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Showing papers in "Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science in 1990"


Journal ArticleDOI
TL;DR: An extensive computer program called ChemSage, based upon the SOLGASMIX Gibbs energy minimizer, was designed to perform three types of thermochemical calculations in complex systems involving phases exhibiting nonideal mixing properties as mentioned in this paper.
Abstract: An extensive computer program called ChemSage, based upon the SOLGASMIX Gibbs energy minimizer, is presented together with several examples which illustrate its use. ChemSage was designed to perform three types of thermochemical calculations in complex systems involving phases exhibiting nonideal mixing properties. These are the calculation of thermodynamic functions, heterogeneous phase equilibria, and steady-state conditions for the simulation of simple multistage reactors. The thermodynamic functions module calculates specific heat, enthalpy, entropy, and Gibbs energy with respect to a chosen reference state for a given phase and, if this phase is a mixture, the partial properties of its components. Chemical equilibrium calculations can be made for a system which has been uniquely defined with respect to temperature, pressure (or volume), and composition. One of these quantities may also be replaced by an extensive property or phase target,e.g., for the calculation of adiabatic and liquidus temperatures, respectively.

394 citations


Journal ArticleDOI
TL;DR: In this article, mass and momentum conservation equations are derived for the flow of interdendritic liquid during solidification using the volume-averaging approach, where the mushy zone is conceived to be two interpenetrating phases; each phase is described with the usual field quantities, which are continuous in that phase but discontinuous over the entire space.
Abstract: In this paper, mass and momentum conservation equations are derived for the flow of interdendritic liquid during solidification using the volume-averaging approach. In this approach, the mushy zone is conceived to be two interpenetrating phases; each phase is described with the usual field quantities, which are continuous in that phase but discontinuous over the entire space. On the microscopic scale, the usual conservation equations along with the appropriate interfacial boundary conditions describe the state of the system. However, the solution to these equations in the microscopic scale is not practical because of the complex interfacial geometry in the mushy zone. Instead, the scale at which the system is described is altered by averaging the microscopic equations over some representative elementary volume within the mushy zone, resulting in macroscopic equations that can be used to solve practical problems. For a fraction of liquid equal to unity, the equations reduce to the usual conservation equations for a single-phase liquid. It is also found that the resistance offered by the solid to the flow of interdendritic liquid in the mushy zone is best described by two coefficients, namely, the inverse of permeability and a second-order resistance coefficient. For the flow in columnar dendritic structures, the second-order coefficient along with the permeability should be evaluated experimentally. For the flow in equiaxial dendritic structures(i.e., isotropic media), the inverse of permeability alone is sufficient to quantify the resistance offered by the solid.

219 citations


Journal ArticleDOI
TL;DR: In this paper, a finite element model was developed and applied to compute the fluid flow distribution inside the shell in the mold region of a continuous, steel slab-casting machine, which allowed this nonlinear, highly turbulent problem to be simulated using the K- e turbulence model.
Abstract: A finite element model has been developed and applied to compute the fluid flow distribution inside the shell in the mold region of a continuous, steel slab-casting machine. The model was produced with the commercial program FIDAP, which allows this nonlinear, highly turbulent problem to be simulated using the K- e turbulence model. It consists of separate two-dimensional (2-D) models of the nozzle and a section through the mold, facing the broad face. The predicted flow patterns and velocity fields show reasonable agreement with experimental observations and measurements conducted using a transparent plastic water model. The effects of nozzle angle, casting speed, mold width, and turbulence simulation parameters on the flow pattern have been investigated. The overall flow field is relatively insensitive to process parameters.

