamics of [...] Read more.

Spectroscopic properties of neodymium-doped yttrium lithium fluoride were measured at different temperatures from 35 K to 350 K in specimens with 1 at% Nd³⁺ concentration. The absorption spectrum was measured at room temperature from 400 to 900 nm. The decay dynamics of the ⁴F_3/2 multiplet was investigated by measuring the fluorescence lifetime as a function of the sample temperature, and the radiative decay time was derived by extrapolation to 0 K. The stimulated-emission cross-sections of the transitions from the ⁴F_3/2 to the ⁴I_9/2, ⁴I_11/2, and ⁴I_13/2 levels were obtained from the fluorescence spectrum measured at different temperatures, using the Aull–Jenssen technique. The results show consistency with most results previously published at room temperature, extending them over a broader range of temperatures. A semi-empirical formula for the magnitude of the stimulated-emission cross-section as a function of temperature in the 250 K to 350 K temperature range, is presented for the most intense transitions to the ⁴I_11/2 and ⁴I_13/2 levels. Full article

(This article belongs to the Section Materials Physics)

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14 pages, 1374 KiB

Open AccessEditor’s ChoiceArticle

Supersulfated Cement Applied to Produce Lightweight Concrete

by Liliya F. Kazanskaya, Olga M. Smirnova, Ángel Palomo, Ignacio Menendez Pidal and Manuel Romana

Materials 2021, 14(2), 403; https://doi.org/10.3390/ma14020403 - 15 Jan 2021

Cited by 17 | Viewed by 2366

Abstract

The physical and mechanical characteristics of expanded-clay lightweight concrete based on a supersulfated binder in comparison with lightweight concrete based on ordinary Portland cement were studied. In replacing CEM 32.5 with a supersulfated binder of 6000 cm²/g specific surface, one can [...] Read more.

The physical and mechanical characteristics of expanded-clay lightweight concrete based on a supersulfated binder in comparison with lightweight concrete based on ordinary Portland cement were studied. In replacing CEM 32.5 with a supersulfated binder of 6000 cm²/g specific surface, one can increase the tensile strength in bending up to 20% and can increase the ratio of the tensile strength in bending to the compressive strength that indicates the crack resistance increase of concrete. Compressive strengths at the age of 28 days were equal to 17.0 MPa and 16.6 MPa for the supersulfated binder of 3500 cm²/g specific surface and CEM 32.5, respectively. Shrinkage deformation of hardening concrete, indicators of fracture toughness, frost resistance, and thermal conductivity were determined during the experimental works. The coefficient of thermal conductivity decreased up to 12% compared to the use of CEM 32.5. An enhancement in concrete properties was associated with the increase of supersulfated binder fineness. Full article

(This article belongs to the Special Issue Recycled Concrete with Waste and By-Products)

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18 pages, 5605 KiB

Open AccessEditor’s ChoiceArticle

Flexible Phase Change Material Fiber: A Simple Route to Thermal Energy Control Textiles

by Yurong Yan, Weipei Li, Ruitian Zhu, Chao Lin and Rudolf Hufenus

Materials 2021, 14(2), 401; https://doi.org/10.3390/ma14020401 - 15 Jan 2021

Cited by 29 | Viewed by 3231

Abstract

A flexible hollow polypropylene (PP) fiber was filled with the phase change material (PCM) polyethylene glycol 1000 (PEG1000), using a micro-fluidic filling technology. The fiber’s latent heat storage and release, thermal reversibility, mechanical properties, and phase change behavior as a function of fiber [...] Read more.

A flexible hollow polypropylene (PP) fiber was filled with the phase change material (PCM) polyethylene glycol 1000 (PEG1000), using a micro-fluidic filling technology. The fiber’s latent heat storage and release, thermal reversibility, mechanical properties, and phase change behavior as a function of fiber drawing, were characterized. Differential scanning calorimetry (DSC) results showed that both enthalpies of melting and solidification of the PCM encased within the PP fiber were scarcely influenced by the constraint, compared to unconfined PEG1000. The maximum filling ratio of PEG1000 within the tubular PP filament was ~83 wt.%, and the encapsulation efficiencies and heat loss percentages were 96.7% and 7.65% for as-spun fibers and 93.7% and 1.53% for post-drawn fibers, respectively. Weak adherence of PEG on the inner surface of the PP fibers favored bubble formation and aggregating at the core–sheath interface, which led to different crystallization behavior of PEG1000 at the interface and in the PCM matrix. The thermal stability of PEG was unaffected by the PP encasing; only the decomposition temperature, corresponding to 50% weight loss of PEG1000 inside the PP fiber, was a little higher compared to that of pure PEG1000. Cycling heating and cooling tests proved the reversibility of latent heat release and storage properties, and the reliability of the PCM fiber. Full article

(This article belongs to the Special Issue Novel Synthetic Fibers for Textile Applications)

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26 pages, 6522 KiB

Open AccessEditor’s ChoiceArticle

Dynamic Response of Angle Ply Laminates with Uncertainties Using MARS, ANN-PSO, GPR and ANFIS

by Bharat Bhushan Mishra, Ajay Kumar, Jacek Zaburko, Barbara Sadowska-Buraczewska and Danuta Barnat-Hunek

Materials 2021, 14(2), 395; https://doi.org/10.3390/ma14020395 - 14 Jan 2021

Cited by 20 | Viewed by 2279

Abstract

In the present work, for the first time, free vibration response of angle ply laminates with uncertainties is attempted using Multivariate Adaptive Regression Spline (MARS), Artificial Neural Network-Particle Swarm Optimization (ANN-PSO), Gaussian Process Regression (GPR), and Adaptive Network Fuzzy Inference System (ANFIS). The [...] Read more.

In the present work, for the first time, free vibration response of angle ply laminates with uncertainties is attempted using Multivariate Adaptive Regression Spline (MARS), Artificial Neural Network-Particle Swarm Optimization (ANN-PSO), Gaussian Process Regression (GPR), and Adaptive Network Fuzzy Inference System (ANFIS). The present approach employed 2D C⁰ stochastic finite element (FE) model based on the Third Order Shear Deformation Theory (TSDT) in conjunction with MARS, ANN-PSO, GPR, and ANFIS. The TSDT model used eliminates the requirement of shear correction factor owing to the consideration of the actual parabolic distribution of transverse shear stress. Zero transverse shear stress at the top and bottom of the plate is enforced to compute higher-order unknowns. C⁰ FE model makes it commercially viable. Stochastic FE analysis done with Monte Carlo Simulation (MCS) FORTRAN inhouse code, selection of design points using a random variable framework, and soft computing with MARS, ANN-PSO, GPR, and ANFIS is implemented using MATLAB in-house code. Following the random variable frame, design points were selected from the input data generated through Monte Carlo Simulation. A total of four-mode shapes are analyzed in the present study. The comparison study was done to compare present work with results in the literature and they were found in good agreement. The stochastic parameters are Young’s elastic modulus, shear modulus, and the Poisson ratio. Lognormal distribution of properties is assumed in the present work. The current soft computation models shrink the number of trials and were found computationally efficient as the MCS-based FE modelling. The paper presents a comparison of MARS, ANN-PSO, GPR, and ANFIS algorithm performance with the stochastic FE model based on TSDT. Full article

(This article belongs to the Special Issue Dynamics and Application of Modern, Smart and Active Elements or Structures)

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17 pages, 5512 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Electrically Parallel Three-Element 980 nm VCSEL Arrays with Ternary and Binary Bottom DBR Mirror Layers

by Nasibeh Haghighi and James A. Lott

Materials 2021, 14(2), 397; https://doi.org/10.3390/ma14020397 - 14 Jan 2021

Cited by 7 | Viewed by 3300

Abstract

To meet the performance goals of fifth generation (5G) and future sixth generation (6G) optical wireless communication (OWC) and sensing systems, we seek to develop low-cost, reliable, compact lasers capable of sourcing 5–20 Gb/s (ideally up to 100 Gb/s by the 2030s) infrared [...] Read more.

