Materials

8538 KiB

Open AccessArticle

The Effect of Sputtering Parameters and Doping of Copper on Surface Free Energy and Magnetic Properties of Iron and Iron Nitride Nano Thin Films on Polymer Substrate

by Waheed Khan, Qun Wang, Xin Jin and Tangfeng Feng

Materials 2017, 10(2), 217; https://doi.org/10.3390/ma10020217 - 22 Feb 2017

Cited by 18 | Viewed by 6502

Abstract

The objective of this study was to deposit thin films on PET polymer substrate and examine the functional properties systematically. Their properties have been studied as a function of the N₂-Ar flow rates, deposition time span and Cu doping. Iron nitride [...] Read more.

The objective of this study was to deposit thin films on PET polymer substrate and examine the functional properties systematically. Their properties have been studied as a function of the N₂-Ar flow rates, deposition time span and Cu doping. Iron nitride film deposited on both sides exhibits ferromagnetic phases, γ′-Fe₄N and ε-Fe₃N co-existed, shows negligible magnetic anisotropy. Other samples show the evolution of N-rich (FeN, Fe₂N) and N-poor (Fe₁₆N₂, Fe₃N, Fe₄N) phases under different deposition time conditions. XPS analysis and free energy calculations confirmed that co-sputtered Fe-Cu thin films are more stable than layer deposited counterparts. From VSM results it is evident that the dominant phase, changes steadily from the ferromagnetic α-Fe (N) to the paramagnetic ξ-Fe₂N with the increase of nitrogen flow rates and the ordering of the nitrogen atoms. Binding energy increases steadily from 733 eV to 740 eV with the increasing thickness of thin films from 74 nm to 94 nm. It was observed that surface energy decreases as the contact angle of glycol increases and changes the thin film surface from polar to nonpolar. TEM images indicate that cubic γ′-Fe₄N and ε-Fe₃N nano particles oriented in preferred directions dispersed uniformly in the amorphous iron nitride matrix. Full article

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3377 KiB

Open AccessArticle

Kinetic Analysis of the Uptake and Release of Fluorescein by Metal-Organic Framework Nanoparticles

by Tobias Preiß, Andreas Zimpel, Stefan Wuttke and Joachim O. Rädler

Materials 2017, 10(2), 216; https://doi.org/10.3390/ma10020216 - 22 Feb 2017

Cited by 24 | Viewed by 6428

Abstract

Metal-organic framework nanoparticles (MOF NPs) are promising guest-host materials with applications in separation, storage, catalysis, and drug delivery. However, on- and off-loading of guest molecules by porous MOF nanostructures are still poorly understood. Here we study uptake and release of fluorescein by two [...] Read more.

Metal-organic framework nanoparticles (MOF NPs) are promising guest-host materials with applications in separation, storage, catalysis, and drug delivery. However, on- and off-loading of guest molecules by porous MOF nanostructures are still poorly understood. Here we study uptake and release of fluorescein by two representative MOF NPs, MIL-100(Fe) and MIL-101(Cr). Suspensions of these MOF NPs exhibit well-defined size distributions and crystallinity, as verified by electron microscopy, dynamic light scattering, and X-ray diffraction. Using absorbance spectroscopy the equilibrium dissociation constants and maximum numbers of adsorbed fluorescein molecules per NP were determined. Time-resolved fluorescence studies reveal that rates of release and loading are pH dependent. The kinetics observed are compared to theoretical estimates that account for bulk diffusion into NPs, and retarded internal diffusion and adsorption rates. Our study shows that, rather than being simple volumetric carriers, MOF-NPs are dominated by internal surface properties. The findings will help to optimize payload levels and develop release strategies that exploit varying pH for drug delivery. Full article

(This article belongs to the Special Issue Metal Organic Framework Materials)

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14325 KiB

Open AccessArticle

Tensile and Flexural Properties of Cement Composites Reinforced with Flax Nonwoven Fabrics

by Josep Claramunt, Heura Ventura, Lucía J Fernández-Carrasco and Mònica Ardanuy

Materials 2017, 10(2), 215; https://doi.org/10.3390/ma10020215 - 22 Feb 2017

Cited by 42 | Viewed by 5376

Abstract

The aim of this study is to develop a process to produce high-performance cement-based composites reinforced with flax nonwoven fabrics, analyzing the influence of the fabric structure—thickness and entanglement—on mechanical behavior under flexural and tensile loadings. For this purpose, composite with flax nonwoven [...] Read more.

The aim of this study is to develop a process to produce high-performance cement-based composites reinforced with flax nonwoven fabrics, analyzing the influence of the fabric structure—thickness and entanglement—on mechanical behavior under flexural and tensile loadings. For this purpose, composite with flax nonwoven fabrics with different thicknesses were first prepared and their cement infiltration was evaluated with backscattered electron (BSE) images. The nonwoven fabrics with the optimized thickness were then subjected to a water treatment to improve their stability to humid environments and the fiber-matrix adhesion. For a fixed thickness, the effect of the nonwoven entanglement on the mechanical behavior was evaluated under flexural and direct tension tests. The obtained results indicate that the flax nonwoven fabric reinforcement leads to cement composites with substantial enhancement of ductility. Full article

(This article belongs to the Special Issue Textile Composites)

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Graphical abstract

26970 KiB

Open AccessArticle

Laser Surface Microstructuring of Biocompatible Materials Using a Microlens Array and the Talbot Effect: Evaluation of the Cell Adhesion

by María Aymerich, Daniel Nieto, Ezequiel Álvarez and María T. Flores-Arias

Materials 2017, 10(2), 214; https://doi.org/10.3390/ma10020214 - 22 Feb 2017

Cited by 5 | Viewed by 4792

Abstract

A laser based technique for microstructuring titanium and tantalum substrates using the Talbot effect and an array of microlenses is presented. By using this hybrid technique; we are able to generate different patterns and geometries on the top surfaces of the biomaterials. The [...] Read more.

A laser based technique for microstructuring titanium and tantalum substrates using the Talbot effect and an array of microlenses is presented. By using this hybrid technique; we are able to generate different patterns and geometries on the top surfaces of the biomaterials. The Talbot effect allows us to rapidly make microstructuring, solving the common problems of using microlenses for multipatterning; where the material expelled during the ablation of biomaterials damages the microlens. The Talbot effect permits us to increase the working distance and reduce the period of the patterns. We also demonstrate that the geometries and patterns act as anchor points for cells; affecting the cell adhesion to the metallic substrates and guiding how they spread over the material. Full article

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4866 KiB

Open AccessArticle

Fabrication of Lead-Free Bi_0.5Na_0.5TiO₃ Thin Films by Aqueous Chemical Solution Deposition

by Mads Christensen, Mari-Ann Einarsrud and Tor Grande

Materials 2017, 10(2), 213; https://doi.org/10.3390/ma10020213 - 22 Feb 2017

Cited by 14 | Viewed by 6902

Abstract

Piezoelectric ceramics are widely used in actuator applications, and currently the vast majority of these devices are based on

Pb (Zr, Ti) O_{3}

, which constitutes environmental and health hazards due to the toxicity of lead. One of the [...] Read more.

