Effect of reaction time, heating and stirring rate on the morphology of HAp obtained by hydrothermal synthesis

Abstract

Hydroxyapatite (HAp) whiskers were prepared in reaction of calcium lactate pentahydrate and orthophosphoric acid. Synthesis were carried out in different conditions with using hydrothermal reactor. The benefit of the hydrothermal technique is the simple and precise control of the HAp crystals morphology, which is achieved by employing varying initial concentrations of starting reagents as well as different conditions of synthesis. The effect of time of synthesis, stirring and heating rate of the reaction on HAp morphology and composition was investigated. During the synthesis the following experimental parameters were varied independently: time of synthesis (3, 5, 7 h), stirring rate (0, 62.5, 125, 250, 500, 750 rpm), the reaction heating rate (0.2, 0.5, 0.7, 1.0, 1.5, 2.5 °C min−1). All syntheses were carried out with the constant molar Ca/P ratio of 1.67 in starting solutions, which is equivalent to that of stoichiometric HAp. The Ca2+ ion concentrations in starting solutions for synthesis were 0.05 and 0.1 mol dm−3. Syntheses were carried out under 20 bar. The obtained products were characterized using different method like XRD, SEM, and FTIR. It was shown that the significant majority of samples prepared were identified as pure HAp.