Self-diffusion of copper in Cu−Al solid solutions

Self-diffusion coefficients of copper in Cu?Al solid solutions in the concentration interval 0 to 19 at. pct Al and in the temperature range 800° to 1040°C have been determined by the residual activity method using the isotope Cu⁶⁴. The values of the self-diffusion coefficients in the concentration interval 0 to 14.5 at. pct Al satisfy the Arrhenius relation and their temperature dependence can be expressed by the following equations $$\eqalign{ & D_{Cu}^{Cu} = \left( {0.43_{ - 0.11}^{ + 0.15} } \right) exp \left( { - {{48,500 \pm 700} \over {RT}}} \right) cm^2 /\sec \cr & D_{Cu - 2.80 at. pct Al}^{Cu} = \left( {0.46_{ - 0.16}^{ + 0.23} } \right) exp \left( { - {{48,000 \pm 900} \over {RT}}} \right) cm^2 /\sec \cr & D_{Cu - 5.50 at. pct Al}^{Cu} = \left( {0.30_{ - 0.07}^{ + 0.09} } \right) exp \left( { - {{47,000 \pm 600} \over {RT}}} \right) cm^2 /\sec \cr & D_{Cu - 8.83 at. pct Al}^{Cu} = \left( {0.46_{ - 0.09}^{ + 0.11} } \right) exp \left( { - {{47,100 \pm 500} \over {RT}}} \right) cm^2 /\sec \cr & D_{Cu - 11.7 at. pct Al}^{Cu} = \left( {0.61_{ - 0.13}^{ + 0.17} } \right) exp \left( { - {{47,200 \pm 600} \over {RT}}} \right) cm^2 /\sec \cr & D_{Cu - 14.5 at. pct Al}^{Cu} = \left( {4.2_{ - 1.5}^{ + 2.2} } \right) exp \left( { - {{51,110 \pm 1000} \over {RT}}} \right) cm^2 /\sec \cr} $$ An analysis of the results leads to the conclusion that, in the concentration interval 0 to 11.7 at. pct Al, the frequency factor and activation enthalpy concentration dependences can be described by the following equations whereD _0Cu ^Cu and ΔH _Cu ^Cu are diffusion characteristics for self-diffusion in pure copper,X _Al is the atomic percent of aluminum, andK andB are experimental constants.     

Interdiffusivities matrix of CaO-Al2O3-SiO2 melt at 1723 K to 1823 K

Ternary oxide mixtures of lime, alumina, and silica were premelted and quenched to produce glassy cylinders. A diffusion couple was selected from the mixtures of six different compositions in such a way that the average composition could be 40 wt pct CaO-20 wt pct A1₂O₃ = 40 wt pct SiO₂. Penetration curves of the components were measured with a X-ray microprobe analyzer. The interdiffusivities matrix defined with the Matano interface has been obtained from 52 successful diffusion runs at 1723 K to 1823 K as follows; 1 $$\begin{gathered} \tilde D_{10 - 10}^{30} = 8.9 \times 10^{ - 11} \exp ( - \frac{{253,700}}{{RT}})(m^2 /s) \hfill \\ \tilde D_{10 - 20}^{30} = - 2.5 \times 10^{ - 11} \exp ( - \frac{{194,300}}{{RT}})(m^2 /s) \hfill \\ \end{gathered} $$ 2 $$\begin{gathered} \tilde D_{20 - 10}^{30} = - 4.0 \times 10^{ - 11} \exp ( - \frac{{177,600}}{{RT}})(m^2 /s) \hfill \\ \tilde D_{20 - 20}^{30} = 6.12 \times 10^{ - 11} \exp ( - \frac{{318,400}}{{RT}})(m^2 /s) \hfill \\ \end{gathered} $$ where symbols, 10, 20, and 30 mean CaO, A1₂O₃, and SiO₂, respectively, and the activation energies are in Joules per mole. The diffusion composition paths obtained are discussed in relation to Cooper’s parallelogram. The composition dependency of the above interdiffusivities is estimated from the quasibinary interdiffusivities in all composition ranges of the present oxide system in liquid state.     

