Coatings

18 pages, 3590 KiB

Open AccessArticle

Preharvest Application of Hexanal as a Surface Treatment Improved the Storage Life and Quality of Mango Fruits

by Palpandian Preethi, Kadambavanasundaram Soorianathasundaram, Athipathi Sadasakthi, Kizhaeral Sevathapandian Subramanian, Sanikommu Vijay Rakesh Reddy, Gopinadhan Paliyath and Jayasankar Subramanian

Coatings 2021, 11(10), 1267; https://doi.org/10.3390/coatings11101267 - 19 Oct 2021

Cited by 8 | Viewed by 2212

Abstract

Mango is a highly preferred seasonal tropical fruit with a maximum shelf-life of five to seven days. Hexanal is a plant volatile compound assayed in green tissues and showing significance in enhancing storage life and fruit quality attributes by preserving membrane integrity. This [...] Read more.

Mango is a highly preferred seasonal tropical fruit with a maximum shelf-life of five to seven days. Hexanal is a plant volatile compound assayed in green tissues and showing significance in enhancing storage life and fruit quality attributes by preserving membrane integrity. This experiment explored the effect of the pre-harvest application of an aqueous hexanal composition (active ingredient: 0.02% hexanal) in altering the post-harvest storage behavior of four mango cultivars. The pre-harvest application of the hexanal formulation to the fruit surface twice before the harvest date drastically slowed down the physiological loss in weight by 70% to 80%, and reduced the ethylene evolution rate by two to three folds, respectively. The pre-harvest hexanal formulation spray combined with post-harvest cold storage prominently improved the storage life along with the total soluble solids, total sugars, ascorbic acid and carotenoid content compared to untreated fruits stored in ambient conditions. Though ripening coincides with the increased activity of enzymes, the hexanal formulation spray acts predominantly in bringing down the activities of fruit softening enzymes viz. pectinmethlyesterase (43%) and polygalacturonases (37%), and antioxidant enzymes viz. peroxidase (67%) and catalase (45%), respectively. Full article

(This article belongs to the Special Issue Natural Based Bioactive Coatings)

► Show Figures

Figure 1

11 pages, 2687 KiB

Open AccessArticle

Properties of Al₂O₃ Thin Films Grown by PE-ALD at Low Temperature Using H₂O and O₂ Plasma Oxidants

by Jhonathan Castillo-Saenz, Nicola Nedev, Benjamín Valdez-Salas, Mario Curiel-Alvarez, María Isabel Mendivil-Palma, Norberto Hernandez-Como, Marcelo Martinez-Puente, David Mateos, Oscar Perez-Landeros and Eduardo Martinez-Guerra

Coatings 2021, 11(10), 1266; https://doi.org/10.3390/coatings11101266 - 19 Oct 2021

Cited by 10 | Viewed by 3194

Abstract

Al₂O₃ layers with thicknesses in the 25–120 nm range were deposited by plasma enhanced atomic layer deposition at 70 °C. Trimethylaluminum was used as organometallic precursor, O₂ and H₂O as oxidant agents and Ar as a purge [...] Read more.

Al₂O₃ layers with thicknesses in the 25–120 nm range were deposited by plasma enhanced atomic layer deposition at 70 °C. Trimethylaluminum was used as organometallic precursor, O₂ and H₂O as oxidant agents and Ar as a purge gas. The deposition cycle consisted of 50 ms TMA pulse/10 s purge time/6 s of plasma oxidation at 200 W/10 s purge time. The optical constants and thicknesses of the grown layers were determined by spectroscopic ellipsometry, while the roughness was measured by atomic force microscopy, giving RMS values in the 0.29–0.32 nm range for films deposited under different conditions and having different thicknesses. High transmittance, ~90%, was measured by UV–Vis spectroscopy. X-ray photoelectron spectroscopy revealed that, with both types of oxidants, the obtained films are close to stoichiometric composition and, with high purity, no carbon was detected. Electrical characterization showed good insulating properties of both types of films, though the H₂O oxidant leads to better I-V characteristics. Full article

► Show Figures

Figure 1

11 pages, 2772 KiB

Open AccessArticle

Measurement of Stress Optic Coefficient for Thermal Barrier Coating Based on Terahertz Time-Domain Spectrum

by Zong Wang, Yanheng Zhang, Ning Lu, Zhiyong Wang and Wei Qiu

Coatings 2021, 11(10), 1265; https://doi.org/10.3390/coatings11101265 - 18 Oct 2021

Cited by 3 | Viewed by 1855

Abstract

The residual stress introduced inside the thermal barrier coating (TBC) top coating during manufacturing and service processes is one of the main causes of thermal barrier failure. Therefore, a nondestructive and accurate measurement of the residual stress in top coating is essential for [...] Read more.

The residual stress introduced inside the thermal barrier coating (TBC) top coating during manufacturing and service processes is one of the main causes of thermal barrier failure. Therefore, a nondestructive and accurate measurement of the residual stress in top coating is essential for the evaluation of TBC life. The terahertz time-domain spectroscopy (THz-TDS) technique, which is based on the calibration or measurement of the stress optical coefficients of the measured materials, is applicable to the measuring of internal stress of nonmetal materials. In this work, to characterize the internal stress in TBC, the stress optic coefficient of the TBC top coating was measured by reflection-type THz-TDS. First, the mechanics model for the internal stress measurement in a TBC top coating was derived based on the photoelastic theory. Then, the THz time-domain spectra of TBC specimens under different loadings were measured in situ by a reflection-type THz-TDS system. Finally, the unimodal fitting, multimodal fitting and barycenter methods were used to carry out the data processing of the THz time-domain spectral-characteristic peaks. By comparing the processed results, the results using the barycenter method were regarded as the calibrated stress optical coefficient of the TBC due to the method’s sufficient accuracy and stability. Full article

(This article belongs to the Special Issue Mechanical Properties of Advanced Multifunctional Coatings)

► Show Figures

Figure 1

7 pages, 1340 KiB

Open AccessArticle

Microfabrication of VO₂ Thin Films via a Photosensitive Sol-Gel Method

by Chuanbao Wu, Yunwei Wang and Guangqiang Ma

Coatings 2021, 11(10), 1264; https://doi.org/10.3390/coatings11101264 - 18 Oct 2021

Cited by 6 | Viewed by 2372

Abstract

VO₂ films are widely used in photoelectric switches, smart glasses, storage media, and terahertz communications. In these applications, microfabrication technology is a very important process for producing microdevices or even improving film properties. In this paper, a novel photoetching microfabrication method is [...] Read more.

