Thermodynamic activities and phase boundaries for the alloys of the Ni3Al-Ni3Ti pseudobinary section in the Ni-Al-Ti system

The pseudobinary section Ni₃Al-Ni₃Ti of the ternary Ni-Al-Ti system has been investigated by ther-mal analysis and Knudsen effusion mass spectrometry. The solidus of the pseudobinary section and the thermodynamic activities of Ni and Al have been determined in the alloys Ni_0.75A1_0.25-xTi_x of the compositionsx = 0.00 to 0.21. Moreover, the thermodynamic activities of Ni and Ti in Ni₃Ti (x = 0.25) as well as the Gibbs energy of mixing of the Ni_0.75Ti_0.25 phase resulted. The ionization cross-sectional ratio Σ(Ni)/Σ(Ti) = 0.77 has been evaluated for the electron impact energy of 50 eV.     

Oxidation of titanium disilicide in A. Nonisothermal regime

Differential-thermal and thermogravimetric analyses are used to study the oxidation of titanium disilicide in a nonisothermal regime in the temperature range 300–1250 K with a heating rate in air of 10 deg/min. Experimental results are compared with theoretical Criado curves. An oxidation mechanism is established. The activation energy for oxidation is calculated: E = 127.03 kJ/mole, and thermodynamic parameters are calculated for activation, i.e., entropy, Gibbs free energy, enthalpy: ΔS^# = ?165.54 J/(mole · K), ΔG^# = 277.53 kJ/mole, ΔH^# = 119.47 kJ/mole, respectively.     

High Temperature Vaporization Chemistry in the Gold-Chlorine System Including Formation of Vapor Complex Species of Gold and Silver with Copper and I ron

The thermodynamic properties of the vaporization reactions in the gold-chlorine system have been investigated in the temperature ranges of 580 to 649 K and 882 to 1107 K. The experimental technique consisted of classical transpiration vapor pressure measurement and analysis with a newly developed Flow Reactor-Mass Spectrometer system, which connects a high temperature, ambient pressure reactor to a TOF mass spectrometer. Metallic gold reacts with chlorine gas at temperatures above 750 K, forming the vapor species Au₂Cl₂(g). The resulting reaction 2Au(c) + Cl₂(g) = Au₂Cl₂(g) was found to have a standard Gibbs free energy change of ΔG° = 89,000 (±2400) ? 27.8 (±1) T (J/mole) ΔG° = 21,300 (±570) ? 6.6 (±0.2) T (cal/ mole) in the temperature range 882 to 1107 K. At lower temperatures, the vaporization reaction is 2Au(c) + 3Cl₂(g) = Au₂Cl₆(g) with a standard Gibbs free energy change of ΔG° = ?102,000 (±20,000) + 235 (±29) T (J/mole) ΔG° = ?24,400 (±4800) +56 (±7) T (cal/mole) in the temperature range 580 to 649 K. The above results are combined with equilibrium dissociation data obtained in the literature for condensed gold chloride phases to construct a phase stability-vapor pressure diagram for the gold-chlorine system. Consideration is given to some possible operating conditions for a gold chlorination-vaporization process to treat low grade and refractory gold ores. Transpiration vapor pressure measurements in the Au-Cu-Cl, Ag-Cu-Cl, and Ag-Fe-Cl systems showed significant enhancement of the vapor pressure of Au₂Cl₂(g) or AgCl(g) in the presence of Cu₃Cl₃(g) or FeCl₃(g). This indicates the formation of binary vapor phase complexes in these systems. The species AuCu₂Cl₃(g), AgCu₂Cl₃(g), and AgFeC₄ have been proposed.     

