Kinetics of manganous oxide sulfidization in carbonyl sulfide (COS) contaminated atmospheres

To contribute to the mitigation of man-made emission of sulfurous compounds, the susceptibility of manganous oxide for carbonyl sulfide under reducing atmospheres (C-O-S system) has been investigated over the temperature range 700 to 1010 °C (973 to 1283 K). The kinetic investigation employed thermogravimetry and anin situ solid electrolyte oxygen probe to follow the topochemical reaction of spherical MnO pellets under various experimental conditions. The apparent activation energy of sulfidization of manganous oxide, under measured oxygen potentials in the C-O-S system, was determined to be 12.06 (±1.5) kcal/mol (52.33 (±6.28) kJ/mol). Overall sulfidization appeared to proceed by mixed control involving convective mass transfer of COS across the boundary layer and diffusion through the product layer. Formerly with the Department of Theoretical Metallurgy, Royal Institute of Technology, Stockholm     

Kinetics of manganous oxide sulfidization in carbonyl sulfide (COS) contaminated atmospheres

To contribute to the mitigation of man-made emission of sulfurous compounds, the susceptibility of manganous oxide for carbonyl sulfide under reducing atmospheres (C-O-S system) has been investigated over the temperature range 700 to 1010 °C (973 to 1283 K). The kinetic investigation employed thermogravimetry and anin situ solid electrolyte oxygen probe to follow the topochemical reaction of spherical MnO pellets under various experimental conditions. The apparent activation energy of sulfidization of manganous oxide, under measured oxygen potentials in the C-O-S system, was determined to be 12.06 (±1.5) kcal/mol (52.33 (±6.28) kJ/mol). Overall sulfidization appeared to proceed by mixed control involving convective mass transfer of COS across the boundary layer and diffusion through the product layer. Formerly with the Department of Theoretical Metallurgy, Royal Institute of Technology, Stockholm     

Eutectic-gradient wear resistance in materials

New iron-base eutectic powder alloys have been developed (Fe−Mn−C−B−Si−Ni−Al−Sc, Fe−Mn−C−B−Si−Cr−Al−Sc, Fe−Mn−C−B−Si−Ni−Cr−Al−Sc) for wear-resistant coatings. The thermodynamic affinity for oxygen has been used in the technology for alloying the liquid with the necessary elements. Institute for Problems of Materials Science, Ukraine, National Academy of Sciences, Kiev, State University “L'vivska Polytechnika”, and Lublin Polytechical Institute, Poland. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(408), pp. 17–21, July–August, 1999.     

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.     

Precipitation-strengthened austenitic Fe−Mn−Ti alloys

The precipitation of intermetallic compounds in the Fe−20Mn−2Ti and Fe−28Mn−2Ti alloy systems has been investigated over the temperature range 700 to 900°C by hardness measurements, optical and scanning electron microscopy, and X-ray diffraction. In both systems only the equilibrium Laves phase was observed. The precipitate was identified as C14(MgZn₂) type hexagonal Laves phase with a chemical composition close to Fe₂ (Ti, Mn). In an as-annealed sample precipitation occurred in a heterogeneous manner, predominantly along grain boundaries. The effect of a cold deformation between the solution annealing and aging processes was also investigated. In addition to a high density of dislocations, martensitic phases were induced by deformation: a γ→∈ transformation occurred in the Fe−28Mn−2Ti alloy while a γ→α′ transformation was predominant in the Fe−20Mn−2Ti alloy. Subsequent aging was conducted at temperatures above theA _f . A large number of very fine precipitates formed randomly in the matrix after a short aging period. This cold work plus aging treatment resulted in an increase in yield strength. The enhancement of mechanical properties is due to the randomly distributed precipitates combined with the high defect density and fine substructure.     