Interdiffusivities matrix of CaO-AI2O3-SiO2 melt at 1723 k to 1823 k

Ternary oxide mixtures of lime, alumina, and silica were premelted and quenched to produce glassy cylinders. A diffusion couple was selected from the mixtures of six different compositions in such a way that the average composition could be 40 wt pct CaO-20 wt pct AI₂O₃ = 40 wt pct SiO₂. Penetration curves of the components were measured with a X-ray microprobe analyzer. The interdiffusivities matrix defined with the Matano interface has been obtained from 52 successful diffusion runs at 1723 K to 1823 K as follows; $$ \begin{gathered} \tilde D_{10 - 10}^{30} = 8.9 \times 10^{ - 11} \exp \left( { - \frac{{253,700}} {{RT}}} \right)\left( {m^2 /s} \right) \hfill \\ \tilde D_{10 - 20}^{30} = - 2.5 \times 10^{ - 11} \exp \left( { - \frac{{194,300}} {{RT}}} \right)\left( {m^2 /s} \right) \hfill \\ \tilde D_{20 - 10}^{30} = - 4.0 \times 10^{ - 11} \exp \left( { - \frac{{177,600}} {{RT}}} \right)\left( {m^2 /s} \right) \hfill \\ \tilde D_{20 - 20}^{30} = 6.12 \times 10^{ - 11} \exp \left( { - \frac{{318,400}} {{RT}}} \right)\left( {m^2 /s} \right) \hfill \\ \end{gathered} $$ where symbols, 10, 20, and 30 mean CaO, A1₂O₃, and SiO₂, respectively, and the activation energies are in Joules per mole. The diffusion composition paths obtained are discussed in relation to Cooper’s parallelogram. The composition dependency of the above interdiffusivities is estimated from the quasibinary interdiffusivities in all composition ranges of the present oxide system in liquid state.     

Kinetics of the reaction of CH4 gas with liquid iron

In iron bath smelting and other processes that use coal, the effective use of volatile matter can improve the energy efficiency of the process. The reaction of simulated volatile (CH₄) with iron was studied. The rate of carburization of liquid iron by CH₄ gas was measured between 1400 °C and 1700 °C under conditions for which the effect of mass transfer can be corrected with reasonable accuracy. The rate was measured for partial pressures of CH₄ in Ar in the range of 0.02 to 0.06 atm and sulfur contents in the metal from 0.0006 to 0.5 mass pct. The results indicate that the rate of carburization may be controlled by the dissociation of CH₄ on the surface. Sulfur was found to decrease the rate, and the residual rate phenomenon was observed for high sulfur contents. The rate constant may be represented by the following equation: $$ k_C = \frac{{k^\circ }}{{1 + K_S a_S }} + \frac{{K_S a_S k_r }}{{1 + K_S a_S }}$$ wherek ^o ,k _r,K _s, anda _s are the bare surface rate constant, residual rate constant, adsorption coefficient for sulfur, and activity of sulfur in the metal, respectively. The second term in the rate equation represents the rate of dissociation on the adsorbed sulfur. The rate constants and adsorption coefficient were determined as functions of temperature to be $$\begin{gathered} log k^\circ = \frac{{ - 12,000}}{T} + 2.95 (mole/cm^2 s atm) \hfill \\ log k_r = \frac{{ - 14,000}}{T} + 3.45 (mole/cm^2 s atm) \hfill \\ log K_S = \frac{{ - 1800}}{T} + 1.04 \hfill \\ \end{gathered} $$      

