Direct measurements of water adsorption enthalpy on hafnia and zirconia

A commercial surface area analyzer and Calvet-type microcalorimeter were combined for measurements of heats of gas-solid interactions, providing enhanced resolution, flexibility, and throughput compared to conventional methods. Integral adsorption enthalpies for half monolayer coverage on HfO2 and ZrO2 surfaces were found to be in the range -130-190 and -110-170 kJ per mole of gaseous H2O for differently prepared monoclinic phases and -70 and -90 kJ/mole for tetragonal phases from precipitation. The surface enthalpy for anhydrous tetragonal ZrO2 was derived as 1.23 +/- 0.04 J/m(2) from water adsorption and high-temperature solution calorimetry data. (C) 2005 American Institute of Physics.