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.     

Calorimetrically measured enthalpies for the reaction of H2(D2) (g) with Ti and Ti-Ni alloys at 323 K

Reaction enthalpies have been measured calorimetrically at 323 K for the reaction 1/2H₂ (g) + Ti (α, hcp) → TiH_1.5 and for the partial molar solution of H₂ in the δ phase. The magnitude of the enthalpy decreases from 68 at H/Ti = 0 to 65 kJ/mol H at H/Ti = 1.5. The enthalpy continues to slowly fall in magnitude with the increase of H content, and then, for (H/Ti) > 1.9, it falls more precipituously. ΔH _f ⁰ (TiH_1.5) = −98.4 kJ and ΔH _f ⁰ (TiH₂) = −130.3 kJ evaluated at 323 K. No differences in enthalpies were found between H and D. The results are discussed in terms of the existing solvus data for this system, which are important for the quantitative understanding of hydride-induced fracture. Enthalpies of reaction with H₂ have been determined for several Ti-Ni alloys which lie in the (Ti(α) + Ti₂Ni) two-phase field. The reaction with H₂ initially occurs with the Ti phase and then with the Ti₂Ni phase. The enthalpies are similar for the Ti phase as for pure Ti, indicating that this phase is relatively pure Ti. Reaction with the Ti₂Ni phase shows a plateau region with an enthalpy of reaction with 1/2H₂ of about −30 kJ/ mol H. Formerly Graduate Student, Department of Chemistry, University of Vermont.     

Oxidation of Fe (II) in sulfuric acid solutions with dissolved molecular oxygen

The oxidation of Fe(II) with dissolved molecular oxygen was studied in sulfuric acid solutions containing 0.2 mol · dm⁻³ FeSO₄ at temperatures ranging from 343 to 363 K. In solutions of sulfuric acid above 0.4 mol · dm⁻³, the oxidation of Fe (II) was found to proceed through two parallel paths. In one path the reaction rate was proportional to both [Fe⁻²⁺]² andp _{o 2} exhibiting an activation energy of 51.6 · kJ mol⁻¹. In another path the reaction rate was proportional to [Fe²⁺]², [SO ₄ ^{2 −}], andp _{o 2} with an activation energy of 144.6 kJ · mol⁻¹. A reaction mechanism in which the SO ₄ ^{2 −} ions play an important role was proposed for the oxidation of Fe(II). In dilute solutions of sulfuric acid below 0.4 mol · dm⁻³, the rate of the oxidation reaction was found to be proportional to both [Fe(II)]² andp _{o 2}, and was also affected by [H⁺] and [SO ₄ ^{2 −}]. The decrease in [H⁺] resulted in the increase of reaction rate. The discussion was further extended to the effect of Fe (III) on the oxidation reaction of Fe (II).     

Thermodynamic properties and diffusion thermodynamic factors in B2-NiAl

The vaporization of Ni-Al alloys has been investigated in the temperature range 1178 to 1574 K by Knudsen effusion mass spectrometry (KEMS). Thirteen different compositions have been examined in the composition range 38 to 57 at. pct Al. The partial pressures and thermodynamic activities of both Ni and Al have been evaluated both directly from the measured ion intensities for a component in both the alloy and the pure element, I _M ⁺ /I _M ⁺ °, and also from the ion intensity ratios of the alloy components, I _Al ⁺ /I _Ni ⁺ , by means of a Gibbs-Duhem integration. Reliable partial molar enthalpies and entropies for both components have been obtained by mass spectrometry for this system for the first time. Both properties are found to be nearly temperature independent over the wide temperature range investigated. Two separate component diffusion thermodynamic factors have also been evaluated for the first time by taking into account the large vacancy concentrations in these alloys. The enthalpy and Gibbs energy of mixing of stoichiometric Ni_0.5Al_0.5 at 1400 K, evaluated using the Gibbs-Duhem ion intensity ratio (GD-IIR) method, are −78.4±1.2 and −49.0 kJ/mol, respectively, with Al(liquid) and completely paramagnetic Ni(fcc, cpm) as reference states.     

