Cooling DSC Analysis of Vicinal Liquids on the Particles Surface of Several Oxides

Abstract

Thermodynamic stability (i.e., bound strength from solid surfaces) of liquid layer on the surface of several crystalline oxide powders in water or in cyclohexane was evaluated by cooling DSC changing of liquid layer thickness, t. Water was firmly bound by the solid surface and the stability of water layers showed an exponential decrease with a distance from the surface. Two or one exothermal peaks depending on the oxides were detected on the DSC thermogram in water/powder samPLes. In the case of two peaks (PL and PH) occurrence, the PL comes from the water layer of the most stable and the nearest to the surface due to the structural changes during cooling. Onset temperature Tr and peak area Ht of the PL were kept constant in regardless of t. But the PH peak which decreases in Tr and Ht with decrease of t comes from the water layers existing outer area of the PL layers in between the most stable and the bulk free states. The close relation was found between thermodynamic stability of surface water and ionicity in the chemical bonding between cation and anion in respective oxides. On the DSC thermograms in case of cyclohexane, single exothermic peak was detected and the Ht did not show a great change with t of cyclohexane. Therefore the stabilization of cyclohexane layer on the surface of oxides was not observed as in the case of water.