Materials

14 pages, 2928 KiB

Open AccessArticle

Effect of Temperature on the Corrosion Behavior and Corrosion Resistance of Copper–Aluminum Laminated Composite Plate

by Qiannan Li, Yifan Zhang, Yulin Cheng, Xiaojiao Zuo, Yinxiao Wang, Xiaoguang Yuan and Hongjun Huang

Materials 2022, 15(4), 1621; https://doi.org/10.3390/ma15041621 - 21 Feb 2022

Cited by 16 | Viewed by 3414

Abstract

In this paper, the effect of temperature on the corrosion behavior and corrosion resistance of the copper–aluminum laminated composite plates were investigated by salt-spray corrosion, potential polarization curve and electrochemical impedance spectroscopy. Moreover, the microstructure of the copper–aluminum laminated composite plate after salt-spray [...] Read more.

In this paper, the effect of temperature on the corrosion behavior and corrosion resistance of the copper–aluminum laminated composite plates were investigated by salt-spray corrosion, potential polarization curve and electrochemical impedance spectroscopy. Moreover, the microstructure of the copper–aluminum laminated composite plate after salt-spray corrosion was observed by scanning electron microscope, and X-ray photoelectron spectroscopy was used to study the composition of corrosion product. The results revealed that the corrosion products of the copper–aluminum laminated composite plate were Al₂O₃ and AlOOH. Due to the galvanic corrosion of the copper–aluminum laminated composite plate, the cathode underwent oxygen absorption corrosion during the corrosion process; therefore, the presence of moisture and the amount of dissolved oxygen in the corrosive environment had a great influence on the corrosion process. The increasing temperature would evaporate a large amount of moisture, resulting in the corrosion product—aluminum oxide dehydrated and covered the surface of the material in the process of salt-spray corrosion, which played a role in protecting the material. Therefore, the corrosion resistance of the copper–aluminum laminated composite plate first decreased and then increased. In the salt-spray corrosion environment, the corrosion resistance of the copper–aluminum laminated composite plate reached the lowest at 45 °C, and its corrosion rate was the fastest, at 0.728 g/m²·h. The electrochemical corrosion occurred in the solution, and the impact was small; however, in addition to the protective corrosion products, the ion mobility in the solution also had a certain influence on the corrosion rate, and the ionic activity increased with the increase of temperature. Therefore, the corrosion resistance of the copper–aluminum laminated composite plate gradually decreased as the temperature increased, and its corrosion resistance was the worst at 50 °C. Full article

(This article belongs to the Topic Metal Matrix Composites: Recent Advancements)

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11 pages, 3622 KiB

Open AccessArticle

Crystal Evolution of Calcium Silicate Minerals Synthesized by Calcium Silicon Slag and Silica Fume with Increase of Hydrothermal Synthesis Temperature

by Zhijie Yang, De Zhang, Yang Jiao, Chengyang Fang, Dong Kang, Changwang Yan and Ju Zhang

Materials 2022, 15(4), 1620; https://doi.org/10.3390/ma15041620 - 21 Feb 2022

Cited by 9 | Viewed by 2236

Abstract

In order to realize high-value utilization of calcium silicon slag (CSS) and silica fume (SF), the dynamic hydrothermal synthesis experiments of CSS and SF were carried out under different hydrothermal synthesis temperatures. In addition, phase category, microstructure, and micropore parameters of the synthesis [...] Read more.

In order to realize high-value utilization of calcium silicon slag (CSS) and silica fume (SF), the dynamic hydrothermal synthesis experiments of CSS and SF were carried out under different hydrothermal synthesis temperatures. In addition, phase category, microstructure, and micropore parameters of the synthesis product were analyzed through testing methods of XRD, SEM, EDS and micropore analysis. The results show that the main mechanism of synthesis reaction is that firstly β-Dicalcium silicate, the main mineral in CSS, hydrates to produce amorphous C–S–H and Ca(OH)₂, and the environment of system is induced to strong alkaline. Therefore, the highly polymerized Si-O bond of SF is broken under the polarization of OH⁻ to form (SiO₄) of Q⁰. Next, amorphous C–S–H, Ca(OH)₂ and (SiO₄) of Q⁰ react each other to gradually produce various of calcium silicate minerals. With an increase of synthesis temperature, the crystal evolution order for calcium silicate minerals is cocoon-like C–S–H, mesh-like C–S–H, large flake-like gyrolite, small flake-like gyrolite, petal-like gyrolite, square flake-like calcium silicate hydroxide hydrate, and strip-like tobermorite. In addition, petal-like calcium silicate with high average pore volume (APV), specific surface area (SSA) and low average pore diameter (APD) can be prepared under the 230 °C synthesis condition. Full article

(This article belongs to the Special Issue Industrial Solid Wastes for Construction and Building Materials)

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19 pages, 6261 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Advanced Carbon Reinforced Concrete Technologies for Façade Elements of Nearly Zero-Energy Buildings

by Robert Kraft, Alexander Kahnt, Otto Grauer, Mike Thieme, Daniel Sebastian Wolz, Dominik Schlüter, Matthias Tietze, Manfred Curbach, Klaus Holschemacher, Hubert Jäger and Robert Böhm

Materials 2022, 15(4), 1619; https://doi.org/10.3390/ma15041619 - 21 Feb 2022

Cited by 11 | Viewed by 4056

Abstract

The building sector accounts for approx. 40% of total energy consumption and approx. 36% of all greenhouse gas emissions in Europe. As the EU climate targets for 2030 call for a reduction of greenhouse gas emissions by more than half compared to the [...] Read more.

The building sector accounts for approx. 40% of total energy consumption and approx. 36% of all greenhouse gas emissions in Europe. As the EU climate targets for 2030 call for a reduction of greenhouse gas emissions by more than half compared to the emissions of 1990 and also aim for climate neutrality by 2050, there is an urgent need to achieve a significant decrease in the energy use in buildings towards Nearly Zero-Energy Buildings (nZEBs). As the energy footprint of buildings includes the energy and greenhouse gas consumption both in the construction phase and during service life, nZEB solutions have to provide energy-efficient and less carbon-intensive building materials, specific thermal insulation solutions, and a corresponding design of the nZEB. Carbon reinforced concrete (CRC) materials have proven to be excellent candidate materials for concrete-based nZEBs since they are characterized by a significantly lower CO₂ consumption during component production and much a longer lifecycle. The corresponding CRC technology has been successively implemented in the last two decades and first pure CRC-based buildings are currently being built. This article presents a novel material system that combines CRC technology and suitable multifunctional insulation materials as a sandwich system in order to meet future nZEB requirements. Because of its importance for the life cycle stage of production, cost-efficient carbon fibers (CF) from renewable resources like lignin are used as reinforcing material, and reinforcement systems based on such CF are developed. Cutting edge approaches to produce ultra-thin lightweight CF reinforced concrete panels are discussed with regard to their nZEB relevance. For the life cycle stage of the utilization phase, the thermal insulation properties of core materials are optimized. In this context, novel sandwich composites with thin CRC layers and a cellular lightweight concrete core are proposed as a promising solution for façade elements as the sandwich core can additionally be combined with an aerogel-based insulation. The concepts to realize such sandwich façade elements will be described here along with a fully automated manufacturing process to produce such structures. The findings of this study provide clear evidence on the promising capabilities of the CRC technology for nZEBs on the one hand and on the necessity for further research on optimizing the energy footprint of CRC-based structural elements on the other hand. Full article

(This article belongs to the Special Issue Composite Materials for Nearly Zero Emission Applications)

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12 pages, 34483 KiB

Open AccessArticle

Effect of Initial Fe Content on Microstructure and Mechanical Properties of Recycled Al-7.0Si-Fe-Mn Alloys with Constant Mn/Fe Ratio

by Dongfu Song, Yiwang Jia, Qing Li, Yuliang Zhao and Weiwen Zhang

Materials 2022, 15(4), 1618; https://doi.org/10.3390/ma15041618 - 21 Feb 2022

Cited by 15 | Viewed by 3150

Abstract

The effect of initial Fe content on the iron removal efficiency, morphology evolution of the Fe-rich phase and the mechanical properties of the recycled Al-7Si-xFe-1.2xMn alloy during melt holding was studied using an optical microscope (OM), scanning electron microscope [...] Read more.

