Showing papers in "Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science in 1984"

A new finite element model for welding heat sources

Abstract: A mathematical model for weld heat sources based on a Gaussian distribution of power density in space is presented. In particular a double ellipsoidal geometry is proposed so that the size and shape of the heat source can be easily changed to model both the shallow penetration arc welding processes and the deeper penetration laser and electron beam processes. In addition, it has the versatility and flexibility to handle non-axisymmetric cases such as strip electrodes or dissimilar metal joining. Previous models assumed circular or spherical symmetry. The computations are performed with ASGARD, a nonlinear transient finite element (FEM) heat flow program developed for the thermal stress analysis of welds.* Computed temperature distributions for submerged arc welds in thick workpieces are compared to the measured values reported by Christensen1 and the FEM calculated values (surface heat source model) of Krutz and Segerlind.2 In addition the computed thermal history of deep penetration electron beam welds are compared to measured values reported by Chong.3 The agreement between the computed and measured values is shown to be excellent.

The formation of oscillation marks in the continuous casting of steel slabs

Abstract: The formation of oscillation marks on the surface of continuously cast slabs has been studied by metallographically examining slab samples and by performing a set of mathematical analyses of heat flow, lubrication, and meniscus shape in the meniscus region of the mold. The metallographic study has revealed that, in agreement with previous work, the oscillation marks can be classified principally according to the presence or absence of a small “hook” in the subsurface structure at the base of individual oscillation marks. The depth of the oscillation marks exhibiting subsurface hooks varies with the carbon content, reaching a maximum at about 0.1 pct carbon, while the oscillation marks without hooks show no carbon dependence. The analysis of heat flow at the meniscus, which is based on a measured mold heat-flux distribution, indicates that depending on the level of superheat, the meniscus may partially freeze within the period of a typical mold oscillation cycle. Lubrication theory has shown that, owing to the geometry of the mold flux channel between the solidifying shell at the meniscus and the straight mold wall, significant pressure gradients capable of deforming the meniscus can be generated in the flux by the reciprocating motion of the mold relative to the shell. A force balance on the interface between the steel and the mold flux has been applied to compute the shape of the meniscus as a function of the pressure developed in the lubricating flux at different stages in the mold oscillation cycle. This has demonstrated that the “contact” point between the meniscus and mold moves out of phase with (by π/2), and has a greater amplitude than, the mold displacement so that just at, or near, the end of the negative strip time molten steel can overflow at the meniscus. From these studies a reasonable mechanism of oscillation-mark formation emerges which involves interaction between the oscillating mold and the meniscusvia pressure gradients in the mold flux, meniscus solidification, and overflow. The mechanism is consistent with industrial observations.

Numerical treatment of rapid solidification

Abstract: Techniques are reviewed for describing crystal nucleation and subsequent advance of the crystallization front in metallic melts under the range of conditions generated during rapid solidification processing. The selection of appropriate boundary conditions in these cases is discussed, with particular reference to coupling between the undercooling at and the velocity of the growth front. It is emphasized that, although solute redistribution may occur, the process is normally under heat flow control and techniques for treating the associated phenomena are described. Some illustrative theoretical curves are presented for unidimensional heat flow toward a massive substrate, while the relevance to other processes, such as gas atomization, is periodically noted. Some attention is devoted to recalescence (removal of the undercooling) of the growth front as a result of latent heat evolution and the degree to which this might be counteracted by external cooling. A rationale is presented enabling the conditions under which recalescence could be arrested (thus permitting strongly enhanced crystal growth rates) to be estimated for different base metals. Mention is made of solute redistribution phenomena during recalescence of alloys. Finally, some implications of the data presented are briefly discussed in practical terms.

Metal vaporization from weld pools

Abstract: Experimental studies of alloy vaporization from aluminum and stainless steel weld pools have been made in order to test a vaporization model based on thermodynamic data and the kinetic theory of gases. It is shown that the model can correctly predict the dominant metal vapors that form but that the absolute rate of vaporization is not known due to insufficient knowledge of the surface temperature distribution and subsequent condensation of the vapor in the cooler regions of the metal. Values of the net evaporation rates for different alloys have been measured and are found to vary by two orders of magnitude. Estimated maximum weld pool temperatures based upon the model are in good agreement with previous experimental measurements of electron beam welds.