Nitrogen diffusion and solubility in tungsten

The diffusion and solubility of nitrogen in tungsten were determed using an ultrahigh vacuum-and mass-spectrometric technique capable of measuring concentrations of 10^?2 ppm and degassing rates of 10^?3 ppm N per hr. The technique is based on measuring the degassing rate of nitrogen as a function of time from a resistivity heated tungsten wire previously engassed with nitrogen between 1 and 25 torr. The diffusion and solubility constants between 1000° and 1800°C may be summarized by $$D = (2.37 \pm 0.43) \times 10^{ - 3} \exp [( - 35,800 \pm 3900)/RT] cm^2 /\sec ,$$ , and $$S = (0.21 \pm 0.06) \exp [( - 17,600 \pm 5900)/RT] torr \cdot liter cm^{ - 3} torr^{ - 1/2} .$$ . The concentration of nitrogen in tungsten at 760 torr according to these results are 0.4 and 9.2 ppm at 1000° and 2000°C, respectively. The expression for the permeation constants calculated fromD andS is $$K = 5 \times 10^{ - 4} \exp ( - 53,400/RT) torr \cdot liter cm^{ - 1} sec^{ - 1} torr^{ - 1/2} .$$ .     

Iron redox equilibria in CaO-Al2O3-SiO2 and MgO-CaO-Al2O3-SiO2 slags

Measurements have been made of the ratio of ferric to ferrous iron in CaO-Al₂O₃-SiO₂ and MgO-CaO-Al₂O₃-SiO₂ slags at oxygen activities ranging from equilibrium with pCO₂/pCO≈0.01 to as high as air at temperatures of 1573 to 1773 K. At 1773 K, values are given by $\begin{gathered} \log {\text{ }}\left( {\frac{{Fe^{3 + } }}{{Fe^{2 + } }}} \right) = 0.3( \pm {\text{ }}0.02){\text{ }}Y + {\text{ }}0.45( \pm {\text{ }}0.01){\text{ }}\log \hfill \\ \left( {\frac{{pCO_2 }}{{pCO}}} \right) - 1.24( \pm {\text{ }}0.01) \hfill \\ \end{gathered} $ where Y=(CaO+MgO)/SiO₂, for melts with the molar ratio of CaO/SiO₂=0.45 to 1.52, 10 to 15 mol pct Al₂O₃, up to 12 mol pct MgO (at CaO/SiO₂≈1.5), and with 3 to 10 wt pct total Fe. Available evidence suggests that, to a good approximation, these redox equilibria are independent of temperature when expressed with respect to pCO₂/pCO, probably from about 1573 to 1873 K. Limited studies have also been carried out on melts containing about 40 mol pct Al₂O₃, up to 12 mol pct MgO (at CaO/SiO₂≈1.5), and 3.6 to 4.7 wt pct Fe. These show a strongly nonideal behavior for the iron redox equilibrium, with $\frac{{Fe^{3 + } }}{{Fe^{2 + } }} \propto \left( {\frac{{pCO_2 }}{{pCO}}} \right)^{0.37} $ The nonideal behavior and the effects of basicity and Al₂O₃ concentration on the redox equilibria are discussed in terms of the charge balance model of alumino-silicates and the published structural information from Mössbauer and NMR (Nuclear Magnetic Resonance) spectroscopy of quenched melts.     

The Solubility and Diffusivity of Fluorine in Solid Copper from Electrochemical Measurements

The solubility and diffusivity of fluorine in solid copper were determined electrochemically using the double solid-state cell $$Ni + NiF_2 \left| {CaF_2 } \right|Cu\left| {CaF_2 } \right|Ni + NiF_2 .$$ In the temperature range 757 to 920°C, the diffusivity of fluorine in solid copper was found to be $$D_F \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. \kern-\nulldelimiterspace} s}} \right) = 9.32 \times 10^{ - 2} \exp \left( {\frac{{ - 98,910 {J \mathord{\left/ {\vphantom {J {mole}}} \right. \kern-\nulldelimiterspace} {mole}}}} {{RT}}} \right).$$ . The results obtained for the dissolution of fluorine as atoms in solid copper showed large scatter. However, the equilibrium dissolution of fluorine follows Sieverts’ law. Above the melting point (770°C) of CuF₂, the mean solubility of fluorine in solid copper, for the equilibrium Cu(s)+ CuF ₂(l), follows the relationship $$N_F^s (atom fraction) = 0.98 \exp \left( {\frac{{ - 79,500 {J \mathord{\left/ {\vphantom {J {mole}}} \right. \kern-\nulldelimiterspace} {mole}}}} {{RT}}} \right).$$      

