Reactivity towards water of silicon nitride: Energy of interaction and hydration dehydration mechanism

The heat of adsorption and adsorbed amounts of H₂O_(vap) have been measured on an industrial crystalline Si₃N₄ outgassed at 400 and 800° C. A nearly uniform surface is present after the 400° C thermal treatment, where H₂O is adsorbed via hydrogen bonding to surface OH and NH groups with a heat of adsorption of 50 kJ mol^–1. After 800° C thermal treatment, which involves the dehydration and condensation of OH and NH groups, water is readily dissociated at the surface (–H > 50 kJ mol^–1) and the pristine surface is formed on which water is hydrogen bonded again. No hydrophobic patches are detected. The results are discussed in comparison with SiO₂ behaviour in similar conditions.