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Volume 12, October-1

Materials, Volume 12, Issue 20 (October-2 2019) – 183 articles

Cover Story (view full-size image): Catalyzed organic solvent-free (ep)oxidation were achieved using H3PM12O40 (M = Mo or W) complexes ionically grafted on APTES-functionalized nano-silica beads obtained from straightforward method (APTES = aminopropyltriethoxysilane). Those catalysts have been extensively analyzed through morphological studies (Dynamic Light Scattering (DLS), TEM) and several spectroscopic qualitative (IR, multinuclear solid-state NMR) and quantitative (1H and 31P solution NMR) methods. Interesting catalytic results were obtained for the epoxidation of cyclooctene, cyclohexene, limonene and oxidation of cyclohexanol with a lower [POM]/olefin ratio. The catalysts were found to be recyclable and reused during three runs with similar catalytic performances. View this paper.
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Open AccessArticle
APD Compressible Aerogel-Like Monoliths with Potential Use in Environmental Remediation
Materials 2019, 12(20), 3459; https://doi.org/10.3390/ma12203459 - 22 Oct 2019
Cited by 1 | Viewed by 688
Abstract
Ambient pressure dried (APD) silica-based aerogel-like monoliths are prepared using vinyltrimethoxysilane (VTMS) as the sole silicon source by a rare-earth-assisted process. The APD method avoids the processes of solvent exchange and surface modification, is cost-effective, and reduces the preparation period from several days [...] Read more.
Ambient pressure dried (APD) silica-based aerogel-like monoliths are prepared using vinyltrimethoxysilane (VTMS) as the sole silicon source by a rare-earth-assisted process. The APD method avoids the processes of solvent exchange and surface modification, is cost-effective, and reduces the preparation period from several days or weeks to 30 h. By controlling the solvent proportions, products with excellent mechanical properties, including exceptional mechanical strength and elasticity, can be synthesized. The monoliths also exhibit the outstanding characteristics of high hydrophobicity and lipophilicity and can rapidly absorb 13.5 times their weight in chloroform, showing great potential as reusable materials for application toward the separation/extraction of organic pollutants and oils. Full article
(This article belongs to the Section Porous Materials)
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Open AccessArticle
Preparation of Imitation Basalt Compound Based on Thermodynamic Calculation
Materials 2019, 12(20), 3458; https://doi.org/10.3390/ma12203458 - 22 Oct 2019
Cited by 2 | Viewed by 642
Abstract
In this paper, imitation basalt compounds using red mud, fly ash or coal gangue as raw materials were designed and prepared with the help of thermodynamic calculations. Thermodynamic calculations were used to obtain the suitable chemical composition. Then, the imitation compounds were prepared [...] Read more.
In this paper, imitation basalt compounds using red mud, fly ash or coal gangue as raw materials were designed and prepared with the help of thermodynamic calculations. Thermodynamic calculations were used to obtain the suitable chemical composition. Then, the imitation compounds were prepared and their phase/compositions were analyzed. Finally, their high-temperature melting performance and crystallization ability were evaluated. The results show that the characteristic temperature and crystallization ability of the imitation basalt compounds were similar to those of basalt. Moreover, the viscosity of red mud imitation basalt compound approached the viscosity of basalt with the increase in temperature. This work suggests that red mud, fly ash and coal gangue can be mixed with quartz and other source materials to produce imitation basalt fiber. Therefore, thermodynamic calculation is an effective method to design and prepare high-performance imitation basalt compounds. Full article
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Open AccessArticle
Influence of Pseudowollastonite on the Performance of Low Calcium Amorphous Hydraulic Binders
Materials 2019, 12(20), 3457; https://doi.org/10.3390/ma12203457 - 22 Oct 2019
Viewed by 833
Abstract
A systematic investigation of the influence of pseudowollastonite on the performance of a new family of low calcium hydraulic binders is described. Samples of the new low calcium binder were produced by an innovative process consisting of heating and homogenizing the mix of [...] Read more.
A systematic investigation of the influence of pseudowollastonite on the performance of a new family of low calcium hydraulic binders is described. Samples of the new low calcium binder were produced by an innovative process consisting of heating and homogenizing the mix of raw materials (limestone, sand, and fuel cracking catalyst) at a constant temperature followed by the rapid cooling of the mixture itself. Different maximum temperatures, close to the melting temperature of the mix, were tested, and materials with CaO/SiO2 (C/S) ratios of 0.9, 1.1, and 1.25 were produced into the form of the amorphous phase with small percentages of pseudowollastonite. Compressive strength results were determined at 7, 28, and 90 days of hydration, and the hydrated phases were analyzed using isothermal calorimetry, X-ray diffraction (XRD) analysis, thermogravimetry analysis (TGA), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The present work is focused on the influence of the percentage of the pseudowollastonite phase on the binder compressive strength performance. Full article
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Open AccessReview
A Review on the Carbonation and Chloride Penetration Resistance of Structural Lightweight Aggregate Concrete
Materials 2019, 12(20), 3456; https://doi.org/10.3390/ma12203456 - 22 Oct 2019
Cited by 10 | Viewed by 820
Abstract
This paper presents a comprehensive review on structural lightweight aggregate concrete (SLWAC) durability. The main transport properties and degradation mechanisms of reinforced concrete are addressed, namely, carbonation and chloride attack. The influence of the main composition parameters, such as type of aggregate, type [...] Read more.
