Iranian Journal of Materials Science and Engineering

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The orthogonal array design has been used to determine the optimum conditions for gold recovery from Zarshuran refractory gold sulfide ore (Iran) by direct cyanidation and roasting-cyanidation. The Taguchi method was used as the experimental design to determine the optimum conditions of dissolution behavior of gold with cyanidation and roasting-cyanidation from Zarshuran refractory gold ore . The experimental conditions were studied in the range of 10–12 for pH, 20-40 for time(h), 400-1200 for cyanide content (g/ton) and 30 -40 for percent solid(%). Orthogonal array (OA) L9 (34) consisting of four parameters each with three levels, was chosen. From this study for direct cyanidation the total optimum gold dissolution (30.11%) obtained at pH (10), Time (40 h), Cyanide content (800g/ton) and Percent solid (30%). Also for roasting- cyanidation the total optimum gold dissolution (34.96%) obtained at pH (12), Time (40 h), Cyanide content (1200g/ton) and Percent solid (35%).

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Metal matrix nano composite coatings possess enhanced properties such as corrosion and wear resistance. This paper aims to study the corrosion behavior of pure Co and Co-BN nano composite coatings deposited with different particles concentration (5-20 g L-1) on copper substrates using electroplating technique. Morphology and elemental compositions of the coatings were investigated by means of scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS). The corrosion behavior was analyzed in a 3.5 wt% NaCl via polarization and impedance techniques. The results obtained in this study indicate that the co-deposition of BN nano particles improved corrosion resistance of electrodeposited cobalt coatings.

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The synthesis of mesoporous CuFe2O4 spinel by several nanocasting strategies (i.e., multi-step nanocasting, one step nanocasting, modified solid-liquid), in which copper and iron nitrates are used as precursors and Pluronic P123 as surfactant, is explored. We have also checked the effect of pH, citric acid and sodium citrate in multi-step nanocasting method. The modified solid-liquid method which contains impregnating mesoporous silica by molten state salts in a non-ionic solvent seems to be the best choice to obtain single phase ordered mesoporous copper ferrite. Other methods suffer from the presence of copper oxide or hematite as impurities or lack of integrity in the mesoporous structure. Increasing pH up to 9.5 does not enhance the phase formation inside the pores of the silica matrix. The citric acid yields a fine structure but does not facilitate the phase formation. Adding sodium citrate neither heals the phase formation nor the structure of the final product. Moreover, vinyl- functionalized mesoporous silica exploited in this study as a hard template entraps both metal nitrates in the pores, assisting impregnation procedure

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This study is focused on the effects of electroslag remelting by prefused slag (CaO, Al2O3, and CaF2) on macrostructure and reduction of inclusions in the medical grad of 316LC (316LVM) stainless steel. Results showed that in order to obtain uniform ingot structures during electroslag remelting, the shape and depth of the molten pool should be carefully controlled. High melting rates lead to deeper pool depths and interior radial solidification characteristics. Furthermore, decrease in the melting rate caused more reduction of non-metallic inclusions. In practice, large shrinkage cavities formed during the conventional casting process in the primary ingots were the cause of the fluctuation in the melting rate, pool depth and extension of equiaxal crystals zone

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Ni-P Electroless coatings provide appropriate resistance to wear and corrosion. Co-deposition of particles between layers can improve their properties, especially general corrosion and erosion-corrosion behavior by means of nano diamond as reinforcing particles. In this study Ni-P/nano diamond composite deposition were deposited on steel substrate. Structure of the coatings and corrosion resistance of theme were investigated by scanning electron microscopy and corrosion tests in salty media. The composite structure of the deposit was evaluated as nano size without using any surfactants. Also results for the composite coating show better corrosion protection and higher hardness comparing with as -deposited Ni-P. The optimum concentration of diamond nanometer particles were found by evaluation of scanning electron microscopy pictures, hardness measurement, linear polarization and electrochemical impedance spectroscopy results

