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Volume 14
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Materials, Volume 14, Issue 2 (January-2 2021) – 237 articles

Cover Story (view full-size image): A graphene oxide aerogel (GOA) was formed inside a melamine sponge (MS) framework. After reduction with hydrazine at 60 °C, the electrical conductive nitrogen-enriched rGOA-MS composite material with a specific density of 20.1 mg/cm3 was used to fabricate an electrode, which proved to be a promising electrocatalyst for the oxygen reduction reaction. The rGOA-MS composite material was characterized by elemental analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. It was found that nitrogen in the material is presented by different types with the maximum concentration of pyrrole-like nitrogen. By using Raman scattering it was established that the rGOA component of the material is graphene-like carbon with an average size of the sp2-domains of 5.7 nm. This explains a quite high conductivity of the composite obtained. View this paper
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15 pages, 2199 KiB  
Article
Assembling Surface Linker Chemistry with Minimization of Non-Specific Adsorption on Biosensor Materials
by Jack Chih-Chieh Sheng, Brian De La Franier and Michael Thompson
Materials 2021, 14(2), 472; https://doi.org/10.3390/ma14020472 - 19 Jan 2021
Cited by 10 | Viewed by 2763
Abstract
The operation of biosensors requires surfaces that are both highly specific towards the target analyte and that are minimally subject to fouling by species present in a biological fluid. In this work, we further examined the thiosulfonate-based linker in order to construct robust [...] Read more.
The operation of biosensors requires surfaces that are both highly specific towards the target analyte and that are minimally subject to fouling by species present in a biological fluid. In this work, we further examined the thiosulfonate-based linker in order to construct robust and durable self-assembling monolayers (SAMs) onto hydroxylated surfaces such as silica. These SAMs are capable of the chemoselective immobilization of thiol-containing probes (for analytes) under aqueous conditions in a single, straightforward, reliable, and coupling-free manner. The efficacy of the method was assessed through implementation as a biosensing interface for an ultra-high frequency acoustic wave device dedicated to the detection of avidin via attached biotin. Fouling was assessed via introduction of interfering bovine serum albumin (BSA), IgG antibody, or goat serum. Improvements were investigated systematically through the incorporation of an oligoethylene glycol backbone employed together with a self-assembling diluent without a functional distal group. This work demonstrates that the incorporation of a diluent of relatively short length is crucial for the reduction of fouling. Included in this work is a comparison of the surface attachment of the linker to Si3N4 and AlN, both materials used in sensor technology. Full article
(This article belongs to the Special Issue Advanced Designs of Materials, Devices and Techniques for Biosensing)
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24 pages, 8000 KiB  
Article
Estimating a Stoichiometric Solid’s Gibbs Free Energy Model by Means of a Constrained Evolutionary Strategy
by Constantino Grau Turuelo, Sebastian Pinnau and Cornelia Breitkopf
Materials 2021, 14(2), 471; https://doi.org/10.3390/ma14020471 - 19 Jan 2021
Cited by 2 | Viewed by 2564
Abstract
Modeling of thermodynamic properties, like heat capacities for stoichiometric solids, includes the treatment of different sources of data which may be inconsistent and diverse. In this work, an approach based on the covariance matrix adaptation evolution strategy (CMA-ES) is proposed and described as [...] Read more.
Modeling of thermodynamic properties, like heat capacities for stoichiometric solids, includes the treatment of different sources of data which may be inconsistent and diverse. In this work, an approach based on the covariance matrix adaptation evolution strategy (CMA-ES) is proposed and described as an alternative method for data treatment and fitting with the support of data source dependent weight factors and physical constraints. This is applied to a Gibb’s Free Energy stoichiometric model for different magnesium sulfate hydrates by means of the NASA9 polynomial. Its behavior is proved by: (i) The comparison of the model to other standard methods for different heat capacity data, yielding a more plausible curve at high temperature ranges; (ii) the comparison of the fitted heat capacity values of MgSO4·7H2O against DSC measurements, resulting in a mean relative error of a 0.7% and a normalized root mean square deviation of 1.1%; and (iii) comparing the Van’t Hoff and proposed Stoichiometric model vapor-solid equilibrium curves to different literature data for MgSO4·7H2O, MgSO4·6H2O, and MgSO4·1H2O, resulting in similar equilibrium values, especially for MgSO4·7H2O and MgSO4·6H2O. The results show good agreement with the employed data and confirm this method as a viable alternative for fitting complex physically constrained data sets, while being a potential approach for automatic data fitting of substance data. Full article
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19 pages, 43847 KiB  
Article
Experimental and Numerical Investigation of AA5052-H32 Al Alloy with U-Profile in Cold Roll Forming
by Mohanraj Murugesan, Muhammad Sajjad and Dong Won Jung
Materials 2021, 14(2), 470; https://doi.org/10.3390/ma14020470 - 19 Jan 2021
Cited by 15 | Viewed by 3936
Abstract
The cold roll forming process is broadly used to produce a specific shape of cold-roll formed products for their applications in automobiles, aerospace, shipbuilding, and construction sectors. Moreover, a proper selection of strip thickness and forming speed to avoid fracture is most important [...] Read more.
The cold roll forming process is broadly used to produce a specific shape of cold-roll formed products for their applications in automobiles, aerospace, shipbuilding, and construction sectors. Moreover, a proper selection of strip thickness and forming speed to avoid fracture is most important for manufacturing a quality product. This research aims to investigate the presence of longitudinal bow, the reason behind flange height deviation, spring-back, and identification of thinning location in the cold roll-forming of symmetrical short U-profile sheets. A room temperature tensile test is performed for the commercially available AA5052–H32 Al alloy sheets using Digital Image Correlation (DIC) technique, which allows complete displacement and strain data information at each time-step. The material properties are estimated from the digital images using correlation software for tested samples; the plastic strain ratios are also calculated from samples at 0°, 45°, and 90° to the rolling direction. The tested sample’s surface morphology and the elemental analysis are conducted using scanning electron microscopy (SEM) method and energy-dispersive X-ray spectroscopy (EDS) analytical technique combined with element mapping analysis, respectively. The cold roll forming experiments are systematically carried out, and then finite element analysis is utilized to correlate the experiment with the model. The performed cold roll forming numerical model outcome indicates a good agreement with the experimental measurements. Overall, the presented longitudinal strain was observed to influence the geometry profile. The spring-back is also noticed at the profile tail end and is more pronounced at high forming speed with lower strip thickness. Conversely, while the forming speed is varied, the strain and stress variations are observed to be insignificant, and the similar results also are recognized for the thinning behavior. Full article
(This article belongs to the Special Issue Recent Advances in Metal Forming Technology)
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24 pages, 10127 KiB  
Article
Residual Mechanical Properties and Constitutive Model of High-Strength Seismic Steel Bars through Different Cooling Rates
by Xianhua Yao, Peiqiao Qin, Junfeng Guan, Lielie Li, Min Zhang and Yongwei Gao
Materials 2021, 14(2), 469; https://doi.org/10.3390/ma14020469 - 19 Jan 2021
Cited by 5 | Viewed by 2102
Abstract
In this study, the high-temperature test (i.e., temperature to 1000 °C) is conducted on 600 MPa seismic steel bars, and its residual mechanical properties and constitutive relations are investigated though three cooling rates, i.e., under air, furnace, and water-cooling conditions. Results show that [...] Read more.
