Heats of Immersion of Hydroxyapatities in Water

Abstract

Heats of immersion have been reported for many polar solids of metal oxides and silicates both in polar and nonpolar liquids. These heats have been determined as a function of outgassing temperatures, specific surface areas, and particle size. Usually they are made on the “bare” sample only. However, with most of the hydrophilic metal oxide surfaces, it is not always known whether the surface was “bare” (i.e. completely dehydroxylated) or had some residual hydroxyl groups still on the surface. How “bare” the surface was, would depend greatly upon the outgassing temperature and pressure at which the sample was prepared. Although the heats measured were relatively insensitive to these factors for a nonpolar liquid such as hexane on silica, titanium dioxide, or alumina¹, for a polar molecule such as water on these solids, large and complex changes have been observed . Wade and Hackerman, et al. measured heats of immersion for water on TiO₂ ³, SiO₂ ^4,5, and on Al₂O₃ ^6,7 as a function of the outgassing temperature and specific surface area. Whalen⁸ and Kiselev, et al.^9,10 measured heats of immersion of different silica gel preparations and quartz.