http:// ijmse.iust.ac.ir Iranian Journal of Materials Science and Engineering - Journal articles for year 2011, Volume 8, Number 1 Yektaweb Collection - https://yektaweb.com en 2011/3/10 http://ee.iust.ac.ir/ijmse/browse.php?a_id=328&sid=1&slc_lang=en Abstract: Reduction of the Titanium dioxide, TiO2, by methane was investigated in this work. The thermodynamic of reaction was examined and found favorable. The reaction of titanium dioxide with methane was carried out in the temperature range 1150°C to 1450°C at atmospheric pressure with industrial high porosity pellets prepared from titanium dioxide powder. The evolved gas analyzing method was used for determination of the extent of reduction rate. The gas products of the reaction are mostly CO and trace amount of CO2 and H2O. The synthesized product powder was characterized by X-ray diffraction (XRD) for elucidating solid phase compositions. The effect of varying temperature was studied during the reduction. The conversion-time data have been interpreted by using the grain model. For first order reaction with respect to methane concentration, the activation energy of titanium dioxide reduction by methane is found to be 51.4 kcal/gmole. No detailed investigation of kinetic and mechanism of the reaction was reported in literatures. R. Alizadeh http://ee.iust.ac.ir/ijmse/browse.php?a_id=329&sid=1&slc_lang=en Abstract: Zirconia solid electrolytes with nonequilibrium composite structure were prepared by impregnation of a porous 8YSZ matrix with a solution of Zirconia. Microstructures were characterized by XRD and SEM. The electrical properties were studied by impedance spectroscopy as a function of temperature. Biaxial flexural strength and fracture toughness of composite samples were measured by ring on ring and Vickers microhardness indentation methods respectively. The microstructures of the composite electrolytes were composed of cubic grains surrounded by tetragonal second phase grains. It was shown that the electrical and mechanical properties of the prepared electrolyte can be adjusted by controlling the amount of doped zirconia. Increasing the amount of doped zirconia increases the tetragonal phase content which improves fracture toughness and fracture strength. In addition, increasing tetragonal phase content of the composite electrolytes decreases the conductivity at high temperatures while the situation is reversed at low temperatures. M. Ghatee http://ee.iust.ac.ir/ijmse/browse.php?a_id=330&sid=1&slc_lang=en 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. M. Kazemimoghadam http://ee.iust.ac.ir/ijmse/browse.php?a_id=331&sid=1&slc_lang=en Abstract: Efforts have been carried out in order to use microsilica to develop a forsterite bond rather than other types of binders in the basic refractory castables. According to the higher drying rate and sinterability of colloidal silica, it has been proposed in the recent years. In the present work, effects of replacement of microsilica by colloidal silica evolution of forsterite bond have been studied in magnesia based refractory castables. In this way, Physical properties of prepared samples with different amount of colloidal silica versus temperature were investigated. In addition, phase variation and microstructural evolution of sintered specimens at 1000, 1200 and 1400 °C were studied by X-ray diffraction (XRD) and scanning electron microscope (SEM) respectively. Results showed that, due to Reaction of magnesia with microsilica and colloidal silica, magnesium hydrate and magnesium silicate hydrate formed in the dried samples strengthening the texture of the samples while forsterite formed from about 1000 °C and gradually increased with temperature rise. Also, better forsterite formation would be appeared by increasing the colloidal silica content. Further investigation carried out on the type of silica addition on properties of the castable refractory samples. It was found that the presence of micro silica and colloidal silica simultaneously (MS3C3 sample) at 1400 °C, caused modifying mechanical strength in compare with sample with only micro silica (MS sample). H. Sarpoolaky http://ee.iust.ac.ir/ijmse/browse.php?a_id=332&sid=1&slc_lang=en Abstract: In this study Al-5 (Vol) % SiCp nanocomposite powder has been successfully synthesized by high-energy planetary milling of Al and SiC powders for a period of 25 h at a ball-to-powder ratio of 15:1. The changes of the lattice strain, the crystallite size of the matrix phase, and the nanocomposite powder microstructure with time have been investigated by X-ray diffraction (XRD), X-ray mapping, and scanning electron microscopy (SEM) analyses. The morphologies of the nanocomposite powders obtained after 25 h of milling have also been studied by transmission electron microscopy (TEM). The results showed that nanocomposite powders were composed of near-spherical particles and, moreover, the SiC particles were uniformly distributed in the aluminum matrix. H. R. Shahverd http://ee.iust.ac.ir/ijmse/browse.php?a_id=333&sid=1&slc_lang=en Abstract: The aim of the present investigation is to study the physical and mechanical characteristics of dental-filling spherical high-copper and silver amalgams and to compare them with a common high-copper domestic unicompositional amalgam. In this study, cylindrical specimens were mechanically condensed according to the ISO 1559:1986 Standard in order to measure the compressive strength, Vickers hardness, static creep and dimensional change on setting. Adding more silver to the amalgam increased its compressive strength, creep resistance and reduced mercury vapor. After 1, 24 and 168h of amalgamation and Modulus of elasticity of specimen S1, the mean hardness and compressive fracture strength were significantly lower than those of . No significant differences were identified for the two alloys in the creep and dimensional changes on setting. It can be concluded that as far as the mechanical properties or corrosion resistance is concerned, the amalgam should be comprised of at least one spherical alloy. S. H. Razavi http://ee.iust.ac.ir/ijmse/browse.php?a_id=334&sid=1&slc_lang=en M. J. Tafreshi