In this paper, Co-based composite coatings were fabricated by laser cladding Co42 + B4C mixed powders on Ti-6Al-4V titanium alloy. The comprehensive effects of laser power and scanning velocity on ...the microstructure evolution and wear property of the laser cladding coatings were studied. Results indicated that the coatings were mainly comprised of γ-Co/Ni, TiC, TiB2, TiB, NiTi, CoTi, CoTi2, and Cr7C3. With the decreasing of laser specific energy (from 12.7 kJ cm−2 to 4.9 kJ cm−2), the TiC dendrites and TiB particles were refined. Compared with the Ti-6Al-4V titanium alloy, the microhardness and wear resistance of the composite coatings were enhanced obviously. Lower laser specific energy led to higher microhardness and better wear resistance owing to more TiB2 bulks distributed in the cladding coating.
•Composite coatings reinforced with multiple phases were fabricated.•The microstructure was refined with the decreasing of laser specific energy.•Lower laser specific energy led to higher microhardness and better wear resistance.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Microstructure curvature, or buckling, is observed in the micromachining of silicon sensors because of the doping of impurities for realizing certain electrical and mechanical processes. This ...behavior can be a key source of error in inertial sensors. Therefore, identifying the factors that influence the buckling value is important in designing MEMS devices. In this study, the curvature in the proof mass of an accelerometer is modeled as a multilayered solid model. Modeling is performed according to the characteristics of the solid diffusion mechanism in the bulk-dissolved wafer process (BDWP) based on the self-stopped etch technique. Moreover, the proposed multilayered solid model is established as an equivalent composite structure formed by a group of thin layers that are glued together. Each layer has a different Young's modulus value and each undergoes different volume shrinkage strain owing to boron doping in silicon. Observations of five groups of proof mass blocks of accelerometers suggest that the theoretical model is effective in determining the buckling value of a fabricated structure.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
This review covers several aspects of the rapid development of magnesium (Mg) alloys from the owned properties and corrosion mechanism to the effect of optimization of mechanical properties, alloying ...and surface coating preparation. Firstly, the category of biomedical materials and commonly used metal-based implant materials are briefly presented. Then, advantages and disadvantages of Mg-based biomedical materials are listed. To solve the poor mechanical properties and high corrosion rate of Mg-based materials, effective methods are adopted. Heat-treated can adjust and transform internal structure, shape and distribution of the second phase, and plastic deformation can enhance mechanical properties by refining grains of dynamic recrystallization and decreasing structure segregation. Alloying will enhance corrosion resistance by improving the structure distribution, grain refinement, and solid solution ability; surface modification can protect the substrate from corrosion by preventing a direct contact with body fluids. Finally, applications as the bone fixation and vascular stent are discussed in detail. This review hopes that it can provide experienced researchers in the field of Mg-based biomedical materials an opportunity and approach to obtain the latest research direction and progress information, and give useful guidance for newcomers to understand the market.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A hyperelastic and hydrophobic silica aerogel has been prepared by using Vinyltriethoxysilane (VTES) and Methyltrimethoxysilane (MTMS) as the composite precursor. The effect of the VTES/MTMS molar ...ratio on the morphology of the VTES/MTMS-based aerogel has been investigated. The VTES/MTMS-based aerogel with a typical nano-porous structure exhibits a high surface area (321 m2/g), a low density (0.143 g·cm−3) and low thermal conductivity (0.024 ± 0.003 W·m−1·K−1). The existence of methyl and vinyl groups is beneficial to enhancing the elasticities of aerogels. The MVTES5, with a VTES/MTMS molar ratio of 0.060, could bear a compressive strain of 55% and quickly recover to its original length after the stress is released. It is demonstrated that the partial replacement of the methyl with vinyl groups can greatly enhance the mechanical properties, and the compressive stress is 0.571 MPa. Furthermore, the VTES/MTMS-based aerogel exhibits hydrophobic properties with a contact angle of 146°.
