Iranian Journal of Materials Science and Engineering

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Abstract: Glassy samples with xTiO2 .3SiO2 .Na2O composition that (8≤x≤40) (molar) were casted in refractory steel molds after melting at air as parallel palates. After polishing and getting to desire thickness, UV-VIS spectrometry in 200 -1100 nm was measured on samples. Glass density was measured by a sensitive micro balance and was found that by increasing titanium dioxide of glasses, glass density increases. Results from UV-VIS spectroscopy show that increase of titanium dioxide decreases light transmission and this value reaches zero for sample with 40 molar percent of titanium dioxide. One reason of this reduction is formation of crystalline phase in glass, in which, by increasing titanium content crystalline phase will be increased, results of X-ray diffraction and electron microscopy confirm this claim.

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C-SiC composites with carbon-based mesocarbon microbeads (MCMB) preforms are new type of highpreformance and high-temperature structural materials for aerospace applications. In this study MCMB-SiC composites with high density (2.41 g.cm-3) and high bending strength (210 MPa,) was prepared by cold isostatic press of mixed mesophase carbon powder derived from mesophase pitch with different amount (0, 2.5, 5%) nano SiC particles. All samples were carbonized under graphite bed until 1000 °C and finally liquid silicon infiltration (LSI). Microstructure observations resultant samples were performed by scanning electron microscopy and transition electron microscopy (SEM & TEM). Density, porosity and bending strength of final samples were also measured and calculated. Results indicates that the density of samples with nano additive increased significantly in compare to the free nano additives samples.

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Colloidal silica bonded refractory castables have been developed recently. It was found that colloidal silica is one of the best binders can substitute other binders such as cement in No Cement Castable (NCC) and Ultra Low Cement Castable (ULCC) refractories. Also composition of colloidal silica with appropriate additives resulted in a gel form which makes the initial strength. Moreover, the nano size silica particles are extremely reactive in high alumina castables and may encourage the mullite formation in the microstructure. In the current study, four castables were prepared. The sample containing 6wt % microsilica was a reference, then microsilica was replaced by different amount of colloidal silica (2.5, 5, 7.5 wt %). Silica and water content was kept constant. It’s concluded that the castables containing the optimum amount of silica sol shows remarkable increase in both castable fluidity and mechanical strength (CCS and MOR) in dried and sintered state. It was also found that nanosilica particles increase the rate of needle-shaped mullite formation during sintering at 1400°C. According to FTIR results, the addition of Calcium Aluminate Cement (CAC) to the silica sol may be responsible for the increment of siloxane bridges (Si-O-Si).

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In this research, the nickel oxide was dissolved in cryolite at temperatures of 880, 940 and 1000°C. In order to reduce the nickel oxide, aluminum was added to the salt. Simultaneously the nickel oxide was reduced and Al3Ni2 intermetallic compound was formed. In the duration intervals of 2.5-40 minutes samples of the salt and metallic phases were taken. The variation of the nickel content in metallic and salt samples was determined by the AAS. The results indicate that increasing the temperature and duration has a positive effect on the reduction process and Al3Ni2 intermetallic compound formation. The nickel content in the metallic sample has its highest amount at 1000°C in 10 minutes. Furthermore, practical results of the studies of nickel content variations in metallic and salt samples confirm the data obtained from theoretical calculations.

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Montmorillonite modified is an efficient environmental friendly catalyst under one-pot-three-component synthesis of 3,4-dihydropyrimidine-2(1H) ones. The preparation was performed with an aldehyde, 1,3-dicarbonyl compounds, urea or thiourea under solvent-free conditions. In comparison with the other methods of Biginelli reaction, this new method has short reaction time inexpensive catalyst and in addition excellent yields were obtained.

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In this research the relationship between graphitization ability and the carbon equivalent (CE %) of a cast iron have been investigated. The first series of moulds were cast at CE of 3.2% and pouring temperature of 1350°C. The other moulds were cast at different CE% with varying Si content. The graphitization ability( c ) was calculated using the thermodynamics aspects of graphitization and CE%. The results showed that the graphitization ability increases with an increase in CE% and decrease with pouring temperature.

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In this study the effect of Al–5Ti–1B grain refiner on the structural characteristics and wear properties of Al–12Zn–3Mg–2.5Cu alloy was investigated. The optimum amount for Ti containing grain refiners was selected as 2 wt.%. T6 heat treatment, (i.e. heating at 460 °C for 1 h before water quenching to room temperature and then aging at 120 °C for 24 h) was applied for all specimens before wear testing. Dry sliding wear resistant of the alloy was performed under normal atmospheric conditions. The experimental results showed that the T6 heat treatment considerably improved the resistance of Al–12Zn–3Mg–2.5Cu alloy to dry sliding wear.

