Journal of Advanced Materials in Engineering (Esteghlal)

Sodium molybdate (Na₂MoO₄) as a grain refiner was used to refine the microstructure of Al-0.7Fe alloy. Al-Fe samples with the addition of 0.1, 0.2, 0.3, 0.4 and 0.5 wt.% sodium molybdate were fabricated by casting in sand molds at 750 ͦC. The microstructures of the as-cast samples were investigated by scanning electron microscopy (SEM) and the present phases were revealed by X-ray diffraction (XRD). The effect of sodium molybdate on the microstructure was examined by measuring the average grain sizes of the alloys, determining the widths of intermetallic compounds and carrying out hardness and tensile tests. The results showed that the addition of sodium molybdate modified the microstructure of Al-Fe alloy by reducing the average grain sizes. Also, it was found that the optimum amount of sodium molybdate to add to Al-0.7Fe alloy melt was 0.3 wt.% in this study.

In this study, the effect of nano-titania addition on the mechanical strength of mullite-bonded alumina-siliconcarbide nano-composites was investigated. To this end, the gel-casting process via nano-silica sol was used for shaping the nano-composite.The firing temperature of composition was determined by use of STA. The compressive and bending strengths of samples were measured after firing at 1300 °C. Besides, the physical properties, phase composition and microstructure of the composites were evaluated after firing. The results showed that the use of nano-titania up to 1 wt.% had a higher effect on improvement of nano-composite mechanical strength. The nano-titania addition led to increasing of mullite phase and higher growth of its needle-like grains. Enhancing of ceramic bonds between grains and the improvement of mechanical strength were obtained by increasing the mullite phase.

Conventionally, a film of TiO₂ particles of ~300 nm size is employed in DSCs as the back reflector film to enhance the light harvesting. In this study, two electrolytes with different transparencies, iodide-based and cobalt-based electrolytes, were used to investigate the transparency effect of electrolytes on light back-scattering from back scattering layer and also to study its effect on the performance of DSCs. The use of cobalt-based electrolyte is recommended from the view point of optical properties as due to the light absorption in electrolytes, the current density losses are 2.9mA/cm² and 4.2 mA/cm² in cobalt- and iodide-based electrolytes, respectively, and the transmission of 100% is observed for cobalt-based electrolyte in 500-600 nm in spite of iodide-based electrolyte. Use of light back-scattering layer, unlike iodide-based cell, causes external quantum efficiency in cobalt-base cell to increase for the wavelengths lower than 350 nm since cobalt-base electrolyte has transparency in this region. In addition, optical calculations demonstrate that in the range 400-500 nm, in which dye has a noticeable absorption, absorption loss is 40% and 30% for iodide- and cobalt-based electrolytes, respectively.

In this research, stiffness of polymer-clay nanocomposites was simulated by Mori-Tanaka and two and three dimensional finite element models. Nanoclays were dispersed into polymer matrix in two ways, namely parallel and random orientations toward loading direction. Effects of microstructural parameters including volume fraction of nanoclays, elastic modulus of nanoclays and interphase, thickness of interphase, aspect ratio of nanoclays and random orientation of nanoclays on elastic modulus of the nanocomposite were investigated by finite element model. Comparing the simulation with experimental results showed that the Mori-Tanak simulation results were closer to the experimental results. Analysis of results showed that the volume fraction of nanoclay, elastic modulus of nanoclay, deviation of nanoclay layers with respect to loading direction, nanoclays aspect ratio, thickness of interphase and the elastic modulus of interphase had respectively the most to the least effect on elastic modulus of nanocomposite.

Titanium dioxide-nickel oxide porous coatings were synthesized by Plasma Electrolytic Oxidation (PEO)/ ElectroPhoretic Deposition (EPD) in one step and within a short time. The main purpose of this research was to increase photocatalytic activity of titanium oxide by increasing surface area and coupling of titanium oxide with nickel oxide. Applied voltage effects on phase structure, surface morphology and photocatalytic efficiency of coatings were studied. Phase structure and surface morphology of the synthesized catalysts were investigated by XRD and SEM, respectively. Photocatalytic efficiency of the samples was studied through measuring the decomposition rate of 4-chlorophenol. The results showed that the coatings mainly consisted of anatase and nickel oxide phases whose amounts in coatings increased with the voltage. There was an enhancement of the photocatalytic efficiency in TiO₂/NiO composite coatings compared with TiO₂ coatings. Besides, there was an optimum amount of NiO to reach maximum photocatalytic efficiently.

