Impurity phases of silicon dioxide in commercial SiC whiskers produced by VLS method

摘要

Silicon dioxide forms two impurity phases in SiC whiskers, namely α-cristobalite and X-ray-amorphous SiO_2. The particles of a-cristobalite form as a result of hydrolysis of silicon compounds with chlorine by water vapor, and these are not bound with SiC surface. During synthesis of SiC whiskers, the layer of X-ray-amorphous silicon dioxide of up to 2.5 nm thickness forms on the surface of whiskers through oxidation of crystal surface by water vapor. Upon drying SiC whiskers at temperature above 120 ℃ and also long-time storing of crystals in contact with air, the surface of whiskers oxidizes and SiO_2 film forms of up to 3 nm thickness. The mechanism is proposed for low-temperature oxidation of SiC whiskers in the presence of water vapor. It is shown that aggregately stable suspensions of whiskers form in alkaline medium in the presence of SiO_2 film on the surface of crystals.