•A low-cost and high-performance VTES/MTMS-based aerogel was prepared.•The VTES/MTMS-based aerogel has higher compressive strain (55%) and compressive stress (0.571 MPa) than MTMS-based aerogel.•The VTES/MTMS-based aerogel exhibits hydrophobic, the contact angle of which is up to 146°.•The VTES/MTMS-based aerogel can return to the original state and display excellent stability during compression-springback.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A low-cost and high-performance quartz fiber/Al2O3-SiO2 aerogel (QF/ASA) composite insulation material has been successfully prepared by vacuum filtration molding and sol-gel impregnation following ...surface-modified ambient pressure drying (APD). The macroporous in the quartz fiber perform are filled by Al2O3-SiO2 aerogels with a large amount of mesoporous. The morphology, microstructure, thermal conductivity and thermal stability of the QF/ASA composite were investigated. Compared to the fiber/aerogel materials dried by supercritical drying, the composite exhibits similar low density (0.36 g·cm−3), high specific surface area (580.5 m2·g−1), low thermal conductivity (0.049 W·m−1·K−1) at room temperature. The compressive strength of the composite up to 0.85 MPa which is approximately triple as much as that of fiber perform. After being heated at 600 to 1100 °C, the specific surface area of composite aerogel decrease from 578.0 to 113.6 m2·g−1 and the linear shrinkage is almost zero. The XRD patterns show that mullite (3Al2O3·2SiO2) appeared in the Al2O3-SiO2 aerogel after heat-treatment at 1100 °C, which is consistent with the molar ratio of silica and alumina of 2:3.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Nano-scale ZrO2/SiC-based fibers were prepared for the first time.•The introduction of Zr could improve the thermal insulation and high-temperature resistance.•Multiple phases enhance phonon ...scattering and interface thermal resistance.
Display omitted
Silicon carbide (SiC) fibers have excellent high temperature resistance and chemical stability in extreme environment. However, the practical application of SiC fibers have been limited by their high intrinsic thermal conductivity. Herein, the novel ZrO2/SiC-based nanofiber membranes with high temperature resistance and low thermal conductivity were prepared for the first time using simple blending method via electrospinning technique combined with subsequent curing and pyrolysis. The microstructure, composition, high temperature resistance and thermal insulation mechanisms were analyzed in detail. The results showed that the introduction of Zr could significantly improve the high temperature resistance of the nanofibers up to 1400 °C, at the same time, the multi-phase microstructure (SiOxCy, ZrO2, β-SiC and residual carbon) endows it with ultralow thermal conductivity at high temperature (0.217 W m-1 K-1 at 1300 °C). Compared with the reported thermal insulation materials, this work not only prepares thermal insulation materials with higher temperature resistance, but also provides a new perspective for the research of SiC-based nanofibers in the field of thermal insulation.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
This paper tries to build a multi-functional downhole nuclear magnetic resonance （NMR） fluid analysis laboratory that can evaluate fluid information in real time at reservoir conditions at a depth of ...several thousand meters. The aim is to monitor the pollution of the formation fluids and quantitatively evaluate NMR characteristics of the fluids. It focuses on the design of the structure and parameters of a sensor with zero stray fields. Two separate coils are designed to measure NMR characteristics of flowing or static fluids. A method is proposed to use the Bloch equation, to guide the optimization of the NMR sensor. Finally, the measured results confirm that the design is reasonable. There is a homogeneous static field （perpendicular to the axial direction） in the center of the sensor, and there are no stray external fields. The novel design of pre-polarization magnet improves the signal to noise ratio, while shortening the sensor length.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We report on a modulated synthesis method that enables the preparation of monodisperse MOF-5 crystals with tunable sizes and shapes. This controlled synthesis involves the base-tuned nucleation and ...the surfactant-modulated facet growth of MOF-5 during its crystallization. Systematic reactions with triethylamine (TEA) as additional base and polyvinylpyrrolidone (PVP) as capping agent were investigated. Under optimized experimental conditions, monodisperse MOF-5 cubes (with tunable sizes ranging from ~400 nm to ~2500 nm), truncated cubes, truncated octahedrons, and octahedrons could be produced with high reproducibility.
A modulated synthesis method was reported to prepare monodisperse MOF-5 crystals with tunable sizes and shapes. Display omitted
•Monodisperse MOF-5 crystals with tunable sizes and shapes were synthesized.•Triethylamine (TEA) was introduced as auxiliary base to tune nucleation of MOF-5 crystals to achieve uniform sizes.•Polyvinylpyrrolidone (PVP) was used as capping agent to modulate facet growth of MOF-5 to yield monodisperse crystals with different shapes.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
PDF
