Oxygen permeability of calcia-stabilized zirconia

Oxygen permeability of commercial calcia-stabilized zirconia has been measured at 1673 to 1823 K by the following cell; O₂ ZrO₂(CaO) N₂ - O₂ (P’tO₂ = 1 atm) solid electrolyte (P″O₂ = 0.39 - 10^10-3 atm). Oxygen permeability of calcia-stabilized zirconia is proportional to (1 - P″O₂ ^1/4). From the permeability measurement, the conduction properties of the electrolyte were log σ-_‡ ^b+ = 0.28- 5100/T and logP_b+ =-0.87 + 15,400/T where σ-_‡ ^b+ is the t-@#@ type electronic conductivity at P_{O 2} = 1 atm, and P_b+ is the oxygen activity at which the t-@#@ type electronic conductivity and the ionic conductivity are equal.     

Electronically driven transport of oxygen from liquid iron to CO + CO2 gas mixtures through stabilized zirconia

Transport of oxygen in the following electrochemical system was investigated;O (liquid iron) Oⁱⁿ²⁻ (in ZrO₂2−CaO) O₂ (CO + CO₂) An alumina crucible was charged with liquid iron containing 580 ± 10 ppm oxygen. A calcia-stabilized zirconia tube (closed at one end) was immersed in the liquid iron. The inside of the zirconia tube was flushed with a stream of CO + CO2 gas mixture. Oxygen was removed from liquid iron to the CO + COO₂ gas mixture without application of an external current. Kinetics of oxygen transport in this system are discussed in terms of mixed ionic and electronic conduction of the zirconia, and also diffusion of oxygen in liquid iron. The rate controlling step for this oxygen removal process was found to be transport of oxygen across a boundary layer in the melt at the melt/electrolyte interface. M. IWASE, on leave from the Department of Metallurgy, Kyoto University, Kyoto, Japan M. TANIDA, Formerly Graduate Student at Kyoto University     

Kinetics of pyrite oxidation in sodium hydroxide solutions

The kinetics of pyrite oxidation in sodium hydroxide solution were investigated in a stirred reactor, under temperatures ranging from 50 °C to 85 °C, oxygen partial pressures of up to 1 atm, particle size fractions from -150 + 106 to -38 + 10μm (-100 + 150 mesh to -400 mesh + 10 μ), and pH values of up to 12.5. The surface reaction is represented by the rate equation:-dN/dt = Sbk″pO^0.5 ₂[oH^{- 0.25}/(1 +k‴ pO₂ ^0.5) where N represents moles of pyrite, S is the surface area of the solid particles,k″ andk″ are constants,b is a stoichiometric factor, pO₂ is the oxygen partial pressure, and [OH^-] is the hydroxyl ion concentration. The corresponding fractional conversion (X) vs time behavior follows the shrinking particle model for chemical reaction control: 1 - (1 -X)^1/3 =k _ct The rate increases with the reciprocal of particle size and has an activation energy of 55.6 kJ/mol (13.6 kcal/mol). The relationship between reaction rate and oxygen partial pressure resembles a Langmuir-type equation and thus suggests that the reaction involves adsorption or desorption of oxygen at the interface. The square-root rate law may be due to the adsorption of a dissociated oxygen molecule. The observed apparent reaction order with respect to the hydroxyl ion concentration is a result of a complex combination of processes involving the oxidation and nydrolysis of iron, oxidation and hydrolysis of sulfur, and the oxygen reduction. Formerly Graduate Student, Department of Mineral Engineering, Pennsylvania State University     

Chemical potentials of oxygen for mixtures of CaO (s) + Ca4P2O9 (s) + {CaO + P2O5 + FexO} melts and Ca4P2O9 (s) + Ca3P2O8 (s) + {CaO + P2O5 + FexO} melts

Electrochemical measurements involving stabilized zirconia as solid electrode and Mo + MoO₂ as reference electrode were conducted in order to determine the chemical potentials of oxygen for threephase assemblages of CaO (s) + Ca₄P₂O₉ (s) + liquid and Ca₄P₂O₉ + Ca₃P₂O₈ + liquid within the system CaO + Fe_xO + P₂O₅. The results for the former are $$\log (P_{O_2 } /atm) = 6.22 - 27,900 (T/K)$$ while for the latter, $$\log (P_{O_2 } /atm) = 6.35 - 27,600 (T/K)$$      

Oxygen Permeability of Calcia-Stabilized Zirconia at Low Oxygen Partial Pressures

The oxygen permeability of commercial ZrO₂ +5.8 to 5.9 wt pct CaO has been measured between 1673 and 1823 K by the following cell: The oxygen permeability of calcia-stabilized zirconia is proportional to . From the permeability measurements, the conduction properties of the electrolyte were obtained.     

