نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 48 (بهار 1398)

Zeolites can be used as one of natural adsorbents for the removal of heavy metals. Treatment of natural zeolites with various chemicals enhances their removal capacity. In this study, manganese dioxide was used to activate the natural zeolite. The modified zeolite sample and several combinations of the synthetic wastewater were contacted together to adsorb heavy metals. The wastewater used contained heavy metal ions with various concentrations such as Cu2+, Cd2+, Zn2+, Co2+, Pb2+, and Ni2+. The adsorption isotherms of Langmuir, Freundlich, BET, and Temkin, as well as adsorption kinetic models, were used to develop models imaging the behavior of adsorption. The BET isotherm provides a model being more acceptable than the other isotherms; however, in term of the prediction of adsorption amounts (qe), its description is weaker than the Langmuir isotherm. Maximum adsorption capacities with respect to Langmuir parameters were obtained under optimal conditions as follows: Ni2+ (10.51 mg/g), Co2+ (14.87 mg/g), Zn2+ (8.97 mg/g), Cu2+ (10.59 mg/g), Cd2+ (13.69 mg/g) and Pb2+(40.65 mg/g). In addition, the pseudo-second kinetic model is more accurate than the pseudo-first order. Thus, the pseudo-second kinetic model was selected to describe the adsorption kinetics.

Lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) compounds were synthesized using the conventional solid state ceramic processing and the effects of Bi2O3 addition on density and electrical properties was investigated. In order to decrease the loss of Bi at high processing temperatures of BCZT, two methods were employed to introduce bismuth oxide; one, in which Bi2O3 was mixed with the raw materials and the composition was balanced for A-site substitution before calcination and the other where Bi2O3 (0.1mol%) was added after calcination, milled, compacted, and sintered (1350-1500 °C) with no compensation at A or B-sites. Phase and microstructure analyses were carried out using x-ray diffractometry and scanning electron microscopy. The temperature and frequency dependence of dielectric properties showed a normal ferroelectric behavior. Our results revealed that Bi incorporation based on the second method was more effective in increasing the density and improving the electrical properties. The highest direct and converse piezoelectric constants, planar coupling factor, and remnant polarization obtained were d33=325 pC/m, d33*=675 pm/V (d33*/d33=2.1), kp=0.42, and Pr=10.4 µC/cm2, respectively, for the BCZT sample with 0.1 mol% Bi2O3, as sintering aid, sintered at 1350 °C, which were attributed to the larger grains and higher density of the corresponding composition.

Significant amounts of nickel products used in different chemical processes and general applications leave them a valuable source of nickel at the end-of-life. Production of nickel from secondary sources is generally performed through hydro-electrometallurgical methods. The resulting solutions from treatment of secondary nickeliferous resources are generally of low Ni concentration and electrowinning of them is challenging, particularly since Ni concentration in commercial operations is usually more than 80 g/L. In this paper, the continuous electrowinning of nickel from dilute sulfate solutions has been investigated. The effects of four variables of temperature, specific flow rate of electrolyte, current density, and nickel concentration on current efficiency and specific energy consumption were studied by a two-level full factorial design. From the statistical analysis of the results, it was found that current efficiency increases by rising all variables, while specific energy consumption decreases with specific flow rate of electrolyte, current density, and nickel concentration. By using the obtained statistical models, the optimum conditions to achieve a nickel deposit with high current efficiency as well as lowest energy consumption are determined to be 55 °C of temperature, 3 A/dm2 of current density, 3 h−1 of electrolyte specific flow rate, and 30 g/L of nickel concentration.

In this study, the hot corrosion resistance of diffusion aluminide coating on Inconel 713C was investigated using electrochemical techniques. In this regard, potentiodynamic polarization tests were performed at 750 °C in two kinds of molten salts. The former contained 70% sodium sulphate and 30% sodium chloride. The latter was composed of 70% sodium sulphate, 25% sodium chloride and 5% vanadium pentoxide. The phase composition and microstructure of coatings and corrosion products were investigated using XRD and SEM-EDS techniques. The results showed that in the presence of vanadium, the protection efficiency of coatings increased and a current-independent region was observed in anodic polarization curve. Here, a compact corrosion product layer was seen. In absence of vanadium, both coated and uncoated samples exhibited similar corrosion rates. However, in comparison to vanadium-containing environment, all samples showed lower corrosion rate. In this case, the coatings exhibited active anodic behavior. The corrosion products were porous and discontinuous in vanadium free environment.

cobalt-tungsten anano structure alloy coating was produced using pulse electrodeposition in 200 Hz pulse frequency from citrate electrolyte at 60 °C. In this study the influence of cobalt ions concentration in solution and duty cycle on crystal structure, grain size, hardness and corrosion resistance of coating was investigated. Surface morphology and composition of coatings was examined by scanning electron microscopy (SEM) and (EDS) analysis. The crystallite size of the coatings calculated from the x-ray diffraction patterns using the Scherrer equation. Micro hardness of the coatings was assessed using a Vickers micro-indenter. Results showed that electrodeposited coating at 0.2 mol/l cobalt sulphate and 60% duty cycle with 1A/dm2had optimum coating on 758 Hv. Annealing amorphous coating was produced at current density of 4 A/dm2 in high vacuum pressure makes crystalline coating. Increasing temperature at 600°C makes a well-developed polycrystalline structure of Co3W and CowO4 in the coating. Microhardness of coating increased from 436 Hv to 1059 Hv after heat treatment at 600 °C. Heat treatment of coating improved the corrosion resistance of coating. The coating heat treated at 400 ºC had minimum corrosion rate.