This paper presents a comprehensive review on structural lightweight aggregate concrete (SLWAC) durability. The main transport properties and degradation mechanisms of reinforced concrete are addressed, namely, carbonation and chloride attack. The influence of the main composition parameters, such as type of aggregate, type of binder and water/binder ratio, as well as the influence of cracking, are also analysed. Finally, the current knowledge of SLWAC’s service life prediction is assessed. Although the knowledge of SLWAC’s durability behaviour is still limited, investigation works performed either in laboratory or in real environments indicate that SLWAC can have similar to better durability performance than normal weight concrete, especially when the same strength level is considered. The importance of the quality of the paste over the characteristics of the lightweight aggregates is highlighted. Durability standardization regarding SLWAC is still insufficient and is one of the main gaps of current knowledge. The objective of this review is to foster a better understanding on the durability and service life prediction of SLWAC, contributing to a greater confidence in using this type of concrete. Full article
(This article belongs to the Special Issue Advances in Lightweight Aggregate Concrete)
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Open AccessTechnical Note
An Examination of the Low Strain Rate Sensitivity of Additively Manufactured Polymer, Composite and Metallic Honeycomb Structures
Materials 2019, 12(20), 3455; https://doi.org/10.3390/ma12203455 - 22 Oct 2019
Cited by 5 | Viewed by 797
Abstract
The characterization of additively manufactured cellular materials, such as honeycombs and lattices, is crucial to enabling their implementation in functional parts. One of the characterization methods commonly employed is mechanical testing under compression. This work focuses specifically on the dependence of these tests [...] Read more.
The characterization of additively manufactured cellular materials, such as honeycombs and lattices, is crucial to enabling their implementation in functional parts. One of the characterization methods commonly employed is mechanical testing under compression. This work focuses specifically on the dependence of these tests to the applied strain rate during the test over low strain rate regimes (considered here as 10−6 to 10−1 s−1). The paper is limited to the study of strain the rate dependence of hexagonal honeycomb structures manufactured with four different additive manufacturing processes: one polymer (fused deposition modeling, or material extrusion with ABS), one composite (nylon and continuous carbon fiber extrusion) and two metallic (laser powder bed fusion of Inconel 718 and electron beam melting of Ti6Al4V). The strain rate sensitivities of the effective elastic moduli, and the peak loads for all four processes were compared. Results show significant sensitivity to strain rate in the polymer and composite process for both these metrics, and mild sensitivity for the metallic honeycombs for the peak load. This study has implications for the characterization and modeling of all mechanical cellular materials and makes the case for evaluation and if appropriate, inclusion, of strain rate effects in all cellular material modeling. Full article
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Open AccessArticle
Avoidance of Interaction between Impression Materials and Tooth Surface Treated for Immediate Dentin Sealing: An In Vitro Study
Materials 2019, 12(20), 3454; https://doi.org/10.3390/ma12203454 - 22 Oct 2019
Cited by 7 | Viewed by 970
Abstract
Immediate dentin sealing (IDS) is an advantageous approach for realizing adhesive restorations, but it interferes with the polymerization of impression material due to the oxygen-inhibition layer (OIL), which leaves residues of impression material on the teeth. The aim of this study is to [...] Read more.
Immediate dentin sealing (IDS) is an advantageous approach for realizing adhesive restorations, but it interferes with the polymerization of impression material due to the oxygen-inhibition layer (OIL), which leaves residues of impression material on the teeth. The aim of this study is to identify a clinical surface cleaning protocol after IDS in order to achieve defect-free impressions. Sixty extracted human teeth were cut to expose fresh dentin and the IDS protocol was performed. Samples were divided into six groups where different surface cleaning protocols were made before taking impressions: G1S and G1P groups, IDS and silicone (S) or polyether (P) impressions; G2S and G2P, treatment with prophy paste and impressions; G3S and G3P, final cleaning phase with surfactant agent and impressions. Teeth were evaluated with a scanning electron microscope to identify the areas (expressed in mm2) where residual impression material was present. The results demonstrate a reduction of residues in the G2 groups and the total disappearance in G3 groups with statistically significant differences between them. Superficial cleaning protocols with the prophy paste and surfactant agent lead to the elimination of the interaction with impression materials and OIL. These results suggest a safe clinical protocol for obtaining defect-free impressions after IDS. Full article
(This article belongs to the Special Issue Advanced Materials for Regenerative and Restorative Dentistry)
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Open AccessArticle
Laser Treatment as Sintering Process for Dispenser Printed Bismuth Telluride Based Paste
Materials 2019, 12(20), 3453; https://doi.org/10.3390/ma12203453 - 22 Oct 2019
Viewed by 731
Abstract
Laser sintering as a thermal post treatment method for dispenser printed p- and n-type bismuth telluride based thermoelectric paste materials was investigated. A high-power fiber laser (600 W, 1064 nm) was used in combination with a scanning system to achieve high processing speed. [...] Read more.
Laser sintering as a thermal post treatment method for dispenser printed p- and n-type bismuth telluride based thermoelectric paste materials was investigated. A high-power fiber laser (600 W, 1064 nm) was used in combination with a scanning system to achieve high processing speed. A Design of Experiment (DoE) approach was used to identify the most relevant processing parameters. Printed layers were laser treated with different process parameters and the achieved sheet resistance, electrical conductivity, and Seebeck coefficient are compared to tube furnace processed reference specimen. For p-type material, electrical conductivity of 22 S/cm was achieved, compared to 15 S/cm in tube furnace process. For n-type material, conductivity achieved by laser process was much lower (7 S/cm) compared to 88 S/cm in furnace process. Also, Seebeck coefficient decreases during laser processing (40–70 µV/K and −110 µV/K) compared to the oven process (251 µV/K and −142 µV/K) for p- and n-type material. DoE did not yet deliver a set of optimum processing parameters, but supports doubts about the applicability of area specific laser energy density as a single parameter to optimize laser sintering process. Full article
(This article belongs to the Special Issue Selected Papers from ISCTA 2018)
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Open AccessArticle
Temperature, Pressure, and Velocity Influence on the Tribological Properties of PA66 and PA46 Polyamides
Materials 2019, 12(20), 3452; https://doi.org/10.3390/ma12203452 - 22 Oct 2019
Cited by 7 | Viewed by 823
Abstract
The tribological properties of PA66, PA46, and PTFE-mixed PA46 were investigated. The tests were achieved on a pin-on-disc tribometer. Before tests with different sets of parameters, a running-in-type test (with constant parameters) was performed for all the materials, under lubricated and dry conditions. [...] Read more.
