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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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14 pages, 2420 KiB  
Article
Construction of Bio-TiO2/Algae Complex and Synergetic Mechanism of the Acceleration of Phenol Biodegradation
by Jinxin Guo, Xiaoman Guo, Haiyan Yang, Daohong Zhang and Xiaogeng Jiang
Materials 2023, 16(10), 3882; https://doi.org/10.3390/ma16103882 - 22 May 2023
Cited by 2 | Viewed by 1425
Abstract
Microalgae have been widely employed in water pollution treatment since they are eco-friendly and economical. However, the relatively slow treatment rate and low toxic tolerance have seriously limited their utilization in numerous conditions. In light of the problems above, a novel biosynthetic titanium [...] Read more.
Microalgae have been widely employed in water pollution treatment since they are eco-friendly and economical. However, the relatively slow treatment rate and low toxic tolerance have seriously limited their utilization in numerous conditions. In light of the problems above, a novel biosynthetic titanium dioxide (bio-TiO2 NPs)—microalgae synergetic system (Bio-TiO2/Algae complex) has been established and adopted for phenol degradation in the study. The great biocompatibility of bio-TiO2 NPs ensured the collaboration with microalgae, improving the phenol degradation rate by 2.27 times compared to that with single microalgae. Remarkably, this system increased the toxicity tolerance of microalgae, represented as promoted extracellular polymeric substances EPS secretion (5.79 times than single algae), and significantly reduced the levels of malondialdehyde and superoxide dismutase. The boosted phenol biodegradation with Bio-TiO2/Algae complex may be attributed to the synergetic interaction of bio-TiO2 NPs and microalgae, which led to the decreased bandgap, suppressed recombination rate, and accelerated electron transfer (showed as low electron transfer resistance, larger capacitance, and higher exchange current density), resulting in increased light energy utilization rate and photocatalytic rate. The results of the work provide a new understanding of the low-carbon treatment of toxic organic wastewater and lay a foundation for further remediation application. Full article
(This article belongs to the Special Issue Heterogeneous Catalysts for Biomass Conversion and Environmental Remediation)
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12 pages, 5403 KiB  
Article
Effects of Steel Slag Powder Content and Curing Condition on the Performance of Alkali-Activated Materials Based UHPC Matrix
by Kangyi Shi, Hongyang Deng, Jinxuan Hu, Junqi Zhou, Xinhua Cai and Zhiwei Liu
Materials 2023, 16(10), 3875; https://doi.org/10.3390/ma16103875 - 21 May 2023
Cited by 10 | Viewed by 1996
Abstract
The accumulation of steel slag and other industrial solid wastes has caused serious environmental pollution and resource waste, and the resource utilization of steel slag is imminent. In this paper, alkali-activated ultra-high-performance concrete (AAM-UHPC) was prepared by replacing ground granulated blast furnace slag [...] Read more.
The accumulation of steel slag and other industrial solid wastes has caused serious environmental pollution and resource waste, and the resource utilization of steel slag is imminent. In this paper, alkali-activated ultra-high-performance concrete (AAM-UHPC) was prepared by replacing ground granulated blast furnace slag (GGBFS) powder with different proportions of steel slag powder, and its workability, mechanical properties, curing condition, microstructure, and pore structure were investigated. The results illustrate that the incorporation of steel slag powder can significantly delay the setting time and improve the flowability of AAM-UHPC, making it possible for engineering applications. The mechanical properties of AAM-UHPC showed a tendency to increase and then decrease with the increase in steel slag dosing and reached their best performance at a 30% dosage of steel slag. The maximum compressive strength and flexural strength are 157.1 MPa and 16.32 Mpa, respectively. High-temperature steam or hot water curing at an early age was beneficial to the strength development of AAM-UHPC, but continuous high-temperature, hot, and humid curing would lead to strength inversion. When the dosage of steel slag is 30%, the average pore diameter of the matrix is only 8.43 nm, and the appropriate steel slag dosage can reduce the heat of hydration and refine the pore size distribution, making the matrix denser. Full article
(This article belongs to the Collection Alkali‐Activated Materials for Sustainable Construction)
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12 pages, 2849 KiB  
Article
Validating the Use of Gaussian Process Regression for Adaptive Mapping of Residual Stress Fields
by Chris M. Fancher, Singanallur Venkatakrishnan, Thomas Feldhausen, Kyle Saleeby and Alex Plotkowski
Materials 2023, 16(10), 3854; https://doi.org/10.3390/ma16103854 - 20 May 2023
Viewed by 1326
Abstract
Probing the stress state using a high density of measurement points is time intensive and presents a limitation for what is experimentally feasible. Alternatively, individual strain fields used for determining stresses can be reconstructed from a subset of points using a Gaussian process [...] Read more.
Probing the stress state using a high density of measurement points is time intensive and presents a limitation for what is experimentally feasible. Alternatively, individual strain fields used for determining stresses can be reconstructed from a subset of points using a Gaussian process regression (GPR). Results presented in this paper evidence that determining stresses from reconstructed strain fields is a viable approach for reducing the number of measurements needed to fully sample a component’s stress state. The approach was demonstrated by reconstructing the stress fields in wire-arc additively manufactured walls fabricated using either a mild steel or low-temperature transition feedstock. Effects of errors in individual GP reconstructed strain maps and how these errors propagate to the final stress maps were assessed. Implications of the initial sampling approach and how localized strains affect convergence are explored to give guidance on how best to implement a dynamic sampling experiment. Full article
(This article belongs to the Special Issue Neutron Scattering Studies in Materials Science)
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38 pages, 9986 KiB  
Review
Advances in Cellulose-Based Composites for Energy Applications
by Choon Peng Teng, Ming Yan Tan, Jessica Pei Wen Toh, Qi Feng Lim, Xiaobai Wang, Daniel Ponsford, Esther Marie JieRong Lin, Warintorn Thitsartarn and Si Yin Tee
Materials 2023, 16(10), 3856; https://doi.org/10.3390/ma16103856 - 20 May 2023
Cited by 16 | Viewed by 5880
Abstract
The various forms of cellulose-based materials possess high mechanical and thermal stabilities, as well as three-dimensional open network structures with high aspect ratios capable of incorporating other materials to produce composites for a wide range of applications. Being the most prevalent natural biopolymer [...] Read more.
The various forms of cellulose-based materials possess high mechanical and thermal stabilities, as well as three-dimensional open network structures with high aspect ratios capable of incorporating other materials to produce composites for a wide range of applications. Being the most prevalent natural biopolymer on the Earth, cellulose has been used as a renewable replacement for many plastic and metal substrates, in order to diminish pollutant residues in the environment. As a result, the design and development of green technological applications of cellulose and its derivatives has become a key principle of ecological sustainability. Recently, cellulose-based mesoporous structures, flexible thin films, fibers, and three-dimensional networks have been developed for use as substrates in which conductive materials can be loaded for a wide range of energy conversion and energy conservation applications. The present article provides an overview of the recent advancements in the preparation of cellulose-based composites synthesized by combining metal/semiconductor nanoparticles, organic polymers, and metal-organic frameworks with cellulose. To begin, a brief review of cellulosic materials is given, with emphasis on their properties and processing methods. Further sections focus on the integration of cellulose-based flexible substrates or three-dimensional structures into energy conversion devices, such as photovoltaic solar cells, triboelectric generators, piezoelectric generators, thermoelectric generators, as well as sensors. The review also highlights the uses of cellulose-based composites in the separators, electrolytes, binders, and electrodes of energy conservation devices such as lithium-ion batteries. Moreover, the use of cellulose-based electrodes in water splitting for hydrogen generation is discussed. In the final section, we propose the underlying challenges and outlook for the field of cellulose-based composite materials. Full article
(This article belongs to the Special Issue Functional Cellulosic Materials)
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17 pages, 20289 KiB  
Article
WO3 Thin-Film Optical Gas Sensors Based on Gasochromic Effect towards Low Hydrogen Concentrations
by Michał Mazur, Paulina Kapuścik, Wiktoria Weichbrodt, Jarosław Domaradzki, Piotr Mazur, Małgorzata Kot and Jan Ingo Flege
Materials 2023, 16(10), 3831; https://doi.org/10.3390/ma16103831 - 19 May 2023
Cited by 4 | Viewed by 2188
Abstract
Hydrogen gas sensors have recently attracted increased interest due to the explosive nature of H2 and its strategic importance in the sustainable global energy system. In this paper, the tungsten oxide thin films deposited by innovative gas impulse magnetron sputtering have been [...] Read more.
Hydrogen gas sensors have recently attracted increased interest due to the explosive nature of H2 and its strategic importance in the sustainable global energy system. In this paper, the tungsten oxide thin films deposited by innovative gas impulse magnetron sputtering have been investigated in terms of their response to H2. It was found that the most favourable annealing temperature in terms of sensor response value, as well as response and recovery times, was achieved at 673 K. This annealing process caused a change in the WO3 cross-section morphology from a featureless and homogenous form to a rather columnar one, but still maintaining the same surface homogeneity. In addition to that, the full-phase transition from an amorphous to nanocrystalline form occurred with a crystallite size of 23 nm. It was found that the sensor response to only 25 ppm of H2 was equal to 6.3, which is one of the best results presented in the literature so far of WO3 optical gas sensors based on a gasochromic effect. Moreover, the results of the gasochromic effect were correlated with the changes in the extinction coefficient and the concentration of the free charge carriers, which is also a novel approach to the understanding of the gasochromic phenomenon. Full article
(This article belongs to the Special Issue Application of Emerging Materials for Advanced Imaging and Sensing)
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16 pages, 6986 KiB  
Article
Polysiloxanes and Silanes with Various Functional Groups—New Compounds for Flax Fibers’ Modification
by Weronika Gieparda, Marcin Przybylak, Szymon Rojewski and Beata Doczekalska
Materials 2023, 16(10), 3839; https://doi.org/10.3390/ma16103839 - 19 May 2023
Cited by 3 | Viewed by 1485
Abstract
There is an increasing desire to use natural products that will be both effective and biodegradable. The aim of this work is to investigate the effect of modifying flax fibers with silicon compounds (silanes and polysiloxanes), as well as examining the effect of [...] Read more.
There is an increasing desire to use natural products that will be both effective and biodegradable. The aim of this work is to investigate the effect of modifying flax fibers with silicon compounds (silanes and polysiloxanes), as well as examining the effect of the mercerization process on their properties. Two types of polysiloxanes have been synthesized and confirmed by infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). Scanning electron microscopy (SEM), FTIR, thermogravimetry analysis (TGA) and pyrolysis-combustion flow calorimetry (PCFC) tests of the fibers were performed. On the SEM pictures, flax fibers purified and covered with silanes were visible after treatment. FTIR analysis showed stable bonds between the fibers and the silicon compounds. Promising results of thermal stability were obtained. It was also found that modification had a positive effect on the flammability. The conducted research showed that the use of such modifications, in the context of using flax fibers for composites, can yield very good results. Full article
(This article belongs to the Section Biomaterials)
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15 pages, 5859 KiB  
Article
Influence of Alumina Grade on Sintering Properties and Possible Application in Binder Jetting Additive Technology
by Maciej Kwiatkowski, Joanna Marczyk, Piotr Putyra, Michał Kwiatkowski, Szymon Przybyła and Marek Hebda
Materials 2023, 16(10), 3853; https://doi.org/10.3390/ma16103853 - 19 May 2023
Cited by 6 | Viewed by 2211
Abstract
Alumina is one of the most popular ceramic materials widely used in both tooling and construction applications due to its low production cost, and high properties. However, the final properties of the product depend not only on the purity of the powder, but [...] Read more.