In this study, the high-temperature test (i.e., temperature to 1000 °C) is conducted on 600 MPa seismic steel bars, and its residual mechanical properties and constitutive relations are investigated though three cooling rates, i.e., under air, furnace, and water-cooling conditions. Results show that three cooling methods have significant effects on the apparent characteristics of 600 MPa steel bars, when the heating temperature is greater than 600 °C. In addition, the ultimate and yield strength of steel bars have been significantly affected by different cooling methods, with increasing heating temperature. However, the elastic modulus is significantly not affected by temperature. Furthermore, the elongation rate after fracture and the total elongation rate at the maximum force do not change significantly, when the heating temperature is less than 650 °C. The elongation rate, after fracture, and the total elongation rate, at the maximum force, have different changes for three cooling methods. The degeneration of the stress–strain curves occurs when the heating temperature is high. The two-fold line, three-fold line, and Ramberg–Osgood models are developed based on the stress–strain curve characteristics of steel bars after cooling. The fire resistance of 600 MPa steel bars of reinforced concrete structure is analyzed, which provides a basis for post-disaster damage assessment, repair, and reinforcement of the building structure. Full article
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18 pages, 11893 KiB  
Article
Determination of the Shear Modulus of Pine Wood with the Arcan Test and Digital Image Correlation
by Piotr Bilko, Aneta Skoratko, Andrzej Rutkiewicz and Leszek Małyszko
Materials 2021, 14(2), 468; https://doi.org/10.3390/ma14020468 - 19 Jan 2021
Cited by 13 | Viewed by 2798
Abstract
Arcan shear tests with digital image correlation were used to evaluate the shear modulus and shear stress–strain diagrams in the plane defined by two principal axes of the material orthotropy. Two different orientation of the grain direction as compared to the direction of [...] Read more.
Arcan shear tests with digital image correlation were used to evaluate the shear modulus and shear stress–strain diagrams in the plane defined by two principal axes of the material orthotropy. Two different orientation of the grain direction as compared to the direction of the shear force in specimens were considered: perpendicular and parallel shear. Two different ways were used to obtain the elastic properties based on the digital image correlation (DIC) results from the full-field measurement and from the virtual strain gauges with the linear strains: perpendicular to each other and directed at the angle of π/4 to the shearing load. In addition, the own continuum structural model for the failure analysis in the experimental tests was used. Constitutive relationships of the model were established in the framework of the mathematical multi-surface elastoplasticity for the plane stress state. The numerical simulations done by the finite element program after implementation of the model demonstrated the failure mechanisms from the experimental tests. Full article
(This article belongs to the Special Issue Testing of Materials and Elements in Civil Engineering)
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18 pages, 5260 KiB  
Article
Short-Term Flexural Stiffness Prediction of CFRP Bars Reinforced Coral Concrete Beams
by Lei Wang, Jin Yi, Jiwang Zhang, Wu Chen and Feng Fu
Materials 2021, 14(2), 467; https://doi.org/10.3390/ma14020467 - 19 Jan 2021
Cited by 16 | Viewed by 2757
Abstract
FRP (Fiber Reinforced Polymer) Bar reinforced coral concrete beam is a new type of structural member that has been used more and more widely in marine engineering in recent years. In order to study and predict the flexural performance of CFRP reinforced coral [...] Read more.
FRP (Fiber Reinforced Polymer) Bar reinforced coral concrete beam is a new type of structural member that has been used more and more widely in marine engineering in recent years. In order to study and predict the flexural performance of CFRP reinforced coral concrete beams, the flexural rigidity, crack morphology and failure mode of concrete were studied in detail. The results show that under the condition of similar reinforcement ratio, the flexural rigidity of CFRP reinforced coral concrete beam is significantly lower than that of ordinary reinforced concrete beam. Increasing the cross-section reinforcement ratio within a certain range can increase the bending stiffness of the test beam or reduce the deflection, but the strength utilization rate of CFRP reinforcement is greatly reduced. The short-term bending stiffness of the CFRP reinforced coral concrete beam calculated by the existing standard formula is obviously higher. This paper proposes a modified formula for introducing the strain inhomogeneity coefficient (ψ) of CFRP bars and considers the relative slip between CFRP bars and coral concrete to predict the short-term flexural stiffness of coral concrete beams reinforced by CFRP bars. The formula was verified with the test results, and it was proved that the formula has a good consistency with the test results. Full article
(This article belongs to the Section Advanced Materials Characterization)
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15 pages, 6501 KiB  
Article
Sustainable Additive Manufacturing: Mechanical Response of Polyamide 12 over Multiple Recycling Processes
by Nectarios Vidakis, Markos Petousis, Lazaros Tzounis, Athena Maniadi, Emmanouil Velidakis, Nikolaos Mountakis and John D. Kechagias
Materials 2021, 14(2), 466; https://doi.org/10.3390/ma14020466 - 19 Jan 2021
Cited by 81 | Viewed by 5300
Abstract
Plastic waste reduction and recycling through circular use has been critical nowadays, since there is an increasing demand for the production of plastic components based on different polymeric matrices in various applications. The most commonly used recycling procedure, especially for thermoplastic materials, is [...] Read more.
Plastic waste reduction and recycling through circular use has been critical nowadays, since there is an increasing demand for the production of plastic components based on different polymeric matrices in various applications. The most commonly used recycling procedure, especially for thermoplastic materials, is based on thermomechanical process protocols that could significantly alter the polymers’ macromolecular structure and physicochemical properties. The study at hand focuses on recycling of polyamide 12 (PA12) filament, through extrusion melting over multiple recycling courses, giving insight for its effect on the mechanical and thermal properties of Fused Filament Fabrication (FFF) manufactured specimens throughout the recycling courses. Three-dimensional (3D) FFF printed specimens were produced from virgin as well as recycled PA12 filament, while they have been experimentally tested further for their tensile, flexural, impact and micro-hardness mechanical properties. A thorough thermal and morphological analysis was also performed on all the 3D printed samples. The results of this study demonstrate that PA12 can be successfully recycled for a certain number of courses and could be utilized in 3D printing, while exhibiting improved mechanical properties when compared to virgin material for a certain number of recycling repetitions. From this work, it can be deduced that PA12 can be a viable option for circular use and 3D printing, offering an overall positive impact on recycling, while realizing 3D printed components using recycled filaments with enhanced mechanical and thermal stability. Full article
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18 pages, 5431 KiB  
Article
CuWO4 with CuO and Cu(OH)2 Native Surface Layers for H2S Detection under in-Field Conditions
by Simona Somacescu, Adelina Stanoiu, Ion Viorel Dinu, Jose Maria Calderon-Moreno, Ovidiu G. Florea, Mihaela Florea, Petre Osiceanu and Cristian E. Simion
Materials 2021, 14(2), 465; https://doi.org/10.3390/ma14020465 - 19 Jan 2021
Cited by 5 | Viewed by 2758
Abstract
The paper presents the possibility of detecting low H2S concentrations using CuWO4. The applicative challenge was to obtain sensitivity, selectivity, short response time, and full recovery at a low operating temperature under in-field atmosphere, which means variable relative humidity [...] Read more.
