Sulfidation of chalcopyrite with elemental sulfur

The sulfidation of chalcopyrite concentrate with elemental sulfur was studied in the temperature range of 325 °C to 500 °C. The effects of temperature, time, and composition of the reactants on the sulfidation were determined. The X-ray diffraction (XRD) and light microscopic analyses showed that the sulfidation of chalcopyrite forms CuS and FeS₂ at temperatures below 400 °C. However, at temperatures above 400 °C, Cu₅FeS₆ and FeS₂ were formed. The sulfidation of chalcopyrite proceeds mainly through the gaseous phase, and temperature has a significant influence on the sulfidation rate in the range of 325 °C to 400 °C. The extraction of copper from the reacted material was determined by leaching in an H₂SO₄-NaCl-O₂ system. Over 90 pct of copper could be extracted by leaching at 100 °C for 60 minutes in the mentioned system.     

Leaching of sulfidized chalcopyrite with H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-NaCl-O<Subscript>2</Subscript>

The recovery of copper from chalcopyrite by leaching is complex not only due to the slow dissolution kinetics of this mineral in most aqueous media but also due to the production of solutions that are heavily contaminated with iron. On the contrary, the leaching of sulfidized chalcopyrite is very attractive because of a faster and more selective dissolution of copper compared to the leaching of the untreated chalcopyrite. In this work, the results of leaching in H₂SO₄-NaCl-O₂ solutions of sulfidized chalcopyrite concentrate are discussed. Experiments were carried out with chalcopyrite concentrates previously reacted with elemental sulfur at 375 °C for 60 minutes. The results showed that the concentration of chloride ions below 0.5 M, temperature, and leaching time are important variables for the extraction of Cu. On the other hand, Fe extraction was little affected by the same variables, remaining below 6 pct for all the experimental conditions tested. Microscopic observations of the leached particles showed that the elemental sulfur produced by the reaction does not form a coherent layer surrounding the particle, but rather concentrates in certain locations as large clusters. The leaching kinetics can be accurately described by a nonreactive core-shrinking rim topochemical expression for spherical particles 1 − (1 − 0.45X)^1/3=kt. The activation energy found was 76 kJ/mol for the range 85 °C to 100 °C.     

The leaching kinetics of chalcopyrite (CuFeS2) in ammonium lodide solutions with iodine

The leaching kinetics of chalcopyrite (CuFeS₂) in ammonium iodide solutions with iodine has been studied using the rotating disc method. The variables studied include the concentrations of lixiviants, rotation speed, pH of the solution, reaction temperature, and reaction product layer. The leaching rate was found to be independent of the disc rotating speed. The apparent activation energy was measured to be about 50 kJ/mole from 16 °C to 35 °C, and 30.3 kJ/mole from 35 °C to 60 °C. The experimental findings were described by an electrochemical reaction-controlled kinetic model: rate =k [NH₃]^0.69[OH⁻]^0.42[I ₃ ⁻ ]^0.5.     

Diffusion-limited sulfidation of wustite

The sulfidation of wustite in H₂S−H₂O−H₂−Ar atmospheres has been studied at temperatures of 700, 800, and 900°C with thermogravimetric techniques. Polycrystalline wustite wafers were equilibrated in a flowing H₂O−H₂−Ar gas stream and then sulfidizedin situ. During an initial transient stage a protective layer of FeS formed on the sample, and an intermediate layer of Fe₃O₄ formed between the FeO and FeS layers. Subsequently, the reaction followed a parabolic rate law. The parabolic rate constant varied from 0.22×10⁻² mg² cm⁻⁴ min⁻¹ at 700°C to 6.5×10⁻² mg² cm⁻⁴ min⁻¹ at 900°C. The reaction rate was limited by the diffusion of iron through the intermediate Fe₃O₄ layer which grew concurrently with the FeS layer and at the expense of the FeO core. After the FeO core was completely converted to Fe₃O₄, the process entered a passive stage during which no further mass changes could be detected. SCOTT McCORMICK, formerly Graduate Student, Purdue University is currently Assistant Professor, Department of Metallurgical and Materials Engineering, Illinois Institute of Technology, Chicago, Illinois 60616.     

