INFLUENCE OF THE CALCINATION CONDITIONS O N THE MORPHOLOGICAL EVOLUTION OF HYDROXYAPATITE

An hydroxyapatite powder prepared by coprecipitation was calcined. The se treatments were carried out between 100-degrees-C and 900-degrees-C , in air or under a controlled pressure of water vapor. In the whole r ange a significant decrease of the specific area is observed, but only above 780-degrees-C this surface reduction, controlled by a gaseous t ransport of matter, occurs with densification. Below 780-degrees-C sup erficial mechanisms are working. Grain size distribution is also very dependent upon the calcination conditions; the very broad repartition of the starting powder transforms progressively into a very narrow one . Such an evolution can be interpreted by the coalescence of the small particles through superficial diffusion, while large grains sinter by grain boundary or volume diffusion.