Piezoelectric ceramics are widely used in actuator applications, and currently the vast majority of these devices are based on

Pb (Zr, Ti) O_{3}

, which constitutes environmental and health hazards due to the toxicity of lead. One of the most promising lead-free material systems for actuators is based on

{Bi}_{0.5} {Na}_{0.5} {TiO}_{3}

(BNT), and here we report on successful fabrication of BNT thin films by aqueous chemical solution deposition. The precursor solution used in the synthesis is based on bismuth citrate stabilized by ethanolamine,

NaOH

, and a Ti-citrate prepared from titanium tetraisopropoxide and citric acid. BNT thin films were deposited on

{SrTiO}_{3}

and platinized silicon substrates by spin-coating, and the films were pyrolized and annealed by rapid thermal processing. The BNT perovskite phase formed after calcination at 500 °C in air. The deposited thin films were single phase according to X-ray diffraction, and the microstructures of the films shown by electron microscopy were homogeneous and dense. Decomposition of the gel was thoroughly investigated, and the conditions resulting in phase pure materials were identified. This new aqueous deposition route is low cost, robust, and suitable for development of BNT based thin film for actuator applications. Full article

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

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6967 KiB

Open AccessArticle

Vibration-Assisted Femtosecond Laser Drilling with Controllable Taper Angles for AMOLED Fine Metal Mask Fabrication

by Wonsuk Choi, Hoon Young Kim, Jin Woo Jeon, Won Seok Chang and Sung-Hak Cho

Materials 2017, 10(2), 212; https://doi.org/10.3390/ma10020212 - 21 Feb 2017

Cited by 20 | Viewed by 7265

Abstract

This study investigates the effect of focal plane variation using vibration in a femtosecond laser hole drilling process on Invar alloy fabrication quality for the production of fine metal masks (FMMs). FMMs are used in the red, green, blue (RGB) evaporation process in [...] Read more.

This study investigates the effect of focal plane variation using vibration in a femtosecond laser hole drilling process on Invar alloy fabrication quality for the production of fine metal masks (FMMs). FMMs are used in the red, green, blue (RGB) evaporation process in Active Matrix Organic Light-Emitting Diode (AMOLED) manufacturing. The taper angle of the hole is adjusted by attaching the objective lens to a micro-vibrator and continuously changing the focal plane position. Eight laser pulses were used to examine how the hole characteristics vary with the first focal plane’s position, where the first pulse is focused at an initial position and the focal planes of subsequent pulses move downward. The results showed that the hole taper angle can be controlled by varying the amplitude of the continuously operating vibrator during femtosecond laser hole machining. The taper angles were changed between 31.8° and 43.9° by adjusting the vibrator amplitude at a frequency of 100 Hz. Femtosecond laser hole drilling with controllable taper angles is expected to be used in the precision micro-machining of various smart devices. Full article

(This article belongs to the Special Issue Ultrafast Laser-Based Manufacturing)

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22188 KiB

Open AccessArticle

Effect of Energy Input on Microstructure and Mechanical Properties of Titanium Aluminide Alloy Fabricated by the Additive Manufacturing Process of Electron Beam Melting

by Ashfaq Mohammad, Abdulrahman M. Alahmari, Muneer Khan Mohammed, Ravi Kottan Renganayagalu and Khaja Moiduddin

Materials 2017, 10(2), 211; https://doi.org/10.3390/ma10020211 - 21 Feb 2017

Cited by 43 | Viewed by 7884

Abstract

Titanium aluminides qualify adequately for advanced aero-engine applications in place of conventional nickel based superalloys. The combination of high temperature properties and lower density gives an edge to the titanium aluminide alloys. Nevertheless, challenges remain on how to process these essentially intermetallic alloys [...] Read more.

Titanium aluminides qualify adequately for advanced aero-engine applications in place of conventional nickel based superalloys. The combination of high temperature properties and lower density gives an edge to the titanium aluminide alloys. Nevertheless, challenges remain on how to process these essentially intermetallic alloys in to an actual product. Electron Beam Melting (EBM), an Additive Manufacturing Method, can build complex shaped solid parts from a given feedstock powder, thus overcoming the shortcomings of the conventional processing techniques such as machining and forging. The amount of energy supplied by the electron beam has considerable influence on the final build quality in the EBM process. Energy input is decided by the beam voltage, beam scan speed, beam current, and track offset distance. In the current work, beam current and track offset were varied to reflect three levels of energy input. Microstructural and mechanical properties were evaluated for these samples. The microstructure gradually coarsened from top to bottom along the build direction. Whereas higher energy favored lath microstructure, lower energy tended toward equiaxed grains. Computed tomography analysis revealed a greater amount of porosity in low energy samples. In addition, the lack of bonding defects led to premature failure in the tension test of low energy samples. Increase in energy to a medium level largely cancelled out the porosity, thereby increasing the strength. However, this trend did not continue with the high energy samples. Electron microscopy and X-ray diffraction investigations were carried out to understand this non-linear behavior of the strength in the three samples. Overall, the results of this work suggest that the input energy should be considered primarily whenever any new alloy system has to be processed through the EBM route. Full article

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

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2605 KiB

Open AccessArticle

Tunable Broadband Nonlinear Optical Properties of Black Phosphorus Quantum Dots for Femtosecond Laser Pulses

by Xiao-Fang Jiang, Zhikai Zeng, Shuang Li, Zhinan Guo, Han Zhang, Fei Huang and Qing-Hua Xu

Materials 2017, 10(2), 210; https://doi.org/10.3390/ma10020210 - 21 Feb 2017

Cited by 57 | Viewed by 7195

Abstract

Broadband nonlinear optical properties from 500 to 1550 nm of ultrasmall black phosphorus quantum dots (BPQDs) have been extensively investigated by using the open-aperture Z-scan technique. Our results show that BPQDs exhibit significant nonlinear absorption in the visible range, but saturable absorption in [...] Read more.

