Directional diffusion-controlled development of spinel interlayer between zinc-orthosilicate glaze and alumina

Metal ion-doped zinc-orthosilicate crystalline glaze was overlain on α-Al2O3 polycrystals at 1270 °C followed by optional devitrification at 1080 °C for cross sectional electron microscopic characterization. An interlayer of gahnite spinel islands with varied Cr-dopant level, possibly in a formula of Zn(CrAl)2O4, was found to develop nonepitaxially at the glaze/substrate interface and follow parabolic growth kinetics due to outward diffusion of Al into the glaze. The spinel islands tended to coalesce with each other to form subgrain boundaries and were occasionally encompassed as nonepitaxial particles within the predominant willemite (α-Zn2SiO4) crystals in the glaze. A secondary Co- and Ti-containing gahnite spinel, possibly in a formula of (ZnCoAl)(TiCoAl)2O4, was found to nucleate epitaxially at the {1 1 1} junctions of the spinel islands when the glaze was further devitrified at 1080 °C. There is negligible glaze infiltration into the substrate or thermal-mismatch induced cracking across the interphase interface, implying potential thermal bonding/sealing applications of the present glaze for alumina-based ceramics.