Activity Coefficient Of Oxygen Research Articles

Thermodynamic properties of zirconium-oxygen solid solution and its deoxidation in calcium chloride molten salt

Thermodynamic properties of zirconium-oxygen (Zr–O) solid solution and its deoxidation by calcium in CaCl2 molten salt were studied using a chemical equilibration technique. In the temperature range from 1173 to 1373 K, the equilibrium oxygen contents in Zr were measured experimentally under coexistence of Ca and CaO in CaCl2 molten salt. The oxygen content in Zr was reduced from about 800 ppm to a minimum of less than 100 ppm. Then aCaO sensor — niobium-oxygen (Nb–O) solid solution was employed to equilibrate with Zr–O solid solution to determine the oxygen activity coefficient in Zr–O solid solution. Zr and Nb specimens were submerged in Ca-saturated CaCl2 molten salt containing different amounts of CaO. CaCl2 melt was used for a homogeneous reaction and composition. The experimental results shown that Henry's law held and the activity coefficient of oxygen was constant within the concentration range of this study. Based on the result, the standard formation Gibbs free energy of Zr–O solid solution was obtained as a function of temperature:1/2O2 (g) = O (in Zr)ΔGZr−Oθ=−543577+64.3T(1173−1373K)The p-t-x relationship of the deoxidation system was obtained simultaneously, which make the deoxidation limit and variation trend of oxygen content in Zr–O solid solution predictable and controllable under different conditions. Oxygen distribution coefficient between Zr–O solid solution and Nb–O solid solution was found in agreement with the theoretical value and independent of oxygen potential of the system.

Effect of Direct Reduced Iron on Ferrous Oxide Capacity of Slag in Electric Arc Furnace.

Slag and the corresponding hot metal samples were collected just before tapping from electric arc furnace of Ezz Flat Steel Company (EFS) and analyzed. The temperature of hot metal was measured before tapping.The analyses of slag and hot metal together with the metal temperature were used to estimate the activity coefficient and activity of total ferrous oxides in slag, also investigate carbon and oxygen activity coefficient in steel according to the statistical theory of regular ionic solutions.The oxides capacity of the slag was also assessed. The variation of carbon and oxygen activity in hot metal with the concentration was also treated.The ratio of activity to concentration of total ferrous oxides is constant and equal to 0.0179. The activity coefficients of oxygen and carbon in steel are 0.810 and 1.0704, respectively.The oxides capacity of the slag increases with increasing carbon concentration in the bath and with increasing DRI proportion in the charge.

Complete thermodynamic description of the Mg-Ca-O phase diagram including the Ca-O, Mg-O and CaO-MgO subsystems

A complete thermodynamic description of the Mg-Ca-O system and phase diagrams is developed. It is based on our extensive thermodynamic analysis of solid CaO and MgO data and validation of the low-temperature Mg-Ca-O phase diagram up to 1050 K. This work presents the high- temperature oxygen solubilities and revisions of calculated melting points of the oxides. An extension of the empirical schemes for predicting the activity coefficient of oxygen in liquid elements is proposed to predict data for the Mg-O system. Consistent thermodynamic descriptions of the complete binary Ca-O and Mg-O systems are developed. It is shown that this framework is crucial to understand recently measured significantly different melting points of CaO under oxidizing versus reducing conditions. The revised description of the MgO-CaO quasibinary oxide system considers all experimental data, revealing significantly different melting equilibria compared to all previous publications.

Activity and diffusivity of oxygen in the liquid dilute BixSb1-x solutions

The diffusivity and activity coefficient of oxygen in liquid antimony, bismuth and antimony-bismuth alloys were determined from coulometric titration experiments, which were performed in the temperature range from 985 to 1185 K. The diffusivity in pure metals (in cm2/s) is: Dbi,O =(9.04 ? 1.82)?10-3 exp (-49115?1809/RT) DSb,O(2.87?0.22)?10-4 exp (-16720?677/RT). The standard free energy of solution of oxygen in liquid antimony, bismuth and antimony-bismuth alloys according to the reaction ? O2 (g) = O (infinite dilution) is calculated. The activity coefficient of oxygen was calculated at 1085 K as a function of the alloy composition. It was demonstrated that Wagner's model with one adjustable parameter h gave a satisfactory description of the experimental data.

