Slag–graphite wettability and reaction kinetics Part 1 Kinetics and mechanism of molten FeO reduction reaction

Abstract

The present paper reports results relating to the kinetics and mechanism of FeO reduction by graphite, the data being obtained from experimental investigations into the wettability of graphite by molten slag containing FeO. The rate of FeO reduction was determined by measuring the volume of CO gas formed as a result of the reduction of FeO in experiments conducted in the same sessile drop apparatus. The reduction reaction initiated by direct slag–graphite contact produces CO gas which spreads into the molten slag droplet causing foaming of the slag; further reduction of FeO proceeds mostly via indirect reduction. The rate of reduction was found to depend directly on the initial FeO content. An increase in temperature improves the rate of reaction, which has an activation energy of 112·18 kJ mol^-1. These results indicate that transport of FeO (Fe²⁺, O^2- ) in the liquid slag phase is probably the slowest step.     

Behaviour of iron ore–fuel oil composite pellets in isothermal and non-isothermal reduction conditions

Abstract

Self-fluxing iron ore pellets as an alternative to the agglomeration process led to the use of low price fuel oil as a binder and reducing material. Composite pellets containing 5–15% fuel oil were isothermally and non-isothermally reduced at 750–1000°C in a flow of H₂ or N₂ gases. The total weight loss resulting from O₂ removal from the reduction of Fe₂ O₃ and from the thermal decomposition of fuel oil was continuously recorded as a function of time at different reduction conditions. The actual reduction extent at a given time was calculated from the chemical analysis of partially reduced samples at a given time and temperature. Microscopic examination and X-ray phase analysis were applied to characterise the reduction products. The isothermal reduction of composite pellets indicated that the reduction rate increased with the increase in fuel oil content at the early stages. At the later stages, the reduction rate increased in the order 12>10>5> 15% fuel oil containing pellets. The non-isothermal reduction of composite pellets in N₂ atmosphere showed the presence of an incubation period at initial reduction stages. The low intensity magnetic separation technique was applied with the aim of increasing the iron content at the expense of associated impurities. The magnetic and non-magnetic fractions were analysed and the overall recovery was determined.     

Preparation of stainless steel master alloy by direct smelting reduction of Fe–Ni–Cr Sinter at 1600°C

Feasibility analysis and experimental studies for the production of a stainless steel master alloy by direct smelting reduction have been investigated in this work, showing that the master alloy with proper compositions and satisfactory metal recoveries can be obtained at 1600°C. When the temperature was increased from 1450 to 1600°C, the grades for Fe, Ni and Cr increased from 50.04, 1.1 and 13.36% up to 73.39, 1.77 and 16.42%, respectively. Experiments were then carried out focusing on the influence of various fluxes on the reduction behaviour, showing that CaO resulted in the increase in the recoveries of Fe, Ni and Cr, SiO₂ improved the recoveries of Fe and Ni, but did not favour the recovery of Cr because of an increase of CrO and Cr₂O₃ within the slag. MgO was not effective as a flux because of the formation of spinel. This increased the effective viscosity of the slag because of the presence of suspended solids, and led to a poor separation between the alloy and slag.     

Influence of cooling rate and composition on formation of intermetallic phases in solidifying Al–Fe–Si melts

Abstract

Aluminium alloys containing 0·3%Fe and 0·05%Si, 0·3%Fe and 0·15%Si, 0·3%Fe and 0·45%Si, and 0·5%Fe and 0·2%Si were solidified with different cooling rates. Shapes of intermetallic particles and their spatial distribution in the alloys were characterised by optical and scanning electron microscopy. X-ray diffraction analysis was used to establish the types of intermetallic phases extracted from the alloys by dissolving the FCC matrix in boiling phenol. The influence of melt superheating on the microstructure was analysed by comparing phase portraits of alloys solidified from melts whose temperatures before casting were 100 and 350°C above the liquidus.

On a solidifié des alliages d’aluminium contenant 0·3%Fe et 0·05%Si, 0·3%Fe et 0·15%Si, 0·3%Fe et 0·45%Si et 0·5%Fe et 0·2%Si, à différentes vitesses de refroidissement. On a caractérisé la forme des particules intermétalliques et leur distribution spatiale dans les alliages, au moyen de la microscopie optique et de la microscopie électronique à balayage. On a utilisé l’analyse de la diffraction des rayons X pour établir les types de phases intermétalliques extraites des alliages par dissolution de la matrice FCC dans du phénol en ébullition. On a analysé l’influence de la surchauffe du bain sur la microstructure en comparant les images de phase des alliages solidifiés à partir des bains dont les températures avant le moulage étaient de 100 et de 350°C au-dessus du liquidus.     

Estimation of rate parameters for reduction of iron ore–graphite composite pellets in packed bed reactor using genetic algorithm

Abstract

A semiempirical kinetic model has been developed to determine the course of reduction of iron ore–graphite composite pellets over time in a laboratory scale side heated packed bed reactor attached with a tailor made bottom hanging thermogravimetric set-up. The rate parameters in the model, especially the three sets of apparent activation energy values and frequency factors associated with the reduction of iron oxides in three elementary steps, namely hematite to magnetite, magnetite to wustite and wustite to iron, have been estimated based on experimental data by employing an optimisation tool, the genetic algorithm (GA). The difference between the predicted and experimental degree of reduction is minimised to obtain the rate parameters. The experimental degree of reduction is calculated based on mass loss data during reduction and the exit gas analysis. Estimated values of apparent rate parameters were found to be of the same order of magnitude to their intrinsic counterparts reported in literature. Finally, by using the predicted rate parameters the temporal evolution of various oxide phases as well as pure iron has been evaluated.     

