C Transformation of Hydroxyapatite into beta-Tricalcium Phosphate

4 800-1100 °C Transformation of Hydroxyapatite into beta-Tricalcium Phosphate [p-TCP] 

Heating bone tissue to a temperature of about 750 °C ensures a complete biological decontamination [3]. When the temperature increases above this threshold the start of a complex metamorphic transformation of the bone tissue occurs. The thermal decomposition of stoichiometric hydroxyapatite undergoes at temperatures over 800 °C, with the initial formation of oxy-hydroxyapatite and oxy-apatite, followed by the oxy-apatite decomposition into various forms of tricalcium phosphate and/or calcium oxide [4,48]. An endothermic phenomenon can be identified in the range 800-1000 C, assigned to the modification of the hydroxyapatite crystalline lattice parameters, which takes place shortly before the initiation of its decomposition in beta-tricalcium phosphate [(3-TCP, CajCPO ) ] [49]. 

In the case of biological hydroxyapatite, the transformation into p-TCP occurs at different temperatures depending on the chemical composition of the bone mineral phase and the atmosphere in which the heating takes place [3,12]. 

Other results, obtained by heating bone samples from different species in air atmosphere, showed that the hydroxyapatite transformation starts around 800 °C, along with the identification at 1000 °C of a reduced quantity of calcium oxide while in argon atmosphere the formation of calcium oxide, tetracalcium phosphate and tricalcium phosphate was observed above the 1000 °C temperature. 

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