Effect of oxygen impurity in sodium–potassium melt on the corrosion processes at the interface between vanadium alloy and eutectic melt

An analysis of available experimental data on thermodynamic activity coefficient of oxygen in binary liquid metal Na–K alloys is carried out. Thermodynamic correlations based on the coordination cluster model are used for theoretical evaluation of the effect of oxygen impurity on the solubility of vanadium in sodium–potassium eutectic alloy in the temperature range of 400–800°C. Isothermal capsule experiments qualitatively confirm the results of calculations of vanadium solubility in Na–K melt. On the basis of derived thermodynamic relationships the threshold concentration for the formation of ternary oxide NaVO2 on the surface of the solid vanadium in the Na0.32K0.68 melt has been calculated. The calculation results are compared with the corresponding values for the sodium coolant.

Deoxidation of Molten Steel by Aluminum

The deoxidation equilibrium of liquid steel was investigated from a new perspective. Dissolved associate MmOn was used to describe the interaction between dissolved M and dissolved oxygen instead of the interaction parameter of Wagner. The concentration of unassociated oxygen could be considered as the activity of oxygen. Or, the percentage of unassociated oxygen in the total dissolved oxygen was the activity coefficient of oxygen. When the content of deoxidizer was low, the dissolved oxygen was mainly composed of the unassociated oxygen, while more and more MxO formed with gradually increasing M content. The present model gave a good description to the aluminum deoxidation equilibrium after considering AlO and Al2O. Furthermore, the higher the content of Al was, the higher the content of Al2O relative to the content of AlO would be.

Thermodynamics of oxygen in dilute liquid silver–selenium alloys

In the present work, the activity coefficient of oxygen in liquid dilute binary Ag–Se alloys has been determined by coulometric titration in the temperature range from 1285 to 1485 K. All experiments were conducted using electrochemical cells with solid zirconia electrolyteKanthal+Ir, [O] in liquid Ag–Se alloy |YSZ| air, PtThe oxygen activity coefficient in dilute Ag–Se–O alloys was measured for variable XSe contents for XSe = 0·01, 0·015 and 0·02. From the obtained results, Wagner’s interaction parameter as a function of temperature was derivedThe electrochemical coulometric titration method seems to be a very useful way to study thermodynamics of oxygen interaction in liquid silver alloys.Au cours du présent travail, on a déterminé le coefficient d’activité de l’oxygène fo dans des alliages liquides binaires dilués d’Ag–Se, par titrage coulométrique, dans la gamme de température de 1285 à 1485 K. On a effectué toutes les expériences à l’aide de cellules électrochimiques avec un électrolyte solide de zircone:Kanthal+Ir, [O] dans l’alliage liquide Ag–Se |YSZ| air, PtOn a mesuré le coefficient d’activité de l’oxygène dans les alliages dilués d’Ag–Se–O pour la variable XSe, avec la teneur de la variable XSe = 0·01, 0·015 et 0·02. À partir des résultats obtenus, on a dérivé le paramètre d’interaction de Wagner en fonction de la températureLa méthode électrochimique de titrage coulométrique semble un moyen bien utile pour l’étude thermodynamique de l’interaction de l’oxygène dans les alliages liquides d’argent.

Thermodynamics of oxygen in dilute liquid silver-tellurium alloys.

The activity coefficient of oxygen f_{text{O}}^{0} in liquid Ag and binary Ag–Te dilute alloys were determined between 1,285 and 1,485 K by coulometric titration using the electrochemical cell (Ir, [O] in liquid metal or alloy | yttria stabilized zirconia | air, Pt). The experimental and evaluation procedures described in the literature were adopted. The oxygen activity coefficient was determined in pure liquid silver to be ln f_{text{O}}^0 = {{ - 1{,}760.2} mathord{left/ {vphantom {{ - 1,760.2} T}} right. kern-nulldelimiterspace} T} + 0.6315. Next, the oxygen activity coefficient in dilute Ag–(Te)–O alloys for variable X Te content (from 0.01 to 0.06) was measured. From the obtained results, Wagner’s interaction parameter varepsilon_{text{O}}^{text{Te}} as a function of temperature was derived in the form varepsilon _{text{O}}^{{text{Te}}} left( { pm 0.32} right) = {{ - 18,483} mathord{left/ {vphantom {{ - 18,483} T}} right. kern-nulldelimiterspace} T} + 7.668. The electrochemical coulometric titration method seems to be very useful to study the thermodynamics of oxygen interaction in liquid silver and its alloys.Graphical abstract