Alumina is one of the most popular ceramic materials widely used in both tooling and construction applications due to its low production cost, and high properties. However, the final properties of the product depend not only on the purity of the powder, but also, e.g., on its particle size, specific surface area, and the production technology used. These parameters are particularly important in the case of choosing additive techniques for the production of details. Therefore, the article presents the results of comparing five grades of Al2O3 ceramic powder. Their specific surface area (via Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) methods), particle size distribution, and phase composition by X-ray diffraction (XRD) were determined. Moreover, the surface morphology was characterized by the scanning electron microscopy (SEM) technique. The discrepancy between generally available data and the results obtained from measurements has been indicated. Moreover, the method of spark plasma sintering (SPS), equipped with the registration system of the position of the pressing punch during the process, was used to determine the sinterability curves of each of the tested grades of Al2O3 powder. Based on the obtained results, a significant influence of the specific surface area, particle size, and the width of their distribution at the beginning of the Al2O3 powder sintering process was confirmed. Furthermore, the possibility of using the analyzed variants of powders for binder jetting technology was assessed. The dependence of the particle size of the powder used on the quality of the printed parts was demonstrated. The procedure presented in this paper, which involves analyzing the properties of alumina varieties, was used to optimize the Al2O3 powder material for binder jetting printing. The selection of the best powder in terms of technological properties and good sinterability makes it possible to reduce the number of 3D printing processes, which makes it more economical and less time-consuming. Full article
(This article belongs to the Special Issue Recent Application of Powder Metallurgy Materials)
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25 pages, 8623 KiB  
Article
Potential of Fe-Mn-Al-Ni Shape Memory Alloys for Internal Prestressing of Ultra-High Performance Concrete
by Maximilian Schleiting, Alexander Wetzel, André Bauer, Johanna-Maria Frenck, Thomas Niendorf and Bernhard Middendorf
Materials 2023, 16(10), 3816; https://doi.org/10.3390/ma16103816 - 18 May 2023
Cited by 5 | Viewed by 1501
Abstract
Prestressing of concrete is a commonly used technique in civil engineering to achieve long spans, reduced structural thicknesses, and resource savings. However, in terms of application, complex tensioning devices are necessary, and prestress losses due to shrinkage and creep of the concrete are [...] Read more.
Prestressing of concrete is a commonly used technique in civil engineering to achieve long spans, reduced structural thicknesses, and resource savings. However, in terms of application, complex tensioning devices are necessary, and prestress losses due to shrinkage and creep of the concrete are unfavourable in terms of sustainability. In this work, a prestressing method using novel Fe-Mn-Al-Ni shape memory alloy rebars as a tensioning system in UHPC is investigated. A generated stress of about 130 MPa was measured for the shape memory alloy rebars. For the application in UHPC, the rebars are prestrained prior to the manufacturing process of the concrete samples. After sufficient hardening of the concrete, the specimens are heated inside an oven to activate the shape memory effect and, thus, to introduce the prestress into the surrounding UHPC. It is clearly shown that an improvement in maximum flexural strength and rigidity is achieved due to the thermal activation of the shape memory alloy rebars compared to non-activated rebars. Future research will have to focus on the design of the shape memory alloy rebars in relation to construction applications and the investigation of the long-term performance of the prestressing system. Full article
(This article belongs to the Section Construction and Building Materials)
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35 pages, 11056 KiB  
Review
Recent Advances in Magnetic Polymer Composites for BioMEMS: A Review
by Zhengwei Liao, Oualid Zoumhani and Clementine M. Boutry
Materials 2023, 16(10), 3802; https://doi.org/10.3390/ma16103802 - 17 May 2023
Cited by 15 | Viewed by 4592
Abstract
The objective of this review is to investigate the potential of functionalized magnetic polymer composites for use in electromagnetic micro-electro-mechanical systems (MEMS) for biomedical applications. The properties that make magnetic polymer composites particularly interesting for application in the biomedical field are their biocompatibility, [...] Read more.
The objective of this review is to investigate the potential of functionalized magnetic polymer composites for use in electromagnetic micro-electro-mechanical systems (MEMS) for biomedical applications. The properties that make magnetic polymer composites particularly interesting for application in the biomedical field are their biocompatibility, their adjustable mechanical, chemical, and magnetic properties, as well as their manufacturing versatility, e.g., by 3D printing or by integration in cleanroom microfabrication processes, which makes them accessible for large-scale production to reach the general public. The review first examines recent advancements in magnetic polymer composites that possess unique features such as self-healing capabilities, shape-memory, and biodegradability. This analysis includes an exploration of the materials and fabrication processes involved in the production of these composites, as well as their potential applications. Subsequently, the review focuses on electromagnetic MEMS for biomedical applications (bioMEMS), including microactuators, micropumps, miniaturized drug delivery systems, microvalves, micromixers, and sensors. The analysis encompasses an examination of the materials and manufacturing processes involved and the specific fields of application for each of these biomedical MEMS devices. Finally, the review discusses missed opportunities and possible synergies in the development of next-generation composite materials and bioMEMS sensors and actuators based on magnetic polymer composites. Full article
(This article belongs to the Special Issue Design, Fabrication, and Characterization of Magnetoresponsive Materials and Devices)
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17 pages, 20268 KiB  
Article
Fabrication of Mechanically Strong Silica Aerogels with the Thermally Induced Phase Separation (TIPS) Method of Poly(methyl methacrylate)
by Hainan Ma, Baomin Wang, Jiarui Qi, Yiheng Pan and Chao Chen
Materials 2023, 16(10), 3778; https://doi.org/10.3390/ma16103778 - 17 May 2023
Viewed by 1444
Abstract
Constructing and maintaining a three-dimensional network structure with high porosity is critical to the preparation of silica aerogel materials because this structure provides excellent properties. However, due to the pearl-necklace-like structure and narrow interparticle necks, aerogels have poor mechanical strength and a brittle [...] Read more.
Constructing and maintaining a three-dimensional network structure with high porosity is critical to the preparation of silica aerogel materials because this structure provides excellent properties. However, due to the pearl-necklace-like structure and narrow interparticle necks, aerogels have poor mechanical strength and a brittle nature. Developing and designing lightweight silica aerogels with distinct mechanical properties is significant to extend their practical applications. In this work, thermally induced phase separation (TIPS) of poly(methyl methacrylate) (PMMA) from a mixture of ethanol and water was used to strengthen the skeletal network of aerogels. Strong and lightweight PMMA-modified silica aerogels were synthesized via the TIPS method and supercritically dried with carbon dioxide. The cloud point temperature of PMMA solutions, physical characteristics, morphological properties, microstructure, thermal conductivities, and mechanical properties were investigated. The resultant composited aerogels not only exhibit a homogenous mesoporous structure but also achieve a significant improvement in mechanical properties. The addition of PMMA increased the flexural strength and compressive strength by as much as 120% and 1400%, respectively, with the greatest amount of PMMA (Mw = 35,000 g/mole), while the density just increased by 28%. Overall, this research suggests that the TIPS method has great efficiency in reinforcing silica aerogels with less sacrifice of low density and large porosity. Full article
(This article belongs to the Section Porous Materials)
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16 pages, 3861 KiB  
Article
Tungsten and Copper (II) Oxide Mixtures as Gasless Time Delay Compositions for Mining Detonators
by Marcin Gerlich, Marcin Hara and Waldemar A. Trzciński
Materials 2023, 16(10), 3797; https://doi.org/10.3390/ma16103797 - 17 May 2023
Cited by 2 | Viewed by 1395
Abstract
The widespread use of pyrotechnic compositions in time delay detonators is the reason for research aimed at expanding knowledge of the combustion properties of new pyrotechnic mixtures, whose components react with each other in the solid or liquid state. Such a method of [...] Read more.
The widespread use of pyrotechnic compositions in time delay detonators is the reason for research aimed at expanding knowledge of the combustion properties of new pyrotechnic mixtures, whose components react with each other in the solid or liquid state. Such a method of combustion would make the rate of combustion independent of the pressure inside the detonator. This paper presents the effect of the parameters of W/CuO mixtures on their properties of combustion. As this composition has not been the subject of previous research and is not described in the literature, the basic parameters, such as the burning rate and the heat of combustion, were determined. In order to determine the reaction mechanism, a thermal analysis was performed, and the combustion products were determined using the XRD technique. Depending on the quantitative composition and density of the mixture, the burning rates were between 4.1–6.0 mm/s and the heat of combustion in the range of 475–835 J/g was measured. The gas-free combustion mode of the chosen mixture was proved using DTA and XRD. Determination of the qualitative composition of the combustion products and the heat of combustion allowed estimation of the adiabatic combustion temperature. Full article
(This article belongs to the Special Issue Newer Paradigms in Advanced Materials Characterisation)
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14 pages, 491 KiB  
Article
Anharmonicity of Plasmons in Metallic Nanostructures Useful for Metallization of Solar Cells
by Zofia Krzemińska and Witold A. Jacak
Materials 2023, 16(10), 3762; https://doi.org/10.3390/ma16103762 - 16 May 2023
Viewed by 1160
Abstract
Metallic nanoparticles are frequently applied to enhance the efficiency of photovoltaic cells via the plasmonic effect, and they play this role due to the unusual ability of plasmons to transmit energy. The absorption and emission of plasmons, dual in the sense of quantum [...] Read more.
Metallic nanoparticles are frequently applied to enhance the efficiency of photovoltaic cells via the plasmonic effect, and they play this role due to the unusual ability of plasmons to transmit energy. The absorption and emission of plasmons, dual in the sense of quantum transitions, in metallic nanoparticles are especially high at the nanoscale of metal confinement, so these particles are almost perfect transmitters of incident photon energy. We show that these unusual properties of plasmons at the nanoscale are linked to the extreme deviation of plasmon oscillations from the conventional harmonic oscillations. In particular, the large damping of plasmons does not terminate their oscillations, even if, for a harmonic oscillator, they result in an overdamped regime. Full article
(This article belongs to the Special Issue Design, Performance, and Application of Lithium-Ion Batteries)
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14 pages, 5703 KiB  
Article
Comparative Study of Iron-Tailings-Based Cementitious Mortars with Incorporated Graphite Ore and Graphite Tailings: Strength Properties and Microstructure
by Jiale Zhang, Qi Wei, Na Zhang, Shuai Zhang and Yihe Zhang
Materials 2023, 16(10), 3743; https://doi.org/10.3390/ma16103743 - 15 May 2023
Cited by 1 | Viewed by 1484
Abstract
Graphite ore and graphite tailings were blended into iron-tailings-based cementitious mortars, and their mechanical properties and microstructure were experimentally investigated. The flexural and compressive strengths of the resulting material were tested to compare the effects of graphite ore and graphite tailings as supplementary [...] Read more.
