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Materials, Volume 11, Issue 6 (June 2018)

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Cover Story (view full-size image) Intermetallic type I clathrates are considered to be potential thermoelectric (TE) materials due to [...] Read more.
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Open AccessArticle Properties of Experimental Dental Composites Containing Antibacterial Silver-Releasing Filler
Materials 2018, 11(6), 1031; https://doi.org/10.3390/ma11061031 (registering DOI)
Received: 20 May 2018 / Revised: 11 June 2018 / Accepted: 11 June 2018 / Published: 18 June 2018
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Abstract
Secondary caries is one of the important issues related to using dental composite restorations. Effective prevention of cariogenic bacteria survival may reduce this problem. The aim of this study was to evaluate the antibacterial activity and physical properties of composite materials with silver
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Secondary caries is one of the important issues related to using dental composite restorations. Effective prevention of cariogenic bacteria survival may reduce this problem. The aim of this study was to evaluate the antibacterial activity and physical properties of composite materials with silver sodium hydrogen zirconium phosphate (SSHZP). The antibacterial filler was introduced at concentrations of 1%, 4%, 7%, 10%, 13%, and 16% (w/w) into model composite material consisting of methacrylate monomers and silanized glass and silica fillers. The in vitro reduction in the number of viable cariogenic bacteria Streptococcus mutans ATCC 33535 colonies, Vickers microhardness, compressive strength, diametral tensile strength, flexural strength, flexural modulus, sorption, solubility, degree of conversion, and color stability were investigated. An increase in antimicrobial filler concentration resulted in a statistically significant reduction in bacteria. There were no statistically significant differences caused by the introduction of the filler in compressive strength, diametral tensile strength, flexural modulus, and solubility. Statistically significant changes in degree of conversion, flexural strength, hardness (decrease), solubility (increase), and in color were registered. A favorable combination of antibacterial properties and other properties was achieved at SSHZP concentrations from 4% to 13%. These composites exhibited properties similar to the control material and enhanced in vitro antimicrobial efficiency. Full article
(This article belongs to the Special Issue Bioactive and Therapeutic Dental Materials)
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Open AccessArticle Degradation of Methylene Blue Dye in the Presence of Visible Light Using SiO2@α-Fe2O3 Nanocomposites Deposited on SnS2 Flowers
Materials 2018, 11(6), 1030; https://doi.org/10.3390/ma11061030 (registering DOI)
Received: 3 April 2018 / Revised: 4 June 2018 / Accepted: 13 June 2018 / Published: 17 June 2018
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Abstract
Semiconductor materials have been shown to have good photocatalytic behavior and can be utilized for the photodegradation of organic pollutants. In this work, three-dimensional flower-like SnS2 (tin sulfide) was synthesized by a facile hydrothermal method. Core-shell structured SiO2@α-Fe2O
[...] Read more.
Semiconductor materials have been shown to have good photocatalytic behavior and can be utilized for the photodegradation of organic pollutants. In this work, three-dimensional flower-like SnS2 (tin sulfide) was synthesized by a facile hydrothermal method. Core-shell structured SiO2@α-Fe2O3 nanocomposites were then deposited on the top of the SnS2 flowers. The as-synthesized nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–Vis Spectroscopy, Brunauer–Emmett–Teller (BET) surface area analysis, and photoluminescence (PL) spectroscopy. The photocatalytic behavior of the SnS2-SiO2@α-Fe2O3 nanocomposites was investigated by observing the degradation of methylene blue (MB). The results show an effective enhancement of photocatalytic activity for the degradation of MB especially for the 15 wt % SiO2@α-Fe2O3 nanocomposites on SnS2 flowers. Full article
(This article belongs to the Section Catalytic Materials)
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Open AccessArticle Concrete Properties Comparison When Substituting a 25% Cement with Slag from Different Provenances
Materials 2018, 11(6), 1029; https://doi.org/10.3390/ma11061029 (registering DOI)
Received: 2 May 2018 / Revised: 12 June 2018 / Accepted: 13 June 2018 / Published: 17 June 2018
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Abstract
Concrete consumption greatly exceeds the use of any other material in engineering. This is due to its good properties as a construction material and the availability of its components. Nevertheless, the present worldwide construction increases and the high-energy consumption for cement production means
