Tomohiro Nagakane

Transparent athermal glass-ceramics in Li 2 O-Al 2 O 3 -SiO 2 system

An attempt has been conducted to develop multicomponent transparent glass-ceramics which have athermal property better than silica glass. Transparent Li2O-Al2O3-SiO2 (LAS) glass-ceramics with small thermal expansion coefficient was chosen as a candidate. Athermal property of the glass-ceramics was improved by the independent control of temperature coefficients of electronic polarizability and thermal expansion coefficient, both of which govern the temperature coefficient of optical path length. It was found that temperature coefficient of electronic polarizability and thermal expansion coefficient of the LAS glass-ceramics were controllable by the additives and crystallization conditions. The doping of B2O3 and the crystallization under a hydrostatic pressure of 196 MPa were very effective to reduce temperature coefficient of electronic polarizability without a remarkable increase in thermal expansion coefficient. It was deduced that the reduction in temperature coefficient of electronic polarizability by the crystallization under 196 MPa resulted from the inhibition of the precipitation of beta-spodumene solid solution. The relative temperature coefficients of optical path length of B2O3-doped glass-ceramic crystallized under 196 MPa was 11.7 x 10-6/°C, which was slightly larger than that of silica glass. Nevertheless, the thermal expansion coefficient of this glass-ceramic was smaller than that of silica glass.

Effect of high pressure on crystallization of LI2O-AL2O3-SIO2 glass

We have investigated the effect of high-pressure on the crystallization of an Li2O-Al2O3-SiO2 glass. The glass was heated for nucleation, followed by heating for crystal growth. Hydrostatic pressure of argon gas of 196 MPa was applied in either the nucleation process or the crystal growth process, and in both the processes. β-quartz solid solution was precipitated in all glass-ceramic specimens. The crystallinity of the glass-ceramics increased by applying high-pressure during the nucleation or the crystal growth process. Lattice constants of the precipitated crystal were decreased by applying high-pressure. Magnitudes of the increase of crystallinity and the decrease of lattice constants by applying pressure in the crystal growth process were larger than these in the nucleation process. Density of glass-ceramic specimens increased by applying pressure in any heat treatment. It was suggested that the increase in density is due to increase of crystallinity, decrease of lattice constant and possibly densification of glass part. The refractive index increased with increasing density. The temperature coefficient of the optical path length, dS/dT, decreased by applying pressure.