Thermodynamic properties of holmium monogermanide

The heat capacity and enthalpy of HoGe is investigated for the first time over a temperature range between 51.62 and 2096 K. The values of heat capacity, entropy, reduced Gibbs energy (J · mole^?1 × × K^?1), and enthalpy (J · mole^?1) are determined at 298.15 K: C °_P(T) = 49.63 ± 0.20; S °(T) = 89.1 ± 0.7; Φ′(T) = 50.9 ± 0.8; H °(T) ? H °(0 K) = 11391 ± 57. Temperature dependences of enthalpy (J · mole^?1) for holmium monogermanide are determined as follows: H °(T) ? H °(298.15 K) = 8.474 × × 10^?3 · T² + 47.13 · T + 226747 · T^?1 ? 15565 and H °(T) ? H °(298.15 K) = 88.91 · T ? 26507, for 298.15–1765 K and 1951–2096 K, respectively. The enthalpy and entropy of HoGe melting are calculated: T_m = 1765 ± 35 K, ΔH_m = 36.3 ± 2.9 kJ · mole^?1, ΔS_m = 20.5 ± 1.6 J · mole^?1 · K^?1.     

Free energies of formation of WC and W2C,and the thermodynamic properties of carbon in solid tungsten

The activity of carbon in the two-phase regions W + WC and W + W₂C has been obtained from the carbon content of iron rods equilibrated with mixtures of metal plus carbide powders. From this activity data the standard free energies of formation of WC and W₂C have been calculated to be ΔG _f ⁰(WC) = -10,100 + 1.19T ± 100 cal/mole (-42,300 + 4.98T ± 400 J/mole) (1150 to 1575 K) ΔG _f ⁰(W₂C) = - 7300 - 0.56T ± 100 cal/mole (- 30,500 - 2.34T ± 400 J/mole). (1575 to 1660 K) The temperature of the eutectoid reaction W₂C = W + WC was fixed at 1575 ± 5K. Using available data for the solubility of C in solid W, the relative partial molar free energy of C in the dilute solid solution was calculated to be $$\Delta \bar G_C^\alpha {\text{ = 23,000 }} - {\text{ }}[{\text{0}}{\text{.68 }} - R\ln X_C^\alpha ]{\text{ }}T \pm 3000 cal/mole (96,200 - [2.85 - R\ln X_C^\alpha ]{\text{ }}T \pm 12,600 J$$ The heat solution of C in W obtained was \(\Delta \bar H_C^\alpha {\text{ = 23,000 }} \pm {\text{ 5000 cal/mole (96,200 }} \pm {\text{ 20,000 J/mole)}}\) and the excess entropy for the interstitial solid solution, assuming that the carbon atoms are in the octahedral sites, \(\Delta \bar S_C^\alpha {\text{ = (}}xs,i{\text{) }} = - {\text{1}}{\text{.5 }} \pm {\text{ 2 cal/deg - mole (}} - {\text{6}}{\text{.3 }} \pm {\text{ 8 J/deg - mole)}}\) .     

Thermodynamic properties and high-temperature behavior of lanthanum selenides La3Se4-La2Se3

The enthalpy of the La₃Se₄ and La₂Se₃ boundary compositions of the La_3?xSe₄ phase (0 ≤ x ≤ 1/3) at temperatures from 370 to 2260 K is studied calorimetrically. The values obtained are used and the equilibria of the La-Se system are analyzed to establish, for the first time, the temperature-concentration relationships for the thermodynamic properties of La_3?xSe₄ selenides in the homogeneity region at 298 K ≤ T ≤ 2123 K. The enthalpy function (J/mole) of La^3?xSe₄ is given by H(T) ? (298 K) = (3837 · 10³T^?1 ? 85852 + 266.925 · T ? 8.7503 · 10^?2 T² + 3.437 · 10^?5 T³) · e^?0.2869x. The formation and melting enthalpies of La₃Se₄ are determined: Δ_fH °(298 K) = ?1340 ± ± 28 kJ/mole), Δ_mH = 147.5 ± 9.6 kJ/mole. It is shown that the high-temperature stability of different La_3?xSe₄ compositions is strongly dependent on pressure: as pressure decreases and temperature increases, the selenium content is reduced and the composition tends to La₃Se₄.     

