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.

Influence of the Fuel/Oxidant Ratio on the Elaboration of Binary Oxide Catalyst by a Microwave-Assisted Solution Combustion Method

“…SC-reaction initiation is achieved through external heating of the reaction mixture up to its ignition temperature. Different electrical heating devices, such as muffle oven, hot plate, aluminum open cylindrical reactor, and pressure reactor [31][32][33][34][35][36] have been used for supplying the required energy for heating the solution mixture. However, most of these traditional heating processes lead to a thermal gradient between the interior and exterior of the heated solution, resulting in a local inhomogeneity of the prepared material.…”

Binary Oxides Prepared by Microwave-Assisted Solution Combustion: Synthesis, Characterization and Catalytic Activity

“…The reaction is initiated by the fast heating of the aqueous solution up to the ignition temperature, followed by the spontaneous combustion of the mixed solution. The heat required for initiating the combustion is often supplied by means of an electrical heating such as muffle ovens [9,10], hot plate [11,12] and heating mantle [13]. These traditional heating processes lead to a temperature gradient between the interior and exterior of the solution, resulting in a regional inhomogeneity of the prepared material.…”

Low temperature preparation of belitic cement clinker

“…6,7 Indeed, the amount of fuel to react completely with the oxidizer depends on the final oxidation state of nitrogen, carbon, and hydrogen. Nitrogen can have a valence of +2 (as NO), +2x (as NO x ), or +4 (as NO 2 ) after the combustion reaction.…”

“…6 Chong Chen et al have studied the low temperature combustion synthesis of alumina. 7 However, it is not always easy to obtain the corresponding metal nitrates. Furthermore, the reaction is complex as the role of atmospheric oxygen cannot be neglected.…”

“…Furthermore, the reaction is complex as the role of atmospheric oxygen cannot be neglected. [6][7][8] If no nitrates are available, as when silicon oxidizer nitrate is needed, oxygen from air can be considered as an external oxidant agent. 9 Thus, the very exothermic combustion of the fuel with air can be used to raise temperature and synthesize ceramics even from other compounds than nitrates.…”