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.     

Partial Thermodynamic Properties of <Emphasis Type="Italic">γ</Emphasis>′-(Ni,Pt)<Subscript>3</Subscript>Al in the Ni-Al-Pt system

Measurements were made to determine how Pt influences the partial thermodynamic properties of Al and Ni in γ′-(Ni,Pt)₃Al and liquid in the Ni-Al-Pt system. The activities of Al and Ni were measured with a multiple effusion-cell mass spectrometer (multi-cell KEMS). For a constant X _Al = 0.24, adding Pt, from X _Pt = 0.02-0.25, reduces a(Al) almost an order of magnitude, from 2 × 10⁻⁴ to 2 × 10⁻⁵, at 1560 K. This occurred for of −203 ± 10 kJ mol⁻¹ and the a(Al) decrease was due to increasing from −60 to −40 J mol⁻¹ K⁻¹ with Pt addition. The large negative and indicate Al-atoms are highly ordered in γ′-(Ni,Pt)₃Al. Nickel activity, a(Ni), remained essentially constant, ∼0.7, indicating an increasing ternary interaction between Ni-atoms and (Al + Pt)-atoms with Pt addition, where γ_Ni increased from about 0.7 to 1.2. This is supported by in the range 6.1-7.1 ± 1.5 kJ mol⁻¹ at 1520 K, and a positive , which suggest disorder on the Ni-lattice. For a consistent X _Al = 0.27, adding Pt, from X _Pt = 0.10–0.25, also reduces a(Al) but only by a factor of about 3, while a(Ni) remained essentially constant, with γ_Ni increasing from about 0.7 to 0.95. A dramatic change in the mixing behavior was observed between the and 0.27 series of alloys, where and are seen to increase about 50 kJ mol⁻¹ and 20 J mol⁻¹ K⁻¹ at T = 1566 K, respectively. In contrast, decreased about 16 kJ mol⁻¹ at T = 1520 K and changed from a positive to a negative value. This article was presented at the Multi-Component Alloy Thermodynamics Symposium sponsored by the Alloy Phase Committee of the joint EMPMD/SMD of The Minerals, Metals, and Materials Society (TMS), held in San Antonio, Texas, March 12–16, 2006, to honor the 2006 William Hume-Rothery Award recipient, Professor W. Alan Oates of the University of Salford, UK. The symposium was organized by Y. Austin Chang of the University of Wisconsin, Madison, WI, Patrice Turchi of the Lawrence Livermore National Laboratory, Livermore, CA, and Rainer Schmid-Fetzer of the Technische Universitat Clausthal, Clauthal-Zellerfeld, Germany.     

Activities and immiscibility in the system Cu-Rh

The thermodynamic activity of rhodium in solid Cu-Rh alloys is measured by the electromotive force method in the temperature range from 1050 to 1325 K with a solid-state cell:

Surface tension, density, and molar volume of liquid Sb-Sn alloys: Experiment versus modeling

Through the application of the maximum bubble pressure and dilatometric method, density and surface tension were investigated. The experiments were conducted in the temperature range from 583 K≤T≤1257 K. The surface tension was measured for pure antimony and for six liquid Sb-Sn alloys (mole fractions X _Sn=0.2, 0.4, 0.6, 0.8, 0.9, and 0.935 mm²) and measurements of the density were only for alloys. It has been observed that both surface tension and density show linear dependence on temperature. The temperature-concentration relation of both surface tension and density were determined with minimization procedures. The surface tension isotherms calculated at 873 K and 1273 K show slight negative deviations from linearity changes, but the observed maximal differences did not exceed 30 mN · m⁻¹. The surface tension calculated from Butler’s model was higher than the experimental value for most concentrations and also showed curvilinear temperature dependence. The experimental densities and the molar volumes of the Sb-Sn liquid alloys conform very closely to ideal behavior with differences comparable to the experimental errors.     

Surface tension,density, and molar volume of liquid Sb-Sn alloys: Experiment versus modeling

Through the application of the maximum bubble pressure and dilatometric method, density and surface tension were investigated. The experiments were conducted in the temperature range from 583 K≤T≤1257 K. The surface tension was measured for pure antimony and for six liquid Sb-Sn alloys (mole fractions X _Sn=0.2, 0.4, 0.6, 0.8, 0.9, and 0.935 mm²) and measurements of the density were only for alloys. It has been observed that both surface tension and density show linear dependence on temperature. The temperature-concentration relation of both surface tension and density were determined with minimization procedures. The surface tension isotherms calculated at 873 K and 1273 K show slight negative deviations from linearity changes, but the observed maximal differences did not exceed 30 mN · m⁻¹. The surface tension calculated from Butler’s model was higher than the experimental value for most concentrations and also showed curvilinear temperature dependence. The experimental densities and the molar volumes of the Sb-Sn liquid alloys conform very closely to ideal behavior with differences comparable to the experimental errors.     

