نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 22 (پاییز 1391)

In this study, Tantalum carbide (TaC) nanoparticles was synthesized through the gas - solid reaction by chemical vapor deposition (CVD) method using carbon nanotubes as the carbon source. The structure of samples were studied by Transmission Electron Microscopy (TEM), Field Emission-Scanning Electron Microscopy (FE-SEM), X-Ray Diffraction (XRD) and Raman Spectroscopy. The thermal behavior of the nanoparticles were examined by TG-DTA thermal analysis. Studies indicated that during the reaction, TaC nanoparticles was formed with quasi-spherical morphology and grain size range of 30-40nm. Also, using phase and thermal analysis, the formation mechanism of Tantalum carbide nanoparticles were discussed with regarding to the role of carbon nanotubes.

Sialon ceramics are widely used in industrial applications because of high corrosion and oxidation resistance and high temperature properties. On the other hand, due to high costs of processing and raw materials, these materials used for special applications. The oxidation resistance of sialons is higher than that of Si3N4. Comparison between sialons showed that the highest amount of oxygen is available in x phase, therefore the oxidation resistance of x phase is higher than the others. X-sialon exhibits excellent chemical stability in contact with iron-based alloys at 1200°C. In this research, andalusite, kaolin, elemental Si powder and α-alumina were used as raw materials and the effects of aluminosilicate sources on the SRN process for x-sialon formation, with and without Y2O3, were studied. In order to study x-sialon formation, the samples were analyzed by XRD in different temperature and the reaction sequence of samples of andalusite precursor determined by DSC results. Results showed that in spite of more nitridation of Si in kaolin precursor samples, Y2O3 restricted nitridation process in all samples. In overall view, andalusite is more suitable precursor for x silaon formation via SRN process in comparison with kaolin, and Y2O3 leads to facilitate formation of x sialon from reaction between mullite and Si3N4. α-alumina is not appropriate source to supply lack of Al in component and it remains especially in kaolin precursor samples.

In this study the effect of heat treatment on the hardness and wear resistance of electroless Ni-P/Ni-B-BN composite Coating was evaluated. Firstly electroless Ni-P Coating layer, with a thickness of 15 microns, and electroless Ni-B-BN coating, with a thickness of 10 microns, on the surface of Ck45 steel samples were deposited, respectively. Samples heat treated at 300, 400 and 500 °C were studied. The effects of heat treatment on the morphology, microstructure and wear behavior of coatings were investigated by means of scanning electron microscopy, X-ray diffraction and pin on disk wear test at ambient temperature. The hardness of the coatings in two states before and after heat treatment were measured by micro Vickers hardness tester and the effect of heat treatment temperature on the hardness of coatings was evaluated.The results of SEM examination showed that the morphology of semi-amorphous structure cauliflower was formed. The X-ray diffraction test revealed that the hard-phase crystallization and deposition of nickel borides (Ni3B) in the nickel. The typical heat treatment at 400° C, had the highest hardness. Pin on disc wear test results prevailed that heat treatment at 400° C reduced the friction coefficient. The heat treatment at 400°C led to a nanocrystalline structure, therefore, the hardness and wear resistance of the amorphous to the crystalline structure and the change in coverage due to the hard phase Ni3B increased.

In this research, nanopowder hydroxyapatite (HAp) synthesized by hydrothermal method with precursors concluded of calcium and phosphor. Phase analysis, structure, particle size and morphology of HAp were investigated by X-ray diffraction pattern analysis (XRD), zetasizer instrument, scanning electron microscopy (SEM). XRD results confirmed the formation of hydroxyapatite phase. Presence of two particle size distribution picks in zetasizer curve presented that a part of powder was agglomerated and SEM images have shown this agglomeration. The results showed the minimum temperature of hydroxyapatite is 150 ○C that formed the mean particle size of HA ≈ 80±10 nm and crystallite size ≈ 18 nm.

In this study, Silica nanoparticles with the size of 50 to 80 nm with were synthesized using a Sol-gel method and different amounts of Lanthanum Nitrate hexahydrate formed during the reaction of the particles, was added to the material. To examine the ability of these Nanostructures in a controlled release of drug such as Lanthanide, SBF (Simulated Body Fluid) was prepared and the release of Lanthanide 10 minute intervals for 48 hours was investigated and released Lanthanide concentration was evaluated by ICP (Inductively Coupled Plasma). According to the results of ICP, loaded Lanthanide was not released from the silica network. Loaded Lanthanides in the mesoporous can be used in radiotherapy, especially in cases of liver cancer.

Influence of Ag+ content on the antibacterial activity of glaze surface was investigated using coating on the glaze surface with different silver nitrat content ranging from 10%wt to 50%wt. The results showed that the Ag concentration on the glaze surface increased with increasing AgNO3 content in the coating. By measuring the antibacterial activity of glaze surface, it was found that the glaze surface with increasing Ag content, showed strong antibacterial functionality in the short period of time (after 2h) against E. coli and S. aureus. With the help of SEM and XRF it was confirmed the Ag existance and its concentration on the glaze surface.