To meet the performance goals of fifth generation (5G) and future sixth generation (6G) optical wireless communication (OWC) and sensing systems, we seek to develop low-cost, reliable, compact lasers capable of sourcing 5–20 Gb/s (ideally up to 100 Gb/s by the 2030s) infrared beams across free-space line-of-sight distances of meters to kilometers. Toward this end, we develop small arrays of electrically parallel vertical cavity surface emitting lasers (VCSELs) for possible future use in short-distance (tens of meters) free-space optical communication and sensing applications in, for example, homes, data centers, manufacturing spaces, and backhaul (pole-to-pole or pole-to-building) optical links. As a starting point, we design, grow by metal–organic vapor phase epitaxy, fabricate, test, and analyze 980 nm top-emitting triple VCSEL arrays. Via on-wafer high-frequency probe testing, our arrays exhibit record bandwidths of 20–25 GHz, optical output powers of 20–50 mW, and error-free data transmission at up to 40 Gb/s—all extremely well suited for the intended 5G short-reach OWC and sensing applications. We employ novel p-metal and top mesa inter-VCSEL connectors to form electrically parallel but optically uncoupled (to reduce speckle) arrays with performance exceeding that of single VCSELs with equal total emitting areas. Full article

(This article belongs to the Special Issue Photonic Materials and Devices)

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24 pages, 7734 KiB

Open AccessEditor’s ChoiceArticle

Penetration of Cement Pastes into Particle-Beds: A Comparison of Penetration Models

by Daniel Weger, Alexandre Pierre, Arnaud Perrot, Thomas Kränkel, Dirk Lowke and Christoph Gehlen

Materials 2021, 14(2), 389; https://doi.org/10.3390/ma14020389 - 14 Jan 2021

Cited by 12 | Viewed by 2228

Abstract

For the selective paste intrusion (SPI) method, thin layers of aggregate are locally bound by cement paste where the structure shall arise. After completion of the printing process, the structure is excavated from the particle-bed and the unbound particles are removed. However, for [...] Read more.

For the selective paste intrusion (SPI) method, thin layers of aggregate are locally bound by cement paste where the structure shall arise. After completion of the printing process, the structure is excavated from the particle-bed and the unbound particles are removed. However, for a sufficient layer bonding and shape accuracy, the rheology of the cement paste must be adapted to the flow resistance of the particle-bed. For practical application, that means mostly time and material consuming “trial and error” tests. To prevent that, analytical models can help to predict the penetration of the cement paste. This paper presents four analytical models to calculate the penetration depth of a cement paste into a particle packing. Based on Darcy’s law, an already existing model is slightly modified (model A+) and a generalized (model C), an advanced generalized (model D) as well as a simplified model (model B/B+) are developed. Compared to conducted tests on the penetration depth, model B showed good accuracy (deviation <1.5 mm) for pastes with a yield stress ≥8.2 Pa, model A+/B+/C for ≥ 5.4 Pa and model D even for <5.4 Pa. Finally, an application guide for each model for practical use will be given. Full article

(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)

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17 pages, 4801 KiB

Open AccessEditor’s ChoiceArticle

A Bio-Inspired Nanotubular Na₂MoO₄/TiO₂ Composite as a High-Performance Anodic Material for Lithium-Ion Batteries

by Bo Yu, Zehao Lin and Jianguo Huang

Materials 2021, 14(2), 357; https://doi.org/10.3390/ma14020357 - 13 Jan 2021

Cited by 2 | Viewed by 2107

Abstract

A train of bio-inspired nanotubular Na₂MoO₄/TiO₂ composites were synthesized by using a natural cellulose substance (e.g., commercial ordinary filter paper) as the structural template. The TiO₂ gel films were coated on the cellulose nanofiber surfaces via a [...] Read more.

A train of bio-inspired nanotubular Na₂MoO₄/TiO₂ composites were synthesized by using a natural cellulose substance (e.g., commercial ordinary filter paper) as the structural template. The TiO₂ gel films were coated on the cellulose nanofiber surfaces via a sol-gel method firstly, followed with the deposition of the poly(diallyldimethylammonium chloride)/Na₂MoO₄ (PDDA/Na₂MoO₄) bi-layers several times, through the layer-by-layer self-assembly route, yielding the (PDDA/Na₂MoO₄)_n/TiO₂-gel/cellulose composite, which was calcined in air to give various Na₂MoO₄/TiO₂ nanocomposites containing different Na₂MoO₄ contents (15.4, 24.1, and 41.4%). The resultant nanocomposites all inherited the three-dimensionally porous network structure of the premier cellulose substance, which were formed by hierarchical TiO₂ nanotubes anchored with the Na₂MoO₄ layers. When employed as anodic materials for lithium-ion batteries, those Na₂MoO₄/TiO₂ nanocomposites exhibited promoted electrochemical performances in comparison with the Na₂MoO₄ powder and pure TiO₂ nanotubes, which was resulted from the high capacity of the Na₂MoO₄ component and the buffering effects of the TiO₂ nanotubes. Among all the nanotubular Na₂MoO₄/TiO₂ composites, the one with a Na₂MoO₄ content of 41.4% showed the best electrochemical properties, such as the cycling stability with a capacity of 180.22 mAh g⁻¹ after 200 charge/discharge cycles (current density: 100 mA g⁻¹) and the optimal rate capability. Full article

(This article belongs to the Section Materials Chemistry)

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36 pages, 9269 KiB

Open AccessEditor’s ChoiceArticle

Advanced Constitutive Modeling of the Thixotropic Elasto-Visco-Plastic Behavior of Blood: Steady-State Blood Flow in Microtubes

by Konstantinos Giannokostas, Yannis Dimakopoulos, Andreas Anayiotos and John Tsamopoulos

Materials 2021, 14(2), 367; https://doi.org/10.3390/ma14020367 - 13 Jan 2021

Cited by 15 | Viewed by 2607

Abstract

The present work focuses on the in-silico investigation of the steady-state blood flow in straight microtubes, incorporating advanced constitutive modeling for human blood and blood plasma. The blood constitutive model accounts for the interplay between thixotropy and elasto-visco-plasticity via a scalar variable that [...] Read more.

The present work focuses on the in-silico investigation of the steady-state blood flow in straight microtubes, incorporating advanced constitutive modeling for human blood and blood plasma. The blood constitutive model accounts for the interplay between thixotropy and elasto-visco-plasticity via a scalar variable that describes the level of the local blood structure at any instance. The constitutive model is enhanced by the non-Newtonian modeling of the plasma phase, which features bulk viscoelasticity. Incorporating microcirculation phenomena such as the cell-free layer (CFL) formation or the Fåhraeus and the Fåhraeus-Lindqvist effects is an indispensable part of the blood flow investigation. The coupling between them and the momentum balance is achieved through correlations based on experimental observations. Notably, we propose a new simplified form for the dependence of the apparent viscosity on the hematocrit that predicts the CFL thickness correctly. Our investigation focuses on the impact of the microtube diameter and the pressure-gradient on velocity profiles, normal and shear viscoelastic stresses, and thixotropic properties. We demonstrate the microstructural configuration of blood in steady-state conditions, revealing that blood is highly aggregated in narrow tubes, promoting a flat velocity profile. Additionally, the proper accounting of the CFL thickness shows that for narrow microtubes, the reduction of discharged hematocrit is significant, which in some cases is up to 70%. At high pressure-gradients, the plasmatic proteins in both regions are extended in the flow direction, developing large axial normal stresses, which are more significant in the core region. We also provide normal stress predictions at both the blood/plasma interface (INS) and the tube wall (WNS), which are difficult to measure experimentally. Both decrease with the tube radius; however, they exhibit significant differences in magnitude and type of variation. INS varies linearly from 4.5 to 2 Pa, while WNS exhibits an exponential decrease taking values from 50 mPa to zero. Full article

(This article belongs to the Special Issue Rheology of Advanced Complex Fluids)

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19 pages, 613 KiB

Open AccessEditor’s ChoiceReview

Evolution of the Study of Phase Diagram of Binary and Ternary Mixtures Involving Fatty Acid Esters

by Gabriel Rubio-Pérez, Natalia Muñoz-Rujas, Fernando Aguilar, Rebecca Ravotti, Lukas Müller and Eduardo Montero

Materials 2021, 14(2), 369; https://doi.org/10.3390/ma14020369 - 13 Jan 2021

Cited by 4 | Viewed by 4201

Abstract

Interest in phase change materials keeps on rising as thermal energy storage grows in popularity in the scientific community as a promising complement for renewable energies in the future. Extending the possibilities beyond pure compounds, the use of mixtures (especially eutectics) widens the [...] Read more.