Thermodynamic properties of SmFeO3(s) and Sm3Fe5O12(s)

The enthalpy increments and the standard molar Gibbs energy (G) of formation of SmFeO₃(s) and Sm₃Fe₅O₁₂(s) have been measured using a Calvet micro-calorimeter and a solid oxide galvanic cell, respectively. A λ-type transition, related to magnetic order-disorder transformation (antiferromagnetic to paramagnetic), is apparent from the heat capacity data at ∼673 K for SmFeO₃(s) and at ∼560 K for Sm₃Fe₅O₁₂(s). Enthalpy increment data for SmFeO₃(s) and Sm₃Fe₅O₁₂(s), except in the vicinity of λ-transition, can be represented by the following polynomial expressions:

Mechanical properties of the cast intermetallic alloy Ti-43Al-7(Nb,Mo)-0.2B (at %) after heat treatment

A new approach to obtaining fine-grained structure in intermetallic-compound alloys such as γ-TiAl + α₂-Ti₃Al has been suggested. This approach is based on the use of alloys that solidify as the β phase, which contain β-stabilizing additives such as Nb and Mo and are characterized by the small size of crystallites already in the cast state; in these alloys, a simple heat treatment makes it possible to substantially decrease the fraction of the lamellar component and to increase the content of the β(B2) phase. It is shown on the example of the Ti-43Al-7(Nb,Mo)-0.2B (at %) alloy that this heat treatment ensures superplastic properties in the material in the temperature range of T = 1050–1130°C at a deformation rate $ \dot \varepsilon A new approach to obtaining fine-grained structure in intermetallic-compound alloys such as γ-TiAl + α₂-Ti₃Al has been suggested. This approach is based on the use of alloys that solidify as the β phase, which contain β-stabilizing additives such as Nb and Mo and are characterized by the small size of crystallites already in the cast state; in these alloys, a simple heat treatment makes it possible to substantially decrease the fraction of the lamellar component and to increase the content of the β(B2) phase. It is shown on the example of the Ti-43Al-7(Nb,Mo)-0.2B (at %) alloy that this heat treatment ensures superplastic properties in the material in the temperature range of T = 1050–1130°C at a deformation rate = 1.7 × 10⁻⁴ K⁻¹. Under these temperature-strain-rate conditions, relative elongations such as δ = 160–230% and low flow stresses such as σ = 36–100 MPa characteristic of superplastic flow have been obtained. It has been shown for the first time for the intermetallic γ-TiAl + ga₂-Ti₃Al alloy that a sheet semifinished product cut out from an ingot subjected only to heat treatment can have plasticity acceptable for press forming. Original Russian Text ? V.M. Imayev, R.M. Imayev, T.G. Khismatullin, 2008, published in Fizika Metallov i Metallovedenie, 2008, Vol. 105, No. 5, pp. 516–522. The author is also known by the name Imayev. The name used here is a transliteration under the BSI/ANSI scheme adopted by this journal.—Ed.     

The adiabatic correction factor for deformation heating during the uniaxial compression test

The isothermal uniaxial compression test is a common method to determine the flow stress of metals. For accurate flow stress data at strain rates >10⁻³ s⁻¹, the data must be corrected for flow softening due to deformation heating. The first step in the correction is to determine the increase in temperature. An adiabatic correction factor, η, is used to determine the temperature between strain rates of 10⁻³ to 10¹ s⁻¹. The adiabatic correction factor is the fraction of adiabatic heat retained in the workpiece after heat loss to the dies, η=(ΔT _ACTUAL)/(ΔT _ADIABATIC), where ΔT _ADIABATIC=(0.95 f σdɛ)/(ρC _p ). The term η is typically taken to be constant with strain and to vary linearly (0 to 1) with log ( ) between 10⁻³) and 10¹ s⁻¹. However, using the finite element method (FEM) and a one-dimensional, lumped parameter method, η has been found to vary with strain, die and workpiece thermal conductivities, and the interface heat-transfer coefficient (HTC). Using the lumped parameter method, an analytical expression for η was derived. In this expression, η is a function of the die and workpiece thermal conductivities, the interface heat-transfer coefficient, workpiece heat capacity, strain, and strain rate. The results show that an increase in the HTC or thermal conductivity decreases η.     

