Materials Science Forum Vol. 724

Abstract: To improve the electrochemical performance of LiFePO₄, LiFePO₄/C composite materials were prepared by solid-state synthesis method with Fe₂O₃ as one of the starting materials. The phase composition, microstructure and morphology of samples were determined by X-ray diffraction (XRD) and scanning electron microscope (SEM). The electrochemical performance of samples were characterized by constant current charge-discharge method. The results show that the prepared samples have the single phase, and the carbon coating lead to no change of the crystal structure of LiFePO₄. The sample with carbon content of 10wt% shows the best electrochemical properties. Its initial discharge capacity is 144.6 mA·h /g at 0.2C rate. After 30 cycles the capacity remains 131.4 mA·h /g, and the capacity retention rate is 91%.

Abstract: Mullite whiskers were prepared from SiC powders in molten Al₂(SO₄)₃-Na₂SO₄ mixture salts at different temperatures. The morphology and phase composition of resulting whiskers were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) techniques. Mullite tiny fiber clusters with diameter about 50 nanometers and lengths of over several microns were obtained in 900°C mixture molten salts system. A new oxidation-dissolution mechanism was proposed for explanation mullite whiskers growth.

Abstract: Antimony doped tin oxide (ATO) is a typical p-type semiconductor and widely used due to its good properties such as electrical conductivity and transparency in visible range, while reflects infrared light. These features allow ATO to be used as transparent electrodes, heat mirrors and energy storage device, display panel. However, the use of tin oxide ceramics is limited by the low densification during sintering due to the dominance of non-densification mechanism such as surface diffusion or evaporation condensation. So, sintering agents such as Cobalt (II) oxide (CoO), zinc oxide (ZnO), manganese dioxide (MnO₂) used to improve the densification of SnO₂ by forming lattice solid solution or liquid phase. In this study, we studied the effect of the sintering agents. The antimony-doped tin oxide nanoparticles were synthesized by a sol-gel method. After sintering ATO with sintering agents such as MnO₂ and CoO, sintered body characteristics were investigated by XRD, SEM, thermal conductivity, resistivity and interesting characteristic.

Abstract: Due to the low density and high specific strength, magnesium and its alloys have been extensively used in the automobile and aerospace applications, where the weight reduction is critical. However, they are highly prone to corrosion, which has greatly limited their application in the automotive and aerospace industries. This paper briefly reviews the technologies for improving the corrosion and wear resistance of magnesium alloys and finds that the widespread application of magnesium alloys is still limited by the lack of proper protective coatings. Therefore, there is still a need to explore new materials and methods for the effective protection of magnesium and its alloys.

Abstract: SiC/0~20% graphite (volume fraction) composites were successfully fabricated by pressureless sintering at 1700 °C for 2 h in nitrogen atmosphere. The impregnating and heat treatment process for the samples with silica sol/phenolic impregnant was carried out at 1450 °C for 2 h in nitrogen atmosphere. The Vickers hardness, oxidation resistance and thermal shock property of the composites before and after treatment were tested, and the microstructure and phase composition were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). The results shown that the Vickers hardness of SiC/20% graphite was increased from 3.35 GPa to 4.90 GPa by heat treatment, and the oxidation resistance and thermal shock property of the heat treated samples were also improved significantly. The SEM and XRD results revealed that the formation of new SiC particles by the reaction of silica sol and phenolic was the main reason for the mechanical properties improvements.

Abstract: Mo modified Ti₂A1C /Al₂O₃ composites were successfully fabricated from an elemental power mixture of Ti, Al, TiC and MoO₃ by an in situ reaction/hot pressing method. The reaction path and effect of the molar ratio of the initial materials on the phase composition were investigated in detail. The as-prepared materials are mainly composed of (Ti_1-xMo_x)₂AlC solid solutions, Al₂O₃, and a small amounts of the Mo rich compounds. It is found that the in situ formed fine Al₂O₃ particles tend to disperse on the matrix grain boundaries. Compared with the monolithic Ti₂A1C, (Ti,Mo)₂AlC/10 wt% Al₂O₃ composite possesses a fine grain sized structure. The Vickers hardness, flexural strength, fracture toughness, and compressive strength of the as composite are 4.75 GPa, 458 MPa, 6.03 MPa·m^1/2, 971 MPa, respectively.

Abstract: Combustion reaction in laminated Ni and Al foils was ignited by plasma activated sintering (PAS) to synthesize metal-intermetallic laminated composites (MILCs). The microstructure evolution in the reaction and the post-heat treatment was investigated. The results showed that thermal explosion (TE) reaction were happened between Ni and Al foils at the melting point of Al. The reaction was incomplete due to the heat loss through the thick foils. The produced phases, Ni₂Al₃ and NiAl₃, were converted to a compositionally gradient series of intermetallic phases in the nal microstructures of the intermetallic layers after the post heat treatment.

Abstract: SnO₂-based varistors were successfully fabricated from the mixed powders, SnO₂, Co₂O₃, Nb₂O₅ and Cr₂O₃. The effects of sintering temperature (1250, 1300, 1350 and 1400 °C) on the microstructure and electrical properties were investigated. The results reveal that the grain size increases with increasing the sintering temperature, and the breakdown electrical filed decreases gradually. When the sintering temperature was 1300 °C, the nonlinear coefficient of the as fabricated SnO₂ based varistors presents the maximum of 27. Meanwhile, the leakage current possesses the minimum of 4.5 µA.

Abstract: ZnO-based linear resistance ceramics were fabricated by the conventional ceramic method. The effect of calcination of the raw materials on the microstructure and electrical properties was investigated in detail. The results show that the electrical properties, such as resistivity, nonlinear coefficient and resistance temperature coefficient, have been obviously influenced by the calcining process. The optimal samples fabricated with the materials calcinated for twice possess the highest stabilization of resistivity. Meanwhile, the resistance temperature coefficient is improved by 30%, and the nonlinear coefficient of voltage decreases to 1.16, decreased by 20.7%.

Abstract: The purpose of this paper is to study the compression ratio per pass, drawing rules of three differential commercial 316L stainless steel wires during drawing extra fine stainless steel processing. In addition, the influence of chemical composite on the mechanical property has been discussed as well. The results indicate that the tensile strength of austenite stainless steel wires was increased obviously by multi-passes drawing. The strength-enhancing effect of wire drawing can be substantial.