Kinetics of dissolution of cobalt oxides in acidic media

The kinetics of dissolution of cobalt oxides Co₂O₃ and Co₃O₄ in aqueous solutions of acids (H₂SO₄, EDTA) is experimentally studied. Dissolution rate W increases with the temperature or the EDTA concentration. The reaction orders of dissolution for hydrogen ions in sulfuric acid and EDTA (dlogW/dpH = 0.5 ± 0.1) and for anions (dlogW/dlog[An ⁻] = 0.5 ± 0.1) are determined. A specific feature of the dissolution kinetics in EDTA is a maximum in the dissolution rate of the cobalt oxides at pH −1. The activation energy of the process E _a is 70 kJ/mol in H₂SO₄ and 60 kJ/mol in EDTA. The modeling of the process shows that the CoOH⁺ ion is a surface particle controlling the dissolution rate in mineral acids and the CoHY⁻ ion, in the complexone.     

Calorimetrically Measured Enthalpies for

The enthalpy for the direct reaction of H₂ (g) with Zr has been measured by calorimetry at moderate, 323 K, and elevated, 928 K, temperatures over a large range of H contents. The elevated temperature enthalpies were determined for solution in the α phase, for the (α + β) phases, the β phase, the(β + γ) phases, and they phase. Simultaneously, the equilibrium pressures were measured. A combination of ΔG_H = 1/2RT In p _{H 2} , values and the enthalpies gives the corresponding entropies. At 323 K, where equilibrium pressures cannot be measured, the enthalpy for the reaction 1/2H₂ (g) + Zr/1.5 → ZrH_1.5 /1.5 was determined as -87 ± 1.5 kJ/mol H. The enthalpy for reaction of H₂ (g) and Zr (2.5 wt pct Nb) has been determined calorimetrically at 323 K and is found to decrease in exothermicity from —86 to —78 kJ/mol H in the range of (H/Zr) values from 0 to 1.5. Enthalpies of reaction were also measured at the same tem- perature for a two-phase alloy consisting of Zr-rich and Zr₂Ni phases with an overall stoichi- ometry of Zr_0.85Ni_0.15. Formerly Graduate Student, Formerly Graduate Student,     

Creep characteristics of single crystalline Ni3Al(Ta,B)

The creep characteristics, including the nature of the creep transient after a stress reduction and activation energy for creep of single crystalline Ni₃Al(Ta,B) in the temperature range 1083 to 1388 K, were investigated. An inverse type of creep transient is exhibited during stress reduction tests in the creep regime where the stress exponent is equal to 3.2. The activation energy for creep in this regime is equal to 340 kJ mol⁻¹. A normal type of creep transient is observed during stress reduction tests in the regime where the stress exponent is equal to 4.3. The activation energy for creep in this regime is equal to 530 kJ mol⁻¹. The different transient creep behavior and activation energies for creep observed in this investigation are consistent with the previous suggestion that then = 4.3 regime is associated with creep controlled by dislocation climb, whereas then = 3.2 regime is associated with a viscous dislocation glide process for Ni₃Al at high temperatures.     

The precipitation of Ni3S2 from sulfate solutions

The formation conditions for the recovery of nickel from sulfate solutions as Ni3S2 have been investigated; this sulfide is more reactive than NiS in subsequent leaching operations. Hydrogen sulfide gas at atmospheric pressure is introduced into a NiSO4-Na2SO4-MgSO4-Al2(SO4)3 solution in the presence of reduced iron powder. Although the formation of Ni3S2 is compctitive with that of NiS, the nickel precipitation efficiency and the ratio of nickel as Ni3S2 to the total nickel precipitated reached 99.5 to 99.9 and 90 to 95 pct, respectively, under the following conditions: 363 K, Ph2s 31 kPa, Ni²⁺ 4.0 g · dm^-3, 3[Fe^o]/[Ni²⁺] 1.25 to 1.5, H2S flow rate 70 to 100 cm³ · min^-1, and 45 to 60 minutes retention time. Selective formation of Ni3S2 is achieved within 10 minutes, and a reaction on the surface of the iron is rate-determining during the early stages of precipitation. Since the iron is almost totally consumed after 1 to 2 hours of reaction, the precipitated Ni₃S₂ is gradually converted to NiS. Calculations considering the buffer action of sulfate ion and sulfate complex formation with polyvalent metal cations as well as with nickel ions confirmed that significant nickel precipitation as Ni₃S₂ should occur under the test conditions.     