Comparison of Numerical Modeling Techniques for Complex, Two-Dimensional, Transient Heat-Conduction Problems

Abstract: The accuracy, stability, and cost of the standard finite-element method, (Standard), Matrix method method of Ohnaka, and alternating-direction, implicit finite-difference method (ADI) have been compared using analytical solutions for two problems approximating different stages in steel ingot processing. The Standard and Matrix methods both employ triangular elements and were compared using the Dupont, Lees, and Crank-Nicolson time-stepping techniques. Other variables include mesh and time-step refinement, type of boundary condition formulation, and the technique for simulating phase change. The best overall combination of methods investigated for modeling two-dimensional, transient, heat conduction problems involving irregular geometry was the Dupont-Matrix method with a lumped boundary condition formulation and temperature dependent properties evaluated at time level two, coupled with the Lemmon latent-heat evolution technique if phase change is involved. For problems with simple geometry, the ADI method was found to be more cost effective.

Thermochemistry of alloys of transition metals: Part IV. Alloys of copper with scandium, yttrium, lanthanum, and lutetium

Abstract: The enthalpies of mixing of liquid copper with liquid lanthanum, and with solid scandium, yttrium, and lutetium have been measured by high temperature reaction calorimetry at 1373 K. After correction for the enthalpies of fusion the limiting enthalpies of solution of the liquid metals in copper are-102 kJ mol-1 (Sc), —105 kJ mol-1 (Y), —103 kJ mol-1 (La), and —120 kJ mol-1 (Lu). We also report approximate enthalpies of solution of chromium and vanadium in copper; all values are compared with predictions published by Miedema and co-workers. The enthalpies of formation of eight congruent melting intermetallic compounds in the system Cu-Sc, Cu-Y, and Cu-La have been determined. The values are compared with corresponding data for the liquid alloys; this comparison provides approximate enthalpies and entropies of fusion for the intermetallic compounds. It is found that these entropies of fusion average 1. 1R to 1.2R,i.e., the values are comparable to those found for close-packed cubic metals. This indicates that the disordering of the two atoms probably contributes little to the entropies of fusion of the compounds.

Alloying element vaporization and weld pool temperature during laser welding of AlSl 202 stainless steel

Abstract: Alloying element vaporization rates, plasma composition, and the changes in weld composition during laser welding of 202 stainless steel are discussed in this paper. Iron, manganese, and chromium were the most dominant species in the plasma. During laser welding it is always a difficult task to measure the temperature of the weld pool since this region is surrounded by hot plasma. In this paper a novel technique for the determination of weld pool temperature is presented. It is demonstrated that the relative rates of vaporization of any two elements from the molten pool can serve as an indicator of weld pool temperature, irrespective of the element pair selected. The composition of the solidified region calculated from the measured values of vaporization rate, plasma composition, and the volume of the solidified region was in good agreement with the weld composition determined by electron probe microanalyis technique.

A new approach to investigate the drop size distribution in basic oxygen steelmaking

Abstract: An experimental study was conducted to investigate the drop size and the drop size distribution resulting from the interaction between an impinging oxygen jet of high velocity and the molten steel bath by employing a new approach. The results on the drop size and the drop size distribution are presented and discussed. It is shown that the drop size produced in BOF steelmaking obeys the Rosin-Rammler-Sperling distribution function. Table I. Symbols and Their Meaning

Convection in the two-phase zone of solidifying alloys

Abstract: The analysis is applicable to alloy solidification which proceeds horizontally to the center of a mold. The model follows the growth of the solid-liquid zone adjacent to the chill face (the initial transient), the movement of the zone across the mold, and the region of final solidification adjacent to the centerline (the final transient). During solidification the density of the liquid varies across the twophase zone. Consequently, there is natural convection which is treated as flow through a porous medium. The equations for convection are coupled with the equation of solute redistribution between the phases in order to calculate macrosegregation after solidification is complete. Results were computed for alloys which show: (1) “inverse segregation≓ at a cooled-surface; (2) macrosegregation resulting from solidification with the initial transient, a period with a complete two-phase zone, and a final transient; and (3) macrosegregation when the width of the two-phase zone exceeds the semi-width of the mold.

