Materials

15 pages, 9893 KiB

Open AccessArticle

Electronic Waste Low-Temperature Processing: An Alternative Thermochemical Pretreatment to Improve Component Separation

by Juliana S. S. Oliveira, Ronald R. Hacha, Felipe S. d’Almeida, Caroline A. Almeida, Francisco J. Moura, Eduardo A. Brocchi and Rodrigo F. M. Souza

Materials 2021, 14(20), 6228; https://doi.org/10.3390/ma14206228 - 19 Oct 2021

Cited by 2 | Viewed by 2365

Abstract

The production of electronic waste due to technological development, economic growth and increasing population has been rising fast, pushing for solutions before the environmental pressure achieves unprecedented levels. Recently, it was observed that many extractive metallurgy alternatives had been considered to recover value [...] Read more.

The production of electronic waste due to technological development, economic growth and increasing population has been rising fast, pushing for solutions before the environmental pressure achieves unprecedented levels. Recently, it was observed that many extractive metallurgy alternatives had been considered to recover value from this type of waste. Regarding pyrometallurgy, little is known about the low-temperature processing applied before fragmentation and subsequent component separation. Therefore, the present manuscript studies such alternative based on scanning electron microscopy characterization. The sample used in the study was supplied by a local recycling center in Rio de Janeiro, Brazil. The mass loss was constant at around 30% for temperatures higher than 300 °C. Based on this fact, the waste material was then submitted to low-temperature processing at 350 °C followed by attrition disassembling, size classification, and magnetic concentration steps. In the end, this first report of the project shows that 15% of the sample was recovered with metallic components with high economic value, such as Cu, Ni, and Au, indicating that such methods could be an interesting alternative to be explored in the future for the development of alternative electronic waste extraction routes. Full article

(This article belongs to the Special Issue Recovery and Treatment of Solid Waste)

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11 pages, 2443 KiB

Open AccessFeature PaperArticle

Effects of Oxide Additives on the Phase Structures and Electrical Properties of SrBi₄Ti₄O₁₅ High-Temperature Piezoelectric Ceramics

by Shaozhao Wang, Huajiang Zhou, Daowen Wu, Lang Li and Yu Chen

Materials 2021, 14(20), 6227; https://doi.org/10.3390/ma14206227 - 19 Oct 2021

Cited by 5 | Viewed by 1824

Abstract

In this work, SrBi₄Ti₄O₁₅ (SBT) high-temperature piezoelectric ceramics with the addition of different oxides (Gd₂O₃, CeO₂, MnO₂ and Cr₂O₃) were fabricated by a conventional solid-state reaction route. [...] Read more.

In this work, SrBi₄Ti₄O₁₅ (SBT) high-temperature piezoelectric ceramics with the addition of different oxides (Gd₂O₃, CeO₂, MnO₂ and Cr₂O₃) were fabricated by a conventional solid-state reaction route. The effects of oxide additives on the phase structures and electrical properties of the SBT ceramics were investigated. Firstly, X-ray diffraction analysis revealed that all these oxides-modified SBT ceramics prepared presented a single SrBi₄Ti₄O₁₅ phase with orthorhombic symmetry and space group of Bb21m, the change in cell parameters indicated that these oxide additives had diffused into the crystalline lattice of SBT and formed solid solutions with it. The SBT ceramics with the addition of MnO₂ achieved a high relative density of up to 97%. The temperature dependence of dielectric constant showed that the addition of Gd₂O₃ could increase the T_C of SBT. At a low frequency of 100 Hz, those dielectric loss peaks appearing around 500 °C were attributed to the space-charge relaxation as an extrinsic dielectric response. The synergetic doping of CeO₂ and Cr₂O₃ could reduce the space-charge-induced dielectric relaxation of SBT. The piezoelectricity measurement and electro-mechanical resonance analysis found that Cr₂O₃ can significantly enhance both d₃₃ and k_p of SBT, and produce a higher phase-angle maximum at resonance. Such an enhanced piezoelectricity was attributed to the further increased orthorhombic distortion after Ti⁴⁺ at B-site was substituted by Cr³⁺. Among these compositions, Sr_0.92Gd_0.053Bi₄Ti₄O₁₅ + 0.2 wt% Cr₂O₃ (SGBT-Cr) presented the best electrical properties including T_C = 555 °C, tan δ = 0.4%, k_p = 6.35% and d₃₃ = 28 pC/N, as well as a good thermally-stable piezoelectricity that the value of d₃₃ was decreased by only 3.6% after being annealed at 500 °C for 4 h. Such advantages provided this material with potential applications in the high-stability piezoelectric sensors operated below 500 °C. Full article

(This article belongs to the Special Issue Microstructural Design and Processing Control of Advanced Ceramics)

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13 pages, 2795 KiB

Open AccessArticle

Mirror-like Bright Al-Mn Coatings Electrodeposition from 1-Ethyl-3 Methylimidazolium Chloride-AlCl₃-MnCl₂ Ionic Liquids with Pyridine Derivatives

by Dong Peng, Dalong Cong, Kaiqiang Song, Xingxing Ding, Xuan Wang, Yixin Bai, Xinrui Yang, Changqing Yin, Yuxin Zhang, Jinsong Rao, Min Zhang and Zhongsheng Li

Materials 2021, 14(20), 6226; https://doi.org/10.3390/ma14206226 - 19 Oct 2021

Cited by 5 | Viewed by 1788

Abstract

The effects of three pyridine derivative additives, 4-hydroxypyridine, 4-picolinic acid, and 4-cyanopyridine, on Al-Mn coatings were investigated in 1-ethyl-3-methylimidazolium chloride-AlCl₃-MnCl₂ (EMIC-AlCl₃-MnCl₂) ionic liquids. The smooth mirror-like bright Al-Mn coatings were obtained only in the EMIC-AlCl₃ [...] Read more.

The effects of three pyridine derivative additives, 4-hydroxypyridine, 4-picolinic acid, and 4-cyanopyridine, on Al-Mn coatings were investigated in 1-ethyl-3-methylimidazolium chloride-AlCl₃-MnCl₂ (EMIC-AlCl₃-MnCl₂) ionic liquids. The smooth mirror-like bright Al-Mn coatings were obtained only in the EMIC-AlCl₃-MnCl₂ ionic liquids containing 4-cyanopyridine, while the matte Al-Mn coatings were electrodeposited from EMIC-AlCl₃-MnCl₂ without additives or containing either 4-hydroxypyridine or 4-picolinic acid. The scanning electron microscope and X-ray diffraction showed that the bright Al-Mn coatings consisted of nanocrystals and had a strong (200) preferential orientation, while the particle size of matte Al-Mn coatings were within the micron range. The brightening mechanism of 4-cyanopyridine is due to it being adsorbed onto the cathode to produce the combined effect of (1) generating an overpotential to promote Al-Mn nucleation; (2) inhibiting the growth of the deposited nuclei and enabling them grow preferentially, making the coating composed of nanocrystals and with a smooth surface. The brightening effect of 4-cyanopyridine on the Al-Mn coatings was far better than that of the 4-hydroxypyridine and the 4-picolinic acid. In addition, the bright Al-Mn coating was prepared in a bath with 6 mmol·L⁻¹ 4-cyanopyridine and displayed superior corrosion resistance relative to the matte coatings, which could be attributed to its unique nanocrystalline structure that increased the number of grain boundaries and accelerated the formation of the protective layer of the corrosion products. Full article

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11 pages, 3466 KiB

Open AccessArticle

Gemological Characteristic Difference between Colorless CVD Synthetic Diamonds and Natural Diamonds

by Qi Lu, Huaiyu Gong, Qingfeng Guo, Xuren Huang and Jiayi Cai

Materials 2021, 14(20), 6225; https://doi.org/10.3390/ma14206225 - 19 Oct 2021

Cited by 3 | Viewed by 3260

Abstract

CVD synthetic diamond plays an important role in the jewelry market due to its excellent performance and low cost. In this paper, colorless CVD synthetic diamonds produced by a Chinese company were investigated in detail with their gemological, spectroscopic, and luminescent properties compared [...] Read more.