The effect of initial Fe content on the iron removal efficiency, morphology evolution of the Fe-rich phase and the mechanical properties of the recycled Al-7Si-xFe-1.2xMn alloy during melt holding was studied using an optical microscope (OM), scanning electron microscope (SEM) and tensile testing. The results show that with the increase of the initial Fe content, the residual Fe concentration of the alloys gradually increased, and the corresponding removal efficiency of Fe gradually was increased to 77.67%. The type of Fe-rich phase in the alloys changes from α-Al₁₅(FeMn)₃Si₂ to a mixture of α-Al₁₅(FeMn)₃Si₂ and β-Al₅FeSi, and its morphological evolution is as follows: coarse Chinese-script + polygon → dense Chinese-script + polygon → polygonal + dense Chinese-script + plate-like. Furthermore, the morphology of the Fe-rich phase in the slag changes from a polygonal shape to an irregular shape with a two-layer structure. The formation and increase of the inner layer with high Mn-content in the irregular-shape phase is the main reason for the increasing residual Fe content. The plasticity of the alloy increases obviously with the increase of the initial Fe content, but the formation of the β-Al₅FeSi with plate-like morphology in higher Fe-containing alloy may hinder further improvement of the plasticity. Full article

(This article belongs to the Topic Advanced Forming Technology of Metallic Materials)

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14 pages, 2296 KiB

Open AccessArticle

Alkali-Activated Red Mud and Construction and Demolition Waste-Based Components: Characterization and Environmental Assessment

by Alessio Occhicone, Mira Vukčević, Ivana Bosković, Serena Mingione and Claudio Ferone

Materials 2022, 15(4), 1617; https://doi.org/10.3390/ma15041617 - 21 Feb 2022

Cited by 22 | Viewed by 3239

Abstract

The aluminum Bayer production process is the most diffused process in the world, but it creates a high amount of basic waste material known as red mud (RM). The use of RM as a precursor of alkali-activated materials is one of the best [...] Read more.

The aluminum Bayer production process is the most diffused process in the world, but it creates a high amount of basic waste material known as red mud (RM). The use of RM as a precursor of alkali-activated materials is one of the best opportunities for both the ecosystem and the economy. In the present work, mortar samples were obtained by alkali activation of RM with various percentages of blast-furnace slag (BFS) and inert construction and demolition sands. This process creates samples that have a low environmental impact and that can be used as an alternative in the construction industry to cement materials or ceramic ones. The development of these new materials could also represent a way to reduce the CO₂ emissions linked to cement and ceramic brick production. In the present study, cubic 40 mm samples reported very interesting values in compressive strength, with a maximum of about 70 MPa for low environmental impact mortars. With such a material, it is possible to create solid bricks for structural use and concrete tiles for road paving or use it for other purposes. Mortar specimens were prepared and characterized, and an LCA analysis with a “cradle-to-gate” approach was carried out for a comparison of the environmental impact of the studied mortars with other materials currently marketed. Full article

(This article belongs to the Collection Alkali‐Activated Materials for Sustainable Construction)

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17 pages, 8101 KiB

Open AccessArticle

Development of an Oxide Layer on Al 6061 Using Plasma Arc Electrolytic Oxidation in Silicate-Based Electrolyte

by Priya Jadhav, Arunkumar Bongale, Satish Kumar, Danil Yurievich Pimenov, Khaled Giasin and Szymon Wojciechowski

Materials 2022, 15(4), 1616; https://doi.org/10.3390/ma15041616 - 21 Feb 2022

Cited by 2 | Viewed by 2233

Abstract

The plasma electrolytic method is one of the techniques which can be used to form an oxide layer on the substrate material surface. This technique employs ion exchange by developing an electrolytic arc between the cathode and the anode. The strong bond at [...] Read more.

The plasma electrolytic method is one of the techniques which can be used to form an oxide layer on the substrate material surface. This technique employs ion exchange by developing an electrolytic arc between the cathode and the anode. The strong bond at high temperatures promotes the formation of an oxide layer on the metal surface. The electrolyte composition has a strong influence on the metal surface characteristics. Hence, the addition of certain nanoparticles in an adequate amount can improve the surface properties like wear and corrosion resistance. In this study, a plasma electrolytic technique based on using a direct current and voltage approach is investigated. The plasma electrolytic technique is utilized to develop an oxide layer on the Al 6061 alloy substrate surface using a DC voltage input on a silicate-based electrolyte. The substrate surface is then investigated for the thickness of the oxide layer formed and the amount of carbon element absorbed, using the SEM and XRD analysis. The experimentation and the study of the results confirmed the presence of a substantial oxide layer on the surface. The influence of the process on the output parameters-direct voltage and electrode distance is studied with the significant changes obtained in the weight percentage of elements like C, Al, Si, and O as supported by SEM and EDAX analysis. Most changes occurred when using a 197 V and in the current range of 0.3 A to 1 A. This can be useful further to improve the mechanical properties of the metal alloy using the plasma arc oxidation method. Full article

(This article belongs to the Section Manufacturing Processes and Systems)

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10 pages, 3103 KiB

Open AccessArticle

Nitrogen-Doped Nanoporous Anodic Stainless Steel Foils towards Flexible Supercapacitors

by Wenlei Zhang, Jianle Xu, Gang Li and Kaiying Wang

Materials 2022, 15(4), 1615; https://doi.org/10.3390/ma15041615 - 21 Feb 2022

Cited by 5 | Viewed by 1977

Abstract

In this work, we report the fabrication and enhanced supercapacitive performance of nitrogen-doped nanoporous stainless steel foils, which have been prepared by electrochemical anodization and subsequent thermal annealing in ammonia atmosphere. The nanoporous oxide layers are grown on type-304 stainless steel foil with [...] Read more.

