Materials

32 pages, 3128 KiB

Open AccessEditor’s ChoiceReview

Lignin as a Renewable Building Block for Sustainable Polyurethanes

by Fernanda Rosa Vieira, Sandra Magina, Dmitry V. Evtuguin and Ana Barros-Timmons

Materials 2022, 15(17), 6182; https://doi.org/10.3390/ma15176182 - 5 Sep 2022

Cited by 26 | Viewed by 6135

Currently, the pulp and paper industry generates around 50–70 million tons of lignin annually, which is mainly burned for energy recovery. Lignin, being a natural aromatic polymer rich in functional hydroxyl groups, has been drawing the interest of academia and industry for its [...] Read more.

Currently, the pulp and paper industry generates around 50–70 million tons of lignin annually, which is mainly burned for energy recovery. Lignin, being a natural aromatic polymer rich in functional hydroxyl groups, has been drawing the interest of academia and industry for its valorization, especially for the development of polymeric materials. Among the different types of polymers that can be derived from lignin, polyurethanes (PUs) are amid the most important ones, especially due to their wide range of applications. This review encompasses available technologies to isolate lignin from pulping processes, the main approaches to convert solid lignin into a liquid polyol to produce bio-based polyurethanes, the challenges involving its characterization, and the current technology assessment. Despite the fact that PUs derived from bio-based polyols, such as lignin, are important in contributing to the circular economy, the use of isocyanate is a major environmental hot spot. Therefore, the main strategies that have been used to replace isocyanates to produce non-isocyanate polyurethanes (NIPUs) derived from lignin are also discussed. Full article

(This article belongs to the Special Issue Synthesis and Application of New Lignin-Based Polymers and Composites)

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11 pages, 3825 KiB

Open AccessArticle

Effect of Multi-Walled Carbon Nanotubes and Carbon Fiber Reinforcements on the Mechanical and Tribological Behavior of Hybrid Mg-AZ91D Nanocomposites

by G. U. Raju, Vinod Kumar V. Meti, N. R. Banapurmath, T. M. Yunus Khan, I. G. Siddhalingeshwar, Vishal Vaikunte, Chandramouli Vadlamudi, Sanjay Krishnappa, A. M. Sajjan and Adarsh Patil

Materials 2022, 15(17), 6181; https://doi.org/10.3390/ma15176181 - 5 Sep 2022

Cited by 5 | Viewed by 2031

Abstract

Magnesium matrix composites are extensively used in automotive and structural applications due to their low density, high strength, and wear-resistant properties. To reach the scope of industry needs, research is carried out regarding enhancing the mechanical and tribological behavior of the magnesium composites [...] Read more.

Magnesium matrix composites are extensively used in automotive and structural applications due to their low density, high strength, and wear-resistant properties. To reach the scope of industry needs, research is carried out regarding enhancing the mechanical and tribological behavior of the magnesium composites by reinforcing the nano-sized reinforcements. In the present work, research has been carried out to enhance the properties of the magnesium AZ91D hybrid composite by reinforcing carbon fibers (CFs) and multi-walled carbon nanotubes (MWCNTs) with varying weight percentages (AZ91D + 0.5% CF’s + 0.5% MWCNT and AZ91D + 0.75% CF’s + 0.75% MWCNT, respectively). The experimental tests were carried out to evaluate the mechanical and tribological behavior of the composites. The test results showed that the addition of CF and MWCNT reinforcements improved the hybrid Mg composite’s hardness, tensile strength, and impact strength compared to the base Mg matrix. The AZ91D + 0.75% CF’s + 0.75% MWCNT hybrid composite showed a 19%, 35%, and 66% increased hardness, tensile strength, and impact strength, respectively, compared to the base Mg AZ91D. The wear test results also showed the improved wear resistance of the Mg composite compared to the base matrix. The enhanced wear resistance of the composite is due to the addition of hard MWCNT and CF reinforcements. The wear rate of the AZ91D + 0.75%CF’s + 0.75% MWCNT composite for a load of 30 N at a sliding distance of 1500 m is lower as compared to the base matrix. The SEM micrographs of the worn surfaces revealed the existence of abrasive wear. The improved mechanical and tribological behavior of the magnesium composite is also due to the homogeneous distribution of the hard reinforcement particles along the grain boundaries. Full article

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15 pages, 2829 KiB

Open AccessArticle

Effect of the Composition of Hybrid Sands on the Change in Thermal Expansion

by Filip Radkovský, Martina Gawronová, Václav Merta, Petr Lichý, Ivana Kroupová, Isabel Nguyenová, Šimon Kielar, Martin Folta, Josef Bradáč and Radim Kocich

Materials 2022, 15(17), 6180; https://doi.org/10.3390/ma15176180 - 5 Sep 2022

Cited by 5 | Viewed by 1997

Abstract

In the foundry industry, silica sands are the most commonly used type of sands for the production of sand foundry moulds using various types of binders. Their greatest disadvantage is their significant volume changes at elevated temperatures, which are associated with the formation [...] Read more.

In the foundry industry, silica sands are the most commonly used type of sands for the production of sand foundry moulds using various types of binders. Their greatest disadvantage is their significant volume changes at elevated temperatures, which are associated with the formation of many foundry defects from stress, such as veining, and thus have a direct influence on the final quality of the casting. In the case of non-silica sands and synthetic sands, the volume stability is more pronounced, but this is accompanied by a higher purchase price. Therefore, a combination of silica sand and synthetic sand CERABEADS is considered in order to influence and reduce the thermal expansion. The hybrid mixtures of sands, and their most suitable ratios, were evaluated in detail using sieve analysis, log W and cumulative curve of granularity. It was found that the addition of 50% CERABEADS achieves a 32.2% reduction in dilatation but may increase the risk of higher stresses. The measurements showed a significant effect of the granulometric composition of the sand on the resulting thermal expansion, where the choice of grain size and sorting can achieve a significant reduction in dilatation with a small addition of CERABEADS. Full article

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12 pages, 3907 KiB

Open AccessCommunication

Effects of Endic Anhydride Grafted PPC on the Properties of PHBV Blends

by Qing Zhang, Yongguang Gao, Huiyuan Liu, Shili Shu and Wei Chen

Materials 2022, 15(17), 6179; https://doi.org/10.3390/ma15176179 - 5 Sep 2022

Cited by 3 | Viewed by 1727

Abstract

Poly(β-hydroxybutyrate-co-β-hydroxyvalerate) (PHBV) was modified with endic anhydride grafted poly(propylene carbonate) (EA–PPC), and then PHBV/EA–PPC composite polymers were prepared by melt blending under the catalysis of stannous octoate (Sn(Oct)₂). The blends were characterized by an electronic universal testing machine, cantilever [...] Read more.