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Concrete consumption greatly exceeds the use of any other material in engineering. This is due to its good properties as a construction material and the availability of its components. Nevertheless, the present worldwide construction increases and the high-energy consumption for cement production means a high environmental impact. On the other hand, one of the main problems in the iron and steel industry is waste generation and byproducts that must be properly processed or reused to promote environmental sustainability. One of these byproducts is steel slag. The cement substitution with slag strategy achieves two goals: raw materials consumption reduction and waste management. In the present work, four different concrete mixtures are evaluated. The 25% cement substitution is carried out with different types of slag. Tests were made to evaluate the advantages and drawbacks of each mixture. Depending on the origin, characteristics, and treatment of the slag, the concrete properties changed. Certain mixtures provided proper concrete properties. Stainless steel slag produced a fluent mortar that reduced water consumption with a slight mechanical strength loss. Mixtures with ground granulated blast furnace slag properties are better than the reference concrete (without slag). Full article
(This article belongs to the Special Issue Additive Manufacturing: Alloy Design and Process Innovations)
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Open AccessArticle Fatigue Behavior of Glass Fiber-Reinforced Polymer Bars after Elevated Temperatures Exposure
Materials 2018, 11(6), 1028; https://doi.org/10.3390/ma11061028 (registering DOI)
Received: 15 May 2018 / Revised: 6 June 2018 / Accepted: 14 June 2018 / Published: 16 June 2018
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Abstract
Fiber-reinforced polymer (FRP) bars have been widely applied in civil engineering. This paper presents the results of an experimental study to investigate the tensile fatigue mechanical properties of glass fiber-reinforced polymer (GFRP) bars after elevated temperatures exposure. For this purpose, a total of
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Fiber-reinforced polymer (FRP) bars have been widely applied in civil engineering. This paper presents the results of an experimental study to investigate the tensile fatigue mechanical properties of glass fiber-reinforced polymer (GFRP) bars after elevated temperatures exposure. For this purpose, a total of 105 GFRP bars were conducted for testing. The specimens were exposed to heating regimes of 100, 150, 200, 250, 300 and 350 °C for a period of 0, 1 or 2 h. The GFRP bars were tested with different times of cyclic load after elevated temperatures exposure. The results show that the tensile strength and elastic modulus of GFRP bars decrease with the increase of elevated temperature and holding time, and the tensile strength of GFRP bars decreases obviously by 19.5% when the temperature reaches 250 °C. Within the test temperature range, the tensile strength of GFRP bars decreases at most by 28.0%. The cyclic load accelerates the degradation of GFRP bars after elevated temperature exposure. The coupling of elevated temperature and holding time enhance the degradation effect of cyclic load on GFRP bars. The tensile strength of GFRP bars after elevated temperatures exposure at 350 °C under cyclic load is reduced by 50.5% compared with that at room temperature and by 36.3% compared with that after exposing at 350 °C without cyclic load. In addition, the elastic modulus of GFRP bars after elevated temperatures exposure at 350 °C under cyclic load is reduced by 17.6% compared with that at room temperature and by 6.0% compared with that after exposing at 350 °C without cyclic load. Full article
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Open AccessArticle An Investigation of the Wear on Silicon Surface at High Humidity
Materials 2018, 11(6), 1027; https://doi.org/10.3390/ma11061027 (registering DOI)
Received: 31 May 2018 / Revised: 12 June 2018 / Accepted: 14 June 2018 / Published: 16 June 2018
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Abstract
Using an atomic force microscope (AFM), the wear of monocrystalline silicon (covered by a native oxide layer) at high humidity was investigated. The experimental results indicated that tribochemistry played an important role in the wear of the silicon at different relative humidity levels