Graphite ore and graphite tailings were blended into iron-tailings-based cementitious mortars, and their mechanical properties and microstructure were experimentally investigated. The flexural and compressive strengths of the resulting material were tested to compare the effects of graphite ore and graphite tailings as supplementary cementitious materials and fine aggregates on the mechanical properties of iron-tailings-based cementitious mortars. Additionally, their microstructure and hydration products were mainly analyzed using scanning electronic microscope and X-ray powder diffraction techniques. The experimental results showed that the mechanical properties of the mortar material incorporating graphite ore were reduced due to the lubricating properties of graphite ore. As a result, the unhydrated particles and aggregates were not tightly bound to the gel phase, making the direct application of graphite ore in construction materials unfeasible. In the iron-tailings-based cementitious mortars prepared in this work, the optimal incorporation rate of graphite ore as a supplementary cementitious material was 4 wt%. The compressive strength of the optimal mortar test block after 28 days of hydration was 23.21 MPa, and the flexural strength was 7.76 MPa. The mechanical properties of the mortar block were found to be optimal with a graphite-tailings content of 40 wt% and an iron-tailings content of 10 wt%, resulting in a 28-day compressive strength of 48.8 MPa and a flexural strength of 11.7 MPa. By observing the microstructure and XRD pattern of the 28-day hydrated mortar block, it was determined that the hydration products of the mortar with graphite tailings as an aggregate included ettringite, Ca(OH)2, and C-A-S-H gel. Full article
(This article belongs to the Special Issue Industrial Solid Wastes for Construction and Building Materials)
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18 pages, 4982 KiB  
Review
Varnish Formation and Removal in Lubrication Systems: A Review
by Sung-Ho Hong and Eun Kyung Jang
Materials 2023, 16(10), 3737; https://doi.org/10.3390/ma16103737 - 15 May 2023
Cited by 3 | Viewed by 2769
Abstract
This study presents the current literature regarding the investigation of varnish contamination among the various types of lubricant contaminations. As the duration of use of lubricants increases, the lubricant deteriorates and may become contaminated. Varnish has been known to cause filter plugging, sticking [...] Read more.
This study presents the current literature regarding the investigation of varnish contamination among the various types of lubricant contaminations. As the duration of use of lubricants increases, the lubricant deteriorates and may become contaminated. Varnish has been known to cause filter plugging, sticking of the hydraulic valves and fuel injection pumps, flow obstruction, clearance reduction, poor heating and cooling performance, and increased friction and wear in various lubrication systems. These problems may also result in mechanical system failures, performance degradation, and increased maintenance and repair costs. To improve the problems caused by varnish contamination, an adequate understanding of varnish is required. Therefore, in this review, the definitions and characteristics, generating machinery, generating mechanisms, causes, measurement methods, and prevention or removal methods of varnish are summarized. Most of the data presented herein are reports from manufacturers related to lubricants and machine maintenance that are included in published works. We expect that this summary will be helpful to those who are engaged in reducing or preventing varnish-related problems. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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11 pages, 2642 KiB  
Article
Transparent Conducting Amorphous IZO Thin Films: An Approach to Improve the Transparent Electrode Quality
by Akhmed K. Akhmedov, Aslan Kh. Abduev, Eldar K. Murliev, Victor V. Belyaev and Abil Sh. Asvarov
Materials 2023, 16(10), 3740; https://doi.org/10.3390/ma16103740 - 15 May 2023
Cited by 8 | Viewed by 2007
Abstract
It is common knowledge that using different oxygen contents in the working gas during sputtering deposition results in fabrication of indium zinc oxide (IZO) films with a wide range of optoelectronic properties. It is also important that high deposition temperature is not required [...] Read more.
It is common knowledge that using different oxygen contents in the working gas during sputtering deposition results in fabrication of indium zinc oxide (IZO) films with a wide range of optoelectronic properties. It is also important that high deposition temperature is not required to achieve excellent transparent electrode quality in the IZO films. Modulation of the oxygen content in the working gas during RF sputtering of IZO ceramic targets was used to deposit IZO-based multilayers in which the ultrathin IZO unit layers with high electron mobility (μ-IZO) alternate with ones characterized by high concentration of free electrons (n-IZO). As a result of optimizing the thicknesses of each type of unit layer, low-temperature 400 nm thick IZO multilayers with excellent transparent electrode quality, indicated by the low sheet resistance (R ≤ 8 Ω/sq.) with high transmittance in the visible range (T¯ > 83%) and a very flat multilayer surface, were obtained. Full article
(This article belongs to the Special Issue Sputter Deposition/Physical Vapor Deposition (PVD) Materials and Processes)
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23 pages, 4718 KiB  
Article
The Usability of Sorbents in Restoring Enzymatic Activity in Soils Polluted with Petroleum-Derived Products
by Jadwiga Wyszkowska, Agata Borowik, Magdalena Zaborowska and Jan Kucharski
Materials 2023, 16(10), 3738; https://doi.org/10.3390/ma16103738 - 15 May 2023
Cited by 13 | Viewed by 1966
Abstract
Due to their ability to adsorb or absorb chemical pollutants, including organic compounds, sorbents are increasingly used in the reclamation of soils subjected to their pressure, which results from their high potential in eliminating xenobiotics. The precise optimization of the reclamation process is [...] Read more.
Due to their ability to adsorb or absorb chemical pollutants, including organic compounds, sorbents are increasingly used in the reclamation of soils subjected to their pressure, which results from their high potential in eliminating xenobiotics. The precise optimization of the reclamation process is required, focused primarily on restoring the condition of the soil. This research are essential for seeking materials sufficiently potent to accelerate the remediation process and for expanding knowledge related to biochemical transformations that lead to the neutralization of these pollutants. The goal of this study was to determine and compare the sensitivity of soil enzymes to petroleum-derived products in soil sown with Zea mays, remediated using four sorbents. The study was conducted in a pot experiment, with loamy sand (LS) and sandy loam (SL) polluted with VERVA diesel oil (DO) and VERVA 98 petrol (P). Soil samples were collected from arable lands, and the effects of the tested pollutants were compared with those used as control uncontaminated soil samples in terms of Zea mays biomass and the activity of seven enzymes in the soil. The following sorbents were applied to mitigate DO and P effects on the test plants and enzymatic activity: molecular sieve (M), expanded clay (E), sepiolite (S), and Ikasorb (I). Both DO and P exerted a toxic effect on Zea mays, with DO more strongly disturbing its growth and development and the activities of soil enzymes than P. In sandy clay (SL), P was found to be a significant inhibitor of dehydrogenases (Deh), catalase (Cat), urease (Ure), alkaline phosphatase (Pal), and arylsulfatase (Aryl) activities, while DO stimulated the activity of all enzymes in this soil. The study results suggest that the sorbents tested, mainlya molecular sieve, may be useful in remediating DO-polluted soils, especially when alleviating the effects of these pollutants in soils of lower agronomic value. Full article
(This article belongs to the Special Issue Advances in Eco-Friendly Adsorbent Materials for Removal of Inorganic and Organic Pollutants (Volume II))
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24 pages, 4826 KiB  
Review
The Integration of Triboelectric Nanogenerators and Supercapacitors: The Key Role of Cellular Materials
by Jiajing Meng, Zequan Zhao, Xia Cao and Ning Wang
Materials 2023, 16(10), 3751; https://doi.org/10.3390/ma16103751 - 15 May 2023
Cited by 4 | Viewed by 2018
Abstract
The growing demand for sustainable and efficient energy harvesting and storage technologies has spurred interest in the integration of triboelectric nanogenerators (TENGs) with supercapacitors (SCs). This combination offers a promising solution for powering Internet of Things (IoT) devices and other low−power applications by [...] Read more.
The growing demand for sustainable and efficient energy harvesting and storage technologies has spurred interest in the integration of triboelectric nanogenerators (TENGs) with supercapacitors (SCs). This combination offers a promising solution for powering Internet of Things (IoT) devices and other low−power applications by utilizing ambient mechanical energy. Cellular materials, featuring unique structural characteristics such as high surface−to−volume ratios, mechanical compliance, and customizable properties, have emerged as essential components in this integration, enabling the improved performance and efficiency of TENG−SC systems. In this paper, we discuss the key role of cellular materials in enhancing TENG−SC systems’ performance through their influence on contact area, mechanical compliance, weight, and energy absorption. We highlight the benefits of cellular materials, including increased charge generation, optimized energy conversion efficiency, and adaptability to various mechanical sources. Furthermore, we explore the potential for lightweight, low−cost, and customizable cellular materials to expand the applicability of TENG−SC systems in wearable and portable devices. Finally, we examine the dual effect of cellular materials’ damping and energy absorption properties, emphasizing their potential to protect TENGs from damage and increase overall system efficiency. This comprehensive overview of the role of cellular materials in the integration of TENG−SC aims to provide insights into the development of next−generation sustainable energy harvesting and storage solutions for IoT and other low−power applications. Full article
(This article belongs to the Special Issue New Advances in Characterization of Cellular Materials)
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20 pages, 12745 KiB  
Article
Durability and Additional Properties of Anodized Aluminum-Based Coatings with Different Wettability under Natural Conditions
by Klaudia Olkowicz, Kamil Kowalczyk, Zofia Buczko, Joanna Czwartos and Barbara Nasiłowska
Materials 2023, 16(10), 3729; https://doi.org/10.3390/ma16103729 - 14 May 2023
Cited by 2 | Viewed by 2369
Abstract
The study aimed to test the durability of coatings under natural conditions. The present study focused on the changes in wettability and additional properties of the coatings under natural conditions. The specimens were subjected to outdoor exposure and additionally immersed in the pond. [...] Read more.
The study aimed to test the durability of coatings under natural conditions. The present study focused on the changes in wettability and additional properties of the coatings under natural conditions. The specimens were subjected to outdoor exposure and additionally immersed in the pond. Impregnating porous anodized aluminum is a popular production method for hydrophobic and superhydrophobic surfaces. However, prolonged exposure of such coatings to natural conditions causes leaching of the impregnate and, thus, the loss of hydrophobic properties. After the loss of hydrophobic properties, all kinds of impurities and fouling adhere better to the porous structure. Additionally, deterioration of anti-icing and anti-corrosion properties was observed. Finally, the self-cleaning, anti-fouling, anti-icing and anti-corrosion properties were comparable or even worse to those of the hydrophilic coating. In the case of superhydrophobic specimens, during outdoor exposure there was no loss of superhydrophobicity, self-cleaning and anti-corrosion properties. Still, despite this, the icing delay time dropped. During outdoor exposure, the structure, which initially had anti-icing properties, may degrade. Nevertheless, the hierarchical structure responsible for the superhydrophobic effect can still be preserved. The superhydrophobic coating initially had the best anti-fouling properties. However, the coating was also gradually losing its superhydrophobic properties during water immersion. Full article
(This article belongs to the Special Issue New Insights in Wettability and Surface Repellency of Advanced Materials)
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15 pages, 4711 KiB  
Article
In Situ Reactive Formation of Mixed Oxides in Additively Manufactured Cobalt Alloy
by Jack Lopez, Rok Cerne, David Ho, Devin Madigan, Qing Shen, Bo Yang, Joseph Corpus, William Jarosinski, Haiyan Wang and Xinghang Zhang
Materials 2023, 16(10), 3707; https://doi.org/10.3390/ma16103707 - 13 May 2023
Cited by 2 | Viewed by 1825
Abstract
Oxide-dispersion-strengthened (ODS) alloys have long been considered for high temperature turbine, spacecraft, and nuclear reactor components due to their high temperature strength and radiation resistance. Conventional synthesis approaches of ODS alloys involve ball milling of powders and consolidation. In this work, a process-synergistic [...] Read more.
