THE SYSTEM HYDROGEN - WATER UP TO 440-DEGREES-C AND 2500 BAR PRESSURE

The system H//2-H//2O has been studied isochorically from 0. 5 to 90 mol-% H//2 and up to 440 degree C and 2500 bar pressure using an autoclave containing two sapphire windows through which phase transitions could be observed at elevated temperatures and pressures. The system was found to exhibit so-called ″gas-gas″ immiscibility with a critical curve proceeding to higher temperatures and pressures from the critical point of pure water. Within the range of these experiments, the critical temperature of H//2-H//2O mixtures does not change greatly from that of pure water (e. g. T//c equals 381. 3 degree C at p//c equals 2520 bar for 38 mol-% H//2). PVT measurements have been made in the homogeneous region and excess volumes are calculated at 400 degree C and at different pressures.