Auto ignition processing of nanocrystalline alpha-Al2O3

This paper reports the results of an investigation aiming at synthesizing nanocrystalline alpha-alumina using the ''Auto Ignition'' processing technique. The process utilizes in-situ exothermic reactions occurring between a suitable oxidizer (e.g., aluminum nitrate) and a fuel (urea). Due to generation of high temperatures for a short time, the resulting crystalline phase(s) is(are) able to nucleate but cannot grow. This work systematically examines and characterizes the resulting powders 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 in nanocrystalline size. it is expected that sinterability of such powders will be better because the question of gamma to alpha phase transformation does not arise.