Sol-Gel Processing and Crystallization of Yttrium Aluminosilicates
Abstract
Glasses in the yttria-aluminum-silica (YAS) system are candidate matrices for SiC reinforced composites because of their high elastic moduli and excellent chemical durability. Moreover, several compositions offer the potential for controlled crystallization into glass ceramics exhibiting low- thermal expansion and elevated temperature stability. In order to exploit the properties of these glasses and glass ceramics, improved processing techniques and detailed investigations of their crystallization behavior are required. Glass in the yttria-alumina-silica system was synthesized using sol-gel techniques. Crystallization behavior of the gel and the glass was examined using variable heating rate data obtained by differential thermal analysis (DTA). The reaction rate constants for crystallization followed an Arrhenius temperature dependence, and the activation energies for crystallization were readily determined. Surface nucleation/crystallization dominated but no appreciable difference in crystallization between the gel and glass powders was evident. In this system it was verified that densification of the gel occurred before the onset of crystallization. Isothermal heat treatment of the gels and glasses produced 3Al2O3-2SiO2 and various polymorphs of Y2O3.2SiO2. Yttrium pyrosilicates, Mullite.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1990
- Accession Number
- ADA220849
Entities
People
- Carlo G. Pantano
- James C. Walck