Experimental investigation of the hydrous characteristics of pressure media

1. Medium Machinable Alumina Exp No. Cell material PTtannealCOH (GPa) (K) (h) (H/106 Si) Graphite (heater) dd067 Hybrid 5 1473 5 70 Boron nitride IR spots dd072 Pyrophyllite 5 1473 5 60 Hard Alumina dd073 Boron epoxy 5 1473 5 110 Olivine dd074 Mullite 5 1473 5 85 Ni capsule Nickel capsule The pressure medium plays an important role in high-pressure studies. Materials such as pyrophyllite, boron epoxy resin, and mullite are commonly used as pressure media for experiments in a D-DIA press because these materials have either the strength necessary to achieve good pressure efficiency or sufficient ductility to form competent gaskets bounding the six anvils used in the D-DIA press. However, some of these materials might release water at or below the experimental temperature. If water is supplied by the pressure medium, it is often problematic for interpreting the measured material properties, many of which are affected by the presence of water. The purpose of this study is to quantify the hydrous characteristic of pressure media in order to provide both a reference for selecting a pressure medium for a specific experiment and a basis for estimating the effect of water on physical properties of the sample. Experimental investigation of the hydrous characteristics of pressure media Ayako Suzuki and Shenghua Mei University of Minnesota, 310 Pillsbury Dr. SE, Minneapolis, MN 55455 Abstract Experimental Details Sample assembly Experimental conditions Samples 1 mm in length x 1.1 mm in diameter were prepared from oriented San Carlosolivine single crystals, encapsulated with 0.025-mm thick Ni foil, and assembled with alumina pistons, a boron nitridesleeve, and a graphite resistance heater into a 6-mm edge length cubic pressure medium. Experiments have been carried out using a D-DIA press off-line. T  1473 K (Based on calibrated heater power vs. temperature curves ) P  5 GPa (Based on calibrated oil load-P curves) fO2 was buffered by oxidation of the nickel surrounding a sample (Ni/NiO) t anneal = 5 hr After anneal, the concentration of water (i.e., OH concentration) in olivine samples was determined using Fourier transformed infrared (FTIR) spectroscopy. Experimental Results Transmitted plane light photomicrograph of an annealedsample. The micrograph is from polished section cut parallel to (010) lattice plane. IR spot (d < 10 m)was transmitted through the areas free of thermal cracks. Acknowledgement This research was supported by NSF through grant EAR-0652852 (Rheology Grand Challenge) . We thank Dr. Tony Withers for technical assistance and/or discussions in conducting experiments. Conclusion Experimental results show that there are ~100 ppm H/Si detected from annealed samples with different pressure media at pressure of ~5 GPa and temperature of 1473 K (At the same experimental conditions, water solubility in -phase olivine could be as high as ~8000 ppm H/Si [Kohlstedt et al., 1996]). In general, people thought that some media such as pyrophyllite and boron epoxy resin might create a hydrous environment for experiments since both of them might release water at or below experimental temperature. However, in terms of water content determined from annealed samples,our experiments show that there is no significant difference among tested pressure media: pyrophyllite, boron epoxy resin, mullite, and pyrophyllite + mullite hybrid.