IN-SITU X-RAY AND NEUTRON POWDER DIFFRACTION STUDIES OF PHASE EQUILIBRIA IN METALS AND CERAMICS. S.T. Misture and C.R. Hubbard, Oak Ridge National Laboratory, Oak Ridge, TN 37831

High temperature x-ray and neutron powder diffraction measurements of reaction chemistry, phase transformations and kinetics in ceramics and metals will be presented, with emphasis on data analysis methods. The capabilities of high temperature x-ray diffraction using conventional and position-sensitive detectors will be described using examples of phase evolution from amorphous precursors and solid-state and peritectic phase equilibria studies. The utility of position-sensitive detectors for time-resolved measurements will be demonstrated for systems including glass crystallization and order-disorder transformations. Rietveld refinement, profile fitting, and powder pattern calibration methods are applied to determine accurate lattice parameters and quantitative phase content, as well as for full structure refinements.

High temperature, high-resolution neutron powder diffraction experiments are critical for many systems where large sampling volumes are required or low-Z elements are of interest. Rietveld refinement for quantitative phase analysis and residual stress determination in metal matrix composites will be presented, as well as structure refinements of high temperature phases of oxide and carbide ionic conductors.

This research was sponsored by the U.S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Transportation Technologies, as part of the High Temperature Materials Laboratory User Program, under contract DE-AC05-96OR22464, managed by Lockheed Martin Energy Research Corp. SM acknowledges the ORNL Postdoctoral Research Associates Program administered jointly by ORNL and Oak Ridge Institute for Science and Education.