In this work, we report the fabrication and enhanced supercapacitive performance of nitrogen-doped nanoporous stainless steel foils, which have been prepared by electrochemical anodization and subsequent thermal annealing in ammonia atmosphere. The nanoporous oxide layers are grown on type-304 stainless steel foil with optimal thickness ~11.9 μm. The N-doped sample exhibits high average areal capacitance of 321.3 mF·cm⁻² at a current density of 1.0 mA·cm⁻², 3.6 times of increment compared with untreated one. Structural and electrochemical characterizations indicate that the significant enhancement is correlated to the high charge transfer efficiency from nitriding nanosheet products Fe₃N. Our report here may provide new insight on the development of high-performance, low-cost and binder-free supercapacitor electrodes for flexible and portable electronic device applications with multiple anions. Full article

(This article belongs to the Special Issue Advanced Energy Storage Materials: Preparation, Characterization and Applications)

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15 pages, 3920 KiB

Open AccessArticle

Guided Wave Phase Velocity Dispersion Reconstruction Based on Enhanced Phased Spectrum Method

by Vykintas Samaitis and Liudas Mažeika

Materials 2022, 15(4), 1614; https://doi.org/10.3390/ma15041614 - 21 Feb 2022

Cited by 1 | Viewed by 2185

Abstract

Fibre-reinforced composite laminates are frequently used in various engineering structures, due to their increased weight-to-stiffness ratio, which allows to fulfil certain regulations of CO₂ emissions. Limited inter-laminar strength makes composites prone to formation of various defects, which leads to progressive degradation of [...] Read more.

Fibre-reinforced composite laminates are frequently used in various engineering structures, due to their increased weight-to-stiffness ratio, which allows to fulfil certain regulations of CO₂ emissions. Limited inter-laminar strength makes composites prone to formation of various defects, which leads to progressive degradation of residual strength and fatigue life of the structure. Using ultrasonic guided waves is a common technique for assessing the structural integrity of composite laminates. Phase velocity is one of the fundamental characteristics of guided waves and can be used for defect detection, material property estimation, and evaluation of dispersion. In this paper, a phase velocity reconstruction approach, based on the phase-shift method, was proposed, which uses frequency sweep excitation to estimate velocity at specific frequency harmonics. In contrast to the conventional phase spectrum technique, the proposed approach is applicable to the narrowband piezoelectric transducers and suitable for the reconstruction of dispersion curves for direct, converted, and multiple co-existing modes with high accuracy. The proposed technique was validated with finite element simulations and experiments, both on isotropic and anisotropic structures, analysing the direct, converted, and overlapped modes. The results demonstrated that, using the proposed technique, the phase velocity dispersion can be reconstructed at −20 dB level bandwidth of the transducer, with a relative error of ±4%, compared to the theoretical velocity predictions. Full article

(This article belongs to the Topic Structural Health Monitoring and Non-destructive Testing for Large-Scale Structures)

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21 pages, 4495 KiB

Open AccessArticle

Study on Mechanical Behavior and Energy Mechanism of Sandstone under Chemical Corrosion

by Lei Chen, Baoxin Jia and Shuguang Zhang

Materials 2022, 15(4), 1613; https://doi.org/10.3390/ma15041613 - 21 Feb 2022

Cited by 7 | Viewed by 1849

Abstract

Chemical corrosion has a significant impact on the properties of rock materials. To study the mechanical behavior and energy mechanism of rock under chemical corrosion, this paper took the sandstone of Haitangshan tunnel in Fuxin as the research object, used a Na₂ [...] Read more.

Chemical corrosion has a significant impact on the properties of rock materials. To study the mechanical behavior and energy mechanism of rock under chemical corrosion, this paper took the sandstone of Haitangshan tunnel in Fuxin as the research object, used a Na₂SO₄ solution to simulate different chemical environments, carried out a triaxial loading test on sandstone through the MTS815.02 test system, and analyzed the mechanical parameters and energy damage evolution law of sandstone under different chemical environments. The test results showed that the basic mechanical parameters (peak strength σ_pk, peak strain ε_pk, elastic modulus E, cohesion c, and internal friction angle φ) and characteristic stress parameters (closure stress σ_cc, initiation stress σ_ci, and dilatancy stress σ_cd) of sandstone first increased and then decreased with the increase of pH in the Na₂SO₄ solution, Poisson’s ratio µ showed the opposite trend, and the extreme values of all parameters were taken when pH = 7. The influence degree of different pHs on the mechanical parameters of sandstone were as follows: strong acid environment (pH ≤ 4) > strong alkali environment (pH ≥ 10) > weak acid environment (4 ≤ pH < 6) > weak alkali environment (8 ≤ pH < 10) > neutral environment (6 < pH< 8). The total energy and elastic strain energy increased first and then decreased, and the dissipated energy was the opposite. The damage variable decreased first and then increased. With the increasing concentration of the Na₂SO₄ solution, all the above parameters changed monotonically. Based on the energy theory, the damage evolution equation considering the effect of the Na₂SO₄ concentration was established. Combined with the test data, the model was verified and the result was good. Under the action of Na₂SO₄ corrosion, Ca²⁺ in calcite and Fe²⁺ in hematite were dissolved and precipitated. With the gradual increase of Ca²⁺ and Fe²⁺ concentration, the damage variable increased gradually. The relationship between the two ion concentrations and the damage variable approximately satisfied a linear function. Full article

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22 pages, 4540 KiB

Open AccessArticle

Experimental Investigation on Ambient-Cured One-Part Alkali-Activated Binders Using Combined High-Calcium Fly Ash (HCFA) and Ground Granulated Blast Furnace Slag (GGBS)

by Wee Teo, Kazutaka Shirai, Jee Hock Lim, Lynne B. Jack and Ehsan Nikbakht

Materials 2022, 15(4), 1612; https://doi.org/10.3390/ma15041612 - 21 Feb 2022

Cited by 13 | Viewed by 2613

Abstract

The challenges of handling user-hostile alkaline solutions in the conventional alkali-activated binders (AAB) have initiated the development of “just add water” or one-part solid-based AAB systems. This paper aims to present a preliminary investigation on the development of one-part ambient-cured alkali-activated binders produced [...] Read more.

The challenges of handling user-hostile alkaline solutions in the conventional alkali-activated binders (AAB) have initiated the development of “just add water” or one-part solid-based AAB systems. This paper aims to present a preliminary investigation on the development of one-part ambient-cured alkali-activated binders produced by synthesising high-calcium fly ash (HCFA) and ground granulated blast furnace slag (GGBS) using sodium metasilicate anhydrous. Three test series were conducted in this study to investigate the effects of GGBS/binder, activator/binder and water/binder ratios on the fresh and hardened properties of the one-part synthesis AAB system. It was found that the SiO₂/Al₂O₃ molar ratio plays an important role in the attainment of compressive strength and limits the amounts of solid activators effective in contributing to the alkali-activation reaction process. The optimum SiO₂/Al₂O₃ molar ratio was found between 3.20 and 3.30. The test results revealed that the optimum proportion between HCFA and GGBS was discovered at a GGBS/binder ratio of 0.50. The optimum activator/binder ratio was between 0.08 and 0.12, and it is recommended that the water/binder ratio should not exceed 0.50. This study demonstrated the potential of the one-part synthesis method in the production of alkali-activated binder for practical structural applications. Full article

(This article belongs to the Collection Alkali‐Activated Materials for Sustainable Construction)

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18 pages, 17851 KiB

Open AccessArticle

Cementitious Composites Reinforced with Waste Fibres from the Production of High-Quality Construction Textiles

by Ana Baričević, Katarina Didulica, Marina Frančić Smrkić and Marija Jelčić Rukavina

Materials 2022, 15(4), 1611; https://doi.org/10.3390/ma15041611 - 21 Feb 2022

Cited by 5 | Viewed by 2431 | Correction

Abstract

In general, 20–25% of the original fibre weight is considered waste in the production of high-quality textiles for the construction sector. A market analysis has shown that in the Republic of Croatia alone, up to 327 tonnes of this waste is produced annually, [...] Read more.