Broadband nonlinear optical properties from 500 to 1550 nm of ultrasmall black phosphorus quantum dots (BPQDs) have been extensively investigated by using the open-aperture Z-scan technique. Our results show that BPQDs exhibit significant nonlinear absorption in the visible range, but saturable absorption in the near-infrared range under femtosecond excitation. The calculated nonlinear absorption coefficients were found to be (7.49 ± 0.23) × 10⁻³, (1.68 ± 0.078) × 10⁻³ and (0.81 ± 0.03) × 10⁻³ cm/GW for 500, 700 and 900 nm, respectively. Femtosecond pump-probe measurements performed on BPQDs revealed that two-photon absorption is responsible for the observed nonlinear absorption. The saturable absorption behaviors observed at 1050, 1350 and 1550 nm are due to ground-state bleaching induced by photo-excitation. Our results suggest that BPQDs have great potential in applications as broadband optical limiters in the visible range or saturable absorbers in the near-infrared range for ultrafast laser pulses. These ultrasmall BPQDs are potentially useful as broadband optical elements in ultrafast photonics devices. Full article

(This article belongs to the Special Issue Two-Photon Absorption Materials)

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3019 KiB

Open AccessArticle

Synergistic Effects of Sm and C Co-Doped Mixed Phase Crystalline TiO₂ for Visible Light Photocatalytic Activity

by Fuchang Peng, Honglin Gao, Genlin Zhang, Zhongqi Zhu, Jin Zhang and Qingju Liu

Materials 2017, 10(2), 209; https://doi.org/10.3390/ma10020209 - 21 Feb 2017

Cited by 26 | Viewed by 6313

Abstract

Mixed phase TiO₂ nanoparticles with element doping by Sm and C were prepared via a facile sol-gel procedure. The UV-Vis light-diffuse reflectance spectroscopy analysis showed that the absorption region of co-doped TiO₂ was shifted to the visible-light region, which was attributed [...] Read more.

Mixed phase TiO₂ nanoparticles with element doping by Sm and C were prepared via a facile sol-gel procedure. The UV-Vis light-diffuse reflectance spectroscopy analysis showed that the absorption region of co-doped TiO₂ was shifted to the visible-light region, which was attributed to incorporation of samarium and carbon into the TiO₂ lattice during high-temperature reaction. Samarium effectively decreased the anatase-rutile phase transformation. The grain size can be controlled by Sm doping to achieve a large specific surface area useful for the enhancement of photocatalytic activity. The photocatalytic activities under visible light irradiation were evaluated by photocatalytic degradation of methylene blue (MB). The degradation rate of MB over the Sm-C co-doped TiO₂ sample was the best. Additionally, first-order apparent rate constants increased by about 4.3 times compared to that of commercial Degusssa P25 under the same experimental conditions. Using different types of scavengers, the results indicated that the electrons, holes, and •OH radicals are the main active species for the MB degradation. The high visible-light photocatalytic activity was attributed to low recombination of the photo-generated electrons and holes which originated from the synergistic effect of the co-doped ions and the heterostructure. Full article

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18751 KiB

Open AccessArticle

Characterization of Bitumen Micro-Mechanical Behaviors Using AFM, Phase Dynamics Theory and MD Simulation

by Yue Hou, Linbing Wang, Dawei Wang, Meng Guo, Pengfei Liu and Jianxin Yu

Materials 2017, 10(2), 208; https://doi.org/10.3390/ma10020208 - 21 Feb 2017

Cited by 66 | Viewed by 7562

Abstract

Fundamental understanding of micro-mechanical behaviors in bitumen, including phase separation, micro-friction, micro-abrasion, etc., can help the pavement engineers better understand the bitumen mechanical performances at macroscale. Recent researches show that the microstructure evolution in bitumen will directly affect its surface structure and micro-mechanical [...] Read more.

Fundamental understanding of micro-mechanical behaviors in bitumen, including phase separation, micro-friction, micro-abrasion, etc., can help the pavement engineers better understand the bitumen mechanical performances at macroscale. Recent researches show that the microstructure evolution in bitumen will directly affect its surface structure and micro-mechanical performance. In this study, the bitumen microstructure and micro-mechanical behaviors are studied using Atomic Force Microscopy (AFM) experiments, Phase Dynamics Theory and Molecular Dynamics (MD) Simulation. The AFM experiment results show that different phase-structure will occur at the surface of the bitumen samples under certain thermodynamic conditions at microscale. The phenomenon can be explained using the phase dynamics theory, where the effects of stability parameter and temperature on bitumen microstructure and micro-mechanical behavior are studied combined with MD Simulation. Simulation results show that the saturates phase, in contrast to the naphthene aromatics phase, plays a major role in bitumen micro-mechanical behavior. A high stress zone occurs at the interface between the saturates phase and the naphthene aromatics phase, which may form discontinuities that further affect the bitumen frictional performance. Full article

(This article belongs to the Special Issue Numerical Analysis of Tribology Behavior of Materials)

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7331 KiB

Open AccessArticle

Mesoscale Characterization of Fracture Properties of Steel Fiber-Reinforced Concrete Using a Lattice–Particle Model

by Francisco Montero-Chacón, Héctor Cifuentes and Fernando Medina

Materials 2017, 10(2), 207; https://doi.org/10.3390/ma10020207 - 21 Feb 2017

Cited by 29 | Viewed by 6389

Abstract

This work presents a lattice–particle model for the analysis of steel fiber-reinforced concrete (SFRC). In this approach, fibers are explicitly modeled and connected to the concrete matrix lattice via interface elements. The interface behavior was calibrated by means of pullout tests and a [...] Read more.

This work presents a lattice–particle model for the analysis of steel fiber-reinforced concrete (SFRC). In this approach, fibers are explicitly modeled and connected to the concrete matrix lattice via interface elements. The interface behavior was calibrated by means of pullout tests and a range for the bond properties is proposed. The model was validated with analytical and experimental results under uniaxial tension and compression, demonstrating the ability of the model to correctly describe the effect of fiber volume fraction and distribution on fracture properties of SFRC. The lattice–particle model was integrated into a hierarchical homogenization-based scheme in which macroscopic material parameters are obtained from mesoscale simulations. Moreover, a representative volume element (RVE) analysis was carried out and the results shows that such an RVE does exist in the post-peak regime and until localization takes place. Finally, the multiscale upscaling strategy was successfully validated with three-point bending tests. Full article

(This article belongs to the Special Issue Numerical Analysis of Concrete using Discrete Elements)

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4441 KiB

Open AccessArticle

Compressive Strength Enhancement of Vertically Aligned Carbon Nanotube Forests by Constraint of Graphene Sheets

by Chih-Chung Su, Ting-Xu Chen and Shuo-Hung Chang

Materials 2017, 10(2), 206; https://doi.org/10.3390/ma10020206 - 21 Feb 2017

Cited by 4 | Viewed by 4713

Abstract

We fabricated a 3D sandwich hybrid material composed of graphene and vertically aligned carbon nanotube forests (VACNTs) using chemical vapor deposition. The graphene was first synthesized on Cu foil. Then it was transferred to a substrate which had a pre-deposited catalyst Fe film [...] Read more.