Thermodynamics of the cadmium-neptunium system: Solute-solvent interaction in liquid alloys

The thermodynamics of the cadmium-rich part of the cadmium-neptunium system have been studied using a high temperature galvanic cell method. The values (cal/mole) of the standard free energy of formation of the two most cadmium-rich intermetallic compounds are given by the equations: NpCd₁₁: ΔGf° (cal/mole) = -42,030 + 38.66T NpCd₆: ΔGf° (cal/mole) = -27,510 + 19.72T. The activity coefficient of neptunium relative to solid Np can be represented by the equation:RT ln γN_p/x_Cd ² = -72,354 + 590.25T - 76.117T lnT + (2,067,115 - 21,105T + 2780.3T lnT) x_{N p}, in which x_Cd and x_Np are the atom fractions of cadmium and neptunium. The Cd-U, Cd-Np, and Cd-Pu systems are discussed in terms of a model which involves the formation of localized bonds between the actinide and cadmium atoms in the solid and the liquid state.     

On the Gibbs energy of formation of wustite

Gibbs energy change for the reactionxFe_(s) + 1/2O_2(g) = Fe _x O_(s) has been redetermined using the galvanic cell (−) Fe_(s), Fe _x O_(s)∥ZrO₂ − CaO∥NiO_(s), Ni_(s)(+) in the temperature range 866 to 1340 K. The results are at variance with earlier works in that they reflect the transformations occurring in the iron phase. The Gibbs energy function is represented by two nonlinear equations,viz., ΔG° (866 to 1184 K) = −251480 − 18.100T + 10.187T lnT ± 210 J/mol and ΔG° (1184 to 1340 K) = −286248 + 181.419T - 13.858T lnT ± 210 J/mol. Formerly Research Assistant at the Department of Theoretical Metallurgy, The Royal Institute of Technology, Stockholm     

Thermodynamic properties of B2-AlFeNi Alloys. Part I: Investigation by knudsen effusion mass spectrometry

The vaporization of Al-Fe-Ni alloys has been investigated in the temperature range 1180 to 1508 K by Knudsen effusion mass spectrometry (KEMS). Fourteen different compositions were examined in the B2 region: 10 compositions at two fixed Al concentrations,x _Al=0.45 andx _Al=0.50 plus four extra compositions at constantx _Ni/x _Fe=1. For the first time, reliable partial pressures and thermodynamic activities of Al, Fe, and Ni have been evaluated from the measured ion intensities for both the alloy and the pure element. Gibbs energies, partial molar enthalpies, and entropies of formation for all the components have also been obtained. The relative partial molar enthalpies and entropies were found to be nearly temperature independent over the wide temperature ranges investigated. At 1400 K, the Gibbs energy of formation of Al_0.50Fe_0.25Ni_0.25 and Al_0.45Fe_0.275Ni_0.275, with Al(liq), Fe(fcc), and completely paramagnetic Ni(fcc,cpm) as reference states, are −37.9±0.42 kJ/mol and −38.1±0.42 kJ/mol, respectively. At the same temperature, the enthalpies of formation of Al_0.50Fe_0.25Ni_0.25 and Al_0.45Fe_0.275Ni_0.275, with the same reference states, are −51.5±1.7 kJ/mol and −49.2±1.7 kJ/mol, respectively.     

