Addition of GeO sub(2) to Reduce the Viscosity of Parent Glasses for Low-Expansion, Transparent Glass-Ceramics Containing High-Quartz Solid Solutions

• Published in: Journal of the American Ceramic Society Vol. 89; no. 10; pp. 3235 - 3239
• Main Authors: Shyu, Jiin-Jyh, Lue, Chun-Yuan, Jean, Ren-Der
• Format: Journal Article
• Language: English
• Published: 01.10.2006
• Subjects: Crystals; Germanium oxides; Glass; Glass ceramics; Parents; Solid solutions; Thermal expansion; Viscosity
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1551-2916.2006.01226.x

Parent glasses for fabricating glass-ceramics with nanometer-sized crystals usually have high viscosities, resulting in high processing temperatures. In this study, GeO sub(2) was added to a transparent, near-zero thermal-expansion Li sub(2)O-Al sub(2)O sub(3)-SiO sub(2) glass-ceramic to reduce the viscosity of the parent glass. The effects of this compositional modification on the viscosity and crystal-nucleation rate of the parent glasses, and on the crystal size, thermal expansion, and optical transparency of the resulting glass-ceramics were investigated. It was found that addition of GeO sub(2) was useful in reducing the glass viscosity. Owing to the reduced nucleating rate with the increase in the GeO sub(2) content, the nucleating times required for reaching the smallest crystal size, the lowest coefficient of thermal expansion, and the highest transparency were all increased. With increasing GeO sub(2) content, the lowest coefficient of thermal expansion that can be reached for glass-ceramics increased (0.14-2.9 x 10 super(-6) K super(-1)). The highest transparency of the GeO sub(2)-containing glass-ceramics is almost as good as that of the GeO sub(2)-free glass-ceramic and is almost independent of GeO sub(2) content when the crystal size is smaller than about 65 nm.