THE EQUILIBRIUM DIASPORE-CORUNDUM AT HIGH-PRESSURES

The equilibrium curve 2 diaspore = corundum + H2O was experimentally i nvestigated by reversal runs in a piston-cylinder apparatus in the pre ssure range 15 kbar-50 kbar. Its position is determined by reversal br ackets at 15 kbar (488-519 degrees C), 25 kbar (581-600 degrees C), 30 kbar (629-648 degrees C), 40 kbar (675-696 degrees C), and 50 kbar (6 95-719 degrees C), thus lying between the curves reported by Kennedy ( 1959) and Matsushima et al. (1967). Ln addition, the behaviour of dias pore during heating at one atmosphere was determined using a Guinier c amera with heating device. The resulting regression function for the v olume has a higher slope in temperature than the function estimated by Berman (1988). Using this newly determined function to describe the t hermal expansion of diaspore, the measurements of the isothermal compr essibility of this phase performed by Xu et al. (1994), and the other thermodynamic data provided by Berman (1988), the calculated curve fit s the reversals presented in this paper rather well.