Application of Garnet Anvil Cell (GAC) to Hydrothermal Studies up to 6,0 GPa and 1200 °C
(Poster)
Martin A. Ziemann¹⁾, Michael R. Riedel¹⁾ and Andy H. Shen²⁾
1) University Potsdam, Projectgroup Thermodynamics, D-14473 Potsdam, Germany
2) Bayerisches Geoinstitut, University Bayreuth, D-95440 Bayreuth, Germany

Abstract

The usage of a garnet anvil cell (GAC) for hydrothermal studies has been suggested previously [1]. The usage of big garnet anvils instead of diamonds avoids some of the shortcomings of the externally heated diamond anvil cell, e.g. graphitization and the strength reduction of necessary tungsten carbide support parts to the diamonds above 900-1000 °C. Among the various materials of the garnet structure, Y₃Al₅O₁₂ (YAG) has the highest melting point (T_m=2273 K) and hence is likely to be the most resistant to plastic deformation at high temperatures. Garnets in general appear to have a creep strength higher by a factor of 3-10 than other oxides, compared at the same homologous temperatures T/T_m [2]. We have performed experiments with a GAC up to 800 °C without any special precautions, and up to 1200°C under protection gas. The reachable pressure depends on the size and shape of the active anvil face, with coned (diamond-like) garnet cylinders of 5 mm outer diameter and a 500 mm anvil face we were able to get 6.0 GPa without any problems. The anvil geometry and the heater localization was optimized using a FEM model for the inner assembly of the cell in order to minimize the temperature gradients over the sample area, and to ensure the stability of the anvils at higher p,T conditions. With a gasket-free preparation, we used a special cell with shear mechanism to study the brittle-ductile transition in calcite by deforming small calcite cylinders (2 mm diameter and 30 mm thickness) in the GAC under visual control. The applicability of the GAC is further demonstrated for hydrothermal studies of phase transformations. The pressure determination at higher temperatures is possible to a high accuracy using the equation of states of H₂O as suggested in [3]. Further geophysical and/or mineralogical applications of the garnet anvil cell, like the investigation of melt inclusions in silicate minerals, are discussed.

References

[1] Riedel, M.R., Buga, S., Shen A.H., AIRAPT meeting, 1995.
[2] Karato, S., Wang, Z. and Fujino, K., J. Mater. Sci. 29 (1994) 6458.
[3] Shen, A.H., Bassett, W.A., Chou, I-M., in: High Pressure Research,
      eds. by Y. Syono and M.H. Manghnani, AGU, Washington D.C., 1992, pp. 61-68.