Heat transfer and fluid flow in plasma spraying

Abstract: A mathematical model is developed to describe the plasma spray process in which particular attention is paid to the fluid flow and temperature fields in the plasma jet, the plasma/particle interaction, and the heat transfer phenomena associated with the deposition process. On the basis of the heat transfer analysis it was possible to define the limiting conditions for satisfactory operation of the deposition process in terms of basic process variables. For high deposition rates, high levels of superheat, and low thermal conductivity of the deposit, the limiting condition is set by the rate at which heat may be removed by the substrate. For large particle sizes and materials with high melting points the limiting condition is determined by the need to transfer sufficient thermal energy to the particles so that they arrive at the substrate in a fully molten state. Wherever possible, the model predictions were compared with experimental measurements and good agreement was obtained.

Influence of MgO addition on mineralogy of iron ore sinter

Abstract: The influence of MgO addition on sinter mineralogy was studied on sinters produced in a laboratory installation, with a wide range of MgO/CaO ratios at several basicity indices [B = (CaO + MgO)/ (SiO2 + A12O3)] between 0.7 to 1.9. The most striking influence of MgO is the suppression of hematite and Ca-ferrite phases and the increase in magnetite phase. In general, MgO favors the formation of glass and suppresses the precipitation of dicalcium silicates in favor of Ca-Fe-Mg olivines and pyroxenes. Microprobe studies revealed that most of the Mg was picked up by the magnetite phase to form mixed spinels of type (Fe, Mg)O · Fe2O3. At a constant basicity index, increased replacement of CaO by MgO also led to increased participation of FeO in the slag formation process, thus increasing the overall FeO content of sinter. A mechanism for the formation of mixed spinels has been proposed. The effect on various sinter properties resulting due to change in sinter mineralogy has been outlined.

Thermodynamics of phosphate and phosphide in CaO-CaF2 melts

Abstract: The thermodynamics of phosphate and phosphide in CaO-CaF2 melts was studied by equilibrating the melts in a graphite boat with CO-Ar mixtures and Ag-P alloys between 1400 and 1550 ‡C. The dependence of phosphate and phosphide concentrations on the partial pressure of phosphorus, the partial pressure of oxygen, and slag composition confirmed the behavior of P3 and PO 4 3 in the melts as thermodynamically expected, giving 0.52 and 8.5 x 10−4 as the values for the activity coefficients of Ca3/2PO4 and Ca3/2P, respectively.

Reaction kinetics of the ferric chloride leaching of sphalerite—an experimental study

Abstract: Chloride leaching processes have significant potential for treating complex sulfides. One advantage of chloride leaching is fast dissolution rates for most sulfide minerals. This experimental study is concerned with ferric chloride leaching of sphalerite, a common component of many complex concentrates. The effects of stirring, temperature, ferric ion concentration, and particle size have been examined. In addition, reaction residues at various levels of zinc extraction were examined by SEM, and the products of reaction were identified by energy dispersive X-ray analysis and X-ray diffraction. These observations indicated that the dissolution reaction is topochemical. Moreover, the leaching results fit a surface reaction control model. The activation energy was calculated to be 58.4 kJ/mole which is reasonable for a rate limiting surface reaction. The order of the reaction was 0.5 with respect to Fe3+ at low concentrations and zero at high concentrations. The change in reaction order occurred at similar Fe3+ concentrations for various particle sizes. This is believed to be indicative of an electrochemical reaction mechanism at low Fe3+ and an adsorption mechanism at higher Fe3+. A kinetic model for the ferric chloride leaching of sphalerite was also obtained for the lower Fe3+ concentrations and is given by: (ie5-01) This model is in excellent agreement with the experimental results for fractions of zinc extracted up to 0.95.