Interest in phase change materials keeps on rising as thermal energy storage grows in popularity in the scientific community as a promising complement for renewable energies in the future. Extending the possibilities beyond pure compounds, the use of mixtures (especially eutectics) widens the range of suitable phase change materials (PCM) available in the market. However, a precise knowledge of the mixtures’ phase behavior is required, making phase diagrams the most appropriate tools to follow. The aim of this work is to collect and analyze published literature concerning the phase diagrams of fatty acid esters mixtures, which constitute promising candidates as PCM due to their attractive properties, such as high latent heat, chemical stability and the possibility of extracting them from vegetable and animal oils. The topic appears as a still open scientific field, where further studies need to be performed to complete, complement and perfect the currently available information. Full article

(This article belongs to the Special Issue Phase Change Materials for Thermal Energy Storage)

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14 pages, 2167 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Encapsulation on Crack-Based Wrinkled Thin Film Soft Strain Sensors

by Thao Nguyen, Michael Chu, Robin Tu and Michelle Khine

Materials 2021, 14(2), 364; https://doi.org/10.3390/ma14020364 - 13 Jan 2021

Cited by 10 | Viewed by 2838

Abstract

Practical wearable applications of soft strain sensors require sensors capable of not only detecting subtle physiological signals, but also of withstanding large scale deformation from body movement. Encapsulation is one technique to protect sensors from both environmental and mechanical stressors. We introduced an [...] Read more.

Practical wearable applications of soft strain sensors require sensors capable of not only detecting subtle physiological signals, but also of withstanding large scale deformation from body movement. Encapsulation is one technique to protect sensors from both environmental and mechanical stressors. We introduced an encapsulation layer to crack-based wrinkled metallic thin film soft strain sensors as an avenue to improve sensor stretchability, linear response, and robustness. We demonstrate that encapsulated sensors have increased mechanical robustness and stability, displaying a significantly larger linear dynamic range (~50%) and increased stretchability (260% elongation). Furthermore, we discovered that these sensors have post-fracture signal recovery. They maintained conductivity to the 50% strain with stable signal and demonstrated increased sensitivity. We studied the crack formation behind this phenomenon and found encapsulation to lead to higher crack density as the source for greater stretchability. As crack formation plays an important role in subsequent electrical resistance, understanding the crack evolution in our sensors will help us better address the trade-off between high stretchability and high sensitivity. Full article

(This article belongs to the Special Issue Advanced Strain and Deformation Sensing Materials and Applications)

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3 pages, 192 KiB

Open AccessEditor’s ChoiceEditorial

Advances in Elastomers

by Michal Sedlačík

Materials 2021, 14(2), 348; https://doi.org/10.3390/ma14020348 - 12 Jan 2021

Cited by 3 | Viewed by 2133

Abstract

Elastomer materials are characteristic for their high elongation and (entropy) elasticity, which makes them indispensable for widespread applications in various engineering areas, medical applications or consumer goods [...] Full article

(This article belongs to the Special Issue Advances in Elastomers)

32 pages, 7428 KiB

Open AccessEditor’s ChoiceReview

Palm Oil Fuel Ash-Based Eco-Efficient Concrete: A Critical Review of the Short-Term Properties

by Mugahed Amran, Gunasekaran Murali, Roman Fediuk, Nikolai Vatin, Yuriy Vasilev and Hakim Abdelgader

Materials 2021, 14(2), 332; https://doi.org/10.3390/ma14020332 - 11 Jan 2021

Cited by 57 | Viewed by 4595

Abstract

The huge demand for concrete is predicted to upsurge due to rapid construction developments. Environmental worries regarding the large amounts of carbon dioxide emanations from cement production have resulted in new ideas to develop supplemental cementing materials, aiming to decrease the cement volume [...] Read more.

The huge demand for concrete is predicted to upsurge due to rapid construction developments. Environmental worries regarding the large amounts of carbon dioxide emanations from cement production have resulted in new ideas to develop supplemental cementing materials, aiming to decrease the cement volume required for making concrete. Palm-oil-fuel-ash (POFA) is an industrial byproduct derived from palm oil waste’s incineration in power plants’ electricity generation. POFA has high pozzolanic characteristics. It is highly reactive and exhibits satisfactory micro-filling ability and unique properties. POFA is commonly used as a partially-alternated binder to Portland cement materials to make POFA-based eco-efficient concrete to build building using a green material. This paper presents a review of the material source, chemical composition, clean production and short-term properties of POFA. A review of related literature provides comprehensive insights into the potential application of POFA-based eco-efficient concrete in the construction industry today. Full article

(This article belongs to the Collection Concrete and Building Materials)

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15 pages, 11464 KiB

Open AccessEditor’s ChoiceArticle

On the Size Effect of Additives in Amorphous Shape Memory Polymers

by Elias M. Zirdehi, Hakan Dumlu, Gunther Eggeler and Fathollah Varnik

Materials 2021, 14(2), 327; https://doi.org/10.3390/ma14020327 - 10 Jan 2021

Cited by 4 | Viewed by 1986

Abstract

Small additive molecules often enhance structural relaxation in polymers. We explore this effect in a thermoplastic shape memory polymer via molecular dynamics simulations. The additive-to-monomer size ratio is shown to play a key role here. While the effect of additive-concentration on the rate [...] Read more.

Small additive molecules often enhance structural relaxation in polymers. We explore this effect in a thermoplastic shape memory polymer via molecular dynamics simulations. The additive-to-monomer size ratio is shown to play a key role here. While the effect of additive-concentration on the rate of shape recovery is found to be monotonic in the investigated range, a non-monotonic dependence on the size-ratio emerges at temperatures close to the glass transition. This work thus identifies the additives’ size to be a qualitatively novel parameter for controlling the recovery process in polymer-based shape memory materials. Full article

(This article belongs to the Special Issue Strong Coupling of Thermo-Chemical and Thermo-Mechanical States in Applied Materials)

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10 pages, 1565 KiB

Open AccessEditor’s ChoiceArticle

Printable Gel Polymer Electrolytes for Solid-State Printed Supercapacitors

by Myeong-Lok Seol, Inho Nam, Ellie Sadatian, Nabanita Dutta, Jin-Woo Han and M. Meyyappan

Materials 2021, 14(2), 316; https://doi.org/10.3390/ma14020316 - 9 Jan 2021

Cited by 8 | Viewed by 2943

Abstract

Supercapacitors prepared by printing allow a simple manufacturing process, easy customization, high material efficiency and wide substrate compatibility. While printable active layers have been widely studied, printable electrolytes have not been thoroughly investigated despite their importance. A printable electrolyte should not only have [...] Read more.

Supercapacitors prepared by printing allow a simple manufacturing process, easy customization, high material efficiency and wide substrate compatibility. While printable active layers have been widely studied, printable electrolytes have not been thoroughly investigated despite their importance. A printable electrolyte should not only have high ionic conductivity, but also proper viscosity, small particle size and chemical stability. Here, gel-polymer electrolytes (GPE) that are compatible with printing were developed and their electrochemical performance was analyzed. Five GPE formulations based on various polymer-conductive substance combinations were investigated. Among them, GPE made of polyvinylidene difluoride (PVDF) polymer matrix and LiClO₄ conductive substance exhibited the best electrochemical performance, with a gravimetric capacitance of 176.4 F/g and areal capacitance of 152.7 mF/cm² at a potential scan rate of 10 mV/s. The in-depth study of the in-plane solid-state supercapacitors based on various printed GPEs suggests that printable electrolytes provide desirable attributes for high-performance printed energy devices such as supercapacitors, batteries, fuel cells and dye-sensitized solar cells. Full article

(This article belongs to the Special Issue Materials Design for Energy Conversion and Storage)

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26 pages, 4585 KiB

Open AccessEditor’s ChoiceReview

Properties and Classification of Diamond-Like Carbon Films

by Naoto Ohtake, Masanori Hiratsuka, Kazuhiro Kanda, Hiroki Akasaka, Masanori Tsujioka, Kenji Hirakuri, Atsushi Hirata, Tsuguyori Ohana, Hiroshi Inaba, Makoto Kano and Hidetoshi Saitoh

Materials 2021, 14(2), 315; https://doi.org/10.3390/ma14020315 - 9 Jan 2021

Cited by 90 | Viewed by 8433

Abstract

Diamond-like carbon (DLC) films have been extensively applied in industries owing to their excellent characteristics such as high hardness. In particular, there is a growing demand for their use as protective films for mechanical parts owing to their excellent wear resistance and low [...] Read more.

