Sintering of tricalcium phosphate–fluorapatite composites with zirconia

Zirconia (ZrO2) addition effects on densification and microstructure of tricalcium phosphate–26.52 wt% fluorapatite composites were investigated, using X-ray diffraction, scanning electron microscopy and by analysis using 31P nuclear magnetic resonance. The tricalcium phosphate–26.52 wt% fluorapatite–zirconia composites densification increases versus temperature. At 1300 °C, the composites apparent porosity reaches 9% with 5 wt% zirconia. XRD analysis of the composites reveals the presence of tricalcium phosphate, fluorapatite and zirconia without any other structures. Above 1300 °C, the densification was hindered by grain growth and the formation of both intragranular porosity and new compounds. The 31P MAS-NMR analysis of composites sintered at various temperatures or with different percentages of zirconia reveals the presence of tetrahedral P sites. At 1400 °C, XRD analysis of the tricalcium phosphate–26.52 wt% fluorapatite–20 wt% zirconia composites shows the presence of calcium zirconate and tetracalcium phosphate. This result indicated that partial decomposition of tricalcium phosphate during sintering process of composites when 20 wt% or less ZrO2 was added. Thus, zirconia reacts with tricalcium phosphate forming calcium zirconate and tetracalcium phosphate.