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Crystallization of Ba1-xSrxZn2Si2O7 from the BaO/SrO/ZnO/SiO2 glass system: Effect of platinum and Sb2O3 on nucleation

: Vladislavova, L.; Thieme, C.; Zscheckel, T.; Höche, T.; Rüssel, C.


Journal of alloys and compounds 793 (2019), pp.705-714
ISSN: 0925-8388
Journal Article
Fraunhofer IMWS ()

Glasses with the chemical composition 8 BaO·8 SrO·34 ZnO·49.5 SiO2·0.5 Sb2O3 with 50 and 100 ppm platinum were crystallized in a two-step treatment. The first step was performed slightly above the glass-transition temperature at temperatures in the range from 680 to 700 °C and the second at a temperature of 780 °C. In the first step, an increasing number of nuclei were formed, while in the second step, the growth of Ba1-xSrxZn2Si2O7 was observed. The latter phase has negative thermal expansion in a wide temperature range and is a promising candidate for the preparation of zero thermal-expansion glass ceramics. Scanning electron micrographs showed that Ba1-xSrxZn2Si2O7 crystals grow around platinum particles. These crystals are oriented with their c-axes parallel to their longest dimension, i.e., the growth direction. Besides, dendrite-like crystals with unique orientations aligned with their c-axes perpendicular to their primary growth direction are formed. It is shown that appropriately crystallized glasses exhibit a thermal expansion close to zero. The addition of antimony results in an increasing number of platinum particles and hence nucleation sites during thermal treatment at temperatures slightly above Tg.