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.     

Enthalpies of formation of liquid and solid (gallium + palladium) alloys

The enthalpies of formation of liquid (Ga + Pd) alloys were determined by direct reaction calorimetry in the temperature range 1322 <T/K < 1761 and the molar fraction range 0 <x _Pd < 0.87. The enthalpies are very negative with a minimum Δ_mix H _m = −70.4 ± 3.0 kJ mol_-1 atx _Pd = 0.6, independent of the temperature. Limiting partial molar enthalpies of palladium and gallium were calculated as Δh _m (Ga liquid in ∞liquid Pd) = −265 ± 10 kJ mol₋₁ and Δh _m (Pd liquid in ∞liquid Ga) = -144 ± 5 kJ mol₋₁. The integral molar enthalpy is given by Δ_mix H _m =x(1-x) (-143.73 -232.47x + 985.77x ²-4457.8.x ³ + 6161.1x ⁴ + 2577.4x ⁵), wherex = x _Pd. Moreover, values for the enthalpies of formation and fusion of PdGa, Pd₂Ga, and the solid solution (withx _Pd = 0.8571) have been proposed. These results have been discussed taking into account the equilibrium phase diagram. Formerly Ph.D. student, Université de Provence     

Enthalpies of formation of liquid binary (copper + iron, cobalt, and nickel) alloys

The enthalpies of formation of liquid binary (Cu+Fe, Co, Ni) alloys are studied by direct reaction calorimetry in the whole range of compositions at 1873, 1823, and 1753 K, respectively. The integral molar enthalpies of mixing are found to be positive in all three systems with the maximum values approaching 10.8±0.7 kJ/mol⁻¹ at x _Fe=0.43, 7.1±0.9 kJ/mol⁻¹ at x _Co=0.55, and 3.7±0.5 kJ/mol⁻¹ at x _N1=0.53. Partial molar enthalpies at infinite dilution constitute 59.4±3.3 kJ/mol⁻¹ for iron, 44.3±4.1 kJ/mol⁻¹ for cobalt, and 14.9±2.2 kJ/mol⁻¹ for nickel in liquid copper. Similar values for copper in liquid iron, cobalt, and nickel are 36.6±3.9, 45.3±6.0, and 17.7±4.4 kJ/mol⁻¹, respectively. The results are compared with the thermodynamic data available in literature and discussed in connection to the equilibrium-phase diagrams. In particular, decreasing from Cu-Fe to Cu-Ni liquid alloys positive values of the excess thermodynamic functions of mixing are fully in accord with the growing stability of phases in these systems. The excess entropies of mixing are estimated by combining the established enthalpies with carefully selected literature data for the excess Gibbs functions. Analysis of possible contributions to the enthalpies of mixing indicates that the experimentally established regularity in ΔH values along the 3d series is likely to arise from the difference in d-band width and d-electron binding energy of the alloy constituents.     

Kinetics of silver leaching from manganese-silver associated ores in sulfuric acid solution in the presence of hydrogen peroxide

Kinetics of silver leaching from a manganese-silver associated ore in sulfuric acid solution in the presence of H₂O₂ has been investigated in this article. It is found that sulfuric acid and hydrogen peroxide have significant effects on the leaching rate of silver. The reaction orders of H₂SO₄ and H₂O₂ were determined as 0.80 and 0.68, respectively. It is found that the effects of temperature on the leaching rate are not marked, the apparent activation energy is attained to be 8.05 kJ/mol within the temperature range of 30 °C to 60 °C in the presence of H₂O₂. Silver leaching is found to be diffusion-controlled and follows the kinetic model: 1−2x/3−(1−x)^2/3=Kt. It is also found that particle size presents a clear effect on silver leaching rate, and the rate constant (k) is proportional to d ₋₂ ⁰ .     