Electron microscopy of crystalline and amorphous Ni-P electrodeposited films: In-situ crystallization of an amorphous solid

Electron microscopy has been used to study the structure of Ni-P electrodeposited thin films with 7, 12, 20 and 22 at. pct P. For the crystalline as-deposited films with 7 and 12 at. pct P (low P films), the crystal structure is fcc and the grains are a supersaturated solid solution of P in Ni. Grain size decreases with increasing P content; the present findings agree with previous ones. For “amorphous” as-deposited films with 20 and 22 at. pet P (high P content films) the amorphous phase is not completely homogeneous and there are regions in which small microcrystals exist. Electron beam heating a low P con-tent film causes the crystalline array of supersaturated Ni grains to decompose to an equilibrium mixture of Ni and Ni₃P; both types of grains are randomly oriented. Electron beam heating a high P content film causes the amorphous regions to undergo several complex transformations. The first reaction to occur is: Amorphous (Ni-P) -Ni_xP_y + Ni (random) where Ni_xP_y is a newly discovered phase with a variable composition. Further beam heating causes a second transformation to equilibrium phases: Ni_xP_y + Ni → Ni₃P + Ni (random). The microstructure resulting from the above transformations depends on variations in composition of the as-deposited specimens, rates of heating and temperature gradients. The mode of phase transformation in microcrystalline regions and amorphous regions is distinctly different. Crystallization in amorphous regions occurs by a nucleation and growth of Ni_xP_y, and Ni; a crystallization front is seen to advance into the amorphous re-gion. Crystallization in microcrystalline regions occurs by nucleation and growth of the Ni₃P phase and grain coarsening of the Ni phase. No distinct crystallization front is ob-served.     

Activities of chromium in molten copper at dilute concentrations by solid-state electrochemical cell

In order to obtain the activities of chromium in molten copper at dilute concentrations (<0.008 chromium mole fractions), liquid copper was brought to equilibrium with molten CaCl₂ + Cr₂O₃ slag saturated with Cr₂O₃ (s), at temperatures between 1423 and 1573 K, and the equilibrium oxygen partial pressures were measured by means of solid-oxide galvanic cells of the type Mo/Mo + MoO₂/ZrO₂(MgO)/(Cu + Cr))alloy + Cr₂O₃ + (CaCl₂ + Cr₂O₃)_slag/Mo. The free energy changes for the dissolution of solid chromium in molten copper at infinite dilution referred to 1 wt pct were determined as Cr (s) = Cr(1 wt pct, in Cu) and ΔG° = + 97,000 + 73.3(T/K) ± 2,000 J mol⁻¹.     

A thermodynamic analysis of the phase equilibria of the Fe-Ni system above 1200 K

A quasi-subregular solution model is used to describe the thermodynamic properties of the liquid phase; values of the solution parameters are obtained from extensive and consistent thermochemical data reported in the literature. For the fcc and bcc phases, the same model is used to account for the nonmagnetic part of the Gibbs energy and the magnetic contribution is taken from the previous paper. Again, the values for the quasi-subregular solution parameters for the fcc phase are obtained from extensive and consistent thermochemical data reported in the literature at high temperatures. The values of the solution parameters for the bcc phase are obtained from the thermodynamic values of the liquid and fcc phases and the known phase boundary data. The calculated phase equilibria are in good agreement with the available data. Based on the thermodynamic data, the metastablel + γ andl + δ phase boundaries as well as theT ₀ (γ + l) andT ₀(δ +l) curves are calculated.     

Thermodynamic investigations on chalcopyrite

The vapor pressures of sulfur in equilibrium with various compositions within the Cu?Fe?S system were measured by a molecular absorption technique. Measurements were made as functions of temperature for the single phase compositions CuFeS_1.62, CuFeS_1.70, CuFeS_1.80 and CuFeS_1.90, for the two-phase fields bornite+chalcopyrite and pyrrhotite+chalcopyrite, and for the three-phase field chalcopyrite+bornite+pyrite. Statistical mechanical equations are derived and used to evaluate the data. Chalcopyrite highly deficient in sulfur behaves similarly to an ideal mixture of Cu₂S and FeS with a random distribution of the constituent cations. Calculated values are given for the Gibbs energy of formation of chalcopyrite at 973 K for compositions CuFeS_1.62 to CuFeS₂, and the entropies and Gibbs energies of formation for CuFeS₂(s) from 800 to 1000 K. Standard entropies, enthalpies, and energies are derived: S⁰ _{CUFeS 2} (298)=32 e.u., ΔH⁰ _{CuFeS 2},f(298)=?42,116 cal, ΔG⁰ _{CuFeS 2} f (298)=?42,800 cal.     