Coordination-cluster model for analyzing interactions in Na-O-H melts

A procedure for calculating the thermodynamic activity coefficients of oxygen and hydrogen in dilute Na-O-H system melts over the temperature range 300–600°C was suggested. The thermodynamic activity coefficients of hydrogen in liquid sodium calculated by the coordination-cluster model equations were used to determine the equilibrium hydrogen pressure over melts. The calculation results were compared with the experimental partial hydrogen pressures over the Na(excess)-Na2O-NaH system at x O = x H. The calculated values were in qualitative agreement with the experimental data.

Effect of Direct Reduced Iron on Oxygen Distribution between Slag and Bath in Electric Arc Furnaces

Test charges containing 40 to 95% direct reduced iron (DRI) were melted in two identical electric arc furnaces. Slag and the corresponding metal samples were collected from the furnace in the course of the steelmaking process and from the ladle after deoxidation and composition adjustment. The temperature was measured just before sampling. The activity coefficient and activity of total ferrous oxide in the slag were determined by using the theory of regular ionic solutions. The activity was used to assess the oxygen concentration in the metal. The effect of slag composition on FetO activity coefficient and activity was investigated. The enthalpy of solution of total ferrous oxide in the slag was found to be 78 kJmol−1. The ratio of activity to concentration of FetO is equal to 0.0138. The effects of DRI proportion and degree of metallization on αFe,O were investigated. The activity coefficients of oxygen and carbon in the bath are 0.7243 and 1.0825, respectively. The activity coefficient and activity of oxygen in the metal decrease with increasing carbon concentration, carbon activity coefficient and activity. An “oxide capacity” has been developed which does not need the use of αFe,O. It correlates strongly with temperature over the range from 1500 to 1670°C. The basicity has only a small influence compared with the large temperature effect. The oxide capacity increases with growing DRI proportion and decreases with increasing metallization between 93.43 and 95.25%. Oxygen distribution between slag and metal was assessed by using the oxide capacity. Calculated values compare well with the corresponding data obtained from slag and metal analyses. The oxide capacity can be used in monitoring the steelmaking operation.

Determination of oxygen and sulfur thermodynamic activity in molten metals

The paper describes computer analysis of concentration dependence of oxygen activity coefficients fo in binary liquid titanium-base alloys containing ions of copper, nickel, molybdenum, vanadium, zirconium and aluminum. The study covers calculations of oxygen activity coefficient fo and sulphur activity coefficient fs in binary melts of the systems Cu - Fe, Cu - Ni, Cu - Co, Ni - Co, Fe - Ni, Fe - Co as a function of the concentration of metal components.

Solubility and Activity of Oxygen in Pb–Bi Melts

In order to obtain the solubility and activity of oxygen in Pb-Bi melts, the research for oxygen analysis and oxygen partial pressure measurement in a lead-bismuth eutectic alloy (LBE) was performed. The analytical condition of oxygen in low melting metals by an inert gas fusion-infrared absorption method was established using Pb or Bi equilibrated with its corresponding oxide at 973 K as a standard sample for the oxygen analysis. After establishing the analytical condition, oxygen analysis in liquid LBE in equilibrium with solid PbO at various temperatures was done. The temperature dependence of oxygen solubility in liquid LBE was expressed by the following equation, log(C 0 /massppm) = -4.74 x 10 3 /T + 7.06(±0.03) (878 ? T/K ? 1073) Oxygen partial pressure in LBE-(PbO and/or PbO + Bi 2 O 3 ) equilibrium was measured using an oxygen sensor of a zirconia solid electrolyte (ZrO 2 - Y 2 O 3 ), and obtained as a function of temperature as log(p O2 /P°) = 10.96 - 2.259 x 10 4 /T (720? T/K? 1098) log(p O2 /P°) = 2.49 - 1.330 x 10 4 /T (1098? T/K? 1252) From the results, the oxygen potential in LBE at the oxygen unsaturated region was estimated as, RT ln(p O2 /P°)/(J/mol) = -58.59T - 2.510 x 10 5 + 38.29Tlog(Co/massppm) The activity coefficient of oxygen in liquid LBE obtained using Blander's oxygen dissolution model was compared with these experimental data and those of other investigators.