Oxygen and sulfur solubilities in Ni-Fe-S-O melts

Oxygen and sulfur solubilities were determined in Ni-Fe-S-O melts under the following conditions: 10^-11.50 ≤ P_O2 ≤ 10^-8.50 atm; 10^-3.00 ≤ P_{s 2} ≤ 10^-2.00 atm; 0.19 ≤ Ni/(Ni + Fe) ≤0.85; and 1473 K ≤T ≤ 1573 K. The oxygen solubility was found to increase with increasing partial pressure of oxygen up to a maximum value at oxide saturation and to decrease with increasing equilibrium partial pressure of sulfur. The ferrous metal content enhanced oxygen solubility. The trends in dissolution behavior of sulfur were opposite to those of oxygen with respect to changing P_{O 2} and P_{S 2} and to the Ni/(Ni + Fe) ratio; however, at high matte grades Ni/(Ni + Fe) > approximately 0.5, sulfur solubility appeared to decrease as a function of the Ni/(Ni + Fe) ratio, as did oxygen solubility. The standard Gibbs energy of oxygen dissolution in Ni-Fe-S-O melts Ni/(Ni + Fe) = 0.47 in the temperature range 1473 to 1573 K can be described by ΔG° = −202.5 + 0.0660 T(K) (±1.5 kJ/mol)     

Photoluminescence of BaGdB9O（16）：Eu^3＋ co-doped Al^3＋ or Sc^3＋ under UV-VUV excitation

Single phase of BaGd0.9-xMxEu0.1B9O16 (M=Al or Sc, 0≤x≤0.3) powder was prepared by the solid-state reaction and its photoluminescence (PL) properties were investigated under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation. Monitored with 613 nm emission, the excitation spectra of BaGd0.9-xMxEu0.1B9O16 consisted of three broad bands peaking at about 242, 208, and 142 nm, respectively. The one at about 242 nm originated from the charge transfer band (CTB) of O2-→Eu3+. The other two were assigned to the absorption of the host, which was overlapped with absorptions among borate groups, f→d transition of RE3+ (RE=Gd, Eu), and the charge transfer transition of O2-→Gd3+. The maximum emission peak was observed at about 613 nm in the emission spectra of BaGd0.9-xMxEu0.1B9O16 under both 254 and 147 nm excitation, which originated from the electric dipole 5D0→7F2 transition of Eu3+. When excited with 254 nm, the integral emission intensity of Eu3+ increased after Al3+ or Sc3+ substituting Gd3+ partly in BaGd0.9Eu0.1B9O16. Under 147 nm excitation, the integral emission intensity of Eu3+ decreased after some Gd3+ was replaced by Sc3+, but increased after adding appropriate Al3+ into BaGd0.9Eu0.1B9O16.     

Kinetics of the water-gas shift reaction on an “FeO” surface

The rate of the water-gas shift reaction, CO₂ + H₂→ CO + H₂O, has been determined on “FeO” as a catalyst between 700 and 1000°C by conversion and isotope-exchange measurements. Results of the two methods are in fair agreement and are consistent with the rate equation, $$\dot n_{CO} /A = k'[a_O ](p_{CO_2 } - a_O p_{CO} ),$$ wherea _O is the oxygen activity on the “FeO” surface. The rate limiting step is the adsorption-dissociation of CO₂ on the surface. The dependence ofk’ on a_O may be empirically expressed ask’[a _O] =k _o a _O ^{- m}, wherem = 2/3 at 900°C. Possible causes for this behavior are discussed. Variation ofk _o with T yieldsk _o = 0.00717 exp(-124,700 ±6300 J/RT) mol/cm² s atm. The activation energy agrees well with those determined from thermogravimetric studies of the linear oxidation of α-Fe (120.9 kJ/mol) and the oxidation-reduction of “FeO” within its range of nonstoichiometry (117.6 kJ/mol). It differs significantly, however, from the activation energy of 226.8 kJ/mol previously obtained for surface controlled oxidation of γ-Fe.     