Kinetics of forward extraction of Ti（IV） from H_2SO_4 medium by P_（507） in kerosene using the single drop technique

The kinetics of forward extraction of Ti(IV) from H2SO4 medium by P507 in kerosene has been investigated using the single drop technique.In the low concentration region of Ti(IV),the rate of forward extraction at 298 K can be represented by F(kmol·m-2·s-1)=10-5.07 [TiO 2 + ][H+]-1 [NaHA 2 ](o)·Analysis of the rate expression reveals that the rate determining step is(TiO)(i)2+ +(HA 2)(i)-[TiO(HA2)](i)+.The values of Ea,H±,S±,and G±298 are calculated to be 22 kJ·mol-1,25 kJ·mol-1,-218 J·mol-1·K-1,and 25 kJ·mol-1,respectively.The experimental negative S± values indicate that the reaction step occurs via SN2 mechanism.     

Contribution to the thermochemistry of rare earth pnictides: The Sm-Bi system

Formation enthalpies of Sm-Bi alloys (in the complete range of compositions) and Er-Bi alloys (for a few compositions) have been measured using a direct, small-furnace, isoperibolic aneroid differential calorimeter. Typical values for the reaction in the solid state at 300 K are: Sm₂Bi,−88 ± 3; Sm₅Bi₃, −94 ± 4; Sm₄Bi₃, −104 ± 2; SmBi, −108 ± 2; SmBi₂, −76 ± 4; and ErBi, −90 ± 5 kJ/g-atom. The experimental data are briefly discussed, compared with those of similar rare earth compounds, and found to be in good agreement with those computed according to the Miedema model and, for the rare earth-rich alloys, also with those calculated according to the Kubaschewski suggestion based on the so-called “effective coordination number” in alloys.     

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.     

Gibbs Energy of Formation of MnO: Measurement and Assessment

Based on the measurements of Alcock and Zador, Grundy et al. estimated an uncertainty of the order of ±5 kJ mol⁻¹ for the standard Gibbs energy of formation of MnO in a recent assessment. Since the evaluation of thermodynamic data for the higher oxides Mn₃O₄, Mn₂O₃, and MnO₂ depends on values for MnO, a redetermination of its Gibbs energy of formation was undertaken in the temperature range from 875 to 1300 K using a solid-state electrochemical cell incorporating yttria-doped thoria (YDT) as the solid electrolyte and Fe + Fe_1 − δO as the reference electrode. The cell can be presented as

Hot deformation mechanisms in Ti-5.5Al-1Fe alloy

The mechanisms of hot deformation in the alloy Ti-5.5Al-1Fe have been studied in the temperature range 750 to 1150 °C and with the true strain rate varying from 0.001 to 100 s⁻¹ by means of isothermal compression tests. At temperatures below β transus and low strain rates, the alloy exhibited steady-state flow behavior, while, at high strain rates, either continuous flow softening or work hardening followed by flow softening was observed. In the β region, the deformation behavior is characterized by steady-state behavior at low strain rates, yield drops at intermediate strain rates, and oscillations at high strain rates. The processing maps revealed two domains. (1) In the temperature range 750 to 1050 °C and at strain rates lower than 0.01 s⁻¹, the material exhibits fine-grained superplasticity. The apparent activation energy for superplastic deformation is estimated to be about 328 kJ/mole. The optimum conditions for superplasticity are 825 °C and 0.001 s⁻¹. (2) In the β region, a domain occurs at temperatures above 1100 °C and at strain rates from 0.001 to 0.1 s⁻¹ with its peak efficiency of 47% occurring at 1150 °C and 0.01 s¹. On the basis of kinetic analysis, tensile ductility, and grain size variation, this domain is interpreted to represent dynamic recrystallization (DRX) of β phase. The apparent activation energy for DRX is estimated to be 238 kJ/mole. The grain size (d) is linearly dependent on the Zener-Hollomon parameter (Z) per the equation

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.     

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.     

The Heusler Phase Ti25(Fe50 − x Ni x )Al25 (0 ≤ x ≤ 50); Structure and Constitution

Alloys with composition Ti₂₅(Fe_50 − x Ni _x )Al₂₅ (0 ≤ x ≤ 50) were investigated employing electron probe microanalysis (EPMA) and X-ray powder diffraction (XPD). For TiFe₂Al, in situ neutron powder diffraction (ND) was used for the inspection of phase constitution covering the temperature range from 27 °C (300 K) to 1277 °C (1550 K). Combined Rietveld refinement of ND and XPD data for TiFe₂Al revealed that Fe atoms occupy the 8c site in space group Ti with a small amount of Al sharing the 4a site, and the remaining Ti and Al atoms adopting the 4b site. This structural model was successfully applied in the refinement of all alloys Ti₂₅(Fe_50 − x Ni _x )Al₂₅ (0 ≤ x ≤ 50). Partial atom order exists on the Fe-rich side while complete order is observed for the Ni-rich side. Profiles recorded by in situ neutron powder diffraction for TiFe₂Al in the range of investigated temperatures show two phases, namely Heusler phase and MgZn₂-type Laves phase. Diffraction peaks from the Heusler phase dominate the profiles at lower temperatures but at higher temperatures the MgZn₂-type Laves phase is the main phase. No CsCl-type phase was found in the alloy in the investigated temperature range. The thermal expansion coefficient of TiFe₂Al is 1.4552 × 10⁻⁵ K⁻¹.     