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In the present research, to form niobium carbide coating on the surface of AISI L2 steel Thermo-Reactive Deposition method (TRD) in a molten bath was used. Niobium carbide coating treatment was carried out at 1173 K, 1273 K, and 1373 K for 2, 4, and 8 hours. The molten bath contained 20wt.% borax (Na2B4O7), 5 wt.% boric acid (B2O3), and 75 wt.% ferro-niobium. The presence and properties of the coated layer were studied by means of Optical Microscopy (OM), Scanning Electron Microscopy (SEM), and X-Ray Diffraction (XRD) analysis. The thickness of coating ranged between 6.6 µm to 33µm depending on treatment time, and temperature. The effects of treatment time and temperature on the coating thickness were studied. Kinetic study of the formation of NbC coating showed that growth of the coating is under the control of diffusion. The activation energy of the process was estimated to be 122 kJ/mol. A practical formula to estimate the coating thickness was suggested.

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In order to improve the corrosion resistance of aluminosilicate refractories by molten aluminum, alkaline fluoride NaF and cryolite Na3AlF6 powders were studied. Both physical and chemical properties are known to influence wetting and corrosion behavior. This paper devoted to determine the influence of alkaline fluoride and cryolite added to andalusite based castable on the reaction with aluminum alloys. These additives led to the in-situ formation of celsian phases within the refractory matrix that led to improved corrosion resistance at 1300°C. Phase analysis revealed that celsian formation suppressed the formation of mullite within refractories, thereby reducing Penetration

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The effect of titanium dioxide addition on bonding strength of CaO-P2O5 -Na 2O-TiO2glass-ceramic system was investigated as a coating on titanium substrate. Thus, different amounts of TiO2 (2, 3.5 and 5mol %) were added to the base glass batch composition. The prepared glaze slips were applied on the substrate by dip coating method, dried and then heat treated at various temperatures. After that, bonding strength of the glass- substrates was determined via shear stress testing method. The de-bonded interfaces were analyzed by scanning electron microscopy (SEM). According to these results, the 5 mol% TiO 2 containing coating showed the best bonding strength, comparing with the other coatings. The bioactivity of the coated samples was investigated by soaking them in simulated body fluid (SBF). The surface of the samples was studied using SEM and X-Ray microprobe and it was observed that an apatite layer was grown on their surface

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Coating of a surface by droplet spreading plays an important role in many novas industrial processes, such as plasma spray coating, ink jet printing, nano safeguard coatings and nano self-assembling. Data analysis of nano and micro droplet spreading can be widely used to predict and optimize coating processes. In this article, we want to select the most appropriate statistical distribution for spread data of aluminum oxide splats reinforced with carbon nanotubes. For this purpose a large class of probability models including generalized exponential (GE), Burr X (BX), Weibull (W), Burr III (BIII) distributions are fitted to data. The performance of the distributions are estimated using several statistical criteria, namely , Akaike Information Criterion (AIC), Baysian Information Criterion (BIC), LogLikelihood (LL) and Kolmogorove-Smirnove distance. Also, the fitted plots of probability distribution function and quantile-quantile (q-q) plots are used to verify the results of different criteria. An important implication of the present study is that the GE distribution function, in contrast to other distributions, may describe more appropriately in these datasets.

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In the present study, CrN, TiN and (Ti, Cr)N coatings were deposited on D6 tool steel substrates. Physical and mechanical properties of coatings such as microstructure, thickness, phase composition, and hardness were evaluated. Phase compositions were studies by X-ray diffraction method. Mechanical properties were determined by nano-indentation technique. The friction and wear behaviour of the coatings were investigated using ball-on-disc tests under normal loads of 5, 7 and 9 N at sliding distance of 500 m, at room temperature. Scanning electron microscope equipped with energy dispersive spectroscopy, optical microscope, and 2D/3D profilometry were utilized to investigate the microstructures and wear mechanisms. Wear test results clarified that the wear resistance of (Ti, Cr)N and TiN coatings was better than that of CrN coating. The wear resistance of the (Ti, Cr)N coatings was related to the Ti content in the coatings and reduced by decreasing the Ti content. The dominant wear mechanisms were characterized to be abrasive and tribochemical wear