CVD synthetic diamond plays an important role in the jewelry market due to its excellent performance and low cost. In this paper, colorless CVD synthetic diamonds produced by a Chinese company were investigated in detail with their gemological, spectroscopic, and luminescent properties compared with natural colorless diamonds. Compared with natural diamonds, CVD synthetic diamonds have high-order interference color and more apparent abnormal birefringence. The results of infrared spectra indicate that all the CVD samples are classified as type IIa, while the natural samples belong to type Ia. The CVD samples show lamellar growth and mottled luminescence pattern and have blue, orange red, purple red, and blue fluorescence, respectively, while most of the natural samples show blue fluorescence. CVD diamonds show lamellar growth structure, and natural diamonds show irregular ring-like growth structure. Thus, multiple methods combined with analysis are required to distinguish synthetic diamonds from natural diamonds. This work provides an experimental basis for the identification of CVD synthetic diamonds. Full article

(This article belongs to the Special Issue Advances in Synthetic Diamond Materials)

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11 pages, 15355 KiB

Open AccessArticle

Incorporation of Temperature and Plastic Strain Effects into Local Approach to Fracture

by Sergiy Kotrechko, Vladislav Kozák, Oleksandra Zatsarna, Galyna Zimina, Nataliya Stetsenko and Ivo Dlouhý

Materials 2021, 14(20), 6224; https://doi.org/10.3390/ma14206224 - 19 Oct 2021

Cited by 2 | Viewed by 2098

Abstract

An unjustified simplification of the local quantitative criterion regarding cleavage nucleation is a key problem in the utilisation of the Local Approach to Fracture (LA), particularly to predict the fracture toughness within the ductile-to-brittle transition (DBT) region. The theoretical concept of the effect [...] Read more.

An unjustified simplification of the local quantitative criterion regarding cleavage nucleation is a key problem in the utilisation of the Local Approach to Fracture (LA), particularly to predict the fracture toughness within the ductile-to-brittle transition (DBT) region. The theoretical concept of the effect of both temperature and the plastic strain value on the crack nuclei (CN) generation rate in iron and ferritic steels is presented. It is shown how the plastic strain and temperature affect CN formation rate and, as a consequence, govern the shape of the temperature dependence of fracture toughness K_Jc and its scatter limits. Within the framework of the microscopic model proposed, dependences of the CN bulk density on the plastic deformation value and temperature are predicted. Convenient approximation dependences for incorporating this effect into the LA are suggested. The experimental data of reactor pressure vessel steel and cast manganese steel demonstrate that the use of these dependences enables one to predict, with sufficient accuracy, the effect of temperature on the value of fracture toughness and its scatter limits over the DBT region. It is shown that accounting for both the temperature and strain dependence of CN bulk density gives rise to the invariance of parameters of the Weibull distribution to temperature. Full article

(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)

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10 pages, 6970 KiB

Open AccessArticle

A Method for Characterising the Influence of Casting Parameters on the Metallurgical Bonding of Copper and Steel Bimetals

by Simon Kammerloher, Julika Hoyer, Philipp Lechner, Tim Mittler and Wolfram Volk

Materials 2021, 14(20), 6223; https://doi.org/10.3390/ma14206223 - 19 Oct 2021

Cited by 3 | Viewed by 1504

Abstract

Traditional casting technology offers two mayor drawbacks towards research activities. On the one hand, time and resources needed for every casting are rather high. The mould has to be able to withstand the high temperatures introduced by the melt and provide cooling for [...] Read more.

Traditional casting technology offers two mayor drawbacks towards research activities. On the one hand, time and resources needed for every casting are rather high. The mould has to be able to withstand the high temperatures introduced by the melt and provide cooling for the cast part. Preparation and installation of measuring equipment therefore takes time. Additionally, due to the high mass of the mould when compared to the cast part, parameter variations are rather limited in their resulting effect on the temperature-time profile being one of the most prominent factors regarding cast quality. Especially when pouring by hand, variations in casting times and rates superimpose effects created intentionally. Therefore, a different process was advanced and evaluated, allowing to minimise some of the drawbacks mentioned before. The key idea is to drastically reduce casting size to the dimensions of one specimen and to apply a highly automated production route. As such, a mirror furnace was modified as to allow the processing of melt. Due to the specimens size, an adaption of mechanical testing equipment was performed and evaluated. As an example, copper-iron bimetal specimens were examined by light microscopy, micro hardness testing, nanoindentation as well as tensile and torsion testing. As the results were consistent, the newly introduced method can be applied successfully in casting research. This allows for highly reproducible results, reducing the uncertainty of temperature measurements of a specimen due to the distance between them. The possibility of separating influencing variables like maximum temperature and cooling rate allows an analysis of the casting process, which would require different moulds to do so in traditional casting methods. The next steps will be directed at a broader variety of metals processed and at a direct comparison between the new process route and traditional casting technology. Full article

(This article belongs to the Special Issue Characterization Methods for Metal Cast Processes)

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18 pages, 6956 KiB

Open AccessArticle

Modeling and Analysis of a SiC Microstructure-Based Capacitive Micro-Accelerometer

by Xiang Tian, Wei Sheng, Zhanshe Guo, Weiwei Xing and Runze Tang

Materials 2021, 14(20), 6222; https://doi.org/10.3390/ma14206222 - 19 Oct 2021

Cited by 6 | Viewed by 1918

Abstract

In this study, a comb-type capacitive accelerometer based on a silicon carbide (SiC) microstructure is presented and investigated by the finite element method (FEM). It has the advantages of low weight, small volume, and low cross-coupling. Compared with silicon(111) accelerometers with the same [...] Read more.

In this study, a comb-type capacitive accelerometer based on a silicon carbide (SiC) microstructure is presented and investigated by the finite element method (FEM). It has the advantages of low weight, small volume, and low cross-coupling. Compared with silicon(111) accelerometers with the same structure, it has a higher natural frequency. When the accelerometer vibrates, its resistive force consists of two main components: a viscous damping and an elastic damping force. It was found that viscous damping dominates at low frequency, and elastic damping dominates at high frequency. The second-order linear system of the accelerometer was analyzed in the time-frequency domain, and its dynamic characteristics were best when the gap between the capacitive plates was 1.23 μm. The range of this accelerometer was 0–100 g, which is 1.64 times that of a silicon(111) accelerometer with the same structure. In addition, the accelerometer could work normally at temperatures of up to 1200 °C, which is much higher than the working temperatures of silicon devices. Therefore, the proposed accelerometer showed superior performance compared to conventional silicon-based sensors for inertial measurements. Full article

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19 pages, 37885 KiB

Open AccessArticle

Numerical Investigation of Composite Behavior and Strength of Rectangular Concrete-Filled Cold-Formed Steel Tubular Stub Columns

by Liping Wang, Yanan An, Faxing Ding, Yachuan Kuang, Qing Ma, Sui Tan, Weizhen Zhang, Pengzhou Zhao and Enhui Ren

Materials 2021, 14(20), 6221; https://doi.org/10.3390/ma14206221 - 19 Oct 2021

Cited by 3 | Viewed by 1864

Abstract

The objective of this study was to investigate the composite behavior of rectangular concrete-filled cold-formed steel (CFS) tubular stub columns under axial compression. A fine finite 3D solid element model of rectangular concrete-filled cold-formed steel tubular stub column was established by ABAQUS, which [...] Read more.