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Using an atomic force microscope (AFM), the wear of monocrystalline silicon (covered by a native oxide layer) at high humidity was investigated. The experimental results indicated that tribochemistry played an important role in the wear of the silicon at different relative humidity levels (RH = 60%, 90%). Since the tribochemical reactions were facilitated at 60% RH, the wear of silicon was serious and the friction force was around 1.58 μN under the given conditions. However, the tribochemical reactions were restrained when the wear pair was conducted at high humidity. As a result, the wear of silicon was very slight and the friction force decreased to 0.85 μN at 90% RH. The slight wear of silicon at high humidity was characterized by etching tests. It was demonstrated that the silicon sample surface was partly damaged and the native oxide layer on silicon sample surface had not been totally removed during the wear process. These results may help us optimize the tribological design of dynamic microelectromechanical systems working in humid conditions. Full article
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Open AccessArticle Grain Size Effect on the Hot Ductility of High-Nitrogen Austenitic Stainless Steel in the Presence of Precipitates
Materials 2018, 11(6), 1026; https://doi.org/10.3390/ma11061026
Received: 16 May 2018 / Revised: 8 June 2018 / Accepted: 13 June 2018 / Published: 15 June 2018
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Abstract
Precipitation occurs easily during the hot forming of high-nitrogen austenitic stainless steels, which reduces their hot ductility significantly. The effect of grain size on the hot ductility of high-nitrogen austenitic stainless steel in the presence of precipitates was investigated. Different grain sizes of
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Precipitation occurs easily during the hot forming of high-nitrogen austenitic stainless steels, which reduces their hot ductility significantly. The effect of grain size on the hot ductility of high-nitrogen austenitic stainless steel in the presence of precipitates was investigated. Different grain sizes of 18Mn18Cr0.5N steel specimens, with and without precipitates, were hot-tension tested. The precipitate morphology, fracture surface, and cracks were studied by scanning electron microscopy, transmission electron microscopy, and electron backscatter diffraction analysis. For the 18Mn18Cr0.5N steel, damage-formation strains of all grain-size specimens were reduced by the precipitates during the hot-tension test. Crack-formation sites were located at grain boundaries and were independent of the Taylor factor. A larger grain size resulted in an increased sensitivity of the fracture strain to precipitates. When the grain size was smaller than 51 μm, the fracture strain became insensitive to the precipitates. A method was suggested to mitigate surface cracking for metal materials with a high precipitation tendency. Full article
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Open AccessArticle Effects of Annealing on the Residual Stress in γ-TiAl Alloy by Molecular Dynamics Simulation
Materials 2018, 11(6), 1025; https://doi.org/10.3390/ma11061025
Received: 21 May 2018 / Revised: 8 June 2018 / Accepted: 13 June 2018 / Published: 15 June 2018
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Abstract
In this paper, molecular dynamics simulations are performed to study the annealing process of γ-TiAl alloy with different parameters after introducing residual stress into prepressing. By mainly focusing on the dynamic evolution process of microdefects during annealing and the distribution of residual stress,
[...] Read more.
In this paper, molecular dynamics simulations are performed to study the annealing process of γ-TiAl alloy with different parameters after introducing residual stress into prepressing. By mainly focusing on the dynamic evolution process of microdefects during annealing and the distribution of residual stress, the relationship between microstructure and residual stress is investigated. The results show that there is no phase transition during annealing, but atom distortion occurs with the change of temperature, and the average grain size slightly increases after annealing. There are some atom clusters in the grains, with a few point defects, and the point defect concentration increases with the rise in temperature, and vice versa; the higher the annealing temperature, the fewer the point defects in the grain after annealing. Due to the grain boundary volume shrinkage and and an increase in the plastic deformation of the grain boundaries during cooling, stress is released, and the average residual stress along Y and Z directions after annealing is less than the average residual stress after prepressing. Full article
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Open AccessArticle Effects of Different Hot Working Techniques on Inclusions in GH4738 Superalloy Produced by VIM and VAR
Materials 2018, 11(6), 1024; https://doi.org/10.3390/ma11061024
Received: 22 April 2018 / Revised: 8 June 2018 / Accepted: 13 June 2018 / Published: 15 June 2018
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Abstract
Hot working is a key process in the production of superalloys; however, it may result in the formation of inclusions that affect the superalloy performance. Therefore, the effects of hot working on inclusions in a superalloy must be studied. GH4738 superalloy was manufactured,
[...] Read more.
