Controlled Crystallization of Amorphous Oxide Fibers
Abstract
The goal of this work is to produce creep resistant reinforcement fibers to improve the toughness and reliability of oxide ceramic composites, which are able to withstand operating temperatures of 1600 deg. C in air. We have studied crystallization mechanisms of quenched mullite (3Al2O3 (dot) 2SiO2) and YAG (Y3Al5O12), from solid amorphous or polycrystalline spheres and determined the parameters of kinetics and thermodynamics. This has enabled us to put together T-T-T curves for both systems. A four-lamp, image furnace, having a narrow hot zone and capable of operating to 2000 deg. c in air has been built and calibrated. Heat treatments can be controlled by two parameters of temperature and traverse rate (from 0.1 mm/sec to 0.025 m/sec, or 1 inch/sec). Grain growth, densification and melting can be achieved in 100 micrometers diameter monofilaments, indicating the feasibility of making textured or single crystal fibers in a continuous process. A process to extrude polycrystalline powders of green diameters approx. 140 micrometers, which densify to approx. 100 micrometers or less, has been developed. Nextel 550, 720, pure and TiO2(-) doped mullite and YAG fibers have been heat treated or melted, and a dense microstructure can been achieved. Needles of mullite form in random orientation.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 20, 2003
- Accession Number
- ADA416322
Entities
People
- Waltraud M. Kriven
Organizations
- University of Illinois Urbana–Champaign