122 citations


Journal ArticleDOI
TL;DR: In this article, the authors present a model for the interaction of nonmetals with other species in metallic systems, which assumes that the nonmetal either repels or attracts tracers (E) in the metallic liquid, causing those tracers to either segregate strongly into the solid metal or to have enhanced solubility in the liquid.
Abstract: As nonmetals are added to the Fe-Ni system, segregation coefficients(k) of trace constituents change dramatically. For example, as the S content of the metallic liquid increases from 0 to ≈31 wt pct, the molar k(Ge) between solid and liquid metal increases from 0.6 to ~120. Little of this change can be ascribed to temperature. Also, these changes are not linear. In the case of the Fe-Ni-S system, the largest changes are seen between 20 and 30 wt pct S. Here we present a model for the interaction of nonmetals with other species in metallic systems. The model assumes that the nonmetal either repels or attracts tracers (E) in the metallic liquid, causing those tracers to either segregate strongly into the solid metal or to have enhanced solubility in the liquid. Examples of both types of behavior are given. The model predicts that the activity coefficient of the tracer (γE) should correlate linearly with (1 - αnXN @#@), where XN is the mole fraction of the nonmetal in the metallic liquid,n is a stoichiometry factor related to the speciation of N in the liquid, and a is a constant. Indeed, good linear correlations of n(k) vs n (1 -αnXN @#@) are found for all elements where there is a measurable effect. Thus, if the composition of the metallic liquid is known, a segregation coefficient of a trace constituent may be pre-dicted— even if the temperature, exact Fe/Ni ratio, and information about the activity coef-ficient in the solid phase are unknown. The nonmetal interaction model presented here can be related to more traditional methods of modeling activity coefficients(i.e., power law expan-sions) and can be shown to be a special case of this type of parameterization. Comparison of model predictions of first-order (sulfur-E) interaction coefficients (e) to measured values yields acceptable agreement for some elements, such as P and Ge, and all elements except Ni agree to within a factor of 3. The predictive model described above, based on equilibrium experi-ments, may be used to evaluate the segregation coefficients extracted from the dynamic (“plane front solidification”) experiments of Sellamuthu and Goldstein.[10,11] Contrary to claims, reliable segregation coefficients are not extractable from dynamic experiments.

120 citations


Journal ArticleDOI
TL;DR: In this article, the relative stability of evaluated oxides in the order of increasing stability follows the sequence CeO2 − ZrO2, Gd2O3, didymium oxide, Sm2O 3, Nd2 O3, Y2 O 3.
Abstract: Attempts have been made to evaluate the thermal stability of rare earth oxide face coats against liquid titanium. Determination of microhardness profiles and concentration profiles of oxygen and metallic constituents of oxide in investment cast titanium rods has allowed grActation of relative stability of rare earth oxides. The relative stability of evaluated oxides in the order of increasing stability follows the sequence CeO2 — ZrO2 — Gd2O3 — didymium oxide — Sm2O3 —Nd2O3 — Y2O3. The grading does not follow the free energy data of the formation of these oxides. A better correlation with the experimental observations is obtained when the solubility of the metallic species in titanium is also taken into consideration.

102 citations


Journal ArticleDOI
TL;DR: In this paper, the Kirchhoff transformation is applied to the heat-flow models of continuous casting processes and a number of solution strategies are compared for interfacing with optimization algorithms.
Abstract: A number of solution strategies for heat-flow models of continuous casting processes are developed and compared for interfacing with optimization algorithms. These two-dimensional (2-D) slice models include nonlinear thermodynamic and transport properties. As a result of the compari-son, a number of modifications are applied to enhance the accuracy of the simulation as well as the efficiency of the solution. Here, we found that by applying the Kirchhoff transformation to the heat-flow equations and by iterative adjustment of temperature-dependent properties, fewer calculations are required per time-step and larger time-steps can be taken. Consequently, this leads to approximately a twentyfold reduction in computation time when using 2-D slice models to determine three-dimensional, steady-state temperature fields. As a result, a complex, 2-D heat-flow model for a cast strand can be solved in 2 to 5 minutes on a Micro VAX II and is thus suitable for incorporation into a systematic optimization procedure and for process simu-lation in real time.

101 citations


Journal ArticleDOI
TL;DR: In this paper, a numerical model is presented simulating heat transfer and buildup of differential thermal contraction stresses during thermal spraying of both metallic and ceramic deposits, which can be used for optimization of deposit integrity and strength.
Abstract: In this paper, a numerical model is presented simulating heat transfer and buildup of differential thermal contraction stresses during thermal spraying. Comparisons are made between prediction and experiment for the substrate/deposit curvatures exhibited during and after spraying of both metallic and ceramic deposits. It is shown that while the basic assumptions of the model seem acceptable, representation of the mechanical response of the materials is important and can be complex. The magnitudes of the stresses are often sufficient to cause plastic flow or other relaxation effects such as microcracking. For the ceramic deposits studied, it was found necessary to employ a simple damage evolution law in which the tensile stiffness of the deposit is progressively reduced, although at a decreasing rate, as straining takes place. Implications for optimization of deposit integrity and strength are briefly mentioned.