VO₂ films are widely used in photoelectric switches, smart glasses, storage media, and terahertz communications. In these applications, microfabrication technology is a very important process for producing microdevices or even improving film properties. In this paper, a novel photoetching microfabrication method is proposed for VO₂ thin films. First, a VO₂ precursor sol with ultraviolet photosensitivity was prepared using vanadyl acetylacetonate as the raw material and anhydrous methanol as the solvent. The dip-coated VO₂ gel film can be directly subjected to photolithography processing without coating additional photoresist by using the photosensitive sol. A fine pattern on the VO₂ film with good phase-transition performance can be obtained after annealing in a nitrogen atmosphere at 550 °C for 1 h. This method can be used to prepare grating, microarray, and various other fine patterns with the remarkable advantages of a low cost and simplified process, and the as-obtained material performances are unaffected using the method. It is a potential alternative method for optics, electronics, and magnetics devices based on VO₂ thin films. Full article

(This article belongs to the Topic Inorganic Thin Film Materials)

► Show Figures

Figure 1

12 pages, 4181 KiB

Open AccessArticle

Prediction of Dissolved Impurities and Movement of Oxide Particles in the Primary Circuit of LBE Fast Reactor

by Jiewei Wu, Rongjun Wu, Yuqing Wang, Jianbo He, Chen Hu, Xian Zeng and Muyi Ni

Coatings 2021, 11(10), 1263; https://doi.org/10.3390/coatings11101263 - 18 Oct 2021

Cited by 3 | Viewed by 2011

Abstract

To better understand the corrosion and corrosion products behavior in the primary circuit of lead-bismuth eutectic (LBE) coolant reactor, the concentration distribution of soluble impurities and the transport of solid particles are investigated through the finite-element method. An axisymmetric model of the primary [...] Read more.

To better understand the corrosion and corrosion products behavior in the primary circuit of lead-bismuth eutectic (LBE) coolant reactor, the concentration distribution of soluble impurities and the transport of solid particles are investigated through the finite-element method. An axisymmetric model of the primary circuit of an LBE reactor was constructed to accelerate the calculation of the thermal hydraulic filed of the circuit. The saturation concentration of solute Fe, Cr and Ni in LBE coolant are identified through the equilibrium of their oxides and PbO, and the very different saturation concentrations of Fe/Cr/Ni in LBE will lead to significant element-selective corrosion. The migration of solid oxide particles in the primary circuit is also investigated by the Euler–Lagrange tracing model. The simulation shows that driving force for the movement of particles >100 μm is buoyancy, which lets particles float on a free surface, while particles <10 μm tend to suspend in coolant. However, the behavior of particles also depends on the formation position, the particles formed above the core have a high possibility of re-entering in the core. Full article

(This article belongs to the Special Issue Friction, Wear Properties and Applications of Coatings)

► Show Figures

Figure 1

12 pages, 3882 KiB

Open AccessArticle

Excellent Properties of Ni-15 wt.% W Alloy Electrodeposited from a Low-Temperature Pyrophosphate System

by Changwei Su, Zhaoyao Sa, Yangyang Liu, Linfu Zhao, Fengjing Wu and Wei Bai

Coatings 2021, 11(10), 1262; https://doi.org/10.3390/coatings11101262 - 18 Oct 2021

Cited by 6 | Viewed by 1892

Abstract

Electrodeposited Ni-W alloy coatings are considered to be one of the most suitable candidate coatings to replace carcinogenic hexavalent chromium coatings. In this work, Ni-W alloys are electrodeposited from pyrophosphate baths containing different concentrations of Na₂WO₄ 2H₂O (C [...] Read more.

Electrodeposited Ni-W alloy coatings are considered to be one of the most suitable candidate coatings to replace carcinogenic hexavalent chromium coatings. In this work, Ni-W alloys are electrodeposited from pyrophosphate baths containing different concentrations of Na₂WO₄ 2H₂O (C_W) at 40 °C. Both C_W and the applied current density can affect the W content in the coatings. The effect of C_W becomes weaker with the increased current density. The Ni-W alloys with 15 ± 5 wt.% W (Ni-15 wt.% W) are obtained from the bath containing 40 g L⁻¹ C_W at a high current of 8 A dm⁻². The microhardness, corrosion resistance and hydrogen evolution reaction (HER) are measured with a microhardness tester and an electrochemical workstation. The modified properties are studied by heat treatment from 200 to 700 °C. The highest microhardness of 895.62 HV and the better HER property is presented after heat treatment at 400 °C, while the best corrosion resistance in 3.5 wt.% NaCl solution appears at 600 °C. Full article

(This article belongs to the Section Surface Characterization, Deposition and Modification)

► Show Figures

Figure 1

12 pages, 6385 KiB

Open AccessArticle

Understanding the Relations between Surface Stress State and Microstructure Feature for Enhancing the Fatigue Performance of TC6 Titanium Alloy

by Song Shu, Xin Huang, Zonghui Cheng, Yizhou Shen, Zhaoru He and Weilan Liu

Coatings 2021, 11(10), 1261; https://doi.org/10.3390/coatings11101261 - 18 Oct 2021

Cited by 2 | Viewed by 1651

Abstract

Fatigue performance has always been an important factor affecting the application of titanium alloy. The service life of TC6 titanium alloy is easily reduced under a continuously alternating load. Therefore, there is an urgent need for a new method to improve fatigue performance. [...] Read more.

Fatigue performance has always been an important factor affecting the application of titanium alloy. The service life of TC6 titanium alloy is easily reduced under a continuously alternating load. Therefore, there is an urgent need for a new method to improve fatigue performance. Laser shock peening (LSP) is a widely proposed method to enhance the fatigue performance. Here, through experiments and finite element simulations, it was found that LSP can prolong the fatigue life of TC6 by improving the surface stress state. In strengthening processes, the generation of residual stress was mainly attributed to the change of microstructure, which could be reflected by the statistical results of grain sizes. The content of grains with a size under 0.8 μm reached 78%, and the microhardness value of treated TC6 was 18.7% higher than that of an untreated sample. In addition, the surface residual compressive stress was increased to −600 MPa at the depth of 1500 μm from the surface. On this basis, the fatigue life was prolonged to 135%, and the ultimate fracture macroscopic was also changed. With the treatment of LSP, the fatigue performance of TC6 is highly promoted. The strengthening mechanism of LSP was established with the aim of revealing the relationship between microstructure and stress state for enhancing the fatigue performance in whatever shapes. Full article

(This article belongs to the Special Issue Laser Nano Fabrication and Nano Deposition)

► Show Figures

Figure 1

22 pages, 13803 KiB

Open AccessArticle

Application of the Electrochemical Permeation Method for Hydrogen Diffusion Coefficient Determination in Pipeline Steel 10G2

by Vladislav I. Borodin, Aleksandr V. Lun-Fu, Victor N. Kudiiarov, Andrey M. Lider, Ivan S. Sakvin, Mikhail A. Bubenchikov, Dmitry S. Kaparulin and Vyacheslav A. Ovchinnikov

Coatings 2021, 11(10), 1260; https://doi.org/10.3390/coatings11101260 - 16 Oct 2021

Viewed by 2704

Abstract

In this article, we conduct research on the effect of corrosion tests on the hydrogen diffusion process in gas steel in electrochemical permeability tests. This tests show that a long corrosion test time reduces the hydrogen diffusion coefficient by an order of magnitude, [...] Read more.

