711. The heats of formation of fluorapatite and hydroxyapatite

Preparation and solubility of hydroxyapatite:

“…-15-Although the weight loss in our sample was not measured, slight weight losses have been reported^in the range 3/300°C-3 / 100°C for synthetic HA samples heated gradually from 25°to 3/200°C; these losses occurred without alteration in their x-ray patterns 0 Also, it has been reported^-3" that at 3 The x-ray powder diffraction pattern of the air-heated sample was the same as that of HA, but it is impossible to rule out a partial disproportionation.…”

“…A more refined method was devised, therefore, for these calculations which entails the simultaneous adjustment of the weighted observables--i. [3] in which M and P are the total molar concentrations of Ca and P in solution, respectively 7 [7] In equations [4][5][6][7] The three condition functions, equations [1] to [3], are based on electroneutrality, the solubility product for HA, and congruency in the dissolution of the solid, respectively. These three conditions were used to obtain the best estimates of Ksp for the preheated hydroxyapatites (in air and steam) .…”

“…Condition [3] defining stoichiometric dissolution, was excluded for the calculations with HA "as prepared" because phosphate was adsorbed in some of these equilibrations, as explained in section 5.1.…”

“…transfer of reagents and materials was done through the other two necks* The top of the condenser was connected by a glass tube to a 6-liter, 3-neck flask containing 3 liters of 10 N NaOH solution? a check valve permitting outward flow of gases was connected to one neck and a tube, extending into the NaOH solution and acting as a relief valve, entered through the third neck.…”

Solubility of hydroxylapatite and some phosphate rocks

“…The negative logarithm of the solubility product constant (pK) that was obtained was 113.7. Gottschal (1958), Smirnova et al (1962), and Jacques (1963) have published values for the heat of formation of hydroxylapatite. Their values, with the entropy value given by Egan et al, give pK values of 130, 116, and 129, respectively.…”