The tribological properties of PA66, PA46, and PTFE-mixed PA46 were investigated. The tests were achieved on a pin-on-disc tribometer. Before tests with different sets of parameters, a running-in-type test (with constant parameters) was performed for all the materials, under lubricated and dry conditions. The tests parameters were variable referring on load, velocity, and temperature. The results are referring on the value of the wear developed during the run-in period and on the variation of friction coefficient with the testing parameters. The results show that the PTFE-mixed PA46 polyamide has better tribological properties than the PA66 and the PA46 polyamide. Full article
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Open AccessArticle
Three-Dimensional (3D) Vertical Resistive Random-Access Memory (VRRAM) Synapses for Neural Network Systems
Materials 2019, 12(20), 3451; https://doi.org/10.3390/ma12203451 - 22 Oct 2019
Cited by 3 | Viewed by 904
Abstract
Memristor devices are generally suitable for incorporation in neuromorphic systems as synapses because they can be integrated into crossbar array circuits with high area efficiency. In the case of a two-dimensional (2D) crossbar array, however, the size of the array is proportional to [...] Read more.
Memristor devices are generally suitable for incorporation in neuromorphic systems as synapses because they can be integrated into crossbar array circuits with high area efficiency. In the case of a two-dimensional (2D) crossbar array, however, the size of the array is proportional to the neural network’s depth and the number of its input and output nodes. This means that a 2D crossbar array is not suitable for a deep neural network. On the other hand, synapses that use a memristor with a 3D structure are suitable for implementing a neuromorphic chip for a multi-layered neural network. In this study, we propose a new optimization method for machine learning weight changes that considers the structural characteristics of a 3D vertical resistive random-access memory (VRRAM) structure for the first time. The newly proposed synapse operating principle of the 3D VRRAM structure can simplify the complexity of a neuron circuit. This study investigates the operating principle of 3D VRRAM synapses with comb-shaped word lines and demonstrates that the proposed 3D VRRAM structure will be a promising solution for a high-density neural network hardware system. Full article
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Open AccessArticle
Assessment of Tendon Prestressing after Long-Term Service via the Barkhausen Noise Technique
Materials 2019, 12(20), 3450; https://doi.org/10.3390/ma12203450 - 22 Oct 2019
Cited by 5 | Viewed by 596
Abstract
This paper deals with the assessment of a real prestressed tendon by the use of Barkhausen noise emission. The tendon was obtained from a real highway bridge after 33 years in service. Barkhausen noise is studied as a function of the stress state, [...] Read more.
This paper deals with the assessment of a real prestressed tendon by the use of Barkhausen noise emission. The tendon was obtained from a real highway bridge after 33 years in service. Barkhausen noise is studied as a function of the stress state, and the Barkhausen noise signals received directly from the tendon on the real bridge are compared with the Barkhausen noise signals received from the tendon during loading in the laboratory. Assessment of the prestressing is based on the analysis of the effective value of the Barkhausen noise signal as well as the position in which the Barkhausen noise envelopes attain a maximum. Full article
(This article belongs to the Special Issue Magnetic Materials and Applications)
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Open AccessReview
Bioengineered Scaffolds as Substitutes for Grafts for Urethra Reconstruction
Materials 2019, 12(20), 3449; https://doi.org/10.3390/ma12203449 - 22 Oct 2019
Viewed by 710
Abstract
Urethral defects originating from congenital malformations, trauma, inflammation or carcinoma still pose a great challenge to modern urology. Recent therapies have failed many times and have not provided the expected results. This negatively affects patients’ quality of life. By combining cells, bioactive molecules, [...] Read more.
Urethral defects originating from congenital malformations, trauma, inflammation or carcinoma still pose a great challenge to modern urology. Recent therapies have failed many times and have not provided the expected results. This negatively affects patients’ quality of life. By combining cells, bioactive molecules, and biomaterials, tissue engineering can provide promising treatment options. This review focused on scaffold systems for urethra reconstruction. We also discussed different technologies, such as electrospinning and 3D bioprinting which provide great possibility for the preparation of a hollow structure with well-defined architecture. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle
Application-Specific Oxide-Based and Metal–Dielectric Thin-Film Materials Prepared by Radio Frequency Magnetron Sputtering
Materials 2019, 12(20), 3448; https://doi.org/10.3390/ma12203448 - 21 Oct 2019
Cited by 2 | Viewed by 827
Abstract
We report on the development of several different thin-film functional material systems prepared by radio frequency (RF) magnetron sputtering at Edith Cowan University nanofabrication labs. While focusing on the RF sputtering process optimizations for new or the previously underexplored material compositions and multilayer [...] Read more.
We report on the development of several different thin-film functional material systems prepared by radio frequency (RF) magnetron sputtering at Edith Cowan University nanofabrication labs. While focusing on the RF sputtering process optimizations for new or the previously underexplored material compositions and multilayer structures, we disclose several unforeseen material properties and behaviours. Among these are an unconventional magnetic hysteresis loop with an intermediate saturation state observed in garnet trilayers, and an ultrasensitive magnetic switching behaviour in garnet-oxide composites (GOC). We also report on the unusually high thermal exposure stability observed in some nanoengineered metal–dielectric multilayers. We communicate research results related to the design, prototyping, and practical fabrication of high-performance magneto-optic (MO) materials, oxide-based sensor components, and heat regulation coatings for advanced construction and solar windows. Full article
(This article belongs to the Special Issue Sputtering Technologies for Growth of Advanced Thin Film)
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Open AccessArticle
Effects of Fineness and Chemical Composition of Blast Furnace Slag on Properties of Alkali-Activated Binder
Materials 2019, 12(20), 3447; https://doi.org/10.3390/ma12203447 - 21 Oct 2019
Cited by 7 | Viewed by 790
Abstract
The effects of fines and chemical composition of three types of ground granulated blast furnace slag (GGBFS) on various concrete properties were studied. Those studied were alkali activated by liquid sodium silicate (SS) and sodium carbonate (SC). Flowability, setting times, compressive strength, efflorescence, [...] Read more.
