Effect of heat treating gel films on the formation of superhydrophobic boehmite flaky structures on austenitic stainless steel

The effect of heat treating gel films at different temperatures on the formation of the boehinite flaky structures on AISI 316 type austenitic stainless steel is investigated. After heating at different temperatures, the reactivity of the gel films with boiling water to form boehmite flakes was different, which resulted in different morphologies and different contact angle values after coating with hydrolyzed (heptadecafluoro- 1, 1,2,2-tetrahydrodecyl)triraethoxysilane (FAS). When the gel film was heat treated from 200 to 600 degrees C, the resulting contact angle was above 150 degrees, indicating superhydrophobic behavior. However, when the gel film was heat treated below 200 degrees C as well as at 700 and 800 degrees C, only some boehmite flakes were formed; when the gel film was heat treated at 900 degrees C, no boehmite flakes were observed. In these cases the surface roughness is insufficient for the superhydrophobicity. The formation condition of the boehmite flakes by reaction of the gel film with boiling water is also tentatively discussed. (C) 2008 Elsevier Ltd and Techna Group S.r.l. All rights reserved.