MECHANICAL STABILITY OF SOL-GEL FILMS

The relationship between film cracking and film thickness has been studied experiemntally for films of ceria gel deposited by spinning on to stainless steel substrates from an aqueous ceria sol. A critical film thickness below which films were crack-free was observed at about 0.6-mu-m. For films thicker than the critical thickness the crack spacing was approximately ten times the film thickness. Existing models for the mechanical stability of the films were examined to explain the observations, encompassing different forms of relaxation of the stress in the vicinity of a crack through the film. The model in best accord with the experimental observations is one in which stable delamination cracks are formed at the film-substrate interface on both sides of a crack through the film. However, for the model to be applicable some rather restrictive conditions must be assumed to be satisfied.