Effects of metal doping and seed introduction on phase transformation of alumina prepared by precipitation method

Abstract

Nanocrystalline alumina is synthesized by precipitation method. The effects of metal doping and sol-seeding on the phase transformation, crystal structure, density, color, size and size distribution of powder are investigated. The secondary metal doping is done by incorporating the nitrate salt of iron, chromium, yttrium or magnesium into the solution with various metal concentrations, in the range of 0.1-10 wt% of the metal precursor. The precipitate transforms to alpha-alumina upon the calcination at high temperature via the formation of metastable gamma-alumina. It is found that small amount of the secondary metal doping is sufficient to increase the phase transformation temperature from gamma- to alpha-alumina up to 1000 ํC. Fabrication of undoped alumina, sol-seeded alumina and metal-doped alumina are also investigated. The compacted bodies were sintered at 1550 ํC for 2 h in air. The relative density of sintered specimens prepared from varioussamples is in the range of 90-96% of theoretical density and grain size is in the range of 1-1.5 micrometre.