The thermodynamics of melts in the system VO2−V2O5

Using a gravimetric technique, the oxygen isobars in the liquid phase field of the system VO₂−V₂O₅ have been determined in the temperature range 1020° to 1100°C and in the oxygen pressure range 0.01 to 0.4 atm, and the VO₂ liquidus and solidus curves have been determined in the temperature range 953° to 1081°C. From these results have been calculated the activities of the components VO₂ and VO_2.5 in the system and the standard free energy change for the reaction 2VO_{2 (S)}+1/2O_{2 (g)}=V₂O_{5 (1)}. The latter was determined to be ΔG ^o=−17780+7.64T in the temperature range 1020° to 1100°C.     

Kinetics of pyrite oxidation in sodium carbonate solutions

The kinetics of pyrite oxidation in sodium carbonate solutions were investigated in a stirred vessel, under temperatures ranging from 50 °C to 85 °C, oxygen partial pressures from 0 to 1 atm, particle size fractions from −150 + 106 to −38 + 10 μm (−100 + 150 Mesh to −400 Mesh + 10 μm) and pH values of up to 12.5. The rate of the oxidation reaction is described by the following expression:−dN/dt = SbkpO ₂ ^0.5 [OH₋]^0.1 whereN represents moles of pyrite,S is the surface area of the solid particles,b is a stoichiometric factor,k is an apparent rate constant, pO```2`` is the oxygen partial pressure, and [OH⁻] is the hydroxyl ion concentration. The experimental data were fitted by a stochastic model for chemically controlled reactions, represented by the following fractional conversion(X) vs time (t) equation: (1−X)^−2/3−1 =k _STt The assumption behind this model,i.e., surface heterogeneity leading to preferential dissolution, is supported by the micrographs of reacted pyrite particles, showing pits created by localized dissolution beneath an oxide layer. In addition to the surface texture, the magnitude of the activation energy (60.9 kJ/mol or 14.6 ± 2.7 kcal/mol), the independence of rate on the stirring speed, the inverse relationship between the rate constant and the initial particle diameter, and the fractional reaction orders are also in agreement with a mechanism controlled by chemical reaction.     

Kinetic effects of particle-size and crystal dislocation density on the dichromate leaching of chalcopyrite

Relatively pure, polycrystalline samples of Golden, New Mexico and Transvaal, South Africa chalcopyrite were ground and polished to fit into a density-compatible titanium alloy sandwich assembly and shock loaded (the Golden at 1.2 GPa, the Transvaal at 18 GPa peak pressure). The recovered samples were examined in the transmission electron microscope and observed to contain roughly 10³ and 10⁴ times more dislocations respectively than the natural, unshocked materials which contained roughly 10⁷ cm⁻². These materials were ground to three size fractions and leached in an acid-dichromate lixiviant at 50 and 70 °C (323 and 343 K). Corresponding size fractions were prepared from the unshocked material and leached for comparison; and these experiments were extended to a range of temperatures up to 90 °C (363 K) using a Bingham Canyon, Utah chalcopyrite. An unambiguous effect of dislocations was observed at the largest size fraction leached at 50 °C (323 K): the reaction rate constant increased from 1.44 × 10⁻³ to 1.62 × 10⁻³ to 2.73 × 10⁻³ min⁻¹ for dislocation densities increasing from roughly 10³ cm⁻² to 10¹¹ cm⁻². A linear relationship in the leaching rate was observed between 25 and 60 °C (298 and 333 K) and the activation energy was calculated to be approximately 12 kcal/mol (50 kJ/mol). Above 60 °C (333 K) a conspicuous rate decrease was observed. This was related to a densification of the sulfur product layer, which at 50 °C (323 K) was a loose, porous precipitate while at 90 °C (363 K) it was a continuous, tenacious, glassy coating on the chalcopyrite particles. In addition, and more importantly, the high-temperature decline in leaching rate was inferred to be associated with adsorption of Cr(VI) ion which decreases with increasing temperature. The anomalous and unpredictable behavior of chalcopyrite leached in acid-dichromate lixiviant was therefore observed to be related to variations in a surface chemisorption mechanism as well as variations in the nature of the sulfur reaction product layer. These effects also mask the influence of crystal defects and other surface-related crystallographic effects in leaching.     