The effects of fines and chemical composition of three types of ground granulated blast furnace slag (GGBFS) on various concrete properties were studied. Those studied were alkali activated by liquid sodium silicate (SS) and sodium carbonate (SC). Flowability, setting times, compressive strength, efflorescence, and carbonation resistance and shrinkage were tested. The chemical composition and microstructure of the solidified matrixes were studied by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) coupled with EDX analyser. The results showed that the particle size distribution of the slags and the activator type had significantly stronger effects on all measured properties than their chemical composition. The highest compressive strength values were obtained for the finest slag, which having also the lowest MgO content. SC-activated mortar produced nearly the same compressive strength values independently of the used slag. The most intensive efflorescence and the lowest carbonation resistance developed on mortars based on slag containing 12% of MgO and the lowest fineness. The slag with the highest specific surface area and the lowest MgO content developed a homogenous microstructure, highest reaction temperature and lowest drying shrinkage. Thermogravimetric analysis indicated the presence of C-(A)-S-H, hydrotalcite HT, and carbonate like-phases in all studied mortars. Full article
(This article belongs to the Special Issue Alkali‐Activated Materials for Sustainable Construction)
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Open AccessArticle
Tailoring the Size and Shape—New Path for Ammonium Metavanadate Synthesis
Materials 2019, 12(20), 3446; https://doi.org/10.3390/ma12203446 - 21 Oct 2019
Cited by 1 | Viewed by 636
Abstract
Ammonium metavanadate, NH4VO3, plays an important role in the preparation of vanadium oxides and other ammonium compounds, such as NH4V3O8, (NH4)2V3O8, and NH4V [...] Read more.
Ammonium metavanadate, NH4VO3, plays an important role in the preparation of vanadium oxides and other ammonium compounds, such as NH4V3O8, (NH4)2V3O8, and NH4V4O10, which were found to possess interesting electrochemical properties. In this work, a new route for the synthesis of NH4VO3 is proposed by mixing an organic ammonium salt and V2O5 in a suitable solvent. The one-step procedure is carried out at room temperature. Additionally, the need for pH control and use of oxidants necessary in known methods is eliminated. The mechanism of the NH4VO3 formation is explained. It is presented that it is possible to tailor the morphology and size of the obtained NH4VO3 crystals, depending on the combination of reagents. Nano- and microcrystals of NH4VO3 are obtained and used as precursors in the hydrothermal synthesis of higher ammonium vanadates. It is proven that the size of the precursor particles can significantly affect the physical and chemical properties of the resulting products. Full article
(This article belongs to the Section Materials Chemistry)
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Open AccessArticle
Enhanced Strength and Ductility in Magnesium Matrix Composites Reinforced by a High Volume Fraction of Nano- and Submicron-Sized SiC Particles Produced by Mechanical Milling and Hot Extrusion
Materials 2019, 12(20), 3445; https://doi.org/10.3390/ma12203445 - 21 Oct 2019
Cited by 4 | Viewed by 682
Abstract
In the present study, Mg nanocomposites with a high volume fraction (10 vol %) of SiC particles were fabricated by two approaches: mechanical milling and mixing, followed by the powder consolidation steps, including isostatic cold pressing, sintering, and extrusion. A uniform distribution of [...] Read more.
In the present study, Mg nanocomposites with a high volume fraction (10 vol %) of SiC particles were fabricated by two approaches: mechanical milling and mixing, followed by the powder consolidation steps, including isostatic cold pressing, sintering, and extrusion. A uniform distribution of the high content SiC particles in a fully dense Mg matrix with ultrafine microstructure was successfully achieved in the mechanically milled composites. The effect of nano- and submicron-sized SiC particles on the microstructure and mechanical properties of the nanocomposites was evaluated. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), and X-ray diffractometry (XRD) were used to characterize microstructures of the milled and mixed composites. Mechanical behavior of the Mg composites was studied under nanoindentation and compressive loading to understand the effects the microstructural modification on the strength and ductility of the Mg/SiC composites. The mechanical properties of the composites showed a significant difference regarding the size and distribution of SiC particles in the Mg matrix. The enhanced strength and superior ductility achieved in the mechanically milled Mg composites are mainly ascribed to the effective load transfer between matrix and SiC particles, grain refinement of the matrix, and strengthening effects of the nano- and submicron-sized SiC particles. Full article
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Open AccessArticle
New Dental Implant with 3D Shock Absorbers and Tooth-Like Mobility—Prototype Development, Finite Element Analysis (FEA), and Mechanical Testing
Materials 2019, 12(20), 3444; https://doi.org/10.3390/ma12203444 - 21 Oct 2019
Viewed by 846
Abstract
Background: Once inserted and osseointegrated, dental implants become ankylosed, which makes them immobile with respect to the alveolar bone. The present paper describes the development of a new and original implant design which replicates the 3D physiological mobility of natural teeth. The first [...] Read more.
Background: Once inserted and osseointegrated, dental implants become ankylosed, which makes them immobile with respect to the alveolar bone. The present paper describes the development of a new and original implant design which replicates the 3D physiological mobility of natural teeth. The first phase of the test followed the resistance of the implant to mechanical stress as well as the behavior of the surrounding bone. Modifications to the design were made after the first set of results. In the second stage, mechanical tests in conjunction with finite element analysis were performed to test the improved implant design. Methods: In order to test the new concept, 6 titanium alloy (Ti6Al4V) implants were produced (milling). The implants were fitted into the dynamic testing device. The initial mobility was measured for each implant as well as their mobility after several test cycles. In the second stage, 10 implants with the modified design were produced. The testing protocol included mechanical testing and finite element analysis. Results: The initial testing protocol was applied almost entirely successfully. Premature fracturing of some implants and fitting blocks occurred and the testing protocol was readjusted. The issues in the initial test helped design the final testing protocol and the new implants with improved mechanical performance. Conclusion: The new prototype proved the efficiency of the concept. The initial tests pointed out the need for design improvement and the following tests validated the concept. Full article
(This article belongs to the Special Issue Selected Papers from BIOMMEDD 2018 Conference—Biomaterials)
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Open AccessArticle
Bending Fatigue Behaviors Analysis and Fatigue Life Prediction of 20Cr2Ni4 Gear Steel with Different Stress Concentrations near Non-metallic Inclusions
Materials 2019, 12(20), 3443; https://doi.org/10.3390/ma12203443 - 21 Oct 2019
Cited by 3 | Viewed by 656
Abstract
To investigate the relationship between inclusions and bending fatigue behaviors in 20Cr2Ni4 steel under different stress concentrations. This paper designs a new experimental method to prefabricate different size stress concentrations near the inclusions, and then conducts a new type of bending fatigue test [...] Read more.
