Formation of mullite thin film via a sol-gel process with polyvinylpyrrolidone additive

Several tasks were tried to prepare crack-free mullite films on silica substrates. Basically, a sol containing TEOS (Tetraethylorthosilicate) and boehmite colloid was used for spin coating on silica substrate. The formulation of the sols was kept in stoichiometric composition 3Al2O3·2SiO2, or contained a crack-limiting agent, Polyvinylpyrrolidone (PVP). These films were then treated up to 1300°C. The properties of the sols and the dried films were characterized by rheometer, various thermal analysis techniques (DTA, TGA and TMA), also by XRD, SEM and TEM. The mullite film shows randomly oriented grains in sizes from 0.1 μm to a few micrometers. The films still contain fine θ- and δ-Al2O3 particles after being treated at 1280°C for 1 h.