Solubility of Oxygen in Iron-Silicon Melts in Equilibrium with Silica at 1873 K

The solubility of oxygen in iron-silicon melts in equilibrium with silica was measured within the range from 0.1 up to 70mass% Si at 1873 K. The experimental procedure involved alloys melting in silica crucibles under argon atmosphere. The sampling was made by melt sucking into quartz tubes, equipped with copper chillers. The oxygen content of analytical samples was determined with inert gas fusion analysis after careful sample preparation. The results obtained were treated by thermodynamic model, which allowed to calculated the activity and solubility of oxygen in Fe-Si melts up to 100 mass% Si. The isotherm of oxygen solubility exhibits both intermediate minimum and maximum at 20 and 85 mass% Si, respectively. The corresponding values of oxygen saturated contents are as follows: 1.4 and 94 μg/g. The activity coefficient of oxygen shows alternating deviations from the additive behaviour. These are positive in the iron rich melts, containing up to 45 mass% Si. In the melts with higher silicon content the deviations from additivity are negative. The following values of interaction parameters were calculated: e S i O ( F e ) =12.9′2.7 and e F e O ( S i ) =-6.5′2.0.

Electrical Resistivity of Liquid Sb-Te Solutions

The specific resistivity of liquid antimony-tellurium alloys was determined by the DC four probe method. The cell with the capillary was used to measure potential drops in the temperature range 820–1150 K for pure antimony and six alloy compositions up to X Te=0.6. Using experimental results obtained in the present study the resistivity change with the alloy composition at constant temperature was derived. It was demonstrated that depending on local ordering in the liquid state there is a interdependence between oxygen activity coefficient, diffusivity and the alloy conductivity measured in Sb-Te binary system.

Thermodynamics of oxygen behaviour in cobalt‐nickel alloys

In this study the concentration and chemical potential of oxygen in liquid Co‐Ni alloys equilibrated with cobalt‐nickel aluminate spinel solid solutions and alumina have been determined at 1773, 1823 and 1873K as a function of nickel concentration. The oxygen content of the melt has been measured by suction sampling and inert gas fusion analysis. The corresponding oxygen potential has been determined with the following solid state cell: Mo, Mo+MoO2 | (MgO)ZrO2 | (Co, Ni) melt + AI2O3 + (Co, Ni)O·(1+x)Al2O3, Mo.The effect of nickel on the activity coefficient of oxygen in Co‐Ni alloys has been determined. The results for the activity coefficient have been modelled with Wagner's interaction parameters and also the more recent exponential method of St. Pierre et al. at the three temperatures.

Structural aspects in crystal growth of anhydrous borates

A crystallochemical interpretation of acid-base properties was developed for the numerous anhydrous borates. A quantitative estimation was made of the correlation between the ratio of the numbers of B 3+ O 2− ions and the oxygen activity coefficient. The stability of borate structures depends on the delocalization of formal charges of the B nO m anions as a result of their polymerization. This analysis and experimental studies consistently explain the high activation energy of borate crystallization by the polymerization of BO 3 triangles and BO 4 tetrahedra in their melts and fluxed melts. It also sets forth the judicious choices of phase systems for the growth of borate crystals. In particular, in order to obtain the orthoborate crystals, a wide range of flux agents can be proposed which destroy boron-oxygen polymers and intensify mass transfer in the fluxed systems.

Thermodynamics of the Deoxidation Equilibrium of Aluminum in Liquid Nickel and Nickel-Iron Alloys.

The deoxidation equilibrium of aluminum in liquid nickel equilibrated with solid alumina has been measured at the temperature ranges from 1823 to 1973 K using the sampling technique in order to investigate the equilibrium between aluminum and oxgen in liquid nickel for the refractory alloy or superalloy. For the deoxidation reaction in pure liquid nickel. i.e.:Al2O3(s) =2Al+3O the temperature dependence of the equilibrium constants, KAl (=aAl2·aO3/aAl2O3), was expressed to be:log KAl=–28770/T+1.67 1823–1973 Kwhile the deoxidation product, K'Al (=[%Al]2[%O]3), and the affect of aluminum on the activity coefficient of oxgen in liquid nickel were obtained to be:log K'Al=log KAl+1.47 (3[%Al]+3.4[%O])log fOAl=–1.47 [%Al]Al<1.1 mass%, 1823–1973 KThe deoxidation equilibrium of aluminum in liquid nickel–iron binary alloys with 0.01–0.1 mass% aluminum has been measured up to 50 mass% iron. The effect of iron on the activity coefficients of oxygen and aluminum in liquid nickel–iron alloys based on pure liquid nickel were estimated as the following expression:log fOFe+2/3log fAlFe=–0.028 [%Fe]up to around 10 mass% iron at 1923 K.The effect of nickel on the activity coefficient of aluminum in liquid iron-nickel based on liquid iron were also discussed using log KAl(Fe) in liquid iron and the present results.

