فهرست مطالب

  • Volume:16 Issue:3, 2019
  • تاریخ انتشار: 1398/05/05
  • تعداد عناوین: 11
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  • Resistance of Alkali-activated Slag Cement Against Sodium Sulfate
    A. Allahverdi*, H. Hashemi, M. Mahinroosta Pages 1-22

    This work evaluates the resistance of alkali-activated slag (AAS) mortar against sodium sulfate attack. The effects of immersion in 5% sodium sulfate solution under room temperature and wetting-drying cycles on the compressive strength of mortar specimens were considered for evaluating the extent of degradation. Mortar specimens prepared from type II and V Portland cements (PC2 and PC5) in accordance with ASTM standard were also used as reference. To characterize the chemical products of the degradation process due to sodium sulfate attack, the specimens were also studied by X-ray diffractometry, scanning electron microscopy, and the elemental analysis by energy dispersive X-ray spectroscopy. After 360 days of exposure to the sodium sulfate solution, PC2, PC5 and AAS cements showed 71, 52 and 45% reduction in compressive strength, respectively. According to the obtained results, AAS cement exhibits a higher sulfate resistance compared to PC2 and PC5.

    Keywords: Sulfate resistance, Compressive strength, Slag, Alkali-activation
  • Thermochemical Heat Storage Properties of Mechanical Activated Co3O4-5 wt. % Al2O3 and Co3O4-5 wt. % Y2O3 Composite Powders
    A. Hasanvand, M. Pourabdoli*, A. Ghaderi Pages 23-33

    The main problem of cobalt oxide as a thermochemical heat storage material is its slow re-oxidation kinetics. In addition, redox (reduction and oxidation) behavior of as-received Co3O4 is degraded with increasing the number of redox cycles. To overcome this drawback, Al2O3 and Y2O3 were added to Co3O4 and  effect of mechanical activation time (2, 4, 8, and 16 h) on the redox behavior (weight change value/rate, redox reversibility, reduction and re-oxidation values, and particle morphologies) of Co3O4-5 wt.% Al2O3 and Co3O4-5 wt. % Y2O3 composites was investigated using thermogravimetry method. The composites were studied by SEM, EDS, and X-ray map analyses before and after redox reactions. Results showed that increasing the mechanical activation time improves the redox kinetics of Co3O4-5wt. % Al2O3 in comparison with as-received Co3O4. Although, the alumina-containing samples, activated in short time showed the better redox kinetics than samples activated in long time. It was found that increasing the activation time to more than 8 h for alumina-containing samples reduces the redox kinetics due to decreasing the positive effect of Al2O3 in controlling the particle size growth and sintering. In the case of Co3O4-5wt. % Y2O3, an increase in activation time generally reduced the redox kinetics. As a result, redox reactions in a 16 h-activated Co3O4-5wt.% Y2O3 composite was completely stopped. In addition, results showed that weak performance of Co3O4-5 wt. % Y2O3 is related to intensive sintering and growth of cobalt oxide particles during redox reactions

    Keywords: Cobalt oxide, Redox reactions, Reversibility, Thermochemical heat storage, Mechanical activation
  • Effect of Minor Amounts of Scandium on Recrystallization Behavior of 7000 series Aluminium
    A. Beigei Kheradmand, S. Mirdamadi*, S. Nategh Pages 34-58

    In the present study, the effect of adding minor amounts of scandium and zirconium elements to the 7075 alloyon the re-crystallization behaviour of one aluminium alloy (7000 series) was investigated. For this purpose, two kinds of Al-Zn-Mg-Cu-Sc-Zr alloys with the same amount of Zr and different amount of Sc were prepared. Homogenization durations and temperatures of alloys after alloying were obtained by DSC analysis and optical microstructure observations. The results showed that the optimum homogenization temperatures for Al-Zn-Mg-Cu-0.05Sc-0.1Zr and Al-Zn-Mg-Cu-0.1Sc-0.1Zr alloys were 5000C and 4900C respectively, and the optimum duration for both alloys was 12hours. After homogenization of alloys, the re-crystallization behaviour of the alloys was investigated by Brinell hardness test. Obtained results showed that although the starting re-crystallization temperature for both alloys was similar in 2 hours, but it was 130°C for alloys with 30% forming, and 120°C for alloys with 50%forming and recrystallization temperature for Al-Zn-Mg-Cu-0.1Sc-0.1Zr alloy was 350in 2 hours. Despite what was expected, the hardness of Al-Zn-Mg-Cu-0.05Sc-0.1

    Keywords: Recrystalyzation, Al-Zn-Mg-Cu-Sc-Zr, 7000 series aluminium
  • Preparation and Characterization of Nanostructured Titania-coated Silica Microsphere Membranes with Simultaneous Photo-catalytic and Separation Applications for Water Treatment
    V. Tajer Kajinebaf*, M. Zarrin Khame, Forosh, H. Sarpoolaky Pages 59-81

