Iranian Journal of Materials Science and Engineering

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Two commercial methods are used for the production of strontium carbonate:1) Direct conversion of Celsetite to strontium carbonate by hot sodium carbonate,2) Carbothermic reduction of celestite with coal followed by water leaching of strontium sulfide(SrS) and its conversion to strontium carbonate.The present study has been made on the carbothermic reduction of celestite ores of Varamin (Iran) mines. Effects of temperature, time, pellet size, particle size of celestite ore, pellet compactness and type of reducing agent have been studied. In the range of 800-1100°C, reduction rate increases notably with temperature, which may mean that the reduction is predominantly chemical controlled. Activation energy of around 22.5 kcal/mol supports the idea of chemical control mechanism. Further support for this postulation is provided by the following facts:1) Increasing rate with carbon reactivity (graphite, coal, and charcoal)2) Small dependency of rate on pellet compactness.3) Small dependency of rate on pellet size

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Abstract: In this paper solid state reduction of high carbon ferrochromium-chromite composite pellets in the temperature range of 900-1350°C was investigated. A two stage reduction mechanism is proposed. The first stage is likely to be controlled by the chemical reaction with activation energy of 127.2kJ/mol. In the second stage, solid state diffusion of carbon through the reaction product layer is suggested to be rate controlling. The activation energy of this stage was calculated to be 93.1kJ/mol. The reduction process was found to be favored by high temperatures as well as high vacuum. The results also show that pre-milling of initial mixture has a negative effect on the reduction degree.

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In this research an ultra-fine grained composite structure consisting of an intermetallic matrix together with dispersed nano-sized Al2O3 obtained via mechanical activation of TiO2 and Al in a high energy ball mill and sintering of consolidated samples. Phase composition and morphology of the milled and sintered samples were evaluated by XRD and SEM techniques Thermal behavior of the powder sample milled for 8 hours was evaluated by DTA technique. DTA results showed that, the reaction happens in two steps. The first step is the aluminothermic reduction of TiO2 with Al. XRD observations reveals that minor amount of Ti3Al phase formed during reduction reaction together with TiAl and Al2O3 major phases. This intermetallic phase disappeared when sintering temperature was increased to 850 ºC. The second step in DTA is related to a reaction between residual Al in the system (partly dissolved in TiAl lattice) and the Ti3Al phase produced earlier at lower temperatures. SEM micrographs reveal that by completion of the reduction reaction more homogeneous and finer microstructure is observable in sintered samples.

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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.

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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:

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 20.8-1 for coke. This behavior provides further support for the postulated reaction mechanism, i.e., carbon

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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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In this research, infiltration behavior of W-Ag composite compacts with Nickel and Cobalt as additives has been investigated. Nickel and Cobalt were added to Tungsten powder by two distinct methods: mixing elementally and reduction of salt solution. The coated Tungsten powders were compacted under controlled pressures to make porous skeleton with 32-37 vol. % porosity. Infiltration process was carried out at 1100 ̊C under a reducing atmosphere for 1h. The effect of additives on infiltration of Ag and density were evaluated by SEM and Archimedes methods. Properties of the specimens were compared following two distinct processes namely: I) sintering simultaneously with infiltration process and II) sintering prior to infiltration (pre-sintering process). It was found that specimens which were pre-sintered and then infiltrated with molten silver represent higher hardness and finer microstructure than the specimens infiltrated simultaneously with sintering.

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Ceramic-matrix composites containing TiC-TiN have been used in a variety of application because of their superior properties such as high hardness, good wear resistance and high chemical stability. In this research, effect of coke and coke/calcium beds in synthesis of Al 2O3-Ti(C, N) composites using alumino-carbothermic reduction of TiO 2 has been investigated. Al, TiO 2 and active carbon with additives of extra carbon and NaCl and without additives, in separate procedures, have been mixed. Afterwards, mixtures were pressed and synthesized in 1200oC for 4hrs, in coke and coke/calcium beds, separately. Al 2O3-Ti(C,N) composite was synthesized in ternary system of Al-TiO 2 -C with excess carbon and NaCl additives in calcium/coke bed in 1200 . X-ray diffraction patterns (XRD) results showed that existence of calcium in bed resulted in intensification of reduction atmosphere in samples and formation of Ti(C,N) phase enriched from carbon was accelerated. Crystallite sizes of synthesis Ti(C,N) at 1200 °C in reducing conditions were 22-28 nm.

