Parametric effects of low-temperature combustion synthesis of alumina

Abstract

The influences of parameters on the low-temperature combustion synthesis of alumina particles from reactant mixture of aluminum nitrate and combustion fuel were studied using the particle size of as-synthesized alumina particles as a performance index. First, when urea was used as combustion fuel, it produced a higher combustion temperature and a larger particle size than the case when carbohydrazide was the fuel. Next, the combustion in air yielded a flame propagating through the reactant mixture, in contrast to a flame simultaneously ruptured from the entire reactant when the combustion was conducted in nitrogen. The particle size of the product obtained in nitrogen was 40% smaller than that obtained in air. Increasing the heating temperature could increase the alumina particle size due to the sintering effect, while combustion failed if the heating temperature was too small. The addition of diluent, excess fuel, and gas-releasing agents reduced the particle size. The increase of stirring speed also reduced the particle size. Next, if the reactant density (the amount of reactant mixture in the reacting container) was below a certain threshold value, the combustion failed to ignite. Increasing the reactant density was found to reduce the particle size due to the simultaneous reduction of combustion time and temperature. Finally, a liquid–gas reaction model was proposed and solved to study the threshold of combustion parameters.