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Thermal explosion mode of combustion synthesis was used to fabricate TiAl-Al2O3 and TiAl-Ti2AlC-Al2O3 composites from elemental powder mixtures of TiO2, Al and C and characterized by XRD and Scanning Electron Microscopy (SEM) coupled with Energy-Dispersive Spectroscopy (EDS). The experimental results showed that thermite reaction of Al with TiO2 caused TiAl-Al2O3 composite formation. By adding carbon powder to the thermite mixture, ternary carbide Ti2AlC and TiAl-Ti2AlC-Al2O3 composite were formed. With low carbon in thermite mixture, direct formation of Ti2AlC without intermediate TiC was observed. After TiAl formation, Ti2AlC precipitated from molten TiAl in the vicinity of carbon particles. SEM micrographs show that addition of carbon to thermite mixture changes the microstructure to a laminated form with plate-like grains.

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Metal matrix composite coatings reinforced with nano-particles have attracted scientific and technological interest due to the enhanced properties exhibited by these coatings. Cobalt/hexagonal boron nitride nano-composite coatings were prepared by means of the pulse current electroplating from a chloride electrolyte on copper substrates and a comparison was made with the pure cobalt in terms of structure and tribological properties. Effects of particles concentration (5-20 gL-1) and current density (50-200 mA cm-2) on the characterization of electroplated coatings were investigated via X-ray diffraction analysis, energy dispersive spectroscopy and Vickers micro-hardness. Moreover, the tribological behavior was studied using pin-on-disc method. The results showed that cobalt/hexagonal boron nitride nano-composite coatings have higher hardness, wear resistance and lower friction coefficient than pure cobalt and the plating parameters strongly affect the coating’s properties

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Several surface modification techniques such as ion implantation, surface laser melting, have been employed to improve pitting corrosion resistance of stainless steel. Electropolishing is a technique in which the surface roughness is eliminated through a selective electrochemical dissolution. The effect of electropolishing on pitting corrosion of 304 stainless steel (SS) was investigated employing polarization technique in conjunction with the scanning electron microcopy examination. Electropolishing process was carried out on wire of 2 mm diameter in 70% phosphoric acid solution at room temperature for 30 min. To elucidate the effect of roughness elimination on pitting corrosion, investigation was carried out on as-received specimen with surface finishing of 60 SiC grit and electropolished specimen in 0.5M NaCl solution at room temperature. A significant decrease on passive current density and also shift of pitting potential towards noble value was recorded on electropolished specimen revealing a pronounce effect of this technique on surface modification. Further investigation was carried out by employing slow ramp anodic potentiodynamic polarization on as received and electropolished specimen. Plot of metastable pitting current transient revealed the reduction on the number and magnitude of metastable pitting transients prior to occurrence of stable pitting on electropolished specimen. EDX analysis of the surface area of as received and electropolished specimens showed modification in surface roughness during electropolishing was the main reason of pitting corrosion improvement. Scanning microscopy investigation of polarized specimens beyond the pitting potential revealed that in as-receives specimen pits were nucleated in at and in the vicinity of surface scratches that was created during surface abrading

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Metakaolinite-based geopolymer has been synthesized at about 25 °C from metakaolin which has been calcined in different temperatures (600-900 °C) and different Na2O/SiO2 ratio activator (0.3-1.1). Compressive strength and microstructure of cement pastes after 7-28 days curing at ambient temperature were measured. Compressive strength tests on the samples showed that the sample made with calcined kaolin at 700 °C and molar ratio of 0.6 has highest average compressive strength of 32 MPa after 28 days of curing. Evaluation of infrared spectroscopy (FTIR) and microstructure showed that geopolymer cement developed and new molecular structure established

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Corrosion behavior of mild steel in chloride contaminated alkaline solution has been studied for the period up to 100days. Saturated Calcium hydroxide solution was used as alkaline solution and 0.5M NaCl solution was used to accelerate mild steel corrosion. The Charge transfer resistance Rct, Current density Icorr and inhibition efficiency values were obtained from tafel polarization and electrochemical impedance spectroscopic technique for sodium nitrite, sodium citrate and sodium benzoate mixed inhibitors. The results were compared with nitrite inhibitive system. The combination of nitrite inhibitor along with benzoate and citrate inhibitors enhanced the durability of mild steel through formation of nanosized -Fe2O3 film on steel suface even in presence of high chloride contamination. The results obtained from gravimetric method proved that the 100 days exposure of mild steel in nitrite with citrate, nitrite with citrate and benzoate mixed inhibitors showed the maximum inhibition efficiency of 98% in comparison with nitrite inhibitive system alone (41.5%). The maximum corrosion resistance performance of these mixed inhibitors system was due to the formation of thick layer of nano : Fe2O3 fibrous film on steel surface.