We fabricated a 3D sandwich hybrid material composed of graphene and vertically aligned carbon nanotube forests (VACNTs) using chemical vapor deposition. The graphene was first synthesized on Cu foil. Then it was transferred to a substrate which had a pre-deposited catalyst Fe film and a buffer film of Al₂O₃ for the growth of VACNTs. The VACNTs were grown underneath the graphene and lifted up the graphene. The graphene, with its edges anchored on the Al₂O₃, provided a constrained boundary condition for the VACNTs and hence affected the growth height and mechanical strength of the VACNTs. We prepared three groups of samples: VACNTs without graphene, VACNTs with graphene transferred once (1-Gr/VACNTs), and VACNTs with graphene transferred twice (2-Gr/VACNTs). A nano-indentation system was used to measure the reduced compressive modulus (Er) and hardness (H). The Er and H of Gr/VACNTs increased with the number of transfers of the anchored graphene. The 2-Gr/VACNTs had the largest Er and H, 23.8 MPa and 912 KPa, which are 6.6 times and 5.2 times those of VACNTs without the anchored graphene, respectively. In this work, we have demonstrated a simple method to increase the mechanical properties and suppress the height of VACNTs with the anchored graphene and number of transfers. Full article

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2591 KiB

Open AccessArticle

Adsorption Behavior of High Stable Zr-Based MOFs for the Removal of Acid Organic Dye from Water

by Ke-Deng Zhang, Fang-Chang Tsai, Ning Ma, Yue Xia, Huan-Li Liu, Xue-Qing Zhan, Xiao-Yan Yu, Xiang-Zhe Zeng, Tao Jiang, Dean Shi and Chang-Jung Chang

Materials 2017, 10(2), 205; https://doi.org/10.3390/ma10020205 - 20 Feb 2017

Cited by 64 | Viewed by 6264

Abstract

Zirconium based metal organic frameworks (Zr-MOFs) have become popular in engineering studies due to their high mechanical stability, thermostability and chemical stability. In our work, by using a theoretical kinetic adsorption isotherm, we can exert MOFs to an acid dye adsorption process, experimentally [...] Read more.

Zirconium based metal organic frameworks (Zr-MOFs) have become popular in engineering studies due to their high mechanical stability, thermostability and chemical stability. In our work, by using a theoretical kinetic adsorption isotherm, we can exert MOFs to an acid dye adsorption process, experimentally exploring the adsorption of MOFs, their external behavior and internal mechanism. The results indicate their spontaneous and endothermic nature, and the maximum adsorption capacity of this material for acid orange 7 (AO7) could be up to 358 mg·g⁻¹ at 318 K, estimated by the Langmuir isotherm model. This is ascribed to the presence of an open active metal site that significantly intensified the adsorption, by majorly increasing the interaction strength with the adsorbates. Additionally, the enhanced π delocalization and suitable pore size of UiO-66 gave rise to the highest host–guest interaction, which further improves both the adsorption capacity and separation selectivity at low concentrations. Furthermore, the stability of UiO-66 was actually verified for the first time, through comparing the structure of the samples before and after adsorption mainly by Powder X-ray diffraction and thermal gravimetric analysis. Full article

(This article belongs to the Special Issue Metal Organic Framework Materials)

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8973 KiB

Open AccessArticle

Study on Damage Evaluation and Machinability of UD-CFRP for the Orthogonal Cutting Operation Using Scanning Acoustic Microscopy and the Finite Element Method

by Dongyao Wang, Xiaodong He, Zhonghai Xu, Weicheng Jiao, Fan Yang, Long Jiang, Linlin Li, Wenbo Liu and Rongguo Wang

Materials 2017, 10(2), 204; https://doi.org/10.3390/ma10020204 - 20 Feb 2017

Cited by 23 | Viewed by 5850

Abstract

Owing to high specific strength and designability, unidirectional carbon fiber reinforced polymer (UD-CFRP) has been utilized in numerous fields to replace conventional metal materials. Post machining processes are always required for UD-CFRP to achieve dimensional tolerance and assembly specifications. Due to inhomogeneity and [...] Read more.

Owing to high specific strength and designability, unidirectional carbon fiber reinforced polymer (UD-CFRP) has been utilized in numerous fields to replace conventional metal materials. Post machining processes are always required for UD-CFRP to achieve dimensional tolerance and assembly specifications. Due to inhomogeneity and anisotropy, UD-CFRP differs greatly from metal materials in machining and failure mechanism. To improve the efficiency and avoid machining-induced damage, this paper undertook to study the correlations between cutting parameters, fiber orientation angle, cutting forces, and cutting-induced damage for UD-CFRP laminate. Scanning acoustic microscopy (SAM) was employed and one-/two-dimensional damage factors were then created to quantitatively characterize the damage of the laminate workpieces. According to the 3D Hashin’s criteria a numerical model was further proposed in terms of the finite element method (FEM). A good agreement between simulation and experimental results was validated for the prediction and structural optimization of the UD-CFRP. Full article

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3183 KiB

Open AccessArticle

Improved Margins Detection of Regions Enriched with Gold Nanoparticles inside Biological Phantom

by Yossef Danan, Inbar Yariv, Zeev Zalevsky and Moshe Sinvani

Materials 2017, 10(2), 203; https://doi.org/10.3390/ma10020203 - 20 Feb 2017

Cited by 8 | Viewed by 4043

Abstract

Utilizing the surface plasmon resonance (SPR) effect of gold nanoparticles (GNPs) enables their use as contrast agents in a variety of biomedical applications for diagnostics and treatment. These applications use both the very strong scattering and absorption properties of the GNPs due to [...] Read more.

