Sol–gel fabrication of compact, crack-free alumina film

Compact, crack-free alumina film was fabricated using an alumina sol with a high Al2O3 content. With the addition of ethylacetoacetate (CH3COCH2COOC2H5, EAcAc), the stable sol could be prepared with a molar ratio of aluminum sec-butoxide (Al(O-sec-Bu)3, ASB) to water up to 1:25. It was found that EAcAc could notably decrease the surface tension of the liquid in the gel pores. The EAcAc modification layer on the colloidal particle retarded greatly the densification of the Al2O3 gel film and provided a long-lasting structural relaxation during heating. Therefore, the formation of cracks was effectively prevented in this alumina material. The alumina gel film contained a high Al2O3 content and there was a rather small mass loss during sintering. The critical thickness of Al2O3 sol–gel film was eight times higher than that could be achieved via the general sol–gel route and a film thicker than 0.8 μm was prepared by a single-step dipping operation.