Diamond-like carbon (DLC) films have been extensively applied in industries owing to their excellent characteristics such as high hardness. In particular, there is a growing demand for their use as protective films for mechanical parts owing to their excellent wear resistance and low friction coefficient. DLC films have been deposited by various methods and many deviate from the DLC regions present in the ternary diagrams proposed for sp³ covalent carbon, sp² covalent carbon, and hydrogen. Consequently, redefining the DLC region on ternary diagrams using DLC coatings for mechanical and electrical components is urgently required. Therefore, we investigate the sp³ ratio, hydrogen content, and other properties of 74 types of amorphous carbon films and present the classification of amorphous carbon films, including DLC. We measured the sp³ ratios and hydrogen content using near-edge X-ray absorption fine structure and Rutherford backscattering-elastic recoil detection analysis under unified conditions. Amorphous carbon films were widely found with nonuniform distribution. The number of carbon atoms in the sp³ covalent carbon without bonding with hydrogen and the logarithm of the hydrogen content were inversely proportional. Further, we elucidated the DLC regions on the ternary diagram, classified the amorphous carbon films, and summarized the characteristics and applications of each type of DLC. Full article

(This article belongs to the Special Issue DLC (Diamond-Like Carbon) Film Formation and Application)

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20 pages, 1744 KiB

Open AccessEditor’s ChoiceArticle

Development and Validation of Optical Methods for Zeta Potential Determination of Silica and Polystyrene Particles in Aqueous Suspensions

by Yannic Ramaye, Marta Dabrio, Gert Roebben and Vikram Kestens

Materials 2021, 14(2), 290; https://doi.org/10.3390/ma14020290 - 8 Jan 2021

Cited by 12 | Viewed by 2504

Abstract

Zeta potential is frequently used to examine the colloidal stability of particles and macromolecules in liquids. Recently, it has been suggested that zeta potential can also play an important role for grouping and read-across of nanoforms in a regulatory context. Although the measurement [...] Read more.

Zeta potential is frequently used to examine the colloidal stability of particles and macromolecules in liquids. Recently, it has been suggested that zeta potential can also play an important role for grouping and read-across of nanoforms in a regulatory context. Although the measurement of zeta potential is well established, only little information is reported on key metrological principles such as validation and measurement uncertainties. This contribution presents the results of an in-house validation of the commonly used electrophoretic light scattering (ELS) and the relatively new particle tracking analysis (PTA) methods. The performance characteristics were assessed by analyzing silica and polystyrene reference materials. The ELS and PTA methods are robust and have particle mass working ranges of 0.003 mg/kg to 30 g/kg and 0.03 mg/kg to 1.5 mg/kg, respectively. Despite different measurement principles, both methods exhibit similar uncertainties for repeatability (2%), intermediate precision (3%) and trueness (4%). These results confirm that the developed methods can accurately measure the zeta potential of silica and polystyrene particles and can be transferred to other laboratories that analyze similar types of samples. If direct implementation is impossible, the elaborated methodologies may serve as a guide to help laboratories validating their own methods. Full article

(This article belongs to the Special Issue Nanomaterial Characterization Methods: Leaping Towards Validation)

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20 pages, 4912 KiB

Open AccessEditor’s ChoiceArticle

Development of a Model of Crack Propagation in Multilayer Hard Coatings under Conditions of Stochastic Force Impact

by Alexey Vereschaka, Sergey Grigoriev, Anatoli Chigarev, Filipp Milovich, Nikolay Sitnikov, Nikolay Andreev, Catherine Sotova and Jury Bublikov

Materials 2021, 14(2), 260; https://doi.org/10.3390/ma14020260 - 7 Jan 2021

Cited by 11 | Viewed by 1807

Abstract

The article deals with the problems of cracking in the structure of multilayered coatings under the conditions of stochastic loading process. A mathematical model has been proposed in order to predict the crack propagation velocity in the coating while taking the influence of [...] Read more.

The article deals with the problems of cracking in the structure of multilayered coatings under the conditions of stochastic loading process. A mathematical model has been proposed in order to predict the crack propagation velocity in the coating while taking the influence of interlayer interfaces into account. A technique for calculating the probability density distribution of the coating fracture (failure rate) has been developed. The probability of a change in the crack growth direction is compared with the experimental data that were obtained as a result of the studies focused on the pattern of cracking in the Zr,Nb-(Zr,Nb)N-(Zr,Nb,Al)N and Ti-TiN-(Ti,Cr,Al)N coatings under the conditions of the real stochastic loading of cutting tools during the turning. The influence of the crystalline structure of the coating on the cracking pattern has been studied. The investigation has found the significant effect of the crystalline structure of the coating layers on the cracking pattern. Full article

(This article belongs to the Special Issue Surface Performance and Wear Mechanisms of Coatings)

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16 pages, 20130 KiB

Open AccessEditor’s ChoiceArticle

Formaldehyde Emissions from Wooden Toys: Comparison of Different Measurement Methods and Assessment of Exposure

by Morgane Even, Olaf Wilke, Sabine Kalus, Petra Schultes, Christoph Hutzler and Andreas Luch

Materials 2021, 14(2), 262; https://doi.org/10.3390/ma14020262 - 7 Jan 2021

Cited by 6 | Viewed by 2453

Abstract

Formaldehyde is considered as carcinogenic and is emitted from particleboards and plywood used in toy manufacturing. Currently, the flask method is frequently used in Europe for market surveillance purposes to assess formaldehyde release from toys, but its concordance to levels measured in emission [...] Read more.

Formaldehyde is considered as carcinogenic and is emitted from particleboards and plywood used in toy manufacturing. Currently, the flask method is frequently used in Europe for market surveillance purposes to assess formaldehyde release from toys, but its concordance to levels measured in emission test chambers is poor. Surveillance laboratories are unable to afford laborious and expensive emission chamber testing to comply with a new amendment of the European Toy Directive; they need an alternative method that can provide reliable results. Therefore, the application of miniaturised emission test chambers was tested. Comparisons between a 1 m³ emission test chamber and 44 mL microchambers with two particleboards over 28 days and between a 24 L desiccator chamber and the microchambers with three puzzle samples over 10 days resulted in a correlation coefficient r² of 0.834 for formaldehyde at steady state. The correlation between the results obtained in microchambers vs. flask showed a high variability over 10 samples (r²: 0.145), thereby demonstrating the error-proneness of the flask method in comparison to methods carried out under ambient parameters. An exposure assessment was also performed for three toy puzzles: indoor formaldehyde concentrations caused by puzzles were not negligible (up to 8 µg/m³), especially when more conservative exposure scenarios were considered. Full article

(This article belongs to the Special Issue Measurement of the Environmental Impact of Materials)

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23 pages, 5783 KiB

Open AccessEditor’s ChoiceArticle

Non-Destructive Assessment of the Dynamic Elasticity Modulus of Eucalyptus nitens Timber Boards

by Alexander Opazo-Vega, Víctor Rosales-Garcés and Claudio Oyarzo-Vera

Materials 2021, 14(2), 269; https://doi.org/10.3390/ma14020269 - 7 Jan 2021

Cited by 6 | Viewed by 2293

Abstract

Eucalyptus nitens is a fast-growing wood species with a relevant presence in countries like Australia and Chile. The sustainable construction goals have driven the search of structural applications for Eucalyptus nitens; however, this process has been complicated due to the defects usually [...] Read more.

Eucalyptus nitens is a fast-growing wood species with a relevant presence in countries like Australia and Chile. The sustainable construction goals have driven the search of structural applications for Eucalyptus nitens; however, this process has been complicated due to the defects usually presented in these timber boards. This study aims to evaluate the dynamic elasticity modulus (E_xd) of Eucalyptus nitens timber boards through non-destructive vibration-based tests. Thirty-six timber boards with different levels of knots and cracks were instrumented and tested in a simply supported condition by measuring longitudinal and transverse vibrations. In the first stage, the E_xd was calculated globally through simplified normative formulas. Then, in a second stage, the local variability of the E_xd was estimated using operational modal analysis (OMA), finite element numerical simulations (FEM), and regional sensitivity analysis (RSA). The positive correlation found between the global static modulus of elasticity and E_xd suggests that non-destructive techniques could be used as a reliable and fast alternative for the assessment of bending stiffness. Finally, the proposed method to estimate the local variability of E_xdt based on the combination of OMA, FEM, and RSA techniques was useful to improve the structural selection process of timber boards for lightweight social housing floors. Full article

(This article belongs to the Special Issue Structural Health Monitoring for Civil Engineering Materials)

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15 pages, 26149 KiB

Open AccessEditor’s ChoiceArticle

Static Mechanical Properties of Expanded Polypropylene Crushable Foam

by Przemysław Rumianek, Tomasz Dobosz, Radosław Nowak, Piotr Dziewit and Andrzej Aromiński

Materials 2021, 14(2), 249; https://doi.org/10.3390/ma14020249 - 6 Jan 2021

Cited by 14 | Viewed by 4954

Abstract

Closed-cell expanded polypropylene (EPP) foam is commonly used in car bumpers for the purpose of absorbing energy impacts. Characterization of the foam’s mechanical properties at varying strain rates is essential for selecting the proper material used as a protective structure in dynamic loading [...] Read more.

