Microstructure and crystallization behavior of Na2O-Al2O3-SiO2 glass-ceramics with MgO additions.

Transparent Na 2 O–MgO–Al 2 O 3 –SiO 2 glass-ceramics containing spinel crystals were prepared by melting and heat treatment method, and the effects of substitution of 2–8 mol% MgO for Na 2 O on the crystallization behavior, microstructure, and properties were investigated. As Na 2 O is replaced by MgO, there is higher concentration of 5-coordinated Al units in the glass structure, which played an important role in the crystallization behavior of the glass. The increasing substitution of MgO for Na 2 O promotes the formation of spinel but inhibits the nepheline and carnegieite. When containing 2 mol% MgO, the large-sized nepheline and carnegieite are the main crystalline phases, making the glass ceramics opaque. When containing 6 mol% MgO, there is no NaAlSiO 4 crystal formed, but only spinel crystals with small size and uniform distribution are detected in glass-ceramics. The glass-ceramics with spinel as the main crystalline phase show high transparency above 82% in the visible wavelength range. The Vicker's hardness of transparent glass-ceramics can be further improved by ion-exchanged with KNO 3 molten salt, which shows significant potential in the applications for the protective covers of mobile displays. [ABSTRACT FROM AUTHOR]