87 citations


Journal ArticleDOI
TL;DR: In this article, an evaluation of the CaO-SiO2 system has been made using a newly developed model, a two-sublattice model for ionic solutions.
Abstract: An evaluation of the CaO-SiO2 system has been made using a newly developed model, a two-sublattice model for ionic solutions. Two alternatives were tested. In the first one, three anions were assumed, O−2, SiO4−4, and SiO3−2. In the second one, SiO3−2 was omitted. A set of parameter values describing the Gibbs energy of the liquid phase and solid phases was fixed for each alternative by a computer-operated optimization procedure called PARROT. Satisfactory assessments were achieved over the whole phase diagram range with both alternatives. The main difference between them occurs at the monotectic point. A comparison between calculated properties and experimental data is given.

72 citations


Journal ArticleDOI
TL;DR: In this paper, a new feeding efficiency parameter integrating all individual thermal variables, denoted as(G · t 2/3)Vs (whereG is the thermal gradient,t is local solidification time, and Vs is solidus velocity), is found satisfactory to predict the formation of porosity.
Abstract: The systematic change of riser size, together with the variation of geometries of solidifying Al-7Si-0.3Mg plate castings, was tested by thermal analysis to model the interdendritic feeding behavior based on Darcy’s law. This law, however, is found to be only applicable to certain thermal conditions in the solidifying casting. The applicability of Darcy’s law depends on the regime of solidification time. A new feeding efficiency parameter integrating all individual ther-mal variables, denoted as(G · t 2/3)Vs (whereG is the thermal gradient,t is local solidification time, and Vs i is solidus velocity), is found satisfactory to predict the formation of porosity. The combined geometries of a casting and its riser size exert a great influence on the thermal vari-ables of Al-7Si-0.3Mg alloy in a complicated way. Together, these thermal variables synergize to govern the feeding behavior of the casting.

72 citations


Journal ArticleDOI
TL;DR: In this paper, the axial and radial components of the velocity of the liquid surrounding the plume have been measured by means of a Laser-Doppler Velocimeter (LDV), and the results show that the circulation patterns are identical, irrespective of the dispersion regime.
Abstract: Various forms of plumes have been identified following the injection of air at different rates through a porous plug into water contained in a ladle-shaped vessel. Discrete bubbles form at the plug and rise uniformly through the column of liquid at gas flow rates up to 14 cm3/s cm2 of plug surface; at higher flow rates, groups of bubbles increasingly coalesce into larger gas pockets, and beyond about 40 cm3/s cm2, the gas globes are large enough to cover the entire plug surface before detachment and gradual disintegration as they rise through the body of liquid. The gas fraction, as well as bubble frequency, bubble velocity, and bubble size, have been measured in the various dispersion regimes by means of an electroresistivity probe. The radial distributions of gas fraction and bubble frequency are approximately bell-shaped about the axis of flow, and the reduced values are close to Gaussian functions of the reduced radial distance from the axis. The gas fraction along the axis has been correlated to the reduced height of the plume; it increases with decreasing distance above the plug and with increasing gas flow rate. The axial bubble frequency shows a decrease in the vicinity of the plug with the onset of bubble coalescence, but the values of the frequencies at all gas injection rates converge to about 12 s−1 toward the surface of the bath. The mean bubble velocity increases with increasing flow rate but drops once coalescence is fully established. Conversely, there is a sudden increase in the mean bubble diameter with the onset of coalescence. The axial and radial components of the velocity of the liquid surrounding the plume have been measured by means of a Laser-Doppler Velocimeter (LDV), and the results show that the circulation patterns are identical, irrespective of the dispersion regime. The axial flow which is upward in the vicinity of the plume decreases in magnitude with increasing radial distance, ultimately reversing to an in-creasing downward flow beyond a certain distance from the plug axis. Similarly, the radial flow which is outward from the plume near the liquid surface decreases steadily with depth and eventually reverses to an inward flow at a depth independent of the gas injection rate. The profiles of the axial velocities are almost sigmoidal, except in the coalescence regime, where the effect of turbulence is profound at the upper liquid layers. The radial liquid velocities are generally small relative to the axial components, only about one-fifth as large, considering the maximum average values.

