Papers by Author: Hamid Reza Rezaie

Abstract: The use of hydroxyapatite (HA) coating on metallic implants has always been a challenge due to a discrepancy between ceramic coating and metallic substrate properties. In this study, functionally graded TiO₂-HA coating (FGC TiO₂-HA), with bottom-up composition: 100% TiO₂, 50% TiO₂ -50% HA, 100% HA, produced by sol-gel method on the Ti-6Al-4V alloy substrate. The XRD, FTIR and DSC results signified desired phase achievement. The quality assessment and scratch resistance of FGC TiO₂-HA in comparison with control samples (single-layer HA and double-layer TiO₂-HA coatings) were assessed by SEM and FESEM images and nanoscratch test. According to the tests outcomes, The TiO₂ intermediate layer increases the HA coating’s strength (22%) and surface hardness, while gradient layer of TiO₂-HA improves (14%) this consequence by progressing the coating integrity.

Abstract: Zirconium carbide (ZrC) has extended application in many ceramic and metal matrix composites especially used for ultra high temperature conditions. The synthesis of zirconium carbide powder is costly and difficult because of its high refractoriness and chemically inert properties. In this research, the synthesis of zirconium carbide nanopowder at low temperature via carbothermal reduction route was investigated according to thermodynamic data. The starting materials were zirconium acetate and sucrose as zirconium and carbon sources, respectively. After preparation of different carbon/zirconium ratio containing precursors, the dried precursors were heat treated at 1400°C and vacuum atmosphere. Also the ZrC formation was followed by thermal analysis of the produced precursors. The phase evolutions and microstructural studies were carried out using X-ray diffraction and scanning electron microscopy. The results showed that it is possible to synthesis zirconium carbide nanopowder with round shape and crystallite sizes smaller than 20 nm at low temperatures. Also according to thermodynamic calculations, it was concluded that by applying vacuum condition, the zirconium carbide formation can occur at less than 1000°C which is very effective on the size reducing of produced ZrC nanopowders.

Abstract: Tantalum and hafnium carbides are classified as Ultra High Temperature Ceramics (UHTC) because of their extreme melting temperatures (above 3900°C). Therefore, these materials can safely operate in the range of temperature that any other materials could hardly exist. However, these applications can be strongly restricted due to (1) processing difficulties and (2) low fracture toughness. In this work, to address these two difficulties we have used two additives, which are multi-walled carbon nanotubes (CNTs) and molybdenum disilicide (MoSi₂). The CNTs were added aimed to improve the fracture toughness of the composites, and the MoSi₂ to facilitate sintering. Application of such a sintering aid, add to the novel SPS technique, allowing quick processing at relatively lower temperature, results in (1) fully densified specimens (> 99%) and (2) well-surviving CNTs after sintering. Moreover, microstructural analysis points out fair-enough dispersion of the CNTs within the ceramics particles, in both the green and sintered bodies. Also the specimens phase characterization shows inter dissolution of TaC and HfC and formation of binary carbides solid solution.

Abstract: In this research Cu-Ni nanostructure powders were prepared by using a chemical procedure including initial precipitating, calcining the precipitates and reducing the calcined powders. The influence of nickel contents on the characteristics of the synthesized powders was investigated. Copper and nickel sulfate and sodium hydroxide were used as raw materials. CuSO4.3Cu(OH)2, NiOOH and Ni(OH)2 precipitates were obtained by addition of sodium hydroxide into aqueous copper and nickel sulfate solution. Oxide powders were produced by calcinations of precipitates. Considering the information obtained from the TGA test, calcination was done on precipitates. Copper-nickel nanostructure powders were synthesized by reduction of calcined powders in a hydrogen atmosphere. Eventually powders were characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Crystallite size of final synthesized powders was in the range of 30 to 33 nm.

Abstract: A homogeneous precipitation process was employed to prepare nanosized W-10%wtCu-10%wtAg powders using ammonium meta tungstate, copper nitrate and silver nitrate as precursors. The initial precipitates were obtained by reacting ammonium meta tungstate, copper nitrate and silver nitrate solutions under certain PH and temperature. In order to synthesis W-Cu-Ag composite powders, the initial precipitates washed, dried, and then calcined in air in order to prepare CuWO4-x, Ag2W4O13 and WO3 oxide powders for the next step reduction. The reduction was carried out in a hydrogen atmosphere to form the final W-Cu-Ag nanocomposite powders. The powders were characterized by X-ray diffraction (XRD) technique. The morphologies of the powders were observed by scanning electron microscopy (SEM).

