ИСТИНА

Nowadays, calcium phosphate bone implants are of great interest bearing in mind their prin- cipal biocompatibility and well-elaborated processing routes. Such materials should be, at least, rather resorbable and facilitate newly bone ingrowth (osteoconductivity). At present, hydroxyapatite (Ca10(PO4)6(OH)2) and tricalcium phosphate (Ca3(PO4)2), the former is less resorbable, are used to treat the damaged bones. Low resorption rate of hydroxyapatite means that an implant cannot dissolve in time and a bone de-novo grows up on implant surface leading to increase of probability of fracture. One of the way to increase resorption rate (that means to increase solubility) of the implant is to enlarge its molar volume (in fact, cell volume of materials lattice). From this viewpoint, a replacement of a part of calcium ions in tricalcium phosphate lattice to sodium or/and potassium one follows such a strategy very well. In this case, Ca3-x(KyNa1-y)2x(PO4)2 can be regarded as almost ideal composition for such an intent. In this study we determined phase relationships in the system of CaKPO4 - CaNaPO4 and described an intermediate phase noted us as X, having a range of its homogeneity and the temperature of its phase transition about 657 °C. As revealed by SEM, ceramics based on these compositions demonstrated domain-like microstructure resulted from phase transfor- mation of complex nature. Strength properties of the ceramics under study was measured by B3B method. Decrease of strength value for x = 0.5-0.7 was attributed to phase transformation accompanied by volume changes. Dissolution behavior of the CaKxNa1-xPO4 ceramics in model solutions at constant pH was studied and compared with other calcium phosphates as well as thermodynamic predictions.