Tie lines and activities in the system NiO-MgO-SiO2 at 1373 K

The isothermal section of the phase diagram for the system NiO-MgO-SiO₂ at 1373 is established. The tie lines between (Ni_xMg_1-x )O solid solution with rock salt structure and orthosilicate solid solution (Ni_yMg_1-y)Si_0.5O₂ and between orthosilicate and metasilicate (Ni_zMg_1-z)SiO₃ crystalline solutions are determined using electron probe microanalysis (EPMA) and lattice parameter measurement on equilibrated samples. Although the monoxides and orthosilicates of Ni and Mg form a continuous range of solid solutions, the metasilicate phase exists only for 0 < Z < 0.096. The activity of NiO in the rock salt solid solution is determined as a function of composition and temperature in the range of 1023 to 1377 using a solid state galvanic cell. The Gibbs energy of mixing of the monoxide solid solution can be expressed by a pseudo-subregular solution model: ΔG^ex = X(l - X)[(-2430 + 0.925T)X + (-5390 + 1.758T)(1 - X)] J/mol. The thermodynamic data for the rock salt phase are combined with information on interphase partitioning of Ni and Mg to generate the mixing properties for the orthosilicate and the metasilicate solid solutions. The regular solution model describes the orthosilicate and the metasilicate solid solutions at 1373 K within experimental uncertainties. The regular solution parameter ΔG^ex/Y(1-Y) is -820 (±70) J/mol for the orthosilicate solid solution. The corresponding value for the metasilicate solid solution is -220 (±150) J/mol. The derived activities for the orthosilicate solid solution are discussed in relation to the intracrystalline ion exchange equilibrium between Ml and M2 sites. The tie line information, in conjunction with the activity data for orthosilicate and metasilicate solid solutions, is used to calculate the Gibbs energy changes for the intercrystalline ion exchange reactions. Combining this with the known data for NiSi_0.5O₂, Gibbs energies of formation of MgSi_0.5O₂, MgSiO₃, and metastable NiSiO₃ are calculated. The Gibbs energy of formation of NiSiO₃, from its component oxides, is equal to 7.67 (±0.6)kJ/mol at 1373K.     

The gallium-iron system: Enthalpy of formation in liquid state

Through the use of a very high-temperature, automated calorimeter, the enthalpy of formation, Δ_f H=f(X _Fe), of the Fe-Ga liquid system was measured in the temperature and molar fraction ranges 0<X _Fe< 0.591 and 1373 <T< 1573 whereT is inK. The molar enthalpies of formation of these liquid alloys are negative with an extremum point atX _Fe = 0.55 and Δ_f H = -5.9 ± 0.6 kj/mol (all results are referred to the liquid state). From measurements performed on the Ga-rich mole fraction side, the limiting partial molar enthalpy was deduced Δh _m ⁰ (Fe_L in Ga_L) = -2 ± 0.2 kJ/mol. These results were compared with those obtained previously for the two similar systems, Ni-Ga and Co-Ga. Moreover a point of the liquidus line was obtained (X _Fe = 0.48 atT = 1466 K).     

Thermodynamic properties and phase equilibria in the Cr-P system

A Knudsen effusion method with mass-spectrometric analysis of gaseous phase has been applied to investigate the thermodynamic properties of the chromium phosphides (1341 to 1704 K) and Cr-P liquid alloys (1664 to 1819 K). Simultaneously, DSC has been used to measure heat capacities of chromium phosphides Cr₃P and Cr₁₂P₇ in the temperature range of113 to 873 K. The entropies of formation of chromium phosphides calculated according to the second and third laws of thermodynamics agree within the limits of experimental error. The Gibbs energies of formation of the phosphides from solid Cr and P₂ gas have been approximated with the following equations (in J/mol): A_fG⁰(Cr₃P) = −(244 112 ±2800) + (70.95 ±1.80)T ΔG⁰(Cr₁₂2P₇) = −(1563 678 ±15 350) + (440.6 ±9.90)T Thermodynamic properties of liquid solutions have been described with the ideal associated-solution model assuming that CrP, Cr₂P, Cr₃P, and Cr₃P₂ complexes exist in the melt. The phase diagram computed with the help of the thermodynamic data agrees with the published information.     

