A NEW DIAMOND-ANVIL CELL FOR HYDROTHERMAL STUDIES TO 2.5 GPA AND FROM- 190-DEGREES-C TO 1200-DEGREES-C

A new style of diamond anvil cell (DAC) has been designed and built fo r conducting research in fluids at pressures to 2.5 GPa and temperatur es from -190 to 1200-degrees-C. The new DAC has been used for optical microscope observations and synchrotron x-ray diffraction studies. Fri nges produced by interference of laser light reflected from top and bo ttom anvil faces and from top and bottom sample faces provide a very s ensitive means of monitoring the volume of sample chamber and for obse rving volume and refractive index changes in samples that have resulte d from transitions and reactions. X-ray diffraction patterns of sample s under hydrothermal conditions have been made by the energy dispersiv e method using synchrotron radiation. The new DAC has individual heate rs and individual thermocouples for the upper and lower anvils that ca n be controlled and can maintain temperatures with an accuracy of +/- 0.5-degrees-C. Low temperatures are achieved by introducing liquid nit rogen directly into the DAC. The equation of state of H2O and the alph a-beta quartz transition are used to determine pressure with an accura cy of +/- 1 % in the aqueous samples. The new DAC has been used to red etermine five isochores of H2O as well as the dehydration curves of br ucite, Mg(OH)2, and muscovite, KAl2(Si3Al)O10(OH)2.