Preparation of fibre-like silicon nitride from amorphous silicon nitride powder

摘要

Silicon nitride is known to be a good ceramic material for high-temperature structural applications because it has a variety of properties such as high specific strength, high fracture toughness and high resistance to thermal shock and oxidation. This material in the form of fibre rather than whisker is expected to be a good ceramic filter, which can be used at high temperature, because its structure has high porosity. Carbothermal reduction of materials based on silica such as diatomaceous earth or rice husk has been used as a process for preparation of whisker or fibre-like silicon nitride [1-5]. Recently, preparation of silicon nitride fibres by heating amorphous silicon nitride powders in nitrogen has been reported. It has been suggested that the fibres were prepared via a vapour-liquid-solid (VLS) mechanism in the process [6,7], However, it is considered that the product prepared through the VLS mechanism is likely to be a small amount of whisker-like product and can be precipitated only in a narrow range. Preparation through a vapour-solid (VS) mechanism is needed in order to obtain large amounts of fibre-like silicon nitride.