Chiang Mai Journal of Science

 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 25^oC (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 (Ca_10−x(HPO₄)_x(PO₄)_6−x(OH)_2−x, x = 0 and         x = 1). To obtain HAp, latex containing calcium phosphate was dried at 60^oC and calcined at 600^oC 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).