Utilizing the surface plasmon resonance (SPR) effect of gold nanoparticles (GNPs) enables their use as contrast agents in a variety of biomedical applications for diagnostics and treatment. These applications use both the very strong scattering and absorption properties of the GNPs due to their SPR effects. Most imaging methods use the light-scattering properties of the GNPs. However, the illumination source is in the same wavelength of the GNPs’ scattering wavelength, leading to background noise caused by light scattering from the tissue. In this paper we present a method to improve border detection of regions enriched with GNPs aiming for the real-time application of complete tumor resection by utilizing the absorption of specially targeted GNPs using photothermal imaging. Phantoms containing different concentrations of GNPs were irradiated with a continuous-wave laser and measured with a thermal imaging camera which detected the temperature field of the irradiated phantoms. By modulating the laser illumination, and use of a simple post processing, the border location was identified at an accuracy of better than 0.5 mm even when the surrounding area got heated. This work is a continuation of our previous research. Full article

(This article belongs to the Special Issue Nanoprobes for Imaging)

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3189 KiB

Open AccessArticle

A Study of the Curing and Flammability Properties of Bisphenol A Epoxy Diacrylate Resin Utilizing a Novel Flame Retardant Monomer, bis[di-acryloyloxyethyl]-p-tert-butyl-phenyl Phosphate

by Syang-Peng Rwei, Yu-Ming Chen, Whe-Yi Chiang and Yi-Tien Ting

Materials 2017, 10(2), 202; https://doi.org/10.3390/ma10020202 - 20 Feb 2017

Cited by 6 | Viewed by 5628

Abstract

A UV-curable, flame-retardant monomer, DAPP (bis[di-acryloyloxyethyl]-p-tert-butyl-phenyl-phosphate), was synthesized based on BPDCP (4-tert-butylphenyl-dichloro phosphate) and HEA (2-hydroxy ethyl acrylate). DAPP was blended with regular bisphenol A epoxy acrylate (BAEA) in various ratios to yield various phosphorus contents. The [...] Read more.

A UV-curable, flame-retardant monomer, DAPP (bis[di-acryloyloxyethyl]-p-tert-butyl-phenyl-phosphate), was synthesized based on BPDCP (4-tert-butylphenyl-dichloro phosphate) and HEA (2-hydroxy ethyl acrylate). DAPP was blended with regular bisphenol A epoxy acrylate (BAEA) in various ratios to yield various phosphorus contents. The TGA-IR (thermogravimetric analyzer interface with an infrared spectrometer) results demonstrate that compounding 30 mol % DAPP with BAEA significantly reduced the amount of released CO gas. In contrast, the peak intensity of CO₂ is independent of phosphorus content. The limiting oxygen index (LOI), reaching the saturated value of 26, and the heat release rate (HRR) measured using a cone-calorimeter, 156.43 KW/m², confirm the saturation point when 30 mol % DAPP was compounded into BAEA. A study of the kinetics of pyrolysis reveals that E_a decreases as the phosphorus content increases. Both the TGA-IR and pyrolysis results reveal that the phosphorus compound DAPP is easily decomposed during the initial stage of burning to form an insulating layer, which inhibits further burning of the resin and the consequent release of other flammable gases. Full article

(This article belongs to the Special Issue Flame Retardant Polymeric Materials)

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4154 KiB

Open AccessArticle

Low Temperature Phase Transformations in Copper-Quenched Ti-44.5Al-8Nb-2.5V Alloy

by Shouzhen Cao, Shulong Xiao, Yuyong Chen, Lijuan Xu, Xiaopeng Wang and Jianchao Han

Materials 2017, 10(2), 201; https://doi.org/10.3390/ma10020201 - 18 Feb 2017

Cited by 1 | Viewed by 4020

Abstract

In this study, an easily controlled transformation similar to the β + α → β + α + γ and the analysis of metastable phases in a β solidifying Ti-44.5Al-8Nb-2.5V alloy were investigated. Therefore, a liquid alloy copper-quenching followed by annealing at an [...] Read more.

In this study, an easily controlled transformation similar to the β + α → β + α + γ and the analysis of metastable phases in a β solidifying Ti-44.5Al-8Nb-2.5V alloy were investigated. Therefore, a liquid alloy copper-quenching followed by annealing at an application temperature (850 °C) has been carried out. Following quenching, a microstructure composed of several supersaturated phases—the basket-weave β₀ (β_bv) phase, the plate-like α₂ (α_p) phase and the stripe-like γ (γ_s) phase—was obtained. In the annealing processes, phase transformations in the prior β_bv and α_p phases domain corresponded nicely to the β + α → β + α + γ transformation during solidification. Also, in the annealed γ_s phase, the kinetics of the phase transformations involving the metastable L1₂ phase was firstly detected by transmission electron microscopy (TEM). The L1₂ phase had a lattice structure similar to the γ phase, whereas the composition of the phase was similar to the α₂ phase. The formation of the γ pre-twin phase with an anti-phase boundary (APB) was detected in the γ_s phase of the matrix. The orientation relationships between the γ_s and precipitated: γ (γ_p) phase are <101]γ_s//<114]γ_p, (10

\bar{1}

)γ_s//(

\bar{1}

10)γ_p and (0

\bar{1}

0)γ_s//(22

\bar{1}

)γ_p. Full article

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Graphical abstract

7244 KiB

Open AccessArticle

HRTEM Microstructural Characterization of β-WO3 Thin Films Deposited by Reactive RF Magnetron Sputtering

by A. Faudoa-Arzate, A. Arteaga-Durán, R.J. Saenz-Hernández, M.E. Botello-Zubiate, P.R. Realyvazquez-Guevara and J.A. Matutes-Aquino

Materials 2017, 10(2), 200; https://doi.org/10.3390/ma10020200 - 17 Feb 2017

Cited by 19 | Viewed by 4575

Abstract

Though tungsten trioxide (WO3) in bulk, nanosphere, and thin film samples has been extensively studied, few studies have been dedicated to the crystallographic structure of WO3 thin films. In this work, the evolution from amorphous WO3 thin films to crystalline WO3 thin films [...] Read more.

Though tungsten trioxide (WO3) in bulk, nanosphere, and thin film samples has been extensively studied, few studies have been dedicated to the crystallographic structure of WO3 thin films. In this work, the evolution from amorphous WO3 thin films to crystalline WO3 thin films is discussed. WO3 thin films were fabricated on silicon substrates (Si/SiO2) by RF reactive magnetron sputtering. Once a thin film was deposited, two successive annealing treatments were made: an initial annealing at 400 °C for 6 h was followed by a second annealing at 350 °C for 1 h. Film characterization was carried out by X-ray diffraction (XRD), high-resolution electron transmission microscopy (HRTEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) techniques. The β-WO3 final phase grew in form of columnar crystals and its growth plane was determined by HRTEM. Full article

(This article belongs to the Section Advanced Materials Characterization)

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11488 KiB

Open AccessArticle

Rust Formation Mechanism on Low Alloy Steels after Exposure Test in High Cl− and High SOx Environmen

by Toshiyasu Nishimura

Materials 2017, 10(2), 199; https://doi.org/10.3390/ma10020199 - 17 Feb 2017

Cited by 10 | Viewed by 4497

Abstract

Exposure tests were performed on low alloy steels in high Cl− and high SOx environment, and the structure of the rust were analyzed by TEM (Transmission Electron Microscopy) and Raman Spectroscopy. In the exposure test site, the concentrations of Cl− and SOx were [...] Read more.