72 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present the mathematical model ALSPEN, in which the thermally induced strains and stresses which develop during direct chill (DC) semicontinuous casting of aluminum billets are calculated by a finite-element method.
Abstract: This paper presents the mathematical model ALSPEN, in which the thermally induced strains and stresses which develop during direct chill (DC) semicontinuous casting of aluminum billets are calculated by a finite-element method. The metal is assumed to be an isotropic elasticviscoplastic material with strongly temperature-dependent properties. In the material description, the viscoplastic strain is treated in a “unified” manner, in which low-temperature (approximately) time-independent plasticity and creep at high temperatures occur as special cases. Furthermore, in the numerical time stepping procedure, all of these plastic material properties, which are present simultaneously in the solution domain as a result of the large temperature differences, are treated in a similar way. To demonstrate some of the capabilities of ALSPEN, we have modeled the casting of an AlMgSi alloy, AA6063. The material properties of this alloy have been studied in parallel with the development of the mathematical model.

Journal ArticleDOI
TL;DR: In this article, a rotary kiln containing ilmenite particles was used to study the residence time distribution of low-density particles, holdup, and bed depth profile.
Abstract: Experiments were conducted in a rotary kiln containing ilmenite particles to study the residence time distribution (RTD) of low-density particles, holdup, and bed depth profile. The variables include feed rate of solids, slope and rotational speed of the kiln, type and size of the tracer, and dam height. Correlations are presented for mean residence time, dispersion number, holdup, and steady-state throughput of solids in terms of the process variables. A simple method is proposed to estimate the dam height that gives rise to a flat profile of solids bed along the length of the kiln.

Journal ArticleDOI
TL;DR: In this paper, measurements of particle size, gas velocity, particle velocity, and spray temperature in gasatomized Sn-Pb sprays were performed using Pitot tube and laser Doppler anemometry (LDA).
Abstract: Spray deposition is a novel manufacturing process which is currently being developed for producing near-net-shape preforms. Spray deposition involves the creation of a spray of droplets by a gas atomizer and the consolidation of these droplets on a substrate to create a preform. In order to maximize the metallurgical benefits of spray deposition, a thorough characterization of momentum and heat transfer in the gas-atomized spray is required. The present paper describes measurements of particle size, gas velocity, particle velocity, and spray temperature in gasatomized Sn-Pb sprays. Measurements were performed on steady-state axisymmetric sprays which were generated using a close-coupled gas atomizer with Sn-5 wt p t Pb and Sn-38 wt p t Pb alloys, atomizer gas flow rates of 2.5 g/s (0.56 MPa) and 3.4 g/s (1.04 MPa), melt flow rates of 35 and 61 g/s, and atomizer-substrate distances of 180 and 360 mm. Gas velocities in the range to 4 m/s were measured using Pitot tube and laser Doppler anemometry (LDA). Droplet velocities in the range 3 to 32 m/s were determined from photographic streak-length measurements and LDA. Oil calorimetry of the spray enthalpy indicated that the spray temperature decreased with increasing axial distance from the gas atomizer, increasing gas flow rate, and decreasing melt flow rate.

Journal ArticleDOI
TL;DR: In this article, a mathematical model was developed to calculate microsegregation in binary metallic alloys, which utilized the mathematical techniques of the method of lines combined with invariant imbedding (MOL/II) to solve the problem of combined heat and mass transfer during and after solidification.
Abstract: A mathematical model was developed to calculate microsegregation in binary metallic alloys. This model utilized the mathematical techniques of the method of lines combined with invariant imbedding (MOL/II) to solve the problem of combined heat and mass transfer during and after solidification. Model predictions were compared to experimental measurements in the Al-Cu system and to other microsegregation models. The MOL/II model predicted nonequilibrium second-phase contents within ±3 pct at low and intermediate cooling rates, when dendrite-arm coarsening was included in the model. It also was able to reproduce concentration profiles reasonably well. The analytical models commonly used (equilibrium cooling, Scheil equation, Brody/ Flemings model, Clyne/Kurz model, Solari/Biloni model, and Basaran equation) in micro-segregation calculations were shown to be considerably less accurate than the numerical models (MOL/II and the Ogilvy/Kirkwood model).