Gaseous complexes formed between trichlorides (A1C13 and FeC13) and dichlorides

It has been found that in general the volatility of dichlorides is much enhanced in the presence of gaseous A1C1₃ and FeCl₃, and the existence of the complexes MA1₂C1₈, MAl₃Cl₁₁, and MFe₂Cl₈ is postulated. ΔH _T, ΔS _T, andT for MCl₂(s) + 2AlCl₃(g) = MAl₂Cl₈(g) are CaCl₂: −17.8 kcal, −25.7 cal K⁻¹ at 900 °K; CoCl₂: −15.2, −19.4 at 750°K; MgCl₂: −13.8, −17.9 at 800°K; MnCl₂: −15.8, −20.9 at 750°K; NiCl₂: −16.3, −24.2 at 750°K. For MCl₂(s) + 3AlCl₃(g) = MAl₃Cl₁₁(g) − CaCl₂: −30.0, −40.5 at 900°K; CoCl₂: −36.6, −47.4 at 700°K; MgCl₂: −42.6, −55.4 at 750°K; MnCl₂: −33.3, −42.0 at 750°K. For MCl₂(s) + 2FeCl₃(g) = MFe₂Cl₈(g) − CdCl₂: −19.4, −20.9 at 700°K: CoCl₂: −16.5, −17.2 at 800°K, MnCl₂: −19.1, −21.2 at 750°K; NiCl₂: −19.7, −24.4 at 800°K. Enhanced volatility was also found for ZnCl₂, PbCl₂, and CuCl, but since the condensed phase was liquid of unknown composition no calculations could be made. Owing to the interplay of the above equilibria with the dimerization equilibria for A1C1₃ and FeCl₃ the effective vapor pressures of the dichlorides in the presence of the trichlorides pass through maxima in the region 600° to 700°C.     

Thermodynamics of the Ca-S-O,Mg-S-O,and La-S-O systems at high temperatures

High temperature thermodynamic data for equilibria in the Ca-S-O, Mg-S-O, and La-S-0 systems were determined by a galvanic cell technique using calcia stabilized zirconia (CSZ) solid electrolytes. The measured emf data were used to calculate the standard free energy changes of the following reactions: [1] CaO(s) + 1/2S₂(g) → CaS(s) + 1/2O₂(g) 1000 to 1350 K ΔG° = 21906.9 − 0.8T(K)(±400 cal) = 91658 − 3.37 (±1700 J) [2] CaS(s) + 2O₂(g) → CaSO₄(s) 1050 to 1450 K ΔG° = -227530.7 + 80.632T(K) (±400 cal) = -951988.5 + 337.4T (±1700 J) [3] CaO(s) + 3/2O₂(g) + 1/2S₂(g) → CaSO₄(s) 1050 to 1340 K ΔG° = -204892.7 + 79.83T(K)(±400 cal) = -857271.1 + 334.0T (±1700 J) [4] MgO(s) + 1/2S₂(g) → MgS(s) + 5O₂(g) 1000 to 1150 K ΔG° = 45708.6 − 2.897(K)(±500 cal) = 191244.8 − 12.1T (±2100 J) [5] La₂O₃(s) + 1/2S₂(g) → La₂O₂S(s) + 1/2O₂(g) 1080 to 1350 K ΔG° = 17507 − 2.32T(K)(±380 cal) = 73249.3 − 9.7T (±1600 J) [6] La₂O₃S(s) + S₂(g) → La₂S₃(s) + O₂(g) 950 to 1120 K ΔG° = 70940 + 2.25T(K)(±500 cal) = 296812.9 + 9.47 (±2100 J) The ΔG° values of reaction [5] were combined with the literature data for ΔG°_f(La₂O₃) to obtain the standard free energy of formation of La₂O₂S at high temperatures. The values of ΔG°_f thus calculated for La₂O₂S were combined with the ΔG° data for reaction [6] to obtain the standard free energy of formation of La₂S₃ at high temperatures.     