In this article, we conduct research on the effect of corrosion tests on the hydrogen diffusion process in gas steel in electrochemical permeability tests. This tests show that a long corrosion test time reduces the hydrogen diffusion coefficient by an order of magnitude, indicating the formation of aging defects in the steel. During operation, the diffusion coefficient decreases by two orders of magnitude, which also indicates the formation of a large number of defects in the steel. Consequently, based on the change in the diffusion coefficient in the material, it is possible to assess the degree of material failure. Full article

(This article belongs to the Topic Surface Treatments for Protecting from Fracture and Fatigue Damage)

► Show Figures

Figure 1

12 pages, 3184 KiB

Open AccessFeature PaperArticle

Melioration of Electrical and Optical Properties of Al and B Co-Doped ZnO Transparent Semiconductor Thin Films

by Chien-Yie Tsay and Shih-Hsun Yu

Coatings 2021, 11(10), 1259; https://doi.org/10.3390/coatings11101259 - 16 Oct 2021

Cited by 8 | Viewed by 2226

Abstract

Undoped, Al-doped and Al-B co-doped ZnO transparent semiconductor thin films were deposited on glass substrates by sol-gel method and spin coating technique. This study investigated the influence of Al (2 at.%) doping and Al (2 at.%)-B (1 or 2 at.%) co-doping on the [...] Read more.

Undoped, Al-doped and Al-B co-doped ZnO transparent semiconductor thin films were deposited on glass substrates by sol-gel method and spin coating technique. This study investigated the influence of Al (2 at.%) doping and Al (2 at.%)-B (1 or 2 at.%) co-doping on the microstructural, surface morphological, electrical and optical properties of the ZnO-based thin films. XRD analysis indicated that all as-prepared ZnO-based thin films were polycrystalline with a single-phase hexagonal wurtzite structure. The substitution of extrinsic dopants (Al or Al-B) into ZnO thin films can significantly degrade the crystallinity, refine the microstructures, improve surface flatness, enhance the optical transparency in the visible spectrum and lead to a shift in the absorption edge toward the short-wavelength direction. Experimental results showed that the Al-doped and Al-B co-doped ZnO thin films exhibited high average transmittance (>91.3%) and low average reflectance (<10%) in the visible region compared with the ZnO thin film. The optical parameters, including the optical bandgap, Urbach energy, extinction coefficient and refractive index, changed with the extrinsic doping level. Measured results of electrical properties revealed that the singly doped and co-doped samples exhibited higher electron concentrations and lower resistivities than those of the undoped sample and suggested that 2 at.% Al and 1 at.% B were the optimum dopant concentrations for achieving the best electrical properties in this study. Full article

(This article belongs to the Special Issue Thin Films for Electronic Applications)

► Show Figures

Graphical abstract

13 pages, 2936 KiB

Open AccessFeature PaperArticle

Durable Superhydrophobic Coating for Efficient Microplastic Removal

by Oriol Rius-Ayra, Alisiya Biserova-Tahchieva and Nuria Llorca-Isern

Coatings 2021, 11(10), 1258; https://doi.org/10.3390/coatings11101258 - 16 Oct 2021

Cited by 9 | Viewed by 2987

Abstract

The pollution caused by microplastics around the world is an increasingly significant issue that has to be tackled with different methods and technologies. Here, we report a straightforward and rapid process combining electrodeposition and electrophoresis to produce a durable superhydrophobic coating on an [...] Read more.

The pollution caused by microplastics around the world is an increasingly significant issue that has to be tackled with different methods and technologies. Here, we report a straightforward and rapid process combining electrodeposition and electrophoresis to produce a durable superhydrophobic coating on an aluminum substrate (UNS A91070) that has a static contact angle (153°), sliding angle (1°), and contact angle hysteresis (1°). Field emission scanning electron microscopy and high-resolution transmission electron microscopy showed the presence of a hierarchical structure with nanolayers that were 70 nm thick. The chemical composition was also analyzed using attenuated total reflectance-Fourier transform infrared spectroscopy and high-resolution X-ray photoelectron spectroscopy, which revealed that the hierarchical structure was composed of zinc laurate (Zn(C₁₁H₂₀COO)₂) that decreased the surface free energy of the system. Moreover, the coating showed high durability against abrasion caused by the P1200 SiC paper due to the presence of TiO₂ particles in the upper layers as well as the homogeneous chemical composition of the hierarchical structure. Finally, taking advantage of the superoleophilic properties of superhydrophobic surfaces, the ability of the coating to remove high-density polyethylene microplastics from water was studied. Full article

(This article belongs to the Special Issue Superhydrophobic and Superoleophobic Surfaces)

► Show Figures

Graphical abstract

19 pages, 5552 KiB

Open AccessFeature PaperArticle

Corrosion Improvement of 304L Stainless Steel by ZrSiN and ZrSi(N,O) Mono- and Double-Layers Prepared by Reactive Cathodic Arc Evaporation

by Mihaela Dinu, Anca Constantina Parau, Alina Vladescu, Adrian Emil Kiss, Iulian Pana, Emile S. Massima Mouele, Leslie Felicia Petrik and Viorel Braic

Coatings 2021, 11(10), 1257; https://doi.org/10.3390/coatings11101257 - 15 Oct 2021

Cited by 10 | Viewed by 2198

Abstract

Zr-based nitrides and oxynitrides were deposited by reactive cathodic arc evaporation in monolayer and double-layer structures with the aim of increasing the corrosion protection of 304L stainless steel (SS) in a biomedical aggressive environment. All coatings had a total thickness of 1.2 µm. [...] Read more.

Zr-based nitrides and oxynitrides were deposited by reactive cathodic arc evaporation in monolayer and double-layer structures with the aim of increasing the corrosion protection of 304L stainless steel (SS) in a biomedical aggressive environment. All coatings had a total thickness of 1.2 µm. Compared to the bare substrate, the surface roughness of the coated samples was higher, the presence of microdroplets being revealed by scanning electron micrography (SEM). The X-ray diffraction investigation of the ZrN phases revealed that the peaks shifted towards lower Bragg angles and the lattice constants increased as a result of Si and O₂ inclusion in ZrN lattice, and of the ion bombardment characteristic of the cathodic arc method, augmented by the applied bias substrate. SS/ZrSiN/ZrSi(N,O) showed the best corrosion performance in an acidic environment (0.9% NaCl and 6% H₂O₂; pH = 4), which was ascribed to the blocking effect of the interfaces, which acted as a corrosion barrier for the electrolyte ingress. Moreover, the aforementioned bilayer had the highest amount of Si and O in the composition of the top layer, forming a stable passive layer with beneficial effects on corrosion protection. Full article

(This article belongs to the Special Issue State-of-the-Art on Coatings Research in Romania 2021-2022)

► Show Figures

Graphical abstract

23 pages, 8781 KiB

Open AccessReview

Microstructure and Oxidation Behavior of Metal-Modified Mo-Si-B Alloys: A Review

by Laihao Yu, Fuqiang Shen, Tao Fu, Yingyi Zhang, Kunkun Cui, Jie Wang and Xu Zhang

Coatings 2021, 11(10), 1256; https://doi.org/10.3390/coatings11101256 - 15 Oct 2021

Cited by 14 | Viewed by 2254

Abstract

With the rapid development of the nuclear industry and the aerospace field, it is urgent to develop structural materials that can work in ultra-high temperature environments to replace nickel-based alloys. Mo-Si-B alloys are considered to have the most potential for new ultra-high temperature [...] Read more.