Effects of Microalloying on Glass Forming Ability and Thermodynamic Fragility of Cu-Pr-Based Amorphous Alloys

The effects of microalloying of Ti and B on the glass formation of Cu60Pr30Ni10Al10-2xTixBx（x = 0, 0.05% （atom fraction）） amorphous alloys was investigated using differential scanning calorimetry （DSC） and X-ray diffraction （XRD）. XRD analysis showed that mieroalloying with 0.05% Ti and 0.05% B improved the glass forming ability （GFA）. The smaller difference in the Gibbs free energy between the liquid and crystalline states at the glass transition temperature （△G1-X（Tg）） and the smaller thermodynamic fragility index （△Sf/Tm, where ASf is the entropy of fusion, and Tm is the melting temperature） after mieroalloying correlated with the higher GFA.     

Thermodynamics of the Ca-S-O,Mg-S-O,and La-S-O systems at high temperatures

High temperature thermodynamic data for equilibria in the Ca-S-O, Mg-S-O, and La-S-0 systems were determined by a galvanic cell technique using calcia stabilized zirconia (CSZ) solid electrolytes. The measured emf data were used to calculate the standard free energy changes of the following reactions: [1] CaO(s) + 1/2S₂(g) → CaS(s) + 1/2O₂(g) 1000 to 1350 K ΔG° = 21906.9 − 0.8T(K)(±400 cal) = 91658 − 3.37 (±1700 J) [2] CaS(s) + 2O₂(g) → CaSO₄(s) 1050 to 1450 K ΔG° = -227530.7 + 80.632T(K) (±400 cal) = -951988.5 + 337.4T (±1700 J) [3] CaO(s) + 3/2O₂(g) + 1/2S₂(g) → CaSO₄(s) 1050 to 1340 K ΔG° = -204892.7 + 79.83T(K)(±400 cal) = -857271.1 + 334.0T (±1700 J) [4] MgO(s) + 1/2S₂(g) → MgS(s) + 5O₂(g) 1000 to 1150 K ΔG° = 45708.6 − 2.897(K)(±500 cal) = 191244.8 − 12.1T (±2100 J) [5] La₂O₃(s) + 1/2S₂(g) → La₂O₂S(s) + 1/2O₂(g) 1080 to 1350 K ΔG° = 17507 − 2.32T(K)(±380 cal) = 73249.3 − 9.7T (±1600 J) [6] La₂O₃S(s) + S₂(g) → La₂S₃(s) + O₂(g) 950 to 1120 K ΔG° = 70940 + 2.25T(K)(±500 cal) = 296812.9 + 9.47 (±2100 J) The ΔG° values of reaction [5] were combined with the literature data for ΔG°_f(La₂O₃) to obtain the standard free energy of formation of La₂O₂S at high temperatures. The values of ΔG°_f thus calculated for La₂O₂S were combined with the ΔG° data for reaction [6] to obtain the standard free energy of formation of La₂S₃ at high temperatures.     

Enthalpies of formation of some solid hafnium nickel compounds and of the Ni-Rich HfNi liquid by direct reaction calorimetry

