Interfacial reactions between a SiO2Al2O3ZnOCaO based glass and alpha alumina

A SiO2Al2O3ZnOCaO based glass coating on alumina was prepared at 900–1100 °C, and a composite specimen was prepared using a powder mixture of the glass and alumina at 1000 °C. The interfacial reactions between the glass and alumina were investigated using X-ray diffraction, scanning electron microscopy, electron probe microanalysis, and transmission electron microscopy. The glass matrix attacked the alumina inclusions in the glass–alumina composite at first, which led to the formation of a great number of nano-sized gahnite crystallites dispersed in the glass. A discontinuous gahnite interlayer in the coated alumina formed firstly, and then became continuous. In addition, some isolated gahnite crystallites formed in the glass adjacent to the interlayer, and then merged into the interlayer. Finally, the interlayer exhibited a special morphology: the interface between the gahnite interlayer and the glass coating was dentritic, while one between the interlayer and the alumina substrate was flattened.