METAL DIFFUSION IN PYROLYTIC GRAPHITE
Abstract
The diffusion coefficients of Nb-95 in PG were measured between 1450 and 1950C in three different types of PG which were chosen to represent substrate nucleated, combination substrate and regeneratively nucleated, and regeneratively nucleated microstructures. The diffusion coefficients parallel and perpendicular to the deposition surface were determined in as-deposited and partially graphitized PG. Autoradiography was used to observe the distribution of diffusing atoms. The structure of the PG was characterized by the application of many techniques of metallography, x-ray diffraction, small angle scattering of x-rays, and density determinations. A mathematical analysis of diffusion in layered structures was made and correlations between the structure and diffusion parameters noted. The activation energies for Nb diffusion in PG depended only upon direction and were independent of microstructure and state of graphitization. The activation energy for Nb diffusion parallel to the deposition plane was 96.2 kcal/mole and that perpendicular to it was 73.1 kcal/ mole. The preexponential factors for a given direction differed only slightly for the various PG's used in this study; these factors were altered by the graphitizing heat-treatment.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1965
- Accession Number
- AD0622874
Entities
People
- Martin L. Hammond
Organizations
- Lockheed Martin Missiles and Space