Role of Annealing Temperatures on Mechanical, Optical, Electrical and Magnetic Properties of Nanohydroxyapatite Biomaterial

Nanosized hydroxyapatite [Ca₁₀(Po₄)₆(OH)₂ or HAp] was prepared by applying wet-chemical precipitation technique. Thermogravimetric and Differential Scanning Calorimetry (TG/DSC) analyses, showed that the prepared sample was stable up to 919.2 °C. X-ray diffraction (XRD) pattern showed that as-prepared and annealed samples are in hexagonal structure. The average crystallite size is found to be 39, 46, 51 and 65 nm for the as-prepared, 700, 800 and 900 °C annealed HAp respectively. The dislocation density, strain and surface area were decreased with increase in annealing temperature. FT-IR and Raman spectra showed both as-prepared and annealed samples having characteristic bands of HAp. FE-SEM and TEM images which depicted and confirmed the hexagonal structure of HAp. The optical band gap calculated from the UV absorption behavior of as-prepared and annealed at 700, 800 and 900 °C HAp are 3.86, 3.84, 3.54, and 3.03 eV respectively. As the annealing temperature increases, the conductivity decreases whereas the impedance increases. The ac conductivity of as-prepared and annealed samples are in the order of 10^-5 Sm^-1. The VSM analysis confirmed that both as-prepared and annealed samples of HAp are in diamagnetic nature. The antibacterial activity of apatite samples depend on the types of bacterial strains and also their activity changed with the crystallite size.