Systematic microstructural investigation of alumina deposited by liquid fuel combustion chemical vapor deposition

An alumina organic-sol miscible to both organic and aqueous solutions was synthesized and used as a liquid feedstock in a combustion chemical vapor deposition process. An air-assisted atomizer allows the attainment of fine droplets with relatively low velocity toward the substrate. The ignited spray heats the substrate above 1000 °C when placed at a distance of 12.5 cm from the atomizer. The microstructure of the films was noted to be strongly sensitive to the combustion stage of the droplets when they hit the substrates. The combustion stage was adjusted by a certain number of parameters, including the distance substrate-atomizer and the flammability of the liquid feedstock. When advanced stage of combustion is allowed, the deposited films were composed of fine particles with an average diameter between 200 and 400 nm. The non-completely burned droplets lead to the deposition of films with high porosity. In contrast, films formed with droplets in the liquid form exhibited dense structure. Finally, it was demonstrated that the improvement of the homogeneity of the films could be attained by using a minimal flow rate of the feedstock with low aluminum concentration.