The thermal lattice expansion of calcium hydroxyapatite

Abstract

In this paper the thermal expansion of the lattice parameters a and c of a pure calcium hydroxyapatite prepared from aqueous solutions is determined and discussed. The lattice parameters were determined at different temperatures up to 600°C using a Guinier-Simon focussing scanning camera. In the temperature range RT to 600°C, the expansion of the lattice parameters is linear with temperature. The numerical values of Δ a / a and Δ c / c per degree are 12.2×10 -16 and 11.5× 10 -6 C -1, respectively. The thermal expansion values are different from hydrothermally produced calcium hydroxyapatites. Apatite from the same batch was investigated by means of IR techniques and by DTA-TGA analysis. The IR results show no noticeable CO 3 peak at 1410 cm -1, and a small peak due to HPO 2- 4 at 875 cm -1. After heating the HPO 4 peak disappeared. The combined results of X-ray, IR and thermal analysis indicate an HPO 4 content of 3–4 wt%. The HPO 4 is most likely adsorbed onto the crystal surfaces in about a monomolecular layer.