Exposure tests were performed on low alloy steels in high Cl− and high SOx environment, and the structure of the rust were analyzed by TEM (Transmission Electron Microscopy) and Raman Spectroscopy. In the exposure test site, the concentrations of Cl− and SOx were found to be high, which caused the corrosion of the steels. The conventional weathering steel (SMA: 0.6% Cr-0.4% Cu-Fe) showed higher corrosion resistance as compared to the carbon steel (SM), and Ni bearing steel exhibited the highest one. Raman spectroscopy showed that the inner rust of Ni bearing steel was mainly composed of α-FeOOH and spinel oxides. On the other hand, SMA contained β- and γ-FeOOH in inner rust, which increased the corrosion. TEM showed that nano-scale complex iron oxides containing Ni or Cr were formed in the rust on the low alloy steels, which suppressed the corrosion of steels in high Cl− and high SOx environment. Full article

(This article belongs to the Special Issue Fundamental and Research Frontier of Atmospheric Corrosion)

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9418 KiB

Open AccessReview

BiCuSeO Thermoelectrics: An Update on Recent Progress and Perspective

by Xiaoxuan Zhang, Cheng Chang, Yiming Zhou and Li-Dong Zhao

Materials 2017, 10(2), 198; https://doi.org/10.3390/ma10020198 - 17 Feb 2017

Cited by 70 | Viewed by 6724

Abstract

A BiCuSeO system has been reported as a promising thermoelectric material and has attracted great attention in the thermoelectric community since 2010. Recently, several remarkable studies have been reported and the ZT of BiCuSeO was pushed to a higher level. It motivates us [...] Read more.

A BiCuSeO system has been reported as a promising thermoelectric material and has attracted great attention in the thermoelectric community since 2010. Recently, several remarkable studies have been reported and the ZT of BiCuSeO was pushed to a higher level. It motivates us to systematically summarize the recent reports on the BiCuSeO system. In this short review, we start with several attempts to optimize thermoelectric properties of BiCuSeO. Then, we introduce several opinions to explore the origins of low thermal conductivity for BiCuSeO. Several approaches to enhance thermoelectric performance are also summarized, including modulation doping, introducing dual-vacancies, and dual-doping, etc. At last, we propose some possible strategies for enhancing thermoelectric performance of BiCuSeO in future research. Full article

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

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4656 KiB

Open AccessFeature PaperArticle

Synthesis of 2D Nitrogen-Doped Mesoporous Carbon Catalyst for Oxygen Reduction Reaction

by Zhipeng Yu, Jinhua Piao and Zhenxing Liang

Materials 2017, 10(2), 197; https://doi.org/10.3390/ma10020197 - 17 Feb 2017

Cited by 25 | Viewed by 5202

Abstract

2D nitrogen-doped mesoporous carbon (NMC) is synthesized by using a mesoporous silica film as hard template, which is then investigated as a non-precious metal catalyst for the oxygen reduction reaction (ORR). The effect of the synthesis conditions on the silica template and carbon [...] Read more.

2D nitrogen-doped mesoporous carbon (NMC) is synthesized by using a mesoporous silica film as hard template, which is then investigated as a non-precious metal catalyst for the oxygen reduction reaction (ORR). The effect of the synthesis conditions on the silica template and carbon is extensively investigated. In this work, we employ dual templates—viz. graphene oxide and triblock copolymer F127—to control the textural features of a 2D silica film. The silica is then used as a template to direct the synthesis of a 2D nitrogen-doped mesoporous carbon. The resultant nitrogen-doped mesoporous carbon is characterized by transmission electron microscopy (TEM), nitrogen ad/desorption isotherms, X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and rotating disk electrode measurements (RDE). The electrochemical test reveals that the obtained 2D-film carbon catalyst yields a highly electrochemically active surface area and superior electrocatalytic activity for the ORR compared to the 3D-particle. The superior activity can be firstly attributed to the difference in the specific surface area of the two catalysts. More importantly, the 2D-film morphology makes more active sites accessible to the reactive species, resulting in a much higher utilization efficiency and consequently better activity. Finally, it is noted that all the carbon catalysts exhibit a higher ORR activity than a commercial Pt catalyst, and are promising for use in fuel cells. Full article

(This article belongs to the Special Issue Advanced Materials in Polymer Electrolyte Fuel Cells)

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10496 KiB

Open AccessArticle

The Effect of Matrix Composition on the Deformation and Failure Mechanisms in Metal Matrix Syntactic Foams during Compression

by Csilla Kádár, Kristián Máthis, Michal Knapek and František Chmelík

Materials 2017, 10(2), 196; https://doi.org/10.3390/ma10020196 - 17 Feb 2017

Cited by 22 | Viewed by 4481

Abstract

The influence of the matrix material on the deformation and failure mechanisms in metal matrix syntactic foams was investigated in this study. Samples with commercially pure Al (Al) and Al-12 wt % Si (AlSi12) eutectic aluminum matrix, reinforced by hollow ceramic spheres, were [...] Read more.

The influence of the matrix material on the deformation and failure mechanisms in metal matrix syntactic foams was investigated in this study. Samples with commercially pure Al (Al) and Al-12 wt % Si (AlSi12) eutectic aluminum matrix, reinforced by hollow ceramic spheres, were compressed at room temperature. Concurrently, the acoustic emission response and the strain field development on the surface were monitored in-situ. The results indicate that the plastic deformation of the cell walls is the governing mechanism in the early stage of straining for both types of foams. At large stresses, deformation bands form both in the Al and AlSi12 foam. In Al foam, cell walls collapse in a large volume. In contrast, the AlSi12 foam is more brittle; therefore, the fracture of precipitates and the crushing of the matrix take place within a distinctive deformation band, along with an occurrence of a significant stress drop. The onset stress of ceramic sphere failure was shown to be not influenced by the matrix material. The in-situ methods provided complementary data which further support these results. Full article

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5513 KiB

Open AccessArticle

Microstructural Characterization of Melt Extracted High-Nb-Containing TiAl-Based Fiber

by Shuzhi Zhang, Shuling Zhang, Yanfei Chen, Jianchao Han, Changjiang Zhang, Xiaopeng Wang and Yuyong Chen

Materials 2017, 10(2), 195; https://doi.org/10.3390/ma10020195 - 17 Feb 2017

Cited by 1 | Viewed by 3440

Abstract

The microstructure of melt extracted Ti-44Al-8Nb-0.2W-0.2B-1.5Si fiber were investigated. When the rotation speed increased from 2000 to 2600 r/min, the appearance of the wire was uniform with no Rayleigh-wave default. The structure was mainly composed of fine α₂ (α) phase dendritic crystal [...] Read more.

