Showing papers in "Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science in 1979"

Reaction mechanism for the acid ferric sulfate leaching of chalcopyrite

Abstract: The acid ferric sulfate leaching of chalcopyrite, CuFeS2 + 4Fe+3 = Cu+2 + 5Fe+2 + 2S0 was studied using monosize particles in a well stirred reactor at ambient pressure and dilute solid phase concentration in order to obtain fundamental details of the reaction kinetics. The principal rate limiting step for this electrochemical reaction appears to be a transport process through the elemental sulfur reaction product. This conclusion has been reached in other investigations and is supported by data from this investigation in which the reaction rate was found to have an inverse second order dependence on the initial particle diameter. Furthermore, the reaction kinetics were found to be independent of Fe+3, Fe+2, Cu+2 and H2SO4 in the range of additions studied. The unique aspect of this particular research effort is that data analysis, using the Wagner theory of oxidation, suggests that the rate limiting process may be the transport of electrons through the elemental sulfur layer. Predicted reaction rates calculated from first principles using the physicochemical properties of the system (conductivity of elemental sulfur and the free energy change for the reaction) agree satisfactorily with experimentally determined rates. Further evidence which supports this analysis includes an experimental activation energy of 20 kcal/mol (83.7 kJ/mol) which is approximately the same as the apparent activation energy for the transfer of electrons through elemental sulfur, 23 kcal/ mol (96.3 kJ/mol) calculated from both conductivity and electron mobility measurements reported in the literature.

Thermodynamics and phase relationships of transition metal-sulfur systems: Part III. Thermodynamic properties of the Fe-S liquid phase and the calculation of the Fe-S phase diagram

Abstract: An associated solution model is applied to describe the thermodynamic behavior of Fe-S liquid. This model assumes the existence of ‘FeS’ species in addition to Fe and S in the liquid. With two solution parameters for each of the binaries Fe-‘FeS’ and ‘FeS’-S, this model accounts for the compositional dependence of the thermodynamic properties of Fe-S liquid from pure Fe to pure S over a wide range of temperature. The binary Fe-S does not contribute significantly to the excess Gibbs energy of the liquid due to the rather small dissociation constant of ‘FeS’ to Fe and S. Using this model for the liquid phase and a defect thermodynamic model for the pyrrhotite phase, the Fe-S phase diagram is calculated. The calculated diagram is in excellent agreement with the experimental data, accounting for the range of homogeneity of pyrrhotite at all temperatures. Both the thermodynamic and phase diagram data are obtained from the literature.

Flow regimes in submerged gas injection

Abstract: The behavior of gas discharging into a liquid has been investigated in the labora-tory and in plant. The laboratory work has involved the injection of different gases from a submerged, horizontal tuyere into water, zinc-chloride solution, and a mercury bath. High speed cinematography and pressure measurements in the tuyere have been carried out to characterize the flow regimes. In the case of the mercury bath, a novel “half-tuyere” has been developed to permit visual observation of the gas. In this way, two regimes of flow, bubbling and steady jetting, have been delineated as a function of the modified Froude number and the ratio of gas to liquid densities. Pressure measurements at the tuyere tip have been correlated to the different stages of bubble growth in the bubbling regime, and can be used to distinguish one flow regime from the other. The measured bubble frequency and volume correspond reasonably well to predictions of a simple model of bubble growth under conditions of constant flow. The forward penetration of the jet centerline from the tuyere tip has been measured and found to depend both onN Fr′ andρg/ρl. In the industrial tests, pressure taps have been installed in the tuyeres of a nickel converter to monitor the pressure wave of the jets under normal, low pressure blowing operations. The measurements show that the converter jets operate in the bubbling mode with a bubble frequency of 10 to 12 s−1, similar to a gas jet in mercury. Tests involving higher pressure injection indicate that the steady jetting, or underexpanded, regime obtains at pressures of about 340 kPa (50 psi). Based on equivalent experiments in the laboratory, it is clear that low pressure blowing has the disadvantage of poor penetration of air into the bath so that the jets rise close to the back wall and locally accelerate refractory wear. Moreover between the formation of successive bubbles, the bath washes against the tuyere mouth and contributes to accretion formation. This necessitates periodic punching of the tuyeres which also contributes to refractory wear at the tuyere line. The use of high pressure injection to achieve steady jetting conditions, as currently practiced in the new bottom blown steelmaking processes, should be considered to solve these prob-lems, and possibly usher in a new generation of nonferrous converters.

