Zhuang Hanrui

Morphologies and growth mechanisms of aluminum nitride whiskers by SHS method—Part 2

The high resolution electron microscopy was used to investigate the microstructure of AlN whiskers. The growth mechanisms of AlN whiskers were VLS and VS mechanism. The phenomenon of stacking fault was analyzed. Moreover, the growth mechanism of dendritic crystal was proposed.

Synthesis of pure molybdenum disilicide by the chemical oven self-propagating combustion method

Abstract A high pure molybdenum disilicide was prepared by using the “chemical oven” enhanced self-propagating combustion method. The mixtures of Si and Ti were ignited as chemical oven. Ammonium chloride was added to the mixed powders to control the propagation rate of combustion. The compostion of product was detected by X-ray diffraction (XRD) and X-fluorescence analysis. Results show the molybdenum disilicide product is single phase with trace impurities. Scanning electron microscopy (SEM) photos show the product by chemical oven self-propating high temperature synthesis (SHS) method is more homogeneous than the product by normal SHS method.

The effect of gravity on the microstructure of TiC material

By using chemical ovens, a series of porous TiC materials have been synthesized on parabolic flight plane. The morphology of combustion product obtained in the present microgravity is quite different from that under gravity condition. TiC materials combustion synthesized in microgravity are more uniform distribution and finer porosity.

Microstructural observation of β′-sialon-12H multiphase ceramics by HREM

Abstract The microstructure of a β′-sialon-12H multiphase material was studied by HREM. The ceramic was composed of equiaxed or elongated β′-sialon and fibre-like 12H AlN polytypoid grains. A mosaic structure of β′ grains in 12H grains was observed. Two kinds of grain boundaries were also observed: one was a coherent grain boundary between β′ and 12H, which could present glassy phase penetration, while the other was a boundary between β′ grains with different crystalline orientation, which was wetted with liquid phase. The U-phase could be partially devitrified out from the Sm-containing liquid phase.

Sintering Behavior of Hot-Pressed Ca–αSialon Ceramics

On the basis of phase relationships in the Ca–Si–Al–O–N system, a Ca–α–sialon ceramic was synthesized using the hot-pressing technique. The reaction sequences and densifications of the Ca–α–sialon vs. firing temperatures have been characterized in detail. The present experiments reveal a reaction sequence as follows: at 1250°C the reactant mixture started to soften, at 1300°C a gehlenite phase was produced, at 1500°C the gehlenite phase was resolved into a liquid phase and a Ca–α–sialon started to form, and at 1600°C the formation of Ca–α–sialon was complete. The product was stable and almost entirely single phase Ca–α–sialon. Accompanying to the above sequences, densification also proceeded via a liquid-phase sintering, particle rearrangement, solution–reprecipitation, and grain growth process. In the final microstructure elongated grains of Ca–α–sialon were obtained, improving the fracture toughness of this Ca–α–sialon ceramic.