Journal of Advanced Processes in Materials Engineering
Year:2014 | Volume:8 | Issue:1 (28)|Papers Count:12

Thin layers of titanium dioxide doped with different amounts of lithium were deposited onto fluorine-doped tin oxide (FTO) substrate by doctor blade method. Structural, optical and morphological properties of the layers were determined by x-ray diffraction (XRD), scanning electron microscopy (SEM) and diffuse reflectance spectroscopy (DRS). Specifications of the fabricated cells were measured by voltage-current density (V-I) method. XRD results showed that anatase was the sole phase produced. Rise in lithium concentration resulted in reduction of the crystallite sizes. SEM images showed homogeneous morphology with 20-40 nm crystallite size. Addition of Li resulted in enhancement of the specific surface area and diminution of the pore dimensions. Addition of 0.7 wt. % Li resulted in current density increase from 1.17 to 2.5 mA/cm2 DRS measurements indicated shifting of the optical absorption edge of the TiO2 layer towards lower wavelengths.

Lead piezoelectric ceramics are containing a high percentage of lead. Due to the toxicity of lead and environmental problems, various attempts have been made to replace the piezoelectric ceramics. In this paper, lead-free piezoelectric powder Potassium Sodium Niobate (KNN) as a compound candidate to replace Lead piezoelectric synthesis with conventional solid-state and the parameters of the two-step sintering ceramics - such as the temperature of the first stage (T1), the second temperature (T2), and hold time at temperature T2 were studied. Also, the effect of two-step sintering on microstructure and density of compound was investigated. SEM images and density measurement results show a higher density (95.3%) and smaller grain size (3.72 mm) and lower porosity (2.45%) KNN piezoceramics have been fabricated by different two-step sintering cycles, while the KNN ceramics with excellent density (93.5%) and grain size (4.42 mm) and porosity (6.48%) were obtained by conventional sintering. increasing T1, and T2 result in lower necessary time in the second step to reach higher density with smaller final grain size. Furthermore, two-step sintering can improve microstructure and density of the KNN piezoceramics. Result showed that the two-step sintering is a promising method in sintering of potassium sodium niobate lead-free piezoelectric ceramics.

Al-2wt. % B4C Nano composites were fabricated through three methods i.e. stir casting, powder metallurgy, and mechanical milling. In the stir casting method, B4C nanoparticles with 80nm mean particle size were added to the melt and the resulting mixture was poured in a steel mold. In the mechanical milling and powder metallurgy methods, after mixing Al and B4C powders, the resulting composite powders were shaped through Cold Isostatic Pressing (CIP). Finally, in all methods, the resulting product was hot extruded. The microstructure of samples was characterized by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. In order to compare the mechanical properties, tensile, compression, and hardness tests were performed. Results demonstrated that the nanocomposites prepared by the mechanical milling method have the most uniform particle distribution and highest hardness and strength.

In this work, TiCr2 intermetallic was successfully synthesized by calciothermic co-reduction of the TiO2 and Cr2O3 powders. Differential thermal analysis and X-ray diffraction were used for determining the formation mechanism of this compound. It was found that the molten Ca reacts with Cr2O3 through an exothermic reaction at about 933oC and Cr and CaO were formed. By increasing the temperature, CaTiO3 was formed because of the reaction of CaO and TiO2. As the temperature increased to about 1063oC, Ti was formed because of the Ca reaction with the remained TiO2 and CaTiO3 through an exothermic reaction. Finally, TiCr2 was formed by the mutual diffusion of Ti and Cr elements. The obtained TiCr2 powder contained 1690 ppm oxygen and showed the capability of a hydrogen absorption material after activation.

In the present work, stoichiometric cordierite powders in MgO-Al2O3-SiO2 system were selected with added CaO and B2O3. The powders were synthesized by tetraethyl orthosilicate and magnesium and aluminium chlorides. Crystallization and sintering behavior of glass-ceramics was investigated at different temperatures. Obtained peroperties were characterized using DSC, FT-IR, XRD and SEM/EDX Results showed that crystallization before sintering hindered good sintering. Microstructural examination revealed that crystals of a-cordierite with hexagonal prismatic morphology were formed and EDX confirmed it. Addition of CaO resulted in decreasing crystallization peak temperature of a-cordierite and increasing its intensity. CaO additive was also developed sinterability than based composition. Formation speed and intensity of a-cordierite was increased with addition ofB2O3 too.