Macrosegregation in a multicomponent low alloy steel

Abstract: Macrosegregation theory is extended to predict the formation of channel-type segregation for multicomponent systems. Specifically, calculations are carried out for 0.7 pct C steel, by considering heat, mass and momentum transport in the mushy zone. In the model used for calculations the momentum transport equation and the energy equation were solved simultaneously. It is confirmed, by comparing calculated results with experimental results, that this model successfully predicts the occurrence of channel-type segregation. This analysis is also more rigorous than previous works on macrosegregation because previous analyses were done by solving for convection in the mushy zone with an “uncoupled” temperature field. Using the model, the effects of adjusting the compositions of silicon and molybdenum in steel were quantitatively evaluated in order to show how channel-type segregates can be avoided by adjusting alloy composition. A method of optimizing composition to minimize segregation is presented. It is recommended that this methodology be applied to alloy design so that ingots of alloys amenable to commercial practice can be obtained readily with a minimum amount of “trial-and-error” development work and expense.

Formation of longitudinal, midface cracks in continuously-cast slabs

Abstract: Based on a series of related investigations, a mechanism for the formation of longitudinal, midface cracks in strand-cast slabs has been elucidated. Metallographic studies, X-ray analyses, and high-temperature tensile testing of as-cast slab samples, together with computer predictions of heat flow, have been combined to show that the cracks open first close to the solidification front where the ductility is extremely low. Tensile strains in the solid shell, resulting from rapid surface cooling or inadequate end-plate taper, concentrate in local regions of high temperature near the meniscus or at the level of nozzlestream impingement on the broad face. While the interior of the shell is opening, the surface which is cooler and more ductile, flows plastically to form a local surface depression. The subsurface cracks may subsequently break through to the surface in the mold or upper sprays if the tensile strains are sufficiently high. The influence of the impinging metal stream, mold-powder practice, metal-level control, steel composition, end-plate taper, submold support and spray practice on the formation of longitudinal, midface cracks is explained in terms of this mechanism.

A structural model for binary silicate systems

Abstract: A structural model is presented for binary silicate systems of the typeMO-SiO2, whereMO is a basic oxide, in which silicate tetrahedra and oxygen “bridges” are treated as structural units. One single formalism applies over the entire composition range from pureMO, where the model reduces to a simple orthosilicate anion model, to pure SiO2, where the model reduces to a simple model of the breaking of oxygen “bridges” upon the addition ofMO. At intermediate compositions, chain length distributions for silicate polymer chains can be calculated from the model, even though these polymeric chains are not explicitly treated as structural units of the model. The calculated chain length distributions are in very good agreement with those calculated from the polymeric model of Masson for all systems studied. Furthermore, two dimensional (cyclic) and three dimensional (network) polymeric structures are accounted for by the present model. The model accounts well for available enthalpy, entropy, activity, and phase diagram data in the binary liquid systemsMO-SiO2 whereM = Ca, Mg, Mn, Fe, or Pb. The observed variations of ΔH with composition and from system to system are explained in terms of the energies of the various bonds and are represented by a three parameter equation. Although the model has been tested here only for liquid slags, it should be useful in understanding the structure of silicate glasses as well.

The mechanism of whisker growth in the reduction of wüstite

Abstract: The growth of iron whiskers on wustite is explained on the basis of C. Wagner’s mechanism for the reduction of nonstoichiometric oxides. The first metal nucleus develops into a whisker if the iron accumulation in the supersaturated wustite particle is nearly uniform, a condition which is favored by chemical control. A mathematical model is proposed in which the “filling ratio” of wustite by iron prior to nucleation is expressed in terms of the reaction constant, the chemical diffusion coefficient of iron, the particle radius, the Fe/o ratio at equilibrium with the gas, and the critical Fe/o ratio for nucleation at the most favorable site. The morphology of iron in the early stages of reduction, which goes from a single cylindrical whisker, through sponge iron to a smooth layer, can be predicted by comparing at all times the map of the actual Fe/o ratio at the surface with the map of the local Fe/O ratio for nucleation. A satisfactory test of the theory is obtained through a survey of the experimental evidence available about the effect of several physico-chemical factors of reduction on the iron morphology,e.g. surface characteristics, particle size, composition of the reducing gas, solute cations in wustite, temperature, and gas transport.