Liquidus Temperatures in the “Cu<Subscript>2</Subscript>O”-FeO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO System at Molten Metallic Copper Saturation

Calcium ferrite slags, which are represented by the “Cu₂O”-FeO-Fe₂O₃-CaO system at copper saturation, have been applied successfully to existing copper-converting processes. Because of the industrial importance of this system, the characterization of the effects of oxygen partial pressure and silica on the phase equilibria is necessary to improve the control of process parameters, which include fluxing and operating temperatures. In the current study, experimental methods, which use the equilibration/quenching/electron probe X-ray microanalysis (EPMA) techniques with primary phase substrate support, were subsequently developed to incorporate fixed oxygen partial pressure experiments. Experiments were carried out at 1200 °C and 1250 °C both with and without silica additions; both liquidus and solidus data were reported for the primary phase field of spinel and dicalcium ferrite between the oxygen partial pressures of 10^−5.0 and 10^−6.5 atm. The analyzed compositions of the liquid and solid phases are used to construct the phase diagram of the pseudoternary “Cu₂O”-“Fe₂O₃”-CaO system in equilibrium with metallic copper at fixed oxygen partial pressures and with additions of silica. The maximum solubility of silica within the liquid slag phase, prior to dicalcium silicate precipitation, was measured at specific conditions. Two empirical equations used for the calculation of the copper oxide concentration in calcium ferrite slag are evaluated with the new experimental data defined in the current study.     

Activities of oxygen in liquid copper and silver from electrochemical measurements

Modified coulometric titrations on the galvanic cell:O in liquid Cu or Ag / ZrO₂( + CaO) / Air, Pt, were performed to determine precisely the oxygen activities in liquid copper and silver in the range of relatively low oxygen concentration. The present experimental results were remarkably reproducible in comparison with the published data. The standard Gibbs energies of solution of oxygen in liquid copper and liquid silver for 1/2 O₂(l atm) → O(l at. pct) were determined respectively to be ΔG° (in Cu) = −18040 −0.03 T(K) (± 120) cal · g-atom−1 = −75500 −0.12 T(K)(± 500) J · g-atom−1, ΔG°(inAg)= -3860+ 1.56 T(K) (±90) cal · g-atom−1 = −16140 + 6.52 T(K)(±380) J · g-atom−1 where the reference state for dissolved oxygen was an infinitely dilute solution. The present value of the partial entropy of oxygen dissolved in liquid copper differs significantly from that suggested by many investigators. Further, the present equation for liquid copper has been found to be consistent with a correlation proposed previously by the present authors. The equation for liquid silver is in good agreement with the published ones.     

The effect of chromium on the activity coefficient of sulfur in liquid Fe−Cr−S alloys

The effect of chromium on the activity coefficient of sulfur in the ternary system Fe−Cr−S has been determined in the temperature range 1525° to 1755°C for chromium concentrations of up to 40 wt pct, using a levitation melting technique in H₂−H₂S atmospheres. The first order free energy interaction coefficient,e _S ^Cr , which is derived on the assumption that the thermal diffusion error is constant for both binary Fe−S and ternary Fe−Cr−S melts under controlled levitation conditions, is given by the relationship:e _S ^Cr =−94.2/T+0.040 The first order enthalpy and entropy interaction coefficients are found to beh _S ^Cr =−430±70 ands _S ^Cr =−0.183±0.007 respectively. These results are in good agreement with recently published data.     

Activities of oxygen in liquid Bi,Sn, and Ge from electrochemical measurements

Modified coulometric titrations on the galvanic cell: O in liquid Bi, Sn or Ge/ZrO₂( + CaO)/Air, Pt, were performed to determine the oxygen activities in liquid bismuth and tin at 973, 1073 and 1173 and in liquid germanium at 1233 and 1373 K. The standard Gibbs energy of solution of oxygen in liquid bismuth, tin and germanium for 1/2 O₂ (1 atm) →O (1 at. pct) were determined respectively to be ΔG° (in Bi) = −24450 + 3.42T (±200), cal· g-atom⁻¹ = − 102310 + 14.29T (±900), J·g-atom⁻¹, ΔG° (in Sn) = −42140 + 4.90T (±350), cal· g-aton⁻¹ = −176300 + 20.52T (± 1500), J-g-atom⁻¹, ΔG° (inGe) = −42310 + 5.31 7 (±300), cal·g-atom⁻¹ = −177020 + 22.21T(± 1300), J· g-atom⁻¹, where the reference state for dissolved oxygen was an infinitely dilute solution. It was reconfirmed that the modified coulometric titration method proposed previously by two of the present authors produced far more reliable results than those reported by other investigators. TOYOKAZU SANO, formerly a Graduate Student, Osaka University     

