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pure and applied geophysics

, Volume 141, Issue 2–4, pp 631–642 | Cite as

A thin film approach for producing mineral diffusion couples

  • Craig S. Schwandt
  • Randall T. Cygan
  • Henry R. Westrich
Advances in High-pressure Calorimetry, Diffusion, Sealing and Calibration

Abstract

Few diffusion coefficient values have been measured for silicate minerals at pertinent geologic conditions because of experimental restrictions. Until recently, analysis of diffusion couples was conducted principally with electron microprobes which have rather poor spatial resolution (micrometer scale). Ion microprobe analyses, however, eliminate many of the previous experimental restrictions; in depth profile mode they have excellent spatial resolution (tens of angstroms) and diffusion couples can be analyzed normal to the interface. Diffusion couples analyzed by ion microprobe must be well-defined and uniform; previous methods using solution precipitates to form the diffusion couples were heterogeneous and had limited success. A new approach, the thermal evaporation of25MgO under high vacuum onto a crystalline substrate (oxide, silicate), produces a 1000 Å thick25MgO x (x<1) thin film. This method yields an excellent diffusion couple for low-temperature diffusion experiments. Diffusion anneal experiments using this approach for garnet provide a Mg self-diffusion coefficient ofD=0.60±0.09×10−21 m2/s at 1000°C (logFO2=−11.3,P=1 atm,XAlmandine=0.24).

Key Words

Thin film diffusion coefficients ion microprobe 

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Copyright information

© Birkhäuser Verlag 1993

Authors and Affiliations

  • Craig S. Schwandt
    • 1
  • Randall T. Cygan
    • 1
  • Henry R. Westrich
    • 1
  1. 1.Geochemistry DepartmentSandia National LaboratoriesAlbuquerqueUSA

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