The clustering of alumina inclusions

Abstract: Factors influencing the tendency of alumina particles in steel to agglomerate and form large clusters during deoxidation and solidification have been investigated by deoxidizing melts of Fe-10 pct Ni alloys with 0.1 pct aluminum under an inert atmosphere. Clusters of alumina inclusions are formed when the melt is stirred by either inductive or mechanical means. Nearly all of the inclusions are found in the clusters if the stirring time is long enough or at moderate stirring rates. Inclusions within the clusters increase in size with time while the size of inclusions in nonclustered regions remains essentially constant. The oxygen content of an ingot solidified soon after deoxidation corresponds well with that calculated from the oxygen content of the charged materials. After most inclusions have migrated to the clusters, the oxygen content in nonclustered regions is found to be as low as 2 ppm.

The kinetics of reduction of iron oxides at moderate temperatures

Abstract: The rates of reduction of wustite with hydrogen were measured in the temperature range 511 to 690 K. The wustite specimens were prepared by oxidizing thin iron foils, 50μm thick. These were reduced in a Cahn electrobalance under isothermal conditions and the weight loss sustained was continuously monitored. The effect of the phase transformation of wustite on the reduction kinetics was investigated. By using thin oxide specimens and a rapid flow of reducing gas, the respective influences of pore diffusion and “film” mass transfer were rendered insignificant. The reduction of the oxides, in the temperature range investigated, appears to be chemically controlled. The fractional reduction (α)time(t) plots are sigmoid shaped and exhibit three distinct features: incubation, acceleratory and decaying periods. The rate constantk s was evaluated from the middle region of the α-t plots. Its temperature dependence may be expressed by: % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabm4Aayaara% WaaSbaaSqaaiaadohaaeqaaOGaeyypa0JaaGimaiaac6cacaaIYaGa% aGOnaiaaiodacaGGOaGaeyySaeRaaGimaiaac6cacaaIWaGaaGinai% aaiEdacaGGPaGaciyzaiaacIhacaGGWbWaamWaaeaadaWcaaqaaiab% gkHiTiaaiEdacaaIXaGaaiilaiaaiwdacaaI1aGaaGimaiabgglaXk% aaiMdacaaIWaGaaGimaaqaaiaadkfacaWGubaaaaGaay5waiaaw2fa% aGqaaiaa-DgacaWFGaGaeS4JPFMaiGjG-fgacGaMa+hDaiacyc4FVb% GaiGjG-1gacaWFGaGaa83taiaa-9cacaWFJbGaa8xBamaaCaaaleqa% baGaa8Nmaaaakiabl+y6NjacWc4FZbGamqnGl+y6Njaa-bcacaWFGa% Gaa8xyaiaa-rhacaWFTbaaaa!7140! $$\bar k_s = 0.263( \pm 0.047)\exp \left[ {\frac{{ - 71,550 \pm 900}}{{RT}}} \right]g atom O/cm^2 s atm$$ g· atom o/cm2 · s · atm. The experimental data was interpreted by means of a nucleation and growth model.

The reduction of stannic oxide with carbon

Abstract: The rate of reduction of stannic oxide (cassiterite) with carbonaceous materials was investigated in the temperature range 1073 to 1273 K, using thermogravimetic analysis. The effects of the type, the particle size, and the relative amount of carbon were studied. The results indicate that cassiterite is reduced directly to Sn proceeding through the gaseous intermediates of CO and CO2. The overall rate of reduction is controlled by the oxidation of carbon by CO2 · An energy of activation of 220.9 kj/mole (52.8 kcal/mole) was calculated for the reduction of SnO2 with coconut charcoal within the temperature range 1073 to 1173 K and 323.8 kjJ.mole (77.4 kcalJ.mole) with graphite within the temperature range 1198 to 1273 K. A direct comparison was made between the rate of oxidation of coconut charcoal in CO2- CO mixtures and the rate of reduction of SnO2 with coconut charcoal, which are not in agreement. The reason for this disagreement was found to be the catalytic action of the tin formed during the reduction.