In general, 20–25% of the original fibre weight is considered waste in the production of high-quality textiles for the construction sector. A market analysis has shown that in the Republic of Croatia alone, up to 327 tonnes of this waste is produced annually, which is enough to reinforce 50 to 150 thousand m³ of cementitious composites. This preliminary study aims to evaluate the contribution of glass, basalt and carbon fibres generated as waste in the local production of high-performance technical textiles, to the fresh and hardened properties of fibre reinforced mortars. In order to investigate the influence of fibres, three types of fibres in two different lengths (5 and 10 mm) were used, while the amount of fibres was constant. The obtained results show that due to the fibre presence, workability is reduced regardless of the type and length of the fibre. The tested fibres have a negligible effect on compressive strength, but the use of basalt and carbon fibres increases the tensile strength. Furthermore, all three types have positive influence on the toughness and volumetric deformations, although to a greater extent in the use of 10 mm long fibres and carbon fibres. Full article

(This article belongs to the Special Issue Fiber-Reinforced Concrete: Design, Characterization, and Applications)

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13 pages, 4586 KiB

Open AccessArticle

Temperature-Dependent Growth and Evolution of Silicene on Au Ultrathin Films—LEEM and LEED Studies

by Tomasz Jaroch and Ryszard Zdyb

Materials 2022, 15(4), 1610; https://doi.org/10.3390/ma15041610 - 21 Feb 2022

Cited by 8 | Viewed by 2051

Abstract

The formation and evolution of silicene on ultrathin Au films have been investigated with low energy electron microscopy and diffraction. Careful control of the annealing rate and temperature of Au films epitaxially grown on the Si(111) surface allows for the preparation of a [...] Read more.

The formation and evolution of silicene on ultrathin Au films have been investigated with low energy electron microscopy and diffraction. Careful control of the annealing rate and temperature of Au films epitaxially grown on the Si(111) surface allows for the preparation of a large scale, of the order of cm², silicene sheets. Depending on the final temperature, three stages of silicene evolution can be distinguished: (i) the growth of the low buckled phase, (ii) the formation of a layered heterostructure of the low buckled and planar phases of silicene and (iii) the gradual destruction of the silicene. Each stage is characterized by its unique surface morphology and characteristic diffraction patterns. The present study gives an overview of structures formed on the surface of ultrathin Au films and morphology changes between room temperature and the temperature at which the formation of Au droplets on the Si(111) surface occurs. Full article

(This article belongs to the Special Issue Multilayer and Hybrid Two-Dimensional Materials)

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17 pages, 9134 KiB

Open AccessReview

Additive Manufacturing as a Solution to Challenges Associated with Heat Pipe Production

by Pawel Szymanski and Dariusz Mikielewicz

Materials 2022, 15(4), 1609; https://doi.org/10.3390/ma15041609 - 21 Feb 2022

Cited by 17 | Viewed by 3565

Abstract

The aim of this review is to present the recent developments in heat pipe production, which respond to the current technical problems related to the wide implementation of this technology. A novel approach in HP manufacturing is to utilise hi-tech additive manufacturing techniques [...] Read more.

The aim of this review is to present the recent developments in heat pipe production, which respond to the current technical problems related to the wide implementation of this technology. A novel approach in HP manufacturing is to utilise hi-tech additive manufacturing techniques where the most complicated geometries are fabricated layer-by-layer directly from a digital file. This technology might be a solution to various challenges that exist in HP production, i.e., (1) manufacturing of complex or unusual geometries HPs; (2) manufacturing complicated and efficient homogenous wick structures with desired porosity, uniform pore sizes, permeability, thickness and where the pores are evenly distributed; (3) manufacturing a gravity friendly wick structures; (4) high customisation and production time; (5) high costs; (6) difficulties in the integration of the HP into a unit chassis that enables direct thermal management of heated element and decrease its total thermal resistance; (7) high weight and material use of the part; (8) difficulties in sealing; (9) deformation of the flat shape HPs caused by the high pressure and uneven distribution of stress in the casing, among others. Full article

(This article belongs to the Special Issue Porous Materials and Advanced Manufacturing Technologies)

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20 pages, 995 KiB

Open AccessReview

Assessing Collagen D-Band Periodicity with Atomic Force Microscopy

by Andreas Stylianou

Materials 2022, 15(4), 1608; https://doi.org/10.3390/ma15041608 - 21 Feb 2022

Cited by 15 | Viewed by 3877

Abstract

The collagen superfamily includes more than fifty collagen and/or collagen-like proteins with fibril-forming collagen type I being the most abundant protein within the extracellular matrix. Collagen type I plays a crucial role in a variety of functions, it has been associated with many [...] Read more.

The collagen superfamily includes more than fifty collagen and/or collagen-like proteins with fibril-forming collagen type I being the most abundant protein within the extracellular matrix. Collagen type I plays a crucial role in a variety of functions, it has been associated with many pathological conditions and it is widely used due to its unique properties. One unique nano-scale characteristic of natural occurring collagen type I fibers is the so-called D-band periodicity, which has been associated with collagen natural structure and properties, while it seems to play a crucial role in the interactions between cells and collagen and in various pathological conditions. An accurate characterization of the surface and structure of collagen fibers, including D-band periodicity, on collagen-based tissues and/or (nano-)biomaterials can be achieved by Atomic Force Microscopy (AFM). AFM is a scanning probe microscope and is among the few techniques that can assess D-band periodicity. This review covers issues related to collagen and collagen D-band periodicity and the use of AFM for studying them. Through a systematic search in databases (PubMed and Scopus) relevant articles were identified. The study of these articles demonstrated that AFM can offer novel information concerning D-band periodicity. This study highlights the importance of studying collagen D-band periodicity and proves that AFM is a powerful tool for investigating a number of different properties related to collagen D-band periodicity. Full article

(This article belongs to the Special Issue Collagens, Collagen-Based and Collagen-Mimetic Biomaterials: Preparation, Characterization and Applications)

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22 pages, 5584 KiB

Open AccessArticle

Strain Hardening of Polypropylene Microfiber Reinforced Composite Based on Alkali-Activated Slag Matrix

by Olga M. Smirnova, Ignacio Menendez Pidal, Aleksandr V. Alekseev, Dmitry N. Petrov and Mikhail G. Popov

Materials 2022, 15(4), 1607; https://doi.org/10.3390/ma15041607 - 21 Feb 2022

Cited by 31 | Viewed by 2337

Abstract

A comparative study of the fracture features, strength and deformation properties of pseudo strain-hardening composites based on alkali-activated slag and Portland cement matrices with polypropylene microfiber was carried out. Correlations between their compositions and characteristics of stress–strain diagrams under tension in bending with [...] Read more.