With the rapid development of the nuclear industry and the aerospace field, it is urgent to develop structural materials that can work in ultra-high temperature environments to replace nickel-based alloys. Mo-Si-B alloys are considered to have the most potential for new ultra-high temperature structural material and are favored by researchers. However, the medium-low temperature oxidizability of Mo-Si-B alloys limits their further application. Therefore, this study carried out extensive research and pointed out that alloying is an effective way to solve this problem. This work provided a comprehensive review for the microstructure and oxidation resistance of low silicon and high silicon Mo-Si-B alloys. Moreover, the influence of metallic elements on the microstructure, phase compositions, oxidation kinetics and behavior of Mo-Si-B alloys were also studied systematically. Finally, the modification mechanism of metallic elements was summarized in order to obtain Mo-Si-B alloys with superior oxidation performance. Full article

(This article belongs to the Special Issue Strengthening, Corrosion and Protection of High Temperature Structural Materials)

► Show Figures

Figure 1

20 pages, 3148 KiB

Open AccessArticle

A Comparative Study of the Mechanical Properties of Selected Dental Composites with a Dual-Curing System with Light-Curing Composites

by Monika Domarecka, Agata Szczesio-Wlodarczyk, Michał Krasowski, Magdalena Fronczek, Tomasz Gozdek, Jerzy Sokolowski and Kinga Bociong

Coatings 2021, 11(10), 1255; https://doi.org/10.3390/coatings11101255 - 15 Oct 2021

Cited by 8 | Viewed by 3014

Abstract

Dual-curing composites have a wide spectrum of use in practice (rebuilding, reconstruction, and luting). The characterization of this type of material and comparative study of selected mechanical properties with light-cured materials were carried out for this paper. In this study, we used six [...] Read more.

Dual-curing composites have a wide spectrum of use in practice (rebuilding, reconstruction, and luting). The characterization of this type of material and comparative study of selected mechanical properties with light-cured materials were carried out for this paper. In this study, we used six materials with a dual-cure system—Bulk EZ, Fill-Up!, StarFill 2B, Rebilda DC, MultiCore Flow, Activa Bioactive-Restorative—and three light-cured materials—Filtek Bulk Fill Posterior, Charisma Classic, and G-aenial Universal Flo. The materials were conditioned for 24 h in water at 37 °C before testing. Selected material properties were determined: three-point bending flexural strength, diametral tensile strength, hardness, microhardness, and shrinkage stress. The highest three-point bending flexural strength (TPB) was 137.0 MPa (G-aenial Universal Flo), while the lowest amounted to 86.5 MPa (Activa Bioactive). The diametral tensile strength (DTS) values were in a range from 39.2 MPa (Rebilda DC) to 54.1 MPa (Charisma Classic). The lowest hardness (HV) value of 26 was obtained by the Activa Bioactive material, while the highest values were recorded for Filtek Bulk Fill Posterior and Charisma Classic-53. The shrinkage stress of the tested materials ranged from 6.3 MPa (Charisma Classic) to 13.2 MPa (G-aenial Universal Flo). Dual-curing composites were found to have similar properties to light-cured composites. Full article

(This article belongs to the Special Issue Surface Properties of Dental Materials and Instruments)

► Show Figures

Figure 1

13 pages, 5262 KiB

Open AccessArticle

Relationship between Friction Coefficient and Surface Roughness of Stone and Ceramic Floors

by Samsiya Khaday, Kai-Way Li, Lu Peng and Ching-Chung Chen

Coatings 2021, 11(10), 1254; https://doi.org/10.3390/coatings11101254 - 15 Oct 2021

Cited by 7 | Viewed by 3446

Abstract

Slips and falls are common occupational incidents worldwide. The friction on a floor surface is one of the critical environmental factors affecting the risk of a slip. In this research, we conducted friction measurements on stone and ceramic floor tiles under dry, wet, [...] Read more.

Slips and falls are common occupational incidents worldwide. The friction on a floor surface is one of the critical environmental factors affecting the risk of a slip. In this research, we conducted friction measurements on stone and ceramic floor tiles under dry, wet, and water–detergent (WD) solution covered conditions using a horizontal pull slip meter (HPS). Our purposes were to quantify the slip resistance of commonly used stone and ceramic floors under different surface conditions and to validate the curvilinear relationship between the coefficient of friction (COF) and surface roughness of the floors proposed in the literature. The COF data were analyzed together with a surface profile parameter (R_a) of the floor samples. The results showed that the COFs of the stone floors were significantly (p < 0.0001) higher than those of the ceramic floors. All the floors under the dry conditions were slip resistant when adopting the ANSI 1264.2 criterion. Two and five ceramic floors were not slip resistant under the wet and WD solution covered conditions, respectively. Three polynomial regression equations were established to describe the relationship between the COF and R_a. The curvilinear functions of these models indicate that the three-zone (initial growth, steady-growth, and plateau) concept concerning the COF–R_a relationship in the literature was valid when static COF values measured using an HPS were adopted. In addition, the three-zone concept was valid not only on WD solution covered surfaces but also on dry and wet surfaces. Full article

(This article belongs to the Section Ceramic Coatings and Engineering Technology)

► Show Figures

Figure 1

12 pages, 1383 KiB

Open AccessArticle

Oxygen Barrier Performance of Poly(vinyl alcohol) Coating Films with Different Induced Crystallinity and Model Predictions

by Alamin Idris, Adrian Muntean, Beko Mesic, Magnus Lestelius and Asif Javed

Coatings 2021, 11(10), 1253; https://doi.org/10.3390/coatings11101253 - 15 Oct 2021

Cited by 14 | Viewed by 3083

Abstract

The presence of the crystalline regions in poly(vinyl alcohol) coating films acts as barrier clusters forcing the gas molecules to diffuse in a longer pathway in the amorphous region of the polymer, where diffusivity and solubility are promoted in comparison. Evaluating the influence [...] Read more.