Structural superplasticity in a fine-grained eutectic intermetallic NiAl−Cr alloy

A rapidly solidified and thermomechanically processed fine-grained eutectic NiAl−Cr alloy of the composition Ni₃₃Al₃₃Cr₃₄ (at, pct) exhibits structural superplasticity in the temperature regime from 900°C to 1000°C at strain rates ranging from 10⁻⁵ to 10⁻³ s⁻¹. The material consists of a B2-ordered intermetallic NiAl(Cr) solid solution matrix containing a fine dispersion of bcc chromium. A high strain-rate-sensitivity exponent of m=0.55 was achieved in strain-rate-change tests at strain rates of about 10⁻⁴ s⁻¹. Maximum uniform elongations up to 350 pct engineering strain were recorded in superplastic strain to failure tests. Activation energy analysis of superplastic flow was performed in order to establish the diffusion-controlled dislocation accommodation process of grain boundary sliding. An activation energy of Q _c=288±15 kJ/mole was determined. This value is comparable with the activation energy of 290 kJ/mole for lattice diffusion of nickel and for ⁶³Ni tracer selfdiffusion in B2-ordered NiAl. The principal deformation mechanism of superplastic flow in this material is grain-boundary sliding accommodated by dislocation climb controlled by lattice diffusion, which is typical for class II solid-solution alloys. Failure in superplastically strained tensile samples of the fine-grained eutectic alloy occurred by cavitation formations along NiAl‖‖Cr interfaces.     

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),

Dissolution of columbite and tantalite in acidic fluoride media

The dissolution reactions of Nb and Ta from columbite and tantalite in the aqueous solutions of HF, HF-HC1, NH₄F-HCI, HF-H₂SO₄, and NH₄F-H₂SO₄ were kinetically studied in the temperature range of 333 to 353 K. The presence of both H⁺ and F^- in the leachant is necessary for the fast dissolution of columbite and tantalite. The increase in these ion concentrations and the elevation of temperature are effective in increasing the dissolution rate. The initial dissolution rate of Nb from columbite under the conditions employed in this work can be expressed as follows:R _i =k _o a(H⁺)^1.2 C(F^2212;)^1.1 exp(−E _a /RT) where an apparent activation energy,E _a , ranges from 53.9 kJ mol⁻¹ to 65.5 kJ mol⁻¹. Formerly Graduate Student, Department of Metallurgy, Kyoto University, Japan     

Dissolution of columbite and tantalite in acidic fluoride media

The dissolution reactions of Nb and Ta from columbite and tantalite in the aqueous solutions of HF, HF-HC1, NH₄F-HCI, HF-H₂SO₄, and NH₄F-H₂SO₄ were kinetically studied in the temperature range of 333 to 353 K. The presence of both H⁺ and F^- in the leachant is necessary for the fast dissolution of columbite and tantalite. The increase in these ion concentrations and the elevation of temperature are effective in increasing the dissolution rate. The initial dissolution rate of Nb from columbite under the conditions employed in this work can be expressed as follows:R _i =k _o a(H⁺)^1.2 C(F^2212;)^1.1 exp(−E _a /RT) where an apparent activation energy,E _a , ranges from 53.9 kJ mol⁻¹ to 65.5 kJ mol⁻¹. Formerly Graduate Student, Department of Metallurgy, Kyoto University, Japan     

Enthalpies of formation of borides of iron,cobalt, and nickel by solution calorimetry in liquid copper

The enthalpies of formation at 1385 ±2 K of the following crystalline borides have been determined by high temperature solution calorimetry using liquid copper as the calorimetric solvent. Fe₂B-67.87 ±8.05 kJ mol⁻¹, Co₂B -58.1 ±7.0 kJ mol⁻¹, Ni₂B -67.66 ±4.12 kJ ml⁻¹, FeB-64.63 ±4.34 kJ mol⁻¹, CoB -69.52 ±6.0 kJ mol⁻¹, and NiB -40.2 ±3.77 kJ mol⁻¹. The enthalpy of fusion of NiB has been determined to be 28.25 ±1.54 kJ mol⁻¹ at its melting point of 1315 K. New data are reported also for the enthalpies of solution of iron, cobalt, and nickel in copper, and for the enthalpies of interaction between these metals and boron in dilute solutions in liquid copper.     

