Characterization of plasma-synthesized alumina

Ultrafine aluminium oxide powder has been synthesized in a thermal plasma reactor by oxidation of aluminium metal powder. The reactor consists of a d.c. plasma torch mounted on to a reaction chamber made of stainless steel with provision for injecting any reactive gas into the plasma jet. A mixture of argon and nitrogen is used as the plasma gas and aluminium metal powder is fed into the plasma using argon as the carrier gas. The metal particles are vaporized in the plasma stream and the vapours of aluminium metal are oxidized to aluminium oxide by compressed air injected downstream in the reactor. The synthesized powder has been characterized by X-ray diffraction, which showed that it consisted of gamma-alumina. Scanning electron microscopy of the synthesized particles showed agglomerates of fine particles. The individual particles, ranging from a few nanometres in size to a few tens of nanometres could be resolved using transmission electron microscopy.