Iranian Journal of Materials Science and Engineering

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An investigation of the electrochemical noise generation during Stress Corrosion Cracking (SCC) of 70-30 Brass in Mattson's solution was conducted. The fluctuations of potential and current were monitored. The relationship between potential and current fluctuations has been evaluated in time domain and the obtained data has been analyzed in the frequency domain using Power Spectral Density (PSD). It is shown that 70-30 Brass has characteristic noise behavior during SCC that is step-by-step change in current and potential up to the final stage of fracture, and this may be used for SCC monitoring.

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Abstract: The theoretical calculation of dislocation density in different regions of a deformed workpiece of 99.99% pure copper has been carried out using different procedures consisting of Finite Element Method (FEM) and hardness measurement. To assess the validity of the results pertaining to these procedures, the dislocation density is experimentally measured utilizing the Differential Scanning Calorimetry (DSC). Comparing the predicted and experimental results, it was found that the average error in prediction of the dislocation density by the hardness measurement and FEM is 12% and 2.5%, respectively. Also, for further confirmation of the evaluated dislocation density of each region of the deformed workpiece, the annealing process was carried out and in the region of higher dislocation density, a finer grain size was observed.

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Abstract: Hardfacing is one of the most useful and economical ways to increase the service life of components subjected to abrasive wear. Iron based hardfacing alloys have long been considered as candidate coatings for wear-resistant applications in industry. In the present work two layer of Fe-34Cr-4.5C%wt hardfacing alloy was deposited on ASTM A36 carbon steel plates by SMAW method. The microstructure consists of large primary and eutectic M7C3 carbides, metastable austenite and small amount of secondary carbides. The microstructure was analyzed by optical and scanning electron microscopes. In the same condition of size, shape, distribution and volume fraction of carbides the as-welded matrix changed to martensite, tempered martensite and ferrite by heat treatment processes. The wear resistance was measured by pin-on-disk method under loads of 5, 10 and 20N and for sliding distance of 1500m. The results showed that the as-welded sample with austenitic matrix has the most and the ferritic matrix specimen has the least wear resistance. The predominate mechanisms for mass losses were determined to be micro-cutting, microploughing.

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Abstract: Nano pore Mordenite membranes were prepared on the outer surface of ceramic tubular tubes via hydrothermal synthesis and evaluated for dehydration pervaporation of water unsymmetrical dimethylhydrazine UDMH mixtures. Highly water-selective mordenite membranes were prepared and the optimum reaction condition was found to be 24 h crystallization time and 170 °C crystallization temperature. Effect of gel composition on separation factor and water flux of the water-UDMH mixtures was investigated. X-ray diffraction (XRD) patterns showed that mordenite is the only zeolite material which presents in the membrane. Morphology of the supports subjected to crystallization was characterized by Scanning electron microscopy (SEM). In PV of the water-UDMH mixtures, the membrane exhibits a hydrophilic behavior, with a high selectivity towards water and a good flux. The best membranes had a water flux of 2.67 kg/m2.h at 27 °C. The best PV selectivity was obtained to be 264.

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trontium hexaferrite (SrFe 12 O 19 ) nanosized powders were synthesized by sol-gel auto-combustion method with and without cetyltrimethylammonium boromide (CTAB) addition in the sol with Fe/Sr ratio of 11 (using additional Sr). The resultant powders were investigated by X-ray Diffraction (XRD), Transmission Electron Microscope (TEM), Field Emission Scanning Electron Microscope (FESEM) and Vibration Sample Magnetometer (VSM) techniques. Phase constituents of the synthesized samples which were heat treated at temperatures in the range of 700- 900 ◦C were studied. XRD results revealed that CTAB addition facilitates the formation of single phase strontium hexaferrite at 800 ◦C. Microstructural evaluations with FESEM represented that CTAB addition causes formation of larger particles with a narrower size distribution. VSM results represented that the highest amount of intrinsic coercivity force ( i H C ) was obtained in the sample without CTAB addition and with additional Sr, calcined at 800 ◦C for 1 h which was equal to 5749.21 Oe, while the value of i H C was equal to 4950.89 Oe without additional Sr. The amount of maximum magnetization (M max ) was raised from 48.41 emu/g to 62.60 emu/g using CTAB and additional Sr. The microstructure and magnetic properties of the samples have been explained