Evaluation of off-diagonal diffusion coefficient from phase diagram information

A theoretical investigation in order to clarify the physico-chemical meaning involved in off-diagonal multicomponent diffusion coefficients has been carried out. From a mathematical expression for the diffusion coefficients of interstitial elements in Fe-Metal-C or Fe-Metal-N ternary solid solutions, it was found that the off-diagonal diffusion coefficient of the interstitial element (C) could be evaluated from phase diagram information on isopotential curves of that element resulting in the following relation:

Al-Cu-Li system electromotive force and calorimetric studies—Phase diagram calculations of the Al-Rich part

Electromotive force (emf) studies were made for solid and liquid AI-Cu-Li alloys. Measurements were conducted on four sets of alloys at temperatures and composition ranges as follows (where X_Li is mole fraction):

Optical absorption and magnetooptical effects in the Heusler alloy NiMnSb

Optical and magnetooptical properties of the Heusler alloy NiMnSb, which refers to the class of half-metallic ferromagnetic materials, have been investigated. The temperature dependence (T = 80?480 K) of the diagonal component of the tensor of dielectric constant $ \hat \varepsilon Optical and magnetooptical properties of the Heusler alloy NiMnSb, which refers to the class of half-metallic ferromagnetic materials, have been investigated. The temperature dependence (T = 80−480 K) of the diagonal component of the tensor of dielectric constant in the spectrum range of ℏω = 0.5–5.0 eV has been studied under conditions of ultrahigh vacuum P ∼ 10⁻⁸ Pa. In the range of photon energies ℏω = 0.18–4.8 eV, measurements of the transverse Kerr effect have been performed and the dispersion of the off-diagonal component of the dielectric-constant tensor has been determined. It has been established that in the region of the fundamental band of interband absorption (ℏω = 1–5 eV) the spectral dependence of the diagonal and off-diagonal components of the tensor can be satisfactorily explained on the basis of existing information on the electronic structure of NiMnSb. The differences between the experimental and theoretical curves are only observed in the IR range of the spectrum. At the photon energies E < 1 eV, contributions from interband electron transitions have been revealed in the optical absorption and magnetooptical characteristics, which indicate the existence of low-energy gaps ΔE ∼ 0.07–0.8 eV in the vicinity of the Fermi level E _F in the energy-band spectrum of NiMnSb. The results obtained support the concept of the formation of a pseudo-gap at E _F in the density of states of electrons with spins opposite to the direction of spontaneous magnetization. For the first time, a magnetooptical effect quadratic in magnetization has been revealed in NiMnSb and its spectral dependence has been studied. Original Russian Text ? Yu.I. Kuz’min, M.M. Kirillova, I.D. Lobov, 2008, published in Fizika Metallov i Metallovedenie, 2008, Vol. 106, No. 6, pp. 577–585.     

High-Temperature Deformation and Ductility of a Modified 5083 Al Alloy

The high-temperature deformation of a 5.5% Mg and 0.6% Ca modified 5083 aluminum alloy was investigated in the temperature range from 573 to 723 K at strain rates in the range of 10⁻⁵-10⁻¹ s⁻¹. Ca was added to form an insoluble second phase in the range of temperatures tested to improve the high-temperature characteristics of this alloy. It was shown that the deformation behavior of the alloy could be divided into two regions with stress exponent, n of 3.5 and 13 at low and high strain rates, respectively. The apparent activation energy determined in both regions suggested that the deformation process is diffusion controlled in both regions. The slightly high value of n at the low-strain rate region (viscous glide) was attributed to the presence of threshold stress. The values of threshold stress showed an exponential increase with decreasing temperature and a dependence with an energy term Qo = 16.5 kJ mol⁻¹. Analysis of creep data in terms of threshold stress and using diffusivity of Mg in normalizing the strain rates, revealed two types of deformation behavior. At high values of normalized strain rate a high value of stress exponent of n = 10 is observed, and the exponential law creep takes place. At low normalized strain rates ≤10⁻⁹, the n value is 3 and the true activation energy, Q, is equal to 123 kJ mol⁻¹ suggesting viscous glide of dislocations as rate-controlling mechanism. Enhanced ductility has been observed in the region of viscous-glide controlled deformation as a result of high strain-rate sensitivity.