Preparation of SiC hollow particles by gas-phase reaction and thermoelectric properties of sintered bodies

Abstract

The formation of SiC hollow particles by gas-phase reaction in the silane-methane-hydrogen system and thermoelectric properties of the sintered bodies were studied. Synthesized powders were analyzed by means of TG, XRD, TEM, IR, etc. The powders synthesized at 1200–1300°C consisted of β-SiC and Si phases, but they became almost hollow β-SiC particles at 1400°C. The composition, particle size, and shell thickness of the synthesized particles were dependent on the reaction conditions. From lattice parameter measurements, a certain amount of excess silicon was verified to be incorporated into β-SiC lattice. On the other hand, excess carbon existed, for the most part, as an amorphous phase not forming solid solutions with β-SiC. TEM observations and IR absorption measurements have shown that excess carbon is contained within shells of hollow particles, while unreacted excess silicon exists as a crystalline phase mostly in the cores of the particles. Synthesized powders were sintered at 1850–2100°C for 3 h in nitrogen atmosphere. The electrical conductivity and thermoelectromotive force were measured at 400–1500°C in argon atmosphere. The density, average grain size and sintering additives had significant effects on the thermoelectric properties of SiC.