The objective of this study was to investigate the composite behavior of rectangular concrete-filled cold-formed steel (CFS) tubular stub columns under axial compression. A fine finite 3D solid element model of rectangular concrete-filled cold-formed steel tubular stub column was established by ABAQUS, which utilized a constitutive model of cold-formed steel considering the cold-forming effect and a triaxial plastic-damage constitutive model of the infilled concrete. Good agreement was achieved and the average discrepancy between the experimental and FE results was less than 5%. Based on the verified models, a further parametric analysis was carried out to reveal the influence of various factors on the strength and behavior of the concrete-filled rectangular cold-formed steel tubular stub columns. The factors included constitutive models adopted for cold-formed steel, length over width ratio of the rectangular section, wall-thickness and width, and concrete strength and yield strength of the cold-formed steel. A total of 144 FE models were analyzed. The stress nephogram was reasonably simplified in accordance with the limit state and a theoretical formula considering confinement coefficient was proposed to estimate the ultimate bearing capacity of concrete-filled rectangular cold-formed steel tubular stub columns using the superposition method. The calculated results showed satisfactory agreement with both the experimental and FE results, which proved the validity and accuracy of the formula proposed in this paper. In the proposed formula, the confinement coefficient of square concrete-filled cold-formed steel tubular stub columns is larger than that of hot-rolled steel counterparts but smaller than that of the stainless steel counterparts. Full article

(This article belongs to the Special Issue Confined Concrete and Its Application in Structural Engineering)

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16 pages, 10163 KiB

Open AccessArticle

The Influence of Physical Properties and Increasing Woven Fabric Layers on the Noise Absorption Capacity

by Bethalihem Teferi Samuel, Marcin Barburski, Ewa Witczak and Izabela Jasińska

Materials 2021, 14(20), 6220; https://doi.org/10.3390/ma14206220 - 19 Oct 2021

Cited by 4 | Viewed by 2171

Abstract

Noise pollution from the environment may wreak havoc on a person’s wellbeing. Numerous sound-absorbing materials are employed to address these issues, one of which is textile-woven fabrics. In this study, 12 woven textiles with four different weave structures (plain, rib, sateen, and twill) [...] Read more.

Noise pollution from the environment may wreak havoc on a person’s wellbeing. Numerous sound-absorbing materials are employed to address these issues, one of which is textile-woven fabrics. In this study, 12 woven textiles with four different weave structures (plain, rib, sateen, and twill) and those formed from three distinct polyester yarns were evaluated for their sound absorption properties using an impedance tube. The study was conducted within the range of 80–5000 (Hz) frequency. Part of the investigation was measuring different layers of woven fabrics under three different measuring conditions. Firstly, only woven fabrics were evaluated. Following that, woven and nonwoven textiles were measured. The third variant, in addition to the woven fabrics, included an air gap. In addition, this study includes tests and analyses of the effect of roughness and porosity of the fabric structure on the effectiveness of noise reduction by woven fabrics. The absorption capacity of plain fabric is higher at lower frequencies than other woven fabrics. Other weave structures noise reduction efficiency is higher as the frequency range increases. The absorption efficiency of plain fabric decreases with fabric layering. Utilizing woven fabric combined with nonwoven fabric reduces noise more effectively than the air gap variant. Low surface roughness and a highly porous surface of the fabric indicate a high noise reduction coefficient (NRC). Full article

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10 pages, 1406 KiB

Open AccessArticle

Dialkyl Succinates and Adipates as Alternative Plasticizers—Even More Efficient Synthesis

by Natalia Barteczko, Justyna Więcławik, Anna Tracz, Ewa Pankalla, Karol Erfurt, Piotr Latos, Sławomir Boncel, Karolina Matuszek and Anna Chrobok

Materials 2021, 14(20), 6219; https://doi.org/10.3390/ma14206219 - 19 Oct 2021

Cited by 8 | Viewed by 2017

Abstract

As a result of strict regulations of phthalate plasticizers, alternative non-phthalate forms are desired and increasingly used. This work presents a synthetic method for alternative plasticizers (dialkyl succinates and adipates) via esterification of succinic and adipic acid with alcohols: butan-1-ol and 2-ethylhexan-1-ol. Ionic [...] Read more.

As a result of strict regulations of phthalate plasticizers, alternative non-phthalate forms are desired and increasingly used. This work presents a synthetic method for alternative plasticizers (dialkyl succinates and adipates) via esterification of succinic and adipic acid with alcohols: butan-1-ol and 2-ethylhexan-1-ol. Ionic liquids were synthesized by the reaction of triethylamine with over-equimolar (1:2.7) amounts of sulfuric(VI) acid, which were used as an acidic catalyst and solvent. The two-phase liquid–liquid system was formed during the reaction due to immiscibility of the esters with the ionic liquid. This phenomenon is a driving force of this process, shifting the equilibrium toward the product formation. As a result, dialkyl succinates and adipates were obtained in high yields (99%) and selectivities (>99%), under mild reaction conditions at 70–80 °C and using a 4:1 molar ratio of alcohol to acid and 15 mol% of catalyst. The catalyst was recycled 10 times without any loss of activity. This alternative method is highly competitive: it involves a simple procedure for product isolation as well as a high yield and purity of the resulting esters. These advantages make this method sustainable and promising for industrial applications. Full article

(This article belongs to the Special Issue Advanced Technologies for Sustainable Materials)

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16 pages, 4910 KiB

Open AccessArticle

Interaction between Thermal Modification Temperature of Spruce Wood and the Cutting and Fracture Parameters

by Luďka Hlásková, Jiří Procházka, Vít Novák, Petr Čermák and Zdeněk Kopecký

Materials 2021, 14(20), 6218; https://doi.org/10.3390/ma14206218 - 19 Oct 2021

Cited by 8 | Viewed by 1842

Abstract

This work examines the effect of thermal modification temperatures in the production of thermally modified wood on the cutting and fracture parameters when cutting heat-treated spruce wood by a circular sawblade machine. The samples were thermally modified at 160, 180, 200, and 220 [...] Read more.

This work examines the effect of thermal modification temperatures in the production of thermally modified wood on the cutting and fracture parameters when cutting heat-treated spruce wood by a circular sawblade machine. The samples were thermally modified at 160, 180, 200, and 220 °C. One sample was unmodified and was used as a reference sample. On the basis of the performed experiments, the fracture parameters (fracture toughness and shear yield strength) were calculated for the axial–perpendicular direction of cutting. In comparison with the theoretical assumptions, the influence of temperature on the cutting and fracture parameters was confirmed. Thermally treated wood is characterized by increased fragility and susceptibility to crack formation, as well as reduced density, bending strength, and shear strength. These properties significantly affect the size of the cutting force and feed force, as well as the fracture parameters. As the temperature increases, the values of these parameters decrease. The mentioned material characteristics could be useful for the optimization of the cutting process, as well as for the issue of energy consumption during the machining of heat-treated wood. Full article

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15 pages, 8797 KiB

Open AccessArticle

Histologic and Histomorphometric Evaluation of a New Bioactive Liquid BBL on Implant Surface: A Preclinical Study in Foxhound Dogs

by Eduard Ferrés-Amat, Ashraf Al Madhoun, Elvira Ferrés-Amat, Saddam Al Demour, Mera A. Ababneh, Eduard Ferrés-Padró, Carles Marti, Neus Carrio, Miguel Barajas and Maher Atari

Materials 2021, 14(20), 6217; https://doi.org/10.3390/ma14206217 - 19 Oct 2021

Cited by 1 | Viewed by 2237

Abstract

Background: Bioactive chemical surface modifications improve the wettability and osseointegration properties of titanium implants in both animals and humans. The objective of this animal study was to investigate and compare the bioreactivity characteristics of titanium implants (BLT) pre-treated with a novel bone bioactive [...] Read more.

