The hydration enthalpies of three inorganic porous materials (sepiolite, MCM41 and synthesized allophane) were measured by means of the adiabatic vapor absorption calorimeter. The average hydration enthalpy (−ΔHh) were in the order, allophane (−57kJ/mol)<sepiolite (−54kJ/mol)<MCM41 (−49kJ/mol) when the samples were hydrated for 10 minutes in the calorimeter, after dehydration in vacuum at 100°C. Samples with smaller pore radius give the larger absolute values of the hydration enthalpy (−ΔHh). The −ΔHh values of sepiolite increased with dehydration temperature and decreased with hydration duration, whereas that of MCM41 remained almost constant regardless of dehydration temperature and hydration duration. The hydration rates for these samples were large in the early stage, but quickly lost the rate. The hydration state of the porous materials with large voids is concluded being similar to that of free water.
Synthetic single crystal forsterites have been shocked up to 82GPa and examined by profile analysis of Raman spectra. Raman bands due to Si–O external vibrations of translational and rotational modes are shifted to higher frequencies with the increase of shock pressure without band broadening. At the internal vibration of Si–O stretching modes, the bands show no shift up to 46GPa, while above that pressure they are shifted to the higher frequencies with distinguishable band broadening. Although Mg(M2)–O translational band is not shifted, its band broadening increases linearly with increasing shock pressure. Over the shock pressure of 46GPa, the Mg–O band is shifted gradually to the lower frequencies as opposed to that all of the internal bands of υ 1 to υ 4 have tendency to move to higher frequencies, whereas the Mg–O band width is doubled. These variations indicate that the lattice deformation resides heterogeneously in the crystal structure of the shocked forsterite, in which the SiO4 tetrahedron is compressed differently between the pressure ranges below and above the 46GPa in the plastic region. In the lower shock region, plastic deformation is caused mainly by the translational and rotational strain, while over the shock pressure of 46GPa, abrupt plastic changes occur in both tetrahedral and octahedral polyhedra, causing positive and negative residual stresses in the structure, respectively. The transition pressure of 46GPa coincides nearly with the onset pressure of phase transition, 50GPa, on the pressure-density Hugoniot of shocked forsterite (Syono et al., 1981).
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