To investigate the relationship between inclusions and bending fatigue behaviors in 20Cr2Ni4 steel under different stress concentrations. This paper designs a new experimental method to prefabricate different size stress concentrations near the inclusions, and then conducts a new type of bending fatigue test to study the inclusions and their surrounding stress distributions in 20Cr2Ni4 steel. A microhardness tester was combined with laser etching equipment to realize the prefabrication of different stress concentrations at arbitrary positions around any inclusion on the gear steel surface. This method provides an experimental basis for the quantitative analysis of the relationship between stress distribution and fatigue life around the inclusions of heavy-duty gear steels. We also predict the bending fatigue lives of heavy-duty gear steels with different types of inclusions, stress states, and spatial distributions. Then, based on the prefabricated notch parameters and the state of inclusions in the steel, a mathematical model of quantitative analysis is proposed, which can accurately predict the fatigue limit of heavy-duty gear steel. The research results can be applied to the actual use of heavy-duty gears and to the accurate life estimation based on the state of gear stress, thereby providing a quantitative reference model for subsequent gear steel production and gear part processing. Full article
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Open AccessArticle
Characterization and Quantitative Analysis of Crack Precursor Size for Rubber Composites
Materials 2019, 12(20), 3442; https://doi.org/10.3390/ma12203442 - 21 Oct 2019
Cited by 3 | Viewed by 614
Abstract
In the field of engineering, the annual economic loss caused by material fatigue failure reaches 4% of the total economic output. The deep understanding of rubber fatigue failure can help develop and prepare rubber composites with high durability. The crack precursor sizes within [...] Read more.
In the field of engineering, the annual economic loss caused by material fatigue failure reaches 4% of the total economic output. The deep understanding of rubber fatigue failure can help develop and prepare rubber composites with high durability. The crack precursor sizes within the rubber composites are vital for the material mechanical and fatigue properties. In this study, we adopted three different characterization methods to analyze crack precursor sizes and their distribution. First, based on the theoretical formula of fracture mechanics, the size of the crack precursor was deduced from 180 μm to 500 μm by the uniaxial tensile experiment combined with tear test (nicked angle tear, planar tear and trouser tear). Second, by combining the uniaxial fatigue test of dumbbell specimen with the fatigue crack growth rate test, the average size of the crack precursor was calculated as 3.3 μm based on the Thomas fatigue crack growth model. Third, the average size of the crack precursor was 3.6 μm obtained by scanning electron microscope. Through theoretical calculations and experimental tests, the size and distribution of the crack precursors of rubber composites were systematically presented. This work can provide theoretical guidance for the improvement of fatigue performance of rubber composites. Full article
(This article belongs to the Special Issue Fatigue Properties and Damage Mechanisms of Polymeric Composites)
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Open AccessArticle
Compositional Engineering of a La1-xBaxCoO3-δ-(1-a) BaZr0.9Y0.1O2.95 (a = 0.6, 0.7, 0.8 and x = 0.5, 0.6, 0.7) Nanocomposite Cathodes for Protonic Ceramic Fuel Cells
Materials 2019, 12(20), 3441; https://doi.org/10.3390/ma12203441 - 21 Oct 2019
Viewed by 854
Abstract
Compositionally engineered a La1-xBaxCoO3-δ-(1-a) BaZr0.9Y0.1O2.95 (a = 0.6, 0.7, 0.8 and x = 0.5, 0.6, 0.7) (LBZ) nanocomposite cathodes were prepared by oxidation driven in situ exsolution of a [...] Read more.
Compositionally engineered a La1-xBaxCoO3-δ-(1-a) BaZr0.9Y0.1O2.95 (a = 0.6, 0.7, 0.8 and x = 0.5, 0.6, 0.7) (LBZ) nanocomposite cathodes were prepared by oxidation driven in situ exsolution of a single-phase material deposited on a BaZr0.9Y0.1O2.95 electrolyte. The processing procedure of the cathode was optimized by reducing the number of thermal treatments as the single-phase precursor was deposited directly on the electrolyte. The exsolution and firing of the cathodes occurred in one step. The electrochemical performance of symmetrical cells with the compositionally engineered cathodes was investigated by impedance spectroscopy in controlled atmospheres. The optimized materials processing gave web-like nanostructured cathodes with superior electrochemical performance for all compositions. The area specific resistances obtained were all below 12 Ω·cm2 at 400 °C and below 0.59 Ω·cm2 at 600 °C in 3% moist synthetic air. The resistances of the nominal 0.6 La0.5Ba0.5CoO3-δ-0.4 BaZr0.9Y0.1O2.95 and 0.8 La0.5Ba0.5CoO3-δ-0.2 BaZr0.9Y0.1O2.95 composite cathodes were among the lowest reported for protonic ceramic fuel cells cathodes in symmetrical cell configuration with ASR equal to 4.04 and 4.84 Ω·cm2 at 400 °C, and 0.21 and 0.27 Ω·cm2 at 600 °C, respectively. Full article
(This article belongs to the Section Energy Materials)
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Open AccessArticle
Development and Evaluation of Fall Impact Protection Pads Using Additive Manufacturing
Materials 2019, 12(20), 3440; https://doi.org/10.3390/ma12203440 - 21 Oct 2019
Cited by 1 | Viewed by 717
Abstract
This paper presents the development and evaluation of fall-impact protection pants for elderly women using additive manufacturing. The protective pants were designed incorporating a protective pad in the hip area to reduce the impact of falls on the human body. The protective pad [...] Read more.