Background: Bioactive chemical surface modifications improve the wettability and osseointegration properties of titanium implants in both animals and humans. The objective of this animal study was to investigate and compare the bioreactivity characteristics of titanium implants (BLT) pre-treated with a novel bone bioactive liquid (BBL) and the commercially available BLT-SLA active. Methods: Forty BLT-SLA titanium implants were placed in in four foxhound dogs. Animals were divided into two groups (n = 20): test (BLT-SLA pre-treated with BBL) and control (BLT-SLA active) implants. The implants were inserted in the post extraction sockets. After 8 and 12 weeks, the animals were sacrificed, and mandibles were extracted, containing the implants and the surrounding soft and hard tissues. Bone-to-implant contact (BIC), inter-thread bone area percentage (ITBA), soft tissue, and crestal bone loss were evaluated by histology and histomorphometry. Results: All animals were healthy with no implant loss or inflammation symptoms. All implants were clinically and histologically osseo-integrated. Relative to control groups, test implants demonstrated a significant 1.5- and 1.7-fold increase in BIC and ITBA values, respectively, at both assessment intervals. Crestal bone loss was also significantly reduced in the test group, as compared with controls, at week 8 in both the buccal crests (0.47 ± 0.32 vs 0.98 ± 0.51 mm, p < 0.05) and lingual crests (0.39* ± 0.3 vs. 0.89 ± 0.41 mm, p < 0.05). At week 12, a pronounced crestal bone loss improvement was observed in the test group (buccal, 0.41 ± 0.29 mm and lingual, 0.54 ± 0.23 mm). Tissue thickness showed comparable values at both the buccal and lingual regions and was significantly improved in the studied groups (0.82–0.92 mm vs. 33–48 mm in the control group). Conclusions: Relative to the commercially available BLT-SLA active implants, BLT-SLA pre-treated with BBL showed improved histological and histomorphometric characteristics indicating a reduced titanium surface roughness and improved wettability, promoting healing and soft and hard tissue regeneration at the implant site. Full article

(This article belongs to the Special Issue Dental Implant Biomaterials: In Vitro and In Vivo Simulations and Applications)

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19 pages, 2900 KiB

Open AccessArticle

Mud-Based Construction Material: Promising Properties of French Gravel Wash Mud Mixed with Byproducts, Seashells and Fly Ash as a Binder

by Yassine El Mendili, Manal Bouasria, Mohammed-Hichem Benzaama, Fouzia Khadraoui, Malo Le Guern, Daniel Chateigner, Stéphanie Gascoin and Jean-François Bardeau

Materials 2021, 14(20), 6216; https://doi.org/10.3390/ma14206216 - 19 Oct 2021

Cited by 5 | Viewed by 2441

Abstract

The French gravel industry produces approximatively 6.5 million tons of gravel wash mud each year. This material offers very promising properties which require an in-depth characterization study before its use as a construction material, otherwise it is removed from value cycles by disposal [...] Read more.

The French gravel industry produces approximatively 6.5 million tons of gravel wash mud each year. This material offers very promising properties which require an in-depth characterization study before its use as a construction material, otherwise it is removed from value cycles by disposal in landfills. We examined the suitability of gravel wash mud and seashells, with fly ash as a binder, as an unfired earth construction material. Thermal and mechanical characterizations of the smart mixture composed of gravel wash mud, Crepidula fornicata shells and fly ash are performed. The new specimens exhibit high compressive strengths compared to usual earth construction materials, which appears as a good opportunity for a reduction in the thickness of walls. The use of fly ash and Crepidula shells in addition to gravel wash mud provides high silica and calcium contents, which both react with clay, leading to the formation of tobermorite and Al-tobermorite as a result of a pozzolanic reaction. Considering the reduction in porosity and improvements in strength, these new materials are good candidates to contribute significantly to the Sustainable Development Goals (SDGs) and reduce carbon emissions. Full article

(This article belongs to the Special Issue Current State of Coal Fly Ash Utilization: Characterization and Application)

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15 pages, 4151 KiB

Open AccessArticle

Space Maintainers Used in Pediatric Dentistry: An Insight of Their Biosecurity Profile by Applying In Vitro Methods

by Magda Mihaela Luca, Malina Popa, Claudia G. Watz, Iulia Pinzaru, George Andrei Draghici, Ciprian V. Mihali, Cristina Adriana Dehelean, Roxana Buzatu and Camelia Szuhanek

Materials 2021, 14(20), 6215; https://doi.org/10.3390/ma14206215 - 19 Oct 2021

Cited by 4 | Viewed by 2446

Abstract

Space maintainers have presented an increased interest due to their chemical composition which influences the electrochemical and electrolytic processes of the oral cavity, leading to important biological activity. The present study was purported to evaluate the biological in vitro activity of three types [...] Read more.

Space maintainers have presented an increased interest due to their chemical composition which influences the electrochemical and electrolytic processes of the oral cavity, leading to important biological activity. The present study was purported to evaluate the biological in vitro activity of three types of space maintainers (S1, S2, and S3, differing from each other in terms of metal composition) used in pediatric dentistry, in terms of their antimicrobial effect and biosecurity profile using two types of keratinocytes (PGK: primary gingival keratinocytes, and HaCaT: human immortalized keratinocytes) by assessing the morphology, viability, cytotoxicity, and gene expression of the cells. Statistical differences were calculated by the one-way ANOVA test, followed by Tukey’s post-test. Antimicrobial screening highlighted a dilution-dependent influence that, in the case of all strains tested, did not show inhibition or stimulation of bacterial growth. The in vitro evaluations revealed that the test samples did not induce important cytotoxic potential on both keratinocyte cell lines (HaCaT and PGK), with the cells manifesting no morphological alteration, a good viability rate (above 90%: PGK–S1, * p < 0.05), and a low cytotoxic activity (less than 11%: PGK, S1 *** p < 0.001 and S3 * p < 0.05; HaCaT, S1 ** p < 0.01). The data obtained in this study highlight the fact that the samples analyzed are biocompatible and do not develop the growth of the studied bacteria or encode the gene expression of primary and immortalized keratinocytes. Full article

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12 pages, 2363 KiB

Open AccessArticle

In Vitro Fracture Resistance of Endodontically Treated Premolar Teeth Restored with Prefabricated and Custom-Made Fibre-Reinforced Composite Posts

by Michal Bialy, Sara Targonska, Agnieszka Szust, Rafal J. Wiglusz and Maciej Dobrzynski

Materials 2021, 14(20), 6214; https://doi.org/10.3390/ma14206214 - 19 Oct 2021

Cited by 1 | Viewed by 1971

Abstract

(1) Background: The study aimed to compare and analyse the differences between the features of prefabricated fibre-reinforced composite (FRC) posts and custom-made FRC posts in the form of a tape and confirm the necessity of using FRC posts in teeth treated endodontically in [...] Read more.