The chemical diffusivity of oxygen in liquid iron oxide and a calcium ferrite

Measurements have been made of the chemical diffusion coefficient of oxygen in liquid iron oxide at temperatures from 1673 to 1888 K and in a calcium ferrite (Fe/Ca = 2.57) at temperatures from 1573 to 1873 K. A gravimetric method was used to measure the oxygen uptake during the oxidation of the melts by oxygen or CO₂-CO mixtures. The rate was shown to be controlled by mass transfer in the liquid melt. The chemical diffusivity of oxygen in liquid iron oxide at oxygen potential between air and oxygen was found to be 4.2±0.3 × 10⁻³ cm²/s at 1888 K. That in iron oxide at oxidation state close to iron saturation was established to be given by the empirical expression log D=−6220/T + 1.12 for temperatures between 1673 and 1773 K. For the calcium ferrite (Fe/Ca=2.57) at oxygen potential between air and oxygen, the diffusivity of oxygen was found to be given by log D=−1760/T−1.31 for temperatures between 1673 and 1873 K. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS.     

Wettability of Aluminum on Alumina

The wettability of molten aluminum on solid alumina substrate has been investigated by the sessile drop technique in a 10⁻⁸ bar vacuum or under argon atmosphere in the temperature range from 1273 K to 1673 K (1000 °C to 1400 °C). It is shown that the reduction of oxide skin on molten aluminum is slow under normal pressures even with ultralow oxygen potential, but it is enhanced in high vacuum. To describe the wetting behavior of the Al-Al₂O₃ system at lower temperatures, a semiempirical calculation was employed. The calculated contact angle at 973 K (700 °C) is approximately 97 deg, which indicates that aluminum does not wet alumina at aluminum casting temperatures. Thus, a priming height is required for aluminum to infiltrate a filter. Wetting in the Al-Al₂O₃ system increases with temperature.     

Kinetics of the solid-state carbothermic reduction of wessel manganese ores

Reduction of manganese ores from the Wessel mine of South Africa has been investigated in the temperature range 1100 °C to 1350 °C with pure graphite as the reductant under argon atmosphere. The rate and degree of reduction were found to increase with increasing temperature and decreasing particle sizes of both the ore and the graphite. The reduction was found to occur in two stages: (1) The first stage includes the rapid reduction of higher oxides of manganese and iron to MnO and FeO. The rate control appears to be mixed, both inward diffusion of CO and outward diffusion of CO₂ across the porous product layer, and the reaction of carbon monoxide on the pore walls of the oxide phase play important roles. The values of effective CO-CO₂ diffusivities generated by the mathematical model are in the range from 2.15 x 10⁻⁵ to 6.17 X 10⁻⁵ cm².s⁻¹ for different ores at 1300 °C. Apparent activation energies range from 81. 3 to 94.6 kJ/kg/mol. (2) The second stage is slower during which MnO and FeO are reduced to mixed carbide of iron and manganese. The chemical reaction between the manganous oxide and carbon dissolved in the metal phase or metal carbide seems to be the rate-controlling process The rate constant of chemical reaction between MnO and carbide on the surface of the impervious core was found to lie in the range from 1.53 x 10⁻⁸ to 1.32 x 10⁻⁷ mol . s⁻¹ . cm⁻². Apparent activation energies calculated are in the range from 102.1 to 141.7 kJ/kg/mol. Formerly Doctoral Student, Department of Metallurgy and Materials Engineering, University of the Witwatersrand, Johannesburg,     