The thermal capacity and enthalpy of gadolinium sesquiselenide over a wide temperature range

Measurements have been made on the thermal capacity of γ-Gd₂Se₃ at 58.88–298.34 K. Values have been obtained for the thermal capacity, entropy, reduced Gibbs energy, and enthalpy under standard conditions: C°_p = 125.87 ± 0.5 J· mole⁻¹ · K⁻¹; S°(298.15 K) = 196.5 · 1.6 J · mole⁻¹ · K⁻¹; Φ°(298.15 K) = 103.6 ± 1.6 J · mole⁻¹ · K⁻¹; H°(298.15 K)-H°(0) = 27681 ± 138 J · mole⁻¹. The enthalpy of Gd₂Se₃ has been measured and the major thermodynamic functions have been calculated for the solid and liquid states over the temperature range 450–2300 K. The temperature dependence of the enthalpy in the ranges 300–1800 K and 2000–2300 K are represented: H°(T)-H°(298.15 K) = = 1.1949 · 10⁻² · T² + 122.38 · T + 347402 · T⁻¹ − 38716 and H°(T)-H°(298.15 K) = 262.81 · T-− 196047, respectively. The calculated temperature, enthalpy, and entropy of melting for Gd₂Se₃ are: T_m = 1925 ± 40 K, Δ_mH° (Gd₂Se₃) = 68.5 kJ · mole^-1, Δ_mS°(Gd₂Se₃) = 35.6 J · mole⁻¹ · K⁻¹. __________ Translated from Poroshkovaya Metallurgiya, Nos. 3–4(448), pp. 56–61, March–April, 2006.     

Kinetic study of the chlorination of gallium oxide

The kinetics of the chlorination of gallium oxide in chlorine atmosphere was studied between 650 °C and 800 °C. The calculations of the Gibbs standard free energy variation with temperature for the reaction Ga₂O_3(S)+3Cl_{2 (g)}→2GaCl_3(g)+1.5O_{2 (g)} show that direct chlorination is favorable above 850 °C. Thermogravimetric experiments were performed under isothermal and nonisothermal conditions. The effect of temperature, gas flow rate, and Cl₂ partial pressure were studied. The solids were characterized by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The nonisothermal results showed that chlorination of Ga₂O₃ starts at approximately 650 °C, with a mass loss of 50 pct at 850 °C. The isothermal results between 650 °C and 800 °C indicated that the reaction rate increased with temperature. The correlation of the experimental data with different solid-gas reaction models showed that the results are adequately represented by the model proposed by Shieh and Lee: X=1−{1−b ₂₂[b ₂₁ t+e ^−b ₂₁ ^t−1]}^1/(1−γ). From this model, it was found that the rate of reaction for the chlorination of Ga₂O₃ is of the order 0.68 with respect to Cl₂ and the activation energy is 113.23 kJ/mol. On the other hand, the order of the activation rate of the interface surface is 0.111 with respect to Cl₂ and its activation energy is 23.81 kJ/mol.     

