The microstructure of alumina coatings prepared by aerosol assisted spray deposition

This paper presents the deposition of alumina coatings using a low cost aerosol assisted spray deposition (AASD) in an open atmosphere at low temperature. AASD is a variant of CVD, which involves spraying atomized precursor droplets into a heated environment where the droplets undergo decomposition and chemical reaction near the heated substrate and produce solid stable coatings. Using the same deposition method but different starting precursor (e.g. solution or suspension), dense or porous deposits could be produced using the AASD method. Dense and thin alumina coatings were deposited using a precursor solution containing aluminium alkoxide. Whereas thick porous alumina deposits were prepared using a suspension of alumina powder in alcohol solution. Such porous alumina deposits could be densified to form thick alumina coatings. Continuous CO2 laser was used to densify the alumina deposits. The microstructure of the coatings and deposits was characterized using a combination of X-ray diffraction and scanning electron microscope methods. The dense and porous alumina coatings could be deposited by varying the processing conditions. The relationships between the growth behavior and microstructure of the coatings were also discussed.