Mass spectrometric determination of activities for alloys with complex vapor species: Bi-Pb and Bi-Tl

For solutions from which complex species vaporize (Bi₂, Si₂, Al₂O, Sb₄, and so forth) new methods of determining the thermodynamic properties from mass spectrometric data are demonstrated. In order to test the feasibility of these new techniques, experiments have been carried out on the liquid Bi-Pb and Bi-Tl systems for which adequate thermodynamic data are available. In evaluating the thermodynamic properties, the ion current ratiosI _Pb ⁺/IBi₂/+ andI _Tl ⁺/IBi₂/+ were employed,e.g. $$\log {\text{ }}\gamma _{{\text{Bi}}} {\text{ = - }}\mathop {\int {\frac{{N_{Pb} }}{{1{\text{ + }}N_{Pb} }}d} }\limits_{N_{Bi} = 1}^{N_{{\text{Bi}}} = N_{Bi} } {\text{ }}\left\{ {{\text{log}}\frac{{{\text{1}}_{{\text{Pb}}}^{\text{ + }} {\text{ }}N_{Bi}^2 }}{{I_{Bi2}^ + {\text{ }}N_{Pb} }}} \right\}$$ Measuring these particular ion current ratios eliminates errors resulting from the fragmentation of the complex vapor species in evaluating the thermodynamic properties. A dimer-monomer technique, which corrects for fragmentation, was also demonstrated. The results using these two independent approaches are in good agreement with each other as well as with previous investigations. The activity coefficients in both systems adhere to the quadratic formalism over large composition ranges,e.g. $$\begin{gathered} \log {\text{ }}\gamma _{{\text{Pb}}} {\text{ = - 0}}{\text{.255 }}N_{Bi}^2 {\text{ }}N_{{\text{Bi}}} {\text{< 0}}{\text{.8}} \hfill \\ \log {\text{ }}\gamma _{{\text{Tl}}} {\text{ = - 0}}{\text{.805 }}N_{Bi}^2 {\text{ }}N_{{\text{Bi}}} {\text{< 0}}{\text{.7}} \hfill \\ \end{gathered} $$      

Ti3Ga and αTi interdiffusion between 660° and 860°C

Diffusion experiments were conducted in vacuum with bimetallic couples of the Ti₃Ga (α₂) composition and unalloyed α titanium. The gallium-composition profiles after various timetemperature exposures were determined by microprobe analyzer transverses and evaluated by established techniques. Results from this evaluation include the definition of the α to α +α₂ and the α + α₂ to α₂ phase boundaries for the Ti?Ga system and the determination of the interdiffusion coefficients for gallium in the α Ti and Ti₃Ga (α₂) phases. The interdiffusion coefficients were found to conform to the relationships: $$\tilde D_{\alpha Ti} = 4.4 \times 10^{ - 4} \exp [ - (43.4 \pm 4.7)10^3 /RT]cm^2 /\sec $$ $$\tilde D_{\alpha Ti_3 Ga} = 7.4 \times 10^{ - 5} \exp [ - (43.8 \pm 10.7)10^3 /RT]cm^2 /\sec $$      

Mass-spectrometric determination of activities in Fe−Cr and Fe−Cr−Ni alloys

The Knudsen cell-mass spectrometer combination has been used to study the Fe?Cr system and some Fe?Cr?Ni liquid alloys. The Fe?Cr liquid alloys at 1600°C are found to be essentially ideal when referred to pure liquids as standard states. Phase equilibria over a limited composition range for this system are derived from the behavior of the ion-current ratios. The necessary equations are derived to apply the integration technique to the measured ion current ratios in a ternary system and the method is applied to the Fe?Cr?Ni system at 1600°C. The results are represented, within experimental error, by the following equations: forN _Fe≥0.6, $$\begin{gathered} ln \gamma _{Fe} = - 0.08 N_{Ni}^2 \hfill \\ \ln \gamma _{Cr} = 0.09 - 0.08 N_{Ni}^2 \hfill \\ \ln \gamma _{Ni} = - 0.26 - 0.08(1 - N_{Ni} )^2 \hfill \\ \end{gathered} $$ forN _Fe=0.45, $$\begin{gathered} \ln \gamma _{Fe} = - 0.20 N_{Ni}^2 \hfill \\ \ln \gamma _{Cr} = 0.09 - 0.20 N_{Ni}^2 \hfill \\ \ln \gamma _{Ni} = - 0.19 - 0.20(1 - N_{Ni} )^2 \hfill \\ \end{gathered} $$      

