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 alumina 1 , for a polar molecule such as water on these solids, large and complex changes have been observed 2 • Wade and Hackerman, et al. measured heats of immersion for water on Ti02 3 , Si02 4 • 5 , and on Al203 6 • 7 as a function of the outgassing tem~erature and specific surface area. Whalen 8 and Kiselev, et al. • 10 measured heats of immersion of different silica gel preparations and quartz. Holmes, Fuller and Secoy 11 -14 did an extensive study on the theria-water system, investigating the effect of outgassing temperature on heat of immersion and relating it to surface hydration of Th02, Morimoto, et al. 15 -18 , who investigated the ZnO-water system quite extensively by the water vapor adsorption method, have also conducted calorimetric measurements of heats of immersion on several metal oxides. The effect of outgassing temperature on loss of surface water and the heats of immersion were measured on both aand y-alumina 15 , Zn0 16 , Ti02 17 , and a-Fe203 18 The heats of immersion were related to change in surface area on heating and to decrease in water content with