Composite Materials V

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Authors: Sea Fue Wang, Yuh Ruey Wang, Thomas C.K. Yang
Abstract: In this study, the feasibility for use of multiphase BaTiO3 ceramics as microwave dielectric resonators was evaluated through the substitution of metal ions in B sites, such as ions of Mn, Co, Mg, In, Fe, Zn, and Ni. The effects of metal ions substitution and sintering conditions on the densification, microstructural evolution and microwave properties of the BaTiO3 ceramics containing cubic and hexagonal phase were examined.
Authors: Qiu Bao Ouyang, Wei Min Zhou, Guo Ding Zhang, Di Zhang
Abstract: The objective of the present paper is to study the wetting phenomenon and improving methods of Al/SiC interfaces. The work of adhesion and contact angle of this system was calculated theoretically from the physicochemical model. The effects of alloy elements such as Mg and the processing temperature on wettability were also investigated theoretically. Based on the theoretical calculation results, some effective methods to improve the wettability were presented.
Authors: Cun Zhu Nie, Jia Jun Gu, Jun Liang Liu, Di Zhang
Abstract: The elevated temperature deformation and fracture behavior of an 10vol%B4CP/7039 aluminum matrix composite plate was investigated by uniaxial tensile tests at temperatures ranging from573 to 773 K and at initial strain rates from 1x10-1 to 1x10-4s-1.The strain rate sensitivity exponent was found to be approximately 0.1-0.15 which was below that of a superplastic material. A maximum elongation of 116% was obtained at an initial strain rate of 10-1 s-1 and at a temperature of 773 K.
Authors: Pai Chia Kuo, San Yuan Chen, Jong Shing Bow
Abstract: After the wurtzite ZbS nanorods were synthesized by hydrothermal treatment in the presence of ethylenediamine (en) aqueous solutions at 200oC, ZnS-ZnO core-shell nanorods were readily obtained by annealing ZnS nanorods under oxygen at 650oC for 3-5 min. A strong broad peak in the 450–550 nm visible range was clearly detected and its peak intensity could be greatly enhanced after the ZnO shell was developed on hydrothermal ZnS nanorods. On the other hand, using AAO as a template, ZnS-ZnO core-shell nanotubes could be synthesized using atomic layer deposition process along with the sulfuration conversion of the ZnO nanotube array. This ZnO-ZnS core-shell nanotube structure could be confirmed by x-ray photoelectron spectroscopy (XPS) analysis. In addition, an enhanced UV emission along with the reduced visible emission was also detected for the ZnO/ZnS core-shell nanotubes..
Authors: Rong Chen, Hong Hua Wang, Di Zhang, Guo Ding Zhang
Abstract: Fretting friction and wear of aluminum alloy, 5 and 10 vol.% SiCp/Al and Ni3Alp/Al composites under 5×10-4 Pa and atmosphere was investigated. Wear mechanism in vacuum was compared to that in atmosphere at different applied loads. The coefficient of friction (COF) of the SiCp/Al composites was larger than aluminum and Ni3Alp/Al composites, however, incorporation of SiC particles into Al alloy increased the fretting wear resistance of Al alloys, especially in vacuum. It should be notices that the maximum wear depth was larger in vacuum under fretting wear, and the Ni3Alp/Al composites show low fretting wear resistance.
Authors: Fu Su Yen, Pei Ling Chang, Pei Ching Yu, Rong Jeh Yang
Abstract: The traditional differential thermal analysis (DTA) techniques are employed to evaluate the kinetic behavior induced by the inter-particle relationships in a nano-particle θ-Al2O3 powder system during θ- to α- phase transformation. Discrepancies in homogeneity and inter-particle distance of the powder system may result in the diagnostic DTA profiles which can be use to evaluate the characteristics of the powder system as well as the formed α-Al2O3 particles. Based on the acknowledgement, a quasi-homogeneous transformation shows that a duration of 90 seconds is needed for one θ-crystallite to transform into one α-nucleus with a heating rate of 10 oC min-1 and fabrication of the high phase-pure and mono-sized α-Al2O3 powders is obtained.
Authors: Guo Qiang Luo, J. Li, Dong Ming Zhang, Qiang Shen, Lian Meng Zhang
Abstract: Dense SnO2 based ceramics are widely used. In this paper, 95SnO2-5MnO2 ceramics were prepared by pressureless sintering in air at different temperatures. Phase compositions and microstructures are examined by XRD, SEM and EDX, respectively. The SEM results show that different morphologies exist at the SnO2 grain boundary of ceramic, which compose of manganese oxidation, testified by EDX. The different manganese oxides phases, found by XRD, are the source of oxygen concentration at the grain boundary during heating and oxygen dissipation when cooling. However, solid solutions of Mn, Sn and O are not observed. The density of 95SnO2-5MnO2 ceramics decreases with increasing the sintering temperature, due to the evaporation of SnO and decreasing concentration of oxygen at grain boundary in the cooling process. Densification of the ceramic is promoted with inhibiting the decomposition of SnO2 by increasing oxygen concentration in the heating process, but it is limited by the dissipation of oxygen at the grain boundary in the cooling process.
Authors: Hao Tung Lin, Jow Lay Huang, Sheng Chang Wang
Abstract: Nanoscaled Cr2O3 powders coated on alumina particles have been produced by means of metal organic chemical vapor deposition (MOCVD) in a fluidized bed, using the pyrolysis of Cr(CO)6 precursor. In order to prepare the nanoscaled Cr3C2 powder from the Cr2O3, carbonizing behavior of the Cr2O3 particles was investigated. The carbon is from the decomposition of Cr(CO)6. It was found that Cr2O3 transformed into Cr3C2 at 1150 oC in graphite furnace in a vacuum level of 10-4 torr, while it could not carbonize at 1150oC in a vacuum level of 100 torr. In the present study, two reactions for Cr2O3 are carried out. One is that Cr2O3 reacts with Al2O3 to form a solid solution; the other is that Cr2O3 reacts with carbon to transform into chromium carbide. Consequently, a nanocomposite comprising the matrix of solid solution of Al2O3 - Cr2O3 and second phase Cr3C2 was prepared after hot-pressed.
Authors: Gang Qin Shao, Z. Xiong, T.G. Wang, Xiao Liang Shi, Xing Long Duan
Abstract: Tungsten carbide (WC) targets with low cobalt (Co) content (0.1 - 0.2 wt.%) were prepared by hot-press sintering at 1700°C for 60 minutes in argon, from element starting powders of tungsten, cobalt and carbon. Results show that the as-fabricated targets yield relatively high relative density above 99% and high HRA above 92. WC with low Co content is formed easily than pure WC. The hot-press sintering process, while element starting powders are used, is an in-situ reaction technique for accelerating the WC’s diffusion rate to obtain a dense sintered body.

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