Papers by Author: Reza Ebrahimi-Kahrizsangi

Abstract: The mechanical activation was employed to study the phase evolution of the Mg–TiO2–CaHPO4–CaO nanocrystalline system. The powders mixture with certain weight percent was grinded. Thermal annealing process at 650°C, 900°C and 1100°C temperatures resulted in generation of different compounds like MgTiO3/MgO/Hydroxyapatite (HAp) and MgTiO3/MgO/β-TCP and MgTiO3/Mg2TiO4/MgO/β-TCP, respectively. The compounds were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). The consequences of XRD analysis revealed that by increasing temperature, some composites with different morphological and structural features were detected. Beside, due to decomposing of HAp around 800°C, HAp converted to whitlockite (β-TCP) with growth of temperature. According to SEM and TEM observations, it was found that the synthesized powder contained large agglomerates which significant content of finer particles and agglomerates with spherical morphology. Because magnesium titanates based dielectric materials are useful for electrical applications, the electrical property of HAp has been proved, and the incorporation of these materials could result in new nanocrystalline dielectric materials.

Abstract: Hydroxyapatite (HAp) is an important bioactive ceramic that possessing beneficial biocompatibility and osteoconductivity resulting in bonding to human bone tissues. The dry mechanochemical process is widely used to prepare nanometer HAp. However, little research has been carried out concerning the correlation between adding alumina and the structural changes during the mechanochemical process. In this research, special attention was paid to the effect of alumina additive on the crystallite size and lattice strain of nanocrystalline HAp. Characterization was accomplished by using powder X-ray diffraction (XRD). The obtained data demonstrated that the diffraction lines corresponding to the HAp phase became broad and weak with increasing alumina additive. In fact, the nanocrystalline HAp with high crystallinity degree can be synthesized in the proper amounts of alumina additive via mechanochemical method. Furthermore, an increase of alumina additive led to increase in lattice strain and decrease in size of the powder grain.

Abstract: Among various biocompatible materials, hydroxyapatite (HA) is widely used in medical applications. Hydroxyapatite can be used as temporary substitute material for the human bone. Despite of the risk of contamination during milling, the mechanochemical method shows higher reproducibility and low processing cost. In this investigation, the mechanochemical method has been carried out to produce nanocrystalline powders of hydroxyapatite using two experimental procedures (HA1: CaHPO4 + Ca (OH) 2; HA2: CaCO3 + CaHPO4) in polymeric and metallic vials at different milling time. The Effects of milling time, milling media and also chemical composition of initial materials on the crystallinity and morphological properties of obtained materials using X-ray diffraction (XRD) and transmission electron microscopy (TEM) were studied. Appropriate equation and graphs for determining crystallinity degree were used. The obtained results show that the crystallites sizes are within the nanometer range and also indicated that nanocrystalline hydroxyapatite with spherical morphology and high crystallinity degree can be produced much better in polymeric vials; therefore using polymeric vials with high wear resistance can have better performance during the mechanochemical process for the production of high quality nanocrystalline hydroxyapatite. Further work is needed to expand the idea for mass production.

Abstract: Mechanochemical process in polymeric vials has been carried out successfully to produce nanocrystalline hydroxyapatite (HAp) through two different reactions R1 and R2. Morphological properties and structural evaluation of obtained materials are studied by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM). The obtained data show that the increase in milling time leads the increasing in lattice strain and decreasing in crystallite size. The average crystallite size of HAp is below 20 and 23 nm for R1 and R2 reactions, respectively. Based on XRD patterns and SEM/TEM micrographs, the possible formation mechanism of nanocrystalline hydroxyapatite by mechanochemical process in polymeric milling media is confirmed. Final results indicate that the nanocrystalline hydroxyapatite with low chemically stable contaminations and suitable morphology can be produced in Polyamide6 vials similar to stainless steel vials, therefore it seems that using polymeric vials could lead to a new way for the mass production of nanocrystalline hydroxyapatite with high performance, low contamination and cost and also suitable morphology.