Oxide-dispersion-strengthened (ODS) alloys have long been considered for high temperature turbine, spacecraft, and nuclear reactor components due to their high temperature strength and radiation resistance. Conventional synthesis approaches of ODS alloys involve ball milling of powders and consolidation. In this work, a process-synergistic approach is used to introduce oxide particles during laser powder bed fusion (LPBF). Chromium (III) oxide (Cr2O3) powders are blended with a cobalt-based alloy, Mar-M 509, and exposed to laser irradiation, resulting in reduction–oxidation reactions involving metal (Ta, Ti, Zr) ions from the metal matrix to form mixed oxides of increased thermodynamic stability. A microstructure analysis indicates the formation of nanoscale spherical mixed oxide particles as well as large agglomerates with internal cracks. Chemical analyses confirm the presence of Ta, Ti, and Zr in agglomerated oxides, but primarily Zr in the nanoscale oxides. Mechanical testing reveals that agglomerate particle cracking is detrimental to tensile ductility compared to the base alloy, suggesting the need for improved processing methods to break up oxide particle clusters and promote their uniform dispersion during laser exposure. Full article
(This article belongs to the Special Issue Advances in Materials Processing Engineering)
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19 pages, 2602 KiB  
Article
Plasmonic Nanodomains Decorated on Two-Dimensional Oxide Semiconductors for Photonic-Assisted CO2 Conversion
by Mohammad Karbalaei Akbari, Nasrin Siraj Lopa, Jihae Park and Serge Zhuiykov
Materials 2023, 16(10), 3675; https://doi.org/10.3390/ma16103675 - 11 May 2023
Cited by 2 | Viewed by 1787
Abstract
Plasmonic nanostructures ensure the reception and harvesting of visible lights for novel photonic applications. In this area, plasmonic crystalline nanodomains decorated on the surface of two-dimensional (2D) semiconductor materials represent a new class of hybrid nanostructures. These plasmonic nanodomains activate supplementary mechanisms at [...] Read more.
Plasmonic nanostructures ensure the reception and harvesting of visible lights for novel photonic applications. In this area, plasmonic crystalline nanodomains decorated on the surface of two-dimensional (2D) semiconductor materials represent a new class of hybrid nanostructures. These plasmonic nanodomains activate supplementary mechanisms at material heterointerfaces, enabling the transfer of photogenerated charge carriers from plasmonic antennae into adjacent 2D semiconductors and therefore activate a wide range of visible-light assisted applications. Here, the controlled growth of crystalline plasmonic nanodomains on 2D Ga2O3 nanosheets was achieved by sonochemical-assisted synthesis. In this technique, Ag and Se nanodomains grew on 2D surface oxide films of gallium-based alloy. The multiple contribution of plasmonic nanodomains enabled the visible-light-assisted hot-electron generation at 2D plasmonic hybrid interfaces, and therefore considerably altered the photonic properties of the 2D Ga2O3 nanosheets. Specifically, the multiple contribution of semiconductor–plasmonic hybrid 2D heterointerfaces enabled efficient CO2 conversion through combined photocatalysis and triboelectric-activated catalysis. The solar-powered acoustic-activated conversion approach of the present study enabled us to achieve the CO2 conversion efficiency of more than 94% in the reaction chambers containing 2D Ga2O3-Ag nanosheets. Full article
(This article belongs to the Special Issue Novel Nanostructured Materials for Optoelectronic Applications)
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29 pages, 4902 KiB  
Review
Review of Potential Drug-Eluting Contact Lens Technologies
by Tina Lovrec-Krstič, Kristjan Orthaber, Uroš Maver and Tomislav Sarenac
Materials 2023, 16(10), 3653; https://doi.org/10.3390/ma16103653 - 11 May 2023
Cited by 5 | Viewed by 4233
Abstract
The field of ophthalmology is expanding exponentially, both in terms of diagnostic and therapeutic capabilities, as well as the worldwide increasing incidence of eye-related diseases. Due to an ageing population and climate change, the number of ophthalmic patients will continue to increase, overwhelming [...] Read more.
The field of ophthalmology is expanding exponentially, both in terms of diagnostic and therapeutic capabilities, as well as the worldwide increasing incidence of eye-related diseases. Due to an ageing population and climate change, the number of ophthalmic patients will continue to increase, overwhelming healthcare systems and likely leading to under-treatment of chronic eye diseases. Since drops are the mainstay of therapy, clinicians have long emphasised the unmet need for ocular drug delivery. Alternative methods, i.e., with better compliance, stability and longevity of drug delivery, would be preferred. Several approaches and materials are being studied and used to overcome these drawbacks. We believe that drug-loaded contact lenses are among the most promising and are a real step toward dropless ocular therapy, potentially leading to a transformation in clinical ophthalmic practice. In this review, we outline the current role of contact lenses in ocular drug delivery, focusing on materials, drug binding and preparation, concluding with a look at future developments. Full article
(This article belongs to the Special Issue Advanced Bio-Based Polymers: Synthesis, Characterization and Applications (Second Volume))
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15 pages, 4464 KiB  
Article
Thermal Programming of Commercially Available Orthodontic NiTi Archwires
by Andrea Wichelhaus, Amelie Mehnert, Thomas Stocker, Uwe Baumert, Matthias Mertmann, Hisham Sabbagh and Corinna L. Seidel
Materials 2023, 16(10), 3683; https://doi.org/10.3390/ma16103683 - 11 May 2023
Cited by 3 | Viewed by 1782
Abstract
The shape of superelastic Nickel-Titanium (NiTi) archwires can be adjusted with thermal treatments using devices such as the Memory-MakerTM (Forestadent), which potentially affects their mechanical properties. The effect of such treatments on these mechanical properties was simulated by means of a laboratory [...] Read more.
The shape of superelastic Nickel-Titanium (NiTi) archwires can be adjusted with thermal treatments using devices such as the Memory-MakerTM (Forestadent), which potentially affects their mechanical properties. The effect of such treatments on these mechanical properties was simulated by means of a laboratory furnace. Fourteen commercially available NiTi wires (0.018″ × 0.025″) were selected from the manufacturers American Orthodontics, Dentaurum, Forestadent, GAC, Ormco, Rocky Mountain Orthodontics and 3M Unitek. Specimens were heat treated using different combinations of annealing duration (1/5/10 min) and annealing temperature (250–800 °C) and investigated using angle measurements and three-point bending tests. Complete shape adaptation was found at distinct annealing durations/temperatures for each wire ranging between ~650–750 °C (1 min), ~550–700 °C (5 min) and ~450–650 °C (10 min), followed by a loss of superelastic properties shortly afterwards at ~750 °C (1 min), ~600–650 °C (5 min) and ~550–600 °C (10 min). Wire-specific working ranges (complete shaping without loss of superelasticity) were defined and a numerical score (e.g., stable forces) was developed for the three-point bending test. Overall, the wires Titanol Superelastic (Forestadent), Tensic (Dentaurum), FLI CuNiTi27 (Rocky Mountain Orthodontics) and Nitinol Classic (3M Unitek) proved to be the most user-friendly. Thermal shape adjustment requires wire-specific working ranges to allow complete shape acceptance and high scores in bending test performance to ensure permanence of the superelastic behaviour. Full article
(This article belongs to the Special Issue Characterization of Shape Memory Alloy Materials)
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19 pages, 8541 KiB  
Review
3D Textiles Based on Warp Knitted Fabrics: A Review
by Lars Hahn, Konrad Zierold, Anke Golla, Danny Friese and Steffen Rittner
Materials 2023, 16(10), 3680; https://doi.org/10.3390/ma16103680 - 11 May 2023
Cited by 9 | Viewed by 5982
Abstract
Fibre-reinforced composites (FRCs) are already well established in several industrial sectors such as aerospace, automotive, plant engineering, shipbuilding and construction. The technical advantages of FRCs over metallic materials are well researched and proven. The key factors for an even wider industrial application of [...] Read more.
Fibre-reinforced composites (FRCs) are already well established in several industrial sectors such as aerospace, automotive, plant engineering, shipbuilding and construction. The technical advantages of FRCs over metallic materials are well researched and proven. The key factors for an even wider industrial application of FRCs are the maximisation of resource and cost efficiency in the production and processing of the textile reinforcement materials. Due to its technology, warp knitting is the most productive and therefore cost-effective textile manufacturing process. In order to produce resource-efficient textile structures with these technologies, a high degree of prefabrication is required. This reduces costs by reducing the number of ply stacks, and by reducing the number of extra operations through final path and geometric yarn orientation of the preforms. It also reduces waste in post-processing. Furthermore, a high degree of prefabrication through functionalisation offers the potential to extend the application range of textile structures as purely mechanical reinforcements by integrating additional functions. So far, there is a gap in terms of an overview of the current state-of-the-art of relevant textile processes and products, which this work aims to fill. The focus of this work is therefore to provide an overview of warp knitted 3D structures. Full article
(This article belongs to the Collection Advanced Composite Materials and Structures for Aerospace, Automotive and Civil Engineering Applications)
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16 pages, 12362 KiB  
Article
Full-Scale Fatigue Test and Finite Element Analysis on External Inclined Strut Welded Joints of a Wide-Flanged Composite Box Girder Bridge
by Bin Wang, Laijun Liu, Yuqing Liu, Xudong Jia, Xiaoqing Xu, Kaixiang Miao and Jiandong Ji
Materials 2023, 16(10), 3637; https://doi.org/10.3390/ma16103637 - 10 May 2023
Cited by 2 | Viewed by 1866
Abstract
For a wide-flanged composite box girder bridge, the risk of fatigue cracking in the external inclined strut welded joint under the fatigue vehicle load is a problem. The main purposes of this research are to verify the safety of the main bridge of [...] Read more.
For a wide-flanged composite box girder bridge, the risk of fatigue cracking in the external inclined strut welded joint under the fatigue vehicle load is a problem. The main purposes of this research are to verify the safety of the main bridge of the Linyi Yellow River Bridge, a continuous composite box girder bridge, and to propose suggestions for optimization. In this research, a finite element model of one segment of the bridge was established to investigate the influence surface of the external inclined strut, and, using the nominal stress method, it was confirmed that the fatigue cracking of the welded details of the external inclined strut was risky. Subsequently, a full-scale fatigue test of the external inclined strut welded joint was carried out, and the crack propagation law and S-N curve of the welded details were obtained. Finally, a parametric analysis was conducted with the three-dimensional refined finite element models. The results showed that the welded joint in the real bridge has a fatigue life larger than that of the design life, and methods such as increasing the flange thickness of the external inclined strut and the diameter of the welding hole are beneficial to improve its fatigue performance. Full article
(This article belongs to the Special Issue Experimental Study, Numerical Simulation & Structural Applications of Construction Materials)
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19 pages, 4852 KiB  
Article
Combined DFT-D3 Computational and Experimental Studies on g-C3N4: New Insight into Structure, Optical, and Vibrational Properties
by Paolo Negro, Federico Cesano, Silvia Casassa and Domenica Scarano
Materials 2023, 16(10), 3644; https://doi.org/10.3390/ma16103644 - 10 May 2023
Cited by 8 | Viewed by 2735
Abstract
Graphitic carbon nitride (g-C3N4) has emerged as one of the most promising solar-light-activated polymeric metal-free semiconductor photocatalysts due to its thermal physicochemical stability but also its characteristics of environmentally friendly and sustainable material. Despite the challenging properties of g-C [...] Read more.
