Pressureless sintering of fluorapatite under oxygen atmosphere

Fluorapatite (Fap) is prepared by precipitation method and sintering in the temperature range 640–1365°C. Linear shrinkage starts at about 715°C and the material reaches its final density at 890°C. Above this value, grain growth becomes important and induces an intragranular porosity which is responsible for density decrease. At 1180°C, a liquid phase is formed as a result of the formation of a binary eutectic between Fap and fluorite contained in the powder as impurity. This liquid phase further promotes the coarsening process and induces formation of large pores at high temperatures.