Closed-cell expanded polypropylene (EPP) foam is commonly used in car bumpers for the purpose of absorbing energy impacts. Characterization of the foam’s mechanical properties at varying strain rates is essential for selecting the proper material used as a protective structure in dynamic loading application. The aim of the study was to investigate the influence of loading strain rate, material density, and microstructure on compressive strength and energy absorption capacity for closed-cell polymeric foams. We performed quasi-static compressive strength tests with strain rates in the range of 0.2 to 25 mm/s, using a hydraulically controlled material testing system (MTS) for different foam densities in the range 20 g/dm³ to 220 g/dm³. The above tests were carried out as numerical simulation using ABAQUS software. The verification of the properties was carried out on the basis of experimental tests and simulations performed using the finite element method. The method of modelling the structure of the tested sample has an impact on the stress values. Experimental tests were performed for various loads and at various initial temperatures of the tested sample. We found that increasing both the strain rate of loading and foam density raised the compressive strength and energy absorption capacity. Increasing the ambient and tested sample temperature caused a decrease in compressive strength and energy absorption capacity. For the same foam density, differences in foam microstructures were causing differences in strength and energy absorption capacity when testing at the same loading strain rate. To sum up, tuning the microstructure of foams could be used to acquire desired global materials properties. Precise material description extends the possibility of using EPP foams in various applications. Full article

(This article belongs to the Special Issue Structure, Properties and Applications of Polymeric Foams)

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12 pages, 7786 KiB

Open AccessEditor’s ChoiceArticle

Effect of Layer Directions on Internal Structures and Tensile Properties of 17-4PH Stainless Steel Parts Fabricated by Fused Deposition of Metals

by Yoshifumi Abe, Takashi Kurose, Marcelo V. A. Santos, Yota Kanaya, Akira Ishigami, Shigeo Tanaka and Hiroshi Ito

Materials 2021, 14(2), 243; https://doi.org/10.3390/ma14020243 - 6 Jan 2021

Cited by 36 | Viewed by 3684

Abstract

17-4PH stainless steel specimens were fabricated by fused deposition of metals (FDMet) technology, which combines 17-4PH particles with an organic binder. FDMet promises a low-cost additive manufacturing process. The present research aims to clarify the influence of layer directions in the 3D printing [...] Read more.

17-4PH stainless steel specimens were fabricated by fused deposition of metals (FDMet) technology, which combines 17-4PH particles with an organic binder. FDMet promises a low-cost additive manufacturing process. The present research aims to clarify the influence of layer directions in the 3D printing process on the mechanical and shrinkage properties of as-sintered and as-aged specimens. All specimens (the as-sintered and as-aged specimens printed in three layer directions) exhibited high relative density (97.5–98%). The highest ultimate strengths (880 and 1140 MPa in the as-sintered and as-aged specimens, respectively) were obtained when the layer direction was perpendicular to the tensile direction. Conversely, the specimens printed with their layer direction parallel to the tensile direction presented a low ultimate strength and low strain at breakage. The fact that the specimens with their layer direction parallel to the tensile direction presented a low ultimate strength and low strain at breakage is a usual behavior of parts obtained by means of FDM. The SEM images revealed oriented binder domains in the printed parts and oriented voids in the sintered parts. It was assumed that large binder domains in the filament were oriented perpendicular to the layer directions during the fused deposition modeling printing, and remained as oriented voids after sintering. Stress concentration in the oriented void defects was likely responsible for the poor tensile properties of these specimens. Full article

(This article belongs to the Section Materials Physics)

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20 pages, 9415 KiB

Open AccessEditor’s ChoiceArticle

Mechanical Performance and Environmental Assessment of Sustainable Concrete Reinforced with Recycled End-of-Life Tyre Fibres

by Magdalena Pawelska-Mazur and Maria Kaszynska

Materials 2021, 14(2), 256; https://doi.org/10.3390/ma14020256 - 6 Jan 2021

Cited by 20 | Viewed by 2210

Abstract

The presented research’s main objective was to develop the solution to the global problem of using steel waste obtained during rubber recovery during the tire recycling. A detailed comparative analysis of mechanical and physical features of the concrete composite with the addition of [...] Read more.

The presented research’s main objective was to develop the solution to the global problem of using steel waste obtained during rubber recovery during the tire recycling. A detailed comparative analysis of mechanical and physical features of the concrete composite with the addition of recycled steel fibres (RSF) in relation to the steel fibre concrete commonly used for industrial floors was conducted. A study was carried out using micro-computed tomography and the scanning electron microscope to determine the fibres’ characteristics, incl. the EDS spectrum. In order to designate the full performance of the physical and mechanical features of the novel composite, a wide range of tests was performed with particular emphasis on the determination of the tensile strength of the composite. This parameter appointed by tensile strength testing for splitting, residual tensile strength test (3-point test), and a wedge splitting test (WST), demonstrated the increase of tensile strength (vs unmodified concrete) by 43%, 30%, and 70% relevantly to the method. The indication of the reinforced composite’s fracture characteristics using the digital image correlation (DIC) method allowed to illustrate the map of deformation of the samples during WST. The novel composite was tested in reference to the circular economy concept and showed 31.3% lower energy consumption and 30.8% lower CO₂ emissions than a commonly used fibre concrete. Full article

(This article belongs to the Special Issue Testing of Materials and Elements in Civil Engineering)

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14 pages, 7597 KiB

Open AccessEditor’s ChoiceArticle

Effect of Equal Channel Angular Pressing on the Dynamic Softening Behavior of Ti-6Al-4V Alloy in the Hot Deformation Process

by Zhiyong Zhao, Jun Gao, Yaoqi Wang, Yanling Zhang and Hongliang Hou

Materials 2021, 14(1), 232; https://doi.org/10.3390/ma14010232 - 5 Jan 2021

Cited by 5 | Viewed by 2432

Abstract

To investigate the effect of equal channel angular pressing (ECAP) on the deformation of Ti-6Al-4V alloy at a higher temperature, hot compression tests were conducted on alloys having two different initial microstructures (the original alloy (Pre-ECAP) and ECAP-deformed alloy (Post-ECAP)). Post-ECAP, the alloy [...] Read more.

To investigate the effect of equal channel angular pressing (ECAP) on the deformation of Ti-6Al-4V alloy at a higher temperature, hot compression tests were conducted on alloys having two different initial microstructures (the original alloy (Pre-ECAP) and ECAP-deformed alloy (Post-ECAP)). Post-ECAP, the alloy showed a higher degree of dynamic softening during the hot deformation process due to its finer grain size and higher distortion energy. The flow stress of Post-ECAP alloy was higher than the Pre-ECAP alloy at 500 °C when

\dot{ε} = 0.003 s^{- 1}

. However, the stress of the Post-ECAP alloy decreased rapidly with increasing temperature and strain rate, until the stress value was much lower than that of Pre-ECAP at 700 °C when

\dot{ε} = 0.03 s^{- 1}

. The value of the dynamic softening coefficient revealed that the dynamic softening behavior of Post-ECAP was more pronounced than that of Pre-ECAP in the hot compression deformation process. The main dynamic softening mechanism of Pre-ECAP is dynamic recovery, while the dynamic recrystallization process plays a more important role in the deformation process of Post-ECAP alloy. The microstructures observation results showed that dynamic recrystallization was more likely to occur to Post-ECAP alloys under the same deformation condition. Almost fully dynamic recrystallization had occurred in the deformation process of Post-ECAP at 700 °C and a strain rate of

\dot{ε} = 0.01 s^{- 1}

. The grains of Post-ECAP alloys were further refined. The Post-ECAP alloy exhibits better plastic deformation at temperatures higher than 600 °C due to its significant dynamic recrystallization. Full article

(This article belongs to the Special Issue Metal Forming: Processes and Analyses)

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13 pages, 2365 KiB

Open AccessEditor’s ChoiceArticle

Natural Building Materials for Interior Fitting and Refurbishment—What about Indoor Emissions?

by Matthias Richter, Wolfgang Horn, Elevtheria Juritsch, Andrea Klinge, Leon Radeljic and Oliver Jann

Materials 2021, 14(1), 234; https://doi.org/10.3390/ma14010234 - 5 Jan 2021

Cited by 18 | Viewed by 3672

Abstract

Indoor air quality can be adversely affected by emissions from building materials, consequently having a negative impact on human health and well-being. In this study, more than 30 natural building materials (earth dry boards and plasters, bio-based insulation materials, and boards made of [...] Read more.

