ION-PAIRING IN AQUEOUS MGSO4 SOLUTIONS ALONG AN ISOCHORE TO 500-DEGREES-C AND 11 KBAR USING RAMAN-SPECTROSCOPY IN CONJUNCTION WITH THE DIAMOND-ANVIL CELL

A high-temperature diamond-anvil cell is used in conjunction with micr o-Raman spectrometer in the study of aqueous fluids containing 0.5 m M gSO4 along an isochore from room conditions to 500-degrees-C and 11 kb ar. Gaskets lined with platinum are used to contain the chemically-rea ctive fluid. Ion-pairing of MgSO4 is shown to increase with increasing pressure along an isochore with a density of approximately 1 g cm-3. Mass-action constants for the reaction Mg2+ + SO4(2-) reversible MgSO4 range from 3.5 . 10(1) at 20-degrees-C, 1 bar to 1.25.10(4) at 500-de grees-C, 11.4 kbar. The results agree favorably with those obtained th rough electrical conductance measurements by V.G. Ritzert and E.U. Fra nck. The relative abundances of the species are shown as a function of temperature and pressure along the isochore.