Journal of Advanced Materials in Engineering (Esteghlal)

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Due to its biocompatibility, bioactivity and high durability properties, hydroxyapatite (HA) has a wide range of applications in medical cases such as bone defect treatment and bone tissue regeneration. Biological apatite as the most important integrity of the mineral part of hard tissues consists of tiny hydroxyapatite crystals in nanoregime. It seems that using the artificial hydroxyapatite with similar structure and chemical composition to biological apatite could increase its durability inside the natural hard tissues. The aim of the present work was the synthesis of nano structured hydroxyapatite via different routes, comparison of their characterization and enhancement of the bioactivity and bioresorbability of prepared hydroxyapatite by controlling its crystal size and chemical composition. Nano structured hydroxyapatite was prepared by mechanical activation and sol-gel routes. X-ray diffraction technique (XRD), Fourier transform infra red spectroscopy (FTIR) and transmission electron microscopy (TEM) were used to characterize the prepared hydroxyapatite powders. The synthesized powder was soaked in simulated body fluid (SBF) for various periods of time in order to evaluate its bioresorbability and bioactivity after immersion in SBF. Atomic absorption spectroscopy (AAS) was used to determine the dissolution rate of calcium ions in SBF media. Results showed that the mechanical activation prepared HA powder had nano scale structure with mean size of 29 nm and the sol gel prepared HA powder had nano scale structure with mean size of 25 nm. Ionic dissolution rate of prepared nano structured powders was higher than the conventional HA (with micron size) and were similar to biological apatite. It could be concluded that bioactivity behavior of hydroxyapatite powder is affected by its crystalline size. By using the nano structure HA powder with less than 50 nm crystalline size, the optimum bioactivity and bioresorbability would be achieved.

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In this research, investigation of the microstructure and magnetic properties of doped barium hexaferrite with cobalt, chromium and tin with BaCo_xCr_xSn_xFe_12-3xO₁₉ (x=0.3,0.5) formula, was performed using solid state method. Phase and structural investigation by X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) Spectroscopy respectively, confirmed the formation of barium hexaferrites single phase without the presence of non-magnetic secondary phase after heat treatment for 5 h at temperature of 1000 °C. Also, according to scanning electron microscopy (SEM) images, morphology of particles was perfectly hexagonal with average particle size 200-250 nm. Based on magnetic parameters measured by Vibrating Sample Magnetometer (VSM), both samples were soft magnetic and the highest saturation magnetization was obtained for the sample with composition of BaCo_0.3Cr_0.3Sn_0.3Fe_11.1O₁₉. The values of saturation magnetization (M_s) and the coercivity (H_c) were 42.21 emu/g and 656 Oe respectively for this compound.

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In this study, the effect of Fe/Ba molar ratio was investigated on the phase composition, synthesis temperature, microstructure and magnetic properties of barium hexaferrite prepared via mechanical activation. In order to synthesize this compound, Fe/Ba molar ratios of 12 and 6 were used. The effect of Fe/Ba molar ratio, milling time and heat treatment temperature for achieving the optimal conditions in producing this compound was studied. In order to study the phase, morphology and magnetic properties of the final product, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Vibrating Sample Magnetometer (VSM) were used respectively. According to the results, Fe/Ba molar ratio of 6, 10 h milling time and temperature of 800 °C were found to be the optimal conditions for producing this compound in a single phase. Scanning electron microscopy images show the hexagonal morphology and almost spherical particles respectively for samples prepared with Fe/Ba molar ratio equal to 12 and 6. Moreover, according to the magnetic studies, the maximum amount of saturation magnetization (56.48 emu/g) and the coercivity force (5247.2 Oe) were obtained for the sample synthesized with Fe/Ba molar ratio of 6.