COOLING DSC ANALYSIS OF VICINAL LIQUIDS O N THE PARTICLES SURFACE OF SEVERAL OXIDES

Thermodynamic stability (i.e., bound strength from solid surfaces) of liquid layer on the surface of several crystalline oxide powders in wa ter or in cyclohexane was evaluated by cooling DSC changing of liquid layer thickness, t. Water was firmly bound by the solid surface and th e stability of water layers showed an exponential decrease with a dist ance from the surface, Two or one exothermal peaks depending on the ox ides were detected on the DSC thermogram in water/powder samples, In t he case of two peaks (P-L and P-H) occurrence, the P-L comes from the water layer of the most stable and the nearest to the surface due to t he structural changes during cooling, Onset temperature Tr and peak ar ea Ht of the P-L were kept constant in regardless of t. But the P-H pe ak which decreases in Tr and Ht with decrease of t comes from the wate r layers existing outer area of the P-L layers in between the most sta ble and the bulk free states, The close relation was found between the rmodynamic stability of surface water and ionicity in the chemical bon ding between cation and anion in respective oxides, On the DSC thermog rams in case of cyclohexane, single exothermic peak was detected and t he Ht did not show a great change with t of cyclohexane, Therefore the stabilization of cyclohexane layer on the surface of oxides was not o bserved as in the case of water.