The presence of the crystalline regions in poly(vinyl alcohol) coating films acts as barrier clusters forcing the gas molecules to diffuse in a longer pathway in the amorphous region of the polymer, where diffusivity and solubility are promoted in comparison. Evaluating the influence of crystalline regions on the oxygen barrier property of a semi-crystalline polymer is thus essential to prepare better coating films. Poly(vinyl alcohol) coating films with varying induced crystallinity were prepared on a polyethylene terephthalate (PET) substrate by drying at different annealing temperatures for 10 min. The coating films were first delaminated from the PET substrate and then characterized using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and X-ray diffraction (XRD) techniques to determine and confirm the induced percentage of crystallinity. The barrier performance of the coating films, i.e., the oxygen transmission rate (OTR), was measured at room temperature. Results showed a decrease in the OTR values of poly(vinyl alcohol) film with an increase in the degree of crystallinity of the polymer matrix. Tortuosity-based models, i.e., modified Nielsen models, were adopted to predict the barrier property of the semi-crystalline PVOH film with uniform or randomly distributed crystallites. A modified Nielsen model for orderly distributed crystallites with an aspect ratio of 3.4 and for randomly distributed crystallites with an aspect ratio of 10.4 resulted in a good correlation with the experimental observation. For the randomly distributed crystallites, lower absolute average relative errors of 4.66, 4.45, and 5.79% were observed as compared to orderly distributed crystallites when the degree of crystallinity was obtained using FTIR, DSC, and XRD data, respectively. Full article

(This article belongs to the Section Coatings for Food Technology and System)

► Show Figures

Figure 1

9 pages, 1748 KiB

Open AccessArticle

Dataset on a Small-Scale Film-Coating Process Developed for Self-Expanding 4D Printed Drug Delivery Devices

by Marco Uboldi, Alice Melocchi, Saliha Moutaharrik, Matteo Cerea, Andrea Gazzaniga and Lucia Zema

Coatings 2021, 11(10), 1252; https://doi.org/10.3390/coatings11101252 - 14 Oct 2021

Cited by 10 | Viewed by 1876

Abstract

Film-coating is widely applied in pharmaceutics to enhance aspect/taste and mechanical properties of dosage forms, to protect them from the environment and to modify their release performance. In this respect, a film-coating process was recently involved in the development of 4D printed prolonged-release [...] Read more.

Film-coating is widely applied in pharmaceutics to enhance aspect/taste and mechanical properties of dosage forms, to protect them from the environment and to modify their release performance. In this respect, a film-coating process was recently involved in the development of 4D printed prolonged-release systems intended for organ retention. During coating processes, liquid formulations are sprayed onto moving cores, whose shape, weight and surface characteristics are essential to attain a homogeneous film. Devices of complex shapes, composed of smart materials and fabricated by hot-processing techniques, such as extrusion and fused deposition modeling 3D printing, might be poorly compatible with the requirements of traditional coating methods, e.g., need for spherical substrates with smooth surface and stable under process temperatures. This work was aimed at evaluating, at a small scale level, the feasibility of a versatile equipment for film-coating of rod-shaped extruded and printed prototypes with different section. Equipment design and set up of process parameters were performed starting from polymeric solutions and suspensions and selecting as cores 50 mm-long rod-shaped samples based on shape memory poly(vinyl alcohol). Integrity and thickness of the applied layer and its impact on shape memory and release performance of prototypes were investigated. Full article

► Show Figures

Figure 1

9 pages, 4700 KiB

Open AccessArticle

Formation of Aligned α-Si3N4 Microfibers by Plasma Nitridation of Si (110) Substrate Coated with SiO₂

by Chang-Hua Yu, Kun-An Chiu, Thi-Hien Do, Li Chang and Wei-Chun Chen

Coatings 2021, 11(10), 1251; https://doi.org/10.3390/coatings11101251 - 14 Oct 2021

Cited by 2 | Viewed by 1886

Abstract

Plasma nitridation of an amorphous SiO₂ layer on Si (110) substrate can form well-aligned α-Si₃N₄ crystallites in fibrous morphology. Nitriding is performed at a temperature in the range of 800–1000 °C by using microwave plasma with a gas mixture [...] Read more.

Plasma nitridation of an amorphous SiO₂ layer on Si (110) substrate can form well-aligned α-Si₃N₄ crystallites in fibrous morphology. Nitriding is performed at a temperature in the range of 800–1000 °C by using microwave plasma with a gas mixture of N₂ and H₂. Raman spectroscopy shows the characteristics of an α-Si₃N₄ phase without other crystalline nitrides. As shown by scanning electron microscopy, the formed α-Si₃N₄ microfibers on the Si substrate can be in a dense and straight array nearly along with Si <

1 \bar{1} 0

>, and can have a length over 2 mm with a diameter in the range of 5–10 μm. Structural characterization of scanning transmission electron microscopy in cross section view reveals that the elongated α-Si₃N₄ crystallites are formed on the surface of the nitrided SiO₂/Si (110) substrate without any interlayers between Si₃N₄ and Si, and the longitudinal direction of α-Si₃N₄ appears mainly along <

11 \bar{2} 0

>, which is approximately parallel to Si <

1 \bar{1} 0

>. Full article

(This article belongs to the Section Ceramic Coatings and Engineering Technology)

► Show Figures

Figure 1

24 pages, 6099 KiB

Open AccessArticle

Well Rehabilitation via the Ultrasonic Method and Evaluation of Its Effectiveness from the Pumping Test

by Daniel Kahuda, Pavel Pech, Václav Ficaj and Hana Pechová

Coatings 2021, 11(10), 1250; https://doi.org/10.3390/coatings11101250 - 14 Oct 2021

Cited by 3 | Viewed by 2134

Abstract

The exploitation of groundwater reserves, especially for drinking purposes, is becoming increasingly important. This fact has created the need to maintain wells in the best possible functional condition. However, wells are subject to an ageing process during intensive use, which entails an increase [...] Read more.

The exploitation of groundwater reserves, especially for drinking purposes, is becoming increasingly important. This fact has created the need to maintain wells in the best possible functional condition. However, wells are subject to an ageing process during intensive use, which entails an increase in up-to-date resistances in the well itself and its immediate surroundings (the skin zone). This causes a decrease in the efficiency of the well (a decrease in the pumped quantity, a decrease in the specific yield, an increase of the drawdown in the well, and creation of the skin zone). The increased hydraulic gradient in the skin zone causes an increase in the inflow rate to the well, thereby inducing the movement of fine material towards the casing. This material can clog the well casing and injection ports, which is compounded by an increase in chemical and biological plugging of the skin zone. In cooperation with the company SONIC Technologies, GmbH. (Sailauf, Germany), an experimental ultrasonic technology-based well rehabilitation assembly was developed and successfully tested. This article describes the prototype development of the ultrasonic device, including its incorporation into the rehabilitation set and a demonstration of its pilot deployment in the MO-4 pumping well in Czech Republic with an evaluation of the rehabilitation effects using the authors’ software (Dtest_ULTRA). Based on visual inspection and the results of hydraulic and geophysical analysis, the high efficiency of the tested technology was demonstrated in virtually all monitored parameters, where an improvement in the range of 25–55% compared to the original condition was identified. Full article

► Show Figures

Figure 1

14 pages, 3218 KiB

Open AccessArticle

Study of Slip Effects in Reverse Roll Coating Process Using Non-Isothermal Couple Stress Fluid

by Hasan Shahzad, Xinhua Wang, Muhammad Bilal Hafeez, Zahir Shah and Ahmed Mohammed Alshehri

Coatings 2021, 11(10), 1249; https://doi.org/10.3390/coatings11101249 - 14 Oct 2021

Cited by 15 | Viewed by 1990

Abstract

The non-isothermal couple stress fluid inside a reverse roll coating geometry is considered. The slip condition is considered at the surfaces of the rolls. To develop the flow equations, the mathematical modelling is performed using conservation of momentum, mass, and energy. The LAT [...] Read more.