This paper presents the development and evaluation of fall-impact protection pants for elderly women using additive manufacturing. The protective pants were designed incorporating a protective pad in the hip area to reduce the impact of falls on the human body. The protective pad is a 3D mesh structure with a curved surface to fit the human body. Pads printed with flexible thermoplastic polyurethane were combined with foam to create the final pad. The impact-absorbing performance of the pad was verified through physical impact experiments. When dropping a bowling ball onto the protective pad from heights of 15, 20, and 25 cm, the protective pad was found to reduce the impact force by more than 82% in all cases. The impact force was less than the average fracture threshold of 3472 N. A subject group and an expert group evaluated the appearance, pad characteristics, motion functionality, and the wearability of the protection pants. Despite the insertion of a pad, the pants appeared natural and had a good fit. The pads were evaluated as being well-designed in terms of their position, shape, area, thickness, weight, flexibility, ease of insertion, and ease of use. Users were comfortable performing various motions when wearing the designed protective clothing. Therefore, this work can be considered to have developed protective clothing that provides satisfactory impact-protection performance and comfort thereby advancing the possibility of applying additive manufacturing to the creation of functional garments. Full article
(This article belongs to the Special Issue Multifunctional Textile Materials)
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Open AccessArticle
Parameter Optimization in High-Throughput Testing for Structural Materials
Materials 2019, 12(20), 3439; https://doi.org/10.3390/ma12203439 - 21 Oct 2019
Cited by 1 | Viewed by 700
Abstract
High-throughput screenings are established evaluation methods in the development of functional materials and pharmaceutical active ingredients. The transfer of this approach to the development of structural materials requires extensive adaptations. In addition to the investigation of new test procedures for the determination of [...] Read more.
High-throughput screenings are established evaluation methods in the development of functional materials and pharmaceutical active ingredients. The transfer of this approach to the development of structural materials requires extensive adaptations. In addition to the investigation of new test procedures for the determination of material properties and the treatment of metallic materials, the design of experiments is a research focus. Based on given descriptor target values, the statistical design of experiments determines investigations and treatments for the investigation of these materials. In this context, process parameters also have to be determined, as these have a major influence on the later material properties, especially during the treatment of samples. In this article, a method is presented which determines the process parameters iteratively. The validation of the calculated process parameters takes place based on differential scanning calorimetry used as the furnace for the heat treatment of small batches and particle-oriented peening as the characterization method. Full article
(This article belongs to the Special Issue Advanced Manufacturing of Metallic Alloys)
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Open AccessArticle
Novel Poly(Methyl Methacrylate) Containing Nanodiamond to Improve the Mechanical Properties and Fungal Resistance
Materials 2019, 12(20), 3438; https://doi.org/10.3390/ma12203438 - 21 Oct 2019
Cited by 11 | Viewed by 890
Abstract
Herein we evaluate the effect of nanodiamond (ND) incorporation on the mechanical properties of poly(methyl methacrylate) (PMMA) nanocomposite. Three quantities of ND (0.1, 0.3, and 0.5 wt.%) were tested against the control and zirconium oxide nanoparticles (ZrO). Flexural strength and elastic modulus were [...] Read more.
Herein we evaluate the effect of nanodiamond (ND) incorporation on the mechanical properties of poly(methyl methacrylate) (PMMA) nanocomposite. Three quantities of ND (0.1, 0.3, and 0.5 wt.%) were tested against the control and zirconium oxide nanoparticles (ZrO). Flexural strength and elastic modulus were measured using a three-point bending test, surface hardness was evaluated using the Vickers hardness test, and surface roughness was evaluated using atomic force microscopy (AFM), while fungal adhesion and viability were studied using Candida albicans. Samples were also analyzed for biofilm thickness and biomass in a saliva-derived biofilm model. All groups of ND-PMMA nanocomposites had significantly greater mean flexural strengths and statistically improved elastic modulus, compared to the control and ZrO groups (P < 0.001). The Vickers hardness values significantly increased compared to the control group (P < 0.001) with 0.3% and 0.5% ND. ND addition also gave significant reduction in fungal adhesion and viability (P < 0.001) compared to the control group. Finally, salivary biofilm formation was markedly reduced compared to the ZrO group. Hence, the incorporation of 0.1–0.5 wt.% ND with auto- polymerized PMMA resin significantly improved the flexural strength, elastic modulus, and surface hardness, and provided considerable fungal resistance. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle
Physical Properties of Mineral and Recycled Aggregates Used to Mineral-Asphalt Mixtures
Materials 2019, 12(20), 3437; https://doi.org/10.3390/ma12203437 - 21 Oct 2019
Cited by 3 | Viewed by 643
Abstract
This article presents test results and examines the possibilities of using aggregate from ceramic waste for mineral-asphalt mixtures. In addition, the mineral composition, physical and mechanical properties of aggregates from natural raw materials such as dolomite, granodiorite and waste ceramic aggregate (introduced as [...] Read more.
This article presents test results and examines the possibilities of using aggregate from ceramic waste for mineral-asphalt mixtures. In addition, the mineral composition, physical and mechanical properties of aggregates from natural raw materials such as dolomite, granodiorite and waste ceramic aggregate (introduced as a partial substitute for the main aggregate) were analyzed. The shape of grains was examined by determining the shape and flatness index of aggregates, resistance to grinding and frost resistance. The tested properties have a direct impact on the durability of road surfaces. To this end, the adhesion of asphalt to the surface of the aggregates used was additionally determined. Determination of surface roughness and two-dimensional (2D) topography of tested aggregates was carried out. The aggregates microstructure examination, coupled with the energy-dispersive X-ray spectroscopy (EDS) analysis, was conducted to determine the morphology and texture of the aggregates as well as to identify the basic chemical components. Full article
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Open AccessArticle
Catalytic Soot Oxidation Activity of NiO–CeO2 Catalysts Prepared by a Coprecipitation Method: Influence of the Preparation pH on the Catalytic Performance
Materials 2019, 12(20), 3436; https://doi.org/10.3390/ma12203436 - 21 Oct 2019
Cited by 1 | Viewed by 863
Abstract
A series of NiO–CeO2 mixed oxide catalysts have been synthesized by a modified coprecipitation method at three different pH values (pH = 8, 9, and 10). The NiO–CeO2 mixed oxide samples were characterized by TGA, XRD, inductively coupled plasma atomic emission [...] Read more.