Studies on kinetics of low-temperature chlorination of ZrO2 by gaseous carbon tetrachloride

Studies on the kinetics of chlorination of ZrO₂. powder by carbon tetrachloride vapor in mixture with nitrogen in a low-temperature range of 650 to 825 K at different periods and partial pressures of carbon tetrachloride were carried out. The chlorination results at 650 and 675 K seem to follow a diffusion-controlled reaction model of Jander’s type: [1−(1−R)^1/3]² =k ₁t whereR is the fraction of ZrO₂ chlorinated in timet andk ₁ is the rate constant. The approximate activation energy of the process was calculated fromk ₁ values at the previously mentioned two temperatures and found to be 278 kJ/mole. For the chlorination in the temperature range of 700 to 750 K, the topochemical reaction model 1−(1−R) ^1/3 =k ₂t was followed. The rate constant,k ₂, was found to be proportional to the partial pressure of carbon tetrachloride. The activation energy of this reaction was calculated to be 154 kJ/mole. In the temperature range of 775 to 825 K, the rate of chlorination was found to be directly proportional to the time of chlorination following Langmuir’s Adsorption Isotherm. Because of the very high rate of chlorination and thermodynamic possibility of decomposition of CCl₄ above 773 K, the rate-controlling step has been suggested to be the decomposition of the adsorbed complex formed by ZrO₂ with carbon and chlorine atoms, obtained from the decomposition of CCl₄ vapor. The activation energy of the process was 54 kJ/mole. In view of nearly complete chlorination of ZrO₂ by CCl₄ in a very short period of about 15 minutes, at a temperature around 800 K and lesser possibility of formation of toxic product gases, the process is recommended for commercial application.     

Grain growth of nanocrystalline Ni powders prepared by cryomilling

Grain growth of nanocrystalline Ni powders with an average grain size of ∼22 nm prepared by cryogenic mechanical milling (or cryomilling) was investigated by using X-ray diffraction (XRD) and transmission electron microscopy (TEM). A dispersion of NiO and Ni₃N particles with a size less than 5 nm was formed in the cryomilled powders. The Ni₃N particles decomposed at 773 K. It was found that at 0.56 homologous temperature (T/T _M ), Ni grains were retained at ∼150 nm even after long annealing times (e.g., 4 hours). For 0.45 to 0.62 T/T _M , the time exponent n deduced from D ^1/n −D ₀ ^1/n =kt was 0.16 to 0.32, tending toward 0.5 as T/T _M increased. The activation energy for grain growth in the Ni sample was determined to be 113 kJ/mol, which is close to the activation energy for grain boundary self-diffusion in polycrystalline Ni. The observed high grain size stability was attributed primarily to a grain boundary pinning mechanism arising from the NiO particles as well as impurity segregation.     

The thermodynamic behavior of sulfur in molten nickel and nickel-base alloys

The thermodynamic properties of dilute solutions of sulfur in pure liquid nickel were investigated at 1500, 1550, and 1575°C for sulfur concentrations up to 0.7 wt pct. Based on the infinitely dilute, wt pct standard state, the equilibrium data obtained for the reaction: H₂(g) + S = H₂S(g) were fitted by the equations: logK = − 1489/T − 1.772, and ΔG° = 6812 + 8.11T, cal/mole. For the solution ofS ₂(g) in pure Ni according to the reaction: 1/2S ₂(g) = S (in Ni), the standard free energy of solution is found to be: ΔG° = - 28,342 + 3.62T, cal/mole. For the very dilute solutions of sulfur normally encountered in nickel-base melting, the activity coefficient of sulfur in pure Ni at 1575°C is given by: log f_S= -0.035 (pct S). The effects of alloying elements normally used in nickel-base alloys on the activity coefficient of sulfur in molten nickel were investigated. The activity coefficient of sulfur is increased by all of the alloying elements studied, as evidenced by the interaction parameters: e_S ^fe = +0.005, e_S ^Cr = +0.030, e_S ^Mo = +0.053, e_S ^Ti = +0.160, and e_S ^A1 = +0.133. Measured values of the activity coefficient of sulfur in the quaternary system Ni-S-Cr-Fe agreed reasonably well with those predicted from binary and ternary data. This work constitutes a portion of the work performed by W. F. VENAL for the Ph.D. degree from the University of Illinois at Chicago Circle. Formerly Professor of Metallurgical Engineering at UICC.