مجله مهندسی متالورژی
پیاپی 78 (تابستان 1399)

A recent smelting technology change at Sarcheshmeh Copper Complex, from the reverberatory furnace to the Outotec flash smelting furnace has affected the chemical analysis of the produced copper anodes. This is most likely due to change in the analysis of the smelting dust. The flash smelter flue dust,whichis high in concentration of minor elements, selenium and tellurium, is captured in the electrostatic filters and is recycled back into the flash furnace. The analysis result of 285 anodes in this study showed the rise in concentration of selenium, tellurium, arsenic, antimony, bismuth, lead and iron by 37%, 216%, 18%, 62%, 104%, 185% and 45%, respectively.The likelihood of anodic dissolution is decreased by increasing the impurity content of the anode. Flash smelting flue dust bleed and its hydrometallurgical treatment was suggested as a solution to overcome the decline in anodic dissolution at the refinery plant of Sarcheshmeh.Laboratory scale atmospheric leaching of the flue dust resulted in higher than 90% copper leaching recovery.This is also helping the existing heap leach/SX/EW facility to reach its nominal capacity using the PLS produced from the leaching of the flash smelter flue dust.

Microstructural ‎and Electromagnetically Methods were performed for evaluation of aging phenomenon in 2304 duplex stainless steel. The artificial aging process were carried out at temperatures of 700, 800 and 900 °C and at 15, 60 and 120 minutes. For microscopic and hardness evaluations, optical microscopy equipped with image analysis software, scanning electron microscopy equipped with chemical analyzer, X-ray diffraction device and Vickers method were used. Then, for electromagnetic evaluation, the eddy current test at 100 kHz was performed, and the data were presented and evaluated as an impedance plan. The microscopic studies showed that with increasing aging intensity by increasing aging temperature and time, reduced the amount of ferrite phase. In contrast, the secondary phases of M23C6 carbide, Cr2N nitride, and secondary austenite form and grow in the microstructure. These secondary phases are formed within the ferrite phase and lead to a reduction in the volume fraction of the ferrite phase relative to the annealed sample. The most sever changes were observed at 900 °C and 120 min. The results of electromagnetic evaluation have shown that with increasing the aging temperature and time, formation of more destructive phases and a sharp decreasing of ferrite content in the microstructure, the electromagnetic responses change appropriately by further reducing the inductive reactance and impedance index and further increasing the resistance index. Therefore, the severity of the aging phenomenon in the steel can be seen from its impedance plan.

In this research, the recovery of the gallium from a waste light-emitting diode (LED) was carried out by a hydrometallurgical method. This process involves the chip separation from the LED, oxidation of the chips and gallium leaching in hydrochloric acid medium. Since gallium is present in an insoluble nitride phase in the LED chip, the chip must be separated from the LED, and then an oxidation step is needed to convert the nitride phase to oxide. After these steps, the oxidized chips were subjected to the leaching process. Various variables such as leaching temperature, leaching time and hydrochloric acid concentration have been investigated in the leaching experiments and optimal conditions have been determined. The design of experiment was done through the surface response method. The optimum conditions after performing the experiments and analyzing the final solutions were determined. At optimum leaching conditions of 4 M hydrochloric acid, 93 ºC and 120 minutes, the gallium leaching recovery was 91.4%. It can be found that the leaching temperature is the most effective parameter in this process. Further experiments were performed to determine the mechanism and kinetic analysis of the process. These studies showed that at 50 °C, the chemical reaction controls the rate of the leaching process. However, the reaction mechanism was changed to diffusion-controlled as the temperature increases to 65 and 80 °C.

In this article, the effects of VIM and VAR remelting processes are investigated on the microstructure and absorption/desorption characteristics of MmNi4.8Al0.2 hydrogen storage alloy. The main alloy prepared in a Vacuum induction furnace and remelted in VIM and VAR. The microstructures and phases were analyzed with SEM and XRD. Hydrogen absorption/desorption characteristics is performed on Sievert apparatus. The results showed that the microstructure is consisting of matrix, second phase as a result of Al segregation, porosities and cracks. The second phases in the main alloy and VAR remelted have low content of La and Ce. This phase is solutionized or decreased to low level in VIM remelted alloy. Remelting, also, declined the absorption pressure to 21.55 and 18.17 bar and the desorption pressure to 7.13 and 5.49 bar in VAR and VIM remelted alloy, but increased the hydrogen storage capacity increased to 1.42 and 1.46 wt%  respectively. The more the homogeneity degree, the less the absorption/desorption pressure and the more the hydrogen storage capacity.

In this present work, steel foams were successfully manufactured through powder metallurgy route using urea granules as space holder and influences of WC content (0, 0.5, 1, 2, and 4 wt. %) added into cell walls were studied on porosity percentage, microstructure of cell walls, and mechanical properties of steel foams. The microstructure of cell walls was evaluated using optical microscope and scanning electron microscope equipped with image processing software. Increasing WC has little effect on surface fraction and sphericity of cell, while the surface fraction and sphericity of the pores formed into the cell walls are strongly affected by the addition of WC. The mechanical behavior of the steel foams was conducted using compression test. The porosity of the steel foams is between 73 % and 80 % and with the increase in WC content, the porosity percentage decreases. The results of microscopic evaluations indicated that the microstructure of cell walls contains ferrite and pearlite, with tungsten carbide particles distributed uniformly. The stress vs. strain curves of the steel foam have an elastic region, a long saw-tooth plateau region, and a fracture point and the curves are shifted upward as the WC content increased.

Change in the position of atoms in the material’s crystalline lattice is caused by the radiation. Changes in the macroscopic properties of the material will be created by the change in structure. Knowing the amount of variation of material properties is necessary for materials in high-radiation environments. In this paper, the effect of 2.5 MeV proton irradiation on TSX grade graphite structure is investigated. This graphite is used as a reflector in the Tehran research reactor. The radiation has been carried out with the proton for 276 minutes. Microhardness test, Raman test, and SEM images were used in this study. The results show an increase in the microhardness of the material due to the radiation. Increased vacancy and interstitial clusters have also been observed in the Raman spectrum. The creation of cavities on the surface of irradiated graphite is observed in SEM images. The results can be verified by using the point defect model.

In this work, a multilayer magnetic biosensor (SiO2/CoFeSiB/Al2O3/Cr/Au) based on the giant magnetoimpedance (GMI) effect, is designed and fabricated by micro-electromechanical system (MEMS) technology. Co68.15Fe4.3Si12.5B15‎ alloy ingot was prepared using vacuum arc remelting (VAR) furnace and then amorphous ribbon was produced using melt-spinning process. In order to develop the GMI biosensor, a micro-pattern was implicated on the ribbon on a SiO2 substrate using lithography technique with a meander structure containing 10 arms. Al2O3/Cr/Au layers were deposited on the patterned ribbon using RF-sputtering technique. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were used to evaluate the thermal property and structure of the ribbon. The results showed that the structure of the ribbon is amorphous. Finally, magnetoimpedance evaluation of the sensor was done at frequency range of 1-12 MHz and magnetic field of 0-170 Oe. In the GMI experiment, Fe3O4 nanoparticles were used as sensing elements. Based on the results obtained, it was shown that the maximum GMI ratio was 67% for blank sensor and is reduced by about 13% for sensor with 0.1 mg Fe3O4 at frequency of 9 MHz. Therefore, due to the significant sensitivity of fabricated sensor to iron-oxide nanoparticles, this sensor has potential to be used for bio-magnetic applications.