The paper presents the possibility of detecting low H2S concentrations using CuWO4. The applicative challenge was to obtain sensitivity, selectivity, short response time, and full recovery at a low operating temperature under in-field atmosphere, which means variable relative humidity (%RH). Three different chemical synthesis routes were used for obtaining the samples labeled as: CuW1, CuW2, and CuW3. The materials have been fully characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). While CuWO4 is the common main phase with triclinic symmetry, different native layers of CuO and Cu(OH)2 have been identified on top of the surfaces. The differences induced into their structural, morphological, and surface chemistry revealed different degrees of surface hydroxylation. Knowing the poisonous effect of H2S, the sensing properties evaluation allowed the CuW2 selection based on its specific surface recovery upon gas exposure. Simultaneous electrical resistance and work function measurements confirmed the weak influence of moisture over the sensing properties of CuW2, due to the pronounced Cu(OH)2 native surface layer, as shown by XPS investigations. Moreover, the experimental results obtained at 150 °C highlight the linear sensor signal for CuW2 in the range of 1 to 10 ppm H2S concentrations and a pronounced selectivity towards CO, CH4, NH3, SO2, and NO2. Therefore, the applicative potential deserves to be noted. The study has been completed by a theoretical approach aiming to link the experimental findings with the CuW2 intrinsic properties. Full article
(This article belongs to the Special Issue Advanced Materials for Gas Sensors)
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18 pages, 3625 KiB  
Article
Propolis and Organosilanes as Innovative Hybrid Modifiers in Wood-Based Polymer Composites
by Majka Odalanowska, Magdalena Woźniak, Izabela Ratajczak, Daria Zielińska, Grzegorz Cofta and Sławomir Borysiak
Materials 2021, 14(2), 464; https://doi.org/10.3390/ma14020464 - 19 Jan 2021
Cited by 16 | Viewed by 3266
Abstract
The article presents characteristics of wood/polypropylene composites, where the wood was treated with propolis extract (EEP) and innovative propolis-silane formulations. Special interest in propolis for wood impregnation is due to its antimicrobial properties. One propolis-silane formulation (EEP-TEOS/VTMOS) consisted of EEP, tetraethyl orthosilicate (TEOS), [...] Read more.
The article presents characteristics of wood/polypropylene composites, where the wood was treated with propolis extract (EEP) and innovative propolis-silane formulations. Special interest in propolis for wood impregnation is due to its antimicrobial properties. One propolis-silane formulation (EEP-TEOS/VTMOS) consisted of EEP, tetraethyl orthosilicate (TEOS), and vinyltrimethoxysilane (VTMOS), while the other (EEP-TEOS/OTEOS) contained EEP, tetraethyl orthosilicate (TEOS), and octyltriethoxysilane (OTEOS). The treated wood fillers were characterized by Fourier transform infrared spectroscopy (FTIR), atomic absorption spectrometry (AAS), and X-ray diffraction (XRD), while the composites were investigated using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and optical microscopy. The wood treated with EEP and propolis-silane formulations showed resistance against moulds, including Aspergillus niger, Chaetomium globosum, and Trichoderma viride. The chemical analyses confirmed presence of silanes and constituents of propolis in wood structure. In addition, treatment of wood with the propolis-silane formulations produced significant changes in nucleating abilities of wood in the polypropylene matrix, which was confirmed by an increase in crystallization temperature and crystal conversion, as well as a decrease in half-time of crystallization parameters compared to the untreated polymer matrix. In all the composites, the formation of a transcrystalline layer was observed, with the greatest rate recorded for the composite with the filler treated with EEP-TEOS/OTEOS. Moreover, impregnation of wood with propolis-silane formulations resulted in a considerable improvement of strength properties in the produced composites. A dependence was found between changes in the polymorphic structures of the polypropylene matrix and strength properties of composite materials. It needs to be stressed that to date literature sources have not reported on treatment of wood fillers using bifunctional modifiers providing a simultaneous effect of compatibility in the polymer-filler system or any protective effect against fungi. Full article
(This article belongs to the Special Issue Application of Natural Polymers in Bio-Based Products)
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16 pages, 3032 KiB  
Article
Ecotoxicity and Essential Properties of Fine-Recycled Aggregate
by Diana Mariaková, Klára Anna Mocová, Kristina Fořtová, Pavla Ryparová, Jan Pešta and Tereza Pavlů
Materials 2021, 14(2), 463; https://doi.org/10.3390/ma14020463 - 19 Jan 2021
Cited by 11 | Viewed by 2534
Abstract
This article deals with the possibility of utilization of secondary-raw materials as a natural sand replacement in concrete. Four types of waste construction materials were examined—recycled aggregate from four different sources. The natural aggregate was examined as well as used as the reference [...] Read more.
This article deals with the possibility of utilization of secondary-raw materials as a natural sand replacement in concrete. Four types of waste construction materials were examined—recycled aggregate from four different sources. The natural aggregate was examined as well as used as the reference sample. All the samples were tested to evaluate the water absorption, particle size distribution, and particle density. The basic chemical reactions in the view of ecotoxicology are investigated and measured based on Czech standards. Chemical analysis, Lemna growth inhibition test, freshwater algae, daphnia acute, and mustard germination toxicity test were made and discussed in this paper. Based on the physical and geometrical properties and ecotoxicology of examined waste materials, this work evaluated them as suitable for utilization in concrete as a sand replacement. Full article
(This article belongs to the Special Issue Environmentally Friendly Materials in Construction)
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14 pages, 3123 KiB  
Article
An Analytical Model for Estimating the Bending Curvatures of Metal Sheets in Laser Peen Forming
by Yunxia Ye, Zeng Nie, Xu Huang, Xudong Ren and Lin Li
Materials 2021, 14(2), 462; https://doi.org/10.3390/ma14020462 - 19 Jan 2021
Cited by 1 | Viewed by 2530
Abstract
Laser peen forming (LPF) is suitable for shaping sheet metals without the requirement for die/mold and without causing high temperatures. An analytical model for estimating the bending curvatures of LPF is convenient and necessary for better understanding of the physical processes involved. In [...] Read more.
