Preparation of transparent lithium-mica glass-ceramics

In order to fabricate transparent and machinable mica-type glass-ceramics, parent glasses having chemical compositions corresponding to Li_(1+x)Mg₃AlSi_3(1+x)O_10+6.5xF₂ (x = 0.15, 0.5, 0.65, 1.0 and 1.2) were crystallized. Lithium-micas were precipitated in all the specimens as the main crystal at 650 °C though the content was little. And the micas were changed from trisilicic type to tetrasilicic type as the x increased. After the precipitation of the micas, a large amount of β-eucryptite solid solution was precipitated as the main crystal at higher temperatures and even at 650 °C after a certain period of time. The parent glasses having the spinodal phase separation, of which the x was 1.0 and 1.2, were transparent and colored in light blue. And at 650 °C, the fine mica crystals with size of about 20 nm were precipitated in one continuous glass phase of the spinodal phase separation, which made the phase separation structure become finer. Consequently, the heated specimens showed higher transmittance of visible ray and became colorless. Moreover, because the mica crystals formed the continuous phase, the specimens showed the machinability.