Structure characterization of alumina–silica coatings prepared on polyimide substrate by sol–gel

Abstract

Alumina–silica coatings were prepared on polyimide substrate by sol–gel method using aluminium isopropoxide and tetraethyl orthosilicate as the precursors. The molar ratios of Si/Al were designed as 1∶3, 1∶1 and 3∶1. The surface morphology and structure of as-deposited coatings were investigated by various complementary analysis techniques. The results indicate that all silica–alumina coatings show a smooth and dense surface and have a thickness of ∼400 nm. After treatment at 230°C, the alumina–silica coatings are a diphase structure of AlOOH and amorphous silica, the same as the corresponding gel powders. Moreover, after calcination at 550°C, the alumina–silica gel powders still remain a diphase structure, but AlOOH transforms into γ-Al2O3. The Si content has no obvious effect on the phase structure. However, increasing the Si/Al ratio in the as deposited coatings causes the binding energies of Si 2p, Al 2p and O 1s peaks to shift to higher energy.