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.