Precipitation has always been one of the important methods in the preparation of ceramic nanopowders. In this study, the most important parameters, ageing time and concentration parameters, have been studied. Yttrium oxide (Yttria) nanopowder was synthesized by precipitation method. Yttria micropowder and ammonium hydrogen carbonate were used as precursor materials. The study involved aging time and concentration in four and three levels, repectively (3, 6, 12 and 24h for ageing time and 0.25, 0.5 and 0.75 mol/L for concentration). Synthesized phases, thermal behavior and particle size were studied by X-ray diffraction pattern (XRD), thermogravimetry (TG), differential thermal analysis (DTA) and field emission scanning electron microscopy (FE-SEM). Fourier transform infrared spectroscopy analysis (FTIR) was used for studying bonding before and after the heat treatment at 900, 1000 and 1100 ^°C.

Aluminium 5xxx alloys excellent properties make them suitable for many industrial applications. The corrosion behavior of this alloy family in industrial environments such as sea water is the main focus of many researches. Due to need for joining large segments of this alloys, the effect of single as well as multipass (double and triple pass) gas metal arc welding (GMAW) on microstructure and corrosion behavior of Al5083-H321 alloy was studied. For this purpose, ER5183 filler metal was used. Microstructures were evaluated using optical and scanning electron microscopy (SEM). Corrosion measurements were performed using open circuit potential test, immersion test in 3.5%NaCl solution and polarization tests. Results indicated that the corrosion resistance of the two passes weldment was improved in comparison with the base metal and its icorr and Ecorr were equal to 0.087´10^-6 (µA/cm²) and -0.4395 (V), respectively.

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 650 °C. 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 Field emission 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 1300 ℃ and 22 ℃/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 SrFe_12-2x(Mg,Co)_0.5x Ti_xO₁₉ (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 Mössbauer 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 the ignition 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 -15 ^°C and its reversion to austenite during annealing at 900 ^°C for 1, 5 and 180 min. The corrosion behavior of samples with different grain sizes was investigated by cyclic polarization experiments and  immersion 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 mV_Ag/Agcl for grain size of 12 micrometers to 420 mV_Ag/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 930 ˚C 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 &mu;m to 1-3 &mu;m 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 corrosion 

resistance 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.

This study aims at investigation of the hydrogen damage after dissolution annealing and two-stage aging in aluminum 7075 alloy. Dissolution annealing was performed at 500 to 575 ^°C for duration of 1 to 20 hours. The first stage of two-stage aging was performed at 180, 200 and 220 ^°C for 30 minutes. The second stage was carried out at 120 and 150 ^°C for 10, 15 and 20 hours. Structural characteristics and chemical composition of precipitates was investigated using SEM and EDS methods, respectively. Reduction of the tensile strength in T6 process after hydrogenation reached to 150 MPa, although it decreased only, about 50 MPa in the two-stage process. Overall, tensile strength after hydrogen charging was significantly increased in the two-stage aging compared to the T6 process.

In this study, microstructure and mechanical properties of diffusion joints between 5754, 6061 and 7039 aluminum alloys and AZ31 magnesium alloy were investigated. Diffusion joints were done between the alloys at 440 °C, for duration of 60minutes, at 29 MPa pressure and under 1×10^-4 torr vacuum. The interface of joints was studied using optical (OM) and scanning electron microscopy (SEM) equipped with EDS analysis and the line scan. According to the results of EDS analysis, the presence of intermetallic compounds including Al₁₂Mg₁₇, Al₃Mg₂ and their mixture was observed at the diffusion zone. Also, according to the results of the line scan, the hardness value of aluminum alloys has a considerable effect on diffusion of the magnesium atoms toward aluminum alloy and the greatest diffusion of magnesium was observed when 6061 aluminum alloy was used. More diffusion resulted in a stronger bond between atoms of magnesium and aluminum, and maximum strength of approximately 42 MPa was obtained when 6061 aluminum alloy was used.

In this study, NBG was successfully achieved through a sol-gel technique, and to further improve its dispersibility, a crylate coupling agent was coupled onto the surface of the NBG. The 3-(Trimethoxysilyl)Propylmethacrylate coupling agent was used to the surface modification of the synthesized NBG by a wet-chemical method in a dynamic inert nitrogen atmosphere. The surface properties of the biomaterials before and after modification were characterized and compared using FTIR and AFM techniques. The characteristic peaks in FTIR spectra indicated that –CH2, –CH3 and C=O groups appeared on the surface of modified NBG, and also, AFM analysis revealed that the dispersibility of surface modified NBG was improved, significantly. The above results proved that the desired groups of 3-(Trimethoxysilyl)Propyl methacrylate had been covalently bonded onto the surface of NBG. Besides, a nanocomposite scaffold was synthesized using the synthesized NBG and polyurethane foam as raw materials. The morphology of pores, porosity contents, compress strength and bioactivity of the scaffold were studied. The results showed that the biological scaffolds for use in bone tissue engineering with the basic requirements (90% porosity and 200-600 μm pore diameter) were successfully prepared. The polymer component had no effect on the relationship between the scaffold pores and bioactivity of bioglass nanoparticles. Improvement of compressive strength and proper bioactivity of the resulted scaffold showed that it is an acceptable candidate for biomaterials applications.