Journal ArticleDOI
TL;DR: In this paper, it is shown that spangles form dendritically from a nucleus in the zinc bath, and the spangle diameter is dependent on the alloy addition to the bath, large spangles being obtained with Bi and Sb as well as Pb.
Abstract: Very large grains, termed “spangles,” are produced on galvanized sheet steel coatings when lead is added to the zinc bath. The spangles have been attributed to melt undercooling prior to solidification. The present results indicate this is not the case, undercooling being less than 1 °C. The spangle diameter is shown to be dependent on the alloy addition to the bath, large spangles being obtained with Bi and Sb as well as Pb. The spangle size is related to the surface tension of the alloying addition, the size decreasing as the melt vapor surface tension of the alloying element increases. It is proposed that spangles form dendritically from a nucleus in the melt. Alloy additions with low interfacial energies and very limited solid solubility are highly concentrated ahead of the dendrite tip. This decreases the tip radius and increases the dendrite velocity, producing large grains. The basal plane orientation of the samples varies between 17 and 80 deg with respect to the steel sheet surface, which is inconsistent with basal plane dendritic growth in Zn along (1010) directions. It is proposed that solute additions to the melt and growth in a thin liquid layer can modify the dendrite growth direction, accounting for the spangle orientation.

Journal ArticleDOI
TL;DR: In this article, a combined Kelvin-Helmholtz and Rayleigh-Taylor instability analysis has been applied to bubbles forming at submerged tuyeres, which demonstrates that the instabilities are primarily capillary in nature, not gravity waves, which explains the observation that orientation has little effect on the jetting transition.
Abstract: There has never been any fundamental explanation presented for the transition from the bubbling regime to the jetting regime when gas is injected into liquid at high velocity through submerged tuyeres. This is an important issue in metallurgical processes, since the flow regime is known to influence refining rates, refractory erosion, and the penetration of the liquid into the tuyere. Based on the observation that many small droplets of liquid and gas bubbles are formed to create the jets, a combined Kelvin-Helmholtz and Rayleigh-Taylor instability analysis has been applied to bubbles forming at submerged tuyeres. For particular wavelengths of disturbances, the interface will be unstable and create bubbles and droplets. The critical injection velocity for instability depends on surface tension, tuyere diameter, and the gas-to-liquid density ratio, which can be summarized by We = 10.5(ρ*)−1/2, where We is the Weber number based on the gas velocity and density and tuyere diameter, and ρ* is the gas-to-liquid density ratio. The importance of surface tension had not been appreciated previously for this regime of gas injection. There is considerable controversy in the literature concerning the measurement of the transition from bubbling to jetting. The 70 pct “linking” point, proposed by Ozawa and Mori, describes the situation where 70 pct of the bubbles link with the preceding bubbles and produce a reasonably steady jet. The theoretical correlation developed above predicts the velocity to reach this point ±20 pct (95 pct confidence level) in a variety of systems from six different groups of workers. The theoretical analysis demonstrates that the instabilities are primarily capillary in nature, not gravity waves, which explains the observation that orientation has little effect on the jetting transition.

Journal ArticleDOI
TL;DR: In this paper, a mathematical model has been developed to describe the various processes occurring in a flash furnace shaft, incorporating turbulent fluid dynamics, chemical reaction kinetics, and heat and mass transfer.
Abstract: A mathematical model has been developed to describe the various processes occurring in a flash furnace shaft. The model incorporates turbulent fluid dynamics, chemical reaction kinetics, and heat and mass transfer. The key features include the use of thek-e turbulence model, incorporating the effect of particles on the turbulence, and the four-flux model for radiative heat transfer. The model predictions were compared with measurements obtained in a laboratory flash furnace and a pilot plant flash furnace. Good agreement was obtained between the predicted and measured data in terms of the SO2 and O2 concentrations, the amount of sulfur remaining in the particles, and the gas temperature. Model predictions show that the reactions of sulfide particles are mostly completed within about 1 m of the burner, and the double-entry burner system with radial feeding of the concentrate particles gives better performance than the singleentry burner system. The model thus verified was used to further predict various aspects of industrial flash furnace operation. The results indicate that from the viewpoint of sulfide oxidation, smelting rate can be substantially increased in most existing industrial flash furnaces.