Enthalpy of mixing of liquid Ni-Zr and Cu-Ni-Zr alloys

The partial (Δ and the integral (ΔH) enthalpies of mixing of liquid Ni-Zr and Cu-Ni-Zr alloys have been determined by high-temperature isoperibolic calorimetry at 1565 ± 5 K. The heat capacity (C _p) of liquid Ni₂₆Zr₇₄ has been measured by adiabatic calorimetry (C _p=53.5±2.2 J mol⁻¹ K⁻¹ at 1261±15 K). The integral enthalpy of mixing changes with composition from a small positive (Cu-Ni, ΔH (x _Ni=0.50, T=1473 to 1750 K)=2.9 kJ mol⁻¹) to a moderate negative (Cu-Zr; ΔH(x _Zr=0.46, T=1485 K)=−16.2 kJ mol⁻¹) and a high negative value (Ni-Zr; ΔH(x _Zr=0.37, T=1565 K)=−45.8 kJ mol⁻¹). Regression analysis of new data, together with the literature data for liquid Ni-Zr alloys, results in the following relationships in kJ mol⁻¹ (standard states: Cu (1), Ni (1), and Zr (1)):for Ni-Zr (1281≤T≤2270 K),

The Diffusion Coefficient of Scandium in Dilute Aluminum-Scandium Alloys

The diffusion coefficient of Sc in dilute Al-Sc alloys has been determined at 748 K, 823 K, and 898 K (475 °C, 550 °C, and 625 °C, respectively) using semi-infinite diffusion couples. Good agreement was found between the results of the present study and both the higher temperature, direct measurements and lower temperature, indirect measurements of these coefficients reported previously in the literature. The temperature-dependent diffusion coefficient equation derived from the data obtained in the present investigation was found to be \( D \left( {{\text{m}}^{2} /{\text{s}}} \right) = \left( {2.34 \pm 2.16} \right) \times 10^{ - 4} \left( {{\text{m}}^{2} /{\text{s}}} \right) { \exp }\left( {\frac{{ - \left( {167 \pm 6} \right) \left( {{\text{kJ}}/{\text{mol}}} \right)}}{RT}} \right). \) Combining these results with data from the literature and fitting all data simultaneously to an Arrhenius relationship yielded the expression \( D \left( {{\text{m}}^{2} /{\text{s}}} \right) = \left( {2.65 \pm 0.84} \right) \times 10^{ - 4} \left( {{\text{m}}^{2} /{\text{s}}} \right) { \exp }\left( {\frac{{ - \left( {168 \pm 2} \right) \left( {{\text{kJ}}/{\text{mol}}} \right)}}{RT}} \right). \) In each equation given above, R is 0.0083144 kJ/mol K, T is in Kelvin, and the uncertainties are ±1 standard error.     

Alumina solubility in molten salt systems of interest for aluminum electrolysis and related phase diagram data