Laser peen forming (LPF) is suitable for shaping sheet metals without the requirement for die/mold and without causing high temperatures. An analytical model for estimating the bending curvatures of LPF is convenient and necessary for better understanding of the physical processes involved. In this paper, we describe a new analytical model based on internal force balance and the energy transformation in LPF. Experiments on 2024 aluminum alloy sheets of 1–3 mm thickness were performed to validate the analytical model. The results showed that for 1 mm and 3 mm thick–thin plates, the curvature obtained by the analytical model changes from −14 × 10−4 mm−1 and −1 × 10−4 mm−1 to 55 × 10−4 mm−1 and −21 × 10−4 mm−1, respectively, with the increase of laser energy, which is consistent with the experimental trend. So, when either the stress gradient mechanism (SGM) or the shock bending mechanism (SBM) overwhelmingly dominated the forming process, the analytical model could give relatively accurate predicted curvatures compared with the experimental data. Under those conditions where SGM and SBM were comparable, the accuracy of the model was low, because of the complex stress distributions within the material, and the complex energy coupling process under these conditions. Full article
(This article belongs to the Special Issue Metal Forming and Forging)
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13 pages, 1546 KiB  
Article
Characterization of GaAs Solar Cells under Supercontinuum Long-Time Illumination
by Nikola Papež, Rashid Dallaev, Pavel Kaspar, Dinara Sobola, Pavel Škarvada, Ştefan Ţălu, Shikhgasan Ramazanov and Alois Nebojsa
Materials 2021, 14(2), 461; https://doi.org/10.3390/ma14020461 - 19 Jan 2021
Cited by 8 | Viewed by 3514
Abstract
This work is dedicated to the description of the degradation of GaAs solar cells under continuous laser irradiation. Constant and strong exposure of the solar cell was performed over two months. Time-dependent electrical characteristics are presented. The structure of the solar cells was [...] Read more.
This work is dedicated to the description of the degradation of GaAs solar cells under continuous laser irradiation. Constant and strong exposure of the solar cell was performed over two months. Time-dependent electrical characteristics are presented. The structure of the solar cells was studied at the first and last stages of degradation test. The data from Raman spectroscopy, reflectometry, and secondary ion mass spectrometry confirm displacement of titanium and aluminum atoms. X-ray photoelectron spectroscopy showed a slight redistribution of oxygen bonds in the anti-corrosion coating. Full article
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24 pages, 2534 KiB  
Article
Stress-Based FEM in the Problem of Bending of Euler–Bernoulli and Timoshenko Beams Resting on Elastic Foundation
by Zdzisław Więckowski and Paulina Świątkiewicz
Materials 2021, 14(2), 460; https://doi.org/10.3390/ma14020460 - 19 Jan 2021
Cited by 8 | Viewed by 3148
Abstract
The stress-based finite element method is proposed to solve the static bending problem for the Euler–Bernoulli and Timoshenko models of an elastic beam. Two types of elements—with five and six degrees of freedom—are proposed. The elaborated elements reproduce the exact solution in the [...] Read more.
The stress-based finite element method is proposed to solve the static bending problem for the Euler–Bernoulli and Timoshenko models of an elastic beam. Two types of elements—with five and six degrees of freedom—are proposed. The elaborated elements reproduce the exact solution in the case of the piece-wise constant distributed loading. The proposed elements do not exhibit the shear locking phenomenon for the Timoshenko model. The influence of an elastic foundation of the Winkler type is also taken into consideration. The foundation response is approximated by the piece-wise constant and piece-wise linear functions in the cases of the five-degrees-of-freedom and six-degrees-of-freedom elements, respectively. An a posteriori estimation of the approximate solution error is found using the hypercircle method with the addition of the standard displacement-based finite element solution. Full article
(This article belongs to the Special Issue Modeling and Analysis of Static, Dynamic, and Thermal Behavior of Shell, Plate, and Beam Structures)
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13 pages, 2225 KiB  
Article
Structure of Plasma (re)Polymerized Polylactic Acid Films Fabricated by Plasma-Assisted Vapour Thermal Deposition
by Zdeněk Krtouš, Lenka Hanyková, Ivan Krakovský, Daniil Nikitin, Pavel Pleskunov, Ondřej Kylián, Jana Sedlaříková and Jaroslav Kousal
Materials 2021, 14(2), 459; https://doi.org/10.3390/ma14020459 - 19 Jan 2021
Cited by 6 | Viewed by 2441
Abstract
Plasma polymer films typically consist of very short fragments of the precursor molecules. That rather limits the applicability of most plasma polymerisation/plasma-enhanced chemical vapour deposition (PECVD) processes in cases where retention of longer molecular structures is desirable. Plasma-assisted vapour thermal deposition (PAVTD) circumvents [...] Read more.
Plasma polymer films typically consist of very short fragments of the precursor molecules. That rather limits the applicability of most plasma polymerisation/plasma-enhanced chemical vapour deposition (PECVD) processes in cases where retention of longer molecular structures is desirable. Plasma-assisted vapour thermal deposition (PAVTD) circumvents this limitation by using a classical bulk polymer as a high molecular weight “precursor”. As a model polymer in this study, polylactic acid (PLA) has been used. The resulting PLA-like films were characterised mostly by X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR) spectroscopy. The molecular structure of the films was found to be tunable in a broad range: from the structures very similar to bulk PLA polymer to structures that are more typical for films prepared using PECVD. In all cases, PLA-like groups are at least partially preserved. A simplified model of the PAVTD process chemistry was proposed and found to describe well the observed composition of the films. The structure of the PLA-like films demonstrates the ability of plasma-assisted vapour thermal deposition to bridge the typical gap between the classical and plasma polymers. Full article
(This article belongs to the Special Issue Innovative Plasma-Based Deposition Techniques for the Production of Functional Materials)
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21 pages, 33034 KiB  
Article
Development of Bacterial Cellulose Biocomposites Combined with Starch and Collagen and Evaluation of Their Properties
by Silmar Baptista Nunes, Katharine Valéria Saraiva Hodel, Giulia da Costa Sacramento, Pollyana da Silva Melo, Fernando Luiz Pellegrini Pessoa, Josiane Dantas Viana Barbosa, Roberto Badaró and Bruna Aparecida Souza Machado
Materials 2021, 14(2), 458; https://doi.org/10.3390/ma14020458 - 19 Jan 2021
Cited by 13 | Viewed by 3505
Abstract
One of the major benefits of biomedicine is the use of biocomposites as wound dressings to help improve the treatment of injuries. Therefore, the main objective of this study was to develop and characterize biocomposites based on bacterial cellulose (BC) with different concentrations [...] Read more.
One of the major benefits of biomedicine is the use of biocomposites as wound dressings to help improve the treatment of injuries. Therefore, the main objective of this study was to develop and characterize biocomposites based on bacterial cellulose (BC) with different concentrations of collagen and starch and characterize their thermal, morphological, mechanical, physical, and barrier properties. In total, nine samples were produced with fixed amounts of glycerol and BC and variations in the amount of collagen and starch. The water activity (0.400–0.480), water solubility (12.94–69.7%), moisture (10.75–20.60%), thickness (0.04–0.11 mm), water vapor permeability (5.59–14.06 × 10−8 g·mm/m2·h·Pa), grammage (8.91–39.58 g·cm−2), opacity (8.37–36.67 Abs 600 nm·mm−1), elongation (4.81–169.54%), and tensile strength (0.99–16.32 MPa) were evaluated and defined. In addition, scanning electron microscopy showed that adding biopolymers in the cellulose matrix made the surface compact, which also influenced the visual appearance. Thus, the performance of the biocomposites was directly influenced by their composition. The performance of the different samples obtained resulted in them having different potentials for application considering the injury type. This provides a solution for the ineffectiveness of traditional dressings, which is one of the great problems of the biomedical sector. Full article
(This article belongs to the Special Issue Advanced Biomaterials for Medical Applications)
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12 pages, 6739 KiB  
Article
Gravity-Driven Separation of Oil/Water Mixture by Porous Ceramic Membranes with Desired Surface Wettability
by Chunlei Ren, Wufeng Chen, Chusheng Chen, Louis Winnubst and Lifeng Yan
Materials 2021, 14(2), 457; https://doi.org/10.3390/ma14020457 - 19 Jan 2021
Cited by 11 | Viewed by 2966
Abstract
Porous Al2O3 membranes were prepared through a phase-inversion tape casting/sintering method. The alumina membranes were embedded with finger-like pores perpendicular to the membrane surface. Bare alumina membranes are naturally hydrophilic and underwater oleophobic, while fluoroalkylsilane (FAS)-grafted membranes are hydrophobic and [...] Read more.
