Preparation of nanocrystalline alumina under hydrothermal conditions

Thermodynamic analysis of phase equilibria in the Al2O3-H2O system at temperatures from 120 to 380 degrees C and pressures from 1 to 70 MPa is carried out, and the dehydration of aluminum hydroxide under hydrothermal conditions is studied experimentally. The results indicate that gamma-AlOOH (boehmite), which commonly appears in experimental phase diagrams, is a nonequilibrium phase in these temperature and pressure ranges. The dehydration rate and mechanism are shown to strongly depend on the crystallinity of the parent aluminum hydroxide and the pressure in the hydrothermal system.