The incorporation of “water” in a high-pressure 2:1 layer silicate; a high pressure differential thermal analysis of the 10 Å phase Available to Purchase

The 10 Å phase, a talc- and mica-like high-pressure phase with excess water relative to talc, was investigated using high-pressure differential thermal analysis at pressures to 5.2 kbar, in order to determine the enthalpy of bonding of the interlayer water species. The reaction involving the removal of the interlayer water species shows a monotonic variation with pressure, increasing from 454 °C at I atmosphere to 632°C at 5.15 kbar. The enthalpy of dehydration ΔH_dh is equal to 200 ± 20 kJ/moL This value is much higher than typical dehydration enthalpies of layer silicates but is similar to dehydroxylation enthalpies. It is proposed that O⁻² occupies the 12-coordinated interlayer site and is stabilized by two resonating protons. This model is consistent with the enthalpy data and previously published infrared and thermogravimetric data. In contrast to an earlier model suggesting H₃O⁺ occupancy of this site, the resonating proton model does not require the interaction of neighboring OH groups in the structure. The implication of this model is that, at high pressures, empty sites in a variety of mineral structures can be occupied by O, charge balanced by resonating protons. This model, therefore, provides a mechanism for the storage of “water” in the earth's mantle.