Characterization of spherical alumina particles obtained by melting in a hydrogen-oxygen flame

Spherical oxide particles can be used as mineral fillers, paint pigments, polishing materials and catalysts. They can be prepared using various techniques involving precipitation and spray drying. Melting of particles in a high-temperature flame is a simple technique which produces particles with a high degree of sphericity and high smoothness from non-spherical feed material. In current research the preparation of alumina particles by melting the feed material in a hydrogen-oxygen flame is described. The spherical particles obtained were characterized using scanning electron microscopy, atomic force microscopy, energy dispersive spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and electrokinetic measurements. The particles prepared exhibit a high degree of sphericity and a low level of roughness. The chemical composition of the material after preparation is unchanged, however the crystallographic structure is different. It is suggested that alumina changes from pure a-alumina to a mixture of different transitional forms. Changes in the electrokinetic behavior were also observed for alumina which can be attributed to the strong dehydration of the oxide surface and/or change in the crystallographic structure. Also, the possible accommodation of trace amount of impurities in the surface zone during melting cannot be ignored.