Journal ArticleDOI
TL;DR: In this paper, three principal mechanisms of porous iron growth were identified: a continuous coupled reaction, involving cooperative pore and iron growth, a continuous dendritic growth mechanism, in which pores advance ahead of the iron formation, and a discontinuous mechanism, involving the successive formation and breakdown of dense iron lay-ers on the oxide surface.
Abstract: The iron/iron oxide interface morphologies formed during the reduction of dense wustite and magnetite samples have been examined using scanning electron microscopy. Under conditions where porous iron products are obtained, a range of structures, which depend critically on the gas composition, reaction temperature, and bulk oxide composition, may be formed at the inter-face during reduction. Three principal mechanisms of porous iron growth have been identified: (1) a continuous coupled reaction, involving cooperative pore and iron growth, (2) a continuous dendritic growth mechanism, in which pores advance ahead of the iron formation, and (3) a discontinuous mechanism, involving the successive formation and breakdown of dense iron lay-ers on the oxide surface. The reaction mechanisms are explained in terms of the relative mag-nitudes of the various chemical reactions and mass transport processes which occur during the decomposition of the solids.

Journal ArticleDOI
TL;DR: The thermodynamics of the formation of titanium carbonitride in liquid iron-titanium-carbon-nitrogen alloys were investigated in order to predict under what conditions it will form in liquid steel.
Abstract: The thermodynamics of the formation of titanium carbonitride in liquid iron-titanium-carbon-nitrogen alloys were investigated in order to predict under what conditions it will form in liquid steel. A metal-carbonitride equilibration technique was used. Titanium carbonitride of a desired composition was made by mixing and high-temperature sintering of very fine powders of titanium nitride and carbide. The formation of titanium carbonitride was confirmed by lattice parameter measurements on the samples before and after the experiments. The equilibrium concentrations of titanium, carbon, and nitrogen in equilibrium with a specific titanium carbonitride were obtained at 1873 K. Activities of titanium carbide and nitride relative to pure solid titanium carbide and nitride were calculated. It was found that titanium carbonitride solid solution is almost ideal. From the results, calculations were performed to predict at which composition various carbonitrides will form.

Journal ArticleDOI
TL;DR: In this article, the reduction of dense wustite and magnetite samples in CO/CO2 and H2/H2O gas mixtures has shown that impurity elements in solid solution in the oxides can significantly affect the reaction mechanisms operative during reduction and the conditions for porous iron growth.
Abstract: The reduction of dense wustite and magnetite samples in CO/CO2 and H2/H2O gas mixtures has shown that impurity elements in solid solution in the oxides can significantly affect the reaction mechanisms operative during reduction and the conditions for porous iron growth. In general, the presence of P, Mg, Ti, Si, Ca, K, and Na in wustite favors, in order of increasing strength, the formation of the porous iron product morphology. Aluminum, on the other hand, significantly reduces the range of gas conditions over which the porous iron microstructure may be obtained.

Journal ArticleDOI
TL;DR: In this paper, the authors used a mathematical model to calculate the variables related to moisture transfer in strand sintering and found that the drying of iron ore pellets occurs in two distinct periods: one at a constant drying rate and the other at a decreasing drying rate.
Abstract: Moisture transfer during the strand sintering operation was studied both experimentally and using a mathematical model. The drying of iron ore pellets was found to occur in two distinct periods: one at a constant drying rate and the other at a decreasing drying rate, whereas the drying of zinc ore pellets always occurs at a decreasing drying rate. Characteristic drying curves were determined for both materials. The moisture transfer mechanisms during the sintering process were demonstrated in detail, including the recondensation of water in the cold layers of the bed and the formation of an inert, overmoistened zone. The mathematical model presented simulates all of these phenomena and is used to calculate the variables related to moisture transfer. The model is adaptable to other processes where a hot gas passes through a moist packed bed.

