Development of a ZrO2-Coating Technique by a Sol–Gel Process Assisted with Pre-Silica-Coating

Abstract

The development of techniques for coating thermistors with materials possessing excellent chemical resistance and electrical insulation characteristics is necessary to ensure their protection. The present work proposes a coating technique using zirconia (ZrO2), which has excellent chemical resistance and electrical insulation properties, based on initiating a sol–gel reaction of zirconium alkoxide in the presence of a ceramic substrate consisting of the common components of thermistors. The ZrO2 films on substrates were not damaged, even after annealing at 600 °C in air. Several ZrO2 particles were also deposited on the substrate. Pre-silica (SiO2)-coating the substrate, which was performed through a tetraethoxysilane (TEOS) sol–gel reaction, decreased the amount of ZrO2 particles and promoted the formation of thick ZrO2 films, as the reaction between the Zr butoxide and the alkoxyl groups of incompletely hydrolyzed TEOS on the substrate increased the affinity between the ZrO2 layer and the substrate.