A series of NiO–CeO2 mixed oxide catalysts have been synthesized by a modified coprecipitation method at three different pH values (pH = 8, 9, and 10). The NiO–CeO2 mixed oxide samples were characterized by TGA, XRD, inductively coupled plasma atomic emission spectroscopy (ICP-AES), FTIR, Brunauer–Emmett–Teller (BET) surface area, H2 temperature-programmed reduction (H2-TPR), and electron microscopy (high-angle annular dark-field transmission electron microscopy/energy-dispersive X-ray spectroscopy (HAADF-TEM/EDS)). The catalytic activities of the samples for soot oxidation were investigated under loose and tight contact conditions. The catalysts exhibited a high BET surface area with average crystal sizes that varied with the pH values. Electron microscopy results showed the formation of small crystallites (~5 nm) of CeO2 supported on large plate-shaped particles of NiO (~20 nm thick). XRD showed that a proportion of the Ni2+ was incorporated into the ceria network, and it appeared that the amount on Ni2+ that replaced Ce4+ was higher when the synthesis of the mixed oxides was carried out at a lower pH. Among the synthesized catalysts, Ni-Ce-8 (pH = 8) exhibited the best catalytic performance. Full article
(This article belongs to the Special Issue Heterogeneous Catalysts Synthesis and Characterization)
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Open AccessFeature PaperArticle
PGlu-Modified Nanocrystalline Cellulose Improves Mechanical Properties, Biocompatibility, and Mineralization of Polyester-Based Composites
Materials 2019, 12(20), 3435; https://doi.org/10.3390/ma12203435 - 21 Oct 2019
Viewed by 997
Abstract
The development of biocompatible composite materials is in high demand in many fields such as biomedicine, bioengineering, and biotechnology. In this study, two series of poly (D,L-lactide) and poly (ε-caprolactone)-based films filled with neat and modified with poly (glutamic acid) (PGlu) nanocrystalline cellulose [...] Read more.
The development of biocompatible composite materials is in high demand in many fields such as biomedicine, bioengineering, and biotechnology. In this study, two series of poly (D,L-lactide) and poly (ε-caprolactone)-based films filled with neat and modified with poly (glutamic acid) (PGlu) nanocrystalline cellulose (NCC) were prepared. An analysis of scanning electron and atomic force microscopies’ results shows that the modification of NCC with poly (glutamic acid) favored the better distribution of the nanofiller in the polymer matrix. Investigating the ability of the developed materials to attract and retain calcium ions led to the conclusion that composites containing NCC modified with PGlu induced better mineralization from model solutions than composites containing neat NCC. Moreover, compared to unmodified NCC, functionalization with PGlu improved the mechanical properties of composite films. The subcutaneous implantation of these composite materials into the backs of rats and the further histological investigation of neighboring tissues revealed the better biocompatibility of polyester materials filled with NCC–PGlu. Full article
(This article belongs to the Special Issue Advances in Polysaccharide Biomaterials)
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Open AccessArticle
Direct Reduction of Fe, Ni and Cr from Oxides of Waste Products Used in Briquettes for Slag Foaming in EAF
Materials 2019, 12(20), 3434; https://doi.org/10.3390/ma12203434 - 21 Oct 2019
Cited by 4 | Viewed by 658
Abstract
Environmental aspects and the sustainable manufacturing of steels require producers to pay more and more attention to the efficient utilization of materials and waste products during steelmaking. This study is focused on the evaluation of possibilities for the recovery of metals (such as [...] Read more.
Environmental aspects and the sustainable manufacturing of steels require producers to pay more and more attention to the efficient utilization of materials and waste products during steelmaking. This study is focused on the evaluation of possibilities for the recovery of metals (such as Fe, Ni and Cr) from waste products used for slag foaming in the Electric Arc Furnace (EAF) process. Two types of industrial briquettes were produced by mixing mill-scale from the hot rolling of stainless steels with anthracite and pet-coke, respectively. Thereafter, an assessment of the metal reduction processes in briquettes at high temperatures (1500 °C) was made by using laboratory thermo-gravimetric reduction experiments in an argon atmosphere. The amounts of metal, slag and gas obtained from the briquettes were estimated. In addition, the velocity and time for the removal of metal droplets from the liquid slag depending on the size of the metal droplets was estimated. It was found that up to 97% of metal droplets can be removed from the slag during the first 30 min. Moreover, results showed that most of the Cr, Ni and Fe (up to 93–100%) can be reduced from oxides of these metals in briquettes at 1500 °C. Moreover, the anthracite and pet-coke in the investigated briquettes have similar reduction capabilities. It was found that up to 330 kg of Fe, 28 kg of Ni and 66 kg of Cr per ton of added briquettes can be recovered from waste products by the industrial application of those briquettes for slag foaming in EAF. Full article
(This article belongs to the Special Issue Environmentally Friendly Renewable Materials)
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Open AccessArticle
Ultrasound Axicon: Systematic Approach to Optimize Focusing Resolution through Human Skull Bone
Materials 2019, 12(20), 3433; https://doi.org/10.3390/ma12203433 - 20 Oct 2019
Cited by 1 | Viewed by 822
Abstract
The use of axicon lenses is useful in many high-resolution-focused ultrasound applications, such as mapping, detection, and have recently been extended to ultrasonic brain therapies. However, in order to achieve high spatial resolution with an axicon lens, it is necessary to adjust the [...] Read more.
