High thermal expansion of crystallized glasses in the system BaO–ZnO–NiO–SiO2.

Crystallizing glasses in the system BaO–ZnO–NiO–SiO 2 were studied with respect to the glass formation, crystallization and thermal expansion behavior. A maximum NiO concentration of 8.8 mol% was reached in the glasses. The high thermal expansion phase BaZn 2 Si 2 O 7 and the solid solutions BaZn 2− x Ni x Si 2 O 7 derived hereof can be crystallized from the prepared glasses. The incorporation of NiO in the solid solution strongly increases the transition from the low to the high temperature phase. The introduction of NiO into the solid solution was studied, using ultraviolet–visible-near-infrared spectroscopy. Phase transitions were analyzed using in situ high-temperature X-ray diffraction and dilatometry. The introduction of NiO in the as mentioned phases led to a thermal expansion coefficient in the range from 11.1 to 17.2×10 −6 K −1 . In contrast to other crystallized sealing materials, the thermal expansion coefficient is nearly constant over a wide temperature range (25–1000 °C). Furthermore, it is shown, that the thermal expansion behavior of the multiphase glass ceramics can be predicted from the thermal expansion of the different ceramic phases. The crystallizing glass may be suitable as sealing material for components with high coefficients of thermal expansion such as ferritic stainless steels or nickel alloys. [ABSTRACT FROM AUTHOR]