Grain boundary diffusion and grain boundary chemistry of Cr-doped magnesium oxide. Technical progress report
The grain boundary product D' delta (where D' is the grain boundary diffusion coefficient and delta is the grain boundary width) of /sup 51/Cr in MgO and Cr-doped MgO was determined at 1200 to 1450/sup 0/C for Cr/sup 3 +/ concentrations of 0 to 0.56 atom %. By assuming a grain boundary width to be between 100 and 1000 A the grain boundary diffusion coefficients are 10/sup 5/-10/sup 6/ times larger than the volume diffusion coefficients. D' delta increased with increasing Cr/sup 3 +/ concentration, but the activation energy for diffusion of 180 +- 8 kJ/mole was the same for all specimens. Surface diffusion on MgO and Cr-doped MgO was examined using grain boundary grooving at 1100 to 1400/sup 0/C for a concentration range of 0 to 0.211 atom % chromium. The activation energy for surface diffusion on MgO was found to be 239 +- 5 kJ/mole. The surface diffusivity did not change markedly with chromium concentration; however, an abrupt change in activation energy from 180 kJ/mole occurred between 0.038 and 0.254 atom % chromium. Effect of association of defects on the thermodynamical factor (Darken's equation) for diffusion was studied theoretically. It was shown that in the limit of dilute solution the thermodynamic factor (1 + par. delta 1n ..gamma../delta 1n N) was equal to 3/2 if monomers are the diffusing species, 2 if dimers are the diffusion species and 3 if trimers are the diffusion species. These results are consistent with the atomistic model.
- Research Organization:
- Pennsylvania State Univ., University Park (USA). Dept. of Materials Science and Engineering
- DOE Contract Number:
- AS02-78ER04998
- OSTI ID:
- 6290078
- Report Number(s):
- DOE/ER/04998-T1; ON: DE81028314
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CHROMIUM 51
DIFFUSION
IONIC CRYSTALS
PERMEABILITY
MAGNESIUM OXIDES
ATOM TRANSPORT
ACTIVATION ENERGY
GRAIN BOUNDARIES
SURFACES
TEMPERATURE DEPENDENCE
THERMODYNAMICS
VERY HIGH TEMPERATURE
ALKALINE EARTH METAL COMPOUNDS
BETA DECAY RADIOISOTOPES
CHALCOGENIDES
CHROMIUM ISOTOPES
CRYSTAL STRUCTURE
CRYSTALS
ELECTRON CAPTURE RADIOISOTOPES
ENERGY
EVEN-ODD NUCLEI
INTERMEDIATE MASS NUCLEI
ISOTOPES
MAGNESIUM COMPOUNDS
MICROSTRUCTURE
NEUTRAL-PARTICLE TRANSPORT
NUCLEI
OXIDES
OXYGEN COMPOUNDS
RADIATION TRANSPORT
RADIOISOTOPES
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