Optimization of milling parameters for the mechanosynthesis of nanocrystalline hydroxyapatite

• Nanocrystalline HAP has been synthesized by mechanochemical reaction.
• Powders of around 50–100 nm size can be prepared after 15 h of milling.
• The Ca/P atomic ratio of HAP is close to stoichiometric ratio of HAP i.e. 1.66.

Here we report synthesis of nanocrystalline hydroxyapatite (HAP), a bone substitute, through dry mechano-chemical method using phosphorous pentoxide and calcium hydroxide powders as starting materials, in a specially designed high-energy dual-drive planetary mill which is able to generate a strong gravitational (around 100 g) field inside the planetary mill thereby reducing the synthesis time significantly. Effects of various milling parameters such as milling time, ball to powder weight ratio, ball size and critical speed of the mill were investigated to understand their effect on the milling process and formation of nanocrystalline HAP. The study shows that the optimum conditions for the synthesis of nanocrystalline HAP is achieved when grinding is performed at a critical speed of 60% using a 4 mm diameter ball at a charge ratio of 20:1 for 15 h. X-ray diffraction and Fourier transform infra red (FT-IR) analysis confirmed phase purity of the nanocrystalline HAP powders. Electron microscopy of the milled HAP powder shows that powder particles are spherical and around 100 nm in size.

• Nanocrystalline hydroxyapatite powders were synthesized through dry mechano-chemical method in a specially designed high-energy dual-drive planetary mill from phosphorous pentoxide and calcium hydroxide powders.
• The powders were characterized by different characterizing techniques like x-ray diffraction, scanning electron microscopy, transmission electron microscopy, laser particle size analyzer, Fourier transformed infrared spectroscopy, chemical analysis, differential thermal (DT) and thermo-gravimetric (TG) analysis.
• It takes only 15 h to prepare nanocrystalline HAP powder. The average particle size of the synthesized hydroxyapatite powder is less than 100 nm.XRD pattern of standard hydroxyapatite and powders milled with 4, 6, 8 and 10 mm diameter balls after 15 h of millingFigure optionsDownload as PowerPoint slide