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In the present study, the feasibility of α-Fe ferromagnetic phase formation in glass and glass-ceramic by reduction in hydrogen atmosphere have been investigated. The glass with the composition of 35Na 2 O–24Fe2O3–20B 2O3 – 20SiO 2 –1ZnO (mol %) was melted and quenched by using a twin roller technique. As quenched glass flakes were heat treated in the range of 400-675 °C for 1-2 h in hydrogen atmosphere, which resulted in reduction of iron cations to α-Fe and FeO. The reduction of iron cations in glass was not completely occurred. Saturation magnetization of these samples was 8-37 emu g -1 . For the formation of glass ceramic, As quenched glass flakes heat treated at 590 °C for 1 h. Heat treatment of glass ceramic containing magnetite at 675°C in hydrogen atmosphere for 1 h led to reduction of almost all of the iron cations to α-Fe. Saturation magnetization of this sample increased from 19.8 emu g -1 for glass ceramic to 67 emu g -1

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Nano-sized NiFe2O4 powders were synthesized by sol–gel auto-combustion method using pH values from 7 to 9 in the sol. The effect of pH variations on complexing behavior of the species in the sol has been explained. Changes in phase constituents, microstructure and magnetic properties by changes in pH values were evaluated by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and vibration sample magnetometer (VSM) techniques. Changes in pH value from 7 to 9 changes the amounts of NiFe2O4, FeNi3 and α-Fe2O3 phases. Calculated mean crystallite sizes are in the range of 44 to 51nm. FESEM micrographs revealed that increasing the pH value to 9 causes formation of coarse particles with higher crystallinity. Saturation magnetization was increased from 36.96emu/g to 39.35emu/g by increasing pH value from 7 to 8 which is the result of increased FeNi3 content. Using higher pH values in the sol reduces the Ms value.

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Petroleum coke contains high amounts of carbon and is used in the manufacturing of anode electrodes for the aluminum extraction. In the process of aluminum production, some particles separate from anodes as waste which contain petroleum coke. Therefore, recycling and processing of these petroleum coke particles is the subject of this study. The ash content reduced to 31% and 13% in the jig and shaking table concentrate, respectively. These two steps were considered as the pre-processing methods and heavy media separation was used to decrease the ash content much more. Finally, flotation was performed in order to purify the particles with the size of less than one millimeter.

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Kinetic models are the most important instruments for predicting and evaluating the performance of flotation circuits. To determine the kinetic order and rate of flotation of a gilsonite sample, flotation experiments were carried out in both rougher and cleaner stages. Experiments conducted using the combinations of petroleum-MIBC, gas oil-pine oil, and one test without any collector and frother. Five first order kinetic models were applied to the data obtained from the flotation tests by using the Matrix Laboratory software. Statistical analysis showed that the classic first order model perfectly matched the rougher and cleaner results performed using petroleum-MIBC combination. The kinetic constants (k) were calculated as 0.04 (s^-1) and 0.01 (s^-1) for the rougher and cleaner, respectively. Rougher and cleaner tests without collector and frother also matched with the modified gas/solid adsorption and rectangular models with the k values of 0.05 (s^-1), and 0.01 (s^-1), respectively. The relationship between flotation rate constant, maximum combustible recovery and particle size were also studied. The results showed that the maximum flotation combustible recovery and flotation rate were obtained with an intermediate particle size both in the rougher and cleaner flotation processes. The combustible recovery and flotation rate in the rougher flotation process were higher than that in the cleaner flotation process.

