Effect of the Amount of Water for Hydrolysis on Cracking and Stress Evolution in Alkoxide-Derived Sol-Gel Silica Coating Films
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Silica gel films were deposited on single-crystal Si substrates using starting solutions of mole ratios, Si(OC2H5)4 : H2O : HNO3 C2H5OH=1 : x : 0.01 : 4, where x=2, 4 and 10. Cracking of the gel films was observed in situ on heating using a near infrared image furnace equipped with an optical microscope. The gel films were found to be cracked at lower temperatures when the H2O/TEOS ratios in solutions were larger. In-plane stress in gel films was also measured in situ on heating with a thin film stress measurement apparatus equipped with an electric furnace. Tensile stress generated on heating, and higher stress evolved at larger H2O/TEOS ratios, which was thought to allow cracking at larger H2O/TEOS ratios. However, higher rates of increase in stress at larger H2O/TEOS ratios were seen only up to 100°C, while the slope of the stress-temperature relation was similar over that temperature irrespective of the H2O/TEOS ratios. It was thought to be the higher capillary pressure due to the high surface tension of H2O that gave rise to the higher rates of increase in stress at larger H2O/TEOS ratios observed below 100°C. In other words, higher surface tension of H2O is the most possible cause of the lower cracking temperatures at larger H2O/TEOS ratios. The shape of the cracks tended to shift from scale-like to worm-like, and then to linear shape as the cracking onset temperature increases. In other words, the cracks propagate curled at lower temperature and straight at higher temperatures.
- 公益社団法人 日本セラミックス協会の論文
公益社団法人 日本セラミックス協会 | 論文
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