Iranian Journal of Materials Science and Engineering

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Abstract: Ore mineral characterization and various experimental testwork were carried out on Asian Abe-Garm dolomite, Qazvin province, Iran. The testwork consisted of calcining, chemical characterization, LOI determination, and reduction tests on the calcined dolomite (doloma), using Semnan ferrosilicon. Calcining of dolomite sample was carried out at about 1400 ºC in order to remove the contained CO2, moisture, and other easily volatilised impurities. The doloma was milled, thoroughly mixed with 21% Semnan ferrosilicon and briquetted in hand press applying 30 MPa pressure. The briquettes were heated at 1125-1150 ºC and 500Pa in a Pidgeon-type tube reactor for 10-12 hours to extract the magnesium. Ferrosilicon addition, relative to doloma, was determined based on the chemical analyses of the two reactants using Mintek’s Pyrosim software package. Magnesium extraction calculated as 77.97% and Mg purity of 96.35%. The level of major impurities in the produced magnesium crown is similar to those in the crude metal production.

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Abstract: Composite specimens were prepared by dispersion of various amounts of nano-sized Al2O3 fillers in a monomer system containing 60% Bis-GMA and 40% TEGDMA. For comparative purposes, composite samples containing micrometer size Al2O3 fillers were also prepared following the same procedure. The mechanical properties of the light- cured samples were assessed by three-point flexural strength, diametral tensile strength, and microhardness tests. The results indicated a more than hundred percent increase in the flexural strength and nearly an eighty percent increase in the diametral tensile strength values in the samples containing nano-size Al2O3 filler particles. It is interesting to note that, this improvement was observed at a much lower nano-size filler content. Fracture surfaces analyzed by scanning electron microscopy, indicated a brittle type of fracture in both sets of specimens.

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Abstract: Microwave processing is one of the novel methods for combustion synthesis of intermetallic compounds and
composites. This method brings about a lot of opportunities for processing of uniquely characterized materials. In this
study, the combustion synthesis of TiAl/Al2O3 composite via microwave heating has been investigated by the
development of a heat transfer model including a microwave heating source term. The model was tested and verified
by experiments available in the literature. Parametric studies were carried out by the model to evaluate the effects of
such parameters as input power, sample aspect ratio, and porosity on the rate of process. The results showed that
higher input powers and sample volumes, as well as the use of bigger susceptors made the reaction enhanced. It was
also shown that a decrease in the porosity and aspect ratio of sample leads to the enhancement of the process.

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Shrinkage behavior of a geopolymer cement paste prepared from pumice-type natural pozzolan was studied
by changing parameters of chemical composition including SiO2/Na2O molar ratio of activator and total molar ratios
of Na2O/Al2O3, and H2O/Al2O3. For investigating the effect of curing conditions on shrinkage, hydrothermal curing
was also applied. The obtained results clearly revealed the governing effect of chemical composition on shrinkage.
Mixes with different Na2O/Al2O3 molar ratios exhibited different shrinkage behavior due to variations made in
SiO2/Na2O molar ratio. Application of hydrothermal curing after a 7-day period of precuring in humid atmosphere
also showed strong effect on shrinkage reduction.

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Abstract: There have been lots of studies to control the poor hydration resistance of dolomite refractories one of the
most effective solutions has been the addition of magnesia to doloma. Using a co-clinker of magnesia-doloma as a
starting material would provide more homogeneity in the properties of the product and has been published recently.
On the other hand, addition of iron oxide to doloma has been found to increase the hydration resistance. In this paper,
the effect of iron oxide addition on hydration phase analysis and microstructure of two different magnesia- doloma
samples, one with CaO content of 25 wt% and the other one with that of 35 wt% has been investigated. Ten samples
were prepared by pressing followed by firing at 1750 ºC for 3hrs. Results showed that the hydration resistance of the
samples improved by decreasing the CaO content, because CaO is much more prone to hydration comparing to MgO.
Besides, iron oxide addition lead to the formation of iron-containing phases which increased the hydration resistance
of the samples both by capsulating the CaO and MgO grains and by promoting the liquid phase sintering.