In the course of a systematic study of binary transition metal alloys, the enthalpies of formation of five Hf-Ni compounds were measured by direct reaction calorimetry: Hf_0.17Ni_0.83(l/6HfNi₅): Δ_fH(1323 K) = − 37,000 J/mole of atoms (±3200) Hf_0.22Ni_0.781/9Hf₂Ni₇): Δ_f(1623 K) = −50,700 J/mole of atoms (±2000) Hf_0.45Ni_0.55(l/2OHf₉Ni₁₁): Δ_fH(1473 K) = −54,500 J/mole of atoms (±2200) Hf_0.50Ni_0.50(l/2HfNi): Δ_fH(1573 K) = −47,900 J/mole of atoms (±1800) Hf_0.67Ni_0.33(l/3Hf₂Ni): ΔH(1423 K) = −36,700 J/mole of atoms (±1300) with reference to pure metals in their equilibrium states at the reaction temperatures. The Ni-rich Hf-Ni liquid was also studied by the dissolution of Hf in the liquid alloy of variable composition at 1743 and 1633 K. Results show that the enthalpy of formation of the liquid at a given composition depends strongly on temperature, and this point suggests the existence of associations in the liquid. The melting temperature of Hf_0.22Ni_0.78(Hf₂Ni₇) which was found (1705 K) is slightly lower than the one (1743 K) given in the literature. Formerly Senior Research Student with the Laboratoire de Thermodynamique Métallurgique, Université de Nancy Un, France     

Oxygen potentials in Ni + NiO and Ni + Cr2O3 + NiCr2O4 systems

The chemical potential of O for the coexistence of Ni + NiO and Ni + Cr₂O₃ + NiCr₂O₄ equilibria has been measured employing solid-state galvanic cells, (+) Pt, Cu + Cu₂O // (Y₂O₃)ZrO₂ // Ni + NiO, Pt (-) and (+) Pt, Ni + NiO // (Y₂O₃)ZrO₂ // Ni + Cr₂O₃ + NiCr₂O₄, Pt (-) in the temperature range of 800 to 1300 K and 1100 to 1460 K, respectively. The electromotive force (emf) of both the cells was reversible, reproducible on thermal cycling, and varied linearly with temperature. For the coexistence of the two-phase mixture of Ni + NiO, δΜ_{O 2}(Ni + NiO) = −470,768 + 171.77T (±20) J mol⁻¹ (800 ≤T ≤ 1300 K) and for the coexistence of Ni + Cr₂O₃ + NiCr₂O₄, δΜ_{O 2}(Ni + Cr₂O₃ + NiCr₂O₄) = −523,190 + 191.07T (±100) J mol⁻¹ (1100≤ T≤ 1460 K) The “third-law” analysis of the present results for Ni + NiO gives the value of ‡H ₂₉₈ ^o = -239.8 (±0.05) kJ mol⁻¹, which is independent of temperature, for the formation of one mole of NiO from its elements. This is in excellent agreement with the calorimetric enthalpy of formation of NiO reported in the literature.     

Structure and Properties of Ferrites Based on CuFe2O4

We have studied the magnetic and structural properties of the solid solutions M _x ²⁺ Cu _1?x ²⁺ Fe ₂ ³⁺ O₄, where M = Mg, Ni, Co, Zn, Mn, Me _0.5x ⁺ Cu _1?x ²⁺ Fe _2+0.5x ³⁺ O₄, were Me = Li, Cu, and (Mn₃O₄)_x(CuFe₂O₄)_1?x. We have developed a new method for detecting a tetragonal phase and have used this method to determine the range of existence for solutions with a tetragonal structure. We explain the dependence of these ranges on the nature of M and Me.     

Formation of metastable phases of Ni-C

Mechanical alloying (MA) of nickel and graphite powders was performed in the composition range Ni_1-xC_x (x = 0.10 to 0.90) by use of a conventional ball mill. The structure of me-chanically alloyed samples was examined by X-ray diffraction, transmission electron micros-copy (TEM), scanning electron microscopy (SEM), and differential scanning calorimetry. A remarkable supersaturation of carbon in face-centered cubic (fcc) nickel phase was observed. A metastable phase Ni₃C was formed by a prolonged MA treatment. For the purpose of com-parative study, MA of cobalt and graphite powders was also performed in composition Co_1-xC_x (x = 0.10, 0.15, and 0.30). The supersaturation of carbon in fcc cobalt and formation of a metastable carbide Co₃C were confirmed.