Hot working is a key process in the production of superalloys; however, it may result in the formation of inclusions that affect the superalloy performance. Therefore, the effects of hot working on inclusions in a superalloy must be studied. GH4738 superalloy was manufactured, herein, by vacuum induction melting and vacuum arc remelting. Hot working was performed by unidirectional drawing, upsetting and drawing, and upsetting/drawing with radial forging. The types and distributions of inclusions after these three hot working processes and those in an original ingot were analyzed using scanning electron microscopy, energy dispersive spectroscopy, and Image-Pro Plus software. The results showed that the melting technology essentially determined the inclusion types in GH4738. Four types of inclusions were found in the experiments: TiC–TiN–Mo–S composite, TiC–TiN composite, Ce–Mo–S composite, and SiC inclusions. In the case of hot working by unidirectional drawing, the average inclusion size first decreased, and then increased from the center to the edge. In the case of upsetting and drawing, and upsetting/drawing with radial forging, the average inclusion size decreased from the center to the edge. Full article
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Open AccessArticle Compressive Behavior and Constitutive Model of Austenitic Stainless Steel S30403 in High Strain Range
Materials 2018, 11(6), 1023; https://doi.org/10.3390/ma11061023
Received: 31 March 2018 / Revised: 25 May 2018 / Accepted: 12 June 2018 / Published: 15 June 2018
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Abstract
Material anisotropy for tension and compression is a significant characteristic of austenitic stainless steel compared to carbon steel. Due to limitations during the testing of the restrained jig, the maximum strain value of compressive experiments of austenitic stainless steel is around 2%. This
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Material anisotropy for tension and compression is a significant characteristic of austenitic stainless steel compared to carbon steel. Due to limitations during the testing of the restrained jig, the maximum strain value of compressive experiments of austenitic stainless steel is around 2%. This value cannot satisfy the requirements of accurate finite simulation on austenitic stainless steel columns and beams in the high compressive strain range. In this study, a new type of compressive specimen that satisfies the high compressive strain test was designed. The stress-strain response of austenitic stainless steel S30403 (JISCO, Gansu, China) was investigated in the high compressive strain range up to 10%, and constitutive models were compared with the experimental data. It was found that the new type specimen with length-to-diameter ratio of 1:1 can reliably obtain the stress-strain response of austenitic stainless steel S30403 in the high compressive strain range. It was found that the material anisotropy of austenitic stainless steel S30403 is remarkable in the high compressive strain range up to 10%. The strain-hardening curve of the austenitic stainless steel S30403 can be represented by a straight line in the high compressive strain range. Our study also found that the Quach constitutive model accurately describes the two-stage strain-hardening phenomenon in the high compressive strain range up to 10%. Full article
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Open AccessArticle Synthesis of TiO2NWS@AuNPS Composite Catalyst for Methylene Blue Removal
Materials 2018, 11(6), 1022; https://doi.org/10.3390/ma11061022
Received: 7 May 2018 / Revised: 11 June 2018 / Accepted: 11 June 2018 / Published: 15 June 2018
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Abstract
In this article, HBP-NH2-modified titania nanowire (TiO2NWS)-decorated Au nanoparticles (TiO2NWS@AuNPS) were synthesized by one-step method. The role of HBP-NH2 concentration in the formation of TiO2NWS was investigated. The fineness and uniformity of pure
[...] Read more.
