ADVANCED MATERIALS IN ENGINEERING (ESTEGHLAL)
Year:2016 | Volume:34 | Issue:4|Papers Count:11

In this study, the effect of Al2O3 addition as a diluent during mechanically activated self-propagating high temperature synthesis (MASHS) of Al2O3-ZrB2 composite was investigated. For this purpose, the thermite mixture of Al, ZrO2, H3BO3 and different amounts of Al2O3 (0, 3, 6, 9 wt.%) were used as the raw materials and mechanically activated for 5 h, then furnace sintering was performed at 650oC. The results showed that by increasing the Al2O3 content up to 6 wt. %, the intensity of exothermic peak in the DSC curves increases, but for higher additive contents it decreases. In this case, more homogenous distribution of ZrB2 particles with finer grain size was observed.

In this study, synthesis of silicon nitride by mechanical alloying and the effects of important parameters of milling time and heat treatment temperature, time and rate are presented. Silicon micro powder and nitrogen gas were used as precursor materials. Synthesized phases, morphology and particle size were investigated by X-ray diffraction pattern (XRD) and Fieldemission scanning electron microscopy (FE-SEM), respectively. X-ray fluorescence analysis (XRF) was used for silicon nitride purity investigation.The optimum sample was produced at 30 h milling time, heat treatment at 1300oC and 22 oC /min heating rate conditions. X-ray fluorescence analysis showed more than 98% purity.

Nanoparticles of Mg–Co–Ti substituted strontium hexaferrite with nominal composition of SrFe12-2x (Mg, Co) 0.5x TixO19 (x=0-2.5) were synthesized by a co-precipitation method. The structural, magnetic and electromagnetic properties of samples were studied as a function of x by thermal gravimetric (TG), X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and vector network analysis. It was found that the synthesis temperature increases with an increase in Mg–Co-Ti substitution and hence the particle size decreases. The XRD results showed that whole samples had good crystallinity and with an increase incations, the impurity phase of Fe2O3 appears. The results of hysteresis loops indicated that the saturation of magnetization of ferrite decreases from 40 emu/g to 19 emu/g with an increase in x. The Mossbauer spectroscopy showed that the cations are substituted in the 12k site of magnetoplumbite structure. Vector network measurements showed that the doped samples had much more effective reflection loss values than those of undoped ferrites. As a result, Mg-Co-Ti doped Sr-hexaferrites with x=2 can be proposed as suitable absorbers for applications in microwave technology with a good deal of consistency.

Bio-inspired silver nanoparticles were synthesized with the aid of a novel method, using leaves of the plant Nigella sativa. After drying the leaves in air, they were first sweltered in boiling distilled water and the liquid was filtered subsequently.The result was the brothused to reduce solutions including various concentrations of silver nitrate in a proper amount of pH. The displayed UV–visible spectra identified formation of silver nanoparticles whenever the colorless initial acclimated mixture turned brown. The centrifuged powder samples were examined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (FESEM) and energy dispersive X-ray diffraction analysis (EDX) methods. The results clearly revealed that the final particles of precipitated powder are high purity agglomerates of silver nanoparticles. Besides, the effects of various amounts of the silver salt on particle size of nano silver were studied, using a particle size analyzer. FTIR results also indicated the role of different functional groups in the synthetic process.

With various features such as strong oxidation, biocompatibility and acceptable mechanical properties, titanium dioxide (TiO2) is among the materials that are frequently used in biological and medical applications. Nowadays, with the aim of increasing the efficiency of titanium dioxide and practical use of this material, doping it with elements such as silver, zinc and iron has been favored. In this study, Ag-TiO2 and ZnO-TiO2 nanoparticles were prepared by the sol-gel method and were evaluated and compared. In order to identify the present phases in the structure, X-ray diffraction analysis was used. Also for the characterization of the nanoparticles, Ultraviolet-visible spectroscopy (UV-Vis), Energy-dispersive X-ray spectroscopy (EDS), Field Emission Scanning Electron Microscope (FESEM) and Zeta Potential were used. Inaddition, the antibacterial activities of nanoparticles were investigated and compared. The results showed that sol-gel method could successfully produce nanoparticles of Ag-TiO2 and ZnO-TiO2 with the expected combination. The investigation of antibacterial properties of these particles revealed that at lower inhibitory concentrations, Ag-TiO2 composition has a higher antibacterial activity than ZnO-TiO2 one.

