Key Engineering Materials Vols. 280-283

Abstract: The synthesis and characterization of mullite composite nanocrystaline from high-silica kaolin sampled from Tianyang County of Guangxi Zhuang Autonomous Region is presented in this paper. Rough kaolin is firstly grounded and processed to remove impurities, iron and carbon before burned to produce composite oxides with mullite as major components. The composite oxides are further synthesized into composite mullite nanocrystaline by using hydrothermal crystallization process under low temperature and normal pressure. Tests on the composite nanocrystalline by TEM, TG-TDA, and X-ray diffraction methods show that the nanocrystalline range in size from 40 to 100 nm and are well textured. They also show significantly enhanced thermal stability at temperature as high as 1000oC.

Abstract: Polycrystalline silicon layers were grown on AlN ceramic substrates in a rapid thermal chemical vapor deposition system at high temperature (~1150°C). Larger columnar grains, > 5µm in size, were obtained by the zone melting recrystallization (ZMR) technique. The p-n junction is formed by a phosphorous diffusion process to make a solar cell. Solar cell devices based on this Si layer result possess an open-circuit voltage of about 0.17V and a short-circuit current of about 6.6mA/cm2.

Abstract: Colloidal injection moulding of ceramics (CIMC), an innovative technique combining the advantages of conventional injection moulding and colloidal forming process, is applied to prepare thin-wall rutile tube for high capacity ozone generator. The forming process is studied detailed and the processing parameter of forming, drying and sintering schedule is determined in this research. The wall thickness of the sintered tube is 1.5~2mm and its inner diameter is about 26 mm, length is about 300 mm. The electric properties of the tube are also measured under different conditions. The above-mentioned tube is applied in ozone generator and the yield of ozone is about 55mg·L-1.

Abstract: MgO nanowires combined with C nanotubes have been prepared through method of high-temperature catalytic reaction. The nanostructures consist of nanowires that have right-angled zigzag manner to elongate in three dimensions. Structural characterization and elemental composition analysis identified that the nanowires were made of MgO nanowires combined with C nanotubes. A growth mechanism based on the vapor-liquid-solid (VLS) process is proposed for the formation of the combined nanostructures. With the aid of XRD, SEM, HRTEM and EDS, the morphology, structure and growth mechanism were investigated.

Abstract: Ultrasonic spray pyrolysis has been applied to deposit MgO thin films on Si(100) and quartz glass substrate. The microstructures and properties of the as-grown MgO thin films were examined by X-ray diffraction, scanning electron microscopy, spectrophotometer and semiconductor resistivity meter. The results indicates that the MgO thin films deposited under optimal conditions shows smooth and dense surface without visible pores or defects over the substrate, and as well as good thickness uniformity. Almost completely (100)-oriented MgO films with the transmission higher than 90% in UV/VIS region and the resistivity at least in the order of 107Ω-cm were obtained. MgO thin film with such a crystal quality seems to be very suitable for acting as a buffer layer for the subsequent epitaxial growth of films.

Abstract: A new method for predicting the thermal conductivity of functional carbide crystals and ceramics materials is proposed. The effect of average relative atomic mass and density on thermal conductivities of carbide function crystals and ceramics is considered in the method. Correlations are developed for thermal conductivity with average relative atomic mass and density according to the microscope theories of heat conduction. The thermal conductivities calculated from the prediction equation for many functional carbide crystals and ceramics were compared with the measured dada and found to be agreement. It is show that, for the most of functional carbide crystals and ceramics materials, the relative error between the predicting values and the measuring data is ± 20%. It is discovered in further analysis that the larger the average relative atomic mass and density are, the more accurately the thermal conductivities predict.

Abstract: High temperature structural ceramics based on Al2TiO5-ZrTiO4 (ZAT) having excellent thermal-shock-resistance were synthesized by a reaction sintering. The ZAT ceramics sintered at 1600oC had a negative thermal expansions up to 1000oC and a much lower thermal expansion coefficient (0.3 ~ 1.3 x 10-6 /K) than that of polycrystalline Al2TiO5 (1.5 x 10-6 /K). These low thermal expansion are apparently due to a combination of microcracking caused by the large thermal expansion anisotropy of the crystal axes of the Al2TiO5 phase. The microstructural degradation of the composites after various thermal treatment for high temperature applications were analyzed by scanning electron microscopy, X-ray diffraction, ultrasonic and dilatometer.

Abstract: Aluminium titanate (Al2TiO5) is an excellent oxide ceramic material with a very low thermal expand coefficient. Aiming at improving the bending strength Al2TiO5, spodumene was used as additives for preparing Al2TiO5 and the effect of adding spodumene on the mechanical properties of Al2TiO5 was investigated in this paper. It was found that adding spodumene, instead of simple oxides, may significantly enhance the bending strength of Al2TiO5.

Abstract: In the present paper, magnesium dititanate (MgTi2O5, M2T) was introduced into aluminum titanate (Al2TiO5, AT) to form AT-M2T solid solution so that the thermal shock resistance of Al2TiO5 could be kept still good while without any decomposition. The effect of MgTi2O5 addition on thermal shock resistance of Al2TiO5 was investigated. The experimental results showed that the thermal shock resistance of Al2TiO5 began to decrease when a little amount of MgTi2O5 was added and then rose with the continuous addition of MgTi2O5, even overrunning that of pure Al2TiO5 when 30mol% MgTi2O5 was contained. It was found that fine solid solution was formed between Al2TiO5 and MgTi2O5, which enhanced the thermal shock resistance of Al2TiO5.

Abstract: Since 1990, Ge and his earlier and present groups in LSCPM have made great efforts to investigate the Self-propagating High-temperature Synthesis (SHS) of Si-N2 gas-solid system including the SHS process control and its thermodynamics, structural macrokinetics and formation mechanism of SHS-Si3N4. In this presentation, some results that were firstly reported in the world are reviewed and new progress in recent years is reported.