The solubility of alumina in molten Na₃AlF₆ containing various amounts of AlF₃, CaF₂, and LiF was determined by measuring the weight loss of a rotating sintered corundum disc. The results were fitted to the following empirical expression: 1 $$ [Al_2 O_3 ]_{sat} = A\left( {\frac{t} {{1000}}} \right)^B $$ where 2 $$ \begin{gathered} A = 11.9 - 0.062[AlF_3 ] - 0.003[AlF_3 ]^2 - 0.50[LiF] \hfill \\ - 0.20[CaF_2 ] - 0.30[MgF_2 ] + \frac{{42[LiF] \cdot [AlF_3 ]}} {{2000 + [LiF] \cdot [AlF_3 ]}} \hfill \\ B = 4.8 - 0.048[AlF_3 ] + \frac{{2.2[LiF]^{1.5} }} {{10 + [LiF] + 0.001[AlF_3 ]^3 }} \hfill \\ \end{gathered} $$ where the square brackets denote weight percent of components in the system Na₃AlF₆-Al₂O₃ (sat)-AlF₃-CaF₂-MgF₂-LiF and t is the temperature in degree Celsius. The standard deviation between the equation and the experimental points in the temperature range from 1050 °C to about 850 °C was found to be 0.29 wt pct Al₂O₃. A series of revised phase diagram data of interest for aluminum electrolysis was derived based on the present work and recently published data for primary crystallization of Na₃AlF₆ in the same systems.     

Thermodynamics of iron-aluminum alloys at 1573 K

The activities of iron (Fe) and aluminum (Al) were measured in Fe-Al alloys at 1573 K using the ion-current-ratio technique in a high-temperature Knudsen cell mass spectrometer. The Fe-Al solutions exhibited negative deviations from ideality over the entire composition range. The activity coefficientsγ _Fe, andγ _A1 are given by the following equations as a function of mole fraction (x _Fe,x _Al): 1 $$\begin{gathered} 0< \chi _{A1}< 0.4 \hfill \\ ln \gamma _{Fe} = - 4.511 ( \pm 0.008)\chi _{A1}^2 \hfill \\ ln \gamma _{A1} = - 4.462 ( \pm 0.029)\chi _{Fe}^2 + 0.325( \pm 0.013) \hfill \\ 0.6< \chi _{A1}< 1.0 \hfill \\ ln \gamma _{Fe} = - 4.065 ( \pm 0.006)\chi _{A1}^2 + 0.099( \pm 0.003) \hfill \\ ln \gamma _{A1} = - 4.092 ( \pm 0.026)\chi _{Fe}^2 + 0.002( \pm 0.001) \hfill \\ \end{gathered} $$ The results showed good agreement with those obtained from previous investigations at other temperatures by extrapolation of the activity data to 1573 K.     

Determination of standard gibbs energies of formation of Fe2Mo3O12, Fe2Mo3O8, Fe2MoO4, and FeMoO4 of the Fe-Mo-O ternary system and μ phase of the Fe-Mo binary system by electromotive force measurement using a Y2O3-stabilized ZrO2 solid electrolyte

The standard Gibbs energies of formation of Fe₂Mo₃O₁₂, Fe₂Mo₃O₈, FeMoO₄, and Fe₂MoO₄ of the Fe-Mo-O ternary system and the μ phase of the Fe-Mo binary system have been determined by measuring electromotive forces of galvanic cells having an Y₂O₃-stabilized ZrO₂ solid electrolyte. The results are as follows: $$\begin{gathered} \Delta _f G^\circ (FeMoO_4 )/kJ \cdot mol^{ - 1} = - 1053.5 + 0.2983(T/K) \pm 0.4 \hfill \\ Temperature range: 1112 to 1339 K \hfill \\ \Delta _f G^\circ (Fe_2 Mo_3 O_8 )/kJ \cdot mol^{ - 1} = - 2347 + 0.6814(T/K) \pm 1 \hfill \\ Temperature range: 1112 to 1339 K \hfill \\ \Delta _f G^\circ (Fe_2 Mo_3 O_{12} )/kJ \cdot mol^{ - 1} = - 2993 + 0.9105(T/K) \pm 2 \hfill \\ Temperature range: 1040 to 1145 K \hfill \\ \Delta _f G^\circ (Fe_{0.58} Mo_{0.42} )/kJ \cdot mol^{ - 1} = - 18.7 + 0.0117(T/K) \pm 0.1 \hfill \\ Temperature range: 1162 to 1223 K \hfill \\ \Delta _f G^\circ (Fe_2 MoO_4 )/kJ \cdot mol^{ - 1} = - 1174 + 0.342(T/K) \pm 1 \hfill \\ Temperature range: 1243 to 1466 K \hfill \\ \end{gathered} $$ where the standard pressure is 1 bar (100 kPa).     