The non-isothermal couple stress fluid inside a reverse roll coating geometry is considered. The slip condition is considered at the surfaces of the rolls. To develop the flow equations, the mathematical modelling is performed using conservation of momentum, mass, and energy. The LAT (lubrication approximation theory) is employed to simplify the equations. The closed form solution for velocity, temperature, and pressure gradient is obtained. While the pressure and flow rate are obtained numerically. The impact of involved parameters on important physical quantities such as temperature, pressure, and pressure gradient are elaborated through graphs and in tabular form. The pressure and pressure gradient decreases for variation of the couple stress parameter and velocity ratio parameter K. While the variation of the slip parameter increases the pressure and pressure gradient inside the flow geometry. Additionally, flow rate decreases for the variation of the slip parameter as fluid starts moving rapidly along the roller surface. The most important physical quantity which is responsible for maintaining the quality of the coating and thickness is flow rate. For variation of both the couple stress parameter and the slip parameter, the flow rate decreases compared to the Newtonian case, consequently the coating thickness decreases for the variation of the discussed parameter. Full article

(This article belongs to the Section Liquid–Fluid Coatings, Surfaces and Interfaces)

► Show Figures

Figure 1

14 pages, 4647 KiB

Open AccessArticle

Ce and Y Co-Doping Effects for (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ Lead-Free Ceramics

by Chao Li, Jin-Su Baek and Jung-Hyuk Koh

Coatings 2021, 11(10), 1248; https://doi.org/10.3390/coatings11101248 - 14 Oct 2021

Cited by 4 | Viewed by 1499

Abstract

CeO₂ and Y₂O₃ were co-doped to (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ ceramics and sintered by conventional solid-state reaction process to form x wt.% CeO₂-y wt.% Y₂O₃ doped (Ba_0.85 [...] Read more.

CeO₂ and Y₂O₃ were co-doped to (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ ceramics and sintered by conventional solid-state reaction process to form x wt.% CeO₂-y wt.% Y₂O₃ doped (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (Ce_xY_y-BCZT) ceramics. The effects of different contents of CeO₂-Y₂O₃ dopants to the (Ba_0.85Ca_0.15) (Zr_0.1Ti_0.9)O₃ composition were analyzed by studying the phase, surface microstructure, piezoelectric and ferroelectric properties of BCZT ceramics. In this study, we have shown that co-doping a small amount of CeO₂ and Y₂O₃ will not change the phase structure of (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ ceramics. However, the proper introduction of CeO₂ and Y₂O₃ can improve the piezoelectric constant and electromechanical coupling coefficient of BCZT ceramic samples. Moreover, these dopants can promote the grain growth process in (Ba_0.85Ca_0.15) (Zr_0.1Ti_0.9)O₃ ceramics. C_0.04Y_0.02 doped (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ ceramic has the best piezoelectric properties compared with other composition, the results are as follows: Relative density = 96.9%, K_p = 0.583, and d₃₃ = 678 pC/N, V = 8.9 V. It means that this Ce_0.04Y_0.02 doped (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ ceramic is a desired material in the application of lead-free ceramics. Full article

(This article belongs to the Special Issue Thin Films for Electronic Devices)

► Show Figures

Graphical abstract

3 pages, 169 KiB

Open AccessEditorial

Physicochemical Surface Treatment of Wood Raw Materials

by Ruslan Rushanovich Safin, Ruslan Khasanshin, Shamil Ramilevich Mukhametzyanov and Albina Safina

Coatings 2021, 11(10), 1247; https://doi.org/10.3390/coatings11101247 - 14 Oct 2021

Viewed by 1283

Abstract

Wood is a vital and widespread natural material [...] Full article

(This article belongs to the Special Issue Physicochemical Surface Treatment of Wood Raw Materials)

18 pages, 20026 KiB

Open AccessArticle

Tribological Behavior of NiTi Alloy Produced by Spark Plasma Sintering Method

by Sneha Samal, Jana Cibulková, Radim Čtvrtlík, Jan Tomáštík, Lukáš Václavek, Jaromír Kopeček and Petr Šittner

Coatings 2021, 11(10), 1246; https://doi.org/10.3390/coatings11101246 - 14 Oct 2021

Cited by 16 | Viewed by 2402

Abstract

The tribological behaviors of NiTi alloy produced by the spark plasma sintering (SPS) method before and after annealing were investigated at various loading conditions via indentation, scratch, and wear tests. Indentation tests were performed by a pyramidal Berkovich indenter, while scratch and wear [...] Read more.

The tribological behaviors of NiTi alloy produced by the spark plasma sintering (SPS) method before and after annealing were investigated at various loading conditions via indentation, scratch, and wear tests. Indentation tests were performed by a pyramidal Berkovich indenter, while scratch and wear tests were carried out by a diamond Rockwell spherical indenter at room temperature. The annealing of the as-prepared samples was performed at 350, 450, and 550 °C in the ambient atmosphere. The influence of the annealing temperature on the sample behavior towards tribological study was investigated here. The results indicated that the alloy annealed at 350 °C showed a higher hardness compared to the other annealed alloys. The scratch and wear resistance of the annealed sample at 350 °C showed a better performance in comparison to the other samples under a constant load. The high wear resistance of the annealed NiTi alloy may be attributed to its metastable R-phase. The detection and evaluation of acoustic emissions during the nano/micro-tribomechanical testing proved to be a very effective way for the exploration of the durability of SPS NiTi alloys. Full article

(This article belongs to the Special Issue Thermal Plasma Processing for Coating: Structural, Functional Properties of Thick Films)

► Show Figures

Figure 1

26 pages, 47156 KiB

Open AccessReview

Sol-Gel Coating Membranes for Optical Fiber Sensors for Concrete Structures Monitoring

by Bárbara R. Gomes, Rui Araújo, Tatiana Sousa and Rita B. Figueira

Coatings 2021, 11(10), 1245; https://doi.org/10.3390/coatings11101245 - 13 Oct 2021

Cited by 5 | Viewed by 3538

Abstract

The use of advanced sensing devices for concrete and reinforced concrete structures (RCS) is considered a rational approach for the assessment of repair options and scheduling of inspection and maintenance strategies. The immediate benefits are cost reduction and a reliable prevention of unpredictable [...] Read more.