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In this work, TiN/TiCN & PN/TiCN multilayer films were deposited by plasma- assisted chemical vapour deposition (PACVD). Plasma nitriding (PN) and TiN intermediate layer prior to coating leads to appropriate hardness gradient and it can greatly improve the mechanical properties of the coating. The composition, crystalline structure and phase of the films were investigated by X-ray diffraction. Atomic force microscopy and scanning electron microscopy were employed to observe the morphology and structure of the films. The TiCN layer exhibited a columnar structure. The adhesion force between the film and the tool steel substrate was 30.8 MPa for TiN/TiCN and 25.4 MPa for PN/TiCN film determined by pull off tests. The hardness of TiN/TiCN film was 12.75 GPa while it was 5.4 GPa for PN/TiCN film, respectively. The improvement of the adhesion in TiN/TiCN was attributed to a less gradient hardness configuration. In addition, the mean friction coefficients of the films were about 0.2 for TiN/TiCN and 0.3 for PN/TiCN film determined by nanoindentation tests.

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In this study, corrosion behaviour of A356-10 vol.% SiC composites casted by gravity and squeeze casting is evaluated. For this purpose, prepared samples were immersed in HCl solution for 1h at open circuit potential. Tafel polarization and electrochemical impedance spectroscopy (EIS) were carried out to study the corrosion resistance of composites. The Tafel polarization and EIS studies of the corrosion behaviour of the A356-10 vol.% SiC composites showed that the corrosion resistance of the composite casted by squeeze casting was higher than that of the composites casted by gravity in selected corrosion media. Also, the Tafel polarization and EIS studies revealed that the corrosion current densities of both composites increase with the increase in the concentration of HCl. The micrographs of scanning electron microscope (SEM) clearly showed the squeeze casting composite exhibits a good dispersion/matrix interface compared to that of the composites produced by gravity casting

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In this paper, the possibility of mechanical coating of aluminum with either Ni or SiC using planetary ball mill was studied. The Al substrate was fixed inside of the vial lid of a planetary ball mill filled with milling balls and starting powder. The phase analysis and crystallite size measurement of the coatings were carried out using X-ray diffraction (XRD) method. Scanning electron microscope (SEM) was employed to study the coating/substrate interface and coating thickness. Hardness and wear resistance of coatings were also measured. The results indicated that all coatings have relatively uniform thickness. SiC coating shows poor compaction and adhesion to the Al, while nanostructured Ni coating is well-bonded to the substrate. Moreover, Ni coating showed higher hardness and wear resistance compared to SiC coating. It was found that the balls collision will result in the grain refinement of the coating as well as Al substrate. Mechanically deposited Ni coating shows higher hardness value compared to those obtained by conventional methods. This has been related to the induced grain refinement phenomenon.

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Effect of electro migration on crystal structures of platinum nanowire (Nano bridge) during Nano-gap formation is investigated by means of Transmission Electron Microscopy (TEM). Selected area diffraction patterns as well as bright field images are used for this investigation. There were severely recessions in the polycrystalline Nano bridge and crystal structures around the nanogap changed completely during electro migration. Due to Joule heating, original small crystal with random orientation disappeared and newly crystals with a preferred orientation grew. They have [111] orientations (respect to beam direction) with slight misorientations. α and θ was defined to calculate the misorientation and used to represent Nano-gap formation mechanism. The calculation gives the breaking of Nano bridge occurred along grain boundaries in most of Nano bridges. The controlling system during eletromigration may affect on the shapes of tips so that the shape of tips in Nano bridges, in which feedback control is applied, is more symmetric than others. The effect of temperature on atomic diffusivity might be the reason of the behaviour. {422} could be a preferred surface plane for mass transport in platinum Nano bridge in which atoms move along it

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On time replacement of a cutting tool with a new one is an important task in Flexible Manufacturing Systems (FMS). A fuzzy logic-based approach was used in the present study to predict and simulate the tool wear progress in turning operation. Cutting parameters and cutting forces were considered as the input and the wear rate was regarded as the output data in the fuzzy logic for constructing the system. Flank wear was used as the tool life criterion and the wear ranges were selected between 0 and 0, 3 based on ISO 3685 standard for new and worn tool respectively. For conducting the tests, Taghuchi method was used to design an experimental table. The results of the measurements and estimates confirmed the reliability of the fuzzy logic method for estimating tool wear. One significant feature of the proposed system is that it can predict the wear rate on-line by transferring the cutting force signals from the sensor to the fuzzy logic simulation box.