The use of axicon lenses is useful in many high-resolution-focused ultrasound applications, such as mapping, detection, and have recently been extended to ultrasonic brain therapies. However, in order to achieve high spatial resolution with an axicon lens, it is necessary to adjust the separation, called stand-off (δ), between a conventional transducer and the lens attached to it. Comprehensive ultrasound simulations, using the open-source k-Wave toolbox, were performed for an axicon lens attached to a piezo-disc type transducer with a radius of 14 mm, and a frequency of about 0.5 MHz, that is within the range of optimal frequencies for transcranial transmission. The materials properties were measured, and the lens geometry was modelled. Hydrophone measurements were performed through a human skull phantom. We obtained an initial easygoing design model for the lens angle and optimal stand-off using relatively simple formulas. The skull is not an obstacle for focusing of ultrasound with optimized axicon lenses that achieve an identical resolution to spherical transducers, but with the advantage that the focusing distance is shortened. An adequate stand-off improves the lateral resolution of the acoustic beam by approximately 50%. The approach proposed provides an effective way of designing polydimethylsiloxane (PDMS)-based axicon lenses equipped transducers. Full article
(This article belongs to the Special Issue Ultrasound for Material Characterization and Processing)
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Open AccessArticle
Fabrication of Superhydrophobic Magnetic Sawdust as Effective and Recyclable Oil Sorbents
Materials 2019, 12(20), 3432; https://doi.org/10.3390/ma12203432 - 20 Oct 2019
Viewed by 722
Abstract
In this paper, a novel superhydrophobic magnetic sawdust (SMSD) was fabricated as an oil sorbent. The SMSD was functionalized with Fe3O4 nanoparticles using melamine formaldehyde resin (MFR) as a coupling agent and subsequently hydrophobically-treated with hexadecyltrimethoxysilane (HDTMS). The SMSD showed [...] Read more.
In this paper, a novel superhydrophobic magnetic sawdust (SMSD) was fabricated as an oil sorbent. The SMSD was functionalized with Fe3O4 nanoparticles using melamine formaldehyde resin (MFR) as a coupling agent and subsequently hydrophobically-treated with hexadecyltrimethoxysilane (HDTMS). The SMSD showed excellent superhydrophobicity with the water contact angle of 155.3 ± 0.9°. Meanwhile it had remarkable environmental durability, long-term stability, and mechanical durable properties. Taking advantage of its magnetic characteristics, the SMSD could be easily controlled to absorb oil to separate oil–water mixtures with high oil absorption capacity and good reusability. Moreover, the emulsion was successfully separated by SMSD, including water-in-oil and oil-in-water emulsions. This study developed an effective oil absorbent, which was low cost and environmentally-friendly. Full article
(This article belongs to the Section Materials Chemistry)
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Open AccessArticle
Impact of Mechanical Processes as a Pre-Sulphonitriding Treatment on Tribology Properties of Selected P/M Tool Steels
Materials 2019, 12(20), 3431; https://doi.org/10.3390/ma12203431 - 20 Oct 2019
Cited by 3 | Viewed by 805
Abstract
We have evaluated phase composition changes in the surface layer (SL) and wear resistance of steels investigated after various mechanical processes such as a pre-sulphonitriding treatments. Two various paths of surface modification were employed: Grinding–sulphonitriding (G-SN) and hard turning–slide burnishing–sulphonitriding (T-B-SN). Studies were [...] Read more.
We have evaluated phase composition changes in the surface layer (SL) and wear resistance of steels investigated after various mechanical processes such as a pre-sulphonitriding treatments. Two various paths of surface modification were employed: Grinding–sulphonitriding (G-SN) and hard turning–slide burnishing–sulphonitriding (T-B-SN). Studies were carried out on Vanadis 8 and Vancron 40 tool steels, which are classified as advanced powder metallurgy (P/M) high-alloyed steels with different types and amounts of carbides. Heat treatment to the final hardness of 64 ± 1 HRC (Vanadis 8) and 62 ± 1 HRC (Vancron 40) was performed in vacuum furnaces with gas quenching. Precipitation of different types such as sulfides, nitrides, and carbides was observed using X-ray diffraction analysis. Tribological properties of SL were evaluated by pin-on-disc experiments. Pins of Al2O3 and 19MnB4 steel were used as counterbodies materials. 3D surface geometrical structure measurements were also performed. Wear tracks and cross-sections of SL were observed using optical and scanning electron microscopy. The three-stage process increases the wear resistance about 37% and 30%, respectively for Vanadis 8 and Vancron 40 (in case of alumina pins), whereas values of wear rates after tests performed against steel pins were very similar for two compared processes for both steels. Full article
(This article belongs to the Special Issue Tribology: Friction and Wear of Engineering Materials)
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Open AccessArticle
Evaluation of the Microstructure and Mechanical Properties of a New Modified Cast and Laser-Melted AA7075 Alloy
Materials 2019, 12(20), 3430; https://doi.org/10.3390/ma12203430 - 20 Oct 2019
Cited by 5 | Viewed by 838
Abstract
The mechanical properties and microstructure of as-cast and homogenized AA7075 were investigated. This alloy was modified by adding transition elements 0.3%Sc + 0.5%Zr, 1%Ti + 0.2%B, and 1%Fe + 1%Ni for use in additive manufacturing applications. After adding Ti + B and Sc [...] Read more.
The mechanical properties and microstructure of as-cast and homogenized AA7075 were investigated. This alloy was modified by adding transition elements 0.3%Sc + 0.5%Zr, 1%Ti + 0.2%B, and 1%Fe + 1%Ni for use in additive manufacturing applications. After adding Ti + B and Sc + Zr, the structure became uniform and finer with the formation of the Al3(Sc, Zr) and TiB2 phases. Coarse structures were obtained with the formation of an extremely unfavorable morphology, close to a needle-like structure when Fe + Ni was added. The mechanical properties of the modified alloys were increased compared to those of the standard alloy, where the best ultimate tensile strength (UTS) and yield strength (YS) were obtained in the AA7075-TiB alloy compared to the standard alloy in as-cast and homogenized conditions, and the highest hardness value was provided by Fe + Ni additives. The effect of the laser melting process on the microstructure and mechanical properties was investigated. Single laser melts were performed on these alloys using 330 V and a scanning speed of 8 mm/s. During the laser melting, the liquation of the alloying elements occurred due to non-equilibrium solidification. A change in the microstructures was observed within the melt zone and heat-affected zone (HAZ). The hardness of the laser-melted zone (LMZ) after adding the modification elements was increased in comparison with that of the standard alloy. Corrosion testing was performed using a solution of 100 mL distilled water, 3.1 g NaCl, and 1 mL HCl over 5, 10, and 30 min and 1 and 2 h. The corrosion resistance of the alloy modified with FeNi was low because of the non-uniform elemental distribution along the LMZ, but in the case of modification with ScZr and TiB, the corrosion resistance was better compared to that of the standard alloy. Full article
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