| abstract |
(57) [Abstract] [Problem] To obtain inexpensively and efficiently by a simple and easy means, By using a transparent alumina film that is more controlled so that the unique voids and the shape thereof are aggregated, a film that exhibits more performance as an underlayer film or the like and is more practically usable is obtained. SOLUTION: A petal-like material having voids, which is formed by applying a coating solution containing at least an aluminum alkoxide and a stabilizer on a substrate to form an amorphous alumina film, and then subjecting it to hot water treatment, drying only or drying and firing. A petal-shaped transparent alumina film, which is a transparent alumina film that is randomly aggregated into. In particular, the average surface roughness Ra 'value of the surface layer is 17 nm or more, A petal-like transparent alumina film having a specific surface area S R of 1.5 or more. And its formation method. |