    In this research, the nanostructured titania-coated silica microsphere (NTCSM) membrane consisting of titania-silica core-shell particles on α–alumina substrate was prepared by dip-coating method. The silica microspheres were synthesized by the Stöber method, and the nanostructured titania shell was obtained from a polymeric sol. Then, the prepared core-shell particles were deposited on alumina substrates. The samples were characterized by DLS, TG-DTA, XRD, FTIR and SEM. The photo-catalytic activity of the NTCSM membranes was evaluated using photo-degradation of methyl orange solution by UV–visible spectrophotometer. Also, physical separation capability was investigated by filtration experiment based on methyl orange removal from aqueous solution using a membrane setup. The mean particle size distribution of silica microspheres was determined to be about 650 nm that by deposition of titania nano-particles increased up to about 800 nm. After 60 min UV-irradiation, the dye removal efficiency was determined to be 80% by the membrane. By coupling separation process with photo-catalytic technique, the removal efficiency was improved up to 97%. Thus, the NTCSM membranes showed simultaneous photo-degradation and separation capabilities for dye removal from water.

    Keywords: Membrane, Nanostructured TiO2, SiO2 microsphere, Titania-silica, Photo-degradation, Separation
  • Simulated Porcelain Firing of CO-CR Alloy
    V. Dave, R. Kotian*, P. Madhyastha, K. Boaz, P. Rao, B.P. Charitha Pages 82-93

    The aim of the present study is to assess the hardness, corrosion, and cytotoxicity of a commercially available cobalt-chromium (Co-Cr) alloy before and after simulated heat treatments at porcelain firing temperature. Five Co-Cr samples were fabricated using lost wax casting procedure. Heat treatments were carried out at 650°C, 750°C, 850°C, and 950°C. Vickers hardness was measured for as-cast and heat treated samples. The corrosion test was carried out separately in 0.1 N NaCl, 1% citric acid and artificial saliva at room temperature using potentiodynamic polarization technique. Gingival tissue biopsy of patients was taken and cultured to measure the cell viability by MTT colorimetric assay. Lowest hardness was observed at 650°C. 0.1 N NaCl and 1% citric acid corrosion medium showed a similar trend of corrosion rate. The least corrosion rate was found in artificial saliva. Firing temperature has an impact on the physical, chemical and biological properties of Co-Cr alloy in long-term clinical use.

    Keywords: Cobalt-chromium, Heat treatment, Corrosion, Cytotoxicity, Hardness
  • Mortar Properties Improvement by Using Fine Portland Cement Clinker as Reactive Aggregate
    J. Shafaghat, A. Allahverdi* Pages 94-110

    Microscopic studies has shown that adjacent to the interface between cement paste and aggregate, there exists an area with high porosity and low binding compounds that is referred to as interfacial transition zone (ITZ). ITZ in concrete and mortar imposes a number of negative effects, including flexural and compressive strengths reduction and permeability enhancement. That’s why many research attempts have been devoted to limit ITZ and its negative effects. The present study investigates the possibility of utilizing fine Portland cement (PC) clinker as a reactive aggregate in mortar for the same purpose. For this, natural quartz sand in normal mortar (NM) was totally replaced with PC clinker of the same particle size distribution and the most important engineering properties of the new mortar referred to as Reactive Aggregate Mortar (RAM) were measured and compared with NM as control. The results of compressive strengths measurements represented 65% and 21% increases at curing ages of 7 and 90 days, respectively, for RAM compared to NM. Chloride penetration depth in RAM displayed reductions by about 33% and 26% after 14 and 28 days of exposure, respectively. The effect of PC clinker reactivity on the microstructure and size of ITZ was studied by using scanning electron microscopy.

    Keywords: Portland cement clinker, Compressive strength, Chloride penetration depth, Interfacial transition zone, Mortar
  • Chemical Interaction Between MgO Support and Iron Catalyst
    M. Palizdar*, Z. Aslam, R. Aghababazadeh, A. Mirhabibi, P. Sangpour, Z. Abadi, Y. Palizdar, R. Brydson Pages 111-134

    In this paper the chemical interaction between catalyst and support has been studied to understand the observed different growth rate of CNTs in our previous paper. Both pure MgO and Mg(NO3)2 . 6H2O as sources of the MgO catalyst support and Fe2(SO4)3 · xH2O as the source of the Fe catalyst, were employed. A Fe catalyst supported on MgO has been synthesized using the wet impregnation method followed by calcination. To compare the catalyst grain size and its distribution, the sample were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and BET specific surface area (SSA) measurement and X-ray photoelectron spectroscopy (XPS). XPS technique have utilized complementary to demonstrate the existence of chemical interaction between MgO support and Fe catalyst. Results revealed that the type of precursor used to prepare the support has a significant influence on the morphology of the support and the associated distribution of the Fe catalysts. The highest yield of MgFe2O4 phase was obtained using a pure MgO precursor which after calcination results in a homogenous distribution of nano-sized Fe particles over the support surface