Abstract: In the present article, α-Al₂O₃ nano powder was synthesized by a simple aqueous sol–gel method by using AlCl₃ as precursor. It was shown that the gel calcined at 1000°C, 1100 °C and 1200 °C resulted in the formation of a crystalline α-Al₂O₃ nano powder. In continue TEOS and saccharose was used to prepare SiO₂ xerogels containing carbon nano particles. The conversion of the gel to β-SiC nano powders was accomplished by carbothermal reduction at 1500°C for 1 h in argon atmosphere. In second pace alumina matrix composites with nano particles of 5 vol% SiC were prepared with the addition of TiO₂ as sintering aid and densified by pressureless sintering method at 1600°C and 1630°C for 2 h in nitrogen atmosphere. Green pellets were obtained by uniaxial pressing of 137 MPa. Maximum density (97.3%) was achieved at 1630°C. Vickers hardness was 16.5 GPa after sintering at 1630°C. Scanning electron microscopy revealed that the SiC particles were well distributed throughout the composite matrix. The precursors and the resultant powders were characterized by X-ray diffraction (XRD), thermal analysis (STA) and scanning electron microscopy (SEM).

Abstract: A new porous structure as a bone tissue engineering scaffold was developed by a freeze-drying method. The porous nanocomposite was prepared from Biphasic Calcium Phosphate (BCP) which was a mixture of 70% hydroxy apatite and 30%ß-TCP (ß-Tricalcium Phosphate). Porogen was naphthalene and gelatin from bovine skin type B was used as polymer. Gelatin was stabilized with EDC (N-(3-dimethyl aminopropyl)-N´-ethyl carbodiimide hydrochloride) by a cross-linking method. The scaffold was characterized by scanning electronic microscope (SEM), Fourier-Transformed Infrared spectroscopy (FTIR). The biocompatibility of this nanocomposite carried out through MTT (3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide, a tetrazole) cell viability assay. Also other properties of scaffold such as morphology, grain size, bending strength were investigated. Highly porous structure with interconnected porosities, good mechanical behavior and high biocompatibility with bone tissue, were benefits of this porous nanocomposite for bone tissue engineering.

Abstract: W-25%Cu nanocomposite was produced via a thermochemical co-precipitation procedure. Copper nitrate and sodium tungstate salts were used as Cu and W containing precursors respectively. Aqueous solutions of these salts were reacted under controlled pH condition prepared by ammonia addition and the resulting precipitates were then calcined at 450oC and hydrogen reduced at 800oC. The products of each step were characterized by XRD and Electron Microscope. Using a basic medium with a pH of 13 which caused the formation of complex Cu(NH3)42+ was found to provide suitable condition for precipitation of nanosized composite powders. Cu2WO4(OH)2 and CuWO4.2H2O as raw precipitates, CuWO4-x , CuO, and WO3 as calcined powders, and W-Cu reduced composite powders, all were seen to keep nanosize dimensions through high temperature treatments of fabrication. Sintering of the reduced powders at the temperature of 1150oC led in a density of about 98% theoretical density.

Abstract: Fabrication of alloys in the solid state via mechanical alloying (MA) process has been studied by earlier researchers. The effects of milling time and impact force, defined as the ball-to-powder weight ratio (BPR), on the elemental diffusion during synthesis of nanostructured Fe-50at.%Cu alloy via MA process were evaluated in the current work. X-ray diffraction patterns revealed that increasing the milling time and impact force give rise to increasing the micro-strain, lattice parameter and decreasing the crystallite size during the MA process. Furthermore, scanning electron microscopy (SEM) was utilized not only for evaluating the microstructure of the milled powder particles but also for proving this claim that during MA process, the mutual diffusion of Cu and Fe has occurred. The interpretation of data resulted have been discussed in details.

Abstract: The effects of volume fraction at different milling times and impact forces, defined as the ball-to-powder weight ratio (BPR), on the elemental diffusion during mechanical alloying process of Al-4.5wt%Cu/SiC composite were evaluated and compared with the SiC free samples (Al-4.5wt%Cu alloy) in the current work. X-ray diffraction patterns of the monolithic and composite samples imply the fact that a higher level of mutual diffusion of constituents, Al and Cu, happened in the matrix in the presence of SiC particles. This effect of the reinforcing particles can be attributed to the increased densities of dislocation and vacancy caused by the presence of SiC particles within the matrix giving rise to increasing the micro-strain, lattice parameter and decreasing the crystallite size.