(1) Background: The study aimed to compare and analyse the differences between the features of prefabricated fibre-reinforced composite (FRC) posts and custom-made FRC posts in the form of a tape and confirm the necessity of using FRC posts in teeth treated endodontically in comparison to direct reconstruction with a composite material. (2) Methods: Sixty premolars after endodontic treatment were used. The teeth were divided into four groups (n—15). Group 1: teeth with embedded prefabricated posts (Mirafit White); group 2: teeth with embedded prefabricated posts (Rebilda); group 3 teeth with embedded custom-made posts in the form of a tape (EverStick); group 4: teeth without a post restored with composite material. The compressive strength of the teeth was tested using the Instron-5944 testing machine until the sample broke. The crystal structure of the investigated posts was detected with the X-ray diffractometer (3) Results: During the experiment, the maximum values of forces at which the damage of the restored premolar teeth after endodontic treatment occurred were obtained. The best results were obtained for teeth rebuilt with Rebilda Posts (1119 N), while teeth with cemented Mirafit White posts were the weakest (968 N). Teeth without an embedded FRC post, rebuilt only with light-cured composite material, obtained the lowest value—859 N. (4) Conclusions: The use of FRC posts increases the resistance to damage of an endodontically treated tooth when compared to direct restoration with light-cured composite material. Full article

(This article belongs to the Special Issue Polish Achievements in Materials Science and Engineering)

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12 pages, 10384 KiB

Open AccessArticle

Coatings Based on Phosphate Cements for Fire Protection of Steel Structures

by Cristina Andreea Vijan, Alina Badanoiu, Georgeta Voicu and Adrian Ionut Nicoara

Materials 2021, 14(20), 6213; https://doi.org/10.3390/ma14206213 - 19 Oct 2021

Cited by 5 | Viewed by 1718

Abstract

Fire events in buildings can cause losses to human life and important material damage, therefore a great deal of attention is paid nowadays to fire prevention. Buildings based on steel structures are especially affected in the event of a fire, due to the [...] Read more.

Fire events in buildings can cause losses to human life and important material damage, therefore a great deal of attention is paid nowadays to fire prevention. Buildings based on steel structures are especially affected in the event of a fire, due to the important loss of load-bearing capability when steel is heated at temperatures higher than 500 °C. Therefore, one possible method to mitigate the deleterious effect of fire is to protect steel structures from direct heating by applying protective coatings. In this paper, the ability of magnesium phosphate cement (MPC), based on dead burned magnesite and calcium magnesium phosphate cement (CMPC) coatings, to protect a steel substrate was assessed. CMPCs were obtained by mixing partially calcined dolomite with a KH₂PO₄ (MKP) solution, and in some cases, with a setting retarder (borax). The main mineralogical compounds assessed by X-ray diffraction and electronic microscopy (SEM-EDS) in CMPC are MgO, CaCO₃, and K-struvite (KMgPO₄·6H₂O). The coatings based on MPC and CMPC, applied to steel plates, were tested in direct contact with a flame; the coatings of MPC and CMPC without the borax addition prevented the temperature increase of a metal substrate above 500 °C. No exfoliation of coatings (MPC and CMPC without borax addition) was noticed during the entire period of the test (45 min). Full article

(This article belongs to the Special Issue Emerging Construction Materials for Sustainable Infrastructure)

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17 pages, 7482 KiB

Open AccessArticle

Renovation Effect of Flax FRP-Reinforced Cracked Concrete Slabs under Impact Loadings

by Wenjie Wang, Zonglai Mo, Nawawi Chouw and Krishnan Jayaraman

Materials 2021, 14(20), 6212; https://doi.org/10.3390/ma14206212 - 19 Oct 2021

Cited by 5 | Viewed by 1629

Abstract

The impact behaviour of flax fibre-reinforced polymer (FFRP) renovated coconut fibre-reinforced concrete (CFRC) slabs was investigated through two series of experiments and theoretical analysis. The first experiment was carried out to find out the effectiveness of FFRP retrofitted method for the partly damaged [...] Read more.

The impact behaviour of flax fibre-reinforced polymer (FFRP) renovated coconut fibre-reinforced concrete (CFRC) slabs was investigated through two series of experiments and theoretical analysis. The first experiment was carried out to find out the effectiveness of FFRP retrofitted method for the partly damaged concrete structure and its performance under impact loadings. The renovation process was applied on the pre-cracked rectangular CFRC slabs of 600 mm × 300 mm × 50 mm with FFRP laminates, before the repeated impact tests. Then, the parameters of these slabs, i.e., impact force history, deflection history and damage pattern, were discussed in detail. Another experiment was conducted on the FFRP-CFRC square slabs with a dimension of 600 mm × 600 mm × 50 mm. Based on test results, the effect of different FFRP configurations was discussed to find out the effective reinforcement method. In addition, the two-degree-of-freedom spring-mass model was applied to predict the impact force. Results demonstrate that FFRP composites have a good potential to be utilised as renovated construction materials under dynamic load conditions. Full article

(This article belongs to the Special Issue Environmentally Friendly Materials in Construction)

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2 pages, 175 KiB

Open AccessEditorial

Special Issue “Corrosion in Concrete: Inhibitors and Coatings”

by Luigi Coppola

Materials 2021, 14(20), 6211; https://doi.org/10.3390/ma14206211 - 19 Oct 2021

Cited by 1 | Viewed by 1219

Abstract

The climatic changes that are taking place in recent years have increased awareness of the importance of environmental protection and the urgent need for industrial strategies aimed at a sustainable development [...] Full article

(This article belongs to the Special Issue Corrosion in Concrete: Inhibitors and Coatings)

17 pages, 27194 KiB

Open AccessArticle

Lagrangian Differencing Dynamics for Time-Independent Non-Newtonian Materials

by Martina Bašić, Branko Blagojević, Chong Peng and Josip Bašić

Materials 2021, 14(20), 6210; https://doi.org/10.3390/ma14206210 - 19 Oct 2021

Cited by 3 | Viewed by 1713

Abstract

This paper introduces a novel meshless and Lagrangian approach for simulating non-Newtonian flows, named Lagrangian Differencing Dynamics (LDD). Second-order-consistent spatial operators are used to directly discretize and solve generalized Navier–Stokes equations in a strong formulation. The solution is obtained using a split-step scheme, [...] Read more.

This paper introduces a novel meshless and Lagrangian approach for simulating non-Newtonian flows, named Lagrangian Differencing Dynamics (LDD). Second-order-consistent spatial operators are used to directly discretize and solve generalized Navier–Stokes equations in a strong formulation. The solution is obtained using a split-step scheme, i.e., by decoupling the solutions of the pressure and velocity. The pressure is obtained by solving a Poisson equation, and the velocity is solved in a semi-implicit formulation. The matrix-free solution to the equations, and Lagrangian advection of mesh-free nodes allowed for a fully parallelized implementation on the CPU and GPU, which ensured an affordable computing time and large time steps. A set of four benchmarks are presented to demonstrate the robustness and accuracy of the proposed formulation. The tested two- and three-dimensional simulations used Power Law, Casson and Bingham models. An Abram slump test and a dam break test were performed using the Bingham model, yielding visual and numerical results in accordance with the experimental data. A square lid-driven cavity was tested using the Casson model, while the Power Law model was used for a skewed lid-driven cavity test. The simulation results of the lid-driven cavity tests are in good agreement with velocity profiles and stream lines of published reports. A fully implicit scheme will be introduced in future work. As the method precisely reproduces the pressure field, non-Newtonian models that strongly depend on the pressure will be validated. Full article

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16 pages, 60590 KiB

Open AccessArticle

The Influence of the Type of Electrolyte in the Modifying Solution on the Protective Properties of Vinyltrimethoysilane/Ethanol-Based Coatings Formed on Stainless Steel X20Cr13

by Aleksandra Kucharczyk, Lidia Adamczyk and Krzysztof Miecznikowski

Materials 2021, 14(20), 6209; https://doi.org/10.3390/ma14206209 - 19 Oct 2021

Cited by 8 | Viewed by 1793

Abstract

The paper reports the results of the examination of the protective properties of silane coatings based on vinyltrimethoxysilane (VTMS) and ethanol (EtOH), doped with the following electrolytes: acetic acid (AcOH), lithium perchlorate LiClO₄, sulphuric acid (VI) H₂SO₄ and [...] Read more.

