Solubility of -Ca3(PO4)2 in the system Ca(OH)2-H3PO4-H2O at 5, 15, 25, and 37 C

Abstract

Solu bility isoth erms of beta-trica lcium phos ph ate, j3-Ca3(PO.)" prepared by heating mixtures of CaC0 3 an d CaHP O. above 800°C, were dete rmined in th e tern ary system Ca(OH),·H 3PO.-H 20 a t 5, 15,25, and 37°C in the pH range 6.0-7.5 by equilibrati on with dilute H 3PO ., solutions. The results in dicate that j3-Ca3(P0 4), has a negative therm al coefficien t of solu bility. The solubility produ ct , K" was de termin ed as a fun cti on of te mperature by a ge neral ized least-s qu a res procedure; the res ultin g equ ation is log Ks =-45723. 26/T + 287.4536 -0. 546763 T;th e valu es of K, a nd its dispersion at 25 a nd 37°C are 1.20(0.056), and 0.283(0.011 ) X 10-29. Thermo· dyna mi c fun ctions for the dissolution of the salt at th e four experim enta l te mpe ratures are repo rted. Wh e n treated as an adju stable constant, th e Ca/p ratio in these j3-Ca3(PO.}. solutions was fou nd to have th e value 1.514(0.010), confirmin g th at the stoichi ometry of th e high tempe rature form of thi s salt is correctl y indi cated by the above formula.The co mputed isotherm s at 25°C for se veral calcium phosphates are co mpared; it is shown tha t j3-Ca3(P0 4}, is , next to Ca5(P0 4)aOH, the most stabl e at pH's above 6.36. The singular points of th e j3-Ca3(PO.)2 isotherm with those of CaHP O • . 2H20 and CaHP04 are at pH 's 5.88 a nd 6. 36, respecti vely.

The loss of K, REE, Th, and U from a Martian and a terrestrial basalt by acidic leaching

“…A matrix effect controls the mobilization of the REE. Dissolution experiments have demonstrated that whitlockite dissolves slightly faster than apatite in acidic solution, the rates of both increase with acidity (Gregory et al 1974). The more ready dissolution of REE from whitlockite of Zagami than from apatite of BE-N suggests that the dissolution rate of the matrix material determines the relative amount of REE dissolution.…”

Tailored bioceramics of calcium phosphates for regenerative medicine

“…The pH value of the physiological solution saturated for ¢-TCP was estimated by making a comparison between the calcium concentration in the physiological solution and the solubility curve of ¢-TCP in some aqueous system in previous reports 63) 65) which was simpler than that in the present study. Gregory T.M.…”

“…Gregory T.M. et al 63) reported the temperature dependence of the solubility of ¢-TCP in the system Ca(OH) 2 H 3 PO 4 H 2 O at 5, 15, 25, and 37°C. These solubility isotherms indicated that the solubility of ¢-TCP decreased with increasing temperature.…”

“…The negative logarithm of the solubility product (pK sp = 29.5) for ¢-TCP has been reported previously. 63) previous method. 79) Porous materials of HA and ¢-TCP had cylindrical shapes of 5 mm in diameter and 5 mm in length.…”

“…The pK IAP for ¢-TCP also decreased linearly with increasing pH value. From the pK IAP value and pK sp = 29.5 for ¢-TCP reported previously, 63) the physiological solution would be saturated for ¢-TCP at about pH 6.0. When the pH value is less than 6.0, the solution is unsaturated for ¢-TCP, so ¢-TCP is dissolved in a solution with a pH of under 6.0.…”