Indoor air quality can be adversely affected by emissions from building materials, consequently having a negative impact on human health and well-being. In this study, more than 30 natural building materials (earth dry boards and plasters, bio-based insulation materials, and boards made of wood, flax, reed, straw, etc.) used for interior works were investigated as to their emissions of (semi-)volatile organic compounds ((S)VOC), formaldehyde, and radon. The study focused on the emissions from complete wall build-ups as they can be used for internal partition walls and the internal insulation of external walls. Test chambers were designed, allowing the compounds to release only from the surface of the material facing indoors under testing parameters that were chosen to simulate model room conditions. The emission test results were evaluated using the AgBB evaluation scheme, a procedure for the health-related evaluation of construction products and currently applied for the approval of specific groups of building materials in Germany. Seventeen out of 19 sample build-ups tested in this study would have passed this scheme since they generally proved to be low-emitting and although the combined emissions of multiple materials were tested, 50% of the measurements could be terminated before half of the total testing time. Full article

(This article belongs to the Special Issue Measurement of the Environmental Impact of Materials)

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20 pages, 5548 KiB

Open AccessEditor’s ChoiceReview

Applications of Hydrogel with Special Physical Properties in Bone and Cartilage Regeneration

by Hua Lin, Cuilan Yin, Anchun Mo and Guang Hong

Materials 2021, 14(1), 235; https://doi.org/10.3390/ma14010235 - 5 Jan 2021

Cited by 32 | Viewed by 7210

Abstract

Hydrogel is a polymer matrix containing a large amount of water. It is similar to extracellular matrix components. It comes into contact with blood, body fluids, and human tissues without affecting the metabolism of organisms. It can be applied to bone and cartilage [...] Read more.

Hydrogel is a polymer matrix containing a large amount of water. It is similar to extracellular matrix components. It comes into contact with blood, body fluids, and human tissues without affecting the metabolism of organisms. It can be applied to bone and cartilage tissues. This article introduces the high-strength polymer hydrogel and its modification methods to adapt to the field of bone and cartilage tissue engineering. From the perspective of the mechanical properties of hydrogels, the mechanical strength of hydrogels has experienced from the weak-strength traditional hydrogels to the high-strength hydrogels, then the injectable hydrogels were invented and realized the purpose of good fluidity before the use of hydrogels and high strength in the later period. In addition, specific methods to give special physical properties to the hydrogel used in the field of bone and cartilage tissue engineering will also be discussed, such as 3D printing, integrated repair of bone and cartilage tissue, bone vascularization, and osteogenesis hydrogels that regulate cell growth, antibacterial properties, and repeatable viscosity in humid environments. Finally, we explain the main reasons and contradictions in current applications, look forward to the research prospects in the field of bone and cartilage tissue engineering, and emphasize the importance of conducting research in this field to promote medical progress. Full article

(This article belongs to the Special Issue Dental Materials and Devices)

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20 pages, 5438 KiB

Open AccessEditor’s ChoiceArticle

Lightweight Cement Conglomerates Based on End-of-Life Tire Rubber: Effect of the Grain Size, Dosage and Addition of Perlite on the Physical and Mechanical Properties

by Andrea Petrella and Michele Notarnicola

Materials 2021, 14(1), 225; https://doi.org/10.3390/ma14010225 - 5 Jan 2021

Cited by 8 | Viewed by 2582

Abstract

Lightweight cement mortars containing end-of-life tire rubber (TR) as aggregate were prepared and characterized by rheological, thermal, mechanical, microstructural, and wetting tests. The mixtures were obtained after total replacement of the conventional sand aggregate with untreated TR with different grain sizes (0–2 mm [...] Read more.

Lightweight cement mortars containing end-of-life tire rubber (TR) as aggregate were prepared and characterized by rheological, thermal, mechanical, microstructural, and wetting tests. The mixtures were obtained after total replacement of the conventional sand aggregate with untreated TR with different grain sizes (0–2 mm and 2–4 mm) and distributions (25%, 32%, and 40% by weight). The mortars showed lower thermal conductivities (≈90%) with respect to the sand reference due to the differences in the conductivities of the two phases associated with the low density of the aggregates and, to a minor extent, to the lack of adhesion of tire to the cement paste (evidenced by microstructural detection). In this respect, a decrease of the thermal conductivities was observed with the increase of the TR weight percentage together with a decrease of fluidity of the fresh mixture and a decrease of the mechanical strengths. The addition of expanded perlite (P, 0–1 mm grain size) to the mixture allowed us to obtain mortars with an improvement of the mechanical strengths and negligible modification of the thermal properties. Moreover, in this case, a decrease of the thermal conductivities was observed with the increase of the P/TR dosage together with a decrease of fluidity and of the mechanical strengths. TR mortars showed discrete cracks after failure without separation of the two parts of the specimens, and similar results were observed in the case of the perlite/TR samples thanks to the rubber particles bridging the crack faces. The super-elastic properties of the specimens were also observed in the impact compression tests in which the best performances of the tire and P/TR composites were evidenced by a deep groove before complete failure. Moreover, these mortars showed very low water penetration through the surface and also through the bulk of the samples thanks to the hydrophobic nature of the end-of-life aggregate, which makes these environmentally sustainable materials suitable for indoor and outdoor elements. Full article

(This article belongs to the Special Issue Recycled Materials in Civil and Environmental Engineering)

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12 pages, 5385 KiB

Open AccessEditor’s ChoiceArticle

Four-Fold Multi-Modal X-ray Microscopy Measurements of a Cu(In,Ga)Se₂ Solar Cell

by Christina Ossig, Christian Strelow, Jan Flügge, Andreas Kolditz, Jan Siebels, Jan Garrevoet, Kathryn Spiers, Martin Seyrich, Dennis Brückner, Niklas Pyrlik, Johannes Hagemann, Frank Seiboth, Andreas Schropp, Romain Carron, Gerald Falkenberg, Alf Mews, Christian G. Schroer, Tobias Kipp and Michael E. Stuckelberger

Materials 2021, 14(1), 228; https://doi.org/10.3390/ma14010228 - 5 Jan 2021

Cited by 12 | Viewed by 3148

Abstract

Inhomogeneities and defects often limit the overall performance of thin-film solar cells. Therefore, sophisticated microscopy approaches are sought to characterize performance and defects at the nanoscale. Here, we demonstrate, for the first time, the simultaneous assessment of composition, structure, and performance in four-fold [...] Read more.

Inhomogeneities and defects often limit the overall performance of thin-film solar cells. Therefore, sophisticated microscopy approaches are sought to characterize performance and defects at the nanoscale. Here, we demonstrate, for the first time, the simultaneous assessment of composition, structure, and performance in four-fold multi-modality. Using scanning X-ray microscopy of a Cu(In,Ga)Se

_{2}

(CIGS) solar cell, we measured the elemental distribution of the key absorber elements, the electrical and optical response, and the phase shift of the coherent X-rays with nanoscale resolution. We found structural features in the absorber layer—interpreted as voids—that correlate with poor electrical performance and point towards defects that limit the overall solar cell efficiency. Full article

(This article belongs to the Special Issue Microscopy in Material Science: Imaging, Analytics, and New Materials)

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21 pages, 2286 KiB

Open AccessEditor’s ChoiceArticle

Manufacturing and Recycling Impact on Environmental Life Cycle Assessment of Innovative Wind Power Plant Part 1/2

by Krzysztof Doerffer, Patrycja Bałdowska-Witos, Michał Pysz, Piotr Doerffer and Andrzej Tomporowski

Materials 2021, 14(1), 220; https://doi.org/10.3390/ma14010220 - 5 Jan 2021

Cited by 8 | Viewed by 3316

Abstract

Wind power plants are considered as an ecologically-clean source of energy. However, manufacturing processes cannot be treated that way. Manufacturing processes consume huge amounts of electrical and thermal energy and significant amount of materials, e.g., steel, polymers, oils, and lubricants. All of the [...] Read more.

