The Design and Application of a New Bassett-type Diamond Anvil Cell for Spectroscopic Analysis of Supercritical Aqueous Solutions

Abstract

The Bassett-type hydrothermal diamond anvil cell has been modified to facilitate direct x-ray and Raman spectroscopic analysis of aqueous solutions and/or coexisting solid samples at temperatures and pressures above the critical point of water. The new cell provides more sample-detector geometry options for x-ray micro beam analysis and the reduced size of the cell affords a smaller working distance (> 14 mm) required for better Raman spectroscopic analysis and microscopic inspection. A shallow recess (300 x 300 x 26.5 um) milled into one of the diamond anvils is used instead of a metal gasket to contain the aqueous solution. These modifications significantly improve our ability to directly monitor the composition and structure of supercritical fluids and have eliminated the problem of contamination due to the reaction of a metal gasket with supercritical water. The use of the modified hydrothermal diamond anvil cell to characterize the MoO3-H2O system up to 500 degrees C will be discussed.