AUTO IGNITION PROCESSING OF NANOCRYSTALLINE ALPHA-AL2O3

This paper reports the results of an investigation aiming at synthesiz ing nanocrystalline alpha-alumina using the ''Auto Ignition'' processi ng technique. The process utilizes in-situ exothermic reactions occurr ing between a suitable oxidizer (e.g., aluminum nitrate) and a fuel (u rea). Due to generation of high temperatures for a short time, the res ulting crystalline phase(s) is(are) able to nucleate but cannot grow. This work systematically examines and characterizes the resulting powd ers obtained from various ratios of the oxidizer and fuel. Both X-ray diffraction and transmission electron microscopy results confirm that under certain conditions it is possible to obtain pure alpha-alumina i n nanocrystalline size. it is expected that sinterability of such powd ers will be better because the question of gamma to alpha phase transf ormation does not arise.