Sintering of tricalcium phosphate–fluorapatite composites by addition of alumina

The effect of alumina (Al2O3) addition on the densification of tricalcium phosphate–26.52 wt% fluorapatite composites was investigated. The sintering behaviour was investigated using X-ray diffraction, scanning electron microscopy and by analysis using 31P and 27Al nuclear magnetic resonance. The composites sintering alumina additives have been tested in order to enhance their sinterability. When small amount of Al2O3 was added, densification of the tricalcium phosphate–26.52 wt% fluorapatite composites was markedly enhanced. The densification of the pure tricalcium phosphate–26.52 wt% fluorapatite composites was about 87%, whereas it reached 91% with 2.5 wt% Al2O3 at 1300 °C. High temperatures were not very efficient conditions. About 1400 °C, grain growth becomes important and induces an intragranular porosity which is responsible for decrease in density. The 31P and 27Al MAS-NMR analysis of tricalcium phosphate–26.52 wt% fluorapatite composites sintered with Al2O3 additives reveals the presence of tetrahedral P and octahedral Al sites.