Kinetics of evolution of SO2 from hot metallurgical slags

The kinetics of the evolution of SO₂ gas from a liquid synthetic blast furnace -type slag (CaO-Al₂O₃-SiO₂) in an atmosphere of O₂ + Ar gas at a total pressure of 1 atm for 0.003 ≤ Po₂ ≤ 1.00 atm has been studied in the range 1360 to 1460°C. The process has been followed by collecting and analyzing the SO₂ as it forms, and also by observing the change in weight of the slag sample with time. The effect of slag composition has also been studied. For partial pressures of oxygen less than about 0.1 atm, the rate is very rapid and is controlled by transport in the gas phase. At greater values of Po₂, the rate is much slower and is controlled by a chemical process. In the high Po₂ region, the process is half-order with respect to the concentration of sulfur in the slag. This half-order dependence on sulfur concentration in the slag may be explained by an initial fast irreversible reaction to form two intermediate species which then decompose at equal rates to give the final products. Additions to the slag of iron or manganese oxides greatly accelerate the rate of evolution of SO₂ at Po₂ = 1.00 atm. This is interpreted to mean that a charge transfer process, possibly involving S^2- and O^2- ions, is rate-controlling at Po₂ = 1 atm. It is also apparent that Fe²⁺ and Fe³⁺ (or Mn²⁺ and Mn³⁺) ions can act as charge carriers. Some measurements with actual industrial blast furnace slags are also reported. Formerly Visiting Scientist, Massachusetts Institute of Technology     

Activities in liquid Fe−Al−O and Fe−Ti−O alloys

The solubility and activity of oxygen in Fe?Al and Fe?Ti melts at 1600°C were measured. The activity was measured electrochemically using the following galvanic cells: Cr-Cr₂O₃(s) ? ThO₂(Y₂O₃) ? Fe-Al-O(l), Al₂O₃(s) Cr-Cr₂O₃(s) ? ThO₂(Y₂O₃) ? Fe-Ti-O(l, saturated with oxide) Cr-Cr₂O₃(s) ? ZrO₂(CaO) ? Fe-Ti-O(l, saturated with oxide) Aluminum and titanium decrease the solubility of oxygen in liquid iron to a minimum of 6 ppm at 0.09 wt pct Al and 40 ppm at 0.9 wt pct Ti, respectively. The value of the interaction coefficients ε ₀ ^(Al) and ε ₀ ^(Ti) are ?433 and ?222, respectively. the activity coefficient of aluminum at infinite dilution in liquid iron is 0.021, while that of titanium is 0.038. The value of the aluminum equilibrium constant, the solubility product at infinite dilution, is 5.6×10^?14 at 1600°C. The ThO₂(Y₂O₃) electrolyte exhibited insignificant electronic conductivity at 1600°C down to oxygen partial pressures of 10^?15 atm, which corresponds to about 0.3 ppm O in unalloyed iron.     

Solubility and thermodynamic properties of oxygen in solid molybdenum

The solubility of oxygen in solid Mo, determined in the range 1400 to 1900°C by equilibrating rods of zone-refined Mo with mixtures of Mo and MoO₂ powders, can be expressed as ln Χ_O ^α(sat) (atom fraction) = 5.86 - 27,900/T Using the known value of the free energy of formation of MoO₂, the chemical potential of oxygen in the dilute solid solution is calculated to be μ^α _O1/2μ^o _O2 = ΔG ^α _O = -10,760 + (6.92 +R ln χ^μ _O)T ± 1000 cal/g-atom oxygen The heat of solution of oxygen in Solid Mo, ΔH_Oα = -10,760 ± 3000 cal/g-atom oxygen, and the excess entropy for the interstitial solid solution ΔS_Oα(xs, i) =- 9.10 ± 1.5 cal/degree, g-atom oxygen, assuming that the oxygen atoms reside in the octahedral interstices of bcc Mo.     

Electrical properties of iron doped apatite-type lanthanum silicates

The effect of Fe doping on the electrical properties of lanthanum silicates was investigated. The apatite-type lanthanum silicates La10Si6-xFexO27-x/2 (x=0.2, 0.4, 0.6, 0.8, 1.0) were synthesized via sol-gel process. The unit cell volume increased with Fe doping because the ionic radius of Fe3+ ion is larger than that of Si4+ ion. The conductivities of La10Si6-xFexO27-x/2first increased and then decreased with the in-creasing of Fe content. The increase of the conductivity might be attributed to the distortion of the cell lattice, which assisted the migration of the interstitial oxygen ions. The decrease of the conductivity might be caused by the lower concentration of interstitial oxygen ions. The op-timum Fe doping content in lanthanum silicates was 0.6. La10Si5.4Fe0.6O26.7 exhibited the highest ionic conductivity of 2.712×10-2 S/cm at 800 ℃. The dependence of conductivity on oxygen partial pressure p(O2) suggested that the conductivity of La10Si6-xFexO27-x/2 was mainly con-tributed by ionic conductivity.     

