PARTICLE SIZE AND STRAIN MEASUREMENT IN RHENIUM POWDER BY MEANS OF THE WARREN-AVERBACH METHOD. J.L. Garin, R.L. Mannheim, Department of Metallurgical Engineering, J.A. Costamagna, Department of Chemistry, Universidad de Santiago de Chile, Casilla 10233, Santiago, Chile

Crystallite size, crystallite size distribution and microstrain in polycrystalline rhenium samples, were evaluated from diffraction peak broadening.

The material used in this research was rhenium powder produced by reduction of ammonium perrhenate (NH₄ReO₄) under hydrogen flux inside a tubular furnace, at various temperatures in the range of 673 to 1273 K. Depending upon the process temperature, variable amounts of hydrogen, nitrogen and oxygen remain in the material causing large line broadening. Powder data were collected at room temperature with a SIEMENS D5000 diffractometer equiped with a graphite diffracted beam monochromator, using a normal Cu tube. Measurements of particle size distribution and strain made use of the (101) and (202) powder diffraction profiles. The standard powder sample for the determination of instrumental broadening was obtained from rhenium produced at 1273 K. All experimental profiles were modeled by use of Pearson VII functions, while the calculations were based upon the Warren-Averbach theory, and carried out with the programs PROFILE and WIN-CRYSIZE distributed by SIEMENS.

The particle size varied from 3 nm (673 K) to 80nm (1123 K); no variations were observed at higher reduction temperatures. On the other side, the microstrain changed from an average value of 8.7x10^-3 to 0.8x10^-3, with no further changes at higher temperatures. The overall results are in close agreement with the contents of hydrogen, nitrogen and oxygen impurities, which remain interstitially disolved in the hexagonal structure of the metal.