Porous Al2O3 membranes were prepared through a phase-inversion tape casting/sintering method. The alumina membranes were embedded with finger-like pores perpendicular to the membrane surface. Bare alumina membranes are naturally hydrophilic and underwater oleophobic, while fluoroalkylsilane (FAS)-grafted membranes are hydrophobic and oleophilic. The coupling of FAS molecules on alumina surfaces was confirmed by Thermogravimetric Analysis and X-ray Photoelectron Spectroscopy measurements. The hydrophobic membranes exhibited desired thermal stability and were super durable when exposed to air. Both membranes can be used for gravity-driven oil/water separation, which is highly cost-effective. The as-calculated separation efficiency (R) was above 99% for the FAS-grafted alumina membrane. Due to the excellent oil/water separation performance and good chemical stability, the porous ceramic membranes display potential for practical applications. Full article
(This article belongs to the Section Materials Chemistry)
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14 pages, 8531 KiB  
Article
Microstructure and Mechanical Properties of Laser-Welded DP Steels Used in the Automotive Industry
by Hanbing He, Farnoosh Forouzan, Joerg Volpp, Stephanie M. Robertson and Esa Vuorinen
Materials 2021, 14(2), 456; https://doi.org/10.3390/ma14020456 - 19 Jan 2021
Cited by 19 | Viewed by 4072
Abstract
The aim of this work was to investigate the microstructure and the mechanical properties of laser-welded joints combined of Dual Phase DP800 and DP1000 high strength thin steel sheets. Microstructural and hardness measurements as well as tensile and fatigue tests have been carried [...] Read more.
The aim of this work was to investigate the microstructure and the mechanical properties of laser-welded joints combined of Dual Phase DP800 and DP1000 high strength thin steel sheets. Microstructural and hardness measurements as well as tensile and fatigue tests have been carried out. The welded joints (WJ) comprised of similar/dissimilar steels with similar/dissimilar thickness were consisted of different zones and exhibited similar microstructural characteristics. The trend of microhardness for all WJs was consistent, characterized by the highest value at hardening zone (HZ) and lowest at softening zone (SZ). The degree of softening was 20 and 8% for the DP1000 and DP800 WJ, respectively, and the size of SZ was wider in the WJ combinations of DP1000 than DP800. The tensile test fractures were located at the base material (BM) for all DP800 weldments, while the fractures occurred at the fusion zone (FZ) for the weldments with DP1000 and those with dissimilar sheet thicknesses. The DP800-DP1000 weldment presented similar yield strength (YS, 747 MPa) and ultimate tensile strength (UTS, 858 MPa) values but lower elongation (EI, 5.1%) in comparison with the DP800-DP800 weldment (YS 701 MPa, UTS 868 MPa, EI 7.9%), which showed similar strength properties as the BM of DP800. However, the EI of DP1000-DP1000 weldment was 1.9%, much lower in comparison with the BM of DP1000. The DP800-DP1000 weldment with dissimilar thicknesses showed the highest YS (955 MPa) and UTS (1075 MPa) values compared with the other weldments, but with the lowest EI (1.2%). The fatigue fractures occurred at the WJ for all types of weldments. The DP800-DP800 weldment had the highest fatigue limit (348 MPa) and DP800-DP1000 with dissimilar thicknesses had the lowest fatigue limit (<200 MPa). The fatigue crack initiated from the weld surface. Full article
(This article belongs to the Special Issue Advances in Laser Processing)
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12 pages, 2187 KiB  
Article
Enhancement of Gingival Tissue Adherence of Zirconia Implant Posts: In Vitro Study
by Alexandra Zühlke, Michael Gasik, Khalil Shahramian, Timo Närhi, Yevgen Bilotsky and Ilkka Kangasniemi
Materials 2021, 14(2), 455; https://doi.org/10.3390/ma14020455 - 19 Jan 2021
Cited by 7 | Viewed by 2593
Abstract
Prevention of bacterial inflammation around dental implants (peri-implantitis) is one of the keys to success of the implantation and can be achieved by securing the gingival tissue-abutment interface preventing penetration of bacteria. Modern dental practice has adopted zirconia abutments in place of titanium, [...] Read more.
Prevention of bacterial inflammation around dental implants (peri-implantitis) is one of the keys to success of the implantation and can be achieved by securing the gingival tissue-abutment interface preventing penetration of bacteria. Modern dental practice has adopted zirconia abutments in place of titanium, but the adhesion of gingival tissue to zirconia is inferior to titanium. The aim of this study was to assess and improve the adhesion of mucosal tissues to zirconia posts using sol-gel derived TiO2 coating following dynamic mechanical testing. The posts were cultivated with porcine bone-gingival tissue specimens in vitro for 7 and 14 days and then subjected to dynamic mechanical analysis simulating physiological loading at 1 Hz up to 50 μm amplitude. In parallel in silico analysis of stresses and strains have been made simulating “the worst case” when the fixture fails in osseointegration while the abutment still holds. Results show treatment of zirconia can lead to double interface stiffness (static shear stiffness values from 5–10 to 17–23 kPa and dynamic from 20–50 to 60–125 kPa), invariant viscostiffness (from 5–35 to 45–90 kPa·sα) and material memory values (increased from 0.06–0.10 to 0.17–0.25), which is beneficial in preventing bacterial contamination in dental implants. This suggests TiO2-coated zirconia abutments may have a significant clinical benefit for prevention of the bacterial contamination. Full article
(This article belongs to the Special Issue Translational Research on Dental Materials)
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16 pages, 12794 KiB  
Article
Material Model Development of Magnesium Alloy and Its Strength Evaluation
by Wenjia Huang, Ninshu Ma, Yunwu Ma, Toshiro Amaishi, Kenji Takada and Takayuki Hama
Materials 2021, 14(2), 454; https://doi.org/10.3390/ma14020454 - 19 Jan 2021
Cited by 3 | Viewed by 2767
Abstract
A new material model of magnesium alloys, combining both Hill’48 yield function and Cazacu’06 yield function, was developed and programmed into LS-DYNA using user subroutine, in which both slip dominant and twinning/untwinning dominant hardening phenomena were included. First, a cyclic load test was [...] Read more.