Poly(β-hydroxybutyrate-co-β-hydroxyvalerate) (PHBV) was modified with endic anhydride grafted poly(propylene carbonate) (EA–PPC), and then PHBV/EA–PPC composite polymers were prepared by melt blending under the catalysis of stannous octoate (Sn(Oct)₂). The blends were characterized by an electronic universal testing machine, cantilever impact testing machine, and differential scanning calorimeter (DSC), as well as dynamic mechanical analysis (DMA) and field emission scanning electron microscopy (FESEM). Effects of the amount of Sn(Oct)₂ on the mechanical properties, thermal properties, and morphology of the blends were discussed. The results showed that the addition of Sn(Oct)₂ promoted the transesterification reaction between PHBV and EA–PPC, and the compatibility between PHBV and PPC was greatly improved. When the amount of Sn(Oct)₂ was 3 wt%, the impact strength and elongation at break of the PHBV/EA–PPC blend increased from 3.7 kJ/m² and 4.1% to 5.9 kJ/m² and 387.5%, respectively, and there was no significant decrease in tensile strength. Additionally, four esterification reaction mechanisms for PHBV/EA–PPC blends were proposed. Full article

(This article belongs to the Special Issue Development and Application of Functional Polymer Materials)

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11 pages, 10076 KiB

Open AccessArticle

Controlling the Surface Morphology of ZnO Nano-Thin Film Using the Spin Coating Technique

by I. A. Elsayed and Ahmed S. Afify

Materials 2022, 15(17), 6178; https://doi.org/10.3390/ma15176178 - 5 Sep 2022

Cited by 7 | Viewed by 2260

Abstract

Zinc oxide (ZnO) thin films are significant in various electronic applications. This study introduced an efficient, simple, low cost and timesaving method to obtain an extended and uniform ZnO thin film with tunable surface morphology over the substrate using the spin coating technique. [...] Read more.

Zinc oxide (ZnO) thin films are significant in various electronic applications. This study introduced an efficient, simple, low cost and timesaving method to obtain an extended and uniform ZnO thin film with tunable surface morphology over the substrate using the spin coating technique. Different concentrations of zinc acetate dehydrate were used as precursor solutions mixed with polyvinyl alcohol as a binding polymer to obtain the film’s uniformity and to relieve thermal expansion that may cause a wrinkled surface. Synthesized films were characterized using X-ray diffraction (XRD), X-ray spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and ellipsometry. Findings show that the average size of ZnO particles was less than 50 nm in a uniform film over the whole substrate area regardless of the presence or absence of wrinkles. Additionally, this method was quite fast, attaining the desired viscosity in less than one hour in comparison with the time-consuming aging method, which requires approximately 24 h to achieve the required viscosity. Full article

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20 pages, 4686 KiB

Open AccessArticle

Meshless Chebyshev RPIM Solution for Free Vibration of Rotating Cross-Ply Laminated Combined Cylindrical-Conical Shells in Thermal Environment

by Zhen Li, Shuangwei Hu, Rui Zhong, Bin Qin and Xing Zhao

Materials 2022, 15(17), 6177; https://doi.org/10.3390/ma15176177 - 5 Sep 2022

Cited by 7 | Viewed by 1736

Abstract

This paper provides a numerical solution to the vibration of a rotating cross-ply laminated combined conical-cylindrical shell in the thermal environment. Its numerical discrete solution method uses the meshless method. The combined shell assumed the temperature independence of material property is divided to [...] Read more.

This paper provides a numerical solution to the vibration of a rotating cross-ply laminated combined conical-cylindrical shell in the thermal environment. Its numerical discrete solution method uses the meshless method. The combined shell assumed the temperature independence of material property is divided to the fundamental conical and cylindrical shell substructures, and the theoretical formulation for each substructure is derived based on the first order shear deformation theory (FSDT) and Hamilton’s principle. The effects of the initial hoop tension and temperature change are considered through the kinetic energy reflecting the effects of centrifugal and Coriolis forces and additional strain energy by the nonlinear part of the Green–Lagrange strains. The substructures are then assembled according to the continuity conditions. The boundary and continuity conditions are simulated by introducing artificial virtual spring technology. The displacement component in the theoretical formulation is approximated using a meshless Chebyshev-RPIM shape function. The reliability of the method is verified by comparing with mature and reliable results. The free vibration characteristics of the rotating combined conical-cylindrical shell structure under various sizes, speeds and temperatures are given by numerical examples. Full article

(This article belongs to the Special Issue Characterisation and Modelling of Manufacturing–Microstructure–Property–Mechanism Relationship for Advanced and Emerging Materials)

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17 pages, 6349 KiB

Open AccessArticle

The Transverse Bearing Characteristics of the Pile Foundation in a Calcareous Sand Area

by Haibo Hu, Lina Luo, Gang Lei, Jin Guo, Shaoheng He, Xunjian Hu, Panpan Guo and Xiaonan Gong

Materials 2022, 15(17), 6176; https://doi.org/10.3390/ma15176176 - 5 Sep 2022

Cited by 2 | Viewed by 1983

Abstract

Reviewing literature revealed that the studies on the bearing characteristics of pile foundations mainly focuses on clay, ordinary sand, loess, saline soil, and other areas. However, few studies on the bearing characteristics of the pile foundation in calcareous sand were conducted. Besides, existing [...] Read more.

Reviewing literature revealed that the studies on the bearing characteristics of pile foundations mainly focuses on clay, ordinary sand, loess, saline soil, and other areas. However, few studies on the bearing characteristics of the pile foundation in calcareous sand were conducted. Besides, existing traditional studies ignored the variation of soil compression modulus with depth, and the effect of void ratio on the transverse bearing characteristics of the pile foundation in a calcareous sand area were not well understood. In response of these problems, this study conducted a theoretical investigation on the transverse bearing characteristics of the pile foundation in a calcareous sand area. The transverse bearing characteristics of the pile foundation were derived based on the Pasternak foundation model and the Winkler foundation model, incorporating the heterogeneous distribution of compressive modulus with buried depth. The calculation results of the Pasternak foundation model are closer to the observed results than the Winkler foundation model. Therefore, the following research on the transverse bearing characteristics of the pile foundation in the calcareous sand area adopts the Pasternak foundation model. Then, the effects of the pile length, pile diameter, pile elastic modulus, horizontal load, bending moment, and void ratio on the transverse bearing characteristics of the pile foundation in a calcareous sand area were thoroughly analyzed. Furthermore, the difference between the transverse bearing characteristics of the pile foundation in a calcareous sand area and a quartz sand area was discussed. Results show that the horizontal displacement of the pile top in a calcareous sand area is greater than the quartz sand area under the same conditions. Full article

(This article belongs to the Topic New Trends in Rock Materials Mechanics and Engineering Geology)

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12 pages, 5196 KiB

Open AccessArticle

Electrochemical Impedance Investigation of Dye-Sensitized Solar Cells Based on Electrospun TiO₂ Nanofibers Photoanodes

by Hany M. Abd El-Lateef, Mai M. Khalaf, Van-Duong Dao and Ibrahim M. A. Mohamed

Materials 2022, 15(17), 6175; https://doi.org/10.3390/ma15176175 - 5 Sep 2022

Cited by 9 | Viewed by 2028

Abstract

This work investigates an electrochemical impedance analysis based on synthesized TiO₂ nanofibers (NFs) photoanodes, which were fabricated via electrospinning and calcination. The investigated photoanode substrate NFs were studied in terms of physicochemical tools to investigate their morphological character, crystallinity, and chemical contents [...] Read more.

This work investigates an electrochemical impedance analysis based on synthesized TiO₂ nanofibers (NFs) photoanodes, which were fabricated via electrospinning and calcination. The investigated photoanode substrate NFs were studied in terms of physicochemical tools to investigate their morphological character, crystallinity, and chemical contents via scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) analyses. As a result, the studied photoanode substrate NFs were applied to fabricate dye-sensitized solar cells (DSCs), and the electrochemical impedance analysis (EIS) was studied in terms of equivalent circuit fitting and impacts of N-doping, the latter of which was approved via XPS analysis. N-doping has a considerable role in the enhancement of charge transfers, which could be due to the strong interactions between active-site N atoms and the used photosensitizer. Full article

(This article belongs to the Special Issue Development of Nano-Materials for Catalytic and Biomedical Applications)

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14 pages, 3146 KiB

Open AccessArticle

Iodine-Doped Graphene Oxide: Fast Single-Stage Synthesis and Application as Electrocatalyst

by Adriana Marinoiu, Daniela Ion-Ebrasu, Amalia Soare and Mircea Raceanu

Materials 2022, 15(17), 6174; https://doi.org/10.3390/ma15176174 - 5 Sep 2022

Cited by 4 | Viewed by 2426

Abstract

Iodine-doped graphene oxide is attracting great attention as fuel cell (FC) electrocatalysts with a high activity for the oxygen reduction reaction (ORR). However, most of the reported preparation techniques for iodine-doped graphene (I/rGO) could be transposed into practice as multiple step procedures, a [...] Read more.

Iodine-doped graphene oxide is attracting great attention as fuel cell (FC) electrocatalysts with a high activity for the oxygen reduction reaction (ORR). However, most of the reported preparation techniques for iodine-doped graphene (I/rGO) could be transposed into practice as multiple step procedures, a significant disadvantage for scale-up applications. Herein, we describe an effective, eco-friendly, and fast technique for synthesis by a microwave-tuned one-stage technique. Structural and morphological characterizations evidenced the obtaining of nanocomposite sheets, with iodine bonded in the graphene matrix. The ORR performance of I/rGO was electrochemically investigated and the enhancement of the cathodic peak was noted. Based on the noteworthy electrochemical properties for ORR activity, the prepared I/rGO can be considered an encouraging alternative for a more economical electrode for fuel cell fabrication and commercialization. In this perspective, the iodine-based catalysts synthesis can be considered a step forward for the metal-free electrocatalysts development for the oxygen reduction reaction in fuel cells. Full article

(This article belongs to the Special Issue Materials for Electrochemical Energy Systems)

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Graphical abstract

28 pages, 8262 KiB

Open AccessArticle

Measuring the Effect of Pack Shape on Gravel’s Pore Characteristics and Permeability Using X-ray Diffraction Computed Tomography

by Jiayi Peng, Zhenzhong Shen and Jiafa Zhang

Materials 2022, 15(17), 6173; https://doi.org/10.3390/ma15176173 - 5 Sep 2022

Cited by 1 | Viewed by 2084

Abstract

Particle shape is one of the critical parameter factors that affect gravel’s pore structure and permeability. However, few studies have considered its effects on engineering applications due to the difficulty of conducting laboratory tests. To overcome these difficulties, new methods of estimating the [...] Read more.

Particle shape is one of the critical parameter factors that affect gravel’s pore structure and permeability. However, few studies have considered its effects on engineering applications due to the difficulty of conducting laboratory tests. To overcome these difficulties, new methods of estimating the gravel pack shape that involve manual work and measuring the surface area of particles and pores based on support vector machine segmentation and the reconstruction of X-ray diffraction computed tomography (CT) images were proposed. Under the same conditions, CT tests were carried out on gravel packs and two other regular-shaped particle packs to investigate the influence of particle shape on the fractal dimension of gravel’s pore–particle interface and the specific surface area of the pore network. Additionally, permeability tests were performed to study the effect of particle shape on gravel’s hydraulic conductivity. The results showed that a gravel pack with a larger aspect ratio and a smaller roundness had a larger specific pore network surface area and a more complex pore structure, leading to lower permeability. This kind of gravel had a more significant length, quantity, and tortuosity of the seepage path when seepage occurred in a two-dimensional seepage field simulation. Therefore, we suggest that the filter materials of hydraulic projects should preferably use blasting gravel with a larger aspect ratio and smaller roundness to achieve better anti-seepage properties. In addition, projects can increase pores’ specific surface area using our method as a control factor in filter construction. Full article

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3 pages, 401 KiB

Open AccessEditorial

New Frontiers in Materials Design for Laser Additive Manufacturing

by Silja-Katharina Rittinghaus, Eric A. Jägle, Manfred Schmid and Bilal Gökce

Materials 2022, 15(17), 6172; https://doi.org/10.3390/ma15176172 - 5 Sep 2022

Cited by 5 | Viewed by 2112

Abstract

Laser-based additive manufacturing (LAM) in all its variations is now being established as a technique for manufacturing components from various material types and alloys [...] Full article

(This article belongs to the Special Issue New Frontiers in Materials Design for Laser Additive Manufacturing)

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18 pages, 11653 KiB

Open AccessArticle

PBF-LB/M of Low-Alloyed Steels: Bainite-like Microstructures despite High Cooling Rates

by Dominic Bartels, Tobias Novotny, Andreas Mohr, Frank van Soest, Oliver Hentschel, Carsten Merklein and Michael Schmidt

Materials 2022, 15(17), 6171; https://doi.org/10.3390/ma15176171 - 5 Sep 2022

Cited by 8 | Viewed by 2160

Abstract

Laser-based powder bed fusion of metals (PBF-LB/M) is an emerging technology with enormous potential for the fabrication of highly complex products due to the layer-wise fabrication process. Low-alloyed steels have recently gained interest due to their wide potential range of applications. However, the [...] Read more.

Laser-based powder bed fusion of metals (PBF-LB/M) is an emerging technology with enormous potential for the fabrication of highly complex products due to the layer-wise fabrication process. Low-alloyed steels have recently gained interest due to their wide potential range of applications. However, the correlation between the processing strategy and the material properties remains mostly unclear. The process-inherent high cooling rates support the assumption that a very fine martensitic microstructure is formed. Therefore, the microstructure formation was studied by means of scanning electron microscopy, hardness measurements, and an analysis of the tempering stability. It could be shown that additively manufactured Bainidur AM samples possess a bainitic microstructure despite the high process-specific cooling rates in PBF-LB/M. This bainitic microstructure is characterized by an excellent tempering stability up to temperatures as high as 600 °C. In contrast to this, additively manufactured and martensitic-hardened specimens are characterized by a higher initial hardness but a significantly reduced tempering stability. This shows the potential of manufacturing products from Bainidur AM for high-temperature applications without the necessity of a post-process heat treatment for achieving the desired bainitic microstructure. Full article

(This article belongs to the Special Issue Research and Development of Additive Manufacturing Technology)

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14 pages, 1039 KiB

Open AccessArticle

Experimental Studies on Adaptive-Passive Symmetrical Granular Damper Operation

by Mateusz Żurawski and Robert Zalewski

Materials 2022, 15(17), 6170; https://doi.org/10.3390/ma15176170 - 5 Sep 2022

Cited by 1 | Viewed by 1564

Abstract

This paper presents experimental studies on a controllable granular damper, whose dissipative properties are provided by the friction phenomenon occuring between loose granular material. In addition, in order to adjust to the current trends in vibration suppression, we built a semi-active device, controlled [...] Read more.

This paper presents experimental studies on a controllable granular damper, whose dissipative properties are provided by the friction phenomenon occuring between loose granular material. In addition, in order to adjust to the current trends in vibration suppression, we built a semi-active device, controlled by a single parameter—underpressure. Such granular structures subjected to underpressure are called Vacuum-Packed Particles. The first section presents the state of the art. A brief description of the most often used intelligent and smart materials for the manufacture of dampers is presented. The main advantages of the proposed device are a simple structure, low construction cost, symmetrical principle of operation, and the ability to change the characteristics of the damper by quickly and suddenly changing the negative pressure inside the granular core. The second section provides a detailed description of the construction and operation principles of the original symmetrical granular damper. A description of its application in the laboratory research test stand is also provided. The third section presents the results of the experimental studies including the recorded damping characteristics of the investigated damper. The effectiveness of the ethylene–propylene–diene grains’ application is presented. The two parameters of underpressure and frequency of excitation were considered during the empirical tests. The influence of the system parameters on its global dissipative behavior is discussed in detail. The damper operation characteristics are close to linear, which is positive information from the point of view of the potential adaptive-passive control process. Brief conclusions and the prospective application of vacuum-packed particle dampers are presented in the final section. Full article

(This article belongs to the Special Issue Advanced Materials Structures for Sound and Vibration Damping)

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14 pages, 20270 KiB

Open AccessArticle

Strength Characteristics and Microstructure Analysis of Alkali-Activated Slag–Fly Ash Cementitious Material

by Chenhui Zhu, Yuanyuan Wan, Lei Wang, Yuchen Ye, Houjun Yu and Jie Yang

Materials 2022, 15(17), 6169; https://doi.org/10.3390/ma15176169 - 5 Sep 2022

Cited by 9 | Viewed by 2228

Abstract

Modifying the admixture of alkali-activated cementitious materials using components such as fly ash and fine sand may reduce CO₂ emissions and conserve natural resources and energy. This study adopted strength testing, scanning electron microscopy, and mercury intrusion porosimetry to investigate the influence [...] Read more.

Modifying the admixture of alkali-activated cementitious materials using components such as fly ash and fine sand may reduce CO₂ emissions and conserve natural resources and energy. This study adopted strength testing, scanning electron microscopy, and mercury intrusion porosimetry to investigate the influence of different admixtures on the compressive strength and flexural strength of alkali slag cementing materials and the microstructure characteristics of hardened slurry under the action of load. The flexural strength of alkali slag cement slurry and mortar was reduced by replacing slag powder with fly ash. Content of fine sand less than 20% had little effect on the strength of alkali slag cement mortar; however, when the content of fine sand exceeded 30%, the strength decreased significantly. The hydration degree at 3 d was large, and the density of slurry increased with the extension of age. Increased fly ash or fine sand content decreased the density of the slurry, and increased fly ash resulted in a large number of unhydrated fly ash particles in the cementitious materials. Addition of fine sand resulted in a large number of microcracks in the slurry, which gradually decreased with the extension of hydration age. Full article

(This article belongs to the Special Issue Convergence & Sustainable Technology in Building Materials)

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11 pages, 7658 KiB

Open AccessArticle

Ultrafine-Grained Tungsten Heavy Alloy Prepared by High-Pressure Spark Plasma Sintering

by Shuaihao Zhang, Qiqi Zhu, Qiunan Li, Wei Ji, Weimin Wang and Zhengyi Fu

Materials 2022, 15(17), 6168; https://doi.org/10.3390/ma15176168 - 5 Sep 2022

Cited by 6 | Viewed by 2042

Abstract

Tungsten heavy alloy (WHA) is an ideal material employed for kinetic energy penetrators due to its high density and excellent mechanical properties. However, it is difficult to obtain ultrafine-grained tungsten alloy with excellent properties by traditional powder metallurgy method because of severe grain [...] Read more.

Tungsten heavy alloy (WHA) is an ideal material employed for kinetic energy penetrators due to its high density and excellent mechanical properties. However, it is difficult to obtain ultrafine-grained tungsten alloy with excellent properties by traditional powder metallurgy method because of severe grain growth at a high sintering temperature with a long soaking time. In this study, the sintering behavior of tungsten alloys was studied at 800 to 1300 °C, and highly dense 93W-5.6Ni-1.4Fe (wt.%) WHA was successfully fabricated at a low temperature of 950 °C with a high pressure of 150 MPa by spark plasma sintering. The as-sintered tungsten alloy possesses a high relative density (98.6%), ultrafine grain size (271 nm) and high dislocation density (2.6 × 10¹⁶ m⁻²), which results in excellent properties such as a high hardness (1079 HV1). The high sintering pressure is considered to support an additional driving force for the sintering and lead to a low-temperature densification, which effectively limits grain growth. Full article

(This article belongs to the Special Issue Spark Plasma Sintering of Materials: Processing and Applications)

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13 pages, 1564 KiB

Open AccessArticle

Construction Products between Testing Laboratory and Market Surveillance: Case study of Cementitious Ceramic Tile Adhesives

by Cristina Stancu, Dawid Dębski and Jacek Michalak

Materials 2022, 15(17), 6167; https://doi.org/10.3390/ma15176167 - 5 Sep 2022

Cited by 5 | Viewed by 2439

Abstract

This article presents the results of the interlaboratory comparison (ILC) study of the following four characteristics of ceramic tile adhesives (CTAs): initial tensile adhesion strength, tensile adhesion strength after heat ageing, tensile adhesion strength after immersion in water, and tensile adhesion strength after [...] Read more.

This article presents the results of the interlaboratory comparison (ILC) study of the following four characteristics of ceramic tile adhesives (CTAs): initial tensile adhesion strength, tensile adhesion strength after heat ageing, tensile adhesion strength after immersion in water, and tensile adhesion strength after freeze–thaw cycles. The results showed that the objective of the ILC was achieved—the z-score analysis carried out following ISO 13528 allowed for classifying all results obtained by 23 laboratories out of 27 as satisfactory. The results of the remaining four laboratories were rated worse. Despite the achieved goal, the ILC notes high heterogeneity of the results in terms of failure patterns, as well as significant differences between the lowest and the highest values of tensile adhesion strength for various measurement conditions. The results of the ILC were discussed in terms of the possibility of including them in the risk analysis conducted by the manufacturer. The results of the ILC are also valuable information for market surveillance authorities, who, in the authors’ opinion, should be more cautious about results on samples taken from the market. The ILC results for CTAs are also a valuable recommendation for a possible revision of EN 12004. Full article

(This article belongs to the Special Issue Feature Papers in Refractories and Ceramics: Microstructure, Properties and Applications)

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12 pages, 2985 KiB

Open AccessArticle

Microstructure and Properties of a Graphene Reinforced Cu–Cr–Mg Composite

by Ruiyu Lu, Bin Liu, Huichao Cheng, Shenghan Gao, Tiejun Li, Jia Li and Qihong Fang

Materials 2022, 15(17), 6166; https://doi.org/10.3390/ma15176166 - 5 Sep 2022

Cited by 2 | Viewed by 1888

Abstract

To improve the graphene/copper interfacial bonding and the strength of the copper matrix, Cu–Cr–Mg alloy powder and graphene nanosheets (GNPs) have been used as raw materials in the preparation of a layered graphene/Cu–Cr–Mg composite through high-energy ball-milling and fast hot-pressing sintering. The microstructure [...] Read more.

To improve the graphene/copper interfacial bonding and the strength of the copper matrix, Cu–Cr–Mg alloy powder and graphene nanosheets (GNPs) have been used as raw materials in the preparation of a layered graphene/Cu–Cr–Mg composite through high-energy ball-milling and fast hot-pressing sintering. The microstructure of the composite after sintering, as well as the effect of graphene on the mechanical properties and conductivity of the composite, are also studied. The results show that the tensile strength of the composite material reached a value of 349 MPa, which is 46% higher than that of the copper matrix, and the reinforcement efficiency of graphene is as large as 136. Furthermore, the electrical conductivity of the composite material was 81.6% IACS, which is only 0.90% IACS lower than that of the copper matrix. The Cr and Mg elements are found to diffuse to the interface of the graphene/copper composite during sintering, and finely dispersed chromium carbide particles are found to significantly improve the interfacial bonding strength of the composite. Thus, graphene could effectively improve the mechanical properties of the composite while maintaining a high electrical conductivity. Full article

(This article belongs to the Special Issue Advanced Manufacturing of Metals and Composites: Effect of Processes on Microstructure and Mechanical Properties)

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17 pages, 4370 KiB

Open AccessEditor’s ChoiceArticle

High-Energy Computed Tomography as a Prospective Tool for In Situ Monitoring of Mass Transfer Processes inside High-Pressure Reactors—A Case Study on Ammonothermal Bulk Crystal Growth of Nitrides including GaN

by Saskia Schimmel, Michael Salamon, Daisuke Tomida, Steffen Neumeier, Tohru Ishiguro, Yoshio Honda, Shigefusa F. Chichibu and Hiroshi Amano

Materials 2022, 15(17), 6165; https://doi.org/10.3390/ma15176165 - 5 Sep 2022

Cited by 3 | Viewed by 2725

Abstract

For the fundamental understanding and the technological development of the ammonothermal method for the synthesis and crystal growth of nitrides, an in situ monitoring technique for tracking mass transport of the nitride throughout the entire autoclave volume is desirable. The feasibility of using [...] Read more.

For the fundamental understanding and the technological development of the ammonothermal method for the synthesis and crystal growth of nitrides, an in situ monitoring technique for tracking mass transport of the nitride throughout the entire autoclave volume is desirable. The feasibility of using high-energy computed tomography for this purpose was therefore evaluated using ex situ measurements. Acceleration voltages of 600 kV were estimated to yield suitable transparency in a lab-scale ammonothermal setup for GaN crystal growth designed for up to 300 MPa operating pressure. The total scan duration was estimated to be in the order of 20 to 40 min, which was sufficient given the comparatively slow crystal growth speed in ammonothermal growth. Even shorter scan durations or, alternatively, lower acceleration voltages for improved contrast or reduced X-ray shielding requirements, were estimated to be feasible in the case of ammonoacidic growth, as the lower pressure requirements for this process variant allow for thinned autoclave walls in an adapted setup designed for improved X-ray transparency. Promising nickel-base and cobalt-base alloys for applications in ammonothermal reactors with reduced X-ray absorption in relation to the maximum operating pressure were identified. The applicability for the validation of numerical simulations of the growth process of GaN, in addition to the applicability of the technique to further nitride materials, as well as larger reactors and bulk crystals, were evaluated. Full article

(This article belongs to the Special Issue Wide and Ultra-Wide Bandgap Semiconductor Materials for Power Devices)

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16 pages, 3345 KiB

Open AccessArticle

Effect of Cu Modified Textile Structures on Antibacterial and Antiviral Protection

by Małgorzata Cieślak, Dorota Kowalczyk, Małgorzata Krzyżowska, Martyna Janicka, Ewa Witczak and Irena Kamińska

Materials 2022, 15(17), 6164; https://doi.org/10.3390/ma15176164 - 5 Sep 2022

Cited by 12 | Viewed by 2239

Abstract

Textile structures with various bioactive and functional properties are used in many areas of medicine, special clothing, interior textiles, technical goods, etc. We investigated the effect of two different textile woven structures made of 90% polyester with 10% polyamide (PET) and 100% cotton [...] Read more.

Textile structures with various bioactive and functional properties are used in many areas of medicine, special clothing, interior textiles, technical goods, etc. We investigated the effect of two different textile woven structures made of 90% polyester with 10% polyamide (PET) and 100% cotton (CO) modified by magnetron sputtering with copper (Cu) on bioactive properties against Gram-positive and Gram-negative bacteria and four viruses and also on the some comfort parameters. PET/Cu and CO/Cu fabrics have strong antibacterial activity against Staphylococcus aureus and Klebsiella pneumonia. CO/Cu fabric has good antiviral activity in relation to vaccinia virus (VACV), herpes simplex virus type 1 (HSV-1) and influenza A virus H1N1 (IFV), while its antiviral activity against mouse coronavirus (MHV) is weak. PET/Cu fabric showed weak antiviral activity against HSV-1 and MHV. Both modified fabrics showed no significant toxicity in comparison to the control medium and pristine fabrics. After Cu sputtering, fabric surfaces became hydrophobic and the value of the surface free energy was over four times lower than for pristine fabrics. The modification improved thermal conductivity and thermal diffusivity, facilitated water vapour transport, and air permeability did not decrease. Full article

(This article belongs to the Special Issue Bioactive and Functional Materials)

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15 pages, 4102 KiB

Open AccessArticle

Chemical Distributions of Different Sodium Hydroxide Molarities on Fly Ash/Dolomite-Based Geopolymer

by Wan Mastura Wan Ibrahim, Mohd Mustafa Al Bakri Abdullah, Romisuhani Ahmad, Andrei Victor Sandu, Petrica Vizureanu, Omrane Benjeddou, Afikah Rahim, Masdiyana Ibrahim and Ahmad Syauqi Sauffi

Materials 2022, 15(17), 6163; https://doi.org/10.3390/ma15176163 - 5 Sep 2022

Cited by 18 | Viewed by 2311

Abstract

Geopolymers are an inorganic material in an alkaline environment that is synthesized with alumina–silica gel. The structure of geopolymers consists of an inorganic chain of material and a covalent-bound molecular system. Currently, Ordinary Portland Cement (OPC) has caused carbon dioxide (CO₂) [...] Read more.

Geopolymers are an inorganic material in an alkaline environment that is synthesized with alumina–silica gel. The structure of geopolymers consists of an inorganic chain of material and a covalent-bound molecular system. Currently, Ordinary Portland Cement (OPC) has caused carbon dioxide (CO₂) emissions which causes greenhouse effects. This analysis investigates the impact on fly ash/dolomite-based-geopolymer with various molarities of sodium hydroxide solutions which are 6 M, 8 M, 10 M, 12 M and 14 M. The samples of fly ash/dolomite-based-geopolymer were prepared with the usage of solid to liquid of 2.0, by mass and alkaline activator ratio of 2.5, by mass. After that, the geopolymer was cast in 50 × 50 × 50 mm molds before testing after 7 days of curing. The samples were tested on compressive strength, density, water absorption, morphology, elemental distributions and phase analysis. From the results, the usage of 8 M of NaOH gave the optimum properties for the fly ash/dolomite-based geopolymer. The elemental distribution analysis exposes the Al, Si, Ca, Fe and Mg chemical distribution of the samples from the selected area. The distribution of the elements is related to the compressive strength and compared with the chemical composition of the fly ash and dolomite. Full article

(This article belongs to the Special Issue New Geopolymers Used in Civil Engineering)

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19 pages, 650 KiB

Open AccessArticle

Resistance of 3D-Printed Components, Test Specimens and Products to Work under Environmental Conditions—Review

by Marcin Głowacki, Adam Mazurkiewicz, Małgorzata Słomion and Katarzyna Skórczewska

Materials 2022, 15(17), 6162; https://doi.org/10.3390/ma15176162 - 5 Sep 2022

Cited by 16 | Viewed by 2855

Abstract

The development of additive manufacturing methods known as “3D printing” started in the 1980s. In these methods, spatial models are created from a semi-finished product such as a powder, filament or liquid. The model is most often created in layers, which are created [...] Read more.

The development of additive manufacturing methods known as “3D printing” started in the 1980s. In these methods, spatial models are created from a semi-finished product such as a powder, filament or liquid. The model is most often created in layers, which are created from the semi-finished product, which is most often subjected to thermal treatment or using light or ultraviolet rays. The technology of additive manufacturing has both advantages and disadvantages when compared to the traditionally used methods of processing thermoplastic materials, such as, for example, injection or extrusion. The most important advantages are low cost, flexibility and speed of manufacturing of elements with different spatial shapes. From the point of view of the user of the product, the most important disadvantages are the lower mechanical properties and lower resistance to environmental factors that occur during the use of the manufactured products. The purpose of this review is to present current information and a compilation of features in the field of research on the effects of the interactions of different types of environments on the mechanical properties of 3D-manufactured thermoplastic products. Changes in the structure and mechanical properties of the material under the influence of factors such as humidity, salt, temperature, UV rays, gasoline and the environment of the human body are presented. The presented article enables the effects of environmental conditions on common materials used in 3D printing technology to be collated in one place. Full article

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

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11 pages, 13098 KiB

Open AccessArticle

Internal and Marginal Adaptation of Adhesive Resin Cements Used for Luting Inlay Restorations: An In Vitro Micro-CT Study

by Linah M. Ashy and Hanadi Marghalani

Materials 2022, 15(17), 6161; https://doi.org/10.3390/ma15176161 - 5 Sep 2022

Cited by 6 | Viewed by 2043

Abstract

Adequate internal adaptation and marginal sealing of resin luting cements are of particular importance for the success of cemented ceramic inlays. The purpose of this study was to investigate the initial adaptation of different resin cements at the tooth-inlay restoration interface at enamel [...] Read more.

Adequate internal adaptation and marginal sealing of resin luting cements are of particular importance for the success of cemented ceramic inlays. The purpose of this study was to investigate the initial adaptation of different resin cements at the tooth-inlay restoration interface at enamel versus dentin surfaces. Thirty-two extracted human molars were allocated to four groups. One Class II cavity was prepared in each tooth. In each group, half of the cavities’ gingival floors were on enamel while the other halves were on cementum. Lava Ultimate CAD/CAM inlays were luted to the cavities using the following adhesive systems: RelyX Unicem, RelyX Ultimate, eCement, and Variolink Esthetic DC. After staining teeth with silver nitrate solution, marginal and internal gap volumes were determined using micro-CT images. Statistical analyses were conducted by independent t test and one-way ANOVA followed by post hoc Tukey test (p < 0.05). The internal and marginal gap volume values were the highest for Variolink Esthetic DC at the dentin surface (0.629 ± 0.363) and (2.519 ± 1.007), respectively, and the lowest for RelyX Unicem at the enamel surface (0.005 ± 0.004) and (0.009 ± 0.003), respectively. The internal and marginal adaptation on the enamel surface for RelyX Unicem and RelyX Ultimate resin cements were comparable to each other and to eCement but significantly better than Variolink Esthetic DC cement. Regardless of the adhesive resin system used, adaptation on enamel is superior to that on dentin surfaces. Full article

(This article belongs to the Special Issue Polymeric Materials for Oral and Maxillofacial Reconstructive Treatment)

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9 pages, 2342 KiB

Open AccessArticle

Quantum Cutting in Ultraviolet B-Excited KY(CO₃)₂:Tb³⁺ Phosphors

by Dechuan Li and Guangping Zhu

Materials 2022, 15(17), 6160; https://doi.org/10.3390/ma15176160 - 5 Sep 2022

Cited by 3 | Viewed by 1552

Abstract

Highly efficient quantum cutting KY(CO₃)₂:Tb³⁺ phosphors excited by ultraviolet B (UVB) and ultraviolet C (UVC) were investigated. The structural and spectroscopic properties were characterized by XRD analysis and fluorescence spectrophotometry, respectively. The results showed that the monoclinic crystal [...] Read more.

Highly efficient quantum cutting KY(CO₃)₂:Tb³⁺ phosphors excited by ultraviolet B (UVB) and ultraviolet C (UVC) were investigated. The structural and spectroscopic properties were characterized by XRD analysis and fluorescence spectrophotometry, respectively. The results showed that the monoclinic crystal structure of KY(CO₃)₂:Tb³⁺ remained in the Tb³⁺ doping range of 0~100%. In the excitation spectrum, two intense excitation peaks were observed in the ultraviolet range. Under the excitation of 283 nm, the maximum quantum efficiency of KY(CO₃)₂:0.7Tb³⁺ could reach 119%. However, the most efficient quantum cutting occurred at the ⁵K₈ excited state in the cross-relaxation of ⁵K₈ + ⁷F₆⁵D₄ + ⁵D₄. The Tb³⁺ content could be selected arbitrarily in the KY(CO₃)₂ host without any concentration quenching. Optimal quantum cutting concentrations of Tb³⁺ in KY(CO₃)₂ were 0.7 and 0.3 for the excitation of UVB and UVC, respectively. UVB-excited phosphors are more popular with high transparency in products such as glass or resin. A quick response code was fabricated by resin to show the hidden information clearly. Therefore, the highly efficient phosphor could be a candidate material for the application in information identification technology. Full article

(This article belongs to the Special Issue Inorganic Luminescent Materials: Recent Years of Research and Application)

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13 pages, 20829 KiB

Open AccessArticle

Effect of Dynamic Preheating on the Thermal Behavior and Mechanical Properties of Laser-Welded Joints

by Linyi Xie, Wenqing Shi, Teng Wu, Meimei Gong, Detao Cai, Shanguo Han and Kuanfang He

Materials 2022, 15(17), 6159; https://doi.org/10.3390/ma15176159 - 5 Sep 2022

Cited by 3 | Viewed by 2105

Abstract

The high cooling rate and temperature gradient caused by the rapid heating and cooling characteristics of laser welding (LW) leads to excessive thermal stress and even cracks in welded joints. In order to solve these problems, a dynamic preheating method that uses hybrid [...] Read more.

The high cooling rate and temperature gradient caused by the rapid heating and cooling characteristics of laser welding (LW) leads to excessive thermal stress and even cracks in welded joints. In order to solve these problems, a dynamic preheating method that uses hybrid laser arc welding to add an auxiliary heat source (arc) to LW was proposed. The finite element model was deployed to investigate the effect of dynamic preheating on the thermal behavior of LW. The accuracy of the heat transfer model was verified experimentally. Hardness and tensile testing of the welded joint were conducted. The results show that using the appropriate current leads to a significantly reduced cooling rate and temperature gradient, which are conducive to improving the hardness and mechanical properties of welded joints. The yield strength of welded joints with a 20 A current for dynamic preheating is increased from 477.0 to 564.3 MPa compared with that of LW. Therefore, the use of dynamic preheating to reduce the temperature gradient is helpful in reducing thermal stress and improving the tensile properties of the joint. These results can provide new ideas for welding processes. Full article

(This article belongs to the Topic Advanced Processes in Metallurgical Technologies)

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17 pages, 4382 KiB

Open AccessArticle

Free Vibration Analysis of a Graphene-Platelet-Reinforced, Porous, Two-Cylindrical-Panel System

by Xianguang Sun, Weichao Chi and Jia Luo

Materials 2022, 15(17), 6158; https://doi.org/10.3390/ma15176158 - 5 Sep 2022

Cited by 4 | Viewed by 1935

Abstract

In this study, a novel, dynamic model of a graphene-platelet-reinforced, porous (GPLRP) double-cylindrical-panel system is proposed. The material properties of a graphene-platelet-reinforced, porous, double-cylindrical-panel system were determined by the Halpin–Tsai micromechanics model and the typical mechanical properties of open-cell metal foams. Different types [...] Read more.

In this study, a novel, dynamic model of a graphene-platelet-reinforced, porous (GPLRP) double-cylindrical-panel system is proposed. The material properties of a graphene-platelet-reinforced, porous, double-cylindrical-panel system were determined by the Halpin–Tsai micromechanics model and the typical mechanical properties of open-cell metal foams. Different types of porosity distribution and graphene platelet (GPL) distribution patterns were considered. Love’s shell theory was utilized to derive the theoretical formulation, and the Rayleigh–Ritz method was used to calculate the natural frequencies of the system. The proposed model was validated by several comparison studies with the natural frequencies in the existing literature. Finally, the effects of stiffness of Winkler springs, boundary condition, porosity coefficient, porosity distribution, GPL distribution pattern, and GPL weight fraction on the free vibration characteristics of the system were evaluated. Full article

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19 pages, 6051 KiB

Open AccessArticle

Statistical Assessment of Fracture Toughness Results from the HAZ of X80 Pipeline FCAW Girth Weld

by Hongyuan Chen, Qingshan Feng, Ying Bi, Xiongxiong Gao, Lianshuang Dai and Qiang Chi

Materials 2022, 15(17), 6157; https://doi.org/10.3390/ma15176157 - 5 Sep 2022

Cited by 1 | Viewed by 1942

Abstract

Due to the wide application of flux-cored arc welds (FCAW) susceptible to significant scatter in weld and Heat Affected Zone (HAZ) fracture toughness, there is an interest in methods for evaluating the reliability of welds containing defects. The mechanical properties of the FCAW [...] Read more.

Due to the wide application of flux-cored arc welds (FCAW) susceptible to significant scatter in weld and Heat Affected Zone (HAZ) fracture toughness, there is an interest in methods for evaluating the reliability of welds containing defects. The mechanical properties of the FCAW girth weld of an X80 pipeline are tested and then analyzed. By obtaining fracture toughness results from a statistically significant number of SENB specimens, with notches positioned in different HAZ locations, the effect of variation within the results can be evaluated. The results of the fracture toughness tests were analyzed using statistical methods, to compare both the difference in behavior between HAZ microstructures and the variation when a similar microstructure has been sampled. The range of different characteristic toughness values was analyzed using a postulated ECA case to illustrate the sensitivity of the results to how toughness is defined. The analyses supported recommendations to be made on the optimum approach to characterizing HAZ fracture toughness for reliable pipeline assessments in multi-pass girth welds with complex HAZ microstructure distributions. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Pipeline Steel)

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24 pages, 4589 KiB

Open AccessArticle

Hybrid Ti6Al4V/Silk Fibroin Composite for Load-Bearing Implants: A Hierarchical Multifunctional Cellular Scaffold

by Simone Murchio, Matteo Benedetti, Anastasia Berto, Francesca Agostinacchio, Gianluca Zappini and Devid Maniglio

Materials 2022, 15(17), 6156; https://doi.org/10.3390/ma15176156 - 5 Sep 2022

Cited by 7 | Viewed by 2616

Abstract

Despite the tremendous technological advances that metal additive manufacturing (AM) has made in the last decades, there are still some major concerns guaranteeing its massive industrial application in the biomedical field. Indeed, some main limitations arise in dealing with their biological properties, specifically [...] Read more.

Despite the tremendous technological advances that metal additive manufacturing (AM) has made in the last decades, there are still some major concerns guaranteeing its massive industrial application in the biomedical field. Indeed, some main limitations arise in dealing with their biological properties, specifically in terms of osseointegration. Morphological accuracy of sub-unital elements along with the printing resolution are major constraints in the design workspace of a lattice, hindering the possibility of manufacturing structures optimized for proper osteointegration. To overcome these issues, the authors developed a new hybrid multifunctional composite scaffold consisting of an AM Ti6Al4V lattice structure and a silk fibroin/gelatin foam. The composite was realized by combining laser powder bed fusion (L-PBF) of simple cubic lattice structures with foaming techniques. A combined process of foaming and electrodeposition has been also evaluated. The multifunctional scaffolds were characterized to evaluate their pore size, morphology, and distribution as well as their adhesion and behavior at the metal–polymer interface. Pull-out tests in dry and hydrated conditions were employed for the mechanical characterization. Additionally, a cytotoxicity assessment was performed to preliminarily evaluate their potential application in the biomedical field as load-bearing next-generation medical devices. Full article

(This article belongs to the Special Issue Development of Bioactive Materials and Coatings for Biomedical Applications)

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20 pages, 4058 KiB

Open AccessReview

Steel Fiber-Reinforced Concrete: A Systematic Review of the Research Progress and Knowledge Mapping

by Muhammad Nasir Amin, Waqas Ahmad, Kaffayatullah Khan and Ayaz Ahmad

Materials 2022, 15(17), 6155; https://doi.org/10.3390/ma15176155 - 5 Sep 2022

Cited by 15 | Viewed by 3867

Abstract

This study performed a scientometric-based examination of the literature on steel fiber-reinforced concrete (SFRC) to identify its key elements. Typical review papers are limited in their capacity to link distinct segments of the literature in an organized and systematic method. The most challenging [...] Read more.

This study performed a scientometric-based examination of the literature on steel fiber-reinforced concrete (SFRC) to identify its key elements. Typical review papers are limited in their capacity to link distinct segments of the literature in an organized and systematic method. The most challenging aspects of current research are knowledge mapping, co-occurrence, and co-citation. The Scopus search engine was used to search for and obtain the data required to meet the goals of the study. During the data evaluation, the relevant publication sources, keyword assessment, productive authors based on publications and citations, top papers based on citations received, and areas vigorously involved in SFRC studies were recognized. The VOSviewer software tool was used to evaluate the literature data from 9562 relevant papers, which included citation, abstract, bibliographic, keywords, funding, and other information. Furthermore, the applications and constraints related to the usage of SFRC in the construction sector were examined, as well as potential solutions to these constraints. It was determined that only 17 publication sources (journals/conferences) had published at least 100 articles on SFRC up to June 2022. Additionally, the mostly employed keywords by authors in SFRC research include steel fibers, fiber-reinforced concrete, concrete, steel fiber-reinforced concrete, and reinforced concrete. The assessment of authors revealed that 39 authors had published at least 30 articles. Moreover, China, the United States, and India were found to be the most active and participating countries based on publications on SFRC research. This study can assist academics in building collaborative initiatives and communicating new ideas and techniques because of the quantitative and graphical depiction of participating nations and researchers. Full article

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

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20 pages, 21476 KiB

Open AccessArticle

Dynamic Compressive Mechanical Properties of UR50 Ultra-Early-Strength Cement-Based Concrete Material under High Strain Rate on SHPB Test

by Wei Wang, Zhonghao Zhang, Qing Huo, Xiaodong Song, Jianchao Yang, Xiaofeng Wang, Jianhui Wang and Xing Wang

Materials 2022, 15(17), 6154; https://doi.org/10.3390/ma15176154 - 5 Sep 2022

Cited by 9 | Viewed by 1869

Abstract

UR50 ultra-early-strength cement-based self-compacting high-strength material is a special cement-based material. Compared with traditional high-strength concrete, its ultra-high strength, ultra-high toughness, ultra-impact resistance, and ultra-high durability have received great attention in the field of protection engineering, but the dynamic mechanical properties of impact [...] Read more.

UR50 ultra-early-strength cement-based self-compacting high-strength material is a special cement-based material. Compared with traditional high-strength concrete, its ultra-high strength, ultra-high toughness, ultra-impact resistance, and ultra-high durability have received great attention in the field of protection engineering, but the dynamic mechanical properties of impact compression at high strain rates are not well known, and the dynamic compressive properties of materials are the basis for related numerical simulation studies. In order to study its dynamic compressive mechanical properties, three sets of specimens with a size of Φ100 × 50 mm were designed and produced, and a large-diameter split Hopkinson pressure bar (SHPB) with a diameter of 100 mm was used to carry out impact tests at different speeds. The specimens were mainly brittle failures. With the increase in impact speed, the failure mode of the specimens gradually transits from larger fragments to small fragments and a large amount of powder. The experimental results show that the ultra-early-strength cement-based material has a greater impact compression brittleness, and overall rupture occurs at low strain rates. Its dynamic compressive strength increases with the increase of strain rates and has an obvious strain rate strengthening effect. According to the test results, the relationship curve between the dynamic enhancement factor and the strain rate is fitted. As the impact speed increases, the peak stress rises, the energy absorption density increases, and its growth rate accelerates. Afterward, based on the stress–strain curve, the damage variables under different strain rates were fitted, and the results show that the increase of strain rate has a hindering effect on the increase of damage variables and the increase rate. Full article

(This article belongs to the Special Issue Mechanical Research of Reinforced Concrete Materials)

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20 pages, 5062 KiB

Open AccessArticle

Comprehensive Evaluation of the Sustainability of Waste Concrete towards Structural Concrete Application in Freeze-Thaw Environment

by Da Wei, Pinghua Zhu, Shan Gao, Xiancui Yan, Hui Liu and Haifeng Fan

Materials 2022, 15(17), 6153; https://doi.org/10.3390/ma15176153 - 5 Sep 2022

Cited by 7 | Viewed by 1473

Abstract

To promote the in-situ and structural application of waste concrete in cold regions, the sustainable application potential of waste concrete in a freeze-thaw (F-T) environment was comprehensively evaluated from three aspects of performance, environmental load, and economic benefit. The recycled aggregate concrete (RAC) [...] Read more.

To promote the in-situ and structural application of waste concrete in cold regions, the sustainable application potential of waste concrete in a freeze-thaw (F-T) environment was comprehensively evaluated from three aspects of performance, environmental load, and economic benefit. The recycled aggregate concrete (RAC) was produced by recycled coarse aggregate (RCA), which was obtained from the crushing of natural aggregate concrete (NAC) after every F-T 150 cycles until F-T failure. The effects of F-T damage of parent concrete on the physical properties of RCA and mechanical and frost resistance of RAC under 35% flexural stress were studied. Besides, the sustainability of NAC and RAC was compared and analyzed by emergy theory. The results suggested that the physical properties of RCA deteriorated gradually with the accumulation of F-T damage to parent concrete. The RCA obtained from parent concrete that suffered F-T damage could be used as coarse aggregate for structural concrete when F-T damage is smaller than 0.367. The F-T damage of parent concrete had an adverse effect on the mechanical properties and frost resistance of RAC. The frost resistance of RAC obtained from parent concrete with larger F-T damage was worse. The RAC prepared from parent concrete without F-T failure can serve 50 years in cold regions, while that with F-T failure can only serve 30 years. The F-T damage microelements were dispersed in the adhesive mortar of RCA and transferred to RAC, resulting in the reduction of the mechanical properties and frost resistance of RAC. Emergy analysis showed that the reuse of waste concrete after F-T failure required higher economic input, higher environment load, lower output efficiency, and sustainability. The performance, environmental load and economic benefit of RAC prepared by using waste concrete after F-T failure were inferior to that of waste concrete without F-T failure. Waste concrete after F-T failure is not recommended to be used as coarse aggregate for structural concrete. Full article

(This article belongs to the Special Issue Cement-Based Materials Applied in Sustainable Construction)

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