Tie lines and activities in the system NiO-MgO-SiO2 at 1373 K

The isothermal section of the phase diagram for the system NiO-MgO-SiO₂ at 1373 is established. The tie lines between (Ni_xMg_1-x )O solid solution with rock salt structure and orthosilicate solid solution (Ni_yMg_1-y)Si_0.5O₂ and between orthosilicate and metasilicate (Ni_zMg_1-z)SiO₃ crystalline solutions are determined using electron probe microanalysis (EPMA) and lattice parameter measurement on equilibrated samples. Although the monoxides and orthosilicates of Ni and Mg form a continuous range of solid solutions, the metasilicate phase exists only for 0 < Z < 0.096. The activity of NiO in the rock salt solid solution is determined as a function of composition and temperature in the range of 1023 to 1377 using a solid state galvanic cell. The Gibbs energy of mixing of the monoxide solid solution can be expressed by a pseudo-subregular solution model: ΔG^ex = X(l - X)[(-2430 + 0.925T)X + (-5390 + 1.758T)(1 - X)] J/mol. The thermodynamic data for the rock salt phase are combined with information on interphase partitioning of Ni and Mg to generate the mixing properties for the orthosilicate and the metasilicate solid solutions. The regular solution model describes the orthosilicate and the metasilicate solid solutions at 1373 K within experimental uncertainties. The regular solution parameter ΔG^ex/Y(1-Y) is -820 (±70) J/mol for the orthosilicate solid solution. The corresponding value for the metasilicate solid solution is -220 (±150) J/mol. The derived activities for the orthosilicate solid solution are discussed in relation to the intracrystalline ion exchange equilibrium between Ml and M2 sites. The tie line information, in conjunction with the activity data for orthosilicate and metasilicate solid solutions, is used to calculate the Gibbs energy changes for the intercrystalline ion exchange reactions. Combining this with the known data for NiSi_0.5O₂, Gibbs energies of formation of MgSi_0.5O₂, MgSiO₃, and metastable NiSiO₃ are calculated. The Gibbs energy of formation of NiSiO₃, from its component oxides, is equal to 7.67 (±0.6)kJ/mol at 1373K.     

Optimization of the binary Ge-Ru system

After an experimental study of its phase equilibria by DTA and XRD and thermody namic properties by direct synthesis calorimetry, the Ge-Ru system has been numerically assessed with help of the program Nancy Un. The experimental enthalpies of formation are: Ge_0.6Ru_0.4:δ_f H(1173K) =-34.8 (±1.0) kj/mol-atoms Ge_o.5Ru_o.5:δ_f H(1173K) = -28.7 (±13) kj/mol-atoms The comparison between computation and experimental results leads to new ideas about this system. The liquid phase cannot be described perfectly with a polynomial expansion to the third power, and it seems that associations could explain this behavior.     

Diagrams of Chemical and Electrochemical Stability of Thermal-Diffusion Zinc Coatings

Cutsets are calculated for the Zn-Fe-O system phase diagram at 700 and 298 K and the Zn-Fe-H₂O system potential-pH diagram at 298 K, 1 atm (air), and a _i = 10⁻⁶ mol/l with zinc excess (C _Zn ^al > C _Zn ^cr ) or deficiency (C _Zn ^al < C _Zn ^cr ) in the alloy surface layer of the Zn-Fe alloy. Thermodynamics of corrosion-electrochemical behavior of different phases in thermal-diffusion zinc coatings are discussed. __________ Translated from Zashchita Metallov, Vol. 41, No. 5, 2005, pp. 508–514. Original Russian Text Copyright ? 2005 by Tyurin, Galin.     

Assessment of the Te-Tl (tellurium-thallium) system

The optimized thermodynamic data for the Te- TI binary system have been obtained by the computer operated least squares method from measured data. The Gibbs energy of the liquid phase was modeled as a two- sublattice model for ionic melt after Hillert.³¹ The intermediate compounds, Te₃Tl{2}and TeTl, were treated as stoichiometric phases, and the nonstoichiometric γ phase was expressed as a sublattice model. A strong tendency for chemical short- range order in the liquid state at the composition close to TeTh was confirmed by calculated results, but the existence of the TeTh phase was not justified. The experimental thermodynamic and phase diagram data were closely reproduced by the optimized thermodynamic data. Parameters describing the Gibbs energies of all the phases in this calculation and the calculated phase diagram and thermodynamic functions are presented and compared with experimental information.     