A comparative study of the fracture features, strength and deformation properties of pseudo strain-hardening composites based on alkali-activated slag and Portland cement matrices with polypropylene microfiber was carried out. Correlations between their compositions and characteristics of stress–strain diagrams under tension in bending with an additional determination of acoustic emission parameters were determined. An average strength alkali-activated slag matrix with compressive strength of 40 MPa and a high-strength Portland cement matrix with compressive strength of 70 MPa were used. The matrix compositions were selected for high filling the composites with polypropylene microfiber in the amount of 5%-vol. and 3.5%-vol. ensuring the workability at the low water-to-binder ratios of 0.22 and 0.3 for Portland cement and alkali-activated slag matrices, respectively. Deformation diagrams were obtained for all studied compositions. Peaks in the number of acoustic signals in alkali-activated slag composites were observed only in the strain-softening zone. Graphs of dependence of the rate of acoustic events occurrence in samples from the start of the test experimentally prove that this method of non-destructive testing can be used to monitor structures based on strain-hardening composites. Full article

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39 pages, 72409 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Photothermal and Photodynamic Therapy of Tumors with Plasmonic Nanoparticles: Challenges and Prospects

by Alla B. Bucharskaya, Nikolai G. Khlebtsov, Boris N. Khlebtsov, Galina N. Maslyakova, Nikita A. Navolokin, Vadim D. Genin, Elina A. Genina and Valery V. Tuchin

Materials 2022, 15(4), 1606; https://doi.org/10.3390/ma15041606 - 21 Feb 2022

Cited by 38 | Viewed by 5938

Abstract

Cancer remains one of the leading causes of death in the world. For a number of neoplasms, the efficiency of conventional chemo- and radiation therapies is insufficient because of drug resistance and marked toxicity. Plasmonic photothermal therapy (PPT) using local hyperthermia induced by [...] Read more.

Cancer remains one of the leading causes of death in the world. For a number of neoplasms, the efficiency of conventional chemo- and radiation therapies is insufficient because of drug resistance and marked toxicity. Plasmonic photothermal therapy (PPT) using local hyperthermia induced by gold nanoparticles (AuNPs) has recently been extensively explored in tumor treatment. However, despite attractive promises, the current PPT status is limited by laboratory experiments, academic papers, and only a few preclinical studies. Unfortunately, most nanoformulations still share a similar fate: great laboratory promises and fair preclinical trials. This review discusses the current challenges and prospects of plasmonic nanomedicine based on PPT and photodynamic therapy (PDT). We start with consideration of the fundamental principles underlying plasmonic properties of AuNPs to tune their plasmon resonance for the desired NIR-I, NIR-2, and SWIR optical windows. The basic principles for simulation of optical cross-sections and plasmonic heating under CW and pulsed irradiation are discussed. Then, we consider the state-of-the-art methods for wet chemical synthesis of the most popular PPPT AuNPs such as silica/gold nanoshells, Au nanostars, nanorods, and nanocages. The photothermal efficiencies of these nanoparticles are compared, and their applications to current nanomedicine are shortly discussed. In a separate section, we discuss the fabrication of gold and other nanoparticles by the pulsed laser ablation in liquid method. The second part of the review is devoted to our recent experimental results on laser-activated interaction of AuNPs with tumor and healthy tissues and current achievements of other research groups in this application area. The unresolved issues of PPT are the significant accumulation of AuNPs in the organs of the mononuclear phagocyte system, causing potential toxic effects of nanoparticles, and the possibility of tumor recurrence due to the presence of survived tumor cells. The prospective ways of solving these problems are discussed, including developing combined antitumor therapy based on combined PPT and PDT. In the conclusion section, we summarize the most urgent needs of current PPT-based nanomedicine. Full article

(This article belongs to the Special Issue Feature Paper in Optical and Photonic Materials)

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23 pages, 32680 KiB

Open AccessArticle

Corrosion and Microstructural Investigation on Additively Manufactured 316L Stainless Steel: Experimental and Statistical Approach

by Héctor Maicas-Esteve, Iman Taji, Marc Wilms, Yaiza Gonzalez-Garcia and Roy Johnsen

Materials 2022, 15(4), 1605; https://doi.org/10.3390/ma15041605 - 21 Feb 2022

Cited by 4 | Viewed by 2228

Abstract

The use of metal additive manufacturing (AM) has strongly increased in the industry during the last years. More specifically, selective laser melting (SLM) is one of the most used techniques due to its numerous advantages compared to conventional processing methods. The purpose of [...] Read more.

The use of metal additive manufacturing (AM) has strongly increased in the industry during the last years. More specifically, selective laser melting (SLM) is one of the most used techniques due to its numerous advantages compared to conventional processing methods. The purpose of this study is to investigate the effects of process parameters on the microstructural and corrosion properties of the additively manufactured AISI 316L stainless steel. Porosity, surface roughness, hardness, and grain size were studied for specimens produced with energy densities ranging from 51.17 to 173.91 J/mm³ that resulted from different combinations of processing parameters. Using experimental results and applying the Taguchi model, 99.38 J/mm³ was determined as the optimal energy density needed to produce samples with almost no porosity. The following analysis of variance ANOVA confirmed the scanning speed as the most influential factor in reducing the porosity percentage, which had a 74.9% contribution, followed by the position along the building direction with 22.8%, and finally, the laser energy with 2.3%. The influence on corrosion resistance was obtained by performing cyclic potentiodynamic polarization tests (CPP) in a 3.5 wt % NaCl solution at room temperature for different energy densities and positions (Z axis). The corrosion properties of the AM samples were studied and compared to those obtained from the traditionally manufactured samples. The corrosion resistance of the samples worsened with the increase in the percentage of porosity. The process parameters have consequently been optimized and the database has been extended to improve the quality of the AM-produced parts in which microstructural heterogeneities were observed along the building direction. Full article

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11 pages, 7863 KiB

Open AccessArticle

Comparative Study on Biodegradation of Pure Iron Prepared by Microwave Sintering and Laser Melting

by Yingchao Zhao, Jun Feng, Hui Yu, Wangyang Lin, Xin Li, Yan Tian and Mingchun Zhao

Materials 2022, 15(4), 1604; https://doi.org/10.3390/ma15041604 - 21 Feb 2022

Cited by 7 | Viewed by 1822

Abstract

For biodegradable pure iron implants, a higher biodegradation rate is preferred. In this work, we compared the biodegradation of pure iron prepared by microwave sintering and laser melting (designated as MSed Fe and LMed Fe, respectively). The MSed Fe presented a distinct porous [...] Read more.

For biodegradable pure iron implants, a higher biodegradation rate is preferred. In this work, we compared the biodegradation of pure iron prepared by microwave sintering and laser melting (designated as MSed Fe and LMed Fe, respectively). The MSed Fe presented a distinct porous structure, while the LMed Fe presented a relatively compact structure without any obvious pores. The biodegradation rate of the MSed Fe was higher than that of the LMed Fe, and their biodegradation rates were higher than that of the as-cast Fe. The biodegradation rates of the MSed Fe and the LMed Fe were approximately 44 and 13 times higher than that of the as cast Fe, respectively. The biodegradation was closely related to the microstructure’s compactness and grain size. Moreover, the MSed Fe and the LMed Fe had satisfactory biocompatibility. Full article

(This article belongs to the Special Issue Advances in Surface Modification on Microstructure and Properties of Metals)

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10 pages, 6377 KiB

Open AccessArticle

Fabrication of Fe-Si-B Based Amorphous Powder Cores by Spark Plasma Sintered and Their Magnetic Properties

by Liang Yan, Biao Yan and Yin Jian

Materials 2022, 15(4), 1603; https://doi.org/10.3390/ma15041603 - 21 Feb 2022

Cited by 10 | Viewed by 2590

Abstract

Mechanical ball milling was used to coat SiO₂ nanopowder on a Fe-Si-B amorphous powder in this study. The Fe-Si-B/SiO₂ core–shell amorphous composite powder was obtained after 6h of ball milling. At 490 °C, the amorphous powder is thermally stable. Discharge plasma [...] Read more.