The diffusivity and solubility of oxygen in liquid tin and solid silver and the diffusivity

The diffusivity and solubility of oxygen in liquid tin and solid silver in the temperature range of about 750° to 950°C (1023 to 1223 K) and the diffusivity of oxygen in solid nickel at 1393°C (1666 K) were determined using the electrochemical cell arrangement of cylindrical geometry: Liquid or Solid Metal + O (dissolved) | ZrO₂ + (3 to 4%)CaO | Pt, air The diffusivity and solubility of oxygen in liquid tin are given by:D _O(Sn) = 9.9 × 10⁻⁴ exp(−6300/RT) cm²/s (9.9 × 10⁻⁸ exp − 6300/RT m²/s) andN _O ^S (Sn) = 1.3 × 10⁵ exp(−30,000/RT) at. pct The diffusivity and solubility of oxygen in solid silver follow the relations:D _O(Ag) = 4.9 × 10⁻³ exp (−11,600/RT) cm²/s ( 4.9 × 10⁻⁷ exp − 11,600/RT m²/s) andN _O ^S (Ag) = 7.2 exp (−11,500/RT) at. pct The experimental value for the preexponential in the expression forD _O(Ag) is lower than the value calculated according to Zener’s theory of interstitial diffusion by a factor of 11. The diffusivity of oxygen in solid nickel at 1393°C (1666 K) was found to be 1.3 × 10⁻⁶ cm²/s (1.3 × 10⁻¹⁰ m²/s). Formerly Graduate Student, Department Formerly Graduate Student, Department Formerly Graduate Student, Department This paper is based upon a This paper is based upon a This paper is based upon a This paper is based upon a     

Kinetics of silver leaching from manganese-silver associated ores in sulfuric acid solution in the presence of hydrogen peroxide

Kinetics of silver leaching from a manganese-silver associated ore in sulfuric acid solution in the presence of H₂O₂ has been investigated in this article. It is found that sulfuric acid and hydrogen peroxide have significant effects on the leaching rate of silver. The reaction orders of H₂SO₄ and H₂O₂ were determined as 0.80 and 0.68, respectively. It is found that the effects of temperature on the leaching rate are not marked, the apparent activation energy is attained to be 8.05 kJ/mol within the temperature range of 30 °C to 60 °C in the presence of H₂O₂. Silver leaching is found to be diffusion-controlled and follows the kinetic model: 1−2x/3−(1−x)^2/3=Kt. It is also found that particle size presents a clear effect on silver leaching rate, and the rate constant (k) is proportional to d ₋₂ ⁰ .     

Superplastic behavior and microstructure evolution in a commercial Al-Mg-Sc alloy subjected to intense plastic straining

A commercial Al-6 pct Mg-0.3 pct Sc-0.3 pct Mn alloy subjected to equal-channel angular extrusion (ECAE) at 325 °C to a total strain of about 16 resulted in an average grain size of about 1 μm. Superplastic properties and microstructural evolution of the alloy were studied in tension at strain rates ranging from 1.4 × 10⁻⁵ to 1.4 s⁻¹ in the temperature interval 250 °C to 500 °C. It was shown that this alloy exhibited superior superplastic properties in the wide temperature range 250 °C to 500 °C at strain rates higher than 10⁻² s⁻¹. The highest elongation to failure of 2000 pct was attained at a temperature of 450 °C and an initial strain rate of 5.6 × 10⁻² s⁻¹ with the corresponding strain rate sensitivity coefficient of 0.46. An increase in temperature from 250 °C to 500 °C resulted in a shift of the optimal strain rate for superplasticity, at which highest ductility appeared, to higher strain rates. Superior superplastic properties of the commercial Al-Mg-Sc alloy are attributed to high stability of ultrafine grain structure under static annealing and superplastic deformation at T ≤ 450 °C. Two different fracture mechanisms were revealed. At temperatures higher than 300 °C or strain rates less than 10⁻¹ s⁻¹, failure took place in a brittle manner almost without necking, and cavitation played a major role in the failure. In contrast, at low temperatures or high strain rates, fracture occurred in a ductile manner by localized necking. The results suggest that the development of ultrafine-grained structure in the commercial Al-Mg-Sc alloy enables superplastic deformation at high strain rates and low temperatures, making the process of superplastic forming commercially attractive for the fabrication of high-volume components.     