Assessment of the Te-Tl (tellurium-thallium) system

The optimized thermodynamic data for the Te- TI binary system have been obtained by the computer operated least squares method from measured data. The Gibbs energy of the liquid phase was modeled as a two- sublattice model for ionic melt after Hillert.³¹ The intermediate compounds, Te₃Tl{2}and TeTl, were treated as stoichiometric phases, and the nonstoichiometric γ phase was expressed as a sublattice model. A strong tendency for chemical short- range order in the liquid state at the composition close to TeTh was confirmed by calculated results, but the existence of the TeTh phase was not justified. The experimental thermodynamic and phase diagram data were closely reproduced by the optimized thermodynamic data. Parameters describing the Gibbs energies of all the phases in this calculation and the calculated phase diagram and thermodynamic functions are presented and compared with experimental information.     

Surface tension and thermodynamic properties of liquid Ag-Bi solutions

With the maximum bubble pressure method, the density and surface tension were measured for five Ag-Bi liquid alloys (X _Bi=0.05, 0.15, 0.25, 0.5, and 0.75), as well as for pure silver. The experiments were performed in the temperature range 544–1443 K. Linear dependences of both density and surface tension versus temperature were observed, and therefore the experimental data were described by linear equations. The density dependence on concentration and temperature was derived using the polynomial method. A similar dependence of surface tension on temperature and concentration is presented. Next, the Gibbs energy of formation of solid Bi₂O₃, as well as activities of Bi in liquid Ag-Bi alloys, were determined by a solid-state electromotive force (emf) technique using the following galvanic cells: Ni, NiO, Pt/O ⁻²/W, Ag _X Bi _(1−X), Bi ₂ O _3(s). The Gibbs energy of formation of solid Bi₂O₃ from pure elements was derived: =−598 148 + 309.27T [J · mol⁻¹] and =−548 008 + 258.94T [J · mol⁻¹]; the temperature and the heat of the α → δ transformation for this solid oxide were calculated as 996 K and 50.14 J · mol⁻¹. Activities of Bi in the liquid alloys were determined in the temperature range from 860–1075 K, for five Ag-Bi alloys (X _Ag=0.2, 0.35, 0.5, 0.65, 0.8), and a Redlich-Kister polynomial expansion was used to describe the thermodynamic properties of the liquid phase. Using Thermo-Calc software, the Ag-Bi phase diagram was calculated. Finally, thermodynamic data were used to predict surface tension behavior in the Ag-Bi binary system.     

Thermodynamic properties and phase equilibria in the silicon-phosphorous system

Knudsen effusion mass spectrometry and a static method were used to study the vapor composition and the thermodynamic properties of the Si-P melt with the phosphorous content from 0.09 to 26.5 at.% in the temperature range 1507 to 1831 K. A representative file of experimental data comprising about 100 values of phosphorus activity at various concentrations and/or temperatures was obtained. The thermodynamic characteristics as functions of temperature and concentration were approximated by the ideal associated-solution model under the assumption that SiP and Si₂P complexes exist in the melt. The boundaries of the region of liquid phase stability on the phase diagram were computed, and agreement with the available experimental information was obtained.     

Thermodynamic properties and phase equilibria in the silicon-phosphorous system

Knudsen effusion mass spectrometry and a static method were used to study the vapor composition and the thermodynamic properties of the Si-P melt with the phosphorous content from 0.09 to 26.5 at.% in the temperature range 1507 to 1831 K. A representative file of experimental data comprising about 100 values of phosphorus activity at various concentrations and/or temperatures was obtained. The thermodynamic characteristics as functions of temperature and concentration were approximated by the ideal associated-solution model under the assumption that SiP and Si₂P complexes exist in the melt. The boundaries of the region of liquid phase stability on the phase diagram were computed, and agreement with the available experimental information was obtained.     

Vapor pressure measurements of arsenic and arsenic trioxide over condensed phases

The solid-vapor relations for arsenic in the temperature range from 680 to 840 K and the liquid-vapor relations for arsenic trioxide in the temperature range from 650 to 740 K were determined by direct vapor pressure measurements carried out with a quartz gauge. The resulting InP (total) vsT are : InP (atm) = 2545.1/T + 22.27 InT− 154.02 (for arsenic) and InP (atm) = −50983/T + 6.869 (for arsenic trioxide). Calculated enthalpy of vaporization (ΔH_v,T ⁰) for arsenic trioxide and enthalpy of sublimation (ΔH_s,298 ⁰) for arsenic are 42.36 kJ/mol and 156.13 kJ/mol, respectively.     

