Cooling DSC Analysis on the Samples of the Water/Ultrafine Oxide Powder

Abstract

The thermodynamic stabilities (i.e., bound strength from the solid surface) of water on the surface of three kinds (alumina, silica and titania) of ultrafine oxide particles were evaluated using the cooling DSC by changing the statistical thickness of water layers t and the crystalline state through heat treatment at high temperature. The water layers on the surface of amorphous particles showed two exothermic peaks on the thermograms. Judging from the relation of peaks and t, one peak P_L at lower temperature resulted from the structural change of the most stable water layer on the surface. Another peak P_H at higher temperature resulted from freezing of quasi-stable water layers, stabilities of which decrease with the distance from the surface of particles towards the bulk state of water. The water layers on the surface of the particles crystallized by heat treatment showed only P_H without peak of P_L. The difference in enthalpy changes Ht on the P_H of the surface water between amorphous and crystalline states of the particles was the most remarkable in silica powder among three kinds of ultrafine powders used in the present experiment.