Exploitation of the Sol-Gel Route in Processing of Ceramics and Composites.
Abstract
Compositionally diphasic xerogels. These materials are very intimate mixtures composed of two solid phases each on the order of 10-20 nm. The two phases are only different in composition. Using the mullite (3A12O3SiO2) system as the prototype model, we have shown that the compositionally diphasic materials sinter to a much lower temperature than the single phase gels. Such sintering of compositionally diphasic gels at much lower temperatures may be attributed, at least in part, to the heat of reaction of the two discrete phases at the sintering temperature. This notion was extended to other systems such as Al2TiO5, ZrSiO4, ThSiO4 and Mg2Al4SiO18. Results to data on the Al2TiO5, ZrSiO4 and ThSiO4 systems do not show significant improvements in densification behavior although the use of diphasic gels led to a lowering in the crystallization temperatures of ZrSiO4, ThSiO4, etc. The diphasic Mg2Al4Si5O18 system exhibits metastable melting which could be used for enhanced densification of this low-expansion ceramic. Using the diphasic approach, we have also prepared translucent ultra-low expansion titania-silica glasses with 0 to 10% TiO2. The coefficients of thermal expansion are intermediate between those of fused silica and a commercial titania-silica glass. The glass with 7.2% TiO2 exhibited a zero thermal expansion coefficient at 150-210 C.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 10, 1987
- Accession Number
- ADA185482
Entities
People
- Rustum Roy
Organizations
- Pennsylvania State University