Accession Number:

ADA416322

Title:

Controlled Crystallization of Amorphous Oxide Fibers

Descriptive Note:

Final rept. 1 Jan 2000-31 Dec 2002

Corporate Author:

ILLINOIS UNIV AT URBANA DEPT OF MATERIALS SCIENCE AND ENGINEERING

Personal Author(s):

Report Date:

2003-06-20

Pagination or Media Count:

35.0

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 mmsec to 0.025 msec, or 1 inchsec. 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.

Subject Categories:

  • Ceramics, Refractories and Glass

Distribution Statement:

APPROVED FOR PUBLIC RELEASE