Density Measurements of Low Silica CaO-SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Slags

Density measurements of a low-silica CaO-SiO₂-Al₂O₃ system were carried out using the Archimedes principle. A Pt 30 pct Rh bob and wire arrangement was used for this purpose. The results obtained were in good agreement with those obtained from the model developed in the current group as well as with other results reported earlier. The density for the CaO-SiO₂ and the CaO-Al₂O₃ binary slag systems also was estimated from the ternary values. The extrapolation of density values for high-silica systems also showed good agreement with previous works. An estimation for the density value of CaO was made from the current experimental data. The density decrease at high temperatures was interpreted based on the silicate structure. As the mole percent of SiO₂ was below the 33 pct required for the orthosilicate composition, discrete \textSiO₄^{4 -} {\text{SiO}}_{4}^{4 - } tetrahedral units in the silicate melt would exist along with O^2– ions. The change in melt expansivity may be attributed to the ionic expansions in the order of

thermodynamics of nitrogen in BaO-TiOx melts

Using a gas-slag-metal equilibration technique, nitrogen contents in BaO-TiO^ slags and nitrogen and titanium contents in liquid Cu were measured at 1823, 1873, and 1923 K under controlled partial pressures of oxygen(@#@ P_{O 2} = 10^-11.5 ≈ 10^-13.7 atm) and nitrogen(@#@ P_{N 2} = 0.9 atm). The nitride capacity, C_(N) [=(mass pct N) · PO₂/3/4, (mass pct Ti³⁺)/(mass pct Ti⁴⁺) ratio, and solubility of TiN in BaO-TiO₂-TiO_1.5 slags were obtained as a function of slag com-position(@#@ X_BaO = 0.20 = 0.43) and temperature. Activity coefficients of TiN were estimated, using the values for activity coefficients of Ti in liquid Cu which were calculated from the results of a TiN saturation experiment. Free energy of dissolution of nitrogen into liquid Cu was derived as °GG_N ^o = 32,400 + 46.17 ± 1400 (J/g · atom).     

Activities of phosphorous in liquid Ni + P alloys saturated with solid nickel

By using an electrochemical technique incorporating magnesia-stabilized zirconia electrolyte, the activities of phosphorous in liquid {Ni + P} alloys saturated with solid nickel were determined at temperatures between 1477 and 1663 K. The activities of phosphorus referred to gaseous diatomic phosphorous at 1 arm pressure,a _p, could be expressed by analytical formulas: 2 loga _p = logP _P2 = -5.6 -9700/(T/K) at temperatures between 1477 and 1612 K, and 2 loga _p = logP _P2 = -22.0 -17000/(T/K) at temperatures between 1612 and 1663 K. Formerly with Kyoto University, is retired.     

Glass forming regions and concentration-dependent luminescence properties of Tb~(3+)-activated tellurium-lutetium-tungsten glasses

The glass-forming regions of tellurium-gadolinium-tungsten ternary system prepared at 1000℃for 60 min were firstly determined.To improve density,the full replacement of lutetium for gadolinium to form Tb³⁺-activated tellurium-lutetium-tungsten glasses with the composition of 64 TeO₂-20 WO₃-(16-y)Lu₂O₃-yTb₂O₃were designed for scintillation application.The concentration-dependent optical properties of Tb³⁺-activated tellurium-lutetium-tungsten glasses were fully investigated by transmittance,excitation and emission spectra,together with the luminescence decay curves.The energy transfer mechanism was discussed according to Huang’s rule.The optimized 4 mol%Tb₂O₃activated tellurium-lutetium-tungsten glasses with the density of 6.49 g/cm³and the lifetime of 0.551 ms are developing to be suitable for the potential detection of slow events in the future work.     

Solubility of oxygen and sulfur in copper-iron mattes

The concentrations of oxygen and sulfur in unsaturated and magnetite-saturated Cu-Fe mattes were measured as a function of oxygen and sulfur pressures and iron metal weight fraction of the matte (W _Fe = wt Fe/(wt Fe + wt Cu)). The liquid matte samples were equilibrated with streams of gas of known pressures of S₂ and O₂ at 1468 K. Empirical correlation equations were developed to describe the experimental results. The correlation for oxygen in unsaturated matte is wt pct O = 2.50P _{O 2} ^0.200 P _{S 2} ^-0.142 (1 + 9.0W _Fe ^2.19, and in magnetite-saturated matte it is wt pct O = 0.14 + 2.39W _Fe + 12.0W _Fe ² for 0.001 <P _{S 2} ≤ 0.01 atm and it is wt pct O = −3.06 + 2.39W _Fe + 12.0W _Fe ² − 1.60 logP _{S 2} for 0.01 <P _{S 2} < 0.023 atm. A single complex equation ofP _{O 2},P _{S 2}, andW _Fe describes the sulfur concentrations in both unsaturated and magnetite-saturated mattes. An erratum to this article is available at .     