Activities of oxygen in liquid lead and antimony from electrochemical measurements

Abstract: The activities of oxygen in liquid lead and liquid antimony were measured for the temperature range of 1073 to 1323 and 973 to 1123 K, respectively, using the following electrochemical cell: $$\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{O} in liquid Pb or Sb/ZrO_2 ( + CaO)/Air,Pt.$$ in liquid Pb or Sb/ZrO2(+CaO)/Air, Pt. After measuring the equilibrium emf, the liquid metal was deoxidized by imposing a preselected voltage on the electrodes. The fairly low oxygen concentration in liquid metal could be easily determined by a modified analysis of the quantity of electrical charge passing through the cell. The standard free energies of solution of oxygen in liquid lead and liquid antominy for the reaction of l/2 O2 → O (1 at. pct) were determined respectively to be: ΔG° (in Pb) = −28,300 + 3.38T (± 300) cal/g-atom = −118,600 + 14.1T (± 1300) J/g-atom, ΔG° (in Sb) = −32,880 + 5.20T (± 350) cal/g-atom = −137,600 + 21.8T (± 1500) j/g-atom, where the reference state for dissolved oxygen was an infinitely dilute solution.

The kinetics of formation of h 2 o and co 2 during iron oxide reduction

Abstract: The kinetics of the chemical reaction-controlled reduction of iron oxides by H2/H2O and CO/CO2 gas mixtures are discussed. From an analysis of the systems it is concluded that the decomposition of the oxides takes place by the two dimensional nucleation and lateral growth of oxygen vacancy clusters at the gas/oxide interface. The rates of decomposition of the oxides under conditions of chemical reaction control are dependent not only on the partial pressures of the reacting gases at the reaction temperature but also on the oxygen activity of the prevailing atmosphere. Application of this model to the kinetic data leads to the determination of the maximum chemical reaction rate constants for the decomposition of the iron oxide surfaces. Assuming the reactions H2 (g) + O(ads) → H2O(g) andCO(g) + O(ads) → CO2 (g) to be rate controlling the maximum chemical reaction rate constants for the reduction of iron oxides are given by % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqefavySfgDP5% 2BGWuAU9gD5bxzaGqbaiaa-z6adaWgaaWcbaGaaeisamaaBaaameaa% caqGYaaabeaaaSqabaGccqGH9aqpcaaIXaGaaGimamaaCaaaleqaba% GaaiOlaiaaicdacaaIWaaaaGqaaOGaa4xzaiaa+HhacaGFWbGaa4hi% amaabmaabaWaaSaaaeaacaGFTaGaa4Nnaiaa+LdacaGFSaGaa43mai% aa+bdacaGFWaaabaacbiGaa0Nuaiaa9rfaaaaacaGLOaGaayzkaaGa% a4xBaiaa+9gacaGFSbGaa4hiaiaa+1gadaahaaWcbeqaaiaa+1caca% GFYaaaaGqabOGaaW3CamaaCaaaleqabaGaaWxlaiaa8fdaaaGccaGF% HbGaa4hDaiaa+1gadaahaaWcbeqaaiabgkHiTiaaigdaaaaaaa!5D53! $$\Phi _{{\text{H}}_{\text{2}} } = 10^{.00} exp \left( {\frac{{ - 69,300}}{{RT}}} \right)mol m^{ - 2} s^{ - 1} atm^{ - 1} $$ and % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqefavySfgDP5% 2BGWuAU9gD5bxzaGqbaiaa-z6adaWgaaWcbaGaa83qaiaa-9eaaeqa% aOGaeyypa0JaaGymaiaaicdadaahaaWcbeqaaiaaisdacaGGUaGaaG% inaiaaicdaaaGcciGGLbGaaiiEaiaacchadaqadaqaamaalaaabaGa% aGymaiaaicdacaaIZaGaaiilaiaaiMdacaaIWaGaaGimaaqaaiaadk% facaWGubaaaaGaayjkaiaawMcaaGqaaiaa+1gacaGFVbGaa4hBaiaa% +bcacaGFTbWaaWbaaSqabeaacaGFTaGaa4Nmaaaakiaa+nhadaahaa% Wcbeqaaiaa+1cacaGFXaaaaOGaa4xyaiaa+rhacaGFTbWaaWbaaSqa% beaacaGFTaGaa4xmaaaaaaa!5D50! $$\Phi _{CO} = 10^{4.40} \exp \left( {\frac{{103,900}}{{RT}}} \right)mol m^{ - 2} s^{ - 1} atm^{ - 1} $$ The maximum chemical reaction rate constants do not necessarily indicate the maximum rates which can be achieved in practice since these will depend on the limitations imposed by mass transport in the systems. The rate constants are important however since they indicate for the first time the upper limit of any reduction rate in these systems. The fractions of reaction sites which appear to be active on wustite surfaces in equilibrium with iron are calculated. A direct relationship between chemical reaction rates on liquid iron surfaces and rates on atomically rough iron oxide surfaces is postulated.