The microstructure of melt extracted Ti-44Al-8Nb-0.2W-0.2B-1.5Si fiber were investigated. When the rotation speed increased from 2000 to 2600 r/min, the appearance of the wire was uniform with no Rayleigh-wave default. The structure was mainly composed of fine α₂ (α) phase dendritic crystal and a second phase between dendrite arms and grain boundaries. The precipitated second phases were confirmed to be Ti₅Si₃ from the eutectic reaction L→Ti₅Si₃ + α and TiB. As the lower content of Si and higher cooling rate, a divorced eutectic microstructure was obtained. Segregation of Ti, Nb, B, Si, and Al occurred during rapid solidification. Full article

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3563 KiB

Open AccessArticle

Fretting Corrosion Behavior of Experimental Ti-20Cr Compared to Titanium

by Tomofumi Sawada, Christine Schille, Atif Almadani and Jürgen Geis-Gerstorfer

Materials 2017, 10(2), 194; https://doi.org/10.3390/ma10020194 - 17 Feb 2017

Cited by 12 | Viewed by 4122

Abstract

Experimental cast titanium alloys containing 20 mass% chromium (Ti-20Cr) show preferable mechanical properties and a good corrosion resistance. This study evaluated the fretting corrosion behavior of Ti-20Cr. Ti-20Cr (n = 4) and commercially pure titanium (CP-Ti, n = 6) disk specimens were [...] Read more.

Experimental cast titanium alloys containing 20 mass% chromium (Ti-20Cr) show preferable mechanical properties and a good corrosion resistance. This study evaluated the fretting corrosion behavior of Ti-20Cr. Ti-20Cr (n = 4) and commercially pure titanium (CP-Ti, n = 6) disk specimens were used. The fretting corrosion test was performed by electrochemical corrosion at 0.3 V in 0.9% saline solution and mechanical damage using 10 scratching cycles with three different scratching speeds (10–40 mm/s) at 10 N. After testing, the activation peak, repassivation time and surface morphology of each specimen were analyzed. The differences between the results were tested by parametric tests (α = 0.05). The average activation peaks were significantly higher in CP-Ti than in Ti-20Cr (p < 0.01), except at 20 mm/s. In the series of scratching speeds, faster scratching speeds showed higher activation peaks. The maximum activation peaks were also higher in CP-Ti. Slight differences in the repassivation time were observed between the materials at every scratching speed; faster scratching speeds showed shorter repassivation times in both materials (p < 0.05). CP-Ti showed severe damage and significantly higher wear depth than Ti-20Cr (p < 0.05). In conclusion, adding chromium to titanium reduced surface damage and improved the fretting corrosion resistance. Full article

(This article belongs to the Special Issue Passive Oxide Films and Their Susceptibility to Corrosion)

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15409 KiB

Open AccessArticle

The Effect of Welding Energy on the Microstructural and Mechanical Properties of Ultrasonic-Welded Copper Joints

by Jingwei Yang, Biao Cao and Qinghua Lu

Materials 2017, 10(2), 193; https://doi.org/10.3390/ma10020193 - 16 Feb 2017

Cited by 36 | Viewed by 5855

Abstract

The effects of welding energy on the mechanical and microstructural characteristics of ultrasonic-welded pure copper plates were investigated. Complex dynamic recrystallization and grain growth occurred inside the weld zone during ultrasonic welding. At a low welding energy, a thin band of straight weld [...] Read more.

The effects of welding energy on the mechanical and microstructural characteristics of ultrasonic-welded pure copper plates were investigated. Complex dynamic recrystallization and grain growth occurred inside the weld zone during ultrasonic welding. At a low welding energy, a thin band of straight weld interfaces was observed and had an ultra-fine grain structure. With an increase in welding energy, the weld interface progressively changed from flat to sinusoidal, and eventually turned into a convoluted wavy pattern, bearing similarities to shear instabilities, as observed in fluid dynamics. The lap shear load of the joints initially increased and then remained stable as the welding energy increased. The tensile characteristics of the joints significantly depended on the development of plastic deformation at the interface. The influence of the microstructure on the hardness was also discussed. Full article

(This article belongs to the Special Issue Welding, Joining and Casting of Advanced Materials)

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2587 KiB

Open AccessArticle

Preparation and Investigation of Amphiphilic Block Copolymers/Fullerene Nanocomposites as Nanocarriers for Hydrophobic Drug

by Qinggang Tan, Yanyan Chu, Min Bie, Zihao Wang and Xiaoyan Xu

Materials 2017, 10(2), 192; https://doi.org/10.3390/ma10020192 - 16 Feb 2017

Cited by 11 | Viewed by 4625

Abstract

Biopolymer/inorganic material nanocomposites have attracted increasing interest as nanocarriers for delivering drugs owing to the combined advantages of both biopolymer and inorganic materials. Here, amphiphilic block copolymer/fullerene nanocomposites were prepared as nanocarriers for hydrophobic drug by incorporation of C60 in the core of [...] Read more.

Biopolymer/inorganic material nanocomposites have attracted increasing interest as nanocarriers for delivering drugs owing to the combined advantages of both biopolymer and inorganic materials. Here, amphiphilic block copolymer/fullerene nanocomposites were prepared as nanocarriers for hydrophobic drug by incorporation of C60 in the core of methoxy polyethylene glycol-poly(d,l-lactic acid) (MPEG-PDLLA) micelles. The structure and morphology of MPEG-PDLLA/C60 nanocomposites were characterized using transmission electron microscopy, dynamic light scattering, high-resolution transmission electron microscopy, and thermal gravimetric analysis. It was found that the moderate amount of spherical C60 incorporated in the MPEG-PDLLA micelles may cause an increase in the molecular chain space of PDLLA segments in the vicinity of C60 and, thus, produce a larger cargo space to increase drug entrapment and accelerate the drug release from nanocomposites. Furthermore, sufficient additions of C60 perhaps resulted in an aggregation of C60 within the micelles that decreased the drug entrapment and produced a steric hindrance for DOX released from the nanocomposites. The results obtained provide fundamental insights into the understanding of the role of C60 in adjusting the drug loading and release of amphiphilic copolymer micelles and further demonstrate the future potential of the MPEG-PDLLA/C60 nanocomposites used as nanocarriers for controlled drug-delivery applications. Full article

(This article belongs to the Section Biomaterials)

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5571 KiB

Open AccessCommunication

A Dual-Bonded Approach for Improving Hydrogel Implant Stability in Cartilage Defects

by Yan Liu, Yuxuan Wu, Lei Zhou, Zhengao Wang, Cong Dai, Chengyun Ning and Guoxin Tan

Materials 2017, 10(2), 191; https://doi.org/10.3390/ma10020191 - 16 Feb 2017

Cited by 30 | Viewed by 4850

Abstract

Integration and stability of hydrogels and surrounding cartilage/bone tissue is crucial for both immediate functionality and long-term performance of the tissue. In this work, chondroitin sulphate (CS) a polysaccharide found in cartilage and other tissues was used to synthesize a tough hydrogel that [...] Read more.