    Keywords: Catalyst, Support, Magnesium ferrite
  • Sintering Behavior of Lithium Meta Titanate Nanocrystallites
    A. R. Abbasian*, M. R. Rahimipour, Z. Hamnabard Pages 135-157

    In this work, lithium meta titanate (Li2TiO3) nanocrystallites were synthesized by hydrothermal method and subsequent heat treatment. The shrinkage of the powder compact was measured under constant heating rate in order to study the sintering behavior of the synthesized powders. Densification curves of the synthesized powders were also constructed via the dilatometry analysis and evaluated at several heating rates. Two separate methods of analytical procedure and master curve sintering were employed to determine the activation energy of the initial sintering stage. The activation energy values were estimated based on these two distinct methods as 229±14 and 230 kJ/mol respectively, consistenting with each other. Moreover, surface diffusion was determined as the dominant mechanism of densification on initial sintering of Li2TiO3 nanocrystallites.

    Keywords: Tritium breeding, Sintering, Activation energy, Nano, dilatometry, Li2TiO3 nanocrystallites
  • Investigating the First-Order Flotation Kinetics Models for Iranian Gilsonite
    A. Bahrami, F. Kazemi*, J. Abdolahi Sharif Pages 158-171

    Kinetic models are the most important instruments for predicting and evaluating the performance of flotation circuits. To determine the kinetic order and rate of flotation of a gilsonite sample, flotation experiments were carried out in both rougher and cleaner stages. Experiments conducted using the combinations of petroleum-MIBC, gas oil-pine oil, and one test without any collector and frother. Five first order kinetic models were applied to the data obtained from the flotation tests by using the Matrix Laboratory software. Statistical analysis showed that the classic first order model perfectly matched the rougher and cleaner results performed using petroleum-MIBC combination. The kinetic constants (k) were calculated as 0.04 (s-1) and 0.01 (s-1) for the rougher and cleaner, respectively. Rougher and cleaner tests without collector and frother also matched with the modified gas/solid adsorption and rectangular models with the k values of 0.05 (s-1), and 0.01 (s-1), respectively. The relationship between flotation rate constant, maximum combustible recovery and particle size were also studied. The results showed that the maximum flotation combustible recovery and flotation rate were obtained with an intermediate particle size both in the rougher and cleaner flotation processes. The combustible recovery and flotation rate in the rougher flotation process were higher than that in the cleaner flotation process.

    Keywords: flotation, kinetics models, gilsonite, collector, frother
  • Microstructure and Hardness Evaluation of Magnesium Samples Processed by a New Design of Spread Extrusion Method
    M. Hoghooghi, O. Jafari, S. Amani, G. Faraji*, K. Abrinia Pages 172-189

    Spread extrusion is a capable method to produce different samples with a wider cross-section from the smaller billets in a single processing pass. In this study, dish-shaped samples are successfully produced from the as-cast cylindrical AM60 magnesium alloy at 300 °C, the mechanical properties and microstructural changes of the final specimens are precisely evaluated. Due to the high amount of plastic strain, which is applied to the initial billet during the material flow in the expansion process, grain refinement occurred as a result of recrystallization and subsequently good mechanical properties achieved. Therefore, mean grain size reduced from 160 µm to 14 µm and initial equiaxed grains changed to the elongated ones surrounded by fine grains. Also, microhardness measurements indicate that hardness increased from 51 Hv to 70 Hv. Some fluctuations were also observed in the hardness profile of the sample which was mainly related to the bimodal structure of the final microstructure. Good mechanical properties, fine microstructure, and also the ability to produce samples with higher cross-section make the spread extrusion process a promising type of extrusion.

    Keywords: Spread extrusion, AM60 magnesium alloy, grain refinement, microhardness
  • Effect of ZR Content on Oxide-Scale Spallation of Aluminide Coating
    R. Latifi, S. Rastegari*, S. H. Razavi Pages 190-207

    In the present study, Zirconium modified aluminide coating on the nickel-base superalloy IN-738LC was first created by high activity high temperature aluminizing based on the out-of-pack cementation method. Then, Zr coatings were applied to simple aluminide coatings by sputtering and heat treatment in order to study the effect of Zr on the coating microstructure and oxide spallation. Microstructural studies were conducted by using scanning electron microscopy (SEM), Energy Dispersive X-ray Spectrometry (EDS), and x-ray diffraction (XRD) microanalysis. The results indicated that zirconium modified aluminide coating, like aluminide coating, has a two-layer structure including a uniform outer layer of NiAl and an interdiffusion layer in which zirconium is in a form of solid solution in the coating. Furthermore, the 300nm Zr-coated NiAl demonstrated an excellent scale adhesion, a slow oxidation rate and lower amounts of some other elements such as Ti and Cr in its oxide layer leading to a pure aluminide oxide layer.

    Keywords: diffusion aluminide coating, zirconium modified coating, oxidation resistance, out-of-pack cementation