Temperature effects on characterizations of hydroxyapatite films prepared by sol-gel method

Abstract

In the thesis, hydroxyapatite (HAp) was synthesized in the form of powder and thin film by the sol-gel technique. The spin coating method has been used for the deposition of HAp layer on silicon and stainless steel 316L substrates. The HAp films were annealed at 300, 500, 700, 900 and 1,100 ℃. The results showed the structure development toward more crystalline with an increasing of the temperature. The HAp phase decomposed to β-TCP phase at 1,100 ℃. The SEM micrographs showed that the crystal size increased with an increasing of annealing temperature to 1,100 ℃ and the microstructure of HAp contained a porous structure. The average values of hardness and elastic modulus of HAp films are about 1.2 and 35 GPa, respectively, no significant effects to the annealing temperatures. Strontium-substituted hydroxyapatite (SrHAp) was fabricated to improve a special property. Increasing Sr substitution for Ca exhibited the expansion of the crystal structure, explained by a linear increasing in lattice parameters. The microstructure of SrHAp film annealed at 300 and 500 ℃ exhibited almost rod shape, and then grain size expanded at high annealing temperature with a development of cross-linking structure. The HAp/TiO₂ composite films were also prepared by adding 20% volume of TiO₂ particle to HAp sol. From XRD results, phase of TiO₂ was anatase at temperature below 500 ℃ and transformed to rutile phase at above. The TiO₂ particles can be seen in nano-size linking with HAp structure. HAp was reinforced by TiO₂ inclusions resulting an increasing in hardness and elastic modulus.