Synthesis of Hydroxyapatite Nanostructure by Mechanical Alloying Procedure

Synthetic hydroxyapatite (HA, Ca10(PO4)6(OH)2) has long been recognized as one of the most important bone substitute materials in orthopaedics and dentistry over past few decades because of its chemical and biological similarity to the mineral phase of human bone. A remarkable property of the synthetic HA is its bioactivity, in particular the ability, e.g. after implantation, to form chemical bonding with surrounding hard tissues [1].Several wet and dry procedures can be used to produce HA. The advantages of the wet process are that the by-product is almost water and the possibility of contamination during processing is very low. However, the disadvantages are the composition of the resulting product is greatly affected by even a small difference in the reaction conditions. Therefore, the handling of the materials and the operation of the equipment become complicated, so they lead to poor reproducibility and high processing cost. When producing high crystalline hydroxyapatite, the dry process is more suitable than the wet process because it displays high reproducibility and low processing cost in spite of the risk of contamination during milling [2].Mechanical alloying has been used for almost two decades to produce many unique materials [3], For example: nanostructured alloys, unstable and meta-stable phases and amorphous compounds. Mechanical alloying is a dry milling process in which a metallic and/or nonmetallic powder mixture is actively deformed in a controlled atmosphere, under a highly energetic ball charge, to produce materials [4]. The reaction is activated by mechanical milling: the reactants are crushed between balls or ball and wall. They absorb part of the energy provided by the collisions which allow their reaction.