Decomposition of jarosite

Abstract: Precipitation of iron as a jarosite is used in various hydrometallurgical processes. There are several advantages to this route, for example excellent liquid-solid separation characteristics, selective precipitation of iron in environmentally more stable form, recovery of sulfur as sulfuric acid and higher zinc extraction. However, jarosite precipitation also has disadvantages, the major being the high cost of reagents. A laboratory study was therefore carried out on the conversion of ammonium jarosite to iron oxide with recovery of reagents as byproducts. The investigation resulted in the development of three process possibilities: 1) thermal decomposition with separate recovery of hematite, ammonia and sulfur dioxide, 2) decomposition of jarosite in an aqueous slurry to hematite and ammonium sulfate, or 3) decomposition in an aqueous slurry to magnetite and ammonium sulfate. The conditions affecting the decomposition of jarosite by all three methods have been defined and the chemical, mineralogical and physical characteristics of the iron products are identified.

A statistical mechanical theory for activity coefficients of a dilute solute in a binary solvent

Abstract: A statistical mechanical calculation of the activity coefficients of a dilute solute,C, in a binary solvent,A-B, was made using a model for the interactions of a coordination cluster consisting of a solute atom and its neighboring solvent atoms. The derived equations are applicable to a variety of types of ternary solutions including substitutional and interstitial alloys as well as additive and reciprocal molten salts. The theory takes into account the interactions between solute and solvent atoms (ions) as well as changes in interactions of the solvent atoms (ions) which are neighbors of solute atoms (ions). Prior theories such as those of Wagner and the quasi-chemical theories of Alcock and Richardson and Jacob and Alcock can all be shown to be special cases of the present theory. The dependence of the activity coefficients of a solute on the solvent composition is calculated from a knowledge of the activity coefficients of the solvent components, solute activity coefficients in the two pure solvent components, a coordination number, a geometric factor which depends upon the type of solution, and a term which represents the nonadditivity of pair bond interactions within the cluster of a solute atom (ion) and its neighboring solvent atoms (ions). In the model, the thermodynamic properties of the solute are related to the relative concentrations of the different coordination clusters as well as to the thermodynamic properties of the solvent.

The ductility of continuously-cast steel near the melting point—hot tearing

Abstract: At temperatures near the melting point steels fail in a brittle manner. This brittle failure can lead to the formation of surface and internal cracks in continuously cast steel, during casting, if the steel is subject to a tensile strain. In this investigation the nature of the brittle failure has been considered for a wide range of continuously-cast steels, by examining the strength and ductility of the steels as a function of temperature, composition, and cast structure. The results show that for steels containing 0.05 to 0.12 pct C, brittle failure is due to incipient melting at grain boundaries at temperatures between approximately 40°C below the solidus and the solidus. The incipient melting is ascribed to solute or residual segregation, at the grain boundaries following extensive boundary migration. For steel containing approximately 0.16 pct C, with increasing test temperature brittle failure starts 70°C below the solidus. For steels containing 0.25 to 1.0 pct C brittle failure starts 40°C below the solidus over the entire carbon range. Failure due to melting alone occurs interdendritically at temperatures above the solidus. In general the melting or ductile-brittle transition temperatures are independent of the initial cast structure, or large increases in the solute or residual levels, other than carbon.

Mechanism and the Intrinsic Rates of Reduction of Metallic Oxides

Abstract: The reduction of metallic oxides to metals represents an important class of heterogeneous reactions in which the role of nucleation and growth phenomena, although significant, has not been investigated fully. The micromechanism of reduction involves the formation of metallic nuclei and their subsequent growth at the expense of the parent phase. The present paper systematizes the evidence so far available and reports some experimental work on the nucleation and growth mechanisms in the reduction of wustite. The rate of nucleation, the mode of growth of a metallic nucleus and their relationship to a macroscopic rate parameter such as the mass rate of reduction have been fully explored. The method of determining the intrinsic rate of reduction from high temperature stage optical microscopic measurements has been placed on a firm quantitative basis. The influence of pore diffusion of gaseous species on the shape of the growing nucleus has been examined in some detail.

