Effects of nucleation agents on the preparation of transparent glass-ceramics

Formation of transparent glass-ceramic in the system MgO-SiO2-Al2O3-K2O-B2O3-F with and without addition of LiF and NaF has been investigated. Crystallization of glass-sample was conducted by controlled thermal heat-treatment, at determined nucleation and crystallization temperatures. In this regard, the effects of addition of LiF and NaF were investigated on the crystallization behavior and transparency of the samples. Low transmission (less than 80% at 600 nm) was observed in the basic composition (K). The addition of NaF and LiF caused more intense phase separation in the system. The results indicated that the glass ceramic can remain transparent if fine grains with nano size are precipitated but will turn into opaque when large grains appear, because of the difference in the refractive index between glass and precipitated crystals. (C) 2012 Elsevier Ltd. All rights reserved.