The Resistance Spot Welding (RSW) has lots of industrial application, especially for body construction and some parts like car lamps. The aim of this research was optimizing of the production line efficiency and improving the welding strength of the car lamps. Experimental studies were conducted on the factors affecting the weld strength in a H4 halogen lamp (wing to body connection). The experiments design and results analysis were done by Taguchi method and Minitab software. Welding current, welding time and electrode material were studied as main factors (inputs) in the actual lamp samples. Experimental results and statistical analyzes indicated that the high dependence of welding strength on welding time is primarily and with a quantitative difference in the second order to the welding current. According to the results, it was found that with any kind of electrode material, if welding time and welding current increases to moderate, welding strength will be improved. But in high values of time and current, there is a negative effect on the welding strength. Although the welding electrode has the third highest rating on weld strength. But during the testing process and analyzing it was found that the efficiency of the lamp production line in the case of using tungsten electrodes in the significant amount of 29.17% compared to the electrodes of Copper is more. While the welding strength of the tungsten electrode is only 5.5% lower than the copper electrode. This strength is still within allowed and acceptable limits of the relevant standards.

With the increasing growth and development of Nano science and nanotechnology, applications of the Nano-sensors, Nano-electro-mechanical systems, Nano-electric systems and Nano-photonic devices is rising day-by-day. Nanowires, as one of the key components of these systems, play a significant role in their proper function. Therefore, recognition of the thermo-mechanical behavior of nanowires has a particular importance. Due to the inevitable problems in conducting empirical experiments on nanowires, including the need for highly precise and advanced equipment, as well as the high cost and time needed to carry out these experiments, a number of researchers have simulated the behavior of nanowires. Molecular dynamics simulation is one of the best methods for recognizing the properties of nanowires, which is used in most nano-scale simulations. By using simulation and modeling methods, nanowires properties can be studied at a very low cost and short time, in comparison with experimental methods. In this paper, the effect of temperature (300, 450, 600 and 700 ◦K) and strain rate (2×108, 2×109 and 2×1010 1/s) on the mechanical properties of a gold nanowire (with diameter and length of 3 and 6 nanometers, respectively) such as stress-strain curve, yield stress, stress at failure moment, and the magnitude of nanowire elongation by molecular dynamics method have been investigated to determine the thermo-mechanical behavior of the gold nanowire.

Although tantalum nitride coatings have recently been attracted researchers’ attentions due to their high hardness and corrosion resistance, the fracture toughness and deformation plasticity of thin tantalum nitride film has not been well investigated yet. In this research, for the first time, the fracture toughness, strain rate sensitivity and plasticity of sputter deposited tantalum nitride thin films have been evaluated using nano indentation technique and SEM micrographs. It was shown that the fracture toughness was increases from 0.6 to 7.8 MPa√m with increasing the nitrogen in sputtering chamber. This increase was attributed to the structural evolution from a hexagonal γ-Ta2N phase to the hexagonal ε-TaN and face centered cubic δ-TaN phases, determined by X-Ray Diffraction analysis. The plasticity of the TaN films evaluations indicated that the ratio of plastic work to total work was increased from 50% to 57% and 80%with phase variation from γ-Ta2N to ε-TaN and δ-TaN, respectively.

The purpose of this research is to investigate the possibility of replacement of arc welding under shielding gas with non-consumable Tungsten electrode (TIG) of Al АМГ6М alloy by friction stir welding (FSW). In this regard, after applying primary parameters for both welding processes to obtain optimum parameters, the prepared samples were characterized with Tension, bending, radiography, hardness and distortion tests and also microstructure evaluation. The results of this study showed that the grain size of welding zone of TIG and FSW processes are 14 and 6 µm respectively, which are smaller than the base metal with 30 µm in size. The ultimate tensile strength of the FSW joints in the parallel to rolling direction and in the vertical direction with welding line is much more higher than TIG joints; 364 Mpa versus 278 Mpa. The reduction of microhardness in the welding zone for both process FSW and TIG have been in a range. The amount of distortion measured in the FSW was one-fourth of these values in TIG. The result of bending test of the FSW sample from the plane like to the results of the base metal is crack free. Therefore, in order to improve the mechanical and metallurgical properties, as well as to reduce weld joints distortion in aluminum structures, FSW was considered an appropriate alternative to the replacement of the arc welding under shielding gas with non-consumable tungsten electrode.