Influence of Heat Treatment on the Phase Composition of Biphasic Calcium Phosphates for Biomedical Application

The aim of the present paper is to study the influence of the heat treatment on the phase composition of biphasic calcium phosphates (BCPs) for biomedical applications. The precursors were prepared by the wet precipitation method using calcium nitrate tetrahydrate and diammonium hydrogen phosphate. The as-synthesized powder was subjected to heat treatment at different temperatures and times. Qualitative and quantitative analyses of the phase composition were done by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). A comparative analysis of the phase composition of the obtained BCPs was performed. It was found that the as-synthesized precursor was characterized by a biphasic brushite/monetite structure. The heat treatment at 700°C caused the formation of a triphasic structure of monetite, β-calcium pyrophosphate (β-CPP), and β-tricalcium phosphate (β-TCP). Heat treatment in the temperature range of 900°C-1300°C led to a change in the precursor's phases. The structure of the heat-treated powders was biphasic, consisting of β-CPP as the main phase and β-TCP. Increasing the calcination temperature led to an increase in the β-TCP amount from 23.5 % at 900°C up to 36.5 % at 1300°C and a decrease in the β-CPP amount from 76.5 % to 63.5 %, respectively. The holding time in heat treatment did not strongly influence the phase ratio. Increasing the duration leads to a variation in the β-CPP/β-TCP ratio within a very tight range: 76.8/23.2% to 73.4/26.6%. The new data on the influence of heat treatment on the β-CPP/β-TCP ratio can be used for optimizing process parameters in the design of new BCPs for biomedical applications.