Effect of CaO on the reduction behaviour of iron ore–coal composite pellets in multi-layer bed rotary hearth furnace

The effect of CaO on the reduction behaviour of iron ore–coal composite pellets has been studied in a laboratory scale multi-layer bed rotary hearth furnace at 1250°C for 20?min. Reduced pellets have been characterised through weight loss, porosity measurement, phase analysis by XRD, and morphology study by SEM. The addition of CaO to the composite pellets showed different effects at different carbon levels. For higher carbon-containing pellets (C/Fe₂O₃ molar ratio at the upper stoichiometric level of 3), the addition of CaO increased the extent of reduction for all three layers significantly up to a certain limit (4?wt-%); and thereafter the degree of reduction is decreased with a further increase in CaO percentage in the pellets. For low carbon-containing pellets (C/Fe₂O₃ molar ratio of 1.66), the addition of CaO to the pellets did not show any beneficial effect.     

Influence of the Oxygen Induced Surface Segregation Process of Solutes on the Anti-corrosion Properties of the Fe–Cr and Fe–Cr–Si Alloys

Metallurgical and Materials Transactions A - The influence of the oxygen-induced surface segregation process of Cr and Si solutes on the anti-corrosion properties of Fe–Cr and...     

Mathematical-Thermodynamic Prediction and Kinetics of Eta Phase Formation in Fe–Ni-Based Superalloys

Time–temperature–precipitation diagram of eta phase formation was established for an Fe–Ni based superalloy by means of mathematical-thermodynamic analysis, kinetic investigation, and microstructural observation. The eta phase started to precipitate at the expense of the γ′ phase after prolonged aging. On the basis of thermodynamic prediction, the interaction between Gibbs free energy of eta phase formation and activation energy for diffusion of elements, especially titanium, was considered. The tip of TTP diagram was obtained at 817 °C, on the basis of mathematical-thermodynamic prediction, and 825–840 and 840 °C, on the basis of microstructural evolution and kinetic analysis, respectively. Kinetic investigations predicted that the eta transformation started with diffusion of Ti into Ni. This indicated that, with the progress of transformation, as n in Avrami’s equation predicts, other eta formation mechanisms such as γ′ to eta transformation, instant nucleation from the matrix, coincidence of eta lamellas, etc. increased n and activation energy.     

Composition of C–Si–Mn–Cr–W–V powder wire and quality of surfacing

The influence of the composition of powder wire on the properties of the applied layer on steel samples is studied in the laboratory. If amorphous graphite in 35V9Kh3SF powder wire is replaced by material containing carbon and fluorine, the porosity of the applied layer is reduced, and fewer nonmetallic inclusions (including row oxide inclusions and undeformable silicates) are present. Statistical analysis of the experimental data illustrates the influence of the carbon equivalent of the 35V9Kh3SF powder wire on the hardness of the applied layer (including the mean surface hardness and the microhardness of martensite). With increase in the carbon equivalent calculated by the Paton Institute’s formula, the hardness of the applied layer linearly increases.     

Thermodynamic Properties of Carbon and Manganese in MnC and MnFeC Melts

Carbon solubility in MnFe melts (xMn=0083-0706, xFe=0034-0715) was measured experimentally at various temperatures. By thermodynamic derivation and calculation, the relationship between activity coefficient of carbon in infinite dilute solution of manganese in MnC system and temperature was obtained. Using GibbsDuhem relationship, the experimental results of this study, and experimental data obtained by strict thermodynamic derivation and calculation in references, the relationships between other thermodynamic properties (εCC, εCCC, εCFe, εCCFe, and εCFeFe) in MnFeC system and temperature were obtained.     

Effect of zirconium on the oxygen solubility in liquid nickel and Ni–Fe melts

The oxygen solubility in liquid nickel containing zirconium is studied experimentally for the first time at 1873 K. The equilibrium constants of the reaction of interaction between zirconium and oxygen dissolved in liquid nickel, the interaction parameters characterizing these solutions, and the zirconium activity coefficient in nickel at infinite dilution are found. The equilibrium constants of the reaction of interaction between zirconium and oxygen dissolved in the melt, the Gibbs energy of the reaction of interaction between zirconium and oxygen, and the interaction parameters characterizing these solutions are calculated at 1873 K for a wide composition range of Ni–Fe alloys. The oxygen solubility in various Ni–Fe melts containing zirconium is found at 1873 K. The deoxidizing capacity of zirconium increases as the iron content increases to 30% and decreases at higher iron content in the melt. This can be explained by the fact that an increase in the iron content lead to, on the one hand, a strengthening of the bonding forces of oxygen atoms in a melt and, on the other hand, to a significant weakening of the bonding forces of zirconium atoms with the base metal.     

Interaction of iron and aluminum in the plastic deformation and fast heating of laminar Fe–Al composite

The influence of plastic deformation and the heating rate on the solid-phase interaction of steel strip and aluminum powder is investigated. Recrystallization of the contacting materials determines the phase formation. The layer thickness of the Fe–Al intermetallides is plotted as function of the strain and heating rate. On that basis, the parameters of the transition layer may be predicted in selecting the technological conditions.     

Preparation methods and production of initial materials to prepare gadolinium oxide pellets used in fabrication of composite uranium–gadolinium fuel

The production method of efficient composite uranium–gadolinium fuel, the application of which will make it possible to improve the technical and economic performance of nuclear power plants, is developed in a laboratory. Based on the analysis of results, the substantiation of implementing the proposed method in industrial conditions is performed. Methods for the preparation and production of the initial materials to prepare gadolinium oxide are described. Necessary characteristics of the pellets of the promising composite uranium–gadolinium fuel are established in the course of experiments, and final requirements for these pellets are formulated allowing for them.