The high temperature phase diagrams for zirconium-molybdenum and hafnium-molybdenum

The high temperature regions of the Zr−Mo and Hf−Mo binary phase diagrams have been constructured from temperature-composition data obtained by gravimetric and pyrometric methods. The liquidus curves were obtained directly from the measurements of saturation solubilities of molybdenum (single crystal) in liquid Zr and Hf. The solubility results are supported by electron microprobe analyses which identify the formation of thin (∼10 μm) layers of nearly stoichiometric compounds ZrMo₂ and HfMo₂ on the surface of the single crystal molybdenum below the respective peritectic temperatures 1918±5 and 2206±5°C. These thin layers and the negligible diffusion zones of Zr and Hf in single crystal molybdenum do not significantly affect the measured solubilities. The diffusion coefficient of Hf in Mo-single crystal at 2080°C is ∼5×10⁻¹² m² s⁻¹. The melting, solidus, liquidus, eutectic and peritectic temperatures were directly measured by pyrometrically observing the partial or complete destruction of “black-body” conditions inside an effusion cell with the appearance of a liquid phase that forms a highly reflecting mirror. The melting points of Zr and Hf metals, 1860±3 and 2228±3°C, respectively, are in good agreement with previously assessed values. The respective eutectic temperatures peratures and compositions 1551±2°C, 29.0±0.5 at. pct Mo and 1896±3°C, 40.5 at. pct Mo, are considerably more precise and only in fair agreement with previously measured or estimated values. The liquidus composition at the peritectic temperature for the Zr−Mo binary is precisely fixed at 54.0±1.0 at. pct Mo and that for the Hf−Mo binary is 61 ±3 at. pct Mo. The thermodynamic activities of molybdenum in the liquid Zr−Mo alloy indicate positive deviations from Raoult's Law. temporarily attached to the Chemistry Division, Argonne National Laboratory, Argonne IL 60439 This work was performed at Argonne National Laboratory under the auspices of the U.S. Energy Research and Development Administration     

Oxidation of porous nanocrystalline titanium nitride. I. Kinetics

We used the continuous weighing method to study the oxidation kinetics in air for TiN specimens pressed and sintered from nanocrystalline powders with particle size ≤55 nm. Oxidation was carried out at 500–1000 °C for 240 min. By comparing with the oxidizability of compact titanium, we estimated the total reaction surface S of the porous specimens as a function of their oxidation conditions. The mass of absorbed oxygen Δm was calculated from the mass gain ΔP, taking into account the volatile component N₂. We have shown that the maximum mass gain Δm at 600 °C is due to reaction of oxygen with the largest reaction surface. Within 120 min, external pores close up, S decreases, and then a continuous oxide layer forms in which diffusion of oxygen is slowed down. At 700–800 °C, the process of closing up of the pores is activated, and S decreases by an order of magnitude compared to 600 °C. After the first 40–50 min, a continuous oxide film forms and virtually no further mass gain occurs. As the temperature increases, the oxidation rate increases. At 900 °C, the reaction surface becomes equal to the external surface of the specimen, but the thickness of the scale increases linearly. We hypothesize that for T > 850 °C, counterdiffusion of titanium ions is superimposed on diffusion of oxygen. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), pp. 98–103, January–February, 2006.     