Graphitic carbon nitride (g-C3N4) has emerged as one of the most promising solar-light-activated polymeric metal-free semiconductor photocatalysts due to its thermal physicochemical stability but also its characteristics of environmentally friendly and sustainable material. Despite the challenging properties of g-C3N4, its photocatalytic performance is still limited by the low surface area, together with the fast charge recombination phenomena. Hence, many efforts have been focused on overcoming these drawbacks by controlling and improving the synthesis methods. With regard to this, many structures including strands of linearly condensed melamine monomers, which are interconnected by hydrogen bonds, or highly condensed systems, have been proposed. Nevertheless, complete and consistent knowledge of the pristine material has not yet been achieved. Thus, to shed light on the nature of polymerised carbon nitride structures, which are obtained from the well-known direct heating of melamine under mild conditions, we combined the results obtained from XRD analysis, SEM and AFM microscopies, and UV-visible and FTIR spectroscopies with the data from the Density Functional Theory method (DFT). An indirect band gap and the vibrational peaks have been calculated without uncertainty, thus highlighting a mixture of highly condensed g-C3N4 domains embedded in a less condensed “melon-like” framework. Full article
(This article belongs to the Special Issue Graphene and Other 2D Layered Nanomaterials and Hybrid Structures: Synthesis, Properties and Applications (Volume II))
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15 pages, 9508 KiB  
Article
Evolution of Toughening Mechanisms in PH13-8Mo Stainless Steel during Aging Treatment
by Honglin Zhang, Peng Mi, Luhan Hao, Haichong Zhou, Wei Yan, Kuan Zhao, Bin Xu and Mingyue Sun
Materials 2023, 16(10), 3630; https://doi.org/10.3390/ma16103630 - 10 May 2023
Cited by 2 | Viewed by 1835
Abstract
PH13-8Mo stainless steel has been widely used in aerospace, petroleum and marine construction, obtaining continuous investigation attention in recent years. Based on the response of a hierarchical martensite matrix and possible reversed austenite, a systematic investigation of the evolution of the toughening mechanisms [...] Read more.
PH13-8Mo stainless steel has been widely used in aerospace, petroleum and marine construction, obtaining continuous investigation attention in recent years. Based on the response of a hierarchical martensite matrix and possible reversed austenite, a systematic investigation of the evolution of the toughening mechanisms in PH13-8Mo stainless steel as a function of aging temperature was carried out. It showed there was a desirable combination of high yield strength (~1.3 GPa) and V-notched impact toughness (~220 J) after aging between 540 and 550 °C. With the increase of aging temperature, the martensite matrix was recovered in terms of the refined sub-grains and higher ratio of high-angle grain boundaries (HAGBs). It should be noted there was a reversion of martensite to form austenite films subjected to aging above 540 °C; meanwhile, the NiAl precipitates maintained a well-coherent orientation with the matrix. Based on the post mortem analysis, there were three stages of the changing main toughening mechanisms: Stage I: low-temperature aging at around 510 °C, where the HAGBs contributed to the toughness by retarding the advance of cracks; Stage II: intermediate-temperature aging at around 540 °C, where the recovered laths embedded by soft austenite facilitated the improvement of toughness by synergistically increasing the advance path and blunting the crack tips; and Stage III: without the coarsening of NiAl precipitates around 560 °C, more inter-lath reversed austenite led to the optimum toughness, relying on “soft barrier” and transformation-induced plasticity (TRIP) effects. Full article
(This article belongs to the Special Issue Advanced Special and High-Strength Steels)
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18 pages, 4636 KiB  
Article
Experimental and Numerical Investigation into the Effect of Water Uptake on the Capacitance of an Organic Coating
by Steven A. Policastro, Rachel M. Anderson, Carlos M. Hangarter, Attilio Arcari and Erick B. Iezzi
Materials 2023, 16(10), 3623; https://doi.org/10.3390/ma16103623 - 9 May 2023
Cited by 7 | Viewed by 1492
Abstract
Water uptake by organic coating systems used for corrosion prevention on airframes is one of the principal contributors to the loss of barrier properties of the coating. We used equivalent circuit analyses of electrochemical impedance spectroscopy (EIS) data to track changes in coating [...] Read more.
Water uptake by organic coating systems used for corrosion prevention on airframes is one of the principal contributors to the loss of barrier properties of the coating. We used equivalent circuit analyses of electrochemical impedance spectroscopy (EIS) data to track changes in coating layer capacitance for a two-layer coating system consisting of an epoxy primer and polyurethane topcoat immersed in NaCl solutions with different concentrations and temperatures. The capacitance curve exhibited two different response regions, consistent with the “two-stage kinetics” mechanisms for water uptake by the polymers. We tested several numerical diffusion models of water sorption and found the most successful to be one that varied the diffusion coefficient as a function of polymer type and immersion time and accounted for physical aging processes in the polymer. We employed the Brasher mixing law along with the water sorption model to estimate the coating capacitance as a function of water uptake. The predicted capacitance of the coating was found to be consistent with the capacitance obtained from the EIS data, which is consistent with theories that water uptake occurs via initial rapid transport followed by a much slower aging process. Thus, both these water uptake processes need to be considered when making EIS measurements to assess the state of a coating system. Full article
(This article belongs to the Special Issue Advanced Polymer-Coated Materials: Fabrication, Characterization and Applications)
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22 pages, 13507 KiB  
Article
Signal-Decay Based Approach for Visualization of Buried Defects in 3-D Printed Ceramic Components Imaged with Help of Optical Coherence Tomography
by Malgorzata Kopycinska-Müller, Luise Schreiber, Eric Schwarzer-Fischer, Anne Günther, Conner Phillips, Tassilo Moritz, Jörg Opitz, Yeong-Jin Choi and Hui-suk Yun
Materials 2023, 16(10), 3607; https://doi.org/10.3390/ma16103607 - 9 May 2023
Cited by 2 | Viewed by 1829
Abstract
We propose the use of Optical Coherence Tomography (OCT) as a tool for the quality control of 3-D-printed ceramics. Test samples with premeditated defects, namely single- and two-component samples of zirconia, titania, and titanium suboxides, were printed by stereolithography-based DLP (Digital Light Processing) [...] Read more.
We propose the use of Optical Coherence Tomography (OCT) as a tool for the quality control of 3-D-printed ceramics. Test samples with premeditated defects, namely single- and two-component samples of zirconia, titania, and titanium suboxides, were printed by stereolithography-based DLP (Digital Light Processing) processes. The OCT tomograms obtained on the green samples showed the capability of the method to visualize variations in the layered structure of the samples as well as the presence of cracks and inclusions at depths up to 130 µm, as validated by SEM images. The structural information was visible in cross-sectional images as well as in plan-view images. The optical signal measured from the printed zirconia oxide and titanium oxide samples showed strong attenuation with depth and could be fit with an exponential decay curve. The variations of the decay parameter correlated very well with the presence of defects and material variation. When used as an imaging quantity, the decay parameter projects the position of the defects into 2-D (X,Y) coordinates. This procedure can be used in real time, it reduces the data volume up to 1000 times, and allows for faster subsequent data analysis and transfer. Tomograms were also obtained on sintered samples. The results showed that the method can detect changes in the optical properties of the green ceramics caused by sintering. Specifically, the zirconium oxide samples became more transparent to the light used, whereas the titanium suboxide samples became entirely opaque. In addition, the optical response of the sintered zirconium oxide showed variations within the imaged volume, indicating material density variations. The results presented in this study show that OCT provides sufficient structural information on 3-D-printed ceramics and can be used as an in-line tool for quality control. Full article
(This article belongs to the Special Issue Recent Advances in Ceramic Manufacturing)
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15 pages, 5624 KiB  
Article
The Application of Additive Composites Technologies for Clamping and Manipulation Devices in the Production Process
by Richard Joch, Michal Šajgalík, Mário Drbúl, Jozef Holubják, Andrej Czán, Vladimír Bechný and Miroslav Matúš
Materials 2023, 16(10), 3624; https://doi.org/10.3390/ma16103624 - 9 May 2023
Cited by 6 | Viewed by 1752
Abstract
Additive technologies have been widely adopted in various industries. The choice of additive technology and material directly affects the functionality of the manufactured components. The development of materials with better mechanical properties has led to a growing interest in replacing traditional metal components [...] Read more.
Additive technologies have been widely adopted in various industries. The choice of additive technology and material directly affects the functionality of the manufactured components. The development of materials with better mechanical properties has led to a growing interest in replacing traditional metal components with those manufactured using additive technologies. The application of Onyx as a material comes into consideration, which contains short carbon fibers to increase the mechanical properties. This study aims to experimentally verify the viability of substituting metal gripping elements with nylon and composite materials. The design of the jaws was customized to meet the requirements of a three-jaw chuck of a CNC machining center. The evaluation process involved monitoring the functionality and deformation effects on the clamped PTFE polymer material. When the metal jaws were applied, significant deformation of the clamped material occurred, which varied with the clamping pressure. This deformation was evidenced by the formation of spreading cracks on the clamped material and permanent shape changes in the tested material. Conversely, nylon and composite jaws manufactured using additive technology demonstrated functionality across all tested clamping pressures, without causing permanent deformation of the clamped material, unlike the traditional metal jaws. The results of this study confirm the applicability of the Onyx material and provide practical evidence of the potential for reducing deformation caused by clamping mechanisms. Full article
(This article belongs to the Special Issue 3D & 4D Printing in Engineering Applications)
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15 pages, 2304 KiB  
Article
Fabrication and Arc Erosion Behavior of Ag-SnO2-ZnO Electrical Contact Materials
by Danny Guzmán, Felipe González, Diego Muranda, Claudio Aguilar, Alexis Guzmán, Álvaro Soliz, Lorena Lozada, Iñigo Iturriza and Felipe Castro
Materials 2023, 16(10), 3618; https://doi.org/10.3390/ma16103618 - 9 May 2023
Cited by 10 | Viewed by 2299
Abstract
This study investigated the synthesis of Ag-SnO2-ZnO by powder metallurgy methods and their subsequent electrical contact behavior. The pieces of Ag-SnO2-ZnO were prepared by ball milling and hot pressing. The arc erosion behavior of the material was evaluated using [...] Read more.
This study investigated the synthesis of Ag-SnO2-ZnO by powder metallurgy methods and their subsequent electrical contact behavior. The pieces of Ag-SnO2-ZnO were prepared by ball milling and hot pressing. The arc erosion behavior of the material was evaluated using homemade equipment. The microstructure and phase evolution of the materials were investigated through X-ray diffraction, energy-dispersive spectroscopy and scanning electron microscopy. The results showed that, although the mass loss of the Ag-SnO2-ZnO composite (9.08 mg) during the electrical contact test was higher than that of the commercial Ag-CdO (1.42 mg), its electrical conductivity remained constant (26.9 ± 1.5% IACS). This fact would be related to the reaction of Zn2SnO4’s formation on the material’s surface via electric arc. This reaction would play an important role in controlling the surface segregation and subsequent loss of electrical conductivity of this type of composite, thus enabling the development of a new electrical contact material to replace the non-environmentally friendly Ag-CdO composite. Full article
(This article belongs to the Special Issue Powder Metallurgy: Materials and Processing)
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12 pages, 7301 KiB  
Article
Structure and Wear Performance of a Titanium Alloy by Using Low-Temperature Plasma Oxy-Nitriding
by Haidong Li, Haifeng Wang, Shijie Wang, Yange Yang, Yunsong Niu, Shenglong Zhu and Fuhui Wang
Materials 2023, 16(10), 3609; https://doi.org/10.3390/ma16103609 - 9 May 2023
Cited by 2 | Viewed by 1613
Abstract
To solve the problems of high nitriding temperature and long nitriding time with conventional plasma nitriding technologies, a kind of low-temperature plasma oxy-nitriding technology containing two-stage processes with different ratios of N to O was developed on a TC4 alloy in this paper. [...] Read more.