Integration and stability of hydrogels and surrounding cartilage/bone tissue is crucial for both immediate functionality and long-term performance of the tissue. In this work, chondroitin sulphate (CS) a polysaccharide found in cartilage and other tissues was used to synthesize a tough hydrogel that was chemically functionalized with methacrylate and aldehyde groups, bonding to surrounding tissue via a dual-bonded approach. The hydrogel can not only chemically anchor onto implanted titanium at the subchondral bone, but also on cartilage tissue via the Schiff-base reaction. In vitro experiments confirmed that the strategy improved hydrogel implant stability with cartilage tissue, was favorable for chondrocyte attachment, and has the potential to quickly and effectively repair cartilage defects and maintain joint functionality for a long time. Full article

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2751 KiB

Open AccessArticle

Polyvinylpyrrolidone-Based Bio-Ink Improves Cell Viability and Homogeneity during Drop-On-Demand Printing

by Wei Long Ng, Wai Yee Yeong and May Win Naing

Materials 2017, 10(2), 190; https://doi.org/10.3390/ma10020190 - 16 Feb 2017

Cited by 79 | Viewed by 7735

Abstract

Drop-on-demand (DOD) bioprinting has attracted huge attention for numerous biological applications due to its precise control over material volume and deposition pattern in a contactless printing approach. 3D bioprinting is still an emerging field and more work is required to improve the viability [...] Read more.

Drop-on-demand (DOD) bioprinting has attracted huge attention for numerous biological applications due to its precise control over material volume and deposition pattern in a contactless printing approach. 3D bioprinting is still an emerging field and more work is required to improve the viability and homogeneity of printed cells during the printing process. Here, a general purpose bio-ink was developed using polyvinylpyrrolidone (PVP) macromolecules. Different PVP-based bio-inks (0%–3% w/v) were prepared and evaluated for their printability; the short-term and long-term viability of the printed cells were first investigated. The Z value of a bio-ink determines its printability; it is the inverse of the Ohnesorge number (Oh), which is the ratio between the Reynolds number and a square root of the Weber number, and is independent of the bio-ink velocity. The viability of printed cells is dependent on the Z values of the bio-inks; the results indicated that the cells can be printed without any significant impairment using a bio-ink with a threshold Z value of ≤9.30 (2% and 2.5% w/v). Next, the cell output was evaluated over a period of 30 min. The results indicated that PVP molecules mitigate the cell adhesion and sedimentation during the printing process; the 2.5% w/v PVP bio-ink demonstrated the most consistent cell output over a period of 30 min. Hence, PVP macromolecules can play a critical role in improving the cell viability and homogeneity during the bioprinting process. Full article

(This article belongs to the Special Issue 3D Printing for Biomedical Engineering)

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524 KiB

Open AccessArticle

Boron Partitioning Coefficient above Unity in Laser Crystallized Silicon

by Patrick C. Lill, Morris Dahlinger and Jürgen R. Köhler

Materials 2017, 10(2), 189; https://doi.org/10.3390/ma10020189 - 16 Feb 2017

Cited by 8 | Viewed by 4599

Abstract

Boron pile-up at the maximum melt depth for laser melt annealing of implanted silicon has been reported in numerous papers. The present contribution examines the boron accumulation in a laser doping setting, without dopants initially incorporated in the silicon wafer. Our numerical simulation [...] Read more.

Boron pile-up at the maximum melt depth for laser melt annealing of implanted silicon has been reported in numerous papers. The present contribution examines the boron accumulation in a laser doping setting, without dopants initially incorporated in the silicon wafer. Our numerical simulation models laser-induced melting as well as dopant diffusion, and excellently reproduces the secondary ion mass spectroscopy-measured boron profiles. We determine a partitioning coefficient

k_{p}

above unity with

k_{p} = 1.25 \pm 0.05

and thermally-activated diffusivity

D_{B}

, with a value

D_{B} (1687 K) = (3.53 \pm 0.44) \times 10^{- 4}

cm

^{2}

·s

^{- 1}

of boron in liquid silicon. For similar laser parameters and process conditions, our model predicts the anticipated boron profile of a laser doping experiment. Full article

(This article belongs to the Section Advanced Materials Characterization)

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3528 KiB

Open AccessArticle

Wear Enhancement of Wheel-Rail Interaction by Ultrasonic Nanocrystalline Surface Modification Technique

by Seky Chang, Young-Sik Pyun and Auezhan Amanov

Materials 2017, 10(2), 188; https://doi.org/10.3390/ma10020188 - 16 Feb 2017

Cited by 19 | Viewed by 5219

Abstract

In this study, an ultrasonic nanocrystalline surface modification (UNSM) technique was applied to normal and heat-treated rails made of 60 kgK steel to enhance the wear resistance of the wheel-rail interaction. The hardness and compressive residual stress values of the untreated and UNSM-treated [...] Read more.

In this study, an ultrasonic nanocrystalline surface modification (UNSM) technique was applied to normal and heat-treated rails made of 60 kgK steel to enhance the wear resistance of the wheel-rail interaction. The hardness and compressive residual stress values of the untreated and UNSM-treated rails were measured by the Brinell hardness tester and X-ray diffraction technique, respectively. It was found, according to the measurement results, that the hardness was increased by about 20% and 8%, whereas the compressive residual stress was induced by about 52% and 62% for the UNSM-treated normal and heat-treated rails, respectively. The UNSM-treated normal rail showed a slightly higher hardness than the heat-treated rail. The wear resistance of rails with respect to rotating speed and rolling time was assessed using a rolling contact wear (RCW) tester under dry conditions. The RCW test results revealed that the wear of the UNSM-treated rails was enhanced in comparison with those of the untreated rails. Also, the wear amount of the rails was increased with increasing the rotation speed. The UNSM-treated normal rail exhibited the highest wear resistance with respect to the rotation speed. The wear mechanisms of the rails are also discussed based on microscopic images of the worn out surfaces. Full article

(This article belongs to the Special Issue Tribological Behavior of Materials by Surface Engineering)

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