Wind power plants are considered as an ecologically-clean source of energy. However, manufacturing processes cannot be treated that way. Manufacturing processes consume huge amounts of electrical and thermal energy and significant amount of materials, e.g., steel, polymers, oils, and lubricants. All of the above could be potentially harmful for environment. There are not many works and publications regarding life-cycle analysis of wind power plants. This study’s objective is to use LCA (Life Cycle Assessment) to the manufacturing and utilization of a specific drag force-driven wind turbine. The discussed innovative wind turbine is of the type that assures safety for prosumer application. Drag force-driven turbines become more heavy than other types of lift driven turbines, but at the same time, their characteristic provides opportunity to use easily recyclable materials instead of materials like plastics or composites. The wider look through LCA tools, may change the perspective of view at that type of wind turbines. Analyzed turbine has capacity of 15 kW and is located in Poland. LCA was carried out using Eco-indicator 99 method in eleven impact categories. Among all of the turbine components, the highest negative impact was noted in the case of the tower. The wind turbine under consideration is characterized by high recycling potential. According to the presented research, recycling provides around 30% reduction of the environmental impact. Full article

(This article belongs to the Special Issue Recent Developments in Pro-ecological Materials and Processes)

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19 pages, 6420 KiB

Open AccessEditor’s ChoiceArticle

The Influence of ZnO Oxide Layer on the Physicochemical Behavior of Ti6Al4V Titanium Alloy

by Anna Woźniak, Witold Walke, Agata Jakóbik-Kolon, Bogusław Ziębowicz, Zbigniew Brytan and Marcin Adamiak

Materials 2021, 14(1), 230; https://doi.org/10.3390/ma14010230 - 5 Jan 2021

Cited by 15 | Viewed by 3626

Abstract

Titanium and its alloys are characterized by high biocompatibility and good corrosion resistance as a result of the ability to form a TiO₂ oxide layer. However, based on literature data it can be concluded that titanium degradation products, in the form of [...] Read more.

Titanium and its alloys are characterized by high biocompatibility and good corrosion resistance as a result of the ability to form a TiO₂ oxide layer. However, based on literature data it can be concluded that titanium degradation products, in the form of titanium particles, metal-protein groups, oxides and ions, may cause allergic, inflammatory reactions and bone resorption. The corrosion process of Ti6Al4V in the human body environment may be intensified by a decreased pH and concentration of chloride compounds. The purpose of this article was to analyze the corrosion resistance of the Ti6Al4V alloy, obtained by the selective laser melting method in a corrosion solution of neutral pH and in a solution simulating peri-implant inflammatory conditions. Additionally, the influence of zinc oxide deposited by the atomic layer deposition method on the improvement of the physicochemical behavior of the Ti6Al4V alloy was analyzed. In order to characterize the ZnO layer, tests of chemical and phase composition as well as surface morphology investigation were performed. As part of the assessment of the physicochemical properties of the uncoated samples and those with the ZnO layer, tests of wetting angle, pitting corrosion and impedance corrosion were carried out. The number of ions released after the potentiodynamic test were measured using the inductively coupled plasma atomic emission spectrometry (ICP–AES) method. It can be concluded that samples after surface modification (with the ZnO layer) were characterized by favorable physicochemical properties and had higher corrosion resistance. Full article

(This article belongs to the Special Issue Corrosion Resistance of Alloy and Coating Materials)

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12 pages, 14590 KiB

Open AccessEditor’s ChoiceArticle

Effect of Periodic Water Clusters on AISI 304 Welded Surfaces

by Madhulika Srivastava, Akash Nag, Lucie Krejčí, Jana Petrů, Somnath Chattopadhyaya and Sergej Hloch

Materials 2021, 14(1), 210; https://doi.org/10.3390/ma14010210 - 4 Jan 2021

Cited by 7 | Viewed by 2063

Abstract

This study compared the effect of the interaction time of periodic water clusters on the surface integrity of AISI 304 tungsten inert gas (TIG) welded joints at different excitation frequencies, as the effect of the technological parameters of pulsating water jet (PWJ) on [...] Read more.

This study compared the effect of the interaction time of periodic water clusters on the surface integrity of AISI 304 tungsten inert gas (TIG) welded joints at different excitation frequencies, as the effect of the technological parameters of pulsating water jet (PWJ) on the mechanical properties of TIG welded joints are under-researched. The TIG welded joints were subjected to different frequencies (20 and 40 kHz) and traverse speeds (1–4 mm/s) at a water pressure of 40 MPa and a standoff distance of 70 mm. The effect of the interaction of the pulsating jet on the material and the enhancement in its mechanical properties were compared through residual stress measurements, surface roughness, and sub-surface microhardness. A maximum enhancement in the residual stress values of up to 480 MPa was observed in the heat-affected zone, along with a maximum roughness of 6.03 µm and a maximum hardness of 551 HV using a frequency of 40 kHz. The improvement in the surface characteristics of the welded joints shows the potential of utilizing pulsed water jet technology with an appropriate selection of process parameters in the treatment of welded structures. Full article

(This article belongs to the Collection Machining and Manufacturing of Alloys and Steels)

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16 pages, 7314 KiB

Open AccessEditor’s ChoiceArticle

Immobilization of Heavy Metals in Boroaluminosilicate Geopolymers

by Piotr Rożek, Paulina Florek, Magdalena Król and Włodzimierz Mozgawa

Materials 2021, 14(1), 214; https://doi.org/10.3390/ma14010214 - 4 Jan 2021

Cited by 9 | Viewed by 2801

Abstract

Boroaluminosilicate geopolymers were used for the immobilization of heavy metals. Then, their mechanical properties, phase composition, structure, and microstructure were investigated. The addition of borax and boric acid did not induce the formation of any crystalline phases. Boron was incorporated into the geopolymeric [...] Read more.

Boroaluminosilicate geopolymers were used for the immobilization of heavy metals. Then, their mechanical properties, phase composition, structure, and microstructure were investigated. The addition of borax and boric acid did not induce the formation of any crystalline phases. Boron was incorporated into the geopolymeric network and caused the formation of N–B–A–S–H (hydrated sodium boroaluminosilicate) gel. In the range of a B/Al molar ratio of 0.015–0.075, the compressive strength slightly increased (from 16.1 to 18.7 MPa), while at a ratio of 0.150, the compressive strength decreased (to 12 MPa). Heavy metals (lead and nickel) were added as nitrate salts. The loss of the strength of the geopolymers induced by heavy metals was limited by the presence of boron. However, it caused an increase in heavy metal leaching. Despite this, heavy metals were almost entirely immobilized (with immobilization rates of >99.8% in the case of lead and >99.99% in the case of nickel). The lower immobilization rate of lead was due to the formation of macroscopic crystalline inclusions of PbO·xH₂O, which was vulnerable to leaching. Full article

(This article belongs to the Special Issue Recent Developments in Geopolymers and Alkali-Activated Materials)

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20 pages, 4719 KiB

Open AccessEditor’s ChoiceArticle

Deformation Characteristics and Constitutive Equations for the Semi-Solid Isothermal Compression of Cold Radial Forged 6063 Aluminium Alloy

by Yongfei Wang, Shengdun Zhao, Yi Guo, Kuanxin Liu and Shunqi Zheng

Materials 2021, 14(1), 194; https://doi.org/10.3390/ma14010194 - 3 Jan 2021

Cited by 7 | Viewed by 2198

Abstract

Al-Mg-Si based alloys are popular alloys used in the automotive industry. However, limited studies have been performed to investigate the microstructure, deformation characteristics, and deformation mechanism for the semi-solid 6063 alloys. In this study, the cold radial forging method and semi-solid isothermal treatment [...] Read more.