To solve the problems of high nitriding temperature and long nitriding time with conventional plasma nitriding technologies, a kind of low-temperature plasma oxy-nitriding technology containing two-stage processes with different ratios of N to O was developed on a TC4 alloy in this paper. A thicker permeation coating can be obtained with this new technology compared to conventional plasma nitriding technology. The reason for this is that the oxygen introduction in the first two-hour oxy-nitriding step can break the continuous TiN layer, which facilitates the quick and deep diffusion of the solution-strengthening elements of O and N into the titanium alloy. Moreover, an inter-connected porous structure was formed under a compact compound layer, which acts as a buffer layer to absorb the external wear force. Therefore, the resultant coating showed the lowest COF values during the initial wear state, and almost no debris and cracks were detected after the wear test. For the treated samples with low hardness and no porous structure, fatigue cracks can easily form on the surface, and bulk peeling-offcan occur during the wear course. Full article
(This article belongs to the Special Issue Advances in Coating Materials Research: From Preparation to Application)
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16 pages, 9623 KiB  
Article
Synergistic Effects of 2-Butyne-1,4-Diol and Chloride Ions on the Microstructure and Residual Stress of Electrodeposited Nickel
by Ming Sun, Chao Zhang, Ruhan Ya, Hongyu He, Zhipeng Li and Wenhuai Tian
Materials 2023, 16(9), 3598; https://doi.org/10.3390/ma16093598 - 8 May 2023
Viewed by 1527
Abstract
To assess the individual and synergistic effects of 2-butyne-1,4-diol (BD) and chloride ions on the microstructure and residual stress of electrodeposited nickel, various nickel layers were prepared from sulfamate baths comprising varying concentrations of BD and chloride ions by applying direct-current electrodeposition. And [...] Read more.
To assess the individual and synergistic effects of 2-butyne-1,4-diol (BD) and chloride ions on the microstructure and residual stress of electrodeposited nickel, various nickel layers were prepared from sulfamate baths comprising varying concentrations of BD and chloride ions by applying direct-current electrodeposition. And their surface morphologies, microstructure, and residual stress were tested using SEM, XRD, EBSD, TEM, and AFM. While the nickel layers composed of pyramid morphology were prepared from additive-free baths, the surface flattened gradually as the BD concentration of the baths was increased, and the acicular grains in the deposits were replaced with <100> oriented columnar grains or <111> oriented nanograins; additionally, the residual tensile stress of the deposits increased. The addition of chloride ions to the baths containing BD significantly increased the residual stress in the nickel layers, although it only slightly promoted surface flattening and columnar grain coarsening. The effects of BD and chloride ions on the growth mode and residual stress of nickel deposits were explained via analysis of surface morphologies and microstructure. And the results indicate that the reduction of chloride ion concentration is a feasible way to reduce the residual stress of the nickel deposits when BD is included in the baths. Full article
(This article belongs to the Special Issue Advances in Coatings Prepared by Deposition: Microstructure, Properties and Applications)
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23 pages, 11793 KiB  
Review
Plasmonic Functionality of Optical Fiber Tips: Mechanisms, Fabrications, and Applications
by Bobo Du, Yunfan Xu, Lei Zhang and Yanpeng Zhang
Materials 2023, 16(9), 3596; https://doi.org/10.3390/ma16093596 - 8 May 2023
Cited by 3 | Viewed by 1991
Abstract
Optical fiber tips with the flat end-facets functionalized take the special advantages of easy fabrication, compactness, and ready-integration among the community of optical fiber devices. Combined with plasmonic structures, the fiber tips draw a significant growth of interest addressing diverse functions. This review [...] Read more.
Optical fiber tips with the flat end-facets functionalized take the special advantages of easy fabrication, compactness, and ready-integration among the community of optical fiber devices. Combined with plasmonic structures, the fiber tips draw a significant growth of interest addressing diverse functions. This review aims to present and summarize the plasmonic functionality of optical fiber tips with the current state of the art. Firstly, the mechanisms of plasmonic phenomena are introduced in order to illustrate the tip-compatible plasmonic nanostructures. Then, the strategies of plasmonic functionalities on fiber tips are analyzed and compared. Moreover, the classical applications of plasmonic fiber tips are reviewed. Finally, the challenges and prospects for future opportunities are discussed. Full article
(This article belongs to the Special Issue Advances in Multimaterial Fibers and Devices)
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18 pages, 6570 KiB  
Article
Fracture Response of X80 Pipe Girth Welds under Combined Internal Pressure and Bending Moment
by Li Zhu, Naixian Li, Bin Jia and Yu Zhang
Materials 2023, 16(9), 3588; https://doi.org/10.3390/ma16093588 - 7 May 2023
Cited by 2 | Viewed by 1780
Abstract
In order to determine the effect of defect size on the pipeline fracture performance of girth welds in oil and gas pipelines, ABAQUS was used to simulate the fracture responses of X80 pipelines with girth weld defects under internal pressure and bending moment [...] Read more.
In order to determine the effect of defect size on the pipeline fracture performance of girth welds in oil and gas pipelines, ABAQUS was used to simulate the fracture responses of X80 pipelines with girth weld defects under internal pressure and bending moment conditions based on damage mechanics. In particular, the length and depth of defects were parametrically studied; the defect depth range was 20–80% of the wall thickness, and the circumferential length range of the defects was 5–20% of the pipeline circumference. The results show that, under the combined action of internal pressure and bending moment, the defect depth was more associated with adverse effects than the circumferential length of the defect. The failure load did not linearly decrease as the size of the defect increased, but when the depth of the defect reached a certain value, the failure load suddenly decreased. Full article
(This article belongs to the Special Issue Mechanics Behavior, Fatigue Damage, and Microstructure Evolution of Metallic Material)
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14 pages, 22598 KiB  
Article
Microstructure Evolution and Mechanical Response of a Direct Quenched and Partitioned Steel at Different Finishing Rolling Temperatures
by Yajun Liu, Xiaolong Gan, Wen Liang, Guang Xu, Jianghua Qi and Man Liu
Materials 2023, 16(9), 3575; https://doi.org/10.3390/ma16093575 - 6 May 2023
Cited by 4 | Viewed by 1588
Abstract
The effects of finishing rolling temperature on the microstructure and mechanical properties of a direct quenched and partitioned (DQ&P) steel were investigated by a thermal simulation machine, a field emission scanning electron microscope (FE-SEM), electron backscattering diffraction (EBSD), and a transmission electron microscope [...] Read more.
The effects of finishing rolling temperature on the microstructure and mechanical properties of a direct quenched and partitioned (DQ&P) steel were investigated by a thermal simulation machine, a field emission scanning electron microscope (FE-SEM), electron backscattering diffraction (EBSD), and a transmission electron microscope (TEM). The results show that the original austenite grain size was refined by 31% as the finishing rolling temperature decreased from 920 °C to 840 °C, leading to the formation of the finest martensite lath at 840 °C. At the same time, the lower finishing rolling temperature resulted in a higher dislocation density, and consequently improved the stability of the retained austenite. Moreover, compared to the conventional Q&P process, the comprehensive mechanical properties of a steel with similar chemical composition can be enhanced by DQ&P processing. With the decrease of finishing rolling temperature from 920 °C to 840 °C, the strength and total elongation increases. The yield strength, tensile strength, and total elongation reach the maximum values of 1121 MPa, 1134 MPa, and 11.7%, respectively, at 840 °C. Full article
(This article belongs to the Special Issue Microstructure, Mechanical Properties and Wear Performance of High-Strength Steels)
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30 pages, 16400 KiB  
Review
Recent Progress for Single-Molecule Magnets Based on Rare Earth Elements
by Xiang Yin, Li Deng, Liuxia Ruan, Yanzhao Wu, Feifei Luo, Gaowu Qin, Xiaoli Han and Xianmin Zhang
Materials 2023, 16(9), 3568; https://doi.org/10.3390/ma16093568 - 6 May 2023
Cited by 6 | Viewed by 2431
Abstract
Single-molecule magnets (SMMs) have attracted much attention due to their potential applications in molecular spintronic devices. Rare earth SMMs are considered to be the most promising for application owing to their large magnetic moment and strong magnetic anisotropy. In this review, the recent [...] Read more.
Single-molecule magnets (SMMs) have attracted much attention due to their potential applications in molecular spintronic devices. Rare earth SMMs are considered to be the most promising for application owing to their large magnetic moment and strong magnetic anisotropy. In this review, the recent progress in rare earth SMMs represented by mononuclear and dinuclear complexes is highlighted, especially for the modulation of magnetic anisotropy, effective energy barrier (Ueff) and blocking temperature (TB). The terbium- and dysprosium-based SMMs have a Ueff of 1541 cm−1 and an increased TB of 80 K. They break the boiling point temperature of liquid nitrogen. The development of the preparation technology of rare earth element SMMs is also summarized in an overview. This review has important implications and insights for the design and research of Ln-SMMs. Full article
(This article belongs to the Special Issue Theory and Simulations of Magnetic Materials)
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18 pages, 5619 KiB  
Review
A Review of Numerical Simulation of Laser–Arc Hybrid Welding
by Zhaoyang Wang, Mengcheng Gong, Longzao Zhou and Ming Gao
Materials 2023, 16(9), 3561; https://doi.org/10.3390/ma16093561 - 6 May 2023
Cited by 9 | Viewed by 2429
Abstract
Laser–arc hybrid welding (LAHW) is known to achieve more stable processes, better mechanical properties, and greater adaptability through the synergy of a laser and an arc. Numerical simulations play a crucial role in deepening our understanding of this interaction mechanism. In this paper, [...] Read more.
Laser–arc hybrid welding (LAHW) is known to achieve more stable processes, better mechanical properties, and greater adaptability through the synergy of a laser and an arc. Numerical simulations play a crucial role in deepening our understanding of this interaction mechanism. In this paper, we review the current work on numerical simulations of LAHW, including heat source selection laws, temperature field, flow field, and stress field results. We also discuss the influence of laser–arc interaction on weld defects and mechanical properties and provide suggestions for the development of numerical simulations of LAHW. Full article
(This article belongs to the Special Issue Advances in the Experimentation and Numerical Modeling of Material Joining Processes)
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18 pages, 2294 KiB  
Article
Mechanistic Study of Fast Performance Decay of PtCu Alloy-based Catalyst Layers for Polymer Electrolyte Fuel Cells through Electrochemical Impedance Spectroscopy
by Maximilian Grandi, Matija Gatalo, Ana Rebeka Kamšek, Gregor Kapun, Kurt Mayer, Francisco Ruiz-Zepeda, Martin Šala, Bernhard Marius, Marjan Bele, Nejc Hodnik, Merit Bodner, Miran Gaberšček and Viktor Hacker
Materials 2023, 16(9), 3544; https://doi.org/10.3390/ma16093544 - 5 May 2023
Cited by 1 | Viewed by 1887
Abstract
In the past, platinum–copper catalysts have proven to be highly active for the oxygen reduction reaction (ORR), but transferring the high activities measured in thin-film rotating disk electrodes (TF-RDEs) to high-performing membrane electrode assemblies (MEAs) has proven difficult due to stability issues during [...] Read more.