Repair and rehabilitation of gas transmission pipelines via traditional methods such as cut out, welding and steel sleeves, have a lot of problems and need shutting down the production. As a consequence, it is crucial to use composite laminates as a modern method for repair and rehabilitation of gas pipelines. This work is concerned with the determination of optimum surface roughness, prior to the application of composite laminates, via pull-off and lap-shear experiments. In order to ensure that during cathodic protection any disbondment will not occur for these protective laminates, the resistance of these laminates to cathodic disbondment was also investigated. According to the results, the optimum surface roughness was 60 micrometer and no disbondment was observed for the composite laminates.

In this research Ni–P matrix embedded with WC and BN particles, were applied on low-carbon steel and produced Ni-P-BN, Ni-B-WC and Ni-P-BN-WC composite Coatings. Scanning electron microscopy (SEM) and optical microscope were used to characterize the structures and surface morphologies of coatings which indicated that particles were uniformly distributed throughout the Ni–P matrix. The micro-structure and phases like Ni3P were investigated and analysed by X-ray diffraction (XRD) which reveal that electroless Ni–P coatings are amorphous. Micro-hardness and wear behavior of the electroless composite coatings were assessed respectively, by a micro-hardness tester and a pin on disc wear test apparatus. The comparison between Ni-P coating and Ni-P composite coatings exhibited that Ni-P-BN-WC coatings had combination of tribological properties of Ni-P-BN and Ni-P-WC coatings; it meant that Ni-P-BN-WC coatings had a good wear resistance, anti-sticking performance and self-lubrication properties at high loads. The corrosion behavior of coatings and effect of co-deposited particles on it, were investigated in 3% NaCl solution, which showed bad effect of BN on corrosion resistance. Micro-hardness, friction factor and corrosion resistance of Ni-P-BN-WC coating were also studied after heat- treatment.

In this study, the magnetite (Fe3O4) nanoparticles were synthesized via chemical coprecipitation method. The effects of synthesis on the size and magnetic properties of them were investigated. The precipitation occurred by pH adjustment of ferrous/ferric mixed salt-solution with ammonium hydroxide addition. The synthesis was performed in the temperature range of 25°C to 80°C in ambient atmosphere. The magnetite nanoparticles were characterized by X-ray powder diffraction (XRD), vibrating sample magnetometer (VSM) and transmission electron microscopy (TEM) analysis. The crystallite size was calculated via reclaimed Sherrer formula. The results show that the magnetite is the major phase for all temperatures and both of the synthesis atmospheres. It was revealed that the temperature is effective for magnetic properties enhancement. A similar result was obtained for magnetite phase formation. The saturation magnetization was obtained 31emu/g to 66 emu/g. It was found that the superparamagnetic property of nanoparticles is reduced by synthesis temperature.

The object of this study is to reduce invironmental problems and air pollution in copper extraction process from sulfide concentrate by sulfur fixation. In this research, the effect of mechanical activation on lime roasting process, was studied by ball and platenery millings, and finally the effect of activation and roasting on the leaching sulfuric acid process was investigated as well. The samples of sulfide concentrate mixed with lime were activated for different times, and by using thermal analysis TG, optimum quantity of these samples was obtained. It is used from thermal analysis of TG-DSC for studying kinetic roasting and roasting tests on the optimum samples of mechanical activaty was done between 10-60 minutes, with the temperature between 500-700°C and proportions of S:CaO=1:0.8-1:1.2. the samples reached from roasting and a sample of inactivated concentrate were put under the leaching process at different time. The result of XRD analysis indicated that as a result of activated samples roasting, a significant amount of sulfur in concentrate fixed by existence of CaSO4, and just a little amount of that, as a SO2 gas left. the result of atomic absorption analysis showed that copper recovery is 36 percent through leaching of inactivated concentrate samples 24 hours. While this process, for roasting samples through in first 30 minutes of leaching, is about 70 percent.

In this study, atmospheric corrosivity class of Tehran city was determined using environmental data and corrosion rate of standard specimens during one year exposure time. Accordingly, corrosion rate of Aluminum, Copper and Zinc standard helical and flat specimens were analyzed after each time intervals. Meanwhile, other influential parameters such as deposition rate of Chloride and Sulphur dioxide and time of wetness were evaluated.

In this research, the effects of heat treatment on the the microstructure and mechanical properties of 316L stainless steel coatings sprayed by flame spraying process was studied. Coatings have been heat-treated at a range of temperatures between 800 and 1150 °C. The microstructure characteristics of the deposits were studied using the combined techniques of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Furthermore, the mechanical properties were tested using the adhesion strength and microhardness tests. Results indicate that by heat-treating the coatings at a temperature of 800 and 950 °C, it is possible to achieve higher adhesion strength and hardness values. This was attributed to the improvements in the coating microstructure during the heat-treatment, which resulted in an improvement in coating's mechanical properties through the formation of intermediate phases, and the establishment of metallurgical bonding within the coating microstructure. However, the results also inidate that by increasing the temperature to higher than 1150 °C, there was a reduction in the coating's mechanical properties. This could be attributed to the grain growth, and coarsened precipitation of the equilibrium phases from supersaturated solid solutions.