Thermodynamic properties and phase equilibria in the Si-B system

The vapor composition and thermodynamic properties of Si-B alloys with boron content from 1.5 up to 100 at.% were investigated in the temperature interval of 1522 to 1880 K by Knudsen effusion mass spectrometry. Thermodynamic functions of the SiB₆ and SiB _n borides, primary solid solutions, and liquid solution were obtained. The thermodynamic functions of the Si-B melt were approximated by the ideal associated-solutions model under the assumption that only one complex, SiB₃, existed. The established thermodynamic functions of the melt and of the SiB₆ and SiB _n compounds were used for computation of the phase diagram of the Si-B system. Good agreement with the available experimental data was obtained.     

Surface tension and thermodynamic properties of liquid Ag-Bi solutions

With the maximum bubble pressure method, the density and surface tension were measured for five Ag-Bi liquid alloys (X _Bi=0.05, 0.15, 0.25, 0.5, and 0.75), as well as for pure silver. The experiments were performed in the temperature range 544–1443 K. Linear dependences of both density and surface tension versus temperature were observed, and therefore the experimental data were described by linear equations. The density dependence on concentration and temperature was derived using the polynomial method. A similar dependence of surface tension on temperature and concentration is presented. Next, the Gibbs energy of formation of solid Bi₂O₃, as well as activities of Bi in liquid Ag-Bi alloys, were determined by a solid-state electromotive force (emf) technique using the following galvanic cells: Ni, NiO, Pt/O ⁻²/W, Ag _X Bi _(1−X), Bi ₂ O _3(s). The Gibbs energy of formation of solid Bi₂O₃ from pure elements was derived: =−598 148 + 309.27T [J · mol⁻¹] and =−548 008 + 258.94T [J · mol⁻¹]; the temperature and the heat of the α → δ transformation for this solid oxide were calculated as 996 K and 50.14 J · mol⁻¹. Activities of Bi in the liquid alloys were determined in the temperature range from 860–1075 K, for five Ag-Bi alloys (X _Ag=0.2, 0.35, 0.5, 0.65, 0.8), and a Redlich-Kister polynomial expansion was used to describe the thermodynamic properties of the liquid phase. Using Thermo-Calc software, the Ag-Bi phase diagram was calculated. Finally, thermodynamic data were used to predict surface tension behavior in the Ag-Bi binary system.     

Thermodynamic properties and phase equilibria in the Si-B system

The vapor composition and thermodynamic properties of Si-B alloys with boron content from 1.5 up to 100 at.% were investigated in the temperature interval of 1522 to 1880 K by Knudsen effusion mass spectrometry. Thermodynamic functions of the SiB₆ and SiB _n borides, primary solid solutions, and liquid solution were obtained. The thermodynamic functions of the Si-B melt were approximated by the ideal associated-solutions model under the assumption that only one complex, SiB₃, existed. The established thermodynamic functions of the melt and of the SiB₆ and SiB _n compounds were used for computation of the phase diagram of the Si-B system. Good agreement with the available experimental data was obtained.     

Vapor pressure measurements of arsenic and arsenic trioxide over condensed phases

The solid-vapor relations for arsenic in the temperature range from 680 to 840 K and the liquid-vapor relations for arsenic trioxide in the temperature range from 650 to 740 K were determined by direct vapor pressure measurements carried out with a quartz gauge. The resulting InP (total) vsT are : InP (atm) = 2545.1/T + 22.27 InT− 154.02 (for arsenic) and InP (atm) = −50983/T + 6.869 (for arsenic trioxide). Calculated enthalpy of vaporization (ΔH_v,T ⁰) for arsenic trioxide and enthalpy of sublimation (ΔH_s,298 ⁰) for arsenic are 42.36 kJ/mol and 156.13 kJ/mol, respectively.     

Hot deformation behavior of Mg-7.22Gd-4.84Y-1.26Nd-0.58Zr magnesium alloy

The behavior evolvement of Mg-7.22Gd-4.84Y-1.26Nd-0.58Zr(GWN751K) magnesium alloy during the hot deformation process was discussed.The flow stress behavior of the magnesium alloy over the strain rate range of 0.002 to 2.000 s-1 and in the temperature range of 623 to 773 K was studied on a Gleeble-1500D hot simulator under the maximum deformation degree of 60%.The experimental results showed that the relationship between stress and strain was obviously affected by strain rate and deformation temperature.The flow stress of GWN751K magnesium alloy during high temperature deformation could be represented by the Zener-Hollomon parameter in the hyperbolic Arrhenius-type equation.The stress exponent n and deformation activation energy Q were evaluated by linear regression analysis.The stress exponent n was fitted to be 3.16.The hot deformation activation energy of the alloy during hot deformation was 230.03 kJ/mol.The microstructures of hot deformation were also influenced by strain rate and compression temperature strongly.It was found that the alloy could be extruded at 723 K with the mechanical properties of σ0.2 = 260 MPa,σb = 320 MPa,and δ = 18%.     