The breakdown of dense iron layers on wustite in CO/CO2 and H2/H2O systems

Abstract: Examination of wustite single crystals reduced in CO/CO2 and H2/H2O gas mixtures has shown that in all cases a dense iron layer is formed initially on the oxide surface and that the porous growth of iron which is obtained under certain experimental conditions occurs as a direct result of the breakdown of this initial dense iron layer. Possible mechanisms of the iron layer breakdown are examined and compared with the experimental observations. A qualitative model of the breakdown process involving the nucleation of gas bubbles and the expansion of these bubbles in the iron layer is presented.

Establishment of product morphology during the initial stages of wustite reduction

Abstract: The product morphologies obtained on the reduction of wustite in CO/CO2 gas mixtures between 1073 and 1373 K are reported. Three types of product morphology are identified, namely, type A (porous iron), type B (porous wustite covered with dense iron), and type C (dense wustite covered with dense iron). The reactions which occur during the reduction of wustite in CO/CO2 and H2/H2O systems both before and after iron nucleation are examined. The product morphologies obtained on reduction are explained qualitatively in terms of the relative rates of the chemical reaction with the gas and the mass transport processes both in and on the solid.

The high temperature oxidation of metals forming cation-diffusing scales

Abstract: Short-circuit cation diffusion via scale grain boundaries and dislocations supports oxidation in the intermediate temperature regime, and scale growth at the scale/gas interface takes place at ledges provided by screw dislocations intersecting the surface. These dislocations in the scale are formed by growth stresses or are inherited from the metal. In situ observations of scale growth in a hot-stage environmental scanning electron microscope have provided insight into scale growth mechanisms and the formation of nonplanar oxidation products: whiskers, pyramids, and pits. Specific reference is made to the evolution of oxidation product morphologies for copper, nickel, iron, and chromium. 74 references, 16 figures, 1 table.

Isotope exchange studies of the rate of dissociation of CO2 on liquid iron oxides and CaO-saturated calcium ferrites

Abstract: Measurements of the rates of dissociation of CO2 on liquid iron oxides and CaO-saturated liquid calcium ferrites have been made by the14CO2-CO isotope exchange technique. For temperatures up to about 1550 °C, the apparent first order rate constants for both melts are essentially inversely proportional to the equilibrium CO2/CO ratio over the range studied (≈0.4 to 12). Evidence is presented that the rate limiting step in the interfacial oxidation of these melts by CO2 is the dissociation of CO2- Rates of oxidation, in mol cm−2 s−1, in CO2-CO atmospheres are deduced to be given by the equations:v =( p CO 2 a − p CO) exp(−15,900/T − 2.03) andv = (pCO2 α o -1 −pCO) exp(−3800/T − 6.93) for the iron oxides and CaO-saturated calcium ferrites, respectively, wherea 0 is the oxygen activity of the melt expressed as the equilibrium CO2/CO ratio and the pressures are in atmospheres. The strong dependence on the CO2/CO ratio is shown to be consistent with the need to transfer two charges to the adsorbing or dissociating CO2 molecule. Correlation with the existing surface tension data is inconclusive.

Compression of semi-solid dendritic Sn-Pb alloys at low strain rates

Abstract: The behavior of semi-solid dendritic Sn-Pb alloys was studied at one degree above the eutectic. Small cylindrical samples were deformed at an initial strain rate of 1.3 x 10−2 s−1 in a parallel-plate apparatus. The friction between the sample and the plates was found to affect strongly both the strength of the material in compression and the resultant liquid-solid segregation. For low friction a maximum stress occurred at strains of about 0.3. Above this strain large cracks were observed. High friction resulted in a much higher degree of segregation than observed for low friction. No maximum stress and no cracking was observed, even for strains as large as 1.2 for high friction. Cylindrical samples were extruded through cylindrical dies at constant piston velocities ranging from 8.5 x 10≓5 ms~’ to 8.5 X 10≓4 ms≓1, and with reduction of area ranging from 2:1 to 8:1. The deformation occurred in two distinct modes. First, a “compaction≓ mode, during which liquid was expelled and the solid compacted but did not flow through the die, under increasing stress. Second, a “flow≓ mode, during which compacted solid flowed through the die, under a constant stress, σrextr, which was found to be proportional to the natural logarithm of the area reduction. Experiments involving compression over a filter and compression between parallel plates of alloys of different compositions were performed to examine the effects of the fraction liquid on the rheology of semi-solid dendritic alloys. The stress required for deformation was seen to exhibit the same pseudo-plastic strain-rate dependence for parallel plate, piston-filter and in forward extrusion experiments. This strain-rate dependence can be summarized by the power-law expression: σ ∝ ɛ0.23.