Deoxidation Equilibrium of Hafnium in Liquid Iron, Nickel and Iron-Nickel Alloys.

The deoxidation equilibrium of hafnium in liquid iron, nickel and iron-nickel binary alloys has been studied at the temperature ranges from 1873 to 1973 K using hafnia crucibles. The effect of temperature on the equlibrium constant of the deoxidation reaction in liquid iron with hafnium was found to be: log KHf(Fe)(=aHf·aO2)=-35840/T+11.39 while the deoxidation product in iron was expressed as follows: logK'Hf(Fe) (=[%Hf] [%O]2)=logKHf (Fe)+5.85(2[%Hf]+11.1 [%O]) (0.01-0.1 mass% Hf) The temperature dependence of the equilibrium constant of the deoxidation in liquid nickel was determined as the expression. log KHf(Ni)=aHf·aO2= –33800/T+8.40 in the meantime, the deoxidation product in nickel was given by: log K'Hf (Ni) (=[%Hf] [%O]2)=log KHf (Ni)+9.75 (2 [%Hf]+11.1 [%O]) (0.002-0.1 mass% Hf) The deoxidation of iron-nickel binary with hafnium was measured over whole concentration ranges of the binary system at temperatures of 1873 and 1923 K. The activity coefficients of oxygen and hafnium in the binary based on pure liquid iron were given by the following expression: log fO(Fe)Ni+ 1/2 log fHf(Fe)Ni=0.005 [%Ni] below 60 mass% of nickel, while the activity coefficients on the nickel basis were expressed by: log fO(Ni)Fe+ 1/2 log fHf(Ni)Fe= –0.025 [%Fe] below 10 mass% of iron.

The solubility and activity coefficient of oxygen in salt solutions and brines

Molal oxygen activity coefficients ( γ O 2 ) in aqueous salt solutions from 0–100°C have been calculated from O 2 solubility data and established Henry's law constants. Pitzer specific interaction model parameters λ O 2 c , λ O 2 a and ζ O 2 ca have been determined for the following ions: H +, NH + 4 Li +, Na +, Rb +, Cs +, Mg 2+, Ca 2+, Ba 2+, Al 3+, OH −, Cl −, Br −, I −, NO − 3, SO 2− 3, SO 2- 4, HCO 3 −, CO 3 2- and PO 3- 4. Results confirm that the effect of individual ions on In ( γ O 2 ) is additive. Model calculations of γ O 2 in seawater agree with experimentally derived values at normal salinities to within 0.2% at 298 K and 0.65% at 273 K. Additional data for brines of seawater composition enable the model to be used to represent γ O 2 empirically to a salinity of 255 S%. The model has thus far only been parameterised from measurements for single salt solutions. Comparisons with experimental data for brines suggest that additional model parameters, obtained from ternary solution data, will be required for accurate representation of γ O 2 in mixed salt solutions above about 5 mol kg −1 total ion concentration.

The activity coefficients of oxygen in Ni-S and Co-S melts

Activity coefficients of oxygen,γ o, in nickel-sulfur melts and cobalt-sulfur melts were determined at 1423 K utilizing a modified coulometric titration technique with the following electrochemical cell: O in Ni-S or Co-S melt/ZrO2(+CaO)/air, Pt. Theγ o values around NNI=0.26 and NCO=0.35 are much smaller than those in the hypothetically undercooled liquid nickel and cobalt, respectively, at 1423 K, which were evaluated by extrapolating the literature values at higher temperatures. Theγ o values in the nickel-sulfur and cobalt-sulfur melts are rapidly increased with increasing the sulfur compositions. The shapes of the Inγ o vs solvent composition curves are quite similar to those in Cu-S, Cu-Te, and Tl-Te melts. The present results are discussed in terms of several solution models.