Equilibrations of copper matte and fayalite slag under controlled partial pressures of SO 2

Abstract: Equilibrium distributions of Cu, S and O between silica saturated fayalite slags and copper mattes (25 to 79 pct Cu) have been examined experimentally under controlled partial pressures of SO2. The temperature range of the experiments was 1423 to 1573 K and pSO2 was varied between 0.1 and 1 atm. Concentrations of copper in the experimental slags were found to be low (<1 pct Cu) under these conditions, as long as the grade of the coexistent matte was below 60 pct copper. Copper in slag concentration rose dramatically, however, when matte grade was increased above this level. The work also showed that whereas FeS has a high solubility for oxygen and is itself soluble in slag under oxidizing conditions, Cu2S and slag are almost completely immiscible. Cu-Fe-S mattes behave in an intermediate manner.

Tracer diffusivity of Ca 45 and electrical conductivity in CaO-SiO 2 melts

Abstract: The tracer diffusivity of Ca45 has been measured in CaO-SiO2 melts in the temperature range 1500 to 1700°C. In addition the electrical conductivity has been determined. Both properties decrease with increasing silica content. The activation energies (~30 kcal g-atom−1) are of the same order of magnitude. The electrical conductivity as computed from the diffusivity on the assumption that the total current is transported exclusively by divalent calcium ions and that the usual Nernst-Einstein relationship is valid, is somewhat lower than the measured electrical conductivity with the difference increasing with increasing silica content.

The kinetics of gold cyanide adsorption on activated charcoal

Abstract: Adsorption rates of gold cyanide on activated carbon were determined as a function of temperature, free cyanide concentration and charcoal concentration. The experimental rate data is explained by use of a diffusion controlled model developed by Crank. The adsorption rates were determined to be controlled by pore diffusion with the effective diffusion coefficient having an activation energy of 3.3 kcal/mol. Good agreement between experimental rate data and predicted rate curves by the diffusion model was obtained.

Thermochemistry of liquid alloys of transition metals: I. The systems Mn-Cu and Mn-Sn

Abstract: The enthalpies of mixing of solid manganese with liquid copper and liquid tin have been measured calorimetrically at 1386 K. Correcting the results by means of the known enthalpy of fusion of γ manganese at this temperature one obtains the enthalpies of mixing of undercooled liquid manganese with copper and tin. These values are compared with thermodynamic data reported in the liaterature.

Carbothermic reduction of domestic chromites

Abstract: Maximizing minerals recovery from domestic resources and minimizing the energy requirements of mineral processing constitute two goals of the Bureau of Mines, U.S. Department of the Interior. Accordingly, the Bureau has determined that coal char is generally the preferred reductant among commercially available carbonaceous materials in laboratory scale reduction experiments in argon between 1100 and 1500°C on a domestic metallurgical grade chromite with respect to the degree of reduction and metallization. For a domestic high iron chromite, coal char is preferred between 1100 and 1300°C, whereas metallurgical coke is the reductant of choice at 1400 and 1500°C. Both domestic chromites display generally similar reduction characteristics. The degrees of reduction and metallization are proportional to the time and/or temperature used and generally the rate of reduction is greatest during the first 15 min. The high iron chromite is more easily reduced, especially at the higher temperatures. Relatively simple kinetic equations cannot adequately describe the reduction mechanism for both chromites. The reduction may be nucleation controlled, especially under conditions of interest to commercial operations. The results could be used as a guideline for prereducing domestic chromites for subsequent smelting operations.

The kinetics of the reduction of chromium oxide by hydrogen

Abstract: The reduction kinetics has been studied as function of hydrogen partial pressures,pH2O/pH2 ratio, gas flow rate, and temperature. The reduction follows a linear time law and is dependent on the gas flow rate below a value of approximately 10 cm · s-1, since the rate is determined by the removal of the water vapor being formed. In this range the reduction rate may be calculated from gas dynamical data. At sufficiently high flow rates the phase boundary reaction is rate determining. The activation energy is 123 kJ · mol-1. The reduction rate is proportional to the square root of hydrogen pressure and decreases with increasing water vapor content.

Tracer diffusivity of O18 in CaO-SiO2 melts at 1600 °C

Abstract: The tracer diffusivity of O18 was measured in CaO-SiO2 melts at 1600 °C. The capillary technique was used in the diffusion experiments. Afterwards the samples were exposed to proton bombardment in a compact cyclotron. The O18 is transformed in this treatment to radioactive F18, and the concentration profile is determined by measuring the β+ radiation of this isotope. The diffusivities obtained decrease with increasing silica content and are of the same magnitude, within experimental error, as those determined previously for silicon.

