New Approach to the β→α Polymorphic Transformation in Magnesium‐Substituted Tricalcium Phosphate and its Practical Implications

The transformation β→α in Mg-substituted Ca3(PO4)2 was studied. The results obtained showed that, contrary to common belief, there is, in the system Mg3(PO4)2–Ca3(PO4)2, a binary phase field where β+α-Ca3(PO4)2 solid solutions coexist. This binary field lies between the single-phase fields of β- and α-Ca3(PO4)2 solid solution in the Ca3(PO4)2-rich zone of the mentioned system. In the light of the results and the Palatnik–Landau's Contact Rule of Phase Regions, a corrected phase equilibrium diagram has been proposed. The practical implications of these findings with regard to the synthesis of pure α- and β- Mg-substituted Ca3(PO4)2 powders and to the sintering of related bioceramics with improved mechanical properties are pointed out.