Thermodynamics of the liquid Co-Cu system and calculation of phase diagram

Knudsen-cell mass spectrometric measurements have been carried out in the liquid phase of the Co-Cu system in the concentration range 25.0 to 85.9 at. % Cu in the temperature range 1347 to 1587 °C. The molar excess Gibbs energy, enthalpy and entropy of mixing, as well as the thermodynamic activities of components in the liquid Co-Cu system were determined using the composition and temperature dependence of the ratio of intensities of ⁵⁹Co and ⁶³Cu ions. The results show that a subregular solution model would fit measured data well (2-parameter thermodynamically adapted power (TAP) series: C _n ^H in J·mol⁻¹; C ₁ ^H =35,961, C ₂ ^H =−5573.2; C _n ^S in J·mol^−1·K−1; C ₁ ^S =5.54, C ₂ ^S =−3.35). A special experiment verified solid-liquid phase equilibrium at 1327 °C and the phase diagram was calculated.     

Thermodynamic Interactions of Si and Ti in Liquid Cu

The activity coefficients of titanium in liquid Cu-Ti at 1623 and 1673 K were measured by equilibrating the liquids with Ti₃O₅ in a oxygen partial pressure controlled by C(s)/CO(g) equilibrium. Furthermore, the thermodynamic interaction parameter of silicon on titanium and the self-interaction parameter of titanium in liquid Cu-Ti-Si at 1773 K were determined by equilibrating the 58 mass% TiO₂-42 mass% CaF₂ slag with Cu-Si-Ti liquids. And the interaction parameters e_\textTi^\textTi e_{\text{Ti}}^{\text{Ti}} and e_\textTi^\textSi e_{\text{Ti}}^{\text{Si}} obtained using a multiple regression were as large as −69.32 and 15.44 respectively. Based on the above determined value of e_\textTi^\textTi e_{\text{Ti}}^{\text{Ti}} , the relationship between Henrian constant of titanium in liquid Cu-Ti melt, \upgamma_{\textTi(\texts)}⁰ \upgamma_{{{\text{Ti}}({\text{s}})}}^{0} , from 1473 to 1923 K was evaluated, and is expressed as:

Thermodynamic mixing properties and solid-state immiscibility in the systems Pd-Rh and Pd-Rh-O

The thermodynamic activity of rhodium in solid Pd-Rh alloys is measured in the temperature range 950 to 1350 K using the solid-state cell: Pt-Rh, Rh + Rh₂O₃/(Y₂O₃)ZrO₂/Pd_{1_x}Rh_x + Rh₂O₃, Pt-Rh. The activity of palladium and the free energy, enthalpy, and entropy of mixing are derived. The activities exhibit strong positive deviation from Raoult’s law. The activities obtained by the electrochemical technique, when extrapolated to 1575 K, are found to be significantly lower than those obtained from vapor pressure measurements. The mixing properties can be represented by a pseudosubregular solution model in which excess entropy has the same type of function dependence on composition as the enthalpy of mixing: ΔH- X_Rh(1-X_Rh,)(31 130 + 4585X_Rh,)J/mol, and ΔS^ex = X_Rh(1-X_Rh)(l0.44 + 1.51X_Rh) J/mol. K. The positive enthalpy of mixing obtained in this study in qualitative agreement with predictions of semiempirical models. The results predict a solid-state miscibility gap withT _c = 1210 (±5) K atX _Rh = 0.55 (±0.02). The computed critical temperature is approximately 100 K higher than that reported in the literature. The oxygen chemical potential for the oxidation of Pd-Rh alloys under equilibrium conditions is evaluated as a function of composition and temperature. The Gibbs energy of formation of PdO is measured as a function of temperature. At low temperatures, the alloys are in equilibrium with Rh₂O₃, and PdO coexists with Pd and Rh₂O₃. At high temperatures, PdO is unstable and Pd-rich alloys are in equilibrium with diatomic oxygen gas.