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Abstract: The linear expansion, early-age compressive strength and setting times of the binary mixtures of gypsum and Portland cement clinkers of relatively low C3A-contents were investigated. For this reason, type 1, 2, and 5 of Portland cement-clinkers were selected and a number of binary mixtures were designed. At relatively lower percentages of gypsum (about 5%), the early strength behavior is improved. Results obtained for compressive strength of mixtures with 5% gypsum confirm the possibility of achieving 28- and 90-day compressive strengths up to values higher than 100 MPa and 130 MPa, respectively. At relatively higher percentages of gypsum (more than 25%), excessive expansion caused by ettringite formation results in the formation of micro-cracks effectively weakening the strength behavior. The work suggests that type S expansive cements could be produced from Portland cement clinkers of relatively low C3Acontents.

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TiO2/SiO2 nanocomposite with molar ratio 1:1 was synthesized by a free calcination sol-gel method using titanium tetra chloride and tetraethylorthosilicate as raw materials. In the composite, TiO2 nanocrystals are highly dispersed in the amorphous SiO2 matrix and the mater showed size quantization effect arising from the presence of extremely small titanium oxide species having a low coordination number. Thermal phase transformation studies of the as-prepared composite were carried out by means of X-ray diffraction (XRD) patterns and thermogravimetry–differential scanning calorimetry (TG–DSC) analyses. The studies showed existence of anatase phase in all the tested temperatures. When temperature exceeds 400°C, brookite phase was formed beside anatase phase. At 950°C amorphous silica matrix was transformed to crystobalite and brookite phase disappeared. Finally, small peaks of rutile phase were detectable at 1100°C.

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Electrochemical coating processes are significantly affected by applied magnetic fields due to the generation of electromagnetic forces. The present research work has been undertaken to study the effect of coating parameters such as current density and alumina concentration on the characteristics of Ni-Al2O3 composite coating under static magnetic field. Ni-Al2O3 composite coating was applied on a mild steel substrate using conventional Watts solution containing Al2O3 particles with and without magnetic field. The coating microstructure and Al2O3 particle density in the coating layer were examined by scanning electron microscopy (SEM). It was found that the applied magnetic field made the coating structure finer and leads to the increases of the particle content in the coating. However, the results confirmed that the magnetic forces inversely affected the particle density in the coating at higher current density than that of normal coating process.

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Ultraviolet–Visible (UV–Vis) spectroscopy was used, in the current investigation, to explore the dispersion and stability of titania nanoparticles in an aqueous media with different types of dispersants. Hydrochloric and nitric acids as well as ammonia were used to determine the stability of the suspension in the acidic region (pH=2.5) and basic area (pH=9.5), respectively. In addition, for measuring sustainability of suspension and creating steric, and electrosteric repulsive forces, ethylene glycol and ethylene glycol plus ammonia were employed, respectively. UV–V is
spectrometry was applied to realize the effect of nano titania concentrations and different types of dispersants of samples containing different amounts of nano titania and different types of dispersants on stability of TiO2-containing suspensions. In addition, the stability of dispersion could be evaluated in colloidal mixtures containing ethylene glycol plus ammonia. It was demonstrated that the mixtures containing ethylene glycol plus ammonia were stable over a period of 4 days. To support the UV–Vis results, other techniques such as atomic force microscopy (AFM) and scanning electron microscopy (SEM) were employed to study the degree of agglomeration of titania nanoparticles in terms ofmorphology and size.

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Abstract: This study presents the research results of effect that refining process has on porosity and mechanical properties of high pressure die castings made of AlSi12S alloy. The operation of refining was carried out in a melting furnace with the use of an FDU Mini Degasser. Mechanical properties (UTS, YS, Elongation, Brinell Hardness) were assessed on samples taken from high pressure die castings. The effect of molten metal transfer operation and the time elapsing from completion of the refining process on the alloy mechanical properties was determined.