A new material model of magnesium alloys, combining both Hill’48 yield function and Cazacu’06 yield function, was developed and programmed into LS-DYNA using user subroutine, in which both slip dominant and twinning/untwinning dominant hardening phenomena were included. First, a cyclic load test was performed, and its finite element analysis was carried out to verify the new material model. Then, the deformation behaviors of the magnesium crash box subjected to the compressive impact loading were investigated using the developed material model. Compared with the experimental results, the new material model accurately predicted the deformation characteristics of magnesium alloy parts. Additionally, the effect of the thickness distribution, initial deflection and contact friction coefficient in simulation models on deformation behaviors were investigated using this validated material model. Full article
(This article belongs to the Special Issue Assessment of Metallurgical and Mechanical Properties of Welded Joints via Numerical Simulation and Experiments)
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11 pages, 3418 KiB  
Article
Impact of Zr-Doped Bi2O3 Radiopacifier by Spray Pyrolysis on Mineral Trioxide Aggregate
by Tzu-Yu Peng, May-Show Chen, Ya-Yi Chen, Yao-Jui Chen, Chin-Yi Chen, Alex Fang, Bo-Jiun Shao, Min-Hua Chen and Chung-Kwei Lin
Materials 2021, 14(2), 453; https://doi.org/10.3390/ma14020453 - 19 Jan 2021
Cited by 3 | Viewed by 2547
Abstract
Mineral trioxide aggregates (MTA) have been developed as a dental root repair material for a range of endodontics procedures. They contain a small amount of bismuth oxide (Bi2O3) as a radiopacifier to differentiate adjacent bone tissue on radiographs for [...] Read more.
Mineral trioxide aggregates (MTA) have been developed as a dental root repair material for a range of endodontics procedures. They contain a small amount of bismuth oxide (Bi2O3) as a radiopacifier to differentiate adjacent bone tissue on radiographs for endodontic surgery. However, the addition of Bi2O3 to MTA will increase porosity and lead to the deterioration of MTA’s mechanical properties. Besides, Bi2O3 can also increase the setting time of MTA. To improve upon the undesirable effects caused by Bi2O3 additives, we used zirconium ions (Zr) to substitute the bismuth ions (Bi) in the Bi2O3 compound. Here we demonstrate a new composition of Zr-doped Bi2O3 using spray pyrolysis, a technique for producing fine solid particles. The results showed that Zr ions were doped into the Bi2O3 compound, resulting in the phase of Bi7.38Zr0.62O12.31. The results of materials analysis showed Bi2O3 with 15 mol % of Zr doping increased its radiopacity (5.16 ± 0.2 mm Al) and mechanical strength, compared to Bi2O3 and other ratios of Zr-doped Bi2O3. To our knowledge, this is the first study of fabrication and analysis of Zr-doped Bi2O3 radiopacifiers through the spray pyrolysis procedure. The study reveals that spray pyrolysis can be a new technique for preparing Zr-doped Bi2O3 radiopacifiers for future dental applications. Full article
(This article belongs to the Special Issue Advances in Dental Composite Materials and Biomaterials)
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22 pages, 56259 KiB  
Article
Evaluation Method of the Vibration Reduction Effect Considering the Real Load- and Frequency-Dependent Stiffness of Slab-Track Mats
by Zeming Zhao, Kai Wei, Wenhao Ding, Fang Cheng and Ping Wang
Materials 2021, 14(2), 452; https://doi.org/10.3390/ma14020452 - 18 Jan 2021
Cited by 9 | Viewed by 2441
Abstract
The purpose of this research was to investigate and improve the accuracy of the existing slab-track mat (STM) specifications in the evaluation of the vibration reduction effect. The static nonlinearity and dynamic mechanical characteristics of three types of STMs were tested, and then [...] Read more.
The purpose of this research was to investigate and improve the accuracy of the existing slab-track mat (STM) specifications in the evaluation of the vibration reduction effect. The static nonlinearity and dynamic mechanical characteristics of three types of STMs were tested, and then a modified fractional derivative Poynting–Thomson (FDPT) model was used to characterize the preload and frequency dependence. A modified vehicle–floating slab track (FST) coupled dynamic model was established to analyze the actual insertion loss. The insertion loss error evaluated by the frequency-dependent tangent stiffness increased with the increase in STM nonlinearity, and the error obtained by the third preload tangent stiffness was usually greater than that of the second preload. Compared with the secant stiffness, the second preload frequency-dependent tangent stiffness was more suitable for evaluating STMs with high-static–low-dynamics (HSLD) stiffness. In order to reflect the frequency dependence effect and facilitate engineering applications, it is recommended that second preload tangent stiffness corresponding to the natural frequency of the FST be used for evaluation. Furthermore, the insertion loss of the STMs with monotonically increased stiffness decreased as the axle load increased, and the opposite was true for the STMs with monotonically decreased stiffness. The vibration isolation efficiency of the STMs with HSLD stiffness was both stable and better than that of the STMs with monotonic stiffness. Full article
(This article belongs to the Section Construction and Building Materials)
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12 pages, 4041 KiB  
Article
Acousto-Optic Cells with Phased-Array Transducers and Their Application in Systems of Optical Information Processing
by Vladimir Balakshy, Maxim Kupreychik, Sergey Mantsevich and Vladimir Molchanov
Materials 2021, 14(2), 451; https://doi.org/10.3390/ma14020451 - 18 Jan 2021
Cited by 16 | Viewed by 3098
Abstract
This paper presents the results of theoretical and experimental studies of anisotropic acousto-optic interaction in a spatially periodical acoustic field created by a phased-array transducer with antiphase excitation of adjacent sections. In this case, contrary to the nonsectioned transducer, light diffraction is absent [...] Read more.
This paper presents the results of theoretical and experimental studies of anisotropic acousto-optic interaction in a spatially periodical acoustic field created by a phased-array transducer with antiphase excitation of adjacent sections. In this case, contrary to the nonsectioned transducer, light diffraction is absent when the optical beam falls on the phased-array cell at the Bragg angle. However, the diffraction takes place at some other angles (called “optimal” here), which are situated on the opposite sides to the Bragg angle. Our calculations show that the diffraction efficiency can reach 100% at these optimal angles in spite of a noticeable acousto-optic phase mismatch. This kind of acousto-optic interaction possesses a number of interesting regularities which can be useful for designing acousto-optic devices of a new type. Our experiments were performed with a paratellurite (TeO2) cell in which a shear acoustic mode was excited at a 9∘ angle to the crystal plane (001). The piezoelectric transducer had to nine antiphase sections. The efficiency of electric to acoustic power conversion was 99% at the maximum frequency response, and the ultrasound excitation band extended from 70 to 160 MHz. The experiments have confirmed basic results of the theoretical analysis. Full article
(This article belongs to the Special Issue Acousto-Optical Spectral Technologies)
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24 pages, 5466 KiB  
Article
Multi-Scale Analyses and Modeling of Metallic Nano-Layers
by Zara Moleinia and David F. Bahr
Materials 2021, 14(2), 450; https://doi.org/10.3390/ma14020450 - 18 Jan 2021
Cited by 2 | Viewed by 1955
Abstract
The current work centers on multi-scale approaches to simulate and predict metallic nano-layers’ thermomechanical responses in crystal plasticity large deformation finite element platforms. The study is divided into two major scales: nano- and homogenized levels where Cu/Nb nano-layers are designated as case studies. [...] Read more.
