Preparation of Nano-hydroxyapatite Particles by Ultrasonic Method at 25 kHz Using Natural Rubber Latex as a Templating Agent

Abstract

Natural rubber latex (1% DRC) was used as a templating agent for the preparation of nano-hydroxyapatite (HAp) powder using an ultrasonic technique at a constant temperature of 25oC (25 kHz). Di-ammonium hydrogen phosphate ((NH4)2 HPO4) and calcium nitrate tetrahydrate (Ca(NO3)2.4H2O) were used as starting materials. The study investigated the effects of increasing sonication time (0, 20, 40 and 60 min) and effect of Ca:P ratios (1.67 and 1.50) on the properties of calcium phosphate (Ca10−x(HPO4)x(PO4)6−x(OH)2−x, x = 0 and x = 1). To obtain HAp, latex containing calcium phosphate was dried at 60oC and calcined at 600oC for 2 hours. The thermal properties, crystallinity, functionality and morphology of the powders were evaluated using thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform Raman spectroscopy (FT-Raman) and transmission electron microscopy (TEM). The XRD results confirmed formation of mixed phases of HAp and β-TCP in all synthesised HAp samples. Both the crystalline size and crystalline material fraction (as %) of x = 0 were higher than for x = 1. After 20 minutes, these two properties tended to decrease with increasing sonication time. FT-Raman studies also revealed the presence of OH- in the hydroxyapatite phase with longer sonication times, with the ((PO-34)) mode (962 cm-1) being present for both x = 0 and x = 1. TEM images demonstrated decreasing HAp particle diameters with increasing sonication time. These subsequently formed longer, nano- rod-like shapes in the case of calcium-deficient HAp (x = 1).