The use of advanced sensing devices for concrete and reinforced concrete structures (RCS) is considered a rational approach for the assessment of repair options and scheduling of inspection and maintenance strategies. The immediate benefits are cost reduction and a reliable prevention of unpredictable events. The use of optical fiber sensors (OFS) for such purposes has increased considerably in the last few years due to their intrinsic advantages. In most of the OFS, the chemical transducer consists of immobilized chemical reagents placed in the sensing region of the optical sensor by direct deposition or by encapsulation in a polymeric matrix. The choice of the support matrix impacts directly on the performance of the OFS. In the last two decades, the development of OFS functionalized with organic–inorganic hybrid (OIH) sol–gel membranes have been reported. Sol–gel route is considered a simple method that offers several advantages when compared to traditional synthesis processes, allowing to obtain versatile materials with unique chemical and physical properties, and is particularly valuable in the design of OIH materials. This review will provide an update of the current state-of-the-art of the OFS based on OIH sol-gel materials for concrete and RCS since 2016 until mid-2021. The main achievements in the synthesis of OIH membranes for deposition on OFS will be discussed. The challenges and future directions in this field will also be considered, as well as the main limitations of OFS for RCS monitoring. Full article

(This article belongs to the Special Issue Organic–Inorganic Hybrid Sol–Gel Materials for Corrosion Mitigation)

► Show Figures

Figure 1

16 pages, 7898 KiB

Open AccessArticle

Effects of Specimen Size and Welded Joints on the Very High Cycle Fatigue Properties of Compressor Blade Steel KMN-I

by Pengfei Wang, Weiqiang Wang, Ming Zhang, Qiwen Zhou and Zengliang Gao

Coatings 2021, 11(10), 1244; https://doi.org/10.3390/coatings11101244 - 13 Oct 2021

Cited by 6 | Viewed by 1583

Abstract

The effects of specimen size and welded joints on the very high cycle fatigue properties of compressor blade steel KMN-I were studied by ultrasonic fatigue testing. It was found that the S-N curve of large specimens had a slow decline above 10⁷ [...] Read more.

The effects of specimen size and welded joints on the very high cycle fatigue properties of compressor blade steel KMN-I were studied by ultrasonic fatigue testing. It was found that the S-N curve of large specimens had a slow decline above 10⁷ cycles, and fatigue failure still occurred in the very high cycle regime (>10⁷ cycles), while the very high cycle fatigue characteristics of welded specimens was less obvious, and the fatigue limit was observed. Metallographic observation and SEM analysis were carried out on the fracture of the specimens. The results showed that surface fractures were mostly observed in the large specimens, and only a small number of cracks initiated from non-metallic inclusions above 10⁷ cycles. The cracks of welded specimens initiated from the surface below 10⁷ cycles and initiated from the internal matrix above 10⁷ cycles. In addition, the formation mechanism of GBF (granular bright facet) was analyzed by the “dispersive decohesion of spherical carbide” theory, and the fatigue strength and fatigue life were predicted, which was consistent with the experimental results. Full article

(This article belongs to the Special Issue Progress in Coatings Deposition by Advanced Welding and Welding-Related Processes)

► Show Figures

Graphical abstract

13 pages, 7494 KiB

Open AccessArticle

Defective Microwave Photonic Crystals for Salinity Detection

by Yuxia Zhu and Hongwei Yang

Coatings 2021, 11(10), 1243; https://doi.org/10.3390/coatings11101243 - 13 Oct 2021

Cited by 1 | Viewed by 1280

Abstract

In this paper, defective microwave photonic crystals (MPCs) are designed to sense the salinity of aqueous solutions. The defective MPC sensors are constructed by two kinds of microwave dielectric layers and one defective salt solution layer. Transfer matrix method (TMM) for lossy medium [...] Read more.

In this paper, defective microwave photonic crystals (MPCs) are designed to sense the salinity of aqueous solutions. The defective MPC sensors are constructed by two kinds of microwave dielectric layers and one defective salt solution layer. Transfer matrix method (TMM) for lossy medium is developed to calculate the transmittance spectra of the sensors. It is found that the peak transmittance of both the defective resonance within the microwave band gap (MBG) and transmitting modes outside the MBG monotonously decrease with the increase of salinity, while the resonant and transmitting mode frequencies remain unchanged. By comparing the four MPC sensor structures, the first transmitting mode in the upper frequency band outside the MBG of the 15-layer MPC sensor has the largest salinity sensing range from 0 to 40‰ with relative stable detecting sensitivity. The sensing principle is based on the fact that the dielectric loss factor of saline solution is much more sensitive to salinity than the dielectric constant in the microwave frequency band. The sensitivity, quality factor, and salinity detection range of the MPC sensors are calculated and compared. The reported defective MPC sensors are suitable to be used for non-contact salinity detection. Full article

► Show Figures

Figure 1

20 pages, 4193 KiB

Open AccessArticle

Computational Modeling of Hybrid Sisko Nanofluid Flow over a Porous Radially Heated Shrinking/Stretching Disc

by Umair Khan, Aurang Zaib, Anuar Ishak, Fahad S. Al-Mubaddel, Sakhinah Abu Bakar, Hammad Alotaibi and Hassan M. Aljohani

Coatings 2021, 11(10), 1242; https://doi.org/10.3390/coatings11101242 - 13 Oct 2021

Cited by 6 | Viewed by 1510

Abstract

The present study reveals the behavior of shear-thickening and shear-thinning fluids in magnetohydrodynamic flow comprising the significant impact of a hybrid nanofluid over a porous radially shrinking/stretching disc. The features of physical properties of water-based Ag/TiO₂ hybrid nanofluid are examined. The leading [...] Read more.

The present study reveals the behavior of shear-thickening and shear-thinning fluids in magnetohydrodynamic flow comprising the significant impact of a hybrid nanofluid over a porous radially shrinking/stretching disc. The features of physical properties of water-based Ag/TiO₂ hybrid nanofluid are examined. The leading flow problem is formulated initially in the requisite form of PDEs (partial differential equations) and then altered into a system of dimensionless ODEs (ordinary differential equations) by employing suitable variables. The renovated dimensionless ODEs are numerically resolved using the package of boundary value problem of fourth-order (bvp4c) available in the MATLAB software. The non-uniqueness of the results for the various pertaining parameters is discussed. There is a significant enhancement in the rate of heat transfer, approximately 13.2%, when the impact of suction governs about 10% in the boundary layer. Therefore, the heat transport rate and the thermal conductivity are greater for the new type of hybrid nanofluid compared with ordinary fluid. The bifurcation of the solutions takes place in the problem only for the shrinking case. Moreover, the sketches show that the nanoparticle volume fractions and the magnetic field delay the separation of the boundarylayer. Full article

(This article belongs to the Special Issue Nanofluidics: Interfacial Transport Phenomena)

► Show Figures

Figure 1

14 pages, 6345 KiB

Open AccessArticle

Research on Laser Cladding Co-Based Alloy on the Surface of Vermicular Graphite Cast Iron

by Fuzhen Sun, Keqian Cai, Xiaoxu Li and Ming Pang

Coatings 2021, 11(10), 1241; https://doi.org/10.3390/coatings11101241 - 13 Oct 2021

Cited by 8 | Viewed by 2826

Abstract

To further improve the hardness of the laser cladding layer on the surface of the vermicular graphite cast iron, the structural parameters of the laser cladding Co-base were designed and optimized, and the properties of the clad layer were evaluated using optical microscopy [...] Read more.

