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2013
Journal Article
Titel
High-strength glass-ceramics in the system MgO/Al2O3/SiO2/ZrO2/Y2O3 - microstructure and properties
Abstract
Glasses with the composition 51.9SiO2·21.2MgO·21.2Al2O3·5.7ZrO2 (in mol%) were crystallized in different annealing steps at 950 °C and 1060 °C. Using X-ray diffractometry and high resolution (scanning) transmission electron microscopy with energy-dispersive X-ray spectroscopy, it is found that the annealing-induced devitrification results in glass-ceramics with a-quartz solid solution as the main crystal phase, with a few additional ZrO2 and MgAl2O4 crystals as secondary crystal phases. If 2.5 mol% Y2O3 are added to the base glass, however, an identical heat treatment leads to glass-ceramics with dendritic ZrO2 crystals as the main crystal phase, and subsequently grown MgAl2O4 as the secondary crystal phase. The quartz solid solution was found to be absent in those Y2O3-bearing samples, as Y2O3 is incorporated in the residual glass matrix, thus stabilizing it. It was observed that the bending strength was comparable for both sample sets, thus indicating that the existence of a-quartz is not necessarily an important prerequisite for excellent mechanical properties of glass-ceramic materials based on the MgO/Al2O3/SiO2 system. Strengthening mechanisms for both Y2O3-bearing and Y2O3-free glass-ceramics are discussed.