Cation diffusion rates in selected silicate minerals
In order to develop a procedure for measuring cation diffusion coefficients below 1000{degrees}C, we have examined the suitability of several diffusion couple configurations involving single crystals of garnet. Initial experiments using an enriched {sup 25}MgCl{sup 2} proved ineffective in providing a uniform and coherent surface for analysis by ion microprobe. A technique was developed using thin film deposition. Thin films ({approximately} 1000 {Angstrom}) of MgO{sub x} (x < 1) can be applied to polished mineral surfaces by evaporating MgO powder under high vacuum with a thermal-resistance strip heater. Thermal resistance evaporation is efficient. Samples of single crystal grossular and pyrope garnets with thin films of MgO, as created by these techniques, were annealed for various times at 800, 900, and 1000{degrees}C, at several log fO{sub 2} values, and 1 atm. Optical, SEM, and ion microprobe analyses reveal no disruption of the interface. Profiles of elemental counts vs depth exhibit expected patterns going through the thin film into the garnet substrate. Our experimental matrix of garnet diffusion runs includes over 60 cut and polished crystals of pyrope composition that are being run at various oxygen fugacity conditions from 600 to 1000{degrees}C.
- Research Organization:
- Sandia National Labs., Albuquerque, NM (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 10117875
- Report Number(s):
- SAND--92-2580C; CONF-930162--1; ON: DE93005369
- Country of Publication:
- United States
- Language:
- English
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