Influence of Two-Step Sintering Variables on Phase Stability of Hydrothermally Prepared HAp Nano Powders

Two-step sintering was performed to prepare hydroxyapatite (HAp) with a high density and a fine microstructure utilizing hydrothermally synthesized nano powders. Its effectiveness was dependent on starting chemicals for precursors of HAp, powder processing condition, initial temperature in the two-step sintering, heating rate to the initial temperature, and holding time at final temperature. HAp powder, hydrothermally treated after aging of precipitate of Ca(OH)2 and H3PO4 for 48 h, led to HAp having a high phase stability at elevated temperatures, a high density, and a fine microstructure after two-step sintering with heating rate of 10°C/min to 1275°C.