In the past, platinum–copper catalysts have proven to be highly active for the oxygen reduction reaction (ORR), but transferring the high activities measured in thin-film rotating disk electrodes (TF-RDEs) to high-performing membrane electrode assemblies (MEAs) has proven difficult due to stability issues during operation. High initial performance can be achieved. However, fast performance decay on a timescale of 24 h is induced by repeated voltage load steps with H2/air supplied. This performance decay is accelerated if high relative humidity (>60% RH) is set for a prolonged time and low voltages are applied during polarization. The reasons and possible solutions for this issue have been investigated by means of electrochemical impedance spectroscopy and distribution of relaxation time analysis (EIS–DRT). The affected electrochemical sub-processes have been identified by comparing the PtCu electrocatalyst with commercial Pt/C benchmark materials in homemade catalyst-coated membranes (CCMs). The proton transport resistance (Rpt) increased by a factor of ~2 compared to the benchmark materials. These results provide important insight into the challenges encountered with the de-alloyed PtCu/KB electrocatalyst during cell break-in and operation. This provides a basis for improvements in the catalysts’ design and break-in procedures for the highly attractive PtCu/KB catalyst system. Full article
(This article belongs to the Special Issue Novel Materials for Green Hydrogen Production, Energy Conversion, and Fuel Cell Applications)
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17 pages, 4713 KiB  
Article
Novel Graphene-Based Materials as a Tool for Improving Long-Term Storage of Cultural Heritage
by George Gorgolis, Steffen Ziemann, Maria Kotsidi, George Paterakis, Nikos Koutroumanis, Christos Tsakonas, Manfred Anders and Costas Galiotis
Materials 2023, 16(9), 3528; https://doi.org/10.3390/ma16093528 - 4 May 2023
Cited by 4 | Viewed by 1862
Abstract
The very serious problem of temperature and humidity regulation, especially for small and medium-sized museums, galleries, and private collections, can be mitigated by the introduction of novel materials that are easily applicable and of low cost. Within this study, archive boxes with innovative [...] Read more.
The very serious problem of temperature and humidity regulation, especially for small and medium-sized museums, galleries, and private collections, can be mitigated by the introduction of novel materials that are easily applicable and of low cost. Within this study, archive boxes with innovative technology are proposed as “smart” boxes that can be used for storage and transportation, in combination with a nanocomposite material consisting of polyvinyl alcohol (PVA) and graphene oxide (GO). The synthesis and characterization of the PVA/GO structure with SEM, Raman, AFM, XRD, Optical Microscopy, and profilometry are fully discussed. It is shown that the composite material can be integrated into the archive box either as a stand-alone film or attached onto fitting carriers, for example, those made of corrugated board. By applying the PVA/GO membrane this way, even with strong daily temperature fluctuations of ΔT = ±24.1 °C, strong external humidity fluctuations can be reduced by −87% inside the box. Furthermore, these humidity regulators were examined as Volatile Organic Compounds (VOCs) adsorbers since gas pollutants like formic acid, formaldehyde, acetic acid, and acetaldehyde are known to exist in museums and induce damages in the displayed or stored items. High rates of VOC adsorption have been measured, with the highest ones corresponding to formic acid (521% weight increase) and formaldehyde (223% weight increase). Full article
(This article belongs to the Section Advanced Nanomaterials and Nanotechnology)
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25 pages, 63751 KiB  
Review
Copper-Based Diamond-like Thermoelectric Compounds: Looking Back and Stepping Forward
by Wenying Wang, Lin Bo, Junliang Zhu and Degang Zhao
Materials 2023, 16(9), 3512; https://doi.org/10.3390/ma16093512 - 3 May 2023
Cited by 3 | Viewed by 2317
Abstract
The research on thermoelectric (TE) materials has a long history. Holding the advantages of high elemental abundance, lead-free and easily tunable transport properties, copper-based diamond-like (CBDL) thermoelectric compounds have attracted extensive attention from the thermoelectric community. The CBDL compounds contain a large number [...] Read more.
The research on thermoelectric (TE) materials has a long history. Holding the advantages of high elemental abundance, lead-free and easily tunable transport properties, copper-based diamond-like (CBDL) thermoelectric compounds have attracted extensive attention from the thermoelectric community. The CBDL compounds contain a large number of representative candidates for thermoelectric applications, such as CuInGa2, Cu2GeSe3, Cu3SbSe4, Cu12SbSe13, etc. In this study, the structure characteristics and TE performances of typical CBDLs were briefly summarized. Several common synthesis technologies and effective strategies to improve the thermoelectric performances of CBDL compounds were introduced. In addition, the latest developments in thermoelectric devices based on CBDL compounds were discussed. Further developments and prospects for exploring high-performance copper-based diamond-like thermoelectric materials and devices were also presented at the end. Full article
(This article belongs to the Special Issue Materials Physics in Thermoelectric Materials)
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16 pages, 3316 KiB  
Article
Insights into the Contribution of Oxidation-Reduction Pretreatment for Mn0.2Zr0.8O2−δ Catalyst of CO Oxidation Reaction
by Denis D. Mishchenko, Zakhar S. Vinokurov, Tatyana N. Afonasenko, Andrey A. Saraev, Mikhail N. Simonov, Evgeny Yu. Gerasimov and Olga A. Bulavchenko
Materials 2023, 16(9), 3508; https://doi.org/10.3390/ma16093508 - 2 May 2023
Cited by 1 | Viewed by 1771
Abstract
A Mn0.2Zr0.8O2−δ mixed oxide catalyst was synthesized via the co-precipitation method and studied in a CO oxidation reaction after different redox pretreatments. The surface and structural properties of the catalyst were studied before and after the pretreatment using [...] Read more.
A Mn0.2Zr0.8O2−δ mixed oxide catalyst was synthesized via the co-precipitation method and studied in a CO oxidation reaction after different redox pretreatments. The surface and structural properties of the catalyst were studied before and after the pretreatment using XRD, XANES, XPS, and TEM techniques. Operando XRD was used to monitor the changes in the crystal structure under pretreatment and reaction conditions. The catalytic properties were found to depend on the activation procedure: reducing the CO atmosphere at 400–600 °C and the reaction mixture (O2 excess) or oxidative O2 atmosphere at 250–400 °C. A maximum catalytic effect characterized by decreasing T50 from 193 to 171 °C was observed after a reduction at 400 °C and further oxidation in the CO/O2 reaction mixture was observed at 250 °C. Operando XRD showed a reversible reduction-oxidation of Mn cations in the volume of Mn0.2Zr0.8O2−δ solid solution. XPS and TEM detected the segregation of manganese cations on the surface of the mixed oxide. TEM showed that Mn-rich regions have a structure of MnO2. The pretreatment caused the partial decomposition of the Mn0.2Zr0.8O2−δ solid solution and the formation of surface Mn-rich areas that are active in catalytic CO oxidation. In this work it was shown that the introduction of oxidation-reduction pretreatment cycles leads to an increase in catalytic activity due to changes in the origin of active states. Full article
(This article belongs to the Section Catalytic Materials)
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17 pages, 5358 KiB  
Article
Production of AC from Bamboo, Orange, and Paulownia Waste—Influence of Activation Gas and Biomass Maturation
by Carlos Grima-Olmedo, Laura M. Valle-Falcones, Dulce Gómez-Limón Galindo and Ramón Rodríguez-Pons Esparver
Materials 2023, 16(9), 3498; https://doi.org/10.3390/ma16093498 - 1 May 2023
Cited by 2 | Viewed by 1963
Abstract
The production of agricultural waste is associated with environmental problems and risks to public health. The general interest demands, as an ecological alternative, the proper management of waste generated by industrial activity through its transformation into value-added products. Carbonization/activation (2 h/2 h) at [...] Read more.
The production of agricultural waste is associated with environmental problems and risks to public health. The general interest demands, as an ecological alternative, the proper management of waste generated by industrial activity through its transformation into value-added products. Carbonization/activation (2 h/2 h) at 700 °C in a vertical furnace (20 K/min), to produce biochar and activated carbon (AC) from bamboo, orange, and paulownia residue, was carried out in a laboratory facility with physical activation by CO2 and steam. The characterization of the carbonaceous material obtained was based on the determination of the N2 adsorption–desorption isotherms at 77 K, the specific surface area with the BET procedure, and its internal structure by means of SEM images. The BET surface area values obtained as a function of the CO2/steam agent used were 911/1182 m2/g, 248/388 m2/g, and 800/1166 m2/g for bamboo, orange, and paulownia, respectively. The range of variation of porosity in paulownia residue generated after steam activation was 485–1166 m2/g, varying depending on the degree of maturity of the biomass used. Research has shown that both the type of activation agent used to produce AC and the degree of plant maturation of the precursor residue affect the quality and characteristics of the final product. Full article
(This article belongs to the Section Carbon Materials)
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26 pages, 7496 KiB  
Article
Evaluation of Early Concrete Damage Caused by Chloride-Induced Steel Corrosion Using a Deep Learning Approach Based on RNN for Ultrasonic Pulse Waves
by Julfikhsan Ahmad Mukhti, Kevin Paolo V. Robles, Keon-Ho Lee and Seong-Hoon Kee
Materials 2023, 16(9), 3502; https://doi.org/10.3390/ma16093502 - 1 May 2023
Cited by 9 | Viewed by 2386
Abstract
The objective of this study is to explore the feasibility of using ultrasonic pulse wave measurements as an early detection method for corrosion-induced concrete damages. A series of experiments are conducted using concrete cube specimens, at a size of 200 mm, with a [...] Read more.
The objective of this study is to explore the feasibility of using ultrasonic pulse wave measurements as an early detection method for corrosion-induced concrete damages. A series of experiments are conducted using concrete cube specimens, at a size of 200 mm, with a reinforcing steel bar (rebar) embedded in the center. The main variables include the water-to-cement ratio of the concrete (0.4, 0.5, and 0.6), the diameter of the rebar (10 mm, 13 mm, 19 mm, and 22 mm), and the corrosion level (ranging from 0% to 20% depending on rebar diameter). The impressed current technique is used to accelerate corrosion of rebars in concrete immersed in a 3% NaCl solution. Ultrasonic pulse waves are collected from the concrete specimens using a pair of 50 kHz P-wave transducers in the through-transmission configuration before and after the accelerated corrosion test. Deep learning techniques, specifically three recurrent neural network (RNN) models (long short-term memory, gated recurrent unit, and bidirectional long short-term memory), are utilized to develop a classification model for early detection of concrete damage due to rebar corrosion. The performance of the RNN models is compared to conventional ultrasonic testing parameters, namely ultrasonic pulse velocity and signal consistency. The results demonstrate that the RNN method outperforms the other two methods. Among the RNN methods, the bidirectional long short-term memory RNN model had the best performance, achieving an accuracy of 74% and a Cohen’s kappa coefficient of 0.48. This study establishes the potentiality of utilizing deep learning of ultrasonic pulse waves with RNN models for early detection of concrete damage associated with steel corrosion. Full article
(This article belongs to the Section Construction and Building Materials)
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25 pages, 4714 KiB  
Article
Vibration Analysis of a Unimorph Nanobeam with a Dielectric Layer of Both Flexoelectricity and Piezoelectricity
by Ali Naderi, Tran Quoc-Thai, Xiaoying Zhuang and Xiaoning Jiang
Materials 2023, 16(9), 3485; https://doi.org/10.3390/ma16093485 - 30 Apr 2023
Cited by 4 | Viewed by 1663
Abstract
In this study, for the first time, free and forced vibrational responses of a unimorph nanobeam consisting of a functionally graded base, along with a dielectric layer of both piezoelectricity and flexoelectricity, is investigated based on paradox-free local/nonlocal elasticity. The formulation and boundary [...] Read more.