In this article, HBP-NH2-modified titania nanowire (TiO2NWS)-decorated Au nanoparticles (TiO2NWS@AuNPS) were synthesized by one-step method. The role of HBP-NH2 concentration in the formation of TiO2NWS was investigated. The fineness and uniformity of pure TiO2NWS were enhanced by absorbed amino groups from amino-terminated hyperbranched polymer (HBP-NH2). The morphology and crystal structure of TiO2NWS and TiO2NWS@AuNPS were examined by transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fournier transform infrared (FTIR) spectroscopy. The chemical states of gold, titanium and oxygen were analyzed by X-ray photoelectron spectroscopy (XPS). The results showed that at the concentration of HBP-NH2 100 g/L, the mean diameter of TiO2NWS was nearly 72 nm and Au nanoparticles were uniformly distributed on the surface of TiO2NWS. The presence of AuNPS improved the photocatalytic properties of TiO2NWS under UV light irradiation. The Au load was believed to improve the utilization rate of the photoelectron and activated the adsorbed oxygen. The obtained TiO2NWS@AuNPS decomposed 99.6% methylene blue (MB) after 300 min when subjected to UV light irradiation. After five cycles of the catalyzing process, the TiO2NWS@AuNPS still retained over 90% of its catalytic ability for MB. The Au deposition was found responsible for the high catalytic activity of TiO2NWS@AuNPS. Full article
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Open AccessFeature PaperCommunication Redox Activity of Sodium Vanadium Oxides towards Oxidation in Na Ion Batteries
Materials 2018, 11(6), 1021; https://doi.org/10.3390/ma11061021
Received: 31 May 2018 / Revised: 13 June 2018 / Accepted: 13 June 2018 / Published: 15 June 2018
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Abstract
The search for new materials that could be used as electrode material for Na-ion batteries is one of the most challenging issues of today. Many transition metal oxide families as well as transition metal polyanionic frameworks have been proposed over the last five
[...] Read more.
The search for new materials that could be used as electrode material for Na-ion batteries is one of the most challenging issues of today. Many transition metal oxide families as well as transition metal polyanionic frameworks have been proposed over the last five years. In this work, we report the sodium extraction from Na2V3O7, which is a tunnel type structure built of [V3O7]2− nanotubes held by sodium ions. We report a reversible charge capacity of 80 mAh/g at 2.8 V vs. Na+/Na due to the V5+/V4+ redox activity. No oxygen redox activity has been observed for this material nor for the vanadium (5+) oxide Na4V2O7. Full article
(This article belongs to the Special Issue Electrode Materials for High Performance Sodium-ion Batteries)
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Open AccessArticle Using Spin-Coated Silver Nanoparticles/Zinc Oxide Thin Films to Improve the Efficiency of GaInP/(In)GaAs/Ge Solar Cells
Materials 2018, 11(6), 1020; https://doi.org/10.3390/ma11061020
Received: 29 May 2018 / Revised: 11 June 2018 / Accepted: 13 June 2018 / Published: 15 June 2018
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Abstract
We synthesized a silver nanoparticle/zinc oxide (Ag NP/ZnO) thin film by using spin-coating technology. The treatment solution for Ag NP/ZnO thin film deposition contained zinc acetate (Zn(CH3COO)2), sodium hydroxide (NaOH), and silver nitrate (AgNO3) aqueous solutions. The
[...] Read more.
We synthesized a silver nanoparticle/zinc oxide (Ag NP/ZnO) thin film by using spin-coating technology. The treatment solution for Ag NP/ZnO thin film deposition contained zinc acetate (Zn(CH3COO)2), sodium hydroxide (NaOH), and silver nitrate (AgNO3) aqueous solutions. The crystalline characteristics, surface morphology, content of elements, and reflectivity of the Ag NPs/ZnO thin film at various concentrations of the AgNO3 aqueous solution were investigated using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, atomic force microscopy, and ultraviolet–visible–near infrared spectrophotometry. The results indicated that the crystalline structure, Ag content, and reflectance of Ag NP/ZnO thin films depended on the AgNO3 concentration. Hybrid antireflection coatings (ARCs) composed of SiNx and Ag NPs/ZnO thin films with various AgNO3 concentrations were deposited on GaInP/(In)GaAs/Ge solar cells. We propose that the optimal ARC consists of SiNx and Ag NP/ZnO thin films prepared using a treatment solution of 0.0008 M AgNO3, 0.007 M Zn(CH3COO)2, and 1 M NaOH, followed by post-annealing at 200 °C. GaInP/(Al)GaAs/Ge solar cells with the optimal hybrid ARC and SiNx ARC exhibit a conversion efficiency of 34.1% and 30.2% with Voc = 2.39 and 2.4 V, Jsc = 16.63 and 15.37 mA/cm2, and fill factor = 86.1% and 78.8%. Full article
(This article belongs to the Special Issue Selected Papers from IEEE ICASI 2018)
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Open AccessArticle Peculiarities in the Material Design of Buckling Resistance for Tensioned Laminated Composite Panels with Elliptical Cut-Outs
