Zirconia-doped Mg-Ca-Al-Si-O-N glasses: crystallization

Crystallization of Me-Ca-Si-Al-O-N glasses containing up to 8 wt% ZrO2 has been studied. Crystallization takes place at temperatures above 900-1000 degrees C. The main oxide phases are anorthite and spinel. Further phases formed are diopside, gehlenite, ZrO2 and ZrN, depending on the zirconia and nitrogen content as well as on the crystallization temperature. The only oxynitride phase observed is Mg-petalite. Nitrogen seems to stabilize the tetragonal modification of ZrO2. The microstructure obtained is extremely fine-grained. This is caused by the phase separation of the oxynitride glasses used. Mechanical properties such as hardness and fracture toughness increase with increasing nitrogen content, simultaneously they are influenced by the microstructure of the glass ceramics and, therefore, by the ZrO2 content. (C) 1998 Elsevier Science B.V.