Al-Mg-Si based alloys are popular alloys used in the automotive industry. However, limited studies have been performed to investigate the microstructure, deformation characteristics, and deformation mechanism for the semi-solid 6063 alloys. In this study, the cold radial forging method and semi-solid isothermal treatment (SSIT) are proposed in the semi-solid isothermal compression (SSIC) process to fabricate high-quality semi-solid 6063 billets. The effects of deformation temperature, strain rate, and strain on the microstructure, deformation characteristics, and deformation mechanism of the SSIC of cold radial forged 6063 alloys were investigated experimentally. Constitutive equations were established based on the measured data in experiments to predict the flow stress. Results show that an average grain size in the range from 59.22 to 73.02 μm and an average shape factor in the range from 071 to 078 can be obtained in the microstructure after the cold radial forged 6063 alloys were treated with SSIT process. Four stages (i.e., sharp increase, decrease, steady state, and slow increase) were observed in the true stress- true strain curve. The correlation coefficient of the constitutive equation was obtained as 0.9796 while the average relative error was 5.01%. The deformation mechanism for SSIC of cold radial forged aluminum alloy 6063 mainly included four modes: The liquid phase flow, grain slide or grain rotation along with the liquid film, slide among solid grains, and the plastic deformation of solid grains. Full article

(This article belongs to the Special Issue Hot Deformation and Microstructure Evolution of Metallic Materials)

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13 pages, 2560 KiB

Open AccessEditor’s ChoiceArticle

Performance Assessment of Minimum Quantity Castor-Palm Oil Mixtures in Hard-Milling Operation

by Binayak Sen, Munish Kumar Gupta, Mozammel Mia, Danil Yurievich Pimenov and Tadeusz Mikołajczyk

Materials 2021, 14(1), 198; https://doi.org/10.3390/ma14010198 - 3 Jan 2021

Cited by 33 | Viewed by 2416

Abstract

The necessity to progress towards sustainability has inspired modern researchers to examine the lubrication and cooling effects of vegetable oils on conventional metal cutting operations. Consequently, as an eco-friendly vegetable product, castor oil can be the right choice as Minimum quantity lubrication (MQL) [...] Read more.

The necessity to progress towards sustainability has inspired modern researchers to examine the lubrication and cooling effects of vegetable oils on conventional metal cutting operations. Consequently, as an eco-friendly vegetable product, castor oil can be the right choice as Minimum quantity lubrication (MQL) base fluid. Nonetheless, the high viscosity of castor oil limits its flowability and restricts its industrial application. Conversely, palm oil possesses superior lubricity, as well as flowability characteristics. Hence, an attempt has been made to improve the lubrication behavior of castor oil. Here, six castor-palm mixtures (varying from 1:0.5–1:3) were utilized as MQL-fluid, and the values of machining responses viz. average surface roughness, specific cutting energy, and tool wear were evaluated. Furthermore, an integrated Shannon’s Entropy-based Technique for order preference by similarity to ideal solution (TOPSIS) framework was employed for selecting the most suitable volume ratio of castor-palm oil mixture. The rank provided by the TOPSIS method confirmed that 1:2 was the best volume ratio for castor-palm oil mixture. Afterward, a comparative analysis demonstrated that the best castor-palm volume fraction resulted in 8.262 and 16.146% lowering of surface roughness, 5.459 and 7.971% decrement of specific cutting energy, 2.445 and 3.155% drop in tool wear compared to that of castor and palm oil medium, respectively. Full article

(This article belongs to the Special Issue Additive and Subtractive Manufacturing of Advanced Materials: Applications, Future Trends and Perspectives of Industry 4.0)

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16 pages, 3334 KiB

Open AccessEditor’s ChoiceArticle

Towards Further Understanding the Secondary Fracture during Spaghetti Bent Break

by Long Long, Yuxuan Zheng, Fenghua Zhou and Huilan Ren

Materials 2021, 14(1), 189; https://doi.org/10.3390/ma14010189 - 2 Jan 2021

Cited by 2 | Viewed by 2001

Abstract

When a brittle thin rod, such as a dry spaghetti stick, is bent beyond its flexural limit, it often breaks into more than two pieces, typically three or more. This phenomenon and puzzle has aroused widespread interest and discussion since its first proposal [...] Read more.

When a brittle thin rod, such as a dry spaghetti stick, is bent beyond its flexural limit, it often breaks into more than two pieces, typically three or more. This phenomenon and puzzle has aroused widespread interest and discussion since its first proposal by Feynman. Previous work has partly explained the inevitability of the secondary fracture, but without any adjustable time parameter. In order to further understand this problem, especially the secondary fracture, in this paper we propose and study the dynamics of a half-infinite model to mimic the physics that a spaghetti stick is half-infinite under uniform bending. When the breaking process starts, a gradual release of initial moment of a linearly declining time at the free end, instead of a sudden release, is adopted, resulting in the introduction of a characteristic time parameter to the model and agrees better with the real situation. A specific analytical solution in terms of the excited bending moment using Euler–Bernoulli beam theory is derived, and that the gradual release of initial moment induces a burst of flexural waves, and these flexural waves locally increase the moment in the stick and progressively get to the maximum value, and then lead to the secondary fracture are concluded. The excited moment increases with time and distance, and has an asymptotic extremum value of 1.43 times initial moment. The gradual release in our model requires and gives certain distance and time when the excited bending moment reaches its extremum value, which provides a possibility to predict the detailed fracture parameters such as fragmentation length and time and thus to further understand the secondary fracture during spaghetti bent break. Full article

(This article belongs to the Section Materials Physics)

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15 pages, 6907 KiB

Open AccessEditor’s ChoiceArticle

Modeling of Bridging Law for Bundled Aramid Fiber-Reinforced Cementitious Composite and its Adaptability in Crack Width Evaluation

by Daiki Sunaga, Takumi Koba and Toshiyuki Kanakubo

Materials 2021, 14(1), 179; https://doi.org/10.3390/ma14010179 - 2 Jan 2021

Cited by 1 | Viewed by 2431

Abstract

Tensile performance of fiber-reinforced cementitious composite (FRCC) after first cracking is characterized by fiber-bridging stress–crack width relationships called bridging law. The bridging law can be calculated by an integral calculus of forces carried by individual fibers, considering the fiber orientation. The objective of [...] Read more.

Tensile performance of fiber-reinforced cementitious composite (FRCC) after first cracking is characterized by fiber-bridging stress–crack width relationships called bridging law. The bridging law can be calculated by an integral calculus of forces carried by individual fibers, considering the fiber orientation. The objective of this study was to propose a simplified model of bridging law for bundled aramid fiber, considering fiber orientation for the practical use. By using the pullout characteristic of bundled aramid fiber obtained in the previous study, the bridging laws were calculated for various cases of fiber orientation. The calculated results were expressed by a bilinear model, and each characteristic point is expressed by the function of fiber-orientation intensity. After that, uniaxial tension tests of steel reinforced aramid-FRCC prism specimens were conducted to obtain the crack-opening behavior and confirm the adaptability of the modeled bridging laws in crack-width evaluation. The experimental parameters are cross-sectional dimensions of specimens and volume fraction of fiber. The test results are compared with the theoretical curves calculated by using the modeled bridging law and show good agreements in each parameter. Full article

(This article belongs to the Special Issue Advances in Construction and Building Materials)

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16 pages, 2938 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Filtration Materials Modified with 2D Nanocomposites—A New Perspective for Point-of-Use Water Treatment

by Michał Jakubczak, Ewa Karwowska, Anita Rozmysłowska-Wojciechowska, Mateusz Petrus, Jarosław Woźniak, Joanna Mitrzak and Agnieszka M. Jastrzębska

Materials 2021, 14(1), 182; https://doi.org/10.3390/ma14010182 - 2 Jan 2021

Cited by 27 | Viewed by 5781

Abstract

Point-of-use (POU) water treatment systems and devices play an essential role in limited access to sanitary safe water resources. The filtering materials applied in POU systems must effectively eliminate contaminants, be readily produced and stable, and avoid secondary contamination of the treated water. [...] Read more.

Point-of-use (POU) water treatment systems and devices play an essential role in limited access to sanitary safe water resources. The filtering materials applied in POU systems must effectively eliminate contaminants, be readily produced and stable, and avoid secondary contamination of the treated water. We report an innovative, 2D Ti₃C₂/Al₂O₃/Ag/Cu nanocomposite-modified filtration material with the application potential for POU water treatment. The material is characterized by improved filtration velocity relative to an unmodified reference material, effective elimination of microorganisms, and self-disinfecting potential, which afforded the collection of 99.6% of bacteria in the filter. The effect was obtained with nanocomposite levels as low as 1%. Surface oxidation of the modified material increased its antimicrobial efficiency. No secondary release of the nanocomposites into the filtrate was observed and confirmed the stability of the material and its suitability for practical application in water treatment. Full article

(This article belongs to the Special Issue New Findings of MXenes: Preparation, Properties and Applications in Biotechnology and Catalysis)

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