Techniques of severe plastic deformation have been of continual interest in the production of novel metallic microstructures. Interests in ARB are focused on mechanisms of grain refinement and the effect of strain on microstructural evolution. In the present study, a new manufacturing process for Cu/Fe304-1 vol% and 2vol% Fe3O4 composites was developed by using Copper sheets and micron sized Fe3O4 particles as starting materials. After five ARB passes, showed the Fe3O4 particles properly distributed in the copper matrix. With increasing strain during ARB passes strength and elongation of these composites increased. Mechanical (strength and hardness) and magnetic (saturation, retenevity, coercivity) properties of these composites were studied within different stages of ARB process. The state of Nano composite layer structure improved mechanical properties which includes tension and hardness in Cu matrix. The existence effects of reinforce particles of Iron Oxide in increasing magnetic properties in different process were investigated with magnetic device detector (VSM).

In this study, the effect of solution treatment on DOS (Degree of Sensitization) of AISI 304&321 stainless steels (SS) was investigated by EIS and SEM images in the standard solution of EPR test (0.5M H2SO4+0.01M KSCN). EIS was employed to determine the DOS of the samples in 1.0 and 1.05 V related to the chromium dissolution potential region of SS. The results showed that the intergranular corrosion resistance of the solution-treated samples was improved. The lower R in 1 and 1.05 V, the higher DOS. The SEM images of the samples in the 1.0 and 1.05 V confirm the obtained results of the EIS. In addition healing effect was observed for as-received samples. These samples had lower Rct in comparison with solution treated ones under all the studied condition, but their Ret increased above 600oC. This increase in Rct of as-received samples above 600oC, which is associated with healing effect, may be attributed to formation of chromium carbides in the grain-interiors.

Chemical pulse deposition (or pulsing electrolysis) is a method of producing high purity copper powder. The purpose of this study was to investigate the morphology and particle size of copper powder. One of the parameters that affect the copper powder production process is the material of cathode, which powders precipitate on. Also different substrates were chosen as cathodes: copper, aluminum, lead, stainless steel, titanium and gold. The obtained powders were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy diffraction spectroscopy (EDS). The results showed that gold was the best cathode and aluminum was the worst cathode for the copper powder synthesis. The gold cathode also led to the formation of finer copper powder particles.

Green and blue ultramarine pigments were synthesized using kaolin, sulfur, sodium hydroxide, silica and resin. The properties of pigments were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), CIELAB colorimetry, dynamic light scattering (DLS) and scanning electron microscopy (SEM). XRD results demonstrated ultramarine as major phase in all of the synthesized pigments. The spectrophotometery results showed that by increasing alkalinity of the compositions, the blue color became darker and by decreasing sulfur, S2- radical’s increase and green color is produced. Also, particle size distribution of the synthesized pigments was determined at about 1 micrometer by DLS analysis. The synthesis of blue and green colors by changing sodium to sulfur ratio was the most important result in this research.

In laser welding, shielding gas has the duty of protecting the laser optics from the weld spatter, protection of the weld pool against the atmosphere, and improving the welding efficiency. According to this a good shielding technique of the weld pool is of primary importance in order to obtain sound and reliable beads. An experimental and theoretical study on the role of the helium gas flow rate on the weld characteristics in pulsed laser welding of low carbon steel is investigated. Computational Fluid Dynamics software was used to understand the effect of shielding gas in laser welding. The simulated welding environment was simplified without considering the presence and the effect of the plasma plume. The results indicate the importance of shielding gas flow rate on the characteristics of pulsed Nd:YAG laser weld. The numerical predictions can help to explanation of the experimental results.

In this study, the mechanical properties of dissimilar welding of Super duplex stainless steel UNS 32750 to austenitic stainless steel AISI 304L by gas tungsten arc welding process with direct current electrode negative polarity was investigated. For this purpose, two filler metals including ER25104L and ER309LMo were used. In order to achieve suitable structure and excellent mechanical properties in the mentioned joints, controlling of the heat input and pre heating were among the effective and controllable parameters. Microstructures of the weld metals, were evaluated using optical microscopy and scanning electron microscopy was used to analyze fracture surface. In addition, the mechanical properties including the bend test, ultimate strength, impact resistance and hardness were investigated. All the specimen underwent ductile fracture in HAZ in the tension test. The maximum fracture energy related to the ER 25104L the welded specimen. The maximum and minimum hardness corresponded to the ER 25104L and ER 309LMo, respectively. Finally, it was seen that for the joints, between the super duplex stainless steel UNS 32750 to austenitic stainless steel AISI 304L, the ER 251 04L filler provided the optimum qualities.

In the present study, Al-Al2O3 metal based-composite has been produced by stir casting method. In this method, Al2O3 powder was added to melted A356 alloy, and then casted by pouring down into a metallic mould. The effects of temperature and stirring time on hardness, tensile strength and microstructure for 6 different conditions have been studied. Scanning electron microscopy (SEM) for microstructure investigation, and tensile and hardness test for mechanical properties investigation have been carried out for each condition. The results showed that increasing the stirring time leads to increase of tensile strength and hardness at 750oC as the pouring temperature, but to decrease at 850oC.