Portal de Periódicos da CAPES

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

1974; The National Institute of Standards and Technology; Volume: 78A; Issue: 6 Linguagem: Inglês

10.6028/jres.078a.042

2376-5704

Thomas Grégory, E.C. Moreno, J M Patel, W. E. Brown,

Chemical and Physical Properties in Aqueous Solutions

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.)2isotherm with those of CaHP O • .2H20 and CaHP04 are at pH 's 5.88 a nd 6. 36, respecti vely.