Controversy on the free energy of formation of CaO—Additional evidence in support of thermochemical data

The standard free energies of formation of CaO derived from a variety of high-temperature equilibrium measurements made by seven groups of experimentalists are significantly different from those given in the standard compilations of thermodynamic data. Indirect support for the validity of the compiled data comes from new solid-state electrochemical measurements using single-crystal CaF₂ and SrF₂ as electrolytes. The change in free energy for the following reactions are obtained: $$\begin{gathered} CaO + MgF_2 \to MgO + CaF_2 \hfill \\ \Delta G^ \circ = - 68,050 - 2.47 T( \pm 100) J mol^{ - 1} \hfill \\ SrO + CaF_2 \to SrF_2 + CaO \hfill \\ \Delta G^ \circ = - 35,010 + 6.39 T( \pm 80) J mol^{ - 1} \hfill \\ \end{gathered} $$ The standard free energy changes associated with cell reactions agree with data in standard compilations within ±4 kJ mol^?1. The results of this study do not support recent suggestions for a major revision in thermodynamic data for CaO.     

Thermodynamic properties of the Cu−Sn and Cu−Au systems by mass spectrometry

The activities and partial molar heats of mixing have been determined in the liquid Cu?Sn system at 1320°C and the liquid Cu?Au system at 1460°C. The experimental technique consisted of the analysis of Knudsen cell effusates with a T.O.F. mass spectrometer. The ion current ratio for the alloy components was measured for each system over a range of temperature and composition and the thermodynamic values calculated by a modified Gibbs-Duhem equation. Both systems exhibited negative deviations from ideal behavior. The results can be partially represented by the equations $$\begin{gathered} \log \gamma _{Cu} = - 0.0175x^2 _{Sn} - 0.302 (0 \leqslant x_{Cu} \leqslant 0.20) \hfill \\ log \gamma _{Sn} = - 0.342x^2 _{Cu} + 1.084(0 \leqslant x_{Sn} \leqslant 0.20) \hfill \\ \end{gathered} $$ for the Cu?Sn system at 1320°C and by $$\begin{gathered} \log \gamma _{Cu} = - 0.703x^2 _{Au} - 0.083(0 \leqslant x_{Cu} \leqslant 0.52) \hfill \\ \log \gamma _{Au} = - 1.057x^2 _{Cu} + 0.098(0 \leqslant x_{Au} \leqslant 0.47) \hfill \\ \end{gathered} $$ for the Cu?Au system at 1460°C.     

Influence of chromium and nickel on the dissociation of CO2 on carbon-saturated liquid iron

At 1600 °C, under conditions where the rate was not significantly affected by liquid-phase or gasphase mass transfer, the rate of dissociation of CO₂ was determined from the rate of decarburization of iron-based carbon-saturated melts containing varying amounts of chromium and nickel. The rate was determined by monitoring the change in reacted gas composition with an in-line spectrometer. The results indicate that neither chromium nor nickel had a strong effect on the kinetics of dissociation of CO₂ on the surface of the melt. Sulfur was found to significantly decrease the rate, as is the case for alloys without chromium or nickel, and the rate constant is given by $$k = \frac{{k^0 }}{{1 + K_s a_s }} + k_r $$ where k ⁰ denotes the chemical rate on pure iron, K _s is the adsorption coefficient of sulfur, a _s is the activity of sulfur corrected for Cr, and k _r represents the residual rate at a high sulfur level. The rate constants and adsorption coefficient were determined to be: $$\begin{array}{*{20}c} {k^0 = 1.8 \times 10^{ - 3} mol/cm^2 s atm} \\ {k_r = 6.1 \times 10^{ - 5} mol/cm^2 s atm} \\ {K_s = 330 \pm 20} \\ \end{array} $$ Experiments run at lower carbon contents showed that only a very small quantity of chromium was oxidized, immediately forming a protective layer. However, this oxidation occurred at a higher carbon content (2 pct) than what was expected from the thermodynamics.