synthesis and characterization of nano alumina by gel combustion menthod

This paper reports the synthesis of nano sized alumina powders by the combustion
method using urea and citric acid as fuels. The effect of the three factors, which are type
of fuel- urea/citric acid, fuel to oxidizer ratio and PH of the starting solution, on the
thermal decomposition characteristics of alumina precursor and the properties of
nanocrystalline alumina synthesized using this gel combustion process. The technique
involves the combustion of a urea/citrate-nitrate gel occurring between Al(NO3)3 and
urea/citric acid to yield an ash powder that upon calcination at 1373 K produced nano
alumina. The ignition was restricted to a particular range of urea/citrate to nitrate ratio in
the gel. Once the powder is synthesized, the product was characterized by SEM. The
resulting powder exhibited fine crystallite size. It was established from various
characterization techniques that the alumina powder prepared with a stoichiometric urea
to oxidizer ratio and PH of 10 and citric acid to oxidizer ratio of 1.5 and pH of 10 has got
the optimum powder characteristics compared to the rest of the batches. This shows the
importance of maintaining a stoichiornetric or near stoichiometric urea to oxidizer ratio
and maintain above stoichiometric ratio of citric acid to oxidizer. Generally, the process
has a higher degree of reproducibility and a good potential for large-scale production of
alumina.