In this study, for the first time, free and forced vibrational responses of a unimorph nanobeam consisting of a functionally graded base, along with a dielectric layer of both piezoelectricity and flexoelectricity, is investigated based on paradox-free local/nonlocal elasticity. The formulation and boundary conditions are attained by utilizing the energy method Hamilton’s principle. In order to set a comparison, the formulation of a model in the framework of differential nonlocal is first presented. An effective implementation of the generalized differential quadrature method (GDQM) is then utilized to solve higher-order partial differential equations. This method can be utilized to solve the complex equations whose analytic results are quite difficult to obtain. Lastly, the impact of various parameters is studied to characterize the vibrational behavior of the system. Additionally, the major impact of flexoelectricity compared to piezoelectricity on a small scale is exhibited. The results show that small-scale flexoelectricity, rather than piezoelectricity, is dominant in electromechanical coupling. One of the results that can be mentioned is that the beams with higher nonlocality have the higher voltage and displacement under the same excitation amplitude. The findings can be helpful for further theoretical as well as experimental studies in which dielectric material is used in smart structures. Full article
(This article belongs to the Special Issue Piezoelectric Energy Harvesting and Sensing Technology: Materials, Mechanisms, and Applications)
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13 pages, 1258 KiB  
Article
Understanding Chloride Diffusion Coefficient in Cementitious Materials
by Zhiyuan Xu and Guang Ye
Materials 2023, 16(9), 3464; https://doi.org/10.3390/ma16093464 - 29 Apr 2023
Cited by 3 | Viewed by 2069
Abstract
One of the key problems that affect the durability of reinforced concrete structures is the corrosion of rebar induced by chloride. Despite the complicated transport mechanism of chloride ions in cementitious materials, diffusion is still the key mechanism of chloride ingress. The determination [...] Read more.
One of the key problems that affect the durability of reinforced concrete structures is the corrosion of rebar induced by chloride. Despite the complicated transport mechanism of chloride ions in cementitious materials, diffusion is still the key mechanism of chloride ingress. The determination of the chloride diffusion coefficient will help to predict the chloride profile inside the cementitious materials and estimate the service life with regard to chloride-induced corrosion. However, this paper shows that the chloride diffusion coefficient in the literature is sometimes misunderstood. Such a misunderstanding results in the overestimation of the chloride resistance of cementitious materials. To clarify the chloride diffusion coefficient, this paper first presents the steady- and non-steady-state diffusion equations in cementitious materials. The factors that influence the diffusive flux are identified. The effective and apparent diffusion coefficients are then clearly explained and properly defined. We also point out the obscure definitions of the effective diffusion coefficient in the literature. The varied definitions of the effective diffusion coefficient are the result of the consideration of different factors affecting the diffusion process. Subsequently, this paper discusses two natural diffusion test methods that are frequently employed in cementitious materials to measure the chloride diffusion coefficient. The influencing factors considered by the measured diffusion coefficients are analyzed in detail. Then, the diffusion coefficients determined in some of the studies are reviewed. It is shown that three typical errors could occur when numerically determining the diffusion coefficients. Full article
(This article belongs to the Collection Concrete and Building Materials)
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15 pages, 5346 KiB  
Article
GAM: General Auxetic Metamaterial with Tunable 3D Auxetic Behavior Using the Same Unit Cell Boundary Connectivity
by Ismael Ben-Yelun, Guillermo Gómez-Carano, Francisco J. San Millán, Miguel Ángel Sanz, Francisco Javier Montáns and Luis Saucedo-Mora
Materials 2023, 16(9), 3473; https://doi.org/10.3390/ma16093473 - 29 Apr 2023
Cited by 6 | Viewed by 1835
Abstract
Research on auxetic metamaterials is important due to their high performance against impact loadings and their usefulness in actuators, among other applications. These metamaterials offer a negative Poisson’s ratio at the macro level. However, usual auxetic metamaterials face challenges in (1) grading the [...] Read more.
Research on auxetic metamaterials is important due to their high performance against impact loadings and their usefulness in actuators, among other applications. These metamaterials offer a negative Poisson’s ratio at the macro level. However, usual auxetic metamaterials face challenges in (1) grading the effect, (2) coupling and combining auxetic metamaterials with non-auxetic materials due to boundary compatibility, (3) obtaining the same auxetic behavior in all directions in the transverse plane, and (4) adapting the regular geometry to the component design boundary and shape. The goal of this paper is to present a novel, recently patented tunable 3D metamaterial created to reproduce a wide spectrum of 3D auxetic and non-auxetic Poisson’s ratios and Young’s moduli. This wide range is obtained using the same basic unit cell geometry and boundary connections with neighboring cells, facilitating designs using functionally graded metamaterials as only the connectivity and position of the cell’s internal nodes are modified. Based on simple spatial triangularization, the metamaterial is easily scalable and better accommodates spatial curvatures or boundaries by changing the locations of nodes and lengths of bars. Full article
(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)
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17 pages, 5116 KiB  
Article
Numerical Simulations of the Low-Velocity Impact Response of Semicylindrical Woven Composite Shells
by Luis M. Ferreira, Carlos A. C. P. Coelho and Paulo N. B. Reis
Materials 2023, 16(9), 3442; https://doi.org/10.3390/ma16093442 - 28 Apr 2023
Cited by 13 | Viewed by 2836
Abstract
This paper presents an efficient and reliable approach to study the low-velocity impact response of woven composite shells using 3D finite element models that account for the physical intralaminar and interlaminar progressive damage. The authors’ previous work on the experimental assessment of the [...] Read more.
This paper presents an efficient and reliable approach to study the low-velocity impact response of woven composite shells using 3D finite element models that account for the physical intralaminar and interlaminar progressive damage. The authors’ previous work on the experimental assessment of the effect of thickness on the impact response of semicylindrical composite laminated shells served as the basis for this paper. Therefore, the finite element models were put to the test in comparison to the experimental findings. A good agreement was obtained between the numerical predictions and experimental data for the load and energy histories as well as for the maximum impact load, maximum displacement, and contact time. The use of the mass-scaling technique was successfully implemented, reducing considerably the computing cost of the solutions. The maximum load, maximum displacement, and contact time are negligibly affected by the choice of finite element mesh discretization. However, it has an impact on the initiation and progression of interlaminar damage. Therefore, to accurately compute delamination, its correct definition is of upmost importance. The validation of these finite element models opens the possibility for further numerical studies on of woven composite shells and enables shortening the time and expenses associated with the experimental testing. Full article
(This article belongs to the Special Issue Experimental Testing, Manufacturing and Numerical Modelling of Composite and Sandwich Structures)
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17 pages, 6118 KiB  
Article
CFD–PBM Simulation for Continuous Hydrothermal Flow Synthesis of Zirconia Nanoparticles in a Confined Impinging Jet Reactor
by Qingyun Li, Zihua Wang and Xuezhong Wang
Materials 2023, 16(9), 3421; https://doi.org/10.3390/ma16093421 - 27 Apr 2023
Cited by 3 | Viewed by 1760
Abstract
Computational fluid dynamics (CFD) and population balance models (PBM) were coupled together for the first time to simulate the synthesis of zirconia nanoparticles in a continuous hydrothermal flow synthesis (CHFS) system with a self-designed confined impinging jet mixing (CJM) reactor. The hydrodynamic and [...] Read more.
Computational fluid dynamics (CFD) and population balance models (PBM) were coupled together for the first time to simulate the synthesis of zirconia nanoparticles in a continuous hydrothermal flow synthesis (CHFS) system with a self-designed confined impinging jet mixing (CJM) reactor. The hydrodynamic and thermodynamic behaviors within the CJM reactor strongly influenced the formation of the ZrO2 nanoparticles. Crucial parameters, such as velocities, temperatures, mixing conditions, and reaction rates, were analyzed under various supercritical conditions. Temperature and velocity measurements as functions of distance were also investigated. Normal particle size distribution (PSD) patterns were observed in all cases. The mean particle sizes in this study were calculated and compared using PBM aggregation analysis. Full article
(This article belongs to the Section Advanced Nanomaterials and Nanotechnology)
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11 pages, 4118 KiB  
Article
Charge Transport Enhancement in BiVO4 Photoanode for Efficient Solar Water Oxidation
by Zhidong Li, Zhibin Xie, Weibang Li, Hafiz Sartaj Aziz, Muhammad Abbas, Zhuanghao Zheng, Zhenghua Su, Ping Fan, Shuo Chen and Guangxing Liang
Materials 2023, 16(9), 3414; https://doi.org/10.3390/ma16093414 - 27 Apr 2023
Cited by 2 | Viewed by 1783
Abstract
Photoelectrochemical (PEC) water splitting in a pH-neutral electrolyte has attracted more and more attention in the field of sustainable energy. Bismuth vanadate (BiVO4) is a highly promising photoanode material for PEC water splitting. Additionally, cobaltous phosphate (CoPi) is a material that [...] Read more.
Photoelectrochemical (PEC) water splitting in a pH-neutral electrolyte has attracted more and more attention in the field of sustainable energy. Bismuth vanadate (BiVO4) is a highly promising photoanode material for PEC water splitting. Additionally, cobaltous phosphate (CoPi) is a material that can be synthesized from Earth’s rich materials and operates stably in pH-neutral conditions. Herein, we propose a strategy to enhance the charge transport ability and improve PEC performance by electrodepositing the in situ synthesis of a CoPi layer on the BiVO4. With the CoPi co-catalyst, the water oxidation reaction can be accelerated and charge recombination centers are effectively passivated on BiVO4. The BiVO4/CoPi photoanode shows a significantly enhanced photocurrent density (Jph) and applied bias photon-to-current efficiency (ABPE), which are 1.8 and 3.2 times higher than those of a single BiVO4 layer, respectively. Finally, the FTO/BiVO4/CoPi photoanode displays a photocurrent density of 1.39 mA cm−2 at 1.23 VRHE, an onset potential (Von) of 0.30 VRHE, and an ABPE of 0.45%, paving a potential path for future hydrogen evolution by solar-driven water splitting. Full article
(This article belongs to the Special Issue Novel Nanostructured Materials for Optoelectronic Applications)
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24 pages, 6212 KiB  
Review
A Review of Trends in Corrosion-Resistant Structural Steels Research—From Theoretical Simulation to Data-Driven Directions
by Di Xu, Zibo Pei, Xiaojia Yang, Qing Li, Fan Zhang, Renzheng Zhu, Xuequn Cheng and Lingwei Ma
Materials 2023, 16(9), 3396; https://doi.org/10.3390/ma16093396 - 26 Apr 2023
Cited by 5 | Viewed by 3164
Abstract
This paper provides a review of models commonly used over the years in the study of microscopic models of material corrosion mechanisms, data mining methods and the corrosion-resistant performance control of structural steels. The virtual process of material corrosion is combined with experimental [...] Read more.
This paper provides a review of models commonly used over the years in the study of microscopic models of material corrosion mechanisms, data mining methods and the corrosion-resistant performance control of structural steels. The virtual process of material corrosion is combined with experimental data to reflect the microscopic mechanism of material corrosion from a nano-scale to macro-scale, respectively. Data mining methods focus on predicting and modeling the corrosion rate and corrosion life of materials. Data-driven control of the corrosion resistance of structural steels is achieved through micro-alloying and organization structure control technology. Corrosion modeling has been used to assess the effects of alloying elements, grain size and organization purity on corrosion resistance, and to determine the contents of alloying elements. Full article
(This article belongs to the Special Issue Commemorating the Launch of the Section 'Metals and Alloys')
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