Characterization of eggshell-derived hydroxyapatite on Ti6Al4V metal substrate coated by sol–gel method

The aim of this work was to synthesize hydroxyapatite (HAp) by sol–gel route using eggshell and triethyl phosphite as calcium and phosphorus precursors, respectively. After the preparation of homogeneous solution with aging period for 24 h, hydroxyapatite (HAp) sol–gel coatings were made on Ti6Al4V substrate. Polyethylene glycol (PEG) and triethanolamine (TEA) were added to HAp solution to enhance morphological structure of coatings. PEG- and TEA-added solutions and coatings were labeled as P-Hap and T-Hap, respectively. The coating process was carried out by spin coating method, and the coated samples were heated up to 600 °C for 1 h. Phase development of coatings and dried powder and morphologies of coatings upon heat treatment were detected by XRD and SEM, respectively. Thermal behavior of obtained powder were investigated with DTA/TGA. Surface roughness was determined by XP2 surface profilometer. It was found that all the samples at RT showed amorphous structure and transformed at 600 °C to well-crystallized HAp-phase with no β-TCP. Morphological results indicated that T-HAp coating showed the best morphology with crack-free uniform porous structure, which is necessary for biocompatible implants. P-HAp coating showed non-uniform porous structure with large cracks, whereby HAp coatings had similar structure to T-HAp coatings but with much less porosity.