Phase relationships in the Fe-Cr-C system at solidification temperatures

Abstract: The phase relationships between the liquid phase and the primary solid phases were investigated in the iron-rich corner of the Fe-Cr-C system. The investigation consisted of measurements of tie-lines and the liquidus surface of the liquid-delta (bcc) and liquid-gamma (fcc) equilibria in the Gibbs triangle, bounded by 0 to 1.4 wt pct C and 0 to 25 wt pct Cr (bal. Fe). The peritectic surface of the three-phase equilibrium was also measured. The temperature ranged from 1811 to about 1750 K. The tie-lines were obtained from liquid-solid equilibrium couples, and the liquidus and peritectic surfaces, by differential thermal analysis (DTA). A statistical procedure was applied to determine from the experimental results the parameters required for a thermodynamic model of the system. Calculations by the model are in good agreement with the experimental results. As a consequence the model can be used to interpolate and extrapolate properties and compositions of phases in equilibrium in the system within the composition and temperature field investigated.

Kinetics of leaching of zinc ferrite in aqueous hydrochloric acid solutions

Abstract: The dissolution of synthetic samples of zinc ferrite in aqueous hydrochloric acid is stoichiometric The rate appears to be controlled by a chemical reaction on the solid surface, and dependence of the dissolution rate on hydrochloric acid activity is of the first order Activation energy of 83 kJ mol-1 was found Zinc ferrite leaching is a slow solubilization process in the hydrochloric acid treatment of dead-roasted Iberian pyrite ashes The most favorable conditions are 05-1 M HC1 at 90 to 100 ‡C, when preferential solubilization of the spinel phases takes place on the hematitic matrix Extensive extraction of zinc (~90 pct of total zinc) in one to two hours and low solubilization of iron (~8 pet of total iron) results under these conditions

Structural Effects and Band Segregate Formation during the Electromagnetic Stirring of Strand-Cast Steel

Abstract: Chemical and metallographic studies have been made of the “white band” (a zone of negative segregation) formed by the electromagnetic stirring of 127 mm (5 inch) square strand-cast steel billets. Three stirrer locations were studied. At all locations, the white band was found to consist of a zone of negative segregation corresponding to the position of the solid-liquid interface during stirring, followed by a zone of positive segregation related to the cessation of stirring. Metallographic studies showed the curvature of columnar dendrites within the white band and the presence of a transition zone of nondirectional growth between the white band and the equiaxed core. A mechanism for the formation of the segregated zones at the white band is presented, along with theoretical calculations. Agreement between the calculations and experimental results was good. The role of electromagnetic stirring in the formation of the white band and in the associated columnar-equiaxed transition is discussed.

Numerical models for casting solidification: Part II. Application of the boundary element method to solidification problems

Abstract: A new numerical model, which is based on the boundary element method, was proposed for the simulation of solidification problems, and its application was demonstrated for solidification of metals in metal and sand molds Comparisons were made between results from this model and those from the explicit finite difference method Temperature recovery method was successfully adopted to estimate the liberation of latent heat of freezing in the boundary element method A coupling method was proposed for problems in which the boundary condition of the interface consisting of inhomogeneous bodies is governed by Newton’s law of cooling in the boundary element method It was concluded that the boundary element method which has several advantages, such as the wide variety of element shapes, simplicity of data preparation, and small CPU times, will find wide application as an alternative for finite difference or finite element methods, in the fields of solidification problems, especially for complex, three-dimensional geometries

Numerical models for casting solidification: Part I. The coupling of the boundary element and finite difference methods for solidification problems

Abstract: An investigation on the coupling technique for boundary element and finite difference methods was carried out to simulate solidification processes. In the coupling model, solidification problems in casting and unsteady-state heat conduction problems in mold regions were analyzed by explicit finite difference and boundary element methods, respectively. A comparison was made between the coupling model and the finite difference method on the solidification of castings in metal and sand molds. The proper range of time steps for boundary elements in transient problems was presented for a simple geometry. And two types of time marching schemes were proposed for application of the boundary element method to solidification processes.

