ADSORPTION OF WATER-VAPOR BY IRON-OXIDES .2. WATER ISOTHERMS AND X-RAY PHOTOELECTRON-SPECTROSCOPY

Comparison between nitrogen and water vapor isotherms on alpha-and gamma-Fe2O3 suggests that at the BET point B stage in both cases the structure of the water adlayer is close-packed and nonlocalized. Significant hysteresis and irreversibility on desorption probably reflect, particularly with gamma-Fe2O3, reaction or rehydration effects. Wide energy (survey) X-ray photoelectron spectroscopy (XPS) scans of haematite and magnetite surfaces show the presence of adsorbed water down to pressures as low as 10(-10) mbar after pumping overnight. This conclusion is confirmed by laser induced ion mass analysis (LIMA) experiments. With magnetite the estimated ratio of surface OH to surface O2- from XPS is about 2.