Stress evolution on gel-to-ceramic thin film conversion

In situ cracking observation, uncracking critical thickness evaluation and in situ stress measurement were conducted during heating for alkoxide-derived gel coating films. Higher water-to-alkoxide ratios and lower heating rates were shown to cause cracking at lower temperatures. The in situ stress measurement suggested that higher water-to-alkoxide ratios in solutions and lower heating rates result in larger in-plane tensile stress to be generated in the heating-up stage, which was thought to cause the cracking at lower temperatures. Methyltriethoxysilane, chelating agents and polyvinylpyrrolidone were shown to be effective in increasing uncracking critical thickness and/or thick film formation. The in situ stress measurement suggested that these additives or components are effective in suppressing the stress evolution during heating.