Gibbs energy of formation of nickel chromite

The equilibrium partial pressure of oxygen for a system containing coexisting NiCr₂O₄, Cr₂O₃, and Ni was determined at 1000 to 1300 K using the electrochemical technique. Yttria-stabilized zirconia was employed as a solid-state electrolyte in the open-circuit electromotive force (EMF) measurements. Results were compared to the reported data in the literature. The standard Gibbs energy of NiCr₂O₄ at 1000 to 1300 K was determined to be ΔG°_f(NiCr₂O_{4)=-1327.2+0.314T±2.874 (kJ/mole)}     

Thermodynamics of Calcium Ferrite Slags at 1200 and 1300°

Abstract

Oxygen isobars and liquidus isotherms of the system CaO-FeO-Fe₂O₃ at 1200 and 1300°C were determined by quenching samples equilibrated with CO₂–CO mixtures, The iron liquidus and the melt coexisting with two solids were carefully examined in terms of their composition as well as the equilibrium oxygen partial pressures, p _o2 . At 1200°C, p _o2 was 10^?7.70 atm when the slag coexisted with magnetite and dicalcium ferrite, At 1300°C, the melt region extends to the CaO–Fe₂O₃ join, where p _o2 was 10^?0.68 atm (air) or higher. Within the range of p _o2 from one order above that at iron saturation to 10^?4 atm, the slag composition, p _o2 , and the temperature T are related by the equation:

log (Fe^{+ + +} /Fe^{+ +} ) ? 0.170logp _O2 + 0.018 (wt% CaO) + 5500/T ? 2.52.

Activities of CaO(s), FeO(l), and Fe₃O₄ (S) in the slag were calculated from the p _o2 data by combining the available thermal data and/or by Gibbs-Duhem equation.

Résumé

Les isobares d'oxygene et les isothermes du liquidus du systeme CaO–FeO–Fe₂O₃ à 1200 et 1300°C ont été déterminées en trempant des échantillons équilibrés avec des mélanges CO₂–CO. Le liquidus du fer et le mélange coexistant avec deux solides ont été soigneusement étudiés en terme de composition et de pression partielle d'oxygène à l'équilibre, p _o2 . A 1200°C, p _o2 était de 10^?7.7 atm quand la scorie était en équilibre avec la magnétite et la ferrite de dicalcium. A 1300°C, le domaine du liquide s'étend jusqu'au joint CaO–Fe₂O₃ où p _o2 valait 10^?0.68 atm (air) ou plus. A l'intérieur du domaine de p _o2 qui s'étend d'un ordre au dessus de celle à la saturation en fer jusqu'à 10^?4 atm, la composition de la scorie, p _o2 et la température T sont reliées par l'équation:

log(Fe³⁺/Fe²⁺) ? 0.170logp _o2 + 0.018(pd %CaO) + 5500/T ? 2.52.

Les activités de CaO(s), FeO(l) et Fe₃O₄(S) dans la scorie ont été calculées a partir des valeurs de p _o2 en combinant les données thermodynamiques disponibles et/ou l'équation de Gibbs-Duhem.     

Solubility of carbon in CaO-Al2O3 melts

Carbon distribution ratios between CaO-Al₂O₃ slags and Fe-0.0003 to 0.8 mass pct Al-0.2 to 5.6 mass pct C alloys were measured at 1873 K in an Al₂O₃, CaO, or graphite crucible. The carbon distribution ratios were dependent on the oxygen potential, determined by theAl/(Al₂O₃) equilibrium, not by theC/CO (P _co = 1 atm) equilibrium. The (mass pct C)/a _c ratios were proportional to the activity of Al in logarithmic form with a slope of 2/3, indicating that carbon in slag is dissolved as C^2? ion. Solubilities of carbon in CaO-Al₂O₃ slags were also measured at 1873 K under the CO-CO₂-Ar gas mixtures in an Al₂O₃ or graphite crucible. It was found that C^2? ion is present in the range of log $P_{O_2 } $ (atm) < ?15 and CO ₃ ^2? ion in the range of log $P_{O_2 } $ (atm) > ?7.