Evaluation of the reduction of iron oxide from liquid slags using a graphite rotating disk

The rotating disk methodology has been used for examination of the reduction of FeO from CaO-FeO-SiO₂ liquid slags (20 and 60 pct FeO) with a CaO/SiO₂ ratio equal to 0.66 and 1.27, in the temperature range 1350 °C to 1420 °C. It has been found that the reduction proceeds under diffusion control. The calculated diffusion coefficients fall in the range 0.76·10⁻⁷ to 1.6·10⁻⁶ cm²/s. Comparison of these values with those given in the literature suggests that the calculated coefficients are related to the diffusion of oxygen ions in the slag. The calculated thickness of the limiting diffusion layer, δ, ranges from 0.65·10⁻³ to 5.25·10⁻³ cm, depending on the reduction conditions. The largest decrease in the limiting diffusion layer thickness takes place at low rotational speeds, i.e., 100 and 400 rev/min. The maximum value of the mass transfer coefficient is 1.71·10⁻³ cm/s for reduction from slag with a CaO/SiO₂ ratio of 1.27, 60 pct FeO, at 1420 °C and 2000 rev/min, and the minimum value is 0.27·10⁻⁴ cm/s for reduction from slag with a CaO/SiO₂ ratio of 0.66, 20 pct FeO, at 1350 °C and 100 rev/min. Good agreement has been found between experimental and calculated reduction rates at low disk rotations (100 and 400 rev/min).     

Thermodynamics of sulfur in BaO-CaO-CO2 system

The sulfide and carbonate capacity were measured for the CaO-BaO-CO₂ system in the temperature range from 1000 °C to 1350 °C by equilibrating a BaO-based mixture, silver, and a CO-CO₂-Ar gas mixture. The BaO-CO₂ mixture melted completely in the temperature range from 480 °C to 700 °C in an Ar-CO₂ atmosphere, while the CaO-BaO-CO₂ mixture was solid at experimental temperature under the conditions used. TheC _s ²⁻ concept was extended for solid-state mixture, and the sulfide capacity was measured as a function of composition. The maximum value of this system, logC _s ²⁻ = −0.3 at 1200 °C, was the highest of all of the fluxes reported to date. Experimental results for mol pct BaCO₃ againstP _{CO 2} at 1200 °C indicated that the dissolution of carbon dioxide loweredC _s ²⁻ markedly when the ratio (BaO + BaCO₃ + BaS)/ BaCO₃ exceeded unity. TheC _s ²⁻ of this system increased with increasing temperature from 1050 °C to 1200 °C, and a value of above zero was predicted at hot metal pretreatment temperature, which is roughly 1300 °C. A linear relation between logC _s ²⁻ and logC _{CO 3} ²⁻ with a unit slope was observed. Formerly Contract Research Fellow, Institute of Industrial Science, The University of Tokyo     

Kinetics of hydrothermal oxidation of granular Pb metal to PbO powder in sodium hydroxide solutions

The oxidation kinetics of granular Pb metal in sodium hydroxide solutions were investigated in an autoclave, under temperatures ranging from 110 °C to 175 °C, oxygen pressures of up to 3.0 MPa, particle size fractions from 0.52 to 5 mm, and NaOH concentrations of up to 1.6 mol/L. In most instances, the 1−2/3 α−(1−α)^2/3 vs time relationship, indicative of a diffusion-controlled reaction, was closely obeyed. The oxidation rate increased significantly with increasing temperature, and the apparent activation energy was found to be 29.6 kJ/mol. The oxidation process of lead metal can be improved evidently by using a stronger stirring method to decrease the product layer. The distribution of the various Pb complexes calculated from avaiable thermodynamic data showed that the prominent component in alkaline solution was HPbO ₂ ⁻ ion which determined the amount of Pb²⁺ available for the formation of PbO.     

