Evolution of Stress in Alkoxide-Derived Titania Gel Films under Heat-Treatment: Effects of Polyvinylpyrrolidone and Acetic Acid in Coating Solutions
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Titania gel films were deposited on single-crystal Si wafers using Ti(OC3H7 i)4-HNO3-H2O-C2H5OH solutions with or without PVP and CH3COOH. The gel films were heated up to 500°C, and the stress in films were measured in situ in the heating-up and cooling-down stages. The film prepared without PVP or CH3COOH showed about 50% reduction in thickness and an increase in stress up to 230 MPa at 200°C. The film prepared with CH3-COOH exhibited about 55% decrease in thickness when heated up to 250°C, accompanied by an increase in stress up to ca. 200 MPa. The rate of the increase in stress and of the decrease in thickness was smaller than that observed in the film prepared without PVP or CH3COOH, suggesting that CH3COOH is effective in suppressing the volume shrinkage and stress evolution in the heating-up stage at this temperature range. The film prepared with PVP, on the other hand, showed an increase in stress only up to ca. 70 MPa when heated up to 300°C in spite of the reduction in thickness by about 40%. This suggests that PVP is effective in suppressing the stress evolution via plastic flow as well as via suppressed hydrolysis and condensation reaction. Smaller elastic constant of the film in the presence of the organic polymer might have also contributed to the smaller stress. The decomposition and/or oxidation of PVP occurred at 300-380°C, leading to a further decrease in thickness and an increase in stress up to about 180 MPa. All the films were crystallized between 400 and 500°C, where significant reduction in stress was observed. In the cooling-down stage, the film prepared with PVP showed almost constant stress whereas the other two films exhibited evolution of thermal stress.
- 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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