Accession Number : ADA185482
Title : Exploitation of the Sol-Gel Route in Processing of Ceramics and Composites.
Descriptive Note : Final rept. 15 May 85-14 May 87,
Corporate Author : PENNSYLVANIA STATE UNIV UNIVERSITY PARK MATERIALS RESEARCH LAB
Personal Author(s) : Roy, Rustum
PDF Url : ADA185482
Report Date : 10 Jul 1987
Pagination or Media Count : 106
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.
Descriptors : *CERAMIC MATERIALS, *COMPOSITE MATERIALS, COEFFICIENTS, FUSED SILICA, GELS, HEAT OF REACTION, LOW TEMPERATURE, MELTING, METASTABLE STATE, MODELS, PROCESSING, PROTOTYPES, SINTERING, SOLID PHASES, TEMPERATURE, THERMAL EXPANSION
Subject Categories : Laminates and Composite Materials
Ceramics, Refractories and Glass
Distribution Statement : APPROVED FOR PUBLIC RELEASE