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In the present study, the feasibility of α-Fe ferromagnetic phase formation in glass and glass-ceramic by reduction in hydrogen atmosphere have been investigated. The glass with the composition of 35Na 2 O–24Fe2O3–20B 2O3 – 20SiO 2 –1ZnO (mol %) was melted and quenched by using a twin roller technique. As quenched glass flakes were heat treated in the range of 400-675 °C for 1-2 h in hydrogen atmosphere, which resulted in reduction of iron cations to α-Fe and FeO. The reduction of iron cations in glass was not completely occurred. Saturation magnetization of these samples was 8-37 emu g -1 . For the formation of glass ceramic, As quenched glass flakes heat treated at 590 °C for 1 h. Heat treatment of glass ceramic containing magnetite at 675°C in hydrogen atmosphere for 1 h led to reduction of almost all of the iron cations to α-Fe. Saturation magnetization of this sample increased from 19.8 emu g -1 for glass ceramic to 67 emu g -1

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The volatile matter of non-coking coal was used for the reduction of hematite in argon atmosphere at nonisothermal condition. A thermal gravimeter furnace enable to use an 80 mm-height crucible was designed for the experiments to measure the weight changes of about 10 grams samples. A two-layered array of coal and alumina and four-layered array of iron oxide, alumina, coal and alumina was used for the devolatilization and reduction experiments, respectively. The net effect of volatile reduction of Fe 2O3was determined and it was observe that 45% reduction has been achieved. Three distinct regions were recognized on the reduction curve. The reduction of hematite to magnetite could be completely distinguished from the two other regions on the reduction curve. At 600-950°C, the reduction was accelerated. 63% of volatile matter resulted in 25% of total reduction before 600°C while the remaining volatile matter contributed to 75% of the total reduction. From the reduction rate diagram, the stepwise reduction of the iron oxides could be concluded. The partial overlap of the reduction steps were identified through the XRD studies. The starting temperature of magnetite and wüstite reduction were determined at about 585°C and at 810°C, respectively.

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In the present work, iron recovery from a low-grade hematite ore (containing less than 40% iron), which is not applicable in common methods of ironmaking, was studied. Non-coking coal was used as reducing agent. Reduction experiments were performed under various coal to hematite ratios and temperatures. Reduction degree was calculated using the gravimetric method. Reduced samples were subjected to magnetic separation followed by X-ray diffraction analysis. Total iron content, degree of metallization and recovery efficiency in magnetic part were determined by quantitative chemical analysis, which were obtained about 82%, 95% and 64% respectively under optimal conditions. CaO as an additive improved ore reducibility and separation efficiency. The microstructure of reduced samples and final products were analyzed by scanning electron microscopy. Final product with a high degree of metallization can be used in steel making furnaces and charging of blast furnaces which can improve production efficiency and decrease coke usage.

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The graphene oxide -TiO₂ (GO-TiO₂) and pre-reduced graphene oxide -TiO₂ (rGO-TiO₂) nanocomposites were fabricated successfully by hydrothermal method. The microstructure of synthesized nanocomposites was investigated using field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectroscopy (EDS) analysis. Moreover, galvanostatic charge/discharge (GCD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) methods in three electrode system were applied to evaluate electrochemical properties. The results revealed that nanoparticles distributed more uniformly on graphene sheets, at lower concentrations of TiO₂. The rGO-TiO₂ and GO-TiO₂ nanocomposites showed 224 and 32 F/g specific capacitance at 5 mV s^-1 scan rate in 1 M KOH aqueous electrolyte, respectively. The pre-reduction of graphene oxide is the main reason for the better electrochemical performance of rGO-TiO₂ nanocomposite compared to GO-TiO₂ nanocomposite.

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In this study, Ta powder was produced from Ta scarp via chemical processes using Mg and Ca powders. At first, Tantalum scraps were converted to Tantalum oxide (Ta₂O₅) at 1100˚C in an oxygen atmosphere. Tantalum oxide was reduced to Tantalum powder with Mg in a vacuum environment at 950 to 1200˚C for 3 hours. The obtained Ta powders further were reacted with Ca at 950˚C for 5 hours in a vacuum atmosphere. The powders were analyzed through X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), as well as oxygen measurement. The results show that the average particles size of the produced Ta powders is about 58 nm with oxygen contents of 250 ppm.