The determination of oxygen in gas mixtures by electromotive force measurements using solid oxide electrolytes

The behavior of impervious ZrO₂+ 10 mole pct CaO electrolyte tubes was studied at 500∮ to 1100° in oxygen concentration cells of the type (−) Ar-O₂or CO-CO₂/ZrO₂-CaO/O₂(+) The equilibrium oxygen pressures imposed by Ar-O₂(1 to 10⁻⁶atm) and CO-CO₂ (10⁻⁶to 10⁻¹⁸ atm at 1000°) mixtures of known compositions were determined from electromotive force measurements. The measured and theoretical electromotive forces were compared. For Ar-O₂ mixtures, the oxygen pressures can be measured with accuracies of ±0.4 pct at 1 to 10⁻² atm and ±4 pet at 10⁻⁴ to 10⁻⁵ atm. An accuracy of ±11 pct can be achieved with CO-CO₂ mixtures. The electromotive force of the above cell increases as the gas flow rate at the anode increases at low flow rates and becomes independent of flow rate at high flow rates. The minimum flow rates required to eliminate any significant flow rate dependence are presented as a function of oxygen pressure. Formerly Graduate Student, Department of Metallurgy and Materials Science, University of Toronto, Toronto, Ontario, Canada     

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 thermodynamic studies of liquid copper alloys by electromotive force method: Part I. The Cu−O,Cu−Fe−O,and Cu−Fe systems

Oxygen activities in liquid Cu−O and Cu−Fe−O alloys were measured in the temperature range 1100° to 1300°C by the solid oxide electrolyte emf method with mixtures of Ni−NiO and Co−CoO as reference electrodes. The Cu−O and Cu−Fe−O alloys were analyzed for iron and/or oxygen content. The activity coefficient of oxygen at infinite dilution in liquid copper was found to be 0.115, 0.195, and 0.286 at 1100°, 1200°, and 1300°C, respectively. The results are compared with previous investigations on the Cu−O system. Based on this comparison, the best equation for the free energy of solution has been suggested. The standard free energy of formation of CoO(s) has been calculated at the experimental temperatures. In the liquid Cu−Fe−O system at 1200°C, a minima in oxygen solubility is reached at 1.1 at. pct Fe in the alloy. The value of interaction coefficient, , is −565 at 1200°C. Iron activities in the liquid Cu−Fe alloys have been calculated at 1100° and 1200°C, and a strong positive deviation from ideality is observed. Results of this study were combined with literature data at 1550°C to obtain the values of and at infinite dilution in liquid copper. A. D. KULKARNI, formerly with Chase Brass and Copper Co., Cleveland, Ohio     

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.     

The kinetics of diffusion of hydrogen in niobium

The kinetics of hydrogen diffusion in niobium were studied in the temperature ranges of 200° to 300°C and 600° to 700°C by gas-metal absorption experiments. The hardness profile was correlated with the concentration of hydrogen on specimens of various grain sizes. It was found that the diffusion kinetics of both temperature ranges could be represented by a single Arrhenius-type rate equation. The activation energy and the preexponential factor were found to be 10.000±320 cal per mole, and 1.8±1.0×10⁻² cq cm per sec., respectively. No observable effect of grain size was found on the diffusivity.     

Effect of phosphorus on the mechanical properties of normalized 0.1 pct C, 1.0 pct Mn steels

The effect of phosphorus, in amounts up to 0.2 pct, on the stress-strain characteristics and strain-rate sensitivity of a series of laboratory-produced 0.1C–1.0Mn steels has been determined on normalized 10 mm-thick (0.38 in.) plate at temperatures from −196 to 400°C (−321 to 752°F). It was found that 0.05 pct phosphorus increased the yield strength of the 0.1C–1.0Mn steel about 24 MPa (3.5 ksi) at 22°C (72°F) and above without significantly affecting the Charpy V-notch shelf energy or fracture-appearance transition temperature. Additions of 0.1 and 0.2 pct phosphorus caused a greater increase in the yield strength (48 and 93 MPa or 7 and 13.5 ksi) but also increased the transition temperature. The strengthening effect of phosphorus in these steels is much the same as that found previously for phosphorus in iron, and analysis of the strain-rate-sensitivity data shows that the same deformation models are applicable. Strong elastic interactions between phosphorus atoms and dislocations are believed to be responsible for the observed deformation behavior. Comparison of the present results with those obtained previously on Fe−P alloys and with data in the literature indicates that the strengthening resulting from phosphorus additions to steel is expected to be additive to other strengthening mechanisms.