The Reaction of Oxides with Water at High Pressures and Temperatures

The reactions of the oxides SiO 2 , MoO 3 , and WO 3 with steam at temperatures between 400 and 700 °C and pressures of 5 to 500 atm were studied by means of the transfer method. The results were evaluated by a new method. In the system Sio 2 /H 2 O the formation of gaseous Si(OH) 4 , Si 2 O(OH) 6 , and [SiO 2 (OH) 2 ] x was found to occur in three different water‐density ranges. In the systems MoO 3 /H 2 O and WO 3 /H 2 O the gaseous compounds MoO 2 (OH) 2 and WO 2 (OH) 2 , which were already known, exist up to densities of approximately 0.05g/cm 3 . At higher densities, at which the supercritical phase begins to show the properties of a liquid to an ever increasing extent, isopolymolybdic or isopolytungstic acids appear.