The current work centers on multi-scale approaches to simulate and predict metallic nano-layers’ thermomechanical responses in crystal plasticity large deformation finite element platforms. The study is divided into two major scales: nano- and homogenized levels where Cu/Nb nano-layers are designated as case studies. At the nano-scale, a size-dependent constitutive model based on entropic kinetics is developed. A deep-learning adaptive boosting technique named single layer calibration is established to acquire associated constitutive parameters through a single process applicable to a broad range of setups entirely different from those of the calibration. The model is validated through experimental data with solid agreement followed by the behavioral predictions of multiple cases regarding size, loading pattern, layer type, and geometrical combination effects for which the performances are discussed. At the homogenized scale, founded on statistical analyses of microcanonical ensembles, a homogenized crystal plasticity-based constitutive model is developed with the aim of expediting while retaining the accuracy of computational processes. Accordingly, effective constitutive functionals are realized where the associated constants are obtained via metaheuristic genetic algorithms. The model is favorably verified with nano-scale data while accelerating the computational processes by several orders of magnitude. Ultimately, a temperature-dependent homogenized constitutive model is developed where the effective constitutive functionals along with the associated constants are determined. The model is validated by experimental data with which multiple demonstrations of temperature effects are assessed and analyzed. Full article
(This article belongs to the Section Materials Simulation and Design)
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37 pages, 7570 KiB  
Article
Dependence of Heat Transport in Solids on Length-Scale, Pressure, and Temperature: Implications for Mechanisms and Thermodynamics
by Anne M. Hofmeister
Materials 2021, 14(2), 449; https://doi.org/10.3390/ma14020449 - 18 Jan 2021
Cited by 9 | Viewed by 3352
Abstract
Accurate laser-flash measurements of thermal diffusivity (D) of diverse bulk solids at moderate temperature (T), with thickness L of ~0.03 to 10 mm, reveal that D(T) = D∞(T)[1 − exp(−bL)]. [...] Read more.
Accurate laser-flash measurements of thermal diffusivity (D) of diverse bulk solids at moderate temperature (T), with thickness L of ~0.03 to 10 mm, reveal that D(T) = D∞(T)[1 − exp(−bL)]. When L is several mm, D∞(T) = FT−G + HT, where F is constant, G is ~1 or 0, and H (for insulators) is ~0.001. The attenuation parameter b = 6.19D∞−0.477 at 298 K for electrical insulators, elements, and alloys. Dimensional analysis confirms that D → 0 as L → 0, which is consistent with heat diffusion, requiring a medium. Thermal conductivity (κ) behaves similarly, being proportional to D. Attenuation describing heat conduction signifies that light is the diffusing entity in solids. A radiative transfer model with 1 free parameter that represents a simplified absorption coefficient describes the complex form for κ(T) of solids, including its strong peak at cryogenic temperatures. Three parameters describe κ with a secondary peak and/or a high-T increase. The strong length dependence and experimental difficulties in diamond anvil studies have yielded problematic transport properties. Reliable low-pressure data on diverse thick samples reveal a new thermodynamic formula for specific heat (∂ln(cP)/∂P = −linear compressibility), which leads to ∂ln(κ)/∂P = linear compressibility + ∂lnα/∂P, where α is thermal expansivity. These formulae support that heat conduction in solids equals diffusion of light down the thermal gradient, since changing P alters the space occupied by matter, but not by light. Full article
(This article belongs to the Special Issue High-Pressure Materials)
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14 pages, 5612 KiB  
Article
Impact of Particle Size on Performance of Selective Laser Sintering Walnut Shell/Co-PES Powder
by Yueqiang Yu, Minzheng Jiang, Suling Wang, Yanling Guo, Ting Jiang, Weiliang Zeng and Yu Zhuang
Materials 2021, 14(2), 448; https://doi.org/10.3390/ma14020448 - 18 Jan 2021
Cited by 5 | Viewed by 2173
Abstract
The agricultural and forestry waste walnut shell and copolyester hot-melt adhesives (Co-PES) powder were selected as feedstock. A kind of low-cost, low-power consumption, and environmentally friendly walnut shell/Co-PES powder composites (WSPC) was used for selective laser sintering (SLS). Though analyzing the size and [...] Read more.
The agricultural and forestry waste walnut shell and copolyester hot-melt adhesives (Co-PES) powder were selected as feedstock. A kind of low-cost, low-power consumption, and environmentally friendly walnut shell/Co-PES powder composites (WSPC) was used for selective laser sintering (SLS). Though analyzing the size and morphology of walnut shell particle (≤550 μm) as well as performing an analysis of surface roughness, density, and mechanical test of WSPC parts with different particle sizes, results showed that the optimal mechanical performance (tensile strength of 2.011 MPa, bending strength of 3.5 MPa, impact strength of 0.718 KJ/m2) as walnut shell powder particle size was 80 to 120 μm. When walnut shell powder particle diameter was 120 to 180 μm, the minimum value of surface roughness of WSPC parts was 15.711 μm and density was approximately the maximum (0.926 g/cm3). Full article
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13 pages, 2117 KiB  
Article
Experimental Investigation into the Effect of Pyrolysis on Chemical Forms of Heavy Metals in Sewage Sludge Biochar (SSB), with Brief Ecological Risk Assessment
by Binbin Li, Songxiong Ding, Haihong Fan and Yu Ren
Materials 2021, 14(2), 447; https://doi.org/10.3390/ma14020447 - 18 Jan 2021
Cited by 34 | Viewed by 3332
Abstract
Experimental investigations were carried out to study the effect of pyrolysis temperature on the characteristics, structure and total heavy metal contents of sewage sludge biochar (SSB). The changes in chemical forms of the heavy metals (Zn, Cu, Cr, Ni, Pb and Cd) caused [...] Read more.
Experimental investigations were carried out to study the effect of pyrolysis temperature on the characteristics, structure and total heavy metal contents of sewage sludge biochar (SSB). The changes in chemical forms of the heavy metals (Zn, Cu, Cr, Ni, Pb and Cd) caused by pyrolysis were analyzed, and the potential ecological risk of heavy metals in biochar (SSB) was evaluated. The conversion of sewage sludge into biochar by pyrolysis reduced the H/C and O/C ratios considerably, resulting in stronger carbonization and a higher degree of aromatic condensation in biochar. Measurement results showed that the pH and specific surface area of biochar increased as the pyrolysis temperature increased. It was found that elements Zn, Cu, Cr and Ni were enriched and confined in biochar SSB with increasing pyrolysis temperature from 300–700 °C; however, the residual rates of Pb and Cd in biochar SSB decreased significantly when the temperature was increased from 600 °C to 700 °C. Measurement with the BCR sequential extraction method revealed that the pyrolysis of sewage sludge at a suitable temperature transferred its bioavailable/degradable heavy metals into a more stable oxidizable/residual form in biochar SSB. Toxicity of heavy metals in biochar SSB could be reduced about four times if sewage sludge was pyrolyzed at a proper temperature; heavy metals confined in sludge SSB pyrolyzed at about 600 °C could be assessed as being low in ecological toxicity. Full article
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18 pages, 6755 KiB  
Article
Synthesis and Investigation of Cryogenic Mechanical Properties of Chopped-Glass-Fiber-Reinforced Polyisocyanurate Foam
by Jeong-Dae Kim, Jeong-Hyeon Kim, Dong-Ha Lee, Dong-Ju Yeom and Jae-Myung Lee
Materials 2021, 14(2), 446; https://doi.org/10.3390/ma14020446 - 18 Jan 2021
Cited by 10 | Viewed by 2923
Abstract
Polyisocyanurate foam (PIF) has been adopted as a liquefied natural gas (LNG) insulating material owing to its various mechanical merits such as high structural stability and mechanical strength, and excellent insulating ability. In an attempt to increase the mechanical strength of PIF, chopped-glass-fiber-reinforced [...] Read more.