Anelastic behavior of barium-titanate-based ceramic materials

The internal friction (Qsu−1) and Young’s modulus (E) of BaTiO₃-based ceramics were measured vs temperature from −100 °C to 150 °C. Rectangular bars of high-density (96 to 99 pct) ma-terials were driven electrostatically in flexural vibration at a resonance frequency of about 3 kHz, at maximum strain levels of about 10⁻⁶. The curves ofQ ⁻¹(T) andE(T) allow the study of the following three phase transformations: tetragonal to cubic (about 130 °C in pure material), orthorhombic to tetragonal (about 0 °C in pure material), and rhombohedral to orthorhombic (about −80 °C in pure material). Internal friction and modulus data were obtained on pure material and on materials doped with niobium and cobalt to give semiconducting and insulating X7R behavior. Permittivity, dielectric loss, and microstructure data are given and used to aid interpretation of the mechanical measurement data. This article is based on a presentation given in the Mechanics and Mechanisms of Material Damping Symposium, October 1993, in Pittsburgh, Pennsylvania, under the auspices of the SMD Physical Metallurgy Committee     

Experimental determination of the carbon solubility limit in ferritic steels

Despite the existence of a number of published results, the data on the solubility of carbon in alpha iron are still inaccurate. An analysis of published experimental results shows that available values vary greatly (between 50 and 100 ppm by wt, for example, at 600 °C). These discrepancies make it difficult to optimize the metallurgical processes of low-carbon or ultralow-carbon alloys. An experimental methodology, using the measurement of the thermo-electric power (TEP) of the alloy, was set up. This enabled us to deduce the quantity of free interstitials in the matrix by measuring the amount of interstitials which segregate on dislocations after a deformation of the sample. This technique was used in the case of an Al-killed steel containing 0.2 pct Mn. The limit of solubility of carbon was determined with a precision of ±2 ppm between 550 °C and 730 °C. This limit of solubility can be analytically described by the relation C_{(wt pct)}=6.63 exp (−11.8_kcal·mol ⁻¹/RT), which is shown to be valid only for temperatures above 400 °C. We show experimentally that the residual concentration of carbon at low temperature is much greater than the value predicted by the extrapolation of this relation. Complementary studies on steels with various C and Mn contents allow us to verify the validity of the proposed methodology.     

Diffusion of managenese and silicon in liquid iron over the whole range of composition

The measurement of the diffusivities of manganese and silicon in molten binary ferroalloys over the whole range of composition was undertaken to clarify existing but conflicting data at lower concentrations, to present new data at higher concentrations and to indirectly confirm the behavior of both systems observed in thermodynamic studies. The experiments were carried out under argon atmosphere in a Tammann furnace. The diffusion couples were held in 5 mm ID alumina tubes (98 pct Al₂O₃). Electron probe microanalysis of the samples led to a diffusion-penetration curve for the system under consideration. Results obtained over the whole range of composition showed a slight negative deviation for the Fe−Mn system and a very large positive deviation for the Fe−Si system. At lower concentrations (0 to 4 pct Mn), the temperature dependence of managanese diffusivity for the Fe−Mn binary alloy in the temperature range 1550° to 1700°C is as follows:D _Fe−Mn=1.8×10⁻³ exp (−13,000/RT) cm²/sec The concentration dependence of manganese diffusivity for the same system at 1600°C may be expressed asD _Fe−Mn={5.48−0.0137 (%Mn)+0.000276 (%Mn)²}×10⁻⁵ cm²/sec The temperature dependence of silicon diffusivity for the Fe−Si binary system in the temperature range 1550° to 1725°C at various concentrations is as follows:D _Fe−Si=2.8×10⁻³ exp (−11,900/RT) cm²/sec at 20 pct SiD _Fe−Si=2.1×10⁻³ exp (−13,200/RT) cm²/sec at 12.5 pct SiD _Fe−Si=5.1×10⁻⁴ exp (−9,150/RT) cm²/sec at 2.2 pct Si FELIPE P. CALDERON, formerly Graduate Student. University of Tokyo, Tokyo, Japan. This paper is based on a portion of a thesis submitted by FELIPE P. CALDERON in partial fulfillment of the requirements for the degree of Doctor of Engineering at University of Tokyo.