Mechanical ball milling was used to coat SiO₂ nanopowder on a Fe-Si-B amorphous powder in this study. The Fe-Si-B/SiO₂ core–shell amorphous composite powder was obtained after 6h of ball milling. At 490 °C, the amorphous powder is thermally stable. Discharge plasma sintering was used to create a Fe-Si-B/SiO₂ magnetic powder core (SPS). At a sintering temperature of 420 to 540 °C, the phase composition and magnetic characteristics of the magnetic particle core were investigated. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to examine the structural features of the magnetic particle core. A precision resistance tester and a vibrating sample magnetometer were used to assess the resistivity and magnetic characteristics of the magnetic particle core. The findings showed that Fe₃Si and Fe₂B are the phases generated during spark plasma sintering. High-frequency power loss increases as density rises. However, at the measured frequency, the magnetic permeability of the magnetic particle core changes slightly and has excellent frequency characteristics, making it appropriate for use in high-frequency components. Full article

(This article belongs to the Topic Metal Matrix Composites: Recent Advancements)

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20 pages, 7142 KiB

Open AccessEditor’s ChoiceArticle

The Influence of Microstructure on the Flexural Properties of 3D Printed Zirconia Part via Digital Light Processing Technology

by Boran Wang, Ali Arab, Jing Xie and Pengwan Chen

Materials 2022, 15(4), 1602; https://doi.org/10.3390/ma15041602 - 21 Feb 2022

Cited by 13 | Viewed by 3093

Abstract

In recent years, additive manufacturing of ceramics is becoming of increasing interest due to the possibility of the fabrication of complex shaped parts. However, the fabrication of a fully dense bulk ceramic part without cracks and defects is still challenging. In the presented [...] Read more.

In recent years, additive manufacturing of ceramics is becoming of increasing interest due to the possibility of the fabrication of complex shaped parts. However, the fabrication of a fully dense bulk ceramic part without cracks and defects is still challenging. In the presented work, the digital light processing method was introduced for fabricating zirconia parts. The flexural properties of the printed zirconia were systematically investigated via a three-point bending test with the digital image correlation method, scanning electron microscopy observation and fractography analysis. Due to the anisotropy of the sample, the bending deformation behaviors of the zirconia samples in the parallel and vertical printing directions were significantly different. The flexural strength and the related elastic modulus of the samples under vertical loading were higher than that of the parallel loading, as the in-plane strength is higher than that of the interlayer strength. The maximum horizontal strain always appeared at the bottom center before the failure for the parallel loading case; while the maximum horizontal strain for the vertical loading moved upward from the bottom center to the top center. There was a clear dividing line between the minimum perpendicular strain and the maximum perpendicular strain of the samples under parallel loading; however, under vertical loading, the perpendicular strain declined from the bottom to the top along the crack path. The surrounding dense part of the sintered sample (a few hundred microns) was mainly composed of large and straight cracks between printing layers, whereas the interior contained numerous small winding cracks. The intense cracks inside the sample led to a low flexural property compared to other well-prepared zirconia samples, which the inadequate additive formulations would be the main reason for the generation of cracks. A better understanding of the additive formulation (particularly the dispersant) and the debinding-sintering process are necessary for future improvement. Full article

(This article belongs to the Section Advanced and Functional Ceramics and Glasses)

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14 pages, 2462 KiB

Open AccessArticle

Multi-Parameter Characteristics of Electric Arc Furnace Melting

by Michał Moskal, Piotr Migas and Mirosław Karbowniczek

Materials 2022, 15(4), 1601; https://doi.org/10.3390/ma15041601 - 21 Feb 2022

Cited by 4 | Viewed by 2654

Abstract

The article presents the results of analyses of numerical modelling of selected factors in electric arc furnace melts. The aim of the study was to optimise the melting process in an electric arc furnace using statistical-thermodynamic modelling based on, among other things, multiple [...] Read more.

The article presents the results of analyses of numerical modelling of selected factors in electric arc furnace melts. The aim of the study was to optimise the melting process in an electric arc furnace using statistical-thermodynamic modelling based on, among other things, multiple linear regression (MLR). The article presents tools and methods which make it possible to identify the most significant indicators of the process carried out on the analysed unit from the point of view of improvement. The article presents the characteristics of the process and creation of the MLR model and, by applying its numerical analyses and results of calculations and simulations for selected variables and indicator, identifying the operation of a selected furnace. Developed model to demand of electric energy identification was used for calculations of energy balances, the distribution of the energy used in the furnace was presented. Full article

(This article belongs to the Special Issue Metallurgical Process Simulation and Optimization)

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22 pages, 4532 KiB

Open AccessArticle

Synthesis and Characterization of Imidazolium-Based Ionic Liquids and Evaluating Their Performance as Asphaltene Dispersants

by Alaa Ghanem, Rima D. Alharthy, Saad M. Desouky and Raghda A. El-Nagar

Materials 2022, 15(4), 1600; https://doi.org/10.3390/ma15041600 - 21 Feb 2022

Cited by 25 | Viewed by 3366

Abstract

With the projected increase in the production of heavy oil due to the energy crisis, asphaltene-related issues are likely to come to the forefront. This leads to operational problems, safety hazards, and oil production deficiencies, resulting in huge economic losses for the petroleum [...] Read more.

With the projected increase in the production of heavy oil due to the energy crisis, asphaltene-related issues are likely to come to the forefront. This leads to operational problems, safety hazards, and oil production deficiencies, resulting in huge economic losses for the petroleum industry. Therefore, in this work, we aimed to inhibit asphaltene precipitation using ionic liquid (IL) compounds. ILs with long alkyl chains can inhibit the precipitation of asphaltene molecules due to the π–π* interactions between them and the formation of hydrogen bonds. A series of imidazolium-based ionic liquids, IL-0, IL-4, IL-10, and IL-16, were synthesized with yield percents of 79, 81, 80, and 83%, respectively. The prepared materials were characterized well using FTIR, ¹H-NMR, and Elemental Analysis. The surface tension, interfacial tension (IFT), and different surface parameters were investigated at different temperatures to simulate the reservoir temperature. IL-0, IL-4, IL-10, and IL-16 displayed their γ_cmc values at 35, 34, 31, and 32 mN/m at 303 °K, respectively. It was found that the prepared ILs are good surfactants with low values of interfacial tension. Quantum structure–activity relationships using Density Functional Theory (DFT) were used to investigate the geometry optimization electronic structures, the energy gap (ΔE), and the reactivity of the cations of the prepared ILs. The synthesized ILs were evaluated as asphaltene dispersants using two different techniques. The viscometric technique showed that the asphaltene onset precipitation was 28.5 vol.%. This percent was postponed to 42.8, 50, 78.5, and 64.3 vol.%, after adding IL-0, IL-4, IL-10, and IL-16, respectively, and the spectroscopic technique confirmed the results. Full article

