HYDROTHERMAL STUDIES IN A NEW DIAMOND-ANVIL CELL UP TO 10 GPA AND FROM - 190-DEGREES-C TO 1200-DEGREES-C

The new hydrothermal diamond anvil cell (HDAC) has been designed for o ptical microscopy and X-ray diffraction at pressures up to 10 GPa and temperatures between -190-degrees-C and 1200-degrees-C. Laser light re flected from the top and bottom anvil faces and the top and bottom sol id sample faces produce interference fringes that provide a very sensi tive means of monitoring the volume of sample chamber and for observin g volume and refractive index changes in solid samples due to transiti ons and reactions. Synchrotron radiation has been used to make X-ray d iffraction patterns of samples under hydrothermal conditions. Individu al heaters and individual thermocouples provide temperature control wi th an accuracy of +/-0.5-degrees-C. Liquid nitrogen directly introduce d into the HDAC has been used to reduce the sample temperature to -190 -degrees-C. The alpha - beta phase boundary of quartz has been used to calculate the transition pressures from measured transition temperatu res. With this method we have redetermined 5 isochores of H2O up to 85 0-degrees-C and 1.2 GPa at which the solution rate of the quartz becam e so rapid that the quartz dissolved completely before the alpha-beta transition could be observed. When silica solutions were cooled, opal spherules and rods formed.