Effect of Metal Fluoride on the Formation of alpha-Alumina Particles

alpha-Alumna particles were prepared by a precipitation method with metal fluoride additive. Aluminum nitrate and ammonia solution were used as starting materials. AlF3, CaF2, and MnF2 were utilized as additives. The effects of precipitation solvent and metal fluoride on the phase transformation temperature, size and morphology of alpha-alumna particles were investigated. The solvent for precipitation did not affect the phase transformation temperature, while it influenced the size of alpha-alumna particles. The phase transformation temperature to alpha-alumna was reduced by addition of metal fluoride and was different with metal cation in metal fluoride (AlF3 (800 degrees C) < MnF2 (900 degrees C) < CaF2 (950 degrees C)). The addition of each of three metal fluorides led to the formation of platelike particles and, among the three additives, MnF2 additive resulted in the formation of relatively small particle.