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Crystallization kinetics of Fe52Cr18Mo7B16C4Nb3 alloy was evaluated using X-ray diffraction, differential scanning calorimetric (DSC) tests and TEM observations in this research work. In effect, crystallization and growth mechanisms were investigated using DSC tests in four different heating rates (10, 20, 30, 40 K/min) and kinetic models (i.e. Kissinger- Starink, Ozawa, and Matusita methods). Results showed that a two -step crystallization process occurred in the alloy in which α - Fe and Fe3B phases were crystallized respectively in the structure after heat treatment. Activation energy for the first step of crystallization i.e., α - Fe was measured to be 421 (kj/mol) and 442 (kj/mol) according to both Kissinger- Starink and Ozawa models respectively. Further, Avrami exponent calculated from DSC curves was 1.6 and a two -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. TEM observations reveal that crystalline α – Fe phase nucleated in the structure of the alloy in an average size of 10 nm and completely mottled morphology

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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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In the present study, reduction of zinc oxide from the pellets made of steelmaking electric arc furnace dust has been investigated. Effects of such parameters as the type of carbon material (graphite, coke and charcoal) as well as time and temperature on the reduction reaction have been examined. The reduced (dimensionless) time method was applied to perform a kinetic analysis of the system. Experimental results showed that increasing the temperature in the range of 925-1150°C results in a remarkable increase in the reduction rate. It was also shown that the reduction process is controlled by chemical reaction. Meaningful difference in the activation energy values calculated for reduction with graphite (24.75 kcal/mol), coke (18.13 kcal/mol) and charcoal (11.52 kcal/mol) indicate the predominant role of chemical reaction (carbon gasification) in the overall reaction rate and its rate-controlling mechanism. Carbothermal reduction of pelletized EAF dust proved to be an efficient reduction method, so that above 90% reduction was achieved in about one hour at temperatures around 1100°C.

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The effects of H2SO4 concentration on the electrochemical behaviour of passive films formed on AISI 304 stainless steel were investigated using by potentiodynamic polarization, Mott–Schottky analysis and electrochemical impedance spectroscopy (EIS). Potentiodynamic polarization indicated that the corrosion potentials were found to shift towards negative direction with an increase in solution concentration. Also, the corrosion current densities increase with an increase in solution concentration. Mott–Schottky analysis revealed that the passive films behave as n-type and p-type semiconductors at potentials below and above the flat band potential, respectively. Also, Mott– Schottky analysis indicated that the donor and acceptor densities are in the range 1021 cm-3 and increased with solution concentration. EIS data showed that the equivalent circuit Rs(Qdl[Rct(RrQr)]) by two time constants is applicable.

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Weight loss technique has been used to study the corrosion inhibition efficiency of tin in HNO3 solution by using the leaves and stem extract of different varieties of Holy Basil viz. ocimum basilicum (EB), ocimum cannum (EC) and ocimum sanctum (ES). The results show that all the varieties under study are good corrosion inhibitors, among which leaves extract of EB is the most effective. Corrosion inhibition efficiency increases with increasing concentration of inhibitor and it also increases with increasing concentration of HNO3 solution. Inhibition efficiency was found maximum up to 95.83% for tin in 3.0 M HNO3 solution, with 0.6% leaves extract whereas it was 81.25% in same concentration of HNO3 solution for stem extract

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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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This paper was aimed to address the modeling and optimization of factors affecting the corrosive wear of low alloy and high carbon chromium steel balls. Response surface methodology, central composite design (CCD) was employed to assess the main and interactive effects of the parameters and also to model and minimize the corrosive wear of the steels. The second-order polynomial regression model was proposed for relationship between the corrosion rates and relevant investigated parameters. Model fitted to results indicated that the linear effects of all of factors, interactive effect of pH and grinding time and the quadratic effects of pH and balls charge weight, were statistically significant in corrosive wear of low alloy steel balls. The significant parameters in the corrosive wear of high carbon chromium steel balls were the linear effects of all factors, the interactions effect of solid concentration, mill speed, mill throughout, grinding time, and the quadratic effects of pH and solid content. Also, the results showed that within the range of parameters studied, the corrosion rate of 78.38 and 40.76 could be obtained for low alloy and high carbon chromium steel balls, respectively.

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In this study, porous titanium composites containing 5, 10 and 15 wt. % nanobioglass were fabricated by space holder sintering process. The pore morphology and phase constituents of the porous samples were characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The mechanical properties were determined by compression test. The porosity of the sintered samples showed an upward trend with an increase in bioglass content. As the bioglass content was increased, the compressive strength was first increased and then decreased. The results obtained in this work suggest that the fabricated porous compact with 10 wt. % bioglass with compressive strength value of about 76.7 MPa, high porosity and good biocompatibility has the potential application for bone tissue engineering.