Fluid flow and mass transfer in an inductively stirred four-ton melt of molten steel: A comparison of measurements and predictions

Abstract: Experimental measurements are reported on melt velocities and on the rate at which immersed carbon rods dissolve in a 4-ton induction furnace, holding a low carbon steel melt. These measurements are compared with theoretical predictions, based on the numerical solution of Maxwell’s equations and the turbulent Navier-Stokes equations. In general, good agreement has been obtained, both regarding the absolute values of the velocities and the mass transfer coefficients and the trends predicted by the theoretical analysis. In addition to providing further proof regarding the applicability of the mathematical modeling technique, the principal contribution of the work is that it provides an improved insight into the behavior of inductively stirred melts. In particular it was found that for an inductively stirred melt both the velocities and the rate of turbulence energy dissipation are relatively uniform spatially, in contrast to bubble stirred systems, where most of the agitation is confined to the jet plume and to the near surface region. It was found, furthermore, that the mass transfer coefficient characterizing the rate of dissolution of immersed carbon rods depends both on the absolute values of the melt velocity and on the local values of the turbulence intensity; thus significant mass transfer will occur in the region of the eye of the circulation, where the absolute value of the mean velocity is small.

An alternative method for the recovery of lithium from spodumene

Abstract: Two important processes applied presently for the extraction of lithium from spodumene, the acid method and the lime method, are described in this paper. The less common method of chlorination roasting is also discussed. The behavior of tachydrite and spodumene, individually, during heating is investigated by differential thermal analysis. It was observed that tachydrite gradually loses its water of crystallization, becoming anhydrous at 573 K. Spodumene, on the other hand, is stable, showing a mass loss of 0.3 pct. around 693 K. At the reaction temperatures used in this study, the mixture can then be regarded as a mixture of spodumene plus MgO and CaCl/sub 2/.

The electrochemical oxidation of chalcopyrite in ammoniacal solutions

Abstract: The anodic dissolution of chalcopyrite in ammoniacal solutions was investigated using electrochemical methods. At low overvoltages, the formation of a copper deficient sulfide layer, Cu1-xFeS2 through a charge transfer reaction is proposed based upon the dependence of the rest or open circuit potential on solution composition and the presence of a Tafel region of appropriate slope. In addition, a current peak that occurs at 10−4 A/cm2 is a function of the square root of the voltage scanning speed and is explained in terms of a charge transfer reaction. At larger overvoltages, constant potential experiments and mass balances performed at various anodic potentials indicate that the dissolution is consistent with the overall reaction, CuFeS2 + 4NH3 + 9OH- = Cu(NH3)4+2 + Fe(OH)3 + S2O3= + 3H2O +9e-, although some copper may be released to solution in the cuprous state and some ferrous iron has been identified in the product film. Currentvs time data taken during constant potential experiments were found to obey a linear rate relationship. This was interpreted in terms of the formation of a layer of constant thickness which is corroded at the outer interface at the same rate it is formed at the inner interface.. The model proposed is typical of the corrosion of some metals. An examination of the polarization curves shows the dissolution reaction to be first order with respect to [OH-]. The lack of dependence on [Cu2+] indicates that the catalytic effect of cupric ion during oxygen pressure leaching is related only to the cathodic reduction of O2 in agreement with the results of previous investigations.