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Flash sintering of 8 mol% yttria-stabilized zirconia (8YSZ) as solid oxide fuel cell (SOFC) electrolyte is studied. The relation between relative density, shrinkage, sample temperature during the flash, and incubation time, with the electric field strength, current density, as well as contact paste, are modeled by response surface methodology (RSM). The electric field strength and current density varied from 50 to 400V.cm^-1 and 50 to 200mA.mm^-2, respectively. Also, platinum (Pt) and lanthanum strontium manganite (LSM) used as contact paste. Results show that using LSM paste lead to higher density and more shrinkage compare with Pt paste. Contrary, the electric field strength has no significant effect on density and shrinkage. However, a minimum electric field strength equal to 80 V.cm^-1 is necessary for flash onset. As the field increases, the incubation time decreases dramatically. Compare with samples with LSM paste, samples with Pt contact paste reach to a higher temperature during the flash. Flash sintered 8YSZ shows the mean grain size of 0.3μm, which is about half of the conventionally sintered 8YSZ. Electrochemical Impedance Spectroscopy reveals despite lower mean grain size, the resistivity of flash sintered 8YSZ is lower than conventionally sintered 8YSZ.

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In this study, for the first time, the Forsterite (Mg₂SiO₄) nanoparticles (NPs) with the size of about 25 nm were added to the phosphate-based electrolyte, and the characteristics and properties of the obtained plasma electrolytic oxidation (PEO) coating on AZ31 Mg alloy was investigated. The results of the potentiodynamic polarization measurements revealed that after one week of exposure to simulated body fluid (SBF) solution, the coating with Mg₂SiO₄ NPs possessed 12.30 kΩ cm² polarization resistance, which was more than two times greater than that of the coating without NPs. The thicker coating layer, lower wettability, and also presence of Mg₂SiO₄ NPs inside the pores were responsible for enhanced corrosion protection in the Mg₂SiO₄ NPs incorporated coating. After three weeks of immersion in SBF solution, the in-vitro bioactivity test results indicated the ability of the NPs-containing coating to form apatite (Ca/P ratio of 0.92) was weaker than the coating without NPs (Ca/P ratio of 1.17). This could be attributed to the lower wettability of the coating with NPs and supports that the addition of the nanoparticles is not beneficial to the bioactivity performance of the coating. 

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The goal of the present study is to prepare a room temperature cured hydrophobic and self-cleaning nano-coating for power line insulators. As a result, the installed insulators operating in power lines can be coated without being removed from the circuit and without the need to cut off power. For this purpose, hydrophobic silica nanoparticles were synthesized by sol-gel method using TEOS and HMDS. The synthesized hydrophobic silica nanoparticles were characterized by XRD, FTIR, SEM, and TEM analyses to investigate phase formation, particle size, and morphology. Then the surface of the insulator was cleaned and sprayed by Ultimeg binder solution, an air-dried insulating coating, as the base coating. Then the hydrophobic nano-silica powder was sprayed on the binder coated surface and left to be air-cured at room temperature. After drying the coating, the contact angle was measured to be 149^o. Pull-off test was used to check the adhesion strength of the hydrophobic coating to the base insulator. To evaluate the effect of environmental factors, UV resistance and fog-salt corrosion tests were conducted. The results showed that 150 hours of UV radiation, equivalent to 9 months of placing the samples in normal conditions, did not have any significant effect on reducing the hydrophobicity of the applied coatings.

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Titanium implants are one of the most durable and conventional orthopedic and dental implants. The goal of this research is to improve the bio-compatibility of these implants by implementing nano coating of titanium oxide nanotubes (TNT) to enhance bone graft on the implant surface, and reduction of wound healing duration and risk of implant surgery at the same time. For this purpose, the effects of dimension and atomic structure of titanium oxide nanotubes are examined on the surface properties and biological performance and tried to introduce an optimum status of this nano-tubular structure. TNTs were synthesized by anodizing method on the surface of titanium sheets. Dimensions of TNT can be controlled by anodizing process parameters. Heat treatment affects the atomic structure of TNTs. Contact angle measurement as one of the important surface properties was investigated on different dimensions and structures of TNTs, to study human blood's physical interaction with the implant surface. In addition, the quality and quantity of bone material sediment on the surface were examined by SBF test and SEM analysis. Finally, cell culture provided informative data on bone cells' response to these nanotubular coatings by analyzing MTT results and SEM photography of cells. As a result, the optimum dimension and atomic structure of TNTs were defined and the required process parameters were introduced to obtain this state. This setup can be used as an optimum state of TNT as a nano coating on titanium implant with orthopedic functions to enhance the cell adhesion and acquire the highest proliferation rate which means faster bone graft and shorter convalescence.