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14 pages, 4395 KiB

Open AccessArticle

A U-Shaped Dual-Frequency-Reconfigurable Monopole Antenna Based on Liquid Metal

by Peng Qin, Qian-Yu Wang, Jun-Heng Fu, Chun-Wei Li, Cheng-Lin Zhang, Tian-Ying Liu, Lin Gui, Jing Liu and Zhong-Shan Deng

Materials 2022, 15(4), 1599; https://doi.org/10.3390/ma15041599 - 21 Feb 2022

Cited by 4 | Viewed by 2226

Abstract

This study presents a U-shaped dual-frequency-reconfigurable liquid-metal monopole antenna. Eutectic Gallium–Indium (EGaIn) was used as a conductive fluid and filled in the two branches of the U-shaped glass tube. A precision syringe pump was connected to one of the branches of the U-shaped [...] Read more.

This study presents a U-shaped dual-frequency-reconfigurable liquid-metal monopole antenna. Eutectic Gallium–Indium (EGaIn) was used as a conductive fluid and filled in the two branches of the U-shaped glass tube. A precision syringe pump was connected to one of the branches of the U-shaped tube by a silicone tube to drive EGaIn, forming a height difference between the two liquid levels. When the height of liquid metal in the two branches met the initial condition of L₁ = L₂ = 10 mm, and L₁ increased from 10 mm to 18 mm, the two branches obtained two working bandwidths of 2.27–4.98 GHz and 2.71–8.58 GHz, respectively. The maximum peak gain was 4.00 dBi. The initial amount of EGaIn also affected the available operating bandwidth. When the liquid metal was perfused according to the initial condition: L₁ = L₂ = 12 mm, and L₁ was adjusted within the range of 12–20 mm, the two branches had the corresponding working bandwidths of 2.18–4.32 GHz and 2.57–9.09 GHz, and the measured maximum peak gain was 3.72 dBi. The simulation and measurement data corresponded well. A series of dual-frequency-reconfigurable antennas can be obtained by changing the initial amount of EGaIn. This series of antennas may have broad application prospects in fields such as base stations and navigation. Full article

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14 pages, 288 KiB

Open AccessReview

Research Progress of Wood Cell Wall Modification and Functional Improvement: A Review

by Ting Zhou and Honghai Liu

Materials 2022, 15(4), 1598; https://doi.org/10.3390/ma15041598 - 21 Feb 2022

Cited by 20 | Viewed by 2957

Abstract

The modification of wood cell walls is based on the characteristics of the chemical composition and structure of the cell wall. Various physical and chemical modifications to these characteristics enhance the original properties of the cell wall and give additional functionality. Through complex [...] Read more.

The modification of wood cell walls is based on the characteristics of the chemical composition and structure of the cell wall. Various physical and chemical modifications to these characteristics enhance the original properties of the cell wall and give additional functionality. Through complex modification, wood has also obtained the opportunity to become a multifunctional material. Scholars have paid more attention to the microscopic properties of the cell wall with continuous enrichment of modification methods and improvement of modification mechanisms. This article summarizes the methods of cell wall modification in recent years and proposes prospects for future development: (1) innovation of modifiers and combination with modification mechanism, as well as improvement of cell wall permeability; (2) the application directions of cell wall structures; and (3) the application of nano-technologies in cell wall modification. This review provides further ideas and technologies for wood modifications. Full article

15 pages, 2841 KiB

Open AccessArticle

Sealing Efficacy of the Original and Third-Party Custom-Made Abutments—Microbiological In Vitro Pilot Study

by Igor Smojver, Roko Bjelica, Amir Ćatić, Ana Budimir, Marko Vuletić and Dragana Gabrić

Materials 2022, 15(4), 1597; https://doi.org/10.3390/ma15041597 - 21 Feb 2022

Cited by 4 | Viewed by 2521

Abstract

Implant–abutment connection (IAC) is a key factor for the long-term success and stability of implant-supported prosthodontic restoration and its surrounding tissues. Misfit between prosthodontic abutment and implant at the IAC leads to technical and biological complications. Two kinds of prosthodontic abutments are currently [...] Read more.

Implant–abutment connection (IAC) is a key factor for the long-term success and stability of implant-supported prosthodontic restoration and its surrounding tissues. Misfit between prosthodontic abutment and implant at the IAC leads to technical and biological complications. Two kinds of prosthodontic abutments are currently available on the market: original and third-party abutments. The aim of this pilot study was to test and compare the internal fit (gap) at the implant–abutment interface depending on the abutment fabrication method based on microbial leakage in static conditions and the need for the use of gap sealing material. Two groups of 40 implants were formed on the basis of the type of abutment. In each of the groups of two implant systems, two subgroups of 10 implants were formed. The tested subgroups consisted of 10 implants with sealing material and a negative control subgroups consisting of 10 implants without any sealing material. The test material, GapSeal (Hager and Werken, Duisburg, Germany) was applied in the test subgroups. The implant–abutment assemblies were contaminated with a solution containing Staphylococcus aureus and Candida albicans for 14 days under aerobic conditions. Results showed that there was no statistically significant difference regarding the microbial leakage between the original and third-party custom-made abutments, regardless of the use of sealing material. It can be concluded that the abutment fabrication method has no significant influence on sealing efficacy regarding the bacterial and fungal leakage in static conditions. Full article

(This article belongs to the Special Issue Dental Implants and Materials (Second Volume))

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18 pages, 5642 KiB

Open AccessFeature PaperReview

Recycling of Reinforced Glass Fibers Waste: Current Status

by R. M. Gonçalves, Alberto Martinho and J. P. Oliveira

Materials 2022, 15(4), 1596; https://doi.org/10.3390/ma15041596 - 21 Feb 2022

Cited by 58 | Viewed by 9828

Abstract

In this paper, a review of the current status and future perspectives for reinforced glass fiber waste is undertaken, as well as an evaluation of the management hierarchy for these end-of-life materials. Waste levels are expected to increase in the coming years, but [...] Read more.

In this paper, a review of the current status and future perspectives for reinforced glass fiber waste is undertaken, as well as an evaluation of the management hierarchy for these end-of-life materials. Waste levels are expected to increase in the coming years, but an improvement of collection routes is still necessary. The recycling processes for these materials are presented. The associated advantages and disadvantages, as well as the corresponding mechanical characteristics, are described. Although mechanical shredding is currently the most used process, there is a potential for thermal processes to be more competitive than others due to the fiber quality after the recycling process. However, the energy requirements of each of the processes are not yet well explained, which compromises the determination of the economic value of the recycled fibers when included in other products, as well as the process feasibility. Nevertheless, the work of some authors that successfully integrated recycled glass fibers into other elements with increased mechanical properties is evaluated. Future recommendations for the recycling of glass fiber and its commercialization are made. Full article

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17 pages, 4203 KiB

Open AccessArticle

Variation of Critical Water Pressure for Hydraulic Fracturing in Cement Mortar under Sulfate Attack

by Detan Liu, Hongwei Zhang, Zhenzhong Shen, Liqun Xu, Qiong Wu and Yidong Ge

Materials 2022, 15(4), 1595; https://doi.org/10.3390/ma15041595 - 21 Feb 2022

Cited by 2 | Viewed by 1634

Abstract

Hydraulic fracturing may be induced easily in a cement-based structure in a sulfate-rich environment, which threatens engineering safety. In order to investigate the evolution of critical water pressure, a series of hydraulic fracturing tests and splitting tensile strength tests on the cement mortar [...] Read more.