Hydrogen reduction of wustite single crystals doped with Mg, Mn, Ca, Al, and Si

Abstract: In order to investigate the reduction mechanism of wustite in the presence of impurities usually met in the ironmaking industry, single crystals have been prepared with Mg, Mn, Ca, Al, and Si as dopants. The amounts of dopant in the lattice is around 4,4,2.5,0.5, and 0.01 mol pct, respectively, at 800 ‡C. For reduction with pure hydrogen, from 600 to 950 ‡C, Ca is the most efficient for accelerating the process at high degrees of reduction (75 pct) Mg and Mn are also active in this respect. Al has only a slowing down effect. Si also slows down the reaction at temperatures between 600 850 ‡C. In the presence of 20 torrs of water vapor in the gas, Mg and Mn are less efficient and unable to prevent the same slowing down of reaction observed with pure wustite at around 850 ‡C and classically called the ‡rate minimum‡. Our interpretation of these results is mainly based upon the observations of microstructures of partly reduced crystals which show a change in the texture of the iron produced which can be correlated with the reduction rate. These observations lead to a possible explanation in terms of the role of inclusions of impurity oxides on the sintering process of the metal, correlated with their ability to dissolve into the wustite lattice. However, this suggestion cannot apply in the case of Si at low temperatures, and this element is therefore supposed to play a role in the stages of reaction associated with the surface of the crystals.

A mathematical model for calculation of equilibrium solution speciations for the FeCl3-FeCl2-CuCl2-CuCl-HCl-NaCl-H2O system at 25 ‡C

Abstract: Equilibrium solution speciation computations were performed for the FeCl-FeCl3-CuCl2-CuCl-HCl-NaCl-H2O system at 25 ‡C. In dilute solutions, complexation of Fe(III), Fe(II), and Cu(II) is insignificant but the major Cu(I) species is CuCl2-. In concentrated solutions, FeCl30, FeCl20, and CuCl20 are the major Fe(III), Fe(II), and Cu(II) species, and CuCl32- is the most important cuprous complex. High Cu(I)/Cu(II) ratios are apparently more readily attainable in CuCl2 than in FeCl3 media. The Cu(I)/Cu(II) ratio is increased by making the solution more concentrated in any component except FeCl3 or CuCl2. Neither the ionic strength nor the total chloride concentration is a good predictor of the Cu(I)/Cu(II) ratio.

The Dissolution of titanium in liquid steel

Abstract: The dissolution kinetics of solid cylinders of titanium in liquid steel has been studied. Two separate dissolution periods were identified: asteel shell period anda free dissolution period. During thesteel shell period a customary shell of frozen steel encased the cylinder following its initial immersion. Premature internal dissolution then began as a result of liquid eutectic forming at the inner steel shell boundary.This phenomenon triggered an exothermic dissolution of the inner surface of the steel shell. The net result was to shorten considerably shell melting times. In the second,or free dissolution period it was found that the surface temperature of the exposed titanium cylinder rose above the bath temperature as a result of continued exothermic dissolution phenomena. This caused the dissolution process to become self-accelerating. A simplified mathematical model of the process has been developed to describe the complex coupled heat and mass transfer phenomena involved.

Relationships between the pourbaix diagram for Ag-S-H2O and electrochemical oxidation and reduction of Ag2S

Abstract: The potentialvs pH diagram or Pourbaix diagram for the Ag-S-H2O system has been calculated from available thermodynamic data for 25‡ and 100 ‡C. The diagrams developed show the dependence of the electrochemical equilibria on the concentration of [Ag+] and the total dissolved sulfur. The appearance of the diagram is significantly altered when the solubility product for Ag2SO4 is exceeded. Various electrochemical experiments have been performed in acid solutions using Ag2S electrodes for comparison between anticipated reactions from the diagrams and experimental results. The rest potential in acid solution shows a dependence of 0.055 V/decade change in [Ag+] concentration. Mass balances performed at constant cathodic potentials suggest the reaction Ag2S + 2H+ +2e - = 2Ag + H2S. Hydrogen evolution is a competing reaction which becomes less important as the surface becomes more completely covered with elemental silver due to the large hydrogen overvoltage on Ag. Similar anodic experiments have shown that part of the dissolution can be attributed to Ag2S = 2Ag+ + S +2e - with some of the mineral forming SO 4 = or HSO 4 - directly. The sulfur which forms is not completely protective, since the current observed during anodic potential sweeps is stirring dependent. This is consistent with the formation of Ag2SO4 on the electrode surface, which was confirmed by SEM and X-ray diffraction techniques.