فهرست مطالب

  • Volume:8 Issue: 3, 2011
  • تاریخ انتشار: 1390/08/17
  • تعداد عناوین: 7
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  • M. Sh. Bafghi, A. Yarahmadi, A. Ahmadi, H. Mehrjoo Page 1
    the reduction agent. Pellets of barite ore containing about 95% BaSO temperature, time, ore grain size and the type and grain size of the carbon materials. Graphite, coke and charcoal have been used as the reducing agent and the reduction experiments have been performed in the temperature range of 925-1150 °C. Apart from conducting the experiments using pellets made of ore powder, kinetic analysis of the experimental data by use of the reduced (dimensionless) time method has been another unique feature of the present study.Experimental results show that grain size of either carbon material or barite ore has not appreciable effect on the reaction rate. Kinetic analysis of the experimental data revealed the rate is strongly controlled by the chemical reaction of carbon gasification (Boudouard reaction). The reaction rate is very considerably related to the type of carbon material so that the activation energy varies from 15.6 kcal.mol kcal.mol gasification.The present study deals with the reduction of barium sulfate (Barite) to barium sulfide by use of carbon as4 has been reduced under different conditions of-1 for charcoal to 26.3 kcal.mol-1 for graphite and 20.8-1for coke. This behavior provides further support for the postulated reaction mechanism, i.e., carbon
    Keywords: Barite, carbothermic reduction, kinetic analysis, carbon gasification, activation energy
  • S. Ghafurian, S. H. Seyedein, M. R. Aboutalebi, M. Reza Afshar Page 8
    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.
    Keywords: Combustion Synthesis, Microwave Processing, Aluminum, Titanium Intermetallic Compounds, TiAl, Al2O3 Composite, Numerical Modeling
  • A. A. Hosseini, A. Sadigzadeh, S. Mohammadi Page 17
    In this study, carbon nanotubes (CNTs) were grown directly in the pores of micro porous pyrex membranes and consequently ceramic membranes with very fine pores and high porosity were achieved. Our experiment was done in two stages. Initially cobalt powder with different percent was homogeneously mixed with pyrex powder. In order to produce row membranes, each of these mixtures were compacted in the form of tablet by use of a uniaxial cold press and in a stainless steel mould, and then the tablets were sintered at different temperature in an electric furnace. In second stage chemical vapor deposition (CVD) method was used to grow CNTs within the pores of the membranes.Argon and ammonia were used as carrier and reactive gas respectively and acetylene was used as the carbon feedstock. Morphology of the membranes before and after CVD process was studied by scanning electron microscopy (SEM). After CVD process CNTs were grown in the pores of membranes and the pores size was decreased but total porosity of the membrane was not changed considerably. In this way membranes with high porosity and fine pores were fabricated.
    Keywords: CNTs, Nano Filter, porous membrane, SEM
  • Y. Safaei, Naeini, F. Golestani, Fard, F. Khorasanizadeh, M. Aminzare, S. Zhang Page 23
    composition of MgO and nano boehmite. The reactant and potassium chloride, as the reaction media, were fired at 800-1000 °C at different dwell times (0.5-5 h) in the ambient atmosphere. After washing and filtration, the spinel nano powder was characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) techniques. It was demonstrated that the formation temperature decreased to 850 particles revealed an average size of 30 nm with a narrow size distribution. The mechanism of MgAl was found to be a template type where the morphology and size of product were similar to those of alumina formed from boehmite decomposition. Prolonging the reaction time from 0.5 to 3 h, the reaction was further completed and crystallinity was improved. However, the increase of temperature was more effective in this regard.MgAl2O4 (MA) nano powder was synthesized via molten salt technique, by heating stochiometric°C. The nano spinel2O4 formation.
    Keywords: spinel nano powder, molten salt method, boehmite
  • A. Namiranian, M. Kalantar Page 29
    The process of mullitization of kyanite concentrate was studied at different conditions of heat treatment (1400 – 1600 °C and 0.5 – 3.5 hours) and particle size of raw materials (38-300? m). Kyanite concentrate was obtained from ore-dressing of kyanite deposits of Mishidowan-Bafgh region at 100 km northeastern part of Yazd. The results of microstructure (shape, distribution and size of the grains) and phase evolution studies by SEM and XRD showed thattotal transformation of kyanite to mullite takes place by heat treatment between 1500 –1550 °C during 2.5 hours.. At temperatures below 1500 °C need-like mullite grains are always produced. At higher temperatures the mullite grains reveal rounded and platelet morphology. At 1550 °C, the rate of mullitization and densification were improved by increasing soaking time from 1h to 3h and decreasing particle size of materials from 300 to 38 m.
    Keywords: Kyanite, Kinetic of mullitization, Heat treatments, Densification, Microstructure, Mishidowan, Bafgh deposits
  • R. Swain, L. N. Padhy, R. Bhima Rao Page 37
    Partially Lateritised Khondalite (PLK) rocks are the waste materials generated as a result of mining of bauxite. The major discolouring elemental impurity in the PLK is iron oxides, which render it unsuitable for its use as a refractory material. The iron can be removed by suitable beneficiation methods. The main aim of this present investigation is to prepare a value added material from the mining waste by preparation of PLK rock containing less than 2% Fe2O3 which finds application in the refractory industries and then preparation of brick suitable for industrial applications. The feed sample containing 4.31 % Fe2O3 subjected to hydrocyclone for refractory of low iron content product in the underflow. The results of these studies reveal that the hydrocyclone underflow sample contains 1.9% Fe2O3 is suitable for making bricks due to presence of low iron content. However, bricks are made from a feed sample as well as from hydrocyclone underflow and overflow products. Physical, chemical and thermo-mechanical properties of these bricks are evaluated. Mineralogical properties of these bricks are also correlated with the thermomechanical properties. The developed bricks are compared with the standards for their suitability in industrial applications. Hence the bauxite mining waste can be a value added material but not a waste material which at present creates environmental pollution at the mining site.
    Keywords: PLK Rocks, Underflow, Hydrocyclone, Beneficiation, Brick, Refractories
  • E. Najafi Kani, A. Allahverdi Page 50
    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.
    Keywords: Geopolymer cement, Shrinkage, Chemical Composition, Curing, Natural Pozzolan