Preparation of Zr0₂ and Zr0₂-Si0₂ Coating Films by the Sol-Gel Method

Abstract

Zr02-Si02 coating films of high Zr0₂ contents (over 50 mol%), including pure Zr0₂ films have been prepared from zirconium n-butoxide and silicon ethoxide by the sol-gel method. These alkoxides were hydrolyzed by the moisture in air and the coating was carried out in a humidity-controlled glove box, because zirconium n-butoxide was highly hydrolyzable. It was found that the properties of the films obtained, such as optical transmission and surface roughness, were primarily governed by the relative hum idity in the coating process: The optical transmission decreased and the surface roughness increased as the humidity was increased. The decrease of transmission, as well as the increase in surface roughness, was due to the deposition of zirconium oxide or its hydrates in the films. The transparent films, however, were obtained below 20% of relative humidity. The refractive index of the Zr0₂-Si0₂ films decreased linearly with an increase in the SiO₂ content, going down to 1.48 at 100 mol% Si0₂, which coincides closely with th at of fused silica. This finding indicates that the films obtained are very homogeneous and there is little difference between the compositions of the films produced and the nominal compositions in the starting solutions. The films of high Zr0₂ contents were very durable to alkaline solutions, showing their potential possibility as alkaline-resistant coatings.