The paper reports the results of the examination of the protective properties of silane coatings based on vinyltrimethoxysilane (VTMS) and ethanol (EtOH), doped with the following electrolytes: acetic acid (AcOH), lithium perchlorate LiClO₄, sulphuric acid (VI) H₂SO₄ and ammonia NH₃. The coatings were deposited on stainless steel X20Cr13 by the sol–gel dip-coating method. The obtained VTMS/EtOH/Electrolyte coatings were characterized in terms of corrosion resistance, surface morphology and adhesion to the steel substrate. Corrosion tests were conducted in sulphate media acidified up to pH = 2 with and without chloride ions Cl⁻, respectively. The effectiveness of corrosion protection was determined using potentiometric curves. It has been demonstrated that the coatings under study slow down the processes of corrosion of the steel substrate, thus effectively protecting it against corrosion. Full article

(This article belongs to the Special Issue Corrosion Properties and Mechanism of Steels)

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19 pages, 7022 KiB

Open AccessArticle

Strength and Acid Resistance of Ceramic-Based Self-Compacting Alkali-Activated Concrete: Optimizing and Predicting Assessment

by Hassan Amer Algaifi, Mohammad Iqbal Khan, Shahiron Shahidan, Galal Fares, Yassir M. Abbas, Ghasan Fahim Huseien, Babatunde Abiodun Salami and Hisham Alabduljabbar

Materials 2021, 14(20), 6208; https://doi.org/10.3390/ma14206208 - 19 Oct 2021

Cited by 10 | Viewed by 1806

Abstract

The development of self-compacting alkali-activated concrete (SCAAC) has become a hot topic in the scientific community; however, most of the existing literature focuses on the utilization of fly ash (FA), ground blast furnace slag (GBFS), silica fume (SF), and rice husk ash (RHA) [...] Read more.

The development of self-compacting alkali-activated concrete (SCAAC) has become a hot topic in the scientific community; however, most of the existing literature focuses on the utilization of fly ash (FA), ground blast furnace slag (GBFS), silica fume (SF), and rice husk ash (RHA) as the binder. In this study, both the experimental and theoretical assessments using response surface methodology (RSM) were taken into account to optimize and predict the optimal content of ceramic waste powder (CWP) in GBFS-based self-compacting alkali-activated concrete, thus promoting the utilization of ceramic waste in construction engineering. Based on the suggested design array from the RSM model, experimental tests were first carried out to determine the optimum CWP content to achieve reasonable compressive, tensile, and flexural strengths in the SCAAC when exposed to ambient conditions, as well as to minimize its strength loss, weight loss, and UPVL upon exposure to acid attack. Based on the results, the optimum content of CWP that satisfied both the strength and durability aspects was 31%. In particular, a reasonable reduction in the compressive strength of 16% was recorded compared to that of the control specimen (without ceramic). Meanwhile, the compressive strength loss of SCAAC when exposed to acid attack minimized to 59.17%, which was lower than that of the control specimen (74.2%). Furthermore, the developed RSM models were found to be reliable and accurate, with minimum errors (RMSE < 1.337). In addition, a strong correlation (R > 0.99, R² < 0.99, adj. R² < 0.98) was observed between the predicted and actual data. Moreover, the significance of the models was also proven via ANOVA, in which p-values of less than 0.001 and high F-values were recorded for all equations. Full article

(This article belongs to the Topic Sustainability in Buildings: New Trends in the Management of Construction and Demolition Waste)

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17 pages, 4301 KiB

Open AccessArticle

Effects of Artificial Tooth Brushing and Hydrothermal Aging on the Mechanical Properties and Color Stability of Dental 3D Printed and CAD/CAM Materials

by Na-Eun Nam, Seung-Ho Shin, Jung-Hwa Lim, June-Sung Shim and Jong-Eun Kim

Materials 2021, 14(20), 6207; https://doi.org/10.3390/ma14206207 - 19 Oct 2021

Cited by 24 | Viewed by 3232

Abstract

This study analyzed the surface roughness and waviness, Vickers hardness (VHN), and color changes of six types of 3D printed resins and computer-aided design/computer-aided manufacturing (CAD/CAM) materials after artificial toothbrushing. The average surface roughness height (Ra) change of Formlabs denture teeth A2 resin [...] Read more.

This study analyzed the surface roughness and waviness, Vickers hardness (VHN), and color changes of six types of 3D printed resins and computer-aided design/computer-aided manufacturing (CAD/CAM) materials after artificial toothbrushing. The average surface roughness height (Ra) change of Formlabs denture teeth A2 resin (FMLB) was not significant between after artificial toothbrushing (0.17 ± 0.02 μm and 0.17 ± 0.05 μm, respectively; mean ± standard deviation). However, the Ra value increased significantly in all remaining groups. Regarding waviness, polymethylmethacrylate (PMMA) had the largest increases in average waviness height (Wa) and maximum surface waviness height (Wz) between, before (0.43 ± 0.23 μm and 0.08 ± 0.02 μm), and after (8.67 ± 4.03 μm, 1.30 ± 0.58 μm) toothbrushing. There were no significant changes in Wa for Formlabs denture teeth A2 resin (FMLB) and NextDent C&B (NXT). After artificial toothbrushing, the dispersed-filler composite (DFC) group had the largest color difference (ΔE, of 2.4 ± 0.9), and the remaining materials had smaller changes than the clinical acceptance threshold of ΔE = 2.25. The VHN of FMLB and NXT were 9.1 ± 0.4 and 15.5 ± 0.4, respectively, and were not affected by artificial toothbrushing. The flexural strengths of the 3D printed materials were 139.4 ± 40.5 MPa and 163.9 ± 14.0 MPa for FMLB and NXT, respectively, which were similar to those of the polycarbonate and PMMA groups (155.2 ± 23.6 MPa and 108.0 ± 8.1 MPa, respectively). This study found that the evaluated 3D printed materials had mechanical and optical properties comparable to those of CAD/CAM materials and were stable even after artificial toothbrushing and hydrothermal aging. Full article

(This article belongs to the Special Issue Prospects for Dental Materials in Prosthodontics)

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20 pages, 7068 KiB

Open AccessArticle

Mechanical Properties and Constitutive Model Applied to the High-Speed Impact of Aluminum Foam That Considers Its Meso-Structural Parameters

by Qian Guo, Wenbin Li, Wenjin Yao, Xiaoming Wang and Changqiang Huang

Materials 2021, 14(20), 6206; https://doi.org/10.3390/ma14206206 - 19 Oct 2021

Cited by 2 | Viewed by 1821

Abstract

In this work, quasistatic mechanical compression experiments were used to study the stress–strain relationship of aluminum foam, and the mechanism of the compressive deformation of aluminum foam under quasistatic compression conditions is discussed based on the experimental observations. Since the interactions among cells [...] Read more.