Polyisocyanurate foam (PIF) has been adopted as a liquefied natural gas (LNG) insulating material owing to its various mechanical merits such as high structural stability and mechanical strength, and excellent insulating ability. In an attempt to increase the mechanical strength of PIF, chopped-glass-fiber-reinforced polyisocyanurate foam (CGR-PIF) was synthesized by adding chopped glass fibers to polyol and isocyanate, which are the raw materials used in the polymerization process for producing PIF. The main objective is to closely observe the compression material characteristics of PIF and CGR-PIF in terms of the cryogenic temperature. Therefore, compressive tests were conducted at cryogenic temperature including low temperatures, and microscopic images were obtained to analyze the cell size and distribution that affects the mechanical and thermal properties of the foam. Furthermore, recovery ratio and weight loss which are important factors of brittle fracture were evaluated, and the applicability of the foams to a cryogenic environment was evaluated. Finally, thermal conductivity, an important parameter of insulation, was evaluated. The obtained results confirm that the compressive strength of CGR-PIF significantly increases at cryogenic temperatures; moreover, a relatively higher thermal conductivity was observed in the case of CGR-PIF as compared to that of PIF owing to the chopped glass fibers. Full article
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17 pages, 9920 KiB  
Article
Effect of the Notch-to-Depth Ratio on the Post-Cracking Behavior of Steel-Fiber-Reinforced Concrete
by José Valdez Aguilar, César A. Juárez-Alvarado, José M. Mendoza-Rangel and Bernardo T. Terán-Torres
Materials 2021, 14(2), 445; https://doi.org/10.3390/ma14020445 - 18 Jan 2021
Cited by 7 | Viewed by 2838
Abstract
Concrete barely possesses tensile strength, and it is susceptible to cracking, which leads to a reduction of its service life. Consequently, it is significant to find a complementary material that helps alleviate these drawbacks. The aim of this research was to determine analytically [...] Read more.
Concrete barely possesses tensile strength, and it is susceptible to cracking, which leads to a reduction of its service life. Consequently, it is significant to find a complementary material that helps alleviate these drawbacks. The aim of this research was to determine analytically and experimentally the effect of the addition of the steel fibers on the performance of the post-cracking stage on fiber-reinforced concrete, by studying four notch-to-depth ratios of 0, 0.08, 0.16, and 0.33. This was evaluated through 72 bending tests, using plain concrete (control) and fiber-reinforced concrete with volume fibers of 0.25% and 0.50%. Results showed that the specimens with a notch-to-depth ratio up to 0.33 are capable of attaining a hardening behavior. The study concludes that the increase in the dosage leads to an improvement in the residual performance, even though an increase in the notch-to-depth ratio has also occurred. Full article
(This article belongs to the Special Issue Concrete and Construction Materials)
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8 pages, 10264 KiB  
Article
Fabrication of Highly Transparent Y2O3 Ceramics with CaO as Sintering Aid
by Danlei Yin, Jun Wang, Meng Ni, Peng Liu, Zhili Dong and Dingyuan Tang
Materials 2021, 14(2), 444; https://doi.org/10.3390/ma14020444 - 18 Jan 2021
Cited by 24 | Viewed by 3170
Abstract
Highly transparent Y2O3 ceramics were successfully fabricated with CaO as sintering aid. The microstructure evolution, optical transmittance, hardness and thermal conductivity of the Y2O3 ceramics were investigated. It was found that doping a small amount (0.01–0.15 wt.%) [...] Read more.
Highly transparent Y2O3 ceramics were successfully fabricated with CaO as sintering aid. The microstructure evolution, optical transmittance, hardness and thermal conductivity of the Y2O3 ceramics were investigated. It was found that doping a small amount (0.01–0.15 wt.%) of CaO could greatly improve the densification rate of Y2O3. With an optimized CaO dosage of 0.02 wt.% combined with the low temperature vacuum sintering plus hot isostatic pressing (HIP-ing), Y2O3 ceramics with in-line transmittance of 84.87% at 1200 nm and 81.4% at 600 nm were obtained. Full article
(This article belongs to the Special Issue Novel Laser Ceramic Materials and Applications)
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18 pages, 5571 KiB  
Article
Conformational Stability of Poly (N-Isopropylacrylamide) Anchored on the Surface of Gold Nanoparticles
by Runmei Li, Cong Cheng, Zhuorui Wang, Xuefan Gu, Caixia Zhang, Chen Wang, Xinyue Liang and Daodao Hu
Materials 2021, 14(2), 443; https://doi.org/10.3390/ma14020443 - 18 Jan 2021
Cited by 6 | Viewed by 2834
Abstract
To verify the temperature sensitive failure of poly (N-isopropylacrylamide) (PNIPAM) anchored on the surface of gold nanoparticles (AuNPs), the UV-Vis spectra with temperature variations of the following aqueous solutions respectively containing AuNPs-PNIPAM, Au-PNIPAM/PNIPAM, PNIPAM, in different media (including salt, ethanol, HCl and cetyltrimethylammoniumbromide [...] Read more.
To verify the temperature sensitive failure of poly (N-isopropylacrylamide) (PNIPAM) anchored on the surface of gold nanoparticles (AuNPs), the UV-Vis spectra with temperature variations of the following aqueous solutions respectively containing AuNPs-PNIPAM, Au-PNIPAM/PNIPAM, PNIPAM, in different media (including salt, ethanol, HCl and cetyltrimethylammoniumbromide (CTAB)), were systematically determined. The results indicated that the UV-Vis spectrum of AuNPs-PNIPAM suspension hardly changed even above the Lower Critical Solution Temperature (LCST) of PNIPAM, but that of Au-PNIPAM/PNIPAM sharply increased only in absorbance intensity. A possible mechanism of the failed temperature sensitivity of PNIPAM anchored on the surface of AuNPs was proposed. Being different from free PNIPAM molecules, a strong interaction exists among PNIPAM molecules anchored on the surface of AuNPs, restraining the change in conformation of PNIPAM. The temperature sensitivity of Au-PNIPAM/PNIPAM originates from the free PNIPAM molecules rather than the anchored PNIPAM one. The changing electrostatic interaction could effectively regulate the aggregation behavior of AuNPs-PNIPAM and enhance its sensitivity to temperature. Full article
(This article belongs to the Special Issue Advances in Metal-Based Nanoparticles)
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