Optimization of process variables for the mechanosynthesis of nanocrystalline hydroxyapatite

Abstract

Bone substitute nanocrystalline hydroxyapatite (HAP) has been synthesized through dry mechano-chemical method in a specially designed high-energy dual-drive planetary mill which is able to generate a strong gravitational (around 100g) field inside the planetary mill. Here phosphorous pentoxide and calcium hydroxide powders were used as starting materials for the synthesis of nanocrystalline HAP powders. Different milling parameters like milling time, ball to powder weight ratio, ball size and critical speed of the mill were investigated to optimize the milling process. It has been established in the present investigation that optimum condition for the synthesis of nanocrystalline HAP is achieved when grinding is performed at a critical speed of 60% using 4mm diameter ball at a charge ratio of 20:1 for 15h. Scanning electron micrograph of HAP powder with optimized milling parameter shows that particles are around 100nm in size. Fourier transform infrared (FTIR) spectroscopy of the same powder shows that carbonate is present as an impurity in the sample possibly from the precursor materials. It also shows the presence of water which indicates that absorption of moisture takes place during synthesis.