In the present paper, the two routes of preparation of seven weight% yttria stabilised zirconia (7YSZ) composite sols are proposed under optimised conditions. Sol of route-I was made from zirconium (IV) propoxide, yttrium nitrate hexahydrate-acetylaceone-water-1-propanol solvent, and sol of route-II was made from zirconium (IV) propoxide, yttrium nitrate hexahydrate-acetylacetone-sulphuric-acid-water-1-propanol solvent-2weight% polyvinyl alcohol (2PVA). After preparation of both sol, thermal behaviour was characterised using thermogravimetric analysis (TGA), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) for checking the weight loss with respect to high temperature. Route-II YSZ sol-gel survived with practically no mass loss, while route-I had extensive degradation as well as considerable mass loss. In the second stages, both the sols were deposited onto as-air plasma sprayed CoNiCrAlY bond-coated substrates, i.e. superalloys IN800 and aluminium alloys AA2024-T351. The microstructure of route-I and route-II YSZ sol coating was characterised using scanning electron microscopy. Route-II deposited sol was found to be more porous, homogenised and thick thermal barrier coatings as compared to route-I sol. The presence of sulphuric acid enhanced the better processing control of sol-gel coatings with uniform surface, as confirmed by atomic force microscopy (AFM).