In this research, TiAl/Al2O3 composite was synthesized from mechanically activated TiO2-Al powder mixtures using microwave heating. The initial powder mixtures were mechanically activated and pressed into cylindrical tablets and then heated in a microwave oven. The effect of different amounts of excess Al and microwave susceptor material (SiC or graphite) on theignition time and the resultant reaction products were evaluated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were used for characterization of the synthesized samples. XRD patterns revealed that when there was no excess Al in the initial powder mixture, the main resulting intermetallic phase would be Ti3Al with negligible amounts of TiAl, while with 10 wt% excess Al, TiAl phase could be formed in the composite product. The results also showed that microwave synthesis took place faster and more reproducible when samples were packed in the graphite powder than when placed between two SiC blocks.

In this investigation, the effect of grain size on the corrosion behavior of 304L stainless steel has been studied.Samples with grain sizes of 0.5, 3 and 12 micrometers were fabricated through formation of strain-induced martensite by 80% cold rolling of the stainless steel sheets at -15oC and its reversion to austenite during annealing at 900oC for 1, 5 and 180 min. The corrosion behavior of samples with different grain sizes was investigated by cyclic polarization experiments andimmersion tests in 0.1 M hydrochloric acid (HCl). The polarisation tests showed no differences in uniform corrosion rates of the samples. The results of the cyclic polarisation and immersion tests showed that decreasing the grain size improved the pitting corrosion resistance from 290 mVAg/Agcl for grain size of 12 micrometers to 420 mVAg/Agcl for grain size of 0.5 micrometers.

In the present research, an effective thermo-mechanical processing route in the temperature range of metastable austenite region (Ae3<T<Ar3) was employed to achieve ultra-fine grain size in a plain low carbon steel during integrated extrusion equal channel angular pressing. At first, the effect of preheating temperature on the strain and temperature distributions inside the deformed samples were investigated using 3D finite element simulation. According to the result of FEM simulation, the preheating temperature of 930oC was selected as an appropriate temperature for fabrication of ultra-fine ferrite structure. Severe plastic deformation was then imposed on samples with the predicted preheating temperature and the results showed a great consistency with FEM simulation predictions. Optical micrographs taken from the center point of the samples showed that the ferrite grains could be refined from 32 mm to 1-3 mm by different mechanisms.

Super-hydrophobic nickel and nickel-cobalt alloy coatings with micro-nano structure were successfully electrodeposited on copper substrates with one and two steps electrodeposition. Surface morphology, wettability and corrosionresistance were characterized by scanning electron microscopy, water contact angle measurements, electrochemical impedanc spectroscopy (EIS) and potentiodynamic polarization curves. The results showed that the wettability of the micro-nano Ni and Ni-Co films varied from super-hydrophilicity to super-hydrophobicity by exposure of the surface to air at room temperature. The corrosion results revealed the positive effect of hydrophobicity on corrosion resistance of Ni coating (~ 10 times) and Ni-Co coating (~ 100 times) in comparison with their fresh coatings. The results showed that super-hydrophobic nickel coating had higher corrosion resistance than super-hydrophobic nickel-cobalt coating.

In this study, energy and chemical interaction of ZnO and CdS surfaces interfaced with metal-organic framework (MOF), to improve their properties, have been investigated using density functional theory (DFT). Results show that reformation of structures by hybridation with MOF can increase their stability and improve their properties. Comparison of ZnO and CdS structures predict that deposition of MOF on ZnO substrate can be more effective.