Journal ArticleDOI
TL;DR: In this article, the same authors used scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) to study the bonding and crystalline phases of specular hematite concentrates using bentonite or peat moss as a binder.
Abstract: Pellets in the basicity range of 0.2 to 1.6 were produced from specular hematite concentrates using bentonite or peat moss as a binder. Specific pellet basicities were achieved through the addition of (1) limestone and (2) a combination of dolomite and limestone. Mineralogical study and microanalysis of the bonding and crystalline phases were done using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). In limestone-fluxed pellets with bentonite as a binder, although formation of calcium ferrite was noted at the basicity of 0.8, its formation in appreciable quantities was delayed until the basicity of 1.6. For the pellets produced with a combination of dolomite and limestone, even at the basicity of 1.6, only minor amounts of this phase were present. In these pellets, some magnesioferrites were formed which did not conform to the stoichiometric composition (MgOFe2O2), but they were quite deficient in MgO. The silicate glass phases, which essentially provided the bonding in the pellets, showed a two-zone structure: (1) magnesian-ferruginous and (2) glass containing high quantities of Si and Ca. However, in pellets with only limestone addition, the zoned structure was less prevalent, probably due to low Mg content. The results indicate that using peat moss in conjunction with limestone, pellet sticking can be minimized at higher basicities. The factors influencing the pellet bonding and the change in the physical and chemical properties of these pellets are discussed.

Journal ArticleDOI
TL;DR: In this paper, the intrinsic kinetics of the selective chlorination of iron from ilmenite ore using carbon monoxide as the reducing agent were studied in a shallow fluidized bed and the results indicated that the kinetics in the temperature range 923 to 1123 K are represented by the following poreblocking rate law: λ[ exp (XFe/λ) − 1 ] = 33.7 exp (− E/RT)pco0.5220.
Abstract: The intrinsic kinetics of the selective chlorination of iron from ilmenite ore using carbon monoxide as the reducing agent were studied in a shallow fluidized bed. Experiments on the effects of chlorination temperature, carbon monoxide and chlorine gas partial pressures, and particle size were conducted in the absence of mass- and heat-transfer influences. Results indicate that the kinetics in the temperature range 923 to 1123 K are represented by the following pore-blocking rate law: λ[ exp (XFe/λ) − 1 ] = 33.7 exp (− E/RT)pco0.5220.32t where E is 37.2 kJ/mol and p and t are in atm (=101.3 kPa) and minutes, respectively. The partial pressure of carbon monoxide was found to affect the chlorination rate more strongly than that of chlorine. A reaction mechanism in which iron in ilmenite reacts with chlorine before the liberated oxygen is removed by carbon monoxide is proposed.

Journal ArticleDOI
TL;DR: In this article, the equivalence between a model ladle and a full-scale system can be adequately described via the geometric and dynamic similarities via the similarity of the two systems.
Abstract: Since hydrodynamic studies on ladle flows are often not concerned with thermal and chemical similarity effects, the equivalence between a model ladle and a full-scale system can be adequately describes via the geometric and dynamic similarities

Journal ArticleDOI
TL;DR: In this paper, the thermodynamic activities of Ti at dilution in a series of Ag-Cu alloys and eutectic Ag-cu alloys containing In or Sn were measured using a galvanic cell technique employing a ThO2-8 pct Y2O3 electrolyte.
Abstract: The thermodynamic activities of Ti at dilution in a series of Ag-Cu alloys and eutectic Ag-Cu alloys containing In or Sn were measured using a galvanic cell technique employing a ThO2-8 pct Y2O3 electrolyte. The equilibrium oxide phase formed by the reaction of Ti (XTi > 0.004) in the Ag-Cu alloy melts with an A12O3 or ZrO2 crucible was Ti2O (s). The free energy of formation of Ti2O (s) was estimated from available thermodynamic data. Titanium activities were calculated from measured oxygen potentials and the free energy of formation of Ti2O (s). Titanium in the eutectic Ag-Cu melt showed a positive deviation from ideal solution behavior at 1000°C, and its activity coefficient at infinite dilution was about 6.5 relative to pure solid Ti. Indium and Sn did not increase the activity coefficient of Ti in eutectic Ag-Cu melts. Silver increased the Ti activity coefficient in the Ag-Cu-Ti melts significantly. The Ti activity coefficient value in liquid Ag was about 20 times higher than in eutectic Ag-Cu melt at 1000 °C.