In this work, quasistatic mechanical compression experiments were used to study the stress–strain relationship of aluminum foam, and the mechanism of the compressive deformation of aluminum foam under quasistatic compression conditions is discussed based on the experimental observations. Since the interactions among cells of the aluminum foam and differences in compressive strength among cells substantially impacted the mechanical properties of the material, the cellular structural parameters, namely the cell size and cell wall thickness, were defined. Along with the mechanism of deformation of a single cell, the influence of structural parameters on the micro failure mechanism and the stress–strain relationship of the aluminum foam material was analyzed. In combination with the factors influencing the mechanical properties of the aluminum foam, a mechanical constitutive model of aluminum foam suitable for multi-density and multi-impact environments that considers cellular structure density was established to predict the complete stress–strain relationship of aluminum foam under a high strain rate. The coupling function of strain rate and temperature in the original model was verified and the parameters were determined by the compression experiments under different strain rates and different temperatures. Full article

(This article belongs to the Special Issue Constitutive Model for Porous Metallic Materials)

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24 pages, 33230 KiB

Open AccessArticle

Moisture Vapor Permeability and Thermal Wear Comfort of Ecofriendly Fiber-Embedded Woven Fabrics for High-Performance Clothing

by Hyun-Ah Kim

Materials 2021, 14(20), 6205; https://doi.org/10.3390/ma14206205 - 19 Oct 2021

Cited by 14 | Viewed by 3185

Abstract

This study examined the moisture vapor permeability and thermal wear comfort of ecofriendly fiber-embedded woven fabrics in terms of the yarn structure and the constituent fiber characteristics according to two measuring methods. The moisture vapor permeability measured using the upright cup (CaCl₂ [...] Read more.

This study examined the moisture vapor permeability and thermal wear comfort of ecofriendly fiber-embedded woven fabrics in terms of the yarn structure and the constituent fiber characteristics according to two measuring methods. The moisture vapor permeability measured using the upright cup (CaCl₂) method (JIS L 1099A-1) was primarily dependent on the hygroscopicity of the ecofriendly constituent fibers in the yarns and partly influenced by the pore size in the fabric because of the yarn structure. On the other hand, the moisture vapor resistance measured using the sweating guarded hot plate method (ISO 11092) was governed mainly by the fabric pore size and partly by the hygroscopicity of the constituent ecofriendly fibers. The difference between the two measuring methods was attributed to the different mechanisms in the measuring method. The thermal conductivity as a measure of the thermal wear comfort of the composite yarn fabrics was governed primarily by the pore size in the fabric and partly by the thermal characteristics of the constituent fibers in the yarns. Lastly, considering market applications, the Coolmax^®/Tencel sheath/core fabric appears useful for winter warm feeling clothing because of its the good breathability with low thermal conductivity. The bamboo and Coolmax^®/bamboo fabrics are suitable for summer clothing with a cool feel because of their high thermal conductivity with good breathability. Overall, ecofriendly fibers (bamboo and Tencel) are of practical use for marketing environmentallyfriendly high-performance clothing. Full article

(This article belongs to the Special Issue Advanced Materials for Clothing and Textile Engineering)

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21 pages, 3383 KiB

Open AccessArticle

Critical State Theory for the Magnetic Coupling between Soft Ferromagnetic Materials and Type-II Superconductors

by Muhammad U. Fareed and Harold S. Ruiz

Materials 2021, 14(20), 6204; https://doi.org/10.3390/ma14206204 - 19 Oct 2021

Cited by 2 | Viewed by 2014

Abstract

Improving our understanding of the physical coupling between type-II superconductors (SC) and soft ferromagnetic materials (SFM) is the root for progressing to the application of SC-SFM metastructures in scenarios such as magnetic cloaking, magnetic shielding, and power transmission systems. However, in the latter, [...] Read more.

Improving our understanding of the physical coupling between type-II superconductors (SC) and soft ferromagnetic materials (SFM) is the root for progressing to the application of SC-SFM metastructures in scenarios such as magnetic cloaking, magnetic shielding, and power transmission systems. However, in the latter, some intriguing and yet unexplained phenomena occurred, such as a noticeable rise in the SC energy losses, and a local but not isotropic deformation of its magnetic flux density. These phenomena, which are in apparent contradiction with the most fundamental theory of electromagnetism for superconductivity, that is, the critical state theory (CST), have remained unexplained for about 20 years, given the acceptance of the controversial and yet paradigmatic existence of the so-called overcritical current densities. Therefore, aiming to resolve these long-standing problems, we extended the CST by incorporating a semi-analytical model for cylindrical monocore SC-SFM heterostructures, setting the standards for its validation with a variational approach of multipole functionals for the magnetic coupling between Sc and SFM materials. It is accompanied by a comprehensive numerical study for SFM sheaths of arbitrary dimensions and magnetic relative permeabilities

μ_{r}

, ranging from

μ_{r} = 5

(NiZn ferrites) to

μ_{r}

= 350,000 (pure Iron), showing how the AC-losses of the SC-SFM metastructure radically changes as a function of the SC and the SFM radius for

μ_{r} \geq 100

. Our numerical technique and simulations also revealed a good qualitative agreement with the magneto optical imaging observations that were questioning the CST validness, proving therefore that the reported phenomena for self-field SC-SFM heterostructures can be understood without including the ansatz of overcritical currents. Full article

(This article belongs to the Special Issue Engineering Properties of Superconducting Materials (Second Volume))

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15 pages, 5042 KiB

Open AccessArticle

Thermal Study and Emission Characteristics of Rice Husk Using TG-MS

by José Ignacio Arranz, María Teresa Miranda, Irene Montero and Francisco José Sepúlveda

Materials 2021, 14(20), 6203; https://doi.org/10.3390/ma14206203 - 19 Oct 2021

Cited by 6 | Viewed by 1725

Abstract

Rice husks are a by-product that is generated in large quantities in Spain. However, they are not used efficiently. One of their possible applications is its thermal use in power generation equipment. For that purpose, it is important to know the characteristics of [...] Read more.

Rice husks are a by-product that is generated in large quantities in Spain. However, they are not used efficiently. One of their possible applications is its thermal use in power generation equipment. For that purpose, it is important to know the characteristics of rice husks and their thermal behavior, as well as their possible pollutant emission to the atmosphere with respect to its thermal use as a biofuel. In this work, the thermal characteristics of rice husks and their thermal behavior were studied by using thermogravimetry and mass spectroscopy for two different atmospheres (oxidizing and inert). This way, the thermal profiles and the main characteristics were studied, as well as the emission of possible pollutants to the atmosphere, such as CO₂, CH₄, NO₂, NH₃, SO₂, and H₂S. Moreover, three different methods (FWO, KAS, and Starink) were used to carry out a thermal analysis, in order to obtain the main thermal parameters such as activation energy. The results of the analysis predicted that rice husks could be used as biofuel in industrial thermal equipment based on its acceptable calorific value, good thermal characteristics, and low gas emissions both in oxidizing and inert atmosphere (although they have a high ash content). Full article

(This article belongs to the Special Issue Application of Biomass-Derived Carbonaceous Materials in Energy and Environment)

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21 pages, 35180 KiB

Open AccessArticle

Soft-Landing Dynamic Analysis of a Manned Lunar Lander Em-Ploying Energy Absorption Materials of Carbon Nanotube Buckypaper

by Qi Yuan, Heng Chen, Hong Nie, Guang Zheng, Chen Wang and Likai Hao

Materials 2021, 14(20), 6202; https://doi.org/10.3390/ma14206202 - 19 Oct 2021

Cited by 4 | Viewed by 1938

Abstract

With the rapid development of the aerospace field, traditional energy absorption materials are becoming more and more inadequate and cannot meet the requirements of having a light weight, high energy absorption efficiency, and high energy absorption density. Since existing studies have shown that [...] Read more.