The free energy of formation of Ce 2 O 2 S and the nonstoichiometry of cerium oxides

Abstract: The free energy of formation of Ce2O2S was determined by equilibrating CeO2with COCO2-SO2 gas mixtures in the temperature range 900 to 1400°C. There was no significant sulfur solubility in cerium oxide and the free energy of formation of Ce2O2S was considerably less than previously estimated; it is 12 kcal (50 kJ) lower at 1300°C The oxygen dissociation pressures for the nonstoichiometric cerium oxide was also measured by equilibrating CeO2 with CO-CO2 gas mixtures in the temperature range 1000 to 1450°C and oxygen pressures from 10-6 to 10-18 atm. The results indicate a very large range of nonstoichiometry from CeO2 to at least CeO1.72. The new thermodynamic information was used to estimate the phase equilibria for the Fe-Ce-S-O system. The calculations indicate that for a steel with normal sulfur levels treated with aluminum and rare earth deoxidizers very little Ce2O3will form but rather Ce2O2S or cerium Sulfides. Also the stability range of Ce2O2S is smaller than previously believed.

The adsorption of silver cyanide on activated charcoal

Abstract: Experiments have been carried out on the adsorption of silver cyanide on charcoal from solution having various concentrations of sodium, calcium, free cyanide, and hydrogen ion. It has been found that sodium and calcium ions enhance the adsorption of silver cyanide on charcoal while free cyanide ions reduce the adsorption. A qualitative description of the adsorption based on the structure of the electrical double layer has been proposed to explain the effect of sodium, calcium and free cyanide ions on the adsorption. Increasing acidity of solution enhances the adsorption of silver cyanide on charcoal except in a certain pH range. The adsorption of silver cyanide in acid solution seems to be influenced by the zeta potential of the charcoal particles rather than by the adsorption of hydrogen ions. The adsorbability of different size ions on charcoal has been determined. The larger ions have a greater adsorption potential as shown by the order of adsorption amount with gold cyanide > silver cyanide > cyanide.

Tracer diffusivity of Si 31 in CaO-SiO 2 melts at 1600°C

Abstract: The tracer diffusivity of O18 was measured in CaO-SiO2 melts at 1600 °C. The capillary technique was used in the diffusion experiments. Afterwards the samples were exposed to proton bombardment in a compact cyclotron. The O18 is transformed in this treatment to radioactive F18, and the concentration profile is determined by measuring the β+ radiation of this isotope. The diffusivities obtained decrease with increasing silica content and are of the same magnitude, within experimental error, as those determined previously for silicon.

Oxidation of ferrous sulfate in acid solution by a mixture of sulfur dioxide and oxygen

Abstract: The oxidation of ferrous sulfate with oxygen-sulfur dioxide mixtures in aqueous sulfuric acid has been investigated. In the presence of excess oxygen, sulfur dioxide produces fast oxidation of ferrous ion probably because of the formation of reactive radicals such as HSO3, HO2, and OH. The catalytic effect of cupric ion and activated carbon on the rate of oxidation has also been studied. By appropriately adjusting the SO2/O2 in the gas and Fe+3/Fe+2 in the liquid phase, any of the following reactions can be favorably carried out: 1) oxidation of ferrous ion, 2) reduction of ferric ion, and 3) generation of sulfuric acid.

Metal transfer during vacuum consumable arc remelting

Abstract: An investigation was conducted to determine how metal is transferred during vacuum consumable arc remelting. The transfer mode was found to be dependent on arc length for the electrode sizes (0.10 to 0.20 m diam) and electrical parameters studied (1.9 to 3 kA and 25 V). At short arc lengths ≤0.03 m, metal transfer was found to occur when liquid metal spikes hanging from the cathode form a low resistance bridge (drop short) by touching the anode and then subsequently rupture. The formation and rupture of these molten metal bridges was confirmed with electrical resistance measurements. During the bridge lifetime (0.0003 to 0.020 s) the arc was extinguished and all of the electrical power was directed through the molten bridge. At long arc lengths (>0.1 m) the spikes separate before touching the anode. Experimental observations concerning the coalescence of molten material at the cathode tip were made and they were found to be in agreement with theories on liquid instabilities. A review of pertinent literature concerning vacuum arcs was conducted and this along with general information on vacuum consumable arc re-melting are included as background information.