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Compression springs were prepared from Cr-Si high strength spring steel and coated with pure Zn and ZnNi by electroplating process. The effect of baking after electroplating as well as applying an electroless nickel interlayer on the fatigue and fatigue corrosion of the springs was investigated. The results were analyzed using weibull statistical model. A considerable improvement (8%) in fatigue life of the electroplated springs with Zn-Ni was observed in the presence of Ni interlayer. In addition, baking of these electroplated springs improved fatigue life by 4%. The fatigue life under salt spraying conditions, however, has demonstrated remarkable reduction by 40%, 34% and 30% for Zn-Ni plating, backed and unbaked Zn-Ni plating containing Ni interlayer, respectively

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MgAl2O4/Ti(C,N) composites were synthesized through aluminothermic reaction between Al,TiO 2,MgO powders and phenolic resin in coke bed condition. Effect of addition of carbon black and sugar into the mixture at different temperatures were investigated. The phases and microstructures of samples were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). MgAl 2O4 /Ti(C,N) composites without additive were obtained after heat treatment at 1600˚C. With addition of carbon black TiC, TiN and Ti(C,N) were appeared after firing at 1400˚C and formation of spinel/Ti(C,N) composites were completed at 1600˚C. In sample containing sugar, MgAl2O4 -Ti(C,N) composite were completely synthesized at 1400˚C. In this sample crystallite size of Ti(C,N) were 32 nm and carbon content of titanium carbonitride (Ti(C,N)) reached to 0.442 value.

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A modified strain-induced melt activation (SIMA) process was applied and its effect on the structural characteristics and hardness of the aluminum alloy Al–12Zn–3Mg–2.5Cu was investigated. Specimens subjected to a deformation of 40% at 300 °C were heat treated at various times (10-40 min) and temperatures (550-600 °C). Microstructural studies were carried out using optical and scanning electron microscopies (SEM). Results showed that the best microstructure was obtained at the temperature and time of 575 °C and 20 min, respectively. The hardness test results revealed superior hardness in comparison with the samples prepared without the application of the modified SIMA process.

T6 heat treatment including quenching to 25 °C and aging at 120 °C for 24 h was employed to reach to the maximum strength. After the T6 heat treatment, the average tensile strength increased from 231 MPa to 487 and 215 MPa to 462 for samples before and after strain-induced melt activation process, respectively. Ultimate strength of globular microstructure specimens after SIMA process has a lower value than as-cast specimens without SIMA process

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The micro layers micaceous iron oxide and nano-TiO 2 were incorporated into the epoxy resin by mechanical mixing and sonication process. Optical micrographs showed that the number and diameter size of nanoparticle agglomerates were decreased by sonication. The structure and composition of the nanocomposite was determined using transmission electron microscopy which showed the presence of dispersed nano-TiO 2 in the polymer matrix. The anticorrosive properties of the synthesized nano-composites coating were investigated using salt spray, electrochemical impedance spectroscopy and polarization measurement. The EIS results showed that coating resistance increased by addition of micaceous iron oxide micro layers and nano-TiO 2 particles to the epoxy coatings. It was observed that higher corrosion protection of nanocomposite coatings obtained by the addition of 3 %wt micaceous iron oxide and 4%wt nano-TiO 2 into epoxy resin.

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A homogenous TiO₂ / multi-walled carbon nanotubes(MWCNTs) composite film were prepared by electrophoretic co-deposition from organic suspension on a stainless steel substrate.  In this study, MWCNTs was incorporated to the coating because of their long structure and their capability to be functionalized by different inorganic groups on the surface. FTIR spectroscopy showed the existence of carboxylic groups on the modified carbon nanotubes surface. The effect of applied electrical fields, deposition time and concentration of nanoparticulates on coatings morphology were investigated by scanning electron microscopy. It was found that combination of MWCNTs within TiO₂ matrix eliminating micro cracks presented on TiO₂ coating. Also, by increasing the deposition voltages, micro cracks were increased. SEM observation of the coatings revealed that TiO₂/multi-walled carbon nanotubes coatings produced from optimized electric field was uniform and had good adhesive to the substrate.