화학공학소재연구정보센터
Journal of Materials Science, Vol.34, No.1, 195-208, 1999
Microstructural characterization of grain-oriented glass-ceramics in the system Ba2TiSi2O8-SiO2
In polycrystalline fresnoite, advantage of the piezo- and pyroelectric properties can be taken only if texturing along its polar [0 0 1]-axis can be achieved. We report on a novel technique to prepare grain-oriented glass-ceramics in the system fresnoite-SiO2 by electrochemically induced nucleation. Optimum conditions for grain orientation were determined by characterizing the microstructure of glass-ceramics prepared at 1150, 1200 and 1350 degrees C using electron microscopy and X-ray texture goniometry. At 1150 degrees C-due to the smallest crystal growth rate and highest nucleation rate-the most distinct orientation is obtained. The solidification of the glass-ceramic consist of three subsequent steps. First, dendritic fresnoite crystallizes most rapidly along its [0 0 1]-axis with {1 1 0} facet planes. Due to growth selection, the polar c-axes become oriented. Secondly, within the interdendritic areas, the pseudo-binary eutectic fresnoite-silica solidifies lamellarly. Finally, in the middle of the interspaces, a crystalline barium silicate coexisting with glassy silica is formed at 1200 degrees C and 1350 degrees C. At 1150 degrees C, however, a glass with the composition of the melt solidifies.