Journal ArticleDOI
TL;DR: In this article, the formation of Cu-Al alloys by the thermal explosion mode of the combustion synthesis method was investigated for compositions ranging from 25 to 50 at. pct Al. Through X-ray, differential thermal analysis (DTA), and scanning electron microscopy (SEM) analyses, the nature of the reaction between powders of the two metals was determined.
Abstract: The formation of Cu-Al alloys by the thermal explosion mode of the combustion synthesis method was investigated for compositions ranging from 25 to 50 at. pct Al. Through X-ray, differential thermal analysis (DTA), and scanning electron microscopy (SEM) analyses, the nature of the reaction between powders of the two metals was determined. Solid-state diffusional reactions preceded the main combustion reaction which, in turn, was triggered by the appearance of a liquid phase. The relative amounts of phases formed through solid-state and liquid-phase reactions depended on heating rate. A significant amount of volume growth is observed during the solid-state reaction stage, and it is concluded that it is caused by pore formation by the Kirkendall effect.

Journal ArticleDOI
TL;DR: In this article, the dissolution of galena in 0.3 M FeCl3-0.3M HC1 solutions containing 0 to 6.5 M LiCl was measured over the temperature range of 50 °C to 90 °C.
Abstract: The dissolution of galena in 0.3 M FeCl3-0.3 M HC1 solutions containing 0 to 6 M LiCl was studied at 80 °C, and parabolic kinetics were observed at all LiCl concentrations. The leaching rate increases gradually with increasing LiCl concentrations to ≈4 M LiCl; the presence of >4 M LiCl results in a rapid increase in the leaching rate. The solubility of PbCl2 in 0.3 M FeCl3-0.3 M HC1 solutions containing 0 to 6.5 M LiCl was measured over the temperature range of 50 °C to 90 °C. The solubility increases systematically with increasing temperature and LiCl concentration. The parabolic kinetics, coupled with the correlation between the leaching rate and the solubility of PbCl2, suggest that the dissolution of galena is controlled by the outward diffusion of the PbCl2 reaction product through the constantly thickening layer of elemental sulfur formed during leaching. This conclusion is also supported by various morphological studies which consistently indicated a thin layer of PbCl2 between the corroding galena and the porous elemental sulfur reaction product.

Journal ArticleDOI
TL;DR: In this paper, the reduction of dense magnetite samples in H2/H2O and H 2/N2 gas mixtures between temperatures of 723 and 1373 K has been investigated.
Abstract: The reduction of dense magnetite samples in H2/H2O and H2/N2 gas mixtures between temperatures of 723 and 1373 K has been investigated. A detailed study of partially reduced samples using conventional metallographic and scanning electron microscopy (SEM) techniques has enabled the conditions for the formation of a number of different product microstructures to be clearly defined. The reaction mechanisms involved in various continuous and discontinuous growth processes are discussed.

Journal ArticleDOI
TL;DR: Analyse de l'influence des phenomenes interfaciaux sur les caracteristiques du metal fondu en soudage (ecou element de chaleur, ecoulement du metal) as discussed by the authors.
Abstract: Analyse de l'influence des phenomenes interfaciaux sur les caracteristiques du metal fondu en soudage (ecouelement de chaleur, ecoulement du metal)

Journal ArticleDOI
TL;DR: In this article, a mathematical model has been developed to describe the rate processes in an axisymmetric copper flash smelting furnace shaft, and a particular feature of the model is the incorporation of the four-flux model to describe radiative heat transfer by combining the absorbing, emitting, and anisotropic scattering phenomena.
Abstract: A mathematical model has been developed to describe the rate processes in an axisymmetric copper flash smelting furnace shaft. A particular feature of the model is the incorporation of the four-flux model to describe the radiative heat transfer by combining the absorbing, emitting, and anisotropic scattering phenomena. The importance of various subprocesses of the radiative heat transfer in a flash smelting furnace has been studied. Model predictions showed that the radiation from the furnace walls and between the particles and the surrounding is the dominant mode of heat transfer in a flash smelting furnace.