To further improve the hardness of the laser cladding layer on the surface of the vermicular graphite cast iron, the structural parameters of the laser cladding Co-base were designed and optimized, and the properties of the clad layer were evaluated using optical microscopy (OM), scanning electron microscopy (SEM), energy spectroscopy (EDS), X-ray diffractometer (XRD), electrochemical workstation, and friction wear equipment. The results show that the average hardness of the molten layer of Ni and Co-based composite cladding layer is 504 HV_0.5, which is 0.64 times that of the Co-based cladding layer due to the combined factors of Ni-Cr-Fe equivalent to the dilution of the Ni-based cladding layer to the Co-based cladding layer. Due to the potential difference of the Ni, Cr, and Co elements on the surface of the cladding layer, the self-corrosion potential of the Ni and Co-based composite cladding layer is 1.08 times that of the Co-based cladding layer, and the self-corrosion current density is 0.51 times. Laser cladding Co-based cladding layer has high corrosion resistance. Under the influence of plastic deformation and oxidative wear of the cladding layer of the Ni and Co-based composite cladding layer, the wear amount of the cladding layer of the Ni and Co-based composite cladding layer is less. Full article

(This article belongs to the Special Issue Anti-wear Coatings for High Temperature Applications)

► Show Figures

Figure 1

10 pages, 2205 KiB

Open AccessArticle

Additive Manufacturing of Tungsten Carbide Surfaces with Extreme Wear Resistivity

by Florian Köhn, Michael Sedlmajer, Joachim Albrecht and Markus Merkel

Coatings 2021, 11(10), 1240; https://doi.org/10.3390/coatings11101240 - 13 Oct 2021

Cited by 5 | Viewed by 2897

Abstract

Steel surfaces have been coated with Co-based tungsten carbide (WC) in an additive printing process. This process leads to compact and extremely mechanically stable surfaces. We performed tribological measurements using WC counter bodies under dry conditions and severe mechanical load. Low coefficients of [...] Read more.

Steel surfaces have been coated with Co-based tungsten carbide (WC) in an additive printing process. This process leads to compact and extremely mechanically stable surfaces. We performed tribological measurements using WC counter bodies under dry conditions and severe mechanical load. Low coefficients of friction, even for rough surfaces, were found and the resulting wear rates were extraordinarily small, even when compared to high-quality PVD film with a similar composition. These findings suggest a wide field of application for this novel preparation process for wear-resistive surfaces. Full article

(This article belongs to the Special Issue Advances in Deposition and Characterization of Hard Coatings)

► Show Figures

Figure 1

12 pages, 4568 KiB

Open AccessArticle

Preparation of Degradable Superhydrophobic Mg/P/Z/F/H Composite Materials and Their Anticorrosion

by Zhongxian Xi, Chengqing Yuan, Xiuqin Bai, Chun Wang and Anne Neville

Coatings 2021, 11(10), 1239; https://doi.org/10.3390/coatings11101239 - 12 Oct 2021

Cited by 1 | Viewed by 2179

Abstract

In this study, the degradable superhydrophobic Mg/P/Z/F/H (magnesium/poly(-caprolactone)/zinc oxide/1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTES)/heating process) composite materials were prepared through dip-coating method and heating process, for enhancing the corrosion resistance of the AZ91D magnesium alloys. The electrochemical measurements revealed that the Mg/P/Z/F/H materials significantly improved the corrosion [...] Read more.

In this study, the degradable superhydrophobic Mg/P/Z/F/H (magnesium/poly(-caprolactone)/zinc oxide/1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTES)/heating process) composite materials were prepared through dip-coating method and heating process, for enhancing the corrosion resistance of the AZ91D magnesium alloys. The electrochemical measurements revealed that the Mg/P/Z/F/H materials significantly improved the corrosion resistance of the magnesium alloys in 3.5 wt.% NaCl. The Mg/P/Z/F/H composite materials exhibited efficient self-cleaning properties, good adhesion strength, and stability in wet atmosphere. Full article

(This article belongs to the Topic Multiple Application for Novel and Advanced Materials)

► Show Figures

Figure 1

14 pages, 3616 KiB

Open AccessArticle

Influence of NaCl Freeze–Thaw Cycles on the Mechanical Strength of Reactive Powder Concrete with the Assembly Unit of Sulphoaluminate Cement and Ordinary Portland Cement

by Zhangjie Cai and Hui Wang

Coatings 2021, 11(10), 1238; https://doi.org/10.3390/coatings11101238 - 12 Oct 2021

Cited by 11 | Viewed by 1714

Abstract

The influence of sulphoaluminate cement and the dosage of polypropylene fibers on the basic mechanical strengths (compressive and flexural strengths) of reactive powder concrete (RPC) cured for 1 d, 3 d, 7 d, 14 d and 28 d is studied in this research. [...] Read more.

The influence of sulphoaluminate cement and the dosage of polypropylene fibers on the basic mechanical strengths (compressive and flexural strengths) of reactive powder concrete (RPC) cured for 1 d, 3 d, 7 d, 14 d and 28 d is studied in this research. The content of sulphoaluminate cement ranges from 0% to 100% and the dosages of polypropylene fibers are 0%~3.5%, respectively. Moreover, the mechanical properties (compressive and flexural strengths), the relative dynamic elastic modulus (RDEM) and the chloride permeability of specimens with 50% sulphoaluminate cement and different dosages of polypropylene fibers are determined after the specimens are exposed to different NaCl freeze–thaw cycles. The water–binder ratio in this study is 0.25, and the sand-to-binder ratio is 1.25. Results show that the relationship between the mechanical strengths of RPC at early curing ages (lower than 7 d) and the sulphoaluminate cement content is a linear function with a positive correlation. However, when the curing age reaches 14 d, the compressive and flexural strengths decrease in the form of a linear function with the addition of sulphoaluminate cement. The correlation between the mechanical strengths and polypropylene fiber volume is a positive quadratic function. However, the mass loss rate and flexural strength loss rate increased in the form of a quadratic function, and RDEM shows a negative quadratic function with the freeze–thaw cycles. Moreover, the compressive strength loss rate increases linearly with the freeze–thaw cycle. The addition of polypropylene fibers can effectively improve the freeze–thaw resistance of cement mortar with an assembly unit of ordinary cement and sulphoaluminate cement. Full article

(This article belongs to the Special Issue Interface and Surface Modification for Durable Concretes)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Coatings, Volume 11, Issue 10 (October 2021) – 122 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI