Materials

19 pages, 3522 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Upconversion Luminescence of Silica–Calcia Nanoparticles Co-doped with Tm³⁺ and Yb³⁺ Ions

by Katarzyna Halubek-Gluchowska, Damian Szymański, Thi Ngoc Lam Tran, Maurizio Ferrari and Anna Lukowiak

Materials 2021, 14(4), 937; https://doi.org/10.3390/ma14040937 - 16 Feb 2021

Cited by 27 | Viewed by 4006

Abstract

Looking for upconverting biocompatible nanoparticles, we have prepared by the sol–gel method, silica–calcia glass nanopowders doped with different concentration of Tm³⁺ and Yb³⁺ ions (Tm³⁺ from 0.15 mol% up to 0.5 mol% and Yb³⁺ from 1 mol% up to [...] Read more.

Looking for upconverting biocompatible nanoparticles, we have prepared by the sol–gel method, silica–calcia glass nanopowders doped with different concentration of Tm³⁺ and Yb³⁺ ions (Tm³⁺ from 0.15 mol% up to 0.5 mol% and Yb³⁺ from 1 mol% up to 4 mol%) and characterized their structure, morphology, and optical properties. X-ray diffraction patterns indicated an amorphous phase of the silica-based glass with partial crystallization of samples with a higher content of lanthanides ions. Transmission electron microscopy images showed that the average size of particles decreased with increasing lanthanides content. The upconversion (UC) emission spectra and fluorescence lifetimes were registered under near infrared excitation (980 nm) at room temperature to study the energy transfer between Yb³⁺ and Tm³⁺ at various active ions concentrations. Characteristic emission bands of Tm³⁺ ions in the range of 350 nm to 850 nm were observed. To understand the mechanism of Yb³⁺–Tm³⁺ UC energy transfer in the SiO₂–CaO powders, the kinetics of luminescence decays were studied. Full article

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

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11 pages, 2254 KB

Open AccessEditor’s ChoiceArticle

Dynamic Crosslinking: An Efficient Approach to Fabricate Epoxy Vitrimer

by Yin Ran, Ling-Ji Zheng and Jian-Bing Zeng

Materials 2021, 14(4), 919; https://doi.org/10.3390/ma14040919 - 15 Feb 2021

Cited by 23 | Viewed by 4808

Abstract

Epoxy vitrimers with reprocessability, recyclability, and a self-healing performance have attracted increasingly attention, but are usually fabricated through static curing procedures with a low production efficiency. Herein, we report a new approach to fabricate an epoxy vitrimer by dynamic crosslinking in a torque [...] Read more.

Epoxy vitrimers with reprocessability, recyclability, and a self-healing performance have attracted increasingly attention, but are usually fabricated through static curing procedures with a low production efficiency. Herein, we report a new approach to fabricate an epoxy vitrimer by dynamic crosslinking in a torque rheometer, using diglycidyl ether of bisphenol A and sebacic acid as the epoxy resin and curing agent, respectively, in the presence of zinc acetylacetonate as the transesterification catalyst. The optimal condition for fabricating the epoxy vitrimer (EVD) was dynamic crosslinking at 180 °C for ~11 min. A control epoxy vitrimer (EVS) was prepared by static curing at 180 °C for ~11 min. The structure, properties, and stress relaxation of the EVD and EVS were comparatively investigated in detail. The EVS did not cure completely during static curing, as evidenced by the continuously increasing gel fraction when subjected to compression molding. The gel fraction of the EVD did not change with compression molding at the same condition. The physical, mechanical, and stress relaxation properties of the EVD prepared by dynamic crosslinking were comparable to those of the EVS fabricated by static curing, despite small differences in the specific property parameters. This study demonstrated that dynamic crosslinking provides a new technique to efficiently fabricate an epoxy vitrimer. Full article

(This article belongs to the Special Issue Self-Healing Materials and Devices)

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15 pages, 5431 KB

Open AccessEditor’s ChoiceArticle

Stress-Dependent Particle Interactions of Magnesium Aluminometasilicates as Their Performance Factor in Powder Flow and Compaction Applications

by Pavlína Komínová, Lukáš Kulaviak and Petr Zámostný

Materials 2021, 14(4), 900; https://doi.org/10.3390/ma14040900 - 14 Feb 2021

Cited by 9 | Viewed by 3322

Abstract

In the pharmaceutical industry, silicates are commonly used excipients with different application possibilities. They are especially utilized as glidants in low concentrations, but they can be used in high concentrations as porous carriers and coating materials in oral solid drug delivery systems. The [...] Read more.

In the pharmaceutical industry, silicates are commonly used excipients with different application possibilities. They are especially utilized as glidants in low concentrations, but they can be used in high concentrations as porous carriers and coating materials in oral solid drug delivery systems. The desirable formulations of such systems must exhibit good powder flow but also good compactibility, which brings opposing requirements on inter-particle interactions. Since magnesium aluminometasilicates (MAS) are known for their interesting flow behavior reported as “negative cohesivity” yet they can be used as binders for tablet compression, the objective of this experimental study was to investigate their particle interactions within a broad range of mechanical stress from several kPa to hundreds of MPa. Magnesium aluminometasilicate (Neusilin^® US2 and Neusilin^® S2)-microcrystalline cellulose (Avicel^® PH102) physical powder mixtures with varying silicate concentrations were prepared and examined during their exposure to different pressures using powder rheology and compaction analysis. The results revealed that MAS particles retain their repulsive character and small contact surface area under normal conditions. If threshold pressure is applied, the destruction of MAS particles and formation of new surfaces leading to particle interactions are observed. The ability of MAS particles to form interactions intensifies with increasing pressure and their amount in a mixture. This “function switching” makes MAS suitable for use as multifunctional excipients since they can act as a glidant or a binder depending on the applied pressure. Full article

(This article belongs to the Special Issue Silica and Silica-based Materials for Biotechnology, Polymer Composites and Environmental Protection)

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20 pages, 5243 KB

Open AccessEditor’s ChoiceArticle

Research on the Thermal Properties of Fireplace Concrete Materials Containing Various Mineral Aggregates Enriched by Organic and Inorganic Fibers

by Agata Stempkowska, Joanna Mastalska-Popławska, Piotr Izak, Łukasz Wójcik, Tomasz Gawenda and Marzena Karbowy

Materials 2021, 14(4), 904; https://doi.org/10.3390/ma14040904 - 14 Feb 2021

Cited by 4 | Viewed by 2407

Abstract

This work presents a summary of research on concrete fireplace materials made of various mineral aggregates and enriched with steel and organic fibers. To determine the optimal applications of such concretes, their ability to accumulate heat and their other physicochemical parameters were tested [...] Read more.

This work presents a summary of research on concrete fireplace materials made of various mineral aggregates and enriched with steel and organic fibers. To determine the optimal applications of such concretes, their ability to accumulate heat and their other physicochemical parameters were tested and analyzed. Studies on the behavior of concrete materials during cooling are reported, and the ability of such materials to accumulate heat is evaluated using calculations. In addition, tests were performed on the loss of mass during heating, as well as on the mechanical bending strength and microstructures of these materials. Studies have shown that the behavior of concrete materials at high temperatures can be modified and adapted for specific purposes. The addition of fibers to concrete improves both the mechanical properties of mortars and the heat flow in concrete materials. Full article

(This article belongs to the Special Issue Research and Development of Modified Building Materials)

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29 pages, 6545 KB

Open AccessEditor’s ChoiceArticle

Multiphysics and Multiscale Modeling of Coupled Transport of Chloride Ions in Concrete

by Amit Jain and Bora Gencturk

Materials 2021, 14(4), 885; https://doi.org/10.3390/ma14040885 - 13 Feb 2021

Cited by 10 | Viewed by 3034

Abstract

Chloride ions (Cl⁻)-induced corrosion is one of the main degradation mechanisms in reinforced concrete (RC) structures. In most situations, the degradation initiates with the transport of Cl⁻ from the surface of the concrete towards the reinforcing steel. The accumulation of [...] Read more.

Chloride ions (Cl⁻)-induced corrosion is one of the main degradation mechanisms in reinforced concrete (RC) structures. In most situations, the degradation initiates with the transport of Cl⁻ from the surface of the concrete towards the reinforcing steel. The accumulation of Cl⁻ at the steel-concrete interface could initiate reinforcement corrosion once a threshold Cl⁻ concentration is achieved. An accurate numerical model of the Cl⁻ transport in concrete is required to predict the corrosion initiation in RC structures. However, existing numerical models lack a representation of the heterogenous concrete microstructure resulting from the varying environmental conditions and the indirect effect of time dependent temperature and relative humidity (RH) on the water adsorption and Cl⁻ binding isotherms. In this study, a numerical model is developed to study the coupled transport of Cl⁻ with heat, RH and oxygen (O₂) into the concrete. The modeling of the concrete microstructure is performed using the Virtual Cement and Concrete Testing Laboratory (VCCTL) code developed by the U.S. National Institute of Standards and Technology (NIST). The concept of equivalent maturation time is utilized to eliminate the limitation of simulating concrete microstructure using VCCTL in specific environmental conditions such as adiabatic. Thus, a time-dependent concrete microstructure, which depends on the hydration reactions coupled with the temperature and RH of the environment, is achieved to study the Cl⁻ transport. Additionally, Cl⁻ binding isotherms, which are a function of the pH of the concrete pore solution, Cl⁻ concentration, and weight fraction of mono-sulfate aluminate (AFm) and calcium-silicate-hydrate (C-S-H), obtained from an experimental study by the same authors are utilized to account for the Cl⁻ binding of cement hydration products. The temperature dependent RH diffusion was considered to account for the transport of Cl⁻ with moisture transport. The temperature and RH diffusion in the concrete domain, composite theory, and Cl⁻ binding and water adsorption isotherms are used in combination, to estimate the ensuing Cl⁻ diffusion field within the concrete. The coupled transport process of heat, RH, Cl⁻, and O₂ is implemented in the Multiphysics Object-Oriented Simulation Environment (MOOSE) developed by the U.S. Idaho National Laboratory (INL). The model was verified and validated using data from multiple experimental studies with different concrete mixture proportions, curing durations, and environmental conditions. Additionally, a sensitivity analysis was performed to identify that the water-to-cement (w/c) ratio, the exposure duration, the boundary conditions: temperature, RH, surface Cl⁻ concentration, Cl⁻ diffusion coefficient in the capillary water, and the critical RH are the important parameters that govern the Cl⁻ transport in RC structures. In a case study, the capabilities of the developed numerical model are demonstrated by studying the complex 2D diffusion of Cl⁻ in a RC beam located in two different climatic regions: warm and humid weather in Galveston, Texas, and cold and dry weather in North Minnesota, Minnesota, subjected to time varying temperature, RH, and surface Cl⁻ concentrations. Full article

(This article belongs to the Special Issue Advances in Construction and Building Materials)

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30 pages, 2017 KB

Open AccessEditor’s ChoiceArticle

Numerically Exploring the Potential of Abating the Energy Flow Peaks through Tough, Single Network Hydrogel Vibration Isolators with Chemical and Physical Cross-Links

by Leif Kari

Materials 2021, 14(4), 886; https://doi.org/10.3390/ma14040886 - 13 Feb 2021

Cited by 3 | Viewed by 3508

Abstract

Traditional vibration isolation systems, using natural rubber vibration isolators, display large peaks for the energy flow from the machine source and into the receiving foundation, at the unavoidable rigid body resonance frequencies. However, tough, doubly cross-linked, single polymer network hydrogels, with both chemical [...] Read more.

Traditional vibration isolation systems, using natural rubber vibration isolators, display large peaks for the energy flow from the machine source and into the receiving foundation, at the unavoidable rigid body resonance frequencies. However, tough, doubly cross-linked, single polymer network hydrogels, with both chemical and physical cross-links, show a high loss factor over a specific frequency range, due to the intensive adhesion–deadhesion activities of the physical cross-links. In this study, vibration isolators, made of this tough hydrogel, are theoretically applied in a realistic vibration isolation system, displaying several rigid body resonances and various energy flow transmission paths. A simulation model is developed, that includes a suitable stress–strain model, and shows a significant reduction of the energy flow peaks. In particular, the reduction is more than 30 times, as compared to the corresponding results using the natural rubber. Finally, it is shown that a significant reduction is possible, also without any optimization of the frequency for the maximum physical loss modulus. This is a clear advantage for polyvinyl alcohol hydrogels, that are somewhat missing the possibility to alter the frequency for the maximum physical loss, due to the physical cross-link system involved—namely, that of the borate esterification. Full article

(This article belongs to the Special Issue Advanced Materials for Aerospace Engineering)

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16 pages, 2770 KB

Open AccessEditor’s ChoiceReview

Fibre Bragg Grating Based Acoustic Emission Measurement System for Structural Health Monitoring Applications

by Sagar Jinachandran and Ginu Rajan

Materials 2021, 14(4), 897; https://doi.org/10.3390/ma14040897 - 13 Feb 2021

Cited by 49 | Viewed by 5079

Abstract

Fiber Bragg grating (FBG)-based acoustic emission (AE) detection and monitoring is considered as a potential and emerging technology for structural health monitoring (SHM) applications. In this paper, an overview of the FBG-based AE monitoring system is presented, and various technologies and methods used [...] Read more.

Fiber Bragg grating (FBG)-based acoustic emission (AE) detection and monitoring is considered as a potential and emerging technology for structural health monitoring (SHM) applications. In this paper, an overview of the FBG-based AE monitoring system is presented, and various technologies and methods used for FBG AE interrogation systems are reviewed and discussed. Various commercial FBG AE sensing systems, SHM applications of FBG AE monitoring, and market potential and recent trends are also discussed. Full article

(This article belongs to the Special Issue Recent Advances in Photonic Sensors)

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10 pages, 2254 KB

Open AccessEditor’s ChoiceArticle

Dentin Phosphophoryn-Derived Peptide Promotes Odontoblast Differentiation In Vitro and Dentin Regeneration In Vivo

by Bayarchimeg Altankhishig, Mohammad Ali Akbor Polan, Youjing Qiu, Md Riasat Hasan and Takashi Saito

Materials 2021, 14(4), 874; https://doi.org/10.3390/ma14040874 - 12 Feb 2021

Cited by 7 | Viewed by 2692

Abstract

The purpose of the present study was to investigate the effect of a peptide (i.e., SESDNNSSSRGDASYNSDES) derived from dentin phosphophoryn (DPP) with arginine-glycine-aspartic acid (RGD) motifs on odontoblast differentiation in vitro and to compare it with calcium hydroxide—a material used conventionally for vital [...] Read more.

The purpose of the present study was to investigate the effect of a peptide (i.e., SESDNNSSSRGDASYNSDES) derived from dentin phosphophoryn (DPP) with arginine-glycine-aspartic acid (RGD) motifs on odontoblast differentiation in vitro and to compare it with calcium hydroxide—a material used conventionally for vital pulp therapy—in terms of reparative dentin formation and pulp inflammation in vivo. Alkaline phosphatase activity assay and alizarin red S staining were performed to evaluate odontoblast-differentiation in cell culturing experiments. To observe the reparative dentin formation and pulp inflammation animal experiment was performed and examined by histological methods. The difference between the experimental group and the control group was analyzed statistically using a one-way ANOVA test. The results revealed that the DPP-derived RGD-containing peptide triggered odontoblast differentiation and mineralization in vitro. In rats undergoing direct pulp capping, the DPP-derived RGD-containing peptide was found to induce intensively formed reparative dentin with high compactness at week 4. On histological and morphometrical examinations, a smaller degree of pulpitis was observed in the specimens treated with the peptide than in those treated with calcium hydroxide. This study suggests that the DPP-derived RGD-containing peptide is a biocompatible, biodegradable and bioactive material for dentin regeneration. Full article

(This article belongs to the Special Issue Current Developments in Additive Manufacturing for Tissue Engineering and Regenerative Medicine)

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19 pages, 3824 KB

Open AccessEditor’s ChoiceArticle

A Comparative Analysis of Laser Additive Manufacturing of High Layer Thickness Pure Ti and Inconel 718 Alloy Materials Using Finite Element Method

by Sapam Ningthemba Singh, Sohini Chowdhury, Yadaiah Nirsanametla, Anil Kumar Deepati, Chander Prakash, Sunpreet Singh, Linda Yongling Wu, Hongyu Y. Zheng and Catalin Pruncu

Materials 2021, 14(4), 876; https://doi.org/10.3390/ma14040876 - 12 Feb 2021

Cited by 28 | Viewed by 4750

Abstract

Investigation of the selective laser melting (SLM) process, using finite element method, to understand the influences of laser power and scanning speed on the heat flow and melt-pool dimensions is a challenging task. Most of the existing studies are focused on the study [...] Read more.

Investigation of the selective laser melting (SLM) process, using finite element method, to understand the influences of laser power and scanning speed on the heat flow and melt-pool dimensions is a challenging task. Most of the existing studies are focused on the study of thin layer thickness and comparative study of same materials under different manufacturing conditions. The present work is focused on comparative analysis of thermal cycles and complex melt-pool behavior of a high layer thickness multi-layer laser additive manufacturing (LAM) of pure Titanium (Ti) and Inconel 718. A transient 3D finite-element model is developed to perform a quantitative comparative study on two materials to examine the temperature distribution and disparities in melt-pool behaviours under similar processing conditions. It is observed that the layers are properly melted and sintered for the considered process parameters. The temperature and melt-pool increases as laser power move in the same layer and when new layers are added. The same is observed when the laser power increases, and opposite is observed for increasing scanning speed while keeping other parameters constant. It is also found that Inconel 718 alloy has a higher maximum temperature than Ti material for the same process parameter and hence higher melt-pool dimensions. Full article

(This article belongs to the Special Issue Modeling, Simulation and Data Processing for Additive Manufacturing)

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15 pages, 3130 KB

Open AccessEditor’s ChoiceArticle

Preparation and Characterization of Nanoparticle-Doped Polymer Inclusion Membranes. Application to the Removal of Arsenate and Phosphate from Waters

by Enriqueta Anticó, Ruben Vera, Francisco Vázquez, Clàudia Fontàs, Changyong Lu and Josep Ros

Materials 2021, 14(4), 878; https://doi.org/10.3390/ma14040878 - 12 Feb 2021

Cited by 18 | Viewed by 3136

Abstract

Nanoparticle-doped polymer inclusion membranes (NP-PIMs) have been prepared and characterized as new materials for the removal of arsenate and phosphate from waters. PIMs are made of a polymer, cellulose triacetate (CTA), and an extractant, which interacts with the compound of interest. We have [...] Read more.

Nanoparticle-doped polymer inclusion membranes (NP-PIMs) have been prepared and characterized as new materials for the removal of arsenate and phosphate from waters. PIMs are made of a polymer, cellulose triacetate (CTA), and an extractant, which interacts with the compound of interest. We have used the ionic liquid (IL) trioctylmethylammonium chloride (Aliquat 336) as the extractant and have investigated how the addition of nanoparticles can modify membrane properties. To this end, inorganic nanoparticles, such as ferrite (Fe₃O₄), SiO₂ and TiO₂, and multiwalled carbon nanotubes (MWCNTs), were blended with the polymer/extractant mixture. Scanning electron microscopy (SEM), infrared spectroscopy (FT-IR), and contact angle measurements have been used to characterize the material. Moreover, PIM stability was checked by measuring the mass loss during the experiments. Since Aliquat 336 acts as an anion exchanger, the NP-PIMs have been explored in two different applications: (i) as sorbent materials for the extraction of arsenate and phosphate anions; (ii) as an organic phase for the separation of arsenate and phosphate in a three-phase system. The presence of oleate-coated ferrite NP in the PIM formulation represents an improvement in the efficiency of NP-PIMs used as sorbents; nevertheless, a decrease in the transport efficiency for arsenate but not for phosphate was obtained. The ease with which the NP-PIMs are prepared suggests good potential for future applications in the treatment of polluted water. Future work will address three main aspects: firstly, the implementation of the Fe₃O₄-PIMs for the removal of As(V) in real water containing complex matrices; secondly, the study of phosphate recovery with other cell designs that allow large volumes of contaminated water to be treated; and thirdly, the investigation of the role of MWCNTs in PIM stability. Full article

(This article belongs to the Special Issue New Materials and Technologies for Wastewater Treatment)

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24 pages, 3616 KB

Open AccessEditor’s ChoiceArticle

Assessment of Mechanical and Thermal Properties of Hemp-Lime Mortar

by Eliana Parcesepe, Rosa Francesca De Masi, Carmine Lima, Gerardo Maria Mauro, Maria Rosaria Pecce and Giuseppe Maddaloni

Materials 2021, 14(4), 882; https://doi.org/10.3390/ma14040882 - 12 Feb 2021

Cited by 25 | Viewed by 4349

Abstract

The use of renewable and natural materials characterized by the low environmental impact is nowadays a key issue for the sustainable development of the construction industry. For this reason, the interest for natural fibers, to be used as reinforcement in composites as an [...] Read more.

The use of renewable and natural materials characterized by the low environmental impact is nowadays a key issue for the sustainable development of the construction industry. For this reason, the interest for natural fibers, to be used as reinforcement in composites as an alternative to other fibers, is continuously growing. In this paper, the use of hemp for reinforcing lime mortar used as plaster is considered with a multidisciplinary approach, taking into consideration the structural and thermal performance. Natural fibers have several advantages compared to industrial ones, such as low cost, low environmental impact, biodegradability, renewable nature. Moreover, these can show remarkable mechanical performance in relation to specific weight, and sometimes, as in the case of hemp fibers, these can improve the thermal insulation capacity of the plaster. However, the experimental results on the mechanical features are still lacking, especially to assess their durability, and the variability of thermal parameters with the mechanical characteristics. Therefore, this paper proposes an experimental program, developed at Laboratory of Materials and Structures (LAMAS) of the University of Sannio (Italy), aimed at investigating the main mechanical properties (compression strength, flexural strength) of lime mortar reinforced by hemp fibers and subjected to various environmental exposures and aging processes. The characterization is completed with the measurement for the produced samples of the thermal conductivity by means of the standardized guarded hot plate technique. Full article

(This article belongs to the Special Issue State-of-the-Art Construction Materials in Italy: Challenges for Sustainable, Safe, and Resilient Buildings)

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18 pages, 5512 KB

Open AccessEditor’s ChoiceArticle

A Facile and Scalable Approach in the Fabrication of Tailored 3D Graphene Foam via Freeze Drying

by Tony Thomas and Arvind Agarwal

Materials 2021, 14(4), 864; https://doi.org/10.3390/ma14040864 - 11 Feb 2021

Cited by 20 | Viewed by 5100

Abstract

One of the challenges in the processing of advanced composite materials with 2D reinforcement is their extensive agglomeration in the matrix. 3D architecture of 2D graphene sheets into a Graphene Foam (GrF) assembly has emerged as an effective way to overcome agglomeration. The [...] Read more.

One of the challenges in the processing of advanced composite materials with 2D reinforcement is their extensive agglomeration in the matrix. 3D architecture of 2D graphene sheets into a Graphene Foam (GrF) assembly has emerged as an effective way to overcome agglomeration. The highly reticulated network of branches and nodes of GrF offers a seamless pathway for photon and electron conduction in the matrix along with improved mechanical properties. 3D GrF nano-filler is often fabricated by chemical vapor deposition (CVD) technique, which demands high energy, slow deposition rate, and restricting production to small scale. This work highlights freeze-drying (FD) technique to produce 3D graphene nanoplatelets (GNP) foam with a similar hierarchical structure to the CVD GrF. The FD technique using water as the main chemical in 3D GNP foam production is an added advantage. The flexibility of the FD in producing GNP foams of various pore size and morphology is elucidated. The simplicity with which one can engineer thermodynamic conditions to tailor the pore shape and morphology is presented here by altering the GNP solid loading and mold geometry. The FD 3D GNP foam is mechanically superior to CVD GrF as it exhibited 1280 times higher elastic modulus. However, thermal diffusivity of the FD GNP foam is almost 0.5 times the thermal diffusivity of the CVD GrF due to the defects in GNP particles and pore architecture. The versatility in GNP foam scalability and compatibility to form foam of other 1D and 2D material systems (e.g., carbon nanotubes, boron nitride nanotubes, and boron nitride nanoplatelets) brings a unique dimensionality to FD as an advanced engineering foam development process. Full article

(This article belongs to the Special Issue Graphene Foam Based Composites)

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3 pages, 170 KB

Open AccessEditor’s ChoiceEditorial

Special Issue: “Microstructures and Durability of Cement-Based Materials”

by Jeong Gook Jang and Solmoi Park

Materials 2021, 14(4), 866; https://doi.org/10.3390/ma14040866 - 11 Feb 2021

Cited by 5 | Viewed by 2027

Abstract

Cement-based materials play an irreplaceable role in building and sustaining our society by meeting the performance demand imposed on structures and sustainability. Cement-based materials are no longer limited to derivatives of Portland cement, and appreciate a wider range of binders that come from [...] Read more.

Cement-based materials play an irreplaceable role in building and sustaining our society by meeting the performance demand imposed on structures and sustainability. Cement-based materials are no longer limited to derivatives of Portland cement, and appreciate a wider range of binders that come from various origins. It is therefore of utmost importance for understanding and expanding the relevant knowledge on their microstructure and likely durability performance. This Special Issue “Microstructures and Durability of Cement-Based Materials” presents recent studies reporting microstructural and durability investigation revealing the characteristics of cement-based materials. Full article

(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)

11 pages, 4488 KB

Open AccessEditor’s ChoiceArticle

Thermal Nonlinear Klein–Gordon Equation for Nano-/Micro-Sized Metallic Particle–Attosecond Laser Pulse Interaction

by Mihai Oane, Muhammad Arif Mahmood, Andrei C. Popescu, Alexandra Bănică, Carmen Ristoscu and Ion N. Mihăilescu

Materials 2021, 14(4), 857; https://doi.org/10.3390/ma14040857 - 10 Feb 2021

Cited by 1 | Viewed by 2609

Abstract

In this study, a rigorous analytical solution to the thermal nonlinear Klein–Gordon equation in the Kozłowski version is provided. The Klein–Gordon heat equation is solved via the Zhukovsky “state-of-the-art” mathematical techniques. Our study can be regarded as an initial approximation of attosecond laser–particle [...] Read more.

In this study, a rigorous analytical solution to the thermal nonlinear Klein–Gordon equation in the Kozłowski version is provided. The Klein–Gordon heat equation is solved via the Zhukovsky “state-of-the-art” mathematical techniques. Our study can be regarded as an initial approximation of attosecond laser–particle interaction when the prevalent phenomenon is photon–electron interaction. The electrons interact with the laser beam, which means that the nucleus does not play a significant role in temperature distribution. The particle is supposed to be homogenous with respect to thermophysical properties. This theoretical approach could prove useful for the study of metallic nano-/micro-particles interacting with attosecond laser pulses. Specific applications for Au “nano” particles with a 50 nm radius and “micro” particles with 110, 130, 150, and 1000 nm radii under 100 attosecond laser pulse irradiation are considered. First, the cross-section is supposed to be proportional to the area of the particle, which is assumed to be a perfect sphere of radius R or a rotation ellipsoid. Second, the absorption coefficient is calculated using a semiclassical approach, taking into account the number of atoms per unit volume, the classical electron radius, the laser wavelength, and the atomic scattering factor (10 in case of Au), which cover all the basic aspects for the interaction between the attosecond laser and a nanoparticle. The model is applicable within the 100–2000 nm range. The main conclusion of the model is that for a range inferior to 1000 nm, a competition between ballistic and thermal phenomena occurs. For values in excess of 1000 nm, our study suggests that the thermal phenomena are dominant. Contrastingly, during the irradiation with fs pulses, this value is of the order of 100 nm. This theoretical model’s predictions could be soon confirmed with the new EU-ELI facilities in progress, which will generate pulses of 100 as at a 30 nm wavelength. Full article

(This article belongs to the Special Issue Materials Thermal Behavior during Laser or Electron Beam Irradiation)

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26 pages, 6859 KB

Open AccessEditor’s ChoiceArticle

Anticancer Molecular Mechanism of Protocatechuic Acid Loaded on Folate Coated Functionalized Graphene Oxide Nanocomposite Delivery System in Human Hepatocellular Carcinoma

by Kalaivani Buskaran, Saifullah Bullo, Mohd Zobir Hussein, Mas Jaffri Masarudin, Mohamad Aris Mohd Moklas and Sharida Fakurazi

Materials 2021, 14(4), 817; https://doi.org/10.3390/ma14040817 - 9 Feb 2021

Cited by 32 | Viewed by 3633

Abstract

Liver cancer is listed as the fifth-ranked cancer, responsible for 9.1% of all cancer deaths globally due to its assertive nature and poor survival rate. To overcome this obstacle, efforts have been made to ensure effective cancer therapy via nanotechnology utilization. Recent studies [...] Read more.

Liver cancer is listed as the fifth-ranked cancer, responsible for 9.1% of all cancer deaths globally due to its assertive nature and poor survival rate. To overcome this obstacle, efforts have been made to ensure effective cancer therapy via nanotechnology utilization. Recent studies have shown that functionalized graphene oxide (GO)-loaded protocatechuic acid has shown some anticancer activities in both passive and active targeting. The nanocomposites’ physicochemical characterizations were conducted. A lactate dehydrogenase experiment was conducted to estimate the severity of cell damage. Subsequently, a clonogenic assay was carried out to examine the colony-forming ability during long-term exposure of the nanocomposites. The Annexin V/ propidium iodide analysis showed that nanocomposites induced late apoptosis in HepG2 cells. Following the intervention of nanocomposites, cell cycle arrest was ascertained at G2/M phase. There was depolarization of mitochondrial membrane potential and an upregulation of reactive oxygen species when HepG2 cells were induced by nanocomposites. Finally, the proteomic profiling array and quantitative reverse transcription polymerase chain reaction revealed the expression of pro-apoptotic and anti-apoptotic proteins induced by graphene oxide conjugated PEG loaded with protocatechuic acid drug folic acid coated nanocomposite (GOP–PCA–FA) in HepG2 cells. In conclusion, GOP–PCA–FA nanocomposites treated HepG2 cells exhibited significant anticancer activities with less toxicity compared to pristine protocatechuic acid and GOP–PCA nanocomposites, due to the utilization of a folic acid-targeting nanodrug delivery system. Full article

(This article belongs to the Special Issue Nanomaterials Design towards Biomedical Applications)

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19 pages, 4697 KB

Open AccessEditor’s ChoiceArticle

Between-the-Holes Cryogenic Cooling of the Tool in Hole-Making of Ti-6Al-4V and CFRP

by Asif Iqbal, Guolong Zhao, Juliana Zaini, Munish Kumar Gupta, Muhammad Jamil, Ning He, Malik Muhammad Nauman, Tadeusz Mikolajczyk and Danil Yurievich Pimenov

Materials 2021, 14(4), 795; https://doi.org/10.3390/ma14040795 - 8 Feb 2021

Cited by 39 | Viewed by 3360

Abstract

Lightweight materials are finding plentiful applications in various engineering sectors due to their high strength-to-weight ratios. Hole-making is an inevitable requirement for their structural applications, which is often marred by thermal damages of the drill causing unacceptable shortening of tool life. Efficient cooling [...] Read more.

Lightweight materials are finding plentiful applications in various engineering sectors due to their high strength-to-weight ratios. Hole-making is an inevitable requirement for their structural applications, which is often marred by thermal damages of the drill causing unacceptable shortening of tool life. Efficient cooling of the tool is a prime requirement for enhancing the process viability. The current work presents a novel technique of cooling only the twist drill between drilling of holes with no effect of the applied cryogenic coolant transferred to the work material. The technique is applied in the drilling of two commonly used high-strength lightweight materials: carbon fibers reinforced polymer (CFRP) and an alloy of titanium (Ti-6Al-4V). The efficacy of the cooling approach is compared with those of conventionally applied continuous cryogenic cooling and no-cooling. The effectiveness is quantified in terms of tool wear, thrust force, hole quality, specific cutting energy, productivity, and consumption of the cryogenic fluid. The experimental work leads to a finding that between-the-holes cryogenic cooling possesses a rich potential in curbing tool wear, reducing thrust force and specific energy consumption, and improving hole quality in drilling of CFRP. Regarding the titanium alloy, it yields a much better surface finish and lesser consumption of specific cutting energy. Full article

(This article belongs to the Special Issue Additive and Subtractive Manufacturing of Advanced Materials: Applications, Future Trends and Perspectives of Industry 4.0)

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14 pages, 4374 KB

Open AccessEditor’s ChoiceArticle

Effect of Moisture Distribution on Velocity and Waveform of Ultrasonic-Wave Propagation in Mortar

by Shinichiro Okazaki, Hiroma Iwase, Hiroyuki Nakagawa, Hidenori Yoshida and Ryosuke Hinei

Materials 2021, 14(4), 790; https://doi.org/10.3390/ma14040790 - 7 Feb 2021

Cited by 10 | Viewed by 2722

Abstract

Considering that the ultrasonic method is applied for the quality evaluation of concrete, this study experimentally and numerically investigates the effect of inhomogeneity caused by changes in the moisture content of concrete on ultrasonic wave propagation. The experimental results demonstrate that the propagation [...] Read more.

Considering that the ultrasonic method is applied for the quality evaluation of concrete, this study experimentally and numerically investigates the effect of inhomogeneity caused by changes in the moisture content of concrete on ultrasonic wave propagation. The experimental results demonstrate that the propagation velocity and amplitude of the ultrasonic wave vary for different moisture content distributions in the specimens. In the analytical study, the characteristics obtained experimentally are reproduced by modeling a system in which the moisture content varies between the surface layer and interior of concrete. Full article

(This article belongs to the Special Issue Research on Non-destructive Testing in Civil Engineering Materials)

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16 pages, 7606 KB

Open AccessEditor’s ChoiceArticle

Effects of Ti and Cu Addition on Inclusion Modification and Corrosion Behavior in Simulated Coarse-Grained Heat-Affected Zone of Low-Alloy Steels

by Yuhang Wang, Xian Zhang, Wenzhui Wei, Xiangliang Wan, Jing Liu and Kaiming Wu

Materials 2021, 14(4), 791; https://doi.org/10.3390/ma14040791 - 7 Feb 2021

Cited by 12 | Viewed by 2788

Abstract

In this paper, the effects of Ti and Cu addition on inclusion modification and corrosion behavior in the simulated coarse-grained heat-affected zone (CGHAZ) of low-alloy steels were investigated by using in-situ scanning vibration electrode technique (SVET), scanning electron microscope/energy-dispersive X-ray spectroscopy (SEM/EDS), and [...] Read more.

In this paper, the effects of Ti and Cu addition on inclusion modification and corrosion behavior in the simulated coarse-grained heat-affected zone (CGHAZ) of low-alloy steels were investigated by using in-situ scanning vibration electrode technique (SVET), scanning electron microscope/energy-dispersive X-ray spectroscopy (SEM/EDS), and electrochemical workstation. The results demonstrated that the complex inclusions formed in Cu-bearing steel were (Ti, Al, Mn)-O_x-MnS, which was similar to that in base steel. Hence, localized corrosion was initiated by the dissolution of MnS. However, the main inclusions in Ti-bearing steels were modified into TiN-Al₂O₃/TiN, and the localized corrosion was initiated by the dissolution of high deformation region at inclusion/matrix interface. With increased interface density of inclusions in steels, the corrosion rate increased in the following order: Base steel ≈ Cu-bearing steel < Ti-bearing steel. Owing to the existence of Cu-enriched rust layer, the Cu-bearing steel shows a similar corrosion resistance with base steel. Full article

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

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10 pages, 1734 KB

Open AccessEditor’s ChoiceArticle

Resins for Frontal Photopolymerization: Combining Depth-Cure and Tunable Mechanical Properties

by Catharina Ebner, Julia Mitterer, Joamin Gonzalez-Gutierrez, Gisbert Rieß and Wolfgang Kern

Materials 2021, 14(4), 743; https://doi.org/10.3390/ma14040743 - 5 Feb 2021

Cited by 11 | Viewed by 3236

Abstract

Photopolymerization has undergone significant development in recent years. It enables fast and easy processing of materials with customized properties and allows precise printing of complex surface geometries. Nevertheless, photopolymerization is mainly applied to cure thin films since the low curing depth limits the [...] Read more.

Photopolymerization has undergone significant development in recent years. It enables fast and easy processing of materials with customized properties and allows precise printing of complex surface geometries. Nevertheless, photopolymerization is mainly applied to cure thin films since the low curing depth limits the fast production of large volumes. Frontal photopolymerization (FPP) is suitable to overcome these limitations so that curing of centimeter-thick (meth)acrylic layers can be accomplished within minutes by light induction only. Prerequisites, however, are the low optical density of the resin and bleaching ability of the photoinitiator. To date, tailored FPP-resins are not commercially available. This study discusses the potential of long-chain polyether dimethacrylates, offering high-temperature resistance and low optical density, as crosslinkers in photobleaching resins and investigates the mechanical properties of photofrontally-cured copolymers. Characteristics ranging from ductile to hard and brittle are observed in tensile tests, demonstrating that deep curing and versatile material properties are achieved with FPP. Analyzed components display uniform polymerization over a depth of four centimeters in Fourier transform infrared spectroscopy and swelling tests. Full article

(This article belongs to the Special Issue Structure Property Relationship of Polymeric Materials)

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23 pages, 5366 KB

Open AccessEditor’s ChoiceArticle

Mechanical Properties of Hardened 3D Printed Concretes and Mortars—Development of a Consistent Experimental Characterization Strategy

by Maximilian Meurer and Martin Classen

Materials 2021, 14(4), 752; https://doi.org/10.3390/ma14040752 - 5 Feb 2021

Cited by 55 | Viewed by 6317

Abstract

Today, it is already foreseeable that additive manufacturing of mortar and concrete has groundbreaking potential and will revolutionize or at least fundamentally change the way we build. In recent years, 3D concrete printing (3DCP) with extrusion-based deposition methods has been pushed forward by [...] Read more.

Today, it is already foreseeable that additive manufacturing of mortar and concrete has groundbreaking potential and will revolutionize or at least fundamentally change the way we build. In recent years, 3D concrete printing (3DCP) with extrusion-based deposition methods has been pushed forward by a growing research community. Albeit being regarded one of the most promising innovations in construction industry, a consistent characterization methodology for assessing the constitutive behavior of 3D printed, hardened cementitious materials is missing, so far, which hinders its widespread use in engineering practice. The major objective of this paper is to fill this gap by developing a new experimental framework that can thoroughly describe the mechanical properties of 3D printed cementitious materials. Based on both a review of state-of-the-art test setups and a comprehensive experimental campaign, the present paper proposes a set of easy-to-use experimental methods that allow us to assess flexural, tensile, shear and compressive strength as well as fracture energy of 3D printed concretes and mortars in a reliable and reproducible manner. The experimental results revealed anisotropic material behavior for flexural, tensile, shear and compressive loading. Furthermore, they confirm that interval time (time gap between deposition of subsequent layers) has a crucial effect on investigated material properties leading to a severe reduction in strength and fracture energy for longer interval times. Full article

(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)

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13 pages, 2445 KB

Open AccessEditor’s ChoiceArticle

pH-Sensitive Dairy-Derived Hydrogels with a Prolonged Drug Release Profile for Cancer Treatment

by Oksana A. Mayorova, Ben C. N. Jolly, Roman A. Verkhovskii, Valentina O. Plastun, Olga A. Sindeeva and Timothy E. L. Douglas

Materials 2021, 14(4), 749; https://doi.org/10.3390/ma14040749 - 5 Feb 2021

Cited by 13 | Viewed by 3055

Abstract

A novel versatile biocompatible hydrogel of whey protein isolate (WPI) and two types of tannic acid (TAs) was prepared by crosslinking of WPI with TAs in a one-step method at high temperature for 30 min. WPI is one common protein-based preparation which is [...] Read more.

A novel versatile biocompatible hydrogel of whey protein isolate (WPI) and two types of tannic acid (TAs) was prepared by crosslinking of WPI with TAs in a one-step method at high temperature for 30 min. WPI is one common protein-based preparation which is used for hydrogel formation. The obtained WPI-TA hydrogels were in disc form and retained their integrity after sterilization by autoclaving. Two TA preparations of differing molecular weight and chemical structure were compared, namely a polygalloyl glucose-rich extract-ALSOK 02-and a polygalloyl quinic acid-rich extract-ALSOK 04. Hydrogel formation was observed for WPI solutions containing both preparations. The swelling characteristics of hydrogels were investigated at room temperature at different pH values, namely 5, 7, and 9. The swelling ability of hydrogels was independent of the chemical structure of the added TAs. A trend of decrease of mass increase (MI) in hydrogels was observed with an increase in the TA/WPI ratio compared to the control WPI hydrogel without TA. This dependence (a MI decrease-TA/WPI ratio) was observed for hydrogels with different types of TA both in neutral and acidic conditions (pH 5.7). Under alkaline conditions (pH 9), negative values of swelling were observed for all hydrogels with a high content of TAs and were accompanied by a significant release of TAs from the hydrogel network. Our studies have shown that the release of TA from hydrogels containing ALSOK04 is higher than from hydrogels containing ALSOK 02. Moreover, the addition of TAs, which display a strong anti-cancer effect, increases the cytotoxicity of WPI-TAs hydrogels against the Hep-2 human laryngeal squamous carcinoma (Hep-2 cells) cell line. Thus, WPI-TA hydrogels with prolonged drug release properties and cytotoxicity effect can be used as anti-cancer scaffolds. Full article

(This article belongs to the Special Issue Advances in Polymeric Materials for Biomedical Applications)

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17 pages, 6406 KB

Open AccessEditor’s ChoiceArticle

Adsorption of Pb(II) from Aqueous Solution by Mussel Shell-Based Adsorbent: Preparation, Characterization, and Adsorption Performance

by Quan Wang, Fangyuan Jiang, Xiao-Kun Ouyang, Li-Ye Yang and Yangguang Wang

Materials 2021, 14(4), 741; https://doi.org/10.3390/ma14040741 - 5 Feb 2021

Cited by 35 | Viewed by 4653

Abstract

As a natural biological adsorbent, shell powder is inexpensive, highly efficient, and does not leave any chemical residue; thus, it can be used to remove contaminants from water. In this study, we used mussel shells as a raw material to prepare an adsorbent. [...] Read more.

As a natural biological adsorbent, shell powder is inexpensive, highly efficient, and does not leave any chemical residue; thus, it can be used to remove contaminants from water. In this study, we used mussel shells as a raw material to prepare an adsorbent. Scanning electron microscopy was used to observe the surface morphology of the mussel shell powder before and after calcination, and X-ray diffraction measurements, Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller measurements were performed to analyze the structure and composition of calcined mussel shell powder. Characterization of the shell powder before and after calcination revealed a change from calcium carbonate to calcium oxide, as well as the formation of a surface porous structure. Using Pb(II) as a representative contaminant, various factors affecting the adsorption were explored, and the adsorption mechanism was analyzed. It was found that the adsorption is consistent with the Freundlich adsorption isotherm and the pseudo second-order model. The calcined mussel shell powder exhibits excellent adsorption for Pb(II), with an adsorption capacity reaching 102.04 mg/g. Full article

(This article belongs to the Special Issue Materials for Heavy Metals Removal from Waters)

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15 pages, 5427 KB

Open AccessEditor’s ChoiceArticle

High Temperature Behaviors of a Casting Nickel-Based Superalloy Used for 815 °C

by Jiangping Yu, Donghong Wang, Jingyang Chen, Changlin Yang, Xin Hao, Jianxin Zhou, Dayong Li, Da Shu, Chengbo Xiao and Yinghong Peng

Materials 2021, 14(4), 716; https://doi.org/10.3390/ma14040716 - 4 Feb 2021

Cited by 5 | Viewed by 2442

Abstract

The hot deformation behaviors of the SJTU-1 alloy, the high-throughput scanned casting Nickel-based superalloy, was investigated by compression test in the temperature range of 900 to 1200 °C and strain rate range of 0.1–0.001 s⁻¹. The hot processing map has been [...] Read more.

The hot deformation behaviors of the SJTU-1 alloy, the high-throughput scanned casting Nickel-based superalloy, was investigated by compression test in the temperature range of 900 to 1200 °C and strain rate range of 0.1–0.001 s⁻¹. The hot processing map has been constructed with the instability zone. At the beginning of hot deformation, the flow stress moves rapidly to the peak value with the increased strain rates. Meanwhile, the peak stress is decreased with the increased temperature at the same strain rates. However, the peak stress shows the same tendency with the strain rates at the same temperature. The optimum hot deformation condition was determined in the temperature range of 1000–1075 °C, and the strain rate range of 0.005–0.1 s⁻¹. The microstructure investigation indicates the strain rate significantly affects the characteristics of the microstructure. The deformation constitutive equation has also been discussed as well. Full article

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

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36 pages, 3645 KB

Open AccessEditor’s ChoiceOpinion

Whither Magnetic Hyperthermia? A Tentative Roadmap

by Irene Rubia-Rodríguez, Antonio Santana-Otero, Simo Spassov, Etelka Tombácz, Christer Johansson, Patricia De La Presa, Francisco J. Teran, María del Puerto Morales, Sabino Veintemillas-Verdaguer, Nguyen T. K. Thanh, Maximilian O. Besenhard, Claire Wilhelm, Florence Gazeau, Quentin Harmer, Eric Mayes, Bella B. Manshian, Stefaan J. Soenen, Yuanyu Gu, Ángel Millán, Eleni K. Efthimiadou, Jeff Gaudet, Patrick Goodwill, James Mansfield, Uwe Steinhoff, James Wells, Frank Wiekhorst and Daniel Ortega Show full author list Hide full author list

Materials 2021, 14(4), 706; https://doi.org/10.3390/ma14040706 - 3 Feb 2021

Cited by 112 | Viewed by 10620

Abstract

The scientific community has made great efforts in advancing magnetic hyperthermia for the last two decades after going through a sizeable research lapse from its establishment. All the progress made in various topics ranging from nanoparticle synthesis to biocompatibilization and in vivo testing [...] Read more.

The scientific community has made great efforts in advancing magnetic hyperthermia for the last two decades after going through a sizeable research lapse from its establishment. All the progress made in various topics ranging from nanoparticle synthesis to biocompatibilization and in vivo testing have been seeking to push the forefront towards some new clinical trials. As many, they did not go at the expected pace. Today, fruitful international cooperation and the wisdom gain after a careful analysis of the lessons learned from seminal clinical trials allow us to have a future with better guarantees for a more definitive takeoff of this genuine nanotherapy against cancer. Deliberately giving prominence to a number of critical aspects, this opinion review offers a blend of state-of-the-art hints and glimpses into the future of the therapy, considering the expected evolution of science and technology behind magnetic hyperthermia. Full article

(This article belongs to the Special Issue Magnetic Nanoparticles as High-Frequency Nano-Heaters)

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14 pages, 2305 KB

Open AccessEditor’s ChoiceArticle

Sizing and Topology Optimization of Trusses Using Genetic Algorithm

by Ingrid Delyová, Peter Frankovský, Jozef Bocko, Peter Trebuňa, Jozef Živčák, Barbara Schürger and Sára Janigová

Materials 2021, 14(4), 715; https://doi.org/10.3390/ma14040715 - 3 Feb 2021

Cited by 25 | Viewed by 3650

Abstract

Genetic algorithms are a robust method for a solution of wide variety optimization problems. It explores a big space of design variables in order to find the best solution. From the point of view of a user, the algorithm requires the encoding of [...] Read more.

Genetic algorithms are a robust method for a solution of wide variety optimization problems. It explores a big space of design variables in order to find the best solution. From the point of view of a user, the algorithm requires the encoding of design variables into the form of strings and the procedure of optimization uses them for optimization. Here, for the structural engineer, it is crucial to find the form of objective function including the constraints of the task and also to avoid critical states during the solution of structural responses. This paper presents the use of genetic algorithm for solving truss structures. The use of genetic algorithm approach is shown on three cases of truss structures. Full article

(This article belongs to the Special Issue Computational and Experimental Mechanics of Engineering Materials and Structures)

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19 pages, 3988 KB

Open AccessEditor’s ChoiceArticle

Compacted Anthropogenic Materials as Backfill for Buried Pipes

by Andrzej Głuchowski, Raimondas Šadzevičius, Rytis Skominas and Wojciech Sas

Materials 2021, 14(4), 717; https://doi.org/10.3390/ma14040717 - 3 Feb 2021

Cited by 4 | Viewed by 2371

Abstract

Buried pipe design requires knowledge about the fill to design the backfill structure. The interaction between the backfill envelope and the pipe impacts the structural performance of the buried pipe. The backfill material and compaction level respond to the backfill’s overall strength and, [...] Read more.

Buried pipe design requires knowledge about the fill to design the backfill structure. The interaction between the backfill envelope and the pipe impacts the structural performance of the buried pipe. The backfill material and compaction level respond to the backfill’s overall strength and, therefore, for pipe-soil interaction. The strength of backfill material is described in terms of modulus of soil reaction E’ and constrained modulus E_ode. As the E’ is an empirical parameter, the E_ode can be measured in the laboratory by performing the oedometer tests. In this study, we have performed extensive oedometric tests on five types of anthropogenic materials (AM). Three of them are construction and demolition materials (C–D materials) namely, recycled concrete aggregate (RCA), crushed brick (CB), and recycled asphalt pavement (RAP). Two of them are industrial solid wastes (ISW) namely, fly ash and bottom slag mix (FA + BS) and blast furnace slag (BFS). The results of the tests revealed that AM behaves differently from natural aggregates (NA). In general, the E_ode value for AM is lower than for NA with the same gradation. Despite that, some of AM may be used as NA substitute directly (RCA or BFS), some with special treatment like CB and some with extra compaction efforts like RAP or FA + BS. Full article

(This article belongs to the Special Issue Construction Circular Economy: Recycling Construction and Demolition Wastes)

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15 pages, 4456 KB

Open AccessEditor’s ChoiceArticle

Phase Formation and Thermal Stability of Reactively Sputtered YTaO₄–ZrO₂ Coatings

by Bastian Stelzer, Katrin Pingen, Marcus Hans, Damian M. Holzapfel, Silvia Richter, Joachim Mayer, Konda Gokuldoss Pradeep and Jochen M. Schneider

Materials 2021, 14(3), 692; https://doi.org/10.3390/ma14030692 - 2 Feb 2021

Cited by 7 | Viewed by 3771

Abstract

Y_(1−x)/2Ta_(1−x)/2Zr_xO₂ coatings with 0 to 44 mol% ZrO₂ were synthesized by sputtering. Phase-pure M’-YTaO₄ coatings were obtained at a substrate temperature of 900 °C. Alloying with ZrO₂ resulted in the growth of [...] Read more.

Y_(1−x)/2Ta_(1−x)/2Zr_xO₂ coatings with 0 to 44 mol% ZrO₂ were synthesized by sputtering. Phase-pure M’-YTaO₄ coatings were obtained at a substrate temperature of 900 °C. Alloying with ZrO₂ resulted in the growth of M’ along with t-Zr(Y,Ta)O₂ for ≤15 mol%, while for ≥28 mol%, ZrO₂ X-ray diffraction (XRD) phase-pure metastable t was formed, which may be caused by small grain sizes and/or kinetic limitations. The former phase region transformed into M’ and M and the latter to an M’ + t and M + t phase region upon annealing to 1300 and 1650 °C, respectively. In addition to M and t, T-YTa(Zr)O₄ phase fractions were observed at room temperature for ZrO₂ contents ≥28 mol% after annealing to 1650 °C. T phase fractions increased during in situ heating XRD at 80 °C. At 1650 °C, a reaction with the α-Al₂O₃ substrate resulted in the formation of AlTaO₄ and an Al-Ta-Y-O compound. Full article

(This article belongs to the Section Thin Films and Interfaces)

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14 pages, 3085 KB

Open AccessEditor’s ChoiceArticle

Biofunctionalization of Poly(lactide-co-glycolic acid) Using Potent NorA Efflux Pump Inhibitors Immobilized on Nanometric Alpha-Zirconium Phosphate to Reduce Biofilm Formation

by Monica Pica, Nicla Messere, Tommaso Felicetti, Stefano Sabatini, Donatella Pietrella and Morena Nocchetti

Materials 2021, 14(3), 670; https://doi.org/10.3390/ma14030670 - 1 Feb 2021

Cited by 5 | Viewed by 2621

Abstract

Polymeric composites, where bioactive species are immobilized on inorganic nanostructured matrix, have received considerable attention as surfaces able to reduce bacterial adherence, colonization, and biofilm formation in implanted medical devices. In this work, potent in-house S. aureus NorA efflux pump inhibitors (EPIs), belonging [...] Read more.

Polymeric composites, where bioactive species are immobilized on inorganic nanostructured matrix, have received considerable attention as surfaces able to reduce bacterial adherence, colonization, and biofilm formation in implanted medical devices. In this work, potent in-house S. aureus NorA efflux pump inhibitors (EPIs), belonging to the 2-phenylquinoline class, were immobilized on nanometric alpha-zirconium phosphate (ZrP) taking into advantage of acid-base or intercalation reactions. The ZrP/EPI were used as filler of poly(lactide-co-glycolic acid) (PLGA) to obtain film composites with a homogeneous distribution of the ZrP/EPI fillers. As reference, PLGA films loaded with ZrP intercalated with thioridazine (TZ), that is recognized as both a NorA and biofilm inhibitor, and with the antibiotic ciprofloxacin (CPX) were prepared. Composite films were characterized by X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The ability of the composite films, containing ZrP/EPI, to inhibit biofilm formation was tested on Staphylococcus aureus ATCC 29213 and Staphylococcus epidermidis ATCC 12228, and it was compared with that of the composite loaded with ZrP/TZ. Finally, the antibacterial activity of CPX intercalated in ZrP was evaluated when used in combination with ZrP/EPI in the PLGA films. Full article

(This article belongs to the Section Materials Chemistry)

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20 pages, 3420 KB

Open AccessEditor’s ChoiceArticle

Impact of Glass Composition on Hydrolytic Degradation of Polylactide/Bioactive Glass Composites

by Inari Lyyra, Katri Leino, Terttu Hukka, Markus Hannula, Minna Kellomäki and Jonathan Massera

Materials 2021, 14(3), 667; https://doi.org/10.3390/ma14030667 - 1 Feb 2021

Cited by 13 | Viewed by 3401

Abstract

Understanding the degradation of a composite material is crucial for tailoring its properties based on the foreseen application. In this study, poly-L,DL-lactide 70/30 (PLA70) was compounded with silicate or phosphate bioactive glass (Si-BaG and P-BaG, respectively). The composite processing was carried out without [...] Read more.

Understanding the degradation of a composite material is crucial for tailoring its properties based on the foreseen application. In this study, poly-L,DL-lactide 70/30 (PLA70) was compounded with silicate or phosphate bioactive glass (Si-BaG and P-BaG, respectively). The composite processing was carried out without excessive thermal degradation of the polymer and resulted in porous composites with lower mechanical properties than PLA70. The loss in mechanical properties was associated with glass content rather than the glass composition. The degradation of the composites was studied for 40 weeks in Tris buffer solution Adding Si-BaG to PLA70 accelerated the polymer degradation in vitro more than adding P-BaG, despite the higher reactivity of the P-BaG. All the composites exhibited a decrease in mechanical properties and increased hydrophilicity during hydrolysis compared to the PLA70. Both glasses dissolved through the polymer matrix with a linear, predictable release rate of ions. Most of the P-BaG had dissolved before 20 weeks in vitro, while there was still Si-BaG left after 40 weeks. This study introduces new polymer/bioactive glass composites with tailorable mechanical properties and ion release for bone regeneration and fixation applications. Full article

(This article belongs to the Special Issue Bioactive Ceramics and Their Applications)

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16 pages, 4623 KB

Open AccessEditor’s ChoiceArticle

Polydopamine Ultrathin Film Growth on Mica via In-Situ Polymerization of Dopamine with Applications for Silver-Based Antimicrobial Coatings

by Zheng-Hao Huang, Shi-Wei Peng, Shu-Ling Hsieh, Rajendranath Kirankumar, Po-Feng Huang, Tsao-Ming Chang, Atul Kumar Dwivedi, Nan-Fu Chen, Hao-Ming Wu and Shuchen Hsieh

Materials 2021, 14(3), 671; https://doi.org/10.3390/ma14030671 - 1 Feb 2021

Cited by 13 | Viewed by 4035

Abstract

The development of polydopamine (PDA) coatings with a nanometer-scale thickness on surfaces is highly desirable for exploiting the novel features arising from the specific structure on the molecular level. Exploring the mechanisms of thin-film growth is helpful for attaining desirable control over the [...] Read more.

The development of polydopamine (PDA) coatings with a nanometer-scale thickness on surfaces is highly desirable for exploiting the novel features arising from the specific structure on the molecular level. Exploring the mechanisms of thin-film growth is helpful for attaining desirable control over the useful properties of materials. We present a systematic study demonstrating the growth of a PDA thin film on the surface of mica in consecutive short deposition time intervals. Film growth at each deposition time was monitored through instrumental techniques such as atomic force microscopy (AFM), water contact angle (WCA) analysis, and X-ray photoelectron spectroscopy (XPS). Film growth was initiated by adsorption of the PDA molecules on mica, with subsequent island-like aggregation, and finally, a complete molecular level PDA film was formed on the surface due to further molecular adsorption. A duration of 60−300 s was sufficient for complete formation of the PDA layer within the thickness range of 0.5−1.1 nm. An outstanding feature of PDA ultrathin films is their ability to act as a molecular adhesive, providing a foundation for constructing functional surfaces. We also explored antimicrobial applications by incorporating Ag nanoparticles into a PDA film. The Ag NPs/PDA film was formed on a surgical blade and then characterized and confirmed by SEM-EDS and XPS. The modified film inhibited bacterial growth by up to 42% on the blade after cutting through a pork meat sample. Full article

(This article belongs to the Special Issue Advances in Bio-Inspired Materials for Medical Applications)

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16 pages, 3929 KB

Open AccessEditor’s ChoiceArticle

Coaxial Monitoring of AISI 316L Thin Walls Fabricated by Direct Metal Laser Deposition

by Vito Errico, Sabina Luisa Campanelli, Andrea Angelastro, Michele Dassisti, Marco Mazzarisi and Cesare Bonserio

Materials 2021, 14(3), 673; https://doi.org/10.3390/ma14030673 - 1 Feb 2021

Cited by 34 | Viewed by 3783

Abstract

Direct metal laser deposition (DMLD) is an additive manufacturing technique suitable for coating and repair, which has been gaining a growing interest in 3D manufacturing applications in recent years. However, its diffusion in the manufacturing industry is still limited due to technical challenges [...] Read more.

Direct metal laser deposition (DMLD) is an additive manufacturing technique suitable for coating and repair, which has been gaining a growing interest in 3D manufacturing applications in recent years. However, its diffusion in the manufacturing industry is still limited due to technical challenges to be solved—both the sub-optimal quality of the final parts and the low repeatability of the process make the DMLD inadequate for high-value applications requiring high-performance standards. Thus, real-time monitoring and process control are indispensable requirements for improving the DMLD process. The aim of this study was the optimization of deposition strategies for the fabrication of thin walls in AISI 316L stainless steel. For this purpose, a coaxial monitoring system and image processing algorithms were employed to study the melt pool geometry. The comparison tests carried out highlighted how the region-based active contour algorithm used for image processing is more efficient and stable than others covered in the literature. The results allowed the identification of the best deposition strategy. Therefore, it is shown how this monitoring methodology proved to be suitable for designing and implementing the right building strategy for DMLD manufactured 3D components. A fast and stable image processing method was achieved, which can be considered for future closed-loop monitoring in real-time applications. Full article

(This article belongs to the Special Issue Laser Deposition Processes)

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30 pages, 7098 KB

Open AccessEditor’s ChoiceReview

Silk-Based Materials for Hard Tissue Engineering

by Vanessa J. Neubauer, Annika Döbl and Thomas Scheibel

Materials 2021, 14(3), 674; https://doi.org/10.3390/ma14030674 - 1 Feb 2021

Cited by 35 | Viewed by 5511

Abstract

Hard tissues, e.g., bone, are mechanically stiff and, most typically, mineralized. To design scaffolds for hard tissue regeneration, mechanical, physico-chemical and biological cues must align with those found in the natural tissue. Combining these aspects poses challenges for material and construct design. Silk-based [...] Read more.

Hard tissues, e.g., bone, are mechanically stiff and, most typically, mineralized. To design scaffolds for hard tissue regeneration, mechanical, physico-chemical and biological cues must align with those found in the natural tissue. Combining these aspects poses challenges for material and construct design. Silk-based materials are promising for bone tissue regeneration as they fulfill several of such necessary requirements, and they are non-toxic and biodegradable. They can be processed into a variety of morphologies such as hydrogels, particles and fibers and can be mineralized. Therefore, silk-based materials are versatile candidates for biomedical applications in the field of hard tissue engineering. This review summarizes silk-based approaches for mineralized tissue replacements, and how to find the balance between sufficient material stiffness upon mineralization and cell survival upon attachment as well as nutrient supply. Full article

(This article belongs to the Special Issue Silk-Based Biomaterials)

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11 pages, 8525 KB

Open AccessEditor’s ChoiceArticle

Effect of the Particle Size and Matrix Strength on Strengthening and Damage Process of the Particle Reinforced Metal Matrix Composites

by Zhiyu Yang, Jianzhong Fan, Yanqiang Liu, Junhui Nie, Ziyue Yang and Yonglin Kang

Materials 2021, 14(3), 675; https://doi.org/10.3390/ma14030675 - 1 Feb 2021

Cited by 35 | Viewed by 3962

Abstract

Roles of the particle, strengthening, and weakening during deformation of the particle reinforced metal matrix composite, were studied using in situ technique. Composites with three different strengths Al-Cu-Mg alloy matrices reinforced by three sizes SiC particles were manufactured and subjected to in situ [...] Read more.

Roles of the particle, strengthening, and weakening during deformation of the particle reinforced metal matrix composite, were studied using in situ technique. Composites with three different strengths Al-Cu-Mg alloy matrices reinforced by three sizes SiC particles were manufactured and subjected to in situ tensile testing. Based on in situ observation, damage process, fraction and size distribution of the cracked particles were collected to investigate the behavior of the particle during composite deformation. The presence of the particle strengthens the composite, while the particle cracking under high load weakens the composite. This strengthening to weakening transformation is controlled by the damage process of the particle and decided by the particle strength, size distribution, and the matrix flow behavior together. With a proper match of the particle and matrix, an effective strengthening can be obtained. Finally, the effective match range of the particle and the matrix was defined as a function of the particle size and the matrix strength. Full article

(This article belongs to the Special Issue Advanced Composite Materials: Theory, Design and Applications)

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15 pages, 3266 KB

Open AccessEditor’s ChoiceArticle

Color and Translucency Stability of Three-Dimensional Printable Dental Materials for Crown and Bridge Restorations

by Jong-Eun Kim, Won-Huy Choi, Dasun Lee, Yooseok Shin, Sung-Ho Park, Byoung-Duck Roh and Dohyun Kim

Materials 2021, 14(3), 650; https://doi.org/10.3390/ma14030650 - 31 Jan 2021

Cited by 33 | Viewed by 5363

Abstract

The purpose of this study was to examine and compare color and translucency stability of three-dimensional (3D) printable dental materials for crown and bridge restorations. Five different materials were investigated, and twelve disc-shaped specimens of two different thicknesses (1 and 2 mm) were [...] Read more.

The purpose of this study was to examine and compare color and translucency stability of three-dimensional (3D) printable dental materials for crown and bridge restorations. Five different materials were investigated, and twelve disc-shaped specimens of two different thicknesses (1 and 2 mm) were prepared using a digital light processing 3D printer. Color measurements were made according to the CIELAB color scale (L*, a*, and b*) using a spectrophotometer 1 h, 1 day, 1 week, one month, and six months after post-curing of the materials, and the translucency parameter (TP) was calculated. The L*, a*, b*, and TP values were compared among the different materials and storage periods using repeated measures analysis of variance. Color and translucency changes of the specimens after the different storage periods were compared with 1 h measurements to determine whether they exceeded clinically perceivable thresholds. The L*, a*, b*, and TP values showed significant differences according to the storage periods, as well as among the materials. Until one month, some materials demonstrated distinct color differences, while others showed small color differences below a clinically perceivable threshold. The translucency differences were not clinically perceivable for any specimen. After six months, all specimens demonstrated large color changes, whereas the changes in translucency were relatively small. In conclusion, the color of 3D printable dental materials changed with time, and the differences varied with the materials used. On the contrary, the changes in translucency were small. Overall, the materials became darker, more yellowish, and more opaque after six months of water storage. Full article

(This article belongs to the Special Issue State-of-the-Art Biomaterials in Korea)

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20 pages, 6251 KB

Open AccessEditor’s ChoiceArticle

Influence of Vanillin Acrylate-Based Resin Composition on Resin Photocuring Kinetics and Antimicrobial Properties of the Resulting Polymers

by Aukse Navaruckiene, Danguole Bridziuviene, Vita Raudoniene, Egidija Rainosalo and Jolita Ostrauskaite

Materials 2021, 14(3), 653; https://doi.org/10.3390/ma14030653 - 31 Jan 2021

Cited by 19 | Viewed by 3884

Abstract

The investigation of the influence of vanillin acrylate-based resin composition on photocuring kinetics and antimicrobial properties of the resulting polymers was performed in order to find efficient photocurable systems for optical 3D printing of bio-based polymers with tunable rigidity, as well as with [...] Read more.

The investigation of the influence of vanillin acrylate-based resin composition on photocuring kinetics and antimicrobial properties of the resulting polymers was performed in order to find efficient photocurable systems for optical 3D printing of bio-based polymers with tunable rigidity, as well as with antibacterial and antifungal activity. Two vanillin derivatives, vanillin diacrylate and vanillin dimethacrylate, were tested in photocurable systems using phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide as a photoinitiator. The influence of vanillin acrylate monomer, amount of photoinitiator, presence and amount of dithiol, and presence of solvent on photocuring kinetics was investigated by real-time photoreometry. Polymers of different rigidity were obtained by changing the photocurable resin composition. The photocuring kinetics of the selected vanillin acrylate-based resins was comparable with that of commercial petroleum-based acrylate resins for optical 3D printing. Polymers based on both vanillin acrylates showed a significant antibacterial activity against Escherichia coli and Staphylococcus aureus. Vanillin diacrylate-based polymer films also demonstrated an antifungal activity in direct contact with Aspergillus niger and Aspergillus terreus. Vanillin diacrylate-based dual curing systems were selected as the most promising for optical 3D printing of bio-based polymers with antibacterial and antifungal activity. Full article

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

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15 pages, 5789 KB

Open AccessEditor’s ChoiceArticle

The Impact of Process Conditions on Surge Current Capability of 1.2 kV SiC JBS and MPS Diodes

by Hongyi Xu, Na Ren, Jiupeng Wu, Zhengyun Zhu, Qing Guo and Kuang Sheng

Materials 2021, 14(3), 663; https://doi.org/10.3390/ma14030663 - 31 Jan 2021

Cited by 11 | Viewed by 3589

Abstract

This paper demonstrated the impact of process conditions on the surge current capability of 1.2 kV SiC junction barrier Schottky diode (JBS) and merged PiN Schottky diode (MPS). The influence of ohmic contact and defect density produced by implantation was studied in the [...] Read more.

This paper demonstrated the impact of process conditions on the surge current capability of 1.2 kV SiC junction barrier Schottky diode (JBS) and merged PiN Schottky diode (MPS). The influence of ohmic contact and defect density produced by implantation was studied in the simulation. The device fabricated with high temperature implantation had less defect density in the implant region compared with room temperature implantation, which contributed to higher hole injection in surge current mode and 20% surge capability improvement. In addition, with lower P+ ohmic contact resistance, the device had higher surge capability. When compared to device fabrication with a single Schottky metal layer in the device active area, adding additional P+ ohmic contact on top of the P+ regions in the device active area resulted in the pn junctions sharing a greater portion of surge current, and improved the devices’ surge capability by ~10%. Full article

(This article belongs to the Special Issue SiC Materials and Applications)

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19 pages, 4589 KB

Open AccessEditor’s ChoiceArticle

Alkali Activation of Metallurgical Slags: Reactivity, Chemical Behavior, and Environmental Assessment

by Isabella Lancellotti, Federica Piccolo, Katja Traven, Mark Češnovar, Vilma Ducman and Cristina Leonelli

Materials 2021, 14(3), 639; https://doi.org/10.3390/ma14030639 - 30 Jan 2021

Cited by 31 | Viewed by 4514

Abstract

Alkali-activated materials (AAMs) represent a promising alternative to conventional building materials and ceramics. Being produced in large amounts as aluminosilicate-rich secondary products, such as slags, they can be utilized for the formulation of AAMs. Slags are partially crystalline metallurgical residues produced during the [...] Read more.

Alkali-activated materials (AAMs) represent a promising alternative to conventional building materials and ceramics. Being produced in large amounts as aluminosilicate-rich secondary products, such as slags, they can be utilized for the formulation of AAMs. Slags are partially crystalline metallurgical residues produced during the high temperature separation of metallic and non-metallic materials in the steelmaking processes. In the present study, the electric arc furnace carbon or stainless steel slag (EAF) and secondary metallurgical slag such as ladle furnace basic slag (LS) were used as precursors in an alkali-activation process. EAF slag, with its amorphous fraction of about 56%, presented higher contents of soluble Si and Al species with respect to ladle slag R (35%). However, both are suitable to produce AAM. The leaching behavior shows that all the release values are below the regulation limit. All the bivalent ions (Ba, Cd, Cu, Ni, Pb, and Zn) are well immobilized in a geopolymeric matrix, while amphoteric elements, such as As and Cr, show a slight increase of release with respect to the corresponding slag in alkaline and aqueous environments. In particular, for Sb and As of AAM, release still remains below the regulation limits, while Mo presents an increase of leaching values that slightly exceeds the limit for landfill non-dangerous waste. Full article

(This article belongs to the Special Issue Environmentally Sustainable Materials and Fabrication Techniques)

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13 pages, 48872 KB

Open AccessEditor’s ChoiceArticle

Ultrafine-Grained Ti-31Mo-Type Composites with HA and Ag, Ta₂O₅ or CeO₂ Addition for Implant Applications

by Patrycja Sochacka, Mieczyslawa U. Jurczyk, Kamil Kowalski, Przemyslaw K. Wirstlein and Mieczyslaw Jurczyk

Materials 2021, 14(3), 644; https://doi.org/10.3390/ma14030644 - 30 Jan 2021

Cited by 5 | Viewed by 3419

Abstract

Ultrafine-grained Ti31Mo alloy and Ti31Mo5HA, Ti31Mo5HA-Ag (or Ta₂O₅, CeO₂) composites with a grain size of approximately 2 μm were produced by the application of mechanical alloying and powder metallurgy. Additionally, the surface of the Ti31Mo alloy was [...] Read more.

Ultrafine-grained Ti31Mo alloy and Ti31Mo5HA, Ti31Mo5HA-Ag (or Ta₂O₅, CeO₂) composites with a grain size of approximately 2 μm were produced by the application of mechanical alloying and powder metallurgy. Additionally, the surface of the Ti31Mo alloy was modified. In the first stage, the specimens were immersed in 5M NaOH for 24 h at 60 °C. In the second stage, hydroxyapatite (HA) was deposited on the sample surface. The cathodic deposition at −5 V vs. open circuit potential (OCP) in the electrolyte containing 0.25M CaNa₂-EDTA (di-calcium ethylenediaminetetraacetic acid), 0.25M K₂HPO₄ in 1M NaOH at 120 °C for 2 h was applied. The bulk Ti31Mo alloy is a single β-type phase. In the alkali-modified surface titanium oxide, Ti₃O is formed. After hydrothermal treatment, the surface layer mostly consists of the Ca₁₀(PO₄)₆(OH)₂ (81.23%) with about 19% content of CaHPO₄·2H₂O. Using optical profiler, roughness 2D surface topography parameters were estimated. The in vitro cytocompatibility of synthesized materials was studied. The cell lines of normal human osteoblasts (NHost) and human periodontal ligament fibroblasts (HPdLF) was conducted in the presence of tested biomaterials. Ultrafine-grained Ti-based composites altered with HA and Ag, Ta₂O₅ or CeO₂ have superior biocompatibility than the microcrystalline Ti metal. NHost and HPdLF cells in the contact with the synthesized biomaterial showed stable proliferation activity. Biocompatibility tests carried out indicate that the ultrafine-grained Ti31Mo5HA composites with Ag, Ta₂O_5, or CeO₂ could be a good candidate for implant applications. Full article

(This article belongs to the Section Biomaterials)

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18 pages, 7499 KB

Open AccessEditor’s ChoiceReview

High-Temperature Properties and Applications of Si-Based Polymer-Derived Ceramics: A Review

by Zhongkan Ren, Shakir Bin Mujib and Gurpreet Singh

Materials 2021, 14(3), 614; https://doi.org/10.3390/ma14030614 - 29 Jan 2021

Cited by 77 | Viewed by 9214

Abstract

Ceramics derived from organic polymer precursors, which have exceptional mechanical and chemical properties that are stable up to temperatures slightly below 2000 °C, are referred to as polymer-derived ceramics (PDCs). These molecularly designed amorphous ceramics have the same high mechanical and chemical properties [...] Read more.

Ceramics derived from organic polymer precursors, which have exceptional mechanical and chemical properties that are stable up to temperatures slightly below 2000 °C, are referred to as polymer-derived ceramics (PDCs). These molecularly designed amorphous ceramics have the same high mechanical and chemical properties as conventional powder-based ceramics, but they also demonstrate improved oxidation resistance and creep resistance and low pyrolysis temperature. Since the early 1970s, PDCs have attracted widespread attention due to their unique microstructures, and the benefits of polymeric precursors for advanced manufacturing techniques. Depending on various doping elements, molecular configurations, and microstructures, PDCs may also be beneficial for electrochemical applications at elevated temperatures that exceed the applicability of other materials. However, the microstructural evolution, or the conversion, segregation, and decomposition of amorphous nanodomain structures, decreases the reliability of PDC products at temperatures above 1400 °C. This review investigates structure-related properties of PDC products at elevated temperatures close to or higher than 1000 °C, including manufacturing production, and challenges of high-temperature PDCs. Analysis and future outlook of high-temperature structural and electrical applications, such as fibers, ceramic matrix composites (CMCs), microelectromechanical systems (MEMSs), and sensors, within high-temperature regimes are also discussed. Full article

(This article belongs to the Special Issue Advanced Functional Polymer‐Derived Ceramic Fibers: Preparation, Properties and Applications)

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9 pages, 3146 KB

Open AccessEditor’s ChoiceArticle

Role of Anharmonic Interactions for Vibration Density of States in α-Cristobalite

by Yongda Huang, Jian Zhou, Guanjie Wang and Zhimei Sun

Materials 2021, 14(3), 617; https://doi.org/10.3390/ma14030617 - 29 Jan 2021

Cited by 3 | Viewed by 3008

Abstract

The vibrational density of states (VDOS) of solids in the low-energy regime controls the thermal and transport properties of materials, such as heat capacity, heat conduction, free energy and entropy. In α-Cristobalite, the low-frequency part of vibration density of states (VDOS) has many [...] Read more.

The vibrational density of states (VDOS) of solids in the low-energy regime controls the thermal and transport properties of materials, such as heat capacity, heat conduction, free energy and entropy. In α-Cristobalite, the low-frequency part of vibration density of states (VDOS) has many common features with the Boson peak in silica glass of matched densities. Recent theoretical work reported that anharmonic phonon–phonon interactions were critical for the low-frequency part of VDOS in α-Cristobalite. Therefore, it is urgent to identify the role of different anharmonic interactions from first principles. In this paper, we focus on the main peak of the low-frequency part of VDOS in α-Cristobalite. Calculated by our own developed codes and first principles, we find that the quartic anharmonic interaction can increase the frequency of the peak, while the cubic anharmonic can reduce the frequency and change the shape of the peak. Meanwhile, the anharmonic interactions are critical for the temperature effect. Therefore, we calculated the temperature-dependent property of the peak. We find that the frequency of the peak is directly proportional to the temperature. The atomic displacement patterns of different temperatures also confirm the above conclusion. All our calculations converged well. Moreover, our basic results agree well with other published results. Finally, we highlight that our codes offer a general and reliable way to calculate the VDOS with temperature. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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19 pages, 3796 KB

Open AccessEditor’s ChoiceArticle

Effect of Froude Number on Submerged Gas Blowing Characteristics

by Jonas L. Svantesson, Mikael Ersson and Pär G. Jönsson

Materials 2021, 14(3), 627; https://doi.org/10.3390/ma14030627 - 29 Jan 2021

Cited by 7 | Viewed by 2570

Abstract

The flow behavior of gas in compressible and incompressible systems was investigated at an ambient temperature in an air–water system and at an operating process temperature in the IronArc system, using computational fluid dynamics. The simulation results were verified by experiments in the [...] Read more.

The flow behavior of gas in compressible and incompressible systems was investigated at an ambient temperature in an air–water system and at an operating process temperature in the IronArc system, using computational fluid dynamics. The simulation results were verified by experiments in the air–water system and established empirical equations to enable reliable predictions of the penetration length. The simulations in the air–water system were found to replicate the experimental behavior using both the incompressible and compressible models, with only small deviations of 7–8%. A lower requirement for the modified Froude number of the gas blowing to produce a jetting behavior was also found. For gas blowing below the required modified Froude number, the results illustrate that the gas will form large pulsating bubbles instead of a steady jet, which causes the empirical equation calculations to severely underpredict the penetration length. The lower modified Froude number limit was also found to be system dependent and to have an approximate value of 300 for the studied IronArc system. For submerged blowing applications, it was found that it is important to ensure sufficiently high modified Froude numbers of the gas blowing. Then, the gas penetration length will remain stable as a jet and it will be possible to predict the values using empirical equations. Full article

(This article belongs to the Special Issue Physical and Numerical Modeling of Process Metallurgy)

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13 pages, 3487 KB

Open AccessEditor’s ChoiceArticle

Novel Selenoureas Based on Cinchona Alkaloid Skeleton: Synthesis and Catalytic Investigations

by Mariola Zielińska-Błajet and Joanna Najdek

Materials 2021, 14(3), 600; https://doi.org/10.3390/ma14030600 - 28 Jan 2021

Cited by 5 | Viewed by 2871

Abstract

An efficient approach to the synthesis of chiral selenoureas consisting of Cinchona alkaloid scaffolds was described. The new selenoureas were assessed as bifunctional organocatalysts in the asymmetric Michael addition reactions under mild conditions. The best results were obtained for selenoureas bearing the 4-fluorophenyl [...] Read more.

An efficient approach to the synthesis of chiral selenoureas consisting of Cinchona alkaloid scaffolds was described. The new selenoureas were assessed as bifunctional organocatalysts in the asymmetric Michael addition reactions under mild conditions. The best results were obtained for selenoureas bearing the 4-fluorophenyl group. These catalysts promoted the reactions with enantioselectivities of up to 96% ee. Additionally, the catalytic performance of the thiourea and selenourea counterpart was compared. Full article

(This article belongs to the Special Issue Advances in Organocatalysts: Synthesis and Applications)

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16 pages, 39266 KB

Open AccessEditor’s ChoiceArticle

Combining Thermal Loading System with Acoustic Emission Technology to Acquire the Complete Stress-Deformation Response of Plain Concrete in Direct Tension

by Rui Zhang, Li Guo and Wanjin Li

Materials 2021, 14(3), 602; https://doi.org/10.3390/ma14030602 - 28 Jan 2021

Cited by 12 | Viewed by 2252

Abstract

The tensile properties of plain concrete are very important for the concrete structural design, and the complete tensile stress-strain curve is essential for creating accurate and reliable designs, especially when considering special load cases such as earthquakes and impacts. To study the complete [...] Read more.

The tensile properties of plain concrete are very important for the concrete structural design, and the complete tensile stress-strain curve is essential for creating accurate and reliable designs, especially when considering special load cases such as earthquakes and impacts. To study the complete tensile stress-deformation response of plain concrete, the direct tension tests were conducted on a novel thermal tensile testing machine (TTTM), which was reformed from a hydraulic universal testing machine (UTM). Acoustic emission (AE) technology was applied to monitor the damage process of plain concrete in tests. The TTTM was powered by the thermal expansion of loading columns, and had a stiffness similar to the specimen, thus eliminating the potential AE noises in the UTM, and simulating the rapid fracture process in real concrete structures. A static-dynamic acquisition system was established to obtain the complete tensile stress-strain curves, of which the data before and at the fracture moment were respectively acquired by the static acquisition system and the dynamic acquisition system. The AE technology is a useful approach to analyze the damage process of concrete, and makes it feasible to determine the damage state and the fracture location of the specimen in real time. Full article

(This article belongs to the Special Issue Concrete Technology and Mechanical Properties of Concretes)

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13 pages, 3540 KB

Open AccessEditor’s ChoiceArticle

The Influence of Different Guided Bone Regeneration Procedures on the Contour of Bone Graft after Wound Closure: A Retrospective Cohort Study

by Maoxia Wang, Xiaoqing Zhang, Yazhen Li and Anchun Mo

Materials 2021, 14(3), 583; https://doi.org/10.3390/ma14030583 - 27 Jan 2021

Cited by 15 | Viewed by 3739

Abstract

The aim of this study was to evaluate the impact of different guided bone regeneration (GBR) procedures on bone graft contour after wound closure in lateral ridge augmentation. A total of 48 patients with 63 augmented sites were included in this study. Participants [...] Read more.

The aim of this study was to evaluate the impact of different guided bone regeneration (GBR) procedures on bone graft contour after wound closure in lateral ridge augmentation. A total of 48 patients with 63 augmented sites were included in this study. Participants were divided into 4 groups (n = 12 in each group) based on different surgical procedures: group 1: particulate bone substitute + collagen membrane; group 2: particulate bone substitute + collagen membrane + healing cap, group 3: particulate bone substitute + injectable platelet-rich fibrin (i-PRF) + collagen membrane; group 4: particulate bone substitute + i-PRF + surgical template + collagen membrane. After wound closure, the thickness of labial graft was measured at 0–5 mm apical to the implant shoulder (T0–T5). At T0–T2, the thickness of labial graft in group 4 was significantly higher than the other three groups (p < 0.05). And group 4 showed significantly more labial graft thickness than group 1 and group 2 at T3–T5 (p < 0.05). Within the limitations of this study, the use of i-PRF in combination with the surgical template in GBR may contribute to achieving an appropriate bone graft contour after wound closure. Full article

(This article belongs to the Special Issue Novel Biomaterials and Technology for Dental Clinical Applications)

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23 pages, 5120 KB

Open AccessEditor’s ChoiceArticle

Composite Nitride Nanoceramics in the System Titanium Nitride (TiN)-Aluminum Nitride (AlN) through High Pressure and High Temperature Sintering of Synthesis-Mixed Nanocrystalline Powders

by Mariusz Drygaś, Katarzyna Lejda, Jerzy F. Janik, Bogdan Musielak, Stanisław Gierlotka, Svitlana Stelmakh and Bogdan Pałosz

Materials 2021, 14(3), 588; https://doi.org/10.3390/ma14030588 - 27 Jan 2021

Cited by 4 | Viewed by 3223

Abstract

Presented is a study on the original preparation of individual and in situ intimately mixed composite nanocrystalline powders in the titanium nitride-aluminum nitride system, Ti:Al = 1:1 (at.), which were used in high pressure (7.7 GPa) and high temperature (650 and 1200 °C) [...] Read more.

Presented is a study on the original preparation of individual and in situ intimately mixed composite nanocrystalline powders in the titanium nitride-aluminum nitride system, Ti:Al = 1:1 (at.), which were used in high pressure (7.7 GPa) and high temperature (650 and 1200 °C) sintering with no binding additives for diverse individual and composite nanoceramics. First, variations in precursor processing pathways and final nitridation temperatures, 800 and 1100 °C, afforded a pool of mixed in the nanosized regime cubic TiN (c-TiN) and hexagonal AlN (h-AlN) composite nanopowders both with varying average crystallite sizes. Second, the sintering temperatures were selected either to preserve initial powder nanocrystallinity (650 °C was lower than both nitridation temperatures) or promote crystal growth and recrystallization (1200 °C was higher than both nitridation temperatures). Potential equilibration towards bimetallic compounds upon solution mixing of the organometallic precursors to nanopowders, monomeric Ti[N(CH₃)₂]₄ and dimeric {Al[N(CH₃)₂]₃}₂, was studied with ¹H and ¹³C NMR in C₆D₆ solution. The powders and nanoceramics, both of the composites and individual nitrides, were characterized if applicable by powder XRD, FT-IR, SEM/EDX, Vicker’s hardness, and helium density. The Vicker’s hardness tests confirmed many of the composite and individual nanoceramics having high hardnesses comparable with those of the reference h-AlN and c-TiN ceramics. This is despite extended phase segregation and, frequently, closed microsized pore formation linked mainly to the AlN component. No evidence was found for metastable alloying of the two crystallographically different nitrides under the applied synthesis and sintering conditions. The high pressure and high temperature sintering of the individual and in situ synthesis-mixed composite nanopowders of TiN-AlN was demonstrated to yield robust nanoceramics. Full article

(This article belongs to the Special Issue Relationship between Structure and Properties of Glass/Ceramic Materials)

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17 pages, 10172 KB

Open AccessEditor’s ChoiceArticle

Characteristics of Preplaced Aggregate Concrete Fabricated with Alkali-Activated Slag/Fly Ash Cements

by Salman Siddique, Hyeju Kim, Hyemin Son and Jeong Gook Jang

Materials 2021, 14(3), 591; https://doi.org/10.3390/ma14030591 - 27 Jan 2021

Cited by 6 | Viewed by 3021

Abstract

This study assesses the characteristics of preplaced aggregate concrete prepared with alkali-activated cement grout as an adhesive binder. Various binary blends of slag and fly ash without fine aggregate as a filler material were considered along with different solution-to-solid ratios. The properties of [...] Read more.

This study assesses the characteristics of preplaced aggregate concrete prepared with alkali-activated cement grout as an adhesive binder. Various binary blends of slag and fly ash without fine aggregate as a filler material were considered along with different solution-to-solid ratios. The properties of fresh and hardened grout along with the properties of hardened preplaced concrete were investigated, as were the compressive strength, ultrasonic pulse velocity, density, water absorption and total voids of the preplaced concrete. The results indicated that alkali-activated cement grout has better flowability characteristics and compressive strength than conventional cement grout. As a result, the mechanical performance of the preplaced aggregate concrete was significantly improved. The results pertaining to the water absorption and porosity revealed that the alkali-activated preplaced aggregate concrete is more resistant to water permeation. The filling capacity based on the ultrasonic pulse velocity value is discussed to comment on the wrapping ability of alkali-activated cement grout. Full article

(This article belongs to the Special Issue Concrete Materials: Advancement in Materials Design, Manufacturing, and Applications)

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19 pages, 10148 KB

Open AccessEditor’s ChoiceArticle

The Accuracy of Finishing WEDM of Inconel 718 Turbine Disc Fir Tree Slots

by Jan Burek, Robert Babiarz, Jarosław Buk, Paweł Sułkowicz and Krzysztof Krupa

Materials 2021, 14(3), 562; https://doi.org/10.3390/ma14030562 - 25 Jan 2021

Cited by 22 | Viewed by 4206

Abstract

Servicing aircraft engines sometimes requires manufacturing only a single piece of a given part. Manufacturing a turbine disc using traditional methods is uneconomical. It is necessary to use a different machining method recommended for small lot production. One of the proposed methods is [...] Read more.

Servicing aircraft engines sometimes requires manufacturing only a single piece of a given part. Manufacturing a turbine disc using traditional methods is uneconomical. It is necessary to use a different machining method recommended for small lot production. One of the proposed methods is WEDM (wire electrical discharge machining). The article presents the results of the research on finishing WEDM of Inconel 718 turbine disc fir tree slots. The influence of infeed, mean gap voltage, peak current, pulse off-time, and discharge energy on the shape accuracy, surface roughness, microcracks, and the white layer thickness were determined. Mathematical models were developed based on the DoE (Design of Experiment) analysis. The statistical significance of the models was verified with the ANOVA (Analysis of Variance) test. The machining parameters control methods that allow achieving the required shape accuracy, surface roughness, and surface layer condition were presented. The obtained surface roughness was Ra = 0.84 μm, the shape accuracy of the slot in the normal-to-feed direction was Δd = 0.009 μm, the profile shape accuracy was Δr = 0.033 μm, and the thickness of recast (white) layer was approximately 5 μm. Full article

(This article belongs to the Special Issue Nonconventional Technology in Materials Processing)

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4 pages, 200 KB

Open AccessEditor’s ChoiceEditorial

The Role of Metal Ions in Biology, Biochemistry and Medicine

by Michael Moustakas

Materials 2021, 14(3), 549; https://doi.org/10.3390/ma14030549 - 24 Jan 2021

Cited by 104 | Viewed by 6547

Abstract

Metal ions are fundamental elements for the maintenance of the lifespan of plants, animals and humans [...] Full article

(This article belongs to the Special Issue The Role of Metal Ions in Biology, Biochemistry and Medicine)

21 pages, 13257 KB

Open AccessEditor’s ChoiceArticle

The Effect of Laser Beam Processing on the Properties of WC-Co Coatings Deposited on Steel

by Norbert Radek, Janusz Konstanty, Jacek Pietraszek, Łukasz J. Orman, Marcin Szczepaniak and Damian Przestacki

Materials 2021, 14(3), 538; https://doi.org/10.3390/ma14030538 - 23 Jan 2021

Cited by 38 | Viewed by 2972

Abstract

The main objective of the present work is to determine the effects of laser processing on properties of WC-Co electro-spark deposited (ESD) coatings on steel substrates. Tungsten carbide coatings have been applied to steel substrates using a manual electrode feeder, model EIL-8A. The [...] Read more.

The main objective of the present work is to determine the effects of laser processing on properties of WC-Co electro-spark deposited (ESD) coatings on steel substrates. Tungsten carbide coatings have been applied to steel substrates using a manual electrode feeder, model EIL-8A. The laser beam processing (LBP) of electro-spark coatings was performed using an Nd:YAG fiber laser. The microstructure and properties of laser treated/melted coatings were evaluated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), surface geometric structure (SGS) and roughness measurements and adhesion, microhardness, residual stresses, corrosion resistance and application tests. The obtained experimental data were subjected to statistical analysis and multidimensional numerical and visual exploratory techniques. It has been shown conclusively that the laser-treated ESD WC-Co coatings are characterized by lower microhardness, higher resistance to corrosion, increased roughness and better adhesion to the substrate. LBP homogenizes the chemical composition, refines the microstructure and heals microcracks and pores of ESD coatings. The laser treated ESD WC-Co coatings can be used in frictional sliding nodes (e.g., on the front seal rings used in pumps) and as protective layers. Full article

(This article belongs to the Special Issue Laser Treatment for Surface Layers)

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16 pages, 3807 KB

Open AccessEditor’s ChoiceArticle

Sulfur Detection in Soil by Laser Induced Breakdown Spectroscopy Assisted by Multivariate Analysis

by Odhisea Gazeli, Dimitrios Stefas and Stelios Couris

Materials 2021, 14(3), 541; https://doi.org/10.3390/ma14030541 - 23 Jan 2021

Cited by 18 | Viewed by 3506

Abstract

Laser-induced breakdown spectroscopy (LIBS) is used for the detection and determination of sulfur content in some organic soil samples. The most suitable sulfur spectral lines for such tasks were found to occur in the vacuum ultraviolet (VUV) spectral region and they were used [...] Read more.

Laser-induced breakdown spectroscopy (LIBS) is used for the detection and determination of sulfur content in some organic soil samples. The most suitable sulfur spectral lines for such tasks were found to occur in the vacuum ultraviolet (VUV) spectral region and they were used for the construction of calibration curves. For the analysis, both univariate and multivariate statistical models were employed. The results obtained by the different analysis techniques are evaluated and compared. The present study demonstrates both the applicability and efficiency of LIBS for fast sulfur detection in soil matrices when aided by multivariate analysis methods improving the accuracy and extending the potential use of LIBS in such applications. Full article

(This article belongs to the Special Issue Materials Light Life)

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