Materials 2018, 11(6), 1019; https://doi.org/10.3390/ma11061019
Received: 14 May 2018 / Revised: 8 June 2018 / Accepted: 12 June 2018 / Published: 15 June 2018
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Abstract
The results of analytical and numerical studies of the buckling behavior of laminated multilayered tensioned sheets with circular and elliptical openings are presented. The analysis shows the significant influence of stress concentration effects on buckling modes and loads, particularly taking into consideration variations
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The results of analytical and numerical studies of the buckling behavior of laminated multilayered tensioned sheets with circular and elliptical openings are presented. The analysis shows the significant influence of stress concentration effects on buckling modes and loads, particularly taking into consideration variations in the E1/E2 and E1/G12 ratios. The results of finite element (FE) computations prove that the buckling mode cannot be described by a single buckle localized at the apex of the hole. The optimal design of such structures seems to be much more complicated than classical buckling problems of compressed laminated panels without holes. However, the obtained results indicate that the optimal laminate configurations occur at the boundaries of the feasible regions of the introduced design space. Both continuous and discrete fibre orientations are considered. For continuous fibre orientations, the optimal stacking sequence corresponds to angle-ply symmetric laminates. Full article
(This article belongs to the Section Advanced Composites)
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Open AccessArticle Hierarchically Nanostructured CuO–Cu Current Collector Fabricated by Hybrid Methods for Developed Li-Ion Batteries
Materials 2018, 11(6), 1018; https://doi.org/10.3390/ma11061018
Received: 2 May 2018 / Revised: 12 June 2018 / Accepted: 12 June 2018 / Published: 15 June 2018
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Abstract
We present a simple method of fabricating a hierarchically nanostructured CuO–Cu current collector by using laser ablation and metal mold imprinting to maximize the surface area. The laser ablation of the Cu current collector created the CuO nanostructure on the Cu-collector surface. The
[...] Read more.
We present a simple method of fabricating a hierarchically nanostructured CuO–Cu current collector by using laser ablation and metal mold imprinting to maximize the surface area. The laser ablation of the Cu current collector created the CuO nanostructure on the Cu-collector surface. The microstructure was transferred by subsequent imprinting of the microstructure metal mold on the Cu collector. Then, the laser-ablation nanostructure was formed. Consequently, a hierarchical structure is generated. The laser-ablated hierarchical CuO–Cu current collector exhibited an improved capacity while maintaining a cyclability that is similar to those of conventional graphite batteries. Full article
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Open AccessArticle Properties and Structure of In Situ Transformed PAN-Based Carbon Fibers
Materials 2018, 11(6), 1017; https://doi.org/10.3390/ma11061017
Received: 5 May 2018 / Revised: 10 June 2018 / Accepted: 13 June 2018 / Published: 15 June 2018
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Abstract
Carbon fibers in situ prepared during the hot-pressed sintering in a vacuum is termed in situ transformed polyacrylonitrile-based (PAN-based) carbon fibers, and the fibrous precursors are the pre-oxidized PAN fibers. The properties and structure of in situ transformed PAN-based carbon fibers are investigated
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Carbon fibers in situ prepared during the hot-pressed sintering in a vacuum is termed in situ transformed polyacrylonitrile-based (PAN-based) carbon fibers, and the fibrous precursors are the pre-oxidized PAN fibers. The properties and structure of in situ transformed PAN-based carbon fibers are investigated by Nano indenter, SEM, TEM, XRD, and Raman. The results showed that the microstructure of the fiber surface layer was compact, while the core was loose, with evenly-appearing microvoids. The elastic modulus and nanohardness of the fiber surface layer (303.87 GPa and 14.82 GPa) were much higher than that of the core (16.57 GPa and 1.54 GPa), and its interlayer spacing d002 and crystallinity were about 0.347 nm and 0.97 respectively. It was found that the preferred orientation of the surface carbon layers with ordered carbon atomic arrangement tended to be parallel to the fiber axis, whereas the fiber core in the amorphous region exhibited a random texture and the carbon atomic arrangement was in a disordered state. It indicates that the in situ transformed PAN-based carbon fibers possess significantly turbostratic structure and anisotropy. Full article
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