چكيده
Abstract
The aim of this project is the evaluation of compositional changes on
crystallization and properties of low expansion opal glasses. In order
to achieve this, glass samples with the general composition
71SiO2.2Al2O3.12B2O3.2P2O5. (13-X)Na2O.XRO(X = 0, 1.5, 3, 4.5, 6, 7.5;
R= Mg, Ba, Ca, Zn) were prepared. After heat treatment of glasses at
temperatures corresponding to Differential Thermal Analysis (DTA) curves,
opal glasses were studied by XRD analysis and scanning electron microscopy
(SEM). After that opacity and chemical resistivity (to water and alkaline
solutions) tests were done. Results of XRD and SEM of compositions with CaO,
BaO, and ZnO revealed more crystallization. Studies showed that crystallization
and phase separation of glasses are effective factors on opacity and chemical
durability. Improved opacity and chemical durability were related to
crystallization of desired phases in glasses. Suitable conditions of heat treatment
obtained at 850 C and 1 hour. Loss of chemical durability for longer periods was
related to the formation of cristobalite in some glasses. Results also showed that
CaO and MgO were more effective in opacity and BaO and ZnO were more
effective in chemical durability.
