Preparation of Hydroxyapatite and Calcium Phosphate Bioceramic Materials from the Aqueous Solution at Room Temperature

Abstract

A chemical reaction method was used to study the formation mechanism of hydroxyapatite' on the surfaces of Ca 3 (PO 4 ) 3 , Ca 3 (PO 4 ) 3 /Al 2 O 3 , and Ca 3 (PO 4 ) 3 /ZrO 2 ceramic substrates, when these ceramic substrates were chemically reacted with Ca 2+ , PO 4 3 - and OH ions in the different aqueous solutions. With a dipping coating or soaking technique, brushite (dicalcium phosphate dihydrate, CaHPO 4 2H 2 O) was formed on the surface of ceramic substrate in the phosphate acid solution at pH=2.5. After a subsequent solution treatment in a 2.5M of NaOH aqueous solution at 80°C for 1h, brushite coating was converted into hydroxyapatite (HA). Except for the phase change, the morphologies of surface coatings were also progressively changed from the plate-like structure to the network structure as the pH value increased. In the Ca 3 (PO 4 ) 3 /Al 2 O 3 and Ca 3 (PO 4 ) 3 /ZrO 2 ceramic substrates, HA was much easier to form on these substrate surfaces after an alkaline solution treatment, if the volume ratio of Ca 3 (PO 4 ) 3 /Al 2 O 3 or Ca 3 (PO4) 2 /ZrO 2 in the ceramic substrate was 7/3. As to the effect of basicity, HA was much easier to form on the ceramic substrates at pH=12-14 after a subsequent NaOH-containing solution treatment.