Abstract:
[alpha]-alumina with nanocrystallite size can be successfully synthesized by precipitation, sol-gel and solvothermal method with crystallite size of 9.65, 9.52 and 9.74 nm, respectively. As-synthesized product from these methods can be completely transformed to [alpha]-phase by heat treatment at 1150 ํC for 3 h. The morphology of calcined product is found to be loosely agglomerated powder that can be broken off by milling. For precipitation method, many factors affect size and size distribution of powder, including the speed of mixing, the reaction temperature and pH of the reaction system. Furthermore, all synthesis techniques can be employed for the preparation of chromium-doped alumina in various chromium concentrations, in the range of 0.05-0.5 wt% of chromium precursor. Heat treatment of the obtained samples results in wide range of red-colored alumina, which suggests different amount of chromium ions residing in alumina matrix in Cr[superscript3+] form. Fabrication of undoped alumina and chromium-doped alumina are also investigated and compared with commercial alumina. The compacted bodies were sintered at 1550 ํC for 2 h in air. The relative density of sintered specimens prepared from various techniques were in the range of 93-98% of theoretical density.
