Formation of nano-crystalline quartz crystals from ZnO/MgO/Al2O3/TiO2/ZrO2/SiO2 glasses

Glasses with the compositions 50.9 SiO2 center dot 20.8 Al2O3 center dot (20.8 - x) MgO center dot x ZnO center dot 3.7 TiO2 center dot 3.7 ZrO2 with x = 0, 2.3, 4.6 and 9.3 were annealed at temperatures in the range from 850 to 1100 degrees C. Depending on temperature, high- or low-quartz solid solutions, magnesium aluminosilicate, mullit and spinel precipitated. These glass-ceramics exhibit excellent mechanical properties and are potential candidates for applications in micromechanics or as hard disc substrate. The larger the ZnO concentration, the lower is the glass transition temperature. Also microhardnesses and Young's moduli increased with increasing ZnO concentration. The nucleation temperature was of minor importance. To achieve good mechanical properties, the initially formed high-quartz phase must transform to the corresponding low-quartz phase. This occurs if the quartz phase contains only minor MgO or ZnO concentrations, which can be achieved by increasing the annealing times or temperature. Then MgO, ZnO and Al2O3 occur as separate spinel or gahnite phase. (C) 2010 Elsevier Masson SAS. All rights reserved.