With the rapid development of the aerospace field, traditional energy absorption materials are becoming more and more inadequate and cannot meet the requirements of having a light weight, high energy absorption efficiency, and high energy absorption density. Since existing studies have shown that carbon nanotube (CNT) buckypaper is a promising candidate for energy absorption, owing to its extremely high energy absorption efficiency and remarkable mass density of energy absorption, this study explores the application of buckypaper as the landing buffer material in a manned lunar lander. Firstly, coarse-grained molecular dynamics simulations were implemented to investigate the compression stress-strain relationships of buckypapers with different densities and the effect of the compression rate within the range of the landing velocity. Then, based on a self-designed manned lunar lander, buckypapers of appropriate densities were selected to be the energy absorption materials within the landing mechanisms of the lander. For comparison, suitable aluminum honeycomb materials, the most common energy absorption materials in lunar landers, were determined for the same landing mechanisms. Afterwards, the two soft-landing multibody dynamic models are established, respectively, and their soft-landing performances under three severe landing cases are analyzed, respectively. The results depicted that the landers, respectively, adopting the two energy absorption materials well, satisfy the soft-landing performance requirements in all the cases. It is worth mentioning that the lander employing the buckypaper is proved to demonstrate a better soft-landing performance, mainly reflected in reducing the mass of the energy absorption element by 8.14 kg and lowing the maximum center-of-mass overload of the lander by 0.54 g. Full article

(This article belongs to the Topic Advances and Applications of Carbon Nanotubes)

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21 pages, 7658 KiB

Open AccessArticle

Alumina and Zirconia-Reinforced Polyamide PA-12 Composites for Biomedical Additive Manufacturing

by Damian S. Nakonieczny, Frank Kern, Lukas Dufner, Magdalena Antonowicz and Krzysztof Matus

Materials 2021, 14(20), 6201; https://doi.org/10.3390/ma14206201 - 19 Oct 2021

Cited by 22 | Viewed by 3078

Abstract

This work aimed to prepare a composite with a polyamide (PA) matrix and surface-modified ZrO₂ or Al₂O₃ to be used as ceramic fillers (CFs). Those composites contained 30 wt.% ceramic powder to 70 wt.% polymer. Possible applications for this [...] Read more.

This work aimed to prepare a composite with a polyamide (PA) matrix and surface-modified ZrO₂ or Al₂O₃ to be used as ceramic fillers (CFs). Those composites contained 30 wt.% ceramic powder to 70 wt.% polymer. Possible applications for this type of composite include bioengineering applications especially in the fields of dental prosthetics and orthopaedics. The ceramic fillers were subjected to chemical surface modification with Piranha Solution and suspension in 10 M sodium hydroxide and Si₃N₄ to achieve the highest possible surface development and to introduce additional functional groups. This was to improve the bonding between the CFs and the polymer matrix. Both CFs were examined for particle size distribution (PSD), functional groups (FTIR), chemical composition (XPS), phase composition (XRD), and morphology and chemical composition (SEM/EDS). Filaments were created from the powders prepared in this way and were then used for 3D FDM printing. Samples were subjected to mechanical tests (tensility, hardness) and soaking tests in a high-pressure autoclave in artificial saliva for 14, 21, and 29 days. Full article

(This article belongs to the Special Issue Friction and Wear of Materials Surfaces)

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11 pages, 6318 KiB

Open AccessArticle

The Effect of Different Condition of Pulpal Pressure on Microtensile Bond Strength of Several Dentin Bonding Agents on Deep and Superficial Dentin

by Marco Montanari, Luca Fiorillo, Gabriele Cervino, Sergio Sambataro, Alan Scott Herford and Marco Cicciù

Materials 2021, 14(20), 6200; https://doi.org/10.3390/ma14206200 - 19 Oct 2021

Cited by 1 | Viewed by 2056

Abstract

The objective of this study was to examine the effect of different conditions of simulated hydrostatic pulpal pressure on the μTBS of HEMA-based and HEMA-free dentin bonding agents (DBAs). The influence of dentin location (deep and superficial) on μTBS was also evaluated. Flat [...] Read more.

The objective of this study was to examine the effect of different conditions of simulated hydrostatic pulpal pressure on the μTBS of HEMA-based and HEMA-free dentin bonding agents (DBAs). The influence of dentin location (deep and superficial) on μTBS was also evaluated. Flat coronal dentin surfaces of extracted human molars were prepared. Three groups of resin-bonded specimens were exposed to different pulpal pressures. Pulpal pressure was maintained for 20 min for each group. A flowable resin composite was used for coronal build-up. The bonded teeth were sectioned and, after 24 h of water storage, stressed to failure using the microtensile tester (μTBS). Failed samples were analyzed by SEM inspection. HEMA-based DBAs were much more sensitive to pulpal pressure conditions than non-HEMA-containing DBAs. Pulpal pressure had a greater influence in deep dentin. The HEMA-free DBA was insensitive to the presence or absence of pulpal pressure condition. SEM inspection confirmed a relationship between the presence of voids inside the HEMA-based DBAs layer and the lower μTBS results. HEMA-based DBAs are more sensitive to pulpal pressure conditions than HEMA-free DBAs. Interestingly, HEMA-free DBA showed a greater number of water droplets at resin–dentin interface in all tested conditions. Full article

(This article belongs to the Special Issue Endodontics)

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7 pages, 1390 KiB

Open AccessArticle

Fabricated CAD/CAM Post-Core Using Glass Fiber-Reinforced Resin Shows Innovative Potential in Restoring Pulpless Teeth

by Naoko Suzaki, Satoshi Yamaguchi, Eriko Nambu, Ryousuke Tanaka, Satoshi Imazato and Mikako Hayashi

Materials 2021, 14(20), 6199; https://doi.org/10.3390/ma14206199 - 19 Oct 2021

Cited by 9 | Viewed by 2412

Abstract

The prevention of root fractures of pulpless teeth is an important clinical issue to maintain healthy teeth through lifetime. The aim of this study was to examine a clinically effective treatment method for strengthening vulnerable pulpless teeth using CAD/CAM (computer-aided design/computer-aided manufacturing) fiber-reinforced [...] Read more.

The prevention of root fractures of pulpless teeth is an important clinical issue to maintain healthy teeth through lifetime. The aim of this study was to examine a clinically effective treatment method for strengthening vulnerable pulpless teeth using CAD/CAM (computer-aided design/computer-aided manufacturing) fiber-reinforced post-core by conducting a fracture resistance test. A post-core made with a fiber-reinforced resin disk TRINIA (TR, SHOFU, Kyoto, Japan) was fabricated using a CAD/CAM system. The fiber-layer orientation of the CAD/CAM post-core was parallel to the axis of the restored tooth. A post-core using a conventional composite and a fiber post (CF) was also prepared. A fracture resistance test of teeth restored with the post-cores and zirconia crowns was conducted using a universal testing machine, and fracture patterns were identified by micro-CT observation. The fracture load of the roots restored with TR was 1555.9 ± 231.8 N, whereas that of CF was 1082.1 ± 226.7 N. The fracture load of TR was 43.8% that was significantly higher than that of CF (Student’s t-test, p < 0.05). The restored teeth with CAD/CAM resin post-core were found to be repairable even after fracture. These results suggest that the CAD/CAM indirect fiber post-core has the potential to strengthen the vulnerable pulpless teeth. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymers for Structural Strengthening)

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