Hydraulic fracturing may be induced easily in a cement-based structure in a sulfate-rich environment, which threatens engineering safety. In order to investigate the evolution of critical water pressure, a series of hydraulic fracturing tests and splitting tensile strength tests on the cement mortar under different sulfate-exposure periods are performed. The critical water pressure of the cement mortar under sulfate attack experiences an initial increase stage and a subsequent decrease stage. A stress intensity factor is modified by two proposed damage variables which are crack length and fracture stress. Then, the relationship between the critical water pressure and the tensile strength is established. Moreover, an evolution model of the critical water pressure is proposed, which reveals that the matrix tensile strength and porosity of cement mortar strongly affect the critical water pressure evolution. Additionally, an empirical formula is suggested to describe the critical water pressure evolution of the cement mortar under sulfate attack, and its validity is verified by experimental results. Full article

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9 pages, 1530 KiB

Open AccessArticle

The Influence of Reactive PS-PVD Process Parameters on the Microstructure and Thermal Properties of Yb₂Zr₂O₇ Thermal Barrier Coating

by Paweł Pędrak, Marek Góral, Kamil Dychton, Marcin Drajewicz, Malgorzata Wierzbinska and Tadeusz Kubaszek

Materials 2022, 15(4), 1594; https://doi.org/10.3390/ma15041594 - 21 Feb 2022

Cited by 4 | Viewed by 1903

Abstract

Ytterbium zirconate (Yb₂Zr₂O₇) is one of the most promising materials for yttria-stabilized zirconia (YSZ) replacement as a thermal barrier coating (TBCs) application. In the presented report, the experimental synthesis of Yb₂Zr₂O₇ coating [...] Read more.

Ytterbium zirconate (Yb₂Zr₂O₇) is one of the most promising materials for yttria-stabilized zirconia (YSZ) replacement as a thermal barrier coating (TBCs) application. In the presented report, the experimental synthesis of Yb₂Zr₂O₇ coating using novel Reactive Plasma Spray Physical Vapor Deposition (Reactive PS-PVD) is described. The obtained coating, irrespective of the power current (1800, 2000 and 2200 A), was characterized by a hybrid structure and a thickness of about 80–110 μm. The results of XRD phase analysis showed the formation of ytterbium zirconate in the coating but the presence of ytterbium and zirconium oxides was also detected. The oxides were not observed in calcinated powder. The decrease in thermal conductivity with power current increase was observed. It was the result of higher thickness and better columnar structure of the coating obtained using higher power current of the plasma torch. Full article

(This article belongs to the Special Issue Thermal Barrier Coatings)

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9 pages, 3868 KiB

Open AccessArticle

Hydrogen Generation by Hydrolysis of MgH₂-LiH Composite

by Xiaojuan Wu, Huaqing Xue, Yong Peng, Jifeng Deng, Zewei Xie, Jie Zheng, Xingguo Li and Shuan Li

Materials 2022, 15(4), 1593; https://doi.org/10.3390/ma15041593 - 21 Feb 2022

Cited by 21 | Viewed by 3464

Abstract

As a most promising material for hydrogen generation by hydrolysis, magnesium hydride (MgH₂) is also trapped by its yielded byproduct Mg(OH)₂ whose dense passivated layers prevent the further contact of intimal MgH₂ with water. In this work, LiH, as [...] Read more.

As a most promising material for hydrogen generation by hydrolysis, magnesium hydride (MgH₂) is also trapped by its yielded byproduct Mg(OH)₂ whose dense passivated layers prevent the further contact of intimal MgH₂ with water. In this work, LiH, as a destroyer, has been added to promote the hydrogen properties of MgH₂. The results demonstrate that even 3 wt % LiH was added into MgH₂-G, the hydrogen generation yield can increase about 72% compared to the hydrogen generation yield of MgH₂-G. The possible mechanism is that Mg²⁺ from the hydrolysis of MgH₂ preferentially bound with OH⁻ ions from the hydrolysis of LiH to form Mg(OH)₂ precipitation, which is dispersed in water rather than coated on the surface of MgH₂. Moreover, adding MgCl₂ into hydrolysis solution, using ball milling technology, and increasing the hydrolysis temperature can make the hydrolysis rate higher and reaction process more complete. It is noted that a too high weight ratio of LiH with too high of a hydrolysis temperature will make the reaction too violent to be safe in the experiment. We determinate the best experimental condition is that the LiH ratio added into MgH₂ is 3 wt %, the hydrolysis temperature is 60 °C, and the concentration of MgCl₂ hydrating solution is 1 M. MgH₂-LiH composite hydrogen generation technology can meet the needs of various types of hydrogen supply and has broad application prospects. Full article

(This article belongs to the Special Issue Hydrogen Storage in Metal Hydrides and Related Materials)

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13 pages, 3458 KiB

Open AccessArticle

The Effect of Trace Oxygen Addition on the Interface Behavior of Low-Alloy Steel

by Vlastimil Novák, Lenka Řeháčková, Petra Váňová, Michal Sniegoň, Dalibor Matýsek, Kateřina Konečná, Bedřich Smetana, Silvie Rosypalová, Markéta Tkadlečková, Ľubomíra Drozdová and Petr Klus

Materials 2022, 15(4), 1592; https://doi.org/10.3390/ma15041592 - 20 Feb 2022

Cited by 3 | Viewed by 1828

Abstract

This work aims to assess the effect of an oxygen content graded in minimal quantities, on the order of hundreds of ppms, on the determination of surface tension of low-alloy FeCOCr and FeCONi steels in contact with a corundum substrate. Oxygen, as a [...] Read more.

This work aims to assess the effect of an oxygen content graded in minimal quantities, on the order of hundreds of ppms, on the determination of surface tension of low-alloy FeCOCr and FeCONi steels in contact with a corundum substrate. Oxygen, as a surface-active element, was segregated at the surface where it interacted with the major components of the alloys, leading to a reduction in surface tension. The sessile drop method was used for wetting tests in the temperature range from steel liquidus temperatures to 1600 °C under nonoxidizing conditions. The effect of oxygen on surface tension and wetting angles was verified by statistical analysis using the Kruskal–Wallis test, which supported the results stating that the values of these quantities decreased with increasing oxygen content. Furthermore, liquidus temperatures, which are of practical importance, were determined by the optical and DTA methods and then compared with theoretically calculated temperature values. It turned out that the increased chromium content causes difficulties in determining surface tension up to 1550 °C due to the formation of a thin Cr₂O₃ layer. In addition, SEM and XRD analyses accompanied by calculations in the FactSage oxide database were performed to better understand the wetting mechanism. Full article

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