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Abstract: A thermodynamic model was used to find out the optimum temperature for the growth of ZnS single crystals in closed ampoules by chemical vapor transport technique. Based on this model 1002 °C was found to be optimum temperature for 2 mg/cm3 concentration of transporting agent (iodine). ZnS Crystals were grown in optimum (1002 °C) and non-optimum (902 °C and 1102 °C) temperatures. The composition structure and microstructure of the grown crystals were studied by Atomic absorption spectroscopy, X-ray diffraction and Scanning electron microscopy measurements. Properties of the grown crystals were correlated to the growth conditions especially a stability in mass transport along the closed tube length.

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Abstract: The boundary value problems involving contact are of the great importance in industries related to mechanical and materials engineering. These mixed problems are challenging since a priori unknown deformed surface of the material contacting a rigid indenter is to be determined as a part of the solution. Anisotropic solids represent an important class of engineering materials including crystals, woods, bones, thin solid films, polymer composites, etc. Contact analysis of an anisotropic media, however, is more difficult and is developed less completely in the literature. In this work, both analytical and computational studies of the contact treatment of a semi-infinite orthotropic material indented by a rigid spherical indenter have been considered in two different sections. This approach can be applied to determine the interfacial contact area and pressure distribution for three-dimensional orthotropic materials, and can then be used to calculate the resulting stress and strain fields of the media. Results presented herein can serve as benchmarks with which to compare solutions obtained by ANSYS commercial package.

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Abstract: During solidification and casting in metallic molds, the heat flow is controlled by the thermal resistance at the casting-mold interface. Thus heat transfer coefficient at the metal- mold interface has a predominant effect on the rate of heat transfer. In some processes such as low pressure and die-casting, the effect of pressure on molten metal will affect the rate of heat transfer at least at initial steps of solidification. In this study interfacial heat transfer coefficient at the interface between A356 alloy casting and metallic mold during the solidification of casting under pressure were obtained using the IHCP (Inverse Heat Conduction Problem) method. Temperature measurements are then conducted with the thermocouples aligned in the casting and the metallic mold. The temperature files were used in a finite-difference heat flow program to estimate the transient heat transfer coefficients. The peak values of heat transfer coefficient obtained for no pressure application of A356 alloy is 2923 and for pressure application is 3345 . Empirical equation, relating the interfacial heat transfer coefficient the applied pressure were also derived and presented.

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Abstract: Nickel was electrodeposited onto copper substrates with high {111} and {400} peak intensities. The grain size of coatings deposited onto the copper substrate with a higher {111} peak intensity was finer. Spheroidized pyramid morphology was obtained at low current densities on both copper substrates. By increasing the deposition current density, grain size of the coating was increased for both substrates and eventually a mixed morphology of pyramids and blocks was appeared without further increase in grain size. This decreased the anodic exchange current density probably due to the decrease of surface roughness and led to a lower corrosion rate.

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In automation flexible manufacturing systems, tool wear detection during the cutting process is one of the most important considerations. This study presents an intelligent system for online tool condition monitoring in drilling process .In this paper, analytical and empirical models have been used to predict the thrust and cutting forces on the lip and chisel edges of a new drill. Also an empirical model is used to estimate tool wear rate and force values on the edges of the worn drill. By using of the block diagram of machine tool drives, the changes in the feed and spindle motor currents are simulated, as wear rate increases. To predict tool wear rate in drill, Fuzzy logic capabilities have been used to develop intelligent system. The simulated results presented in MATLAB software show the effectiveness of the proposed system for on-line drill wear monitoring.

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Atomistic simulations are carried out for zeolite with ABW framework. The structure is modeled and force field simulations are preformed to investigate its elastic properties, bulk, shear modulus and auxeticity. Bulk moduli (Ks), Shear moduli (G), and Poissons ratios (ν) were found to be Ks=79.71725 GPa, G=16.93265 GPa, νxy = -0.2207, νxz= -0.5730, νyx= -0.71717, νyz=0.87013, νzx= -0.33097 and νzy=1.54568 for ABW the negative value of Poisson’s ratios reflects an auxetic behavior of material. An evaluation of the directional young’s moduli shows that the compressibility of ABW is not uniform along [100], [010] and [001] axes. All calculations were performed using GULP program.

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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.