engleski

The optimization of hydroxyapatite sol-gel processing from triethyl phosphate

Hydroxyapatite, Ca10(PO4)6(OH)2, is suitable material for various biomedical applications due to a good compatibility with the human organism and strong bonding to the bone, of which is primary constituent. Hydroxyapatite is extensively studied with regard to synthesis, characterisation and applications. Sol-gel synthesis routes are of special interest, due to advantages gained through this technique. Hydroxyapatite powders were prepared by sol-gel method using triethyl phosphate, PO(OC2H5)3, and calcium acetate, Ca(CH3COO)2, as initial compounds, and water as solvent. In order to accelerate low hydrolysis rate of triethyl phosphate, hydrogen peroxide (H2O2), phosphoric acid (H3PO4), ammonia solution (NH4OH) and 2-propanole (C3H7OH), were used in course of synthesis. The gels were aged and dried under different conditions: slow aging/drying at room temperature, rapid drying in oil bath at 75°C and decomposition in electrical furnace at 500°C were performed. The evolution of crystal phases after thermal treatment has been detected and characterized by powder X-ray diffraction. The influence of added agents and aging and drying conditions to relative hydroxyapatite quantity have been investigated and compared. The crystallization path was investigated by simultaneous DTA/TGA analysis. It has been established that the crystallization of hydroxyapatite in investigated samples is always accompanied with crystallization of additional crystal phases, CaO being the most prominent among them. It was found that the most effective agent in promoting the hydrolysis of triethyl phosphate is phosphoric acid. The presence of H3PO4 during the synthesis influences the triethylphosphate hydrolysis mechanism. Rapid aging in oil bath at 75°C yields best results providing enough time and energy for reaction. Treatment of crystallized samples with hydrochloric acid turned out to be effective method of undesired calcium phases removal.

DSC/TGA; Hydroxyapatite; Sol-gel; Triethyl phosphate; XRD

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