The diffusivity and solubility of fluorine in solid nickel from electrochemical measurements

The diffusivity and solubility of fluorine in solid nickel were determined using the following solid-state electrochemical cells: Co + CoF₂| BaF₂| Ni | BaF₂| Co + CoF₂ Co + CoF₂| CaF₂| BaF₂| Ni | BaF₂| CaF₂| Co + CoF₂ In the temperature range 1023 to 1223 K, the diffusion coefficient of fluorine in solid nickel is given by: 1 $$D_F (cm^2 /s) = (2.13_{ - 1.54}^{ + 5.54} ) \times 10^{ - 3} \exp (( - 118,600 \pm 12,000J/mol)/RT)$$ The dissolution of atomic fluorine in solid nickel obeys Sieverts’ law; however, the solubility results showed considerable scatter. In the temperature range 1073 to 1223 K, the mean solubility of fluorine in solid nickel, corresponding to the equilibrium Ni + NiF₂, follows the relationship: N _-F ^S (at. pct) = 5.73 x 10^-3 exp((10,850 J/mol)/RT)     

Thermodynamics of Oxygen Solution in Fe–Ni Melts Containing Boron

Fe–Ni alloys are widely used in engineering today. They are sometimes alloyed with boron. Oxygen is a harmful impurity in Fe–Ni alloys. It may be present in dissolved form or as nonmetallic inclusions. The presence of oxygen in Fe–Ni alloys impairs their performance. Research on the thermodynamics of oxygen solutions in Fe–Ni melts containing boron is of considerable interest in order to improve alloy production. The present work offers a thermodynamic analysis of solutions of oxygen in Fe–Ni melts containing boron. The equilibrium constant of the reaction between boron and oxygen dissolved in the melt in such systems is determined. The activity coefficients at infinite dilution and the interaction parameters in melts of different composition are also calculated. When boron reacts with oxygen in Fe–Ni melts, the oxide phase contains not only B₂O₃ but also FeO and NiO. The mole fractions of B₂O₃, FeO, and NiO in the oxide phase are calculated for different boron concentrations in Fe–Ni melts at 1873 K. For iron melts with low boron content, the mole fraction of boron oxide is ~0.1. With increase in the nickel and boron content in the melts, the boron-oxide content in the oxide phase increases. Its mole fraction is close to one for pure nickel. The solubility of oxygen in Fe–Ni melts is calculated as a function of the nickel and boron content. The deoxidizing ability of the boron improve significantly with increase in nickel content in the melt. The curves of oxygen solubility in Fe?Ni melts containing boron pass through a minimum, which is shifted to higher boron content with increase in nickel content in the melt. The boron content at the minima on the curves of oxygen solubility are determined, as well as the corresponding minimum oxygen concentrations.     

Thermodynamics of oxygen solutions in Fe-Ni-V melts

The oxygen solutions in Fe-Ni melts with up to 5% V are analyzed thermodynamically. The results of the works in which the fields of the vanadium-deoxidized oxide phases in iron and nickel were determined are generalized. The thermodynamic model developed for the calculation of the deoxidation of iron-nickel alloys with vanadium is shown to be adequate. The deoxidizing capacity of vanadium decreases insignificantly as the nickel content in the melt increases to 20% and increases substantially as the nickel content increases further. The oxygen solubility curves pass through a minimum, whose position changes from 2.3192% V for pure iron to 0.7669% V for pure nickel. We determined the equilibrium point [V]* between the (Fe, Ni)V₂O₄ and V₂O₃ oxide phases for alloys of six compositions at 1873 K. In nickel, [V]* is almost 200 times lower than in iron. The deoxidation of the Fe-40% Ni melt with vanadium is studied experimentally, and the experimental results agree satisfactorily with the calculated data.     

Aluminum deoxidation equilibrium in liquid Ni-Fe alloys equilibrated with CaO-Al2O3 slags

The deoxidation equilibrium for Al in Ni-Fe alloys was studied in the equilibrium experiments between CaO-Al₂O₃ slags and Fe-30, 50 and 70 % Ni alloys at 1873 K. By using the values for the first and second order interaction parameters between oxygen and nickel in liquid iron and those between oxygen and iron in liquid nickel, the effect of Ni on the activity coefficient of Al in liquid iron and that of Fe on the activity coefficient of Al in liquid nickel were determined in the whole composition range of Ni-Fe alloys. The oxygen contents in Ni-Fe alloys calculated by the iterative method based on pure iron were in good agreement with those based on pure nickel in the range of [% Al] < 0.03. From this fact, it was found that the Wagner's approximation relating to the multi-component solution was applicable to the deoxidation equilibrium in the whole composition range of Ni-Fe alloys in the restricted concentration of a deoxidizer.     

Measurement and modeling of Alloy-Spinel-Corundum equilibrium in the Ni-Mn-Al-0 system at 1873 K

The oxygen content of liquid Ni-Mn alloy equilibrated with spinel solid solution, (Ni,Mn)O. (1 +x)A1₂O₃, and α-Al₂O₃ has been measured by suction sampling and inert gas fusion analysis. The corresponding oxygen potential of the three-phase system has been determined with a solid state cell incorporating (Y₂O₃)ThO₂ as the solid electrolyte and Cr + Cr₂O₃ as the reference electrode. The equilibrium composition of the spinel phase formed at the interface of the alloy and alumina crucible was obtained using EPMA. The experimental data are compared with a thermodynamic model based on the free energies of formation of end-member spinels, free energy of solution of oxygen in liquid nickel, interaction parameters, and the activities in liquid Ni-Mn alloy and spinel solid solution. Mixing properties of the spinel solid solution are derived from a cation distribution model. The computational results agree with the experimental data on oxygen concentration, potential, and composition of the spinel phase.     

Thermodynamic properties of S-Fe-Co-Ni and Fe-Co-Ni systems

The values of sulfur activity in the liquid S-Fe-Co-Ni system were determined from unpublished equilibrium data for H₂ +S (in alloy) = H₂S. The activity coefficient of sulfur varied from 0.387 to 1.896 and increased with increasing concentrations of Fe and Co. The published values for the activities in the binary systems Fe-Co, Fe-Ni, and Co-Ni were used to calculate the activities in the ternary Fe-Co-Ni alloys, and these results were expressed as a function of composition. This function was used with the activity coefficients of S in the binary metal solvents to express the activity coefficient of S in the ternary metal solvents as a function of mol fractions of Fe, Co, and Ni. The experimental values for S in Fe-Co-Ni agreed well with the calculated values based on the binary metal solvents, and this showed that all the activity values were consistent.     

Measurement and modeling of Alloy-Spinel-Corundum equilibrium in the Ni-Mn-Al-0 system at 1873 K

The oxygen content of liquid Ni-Mn alloy equilibrated with spinel solid solution, (Ni,Mn)O. (1 +x)A1₂O₃, and α-Al₂O₃ has been measured by suction sampling and inert gas fusion analysis. The corresponding oxygen potential of the three-phase system has been determined with a solid state cell incorporating (Y₂O₃)ThO₂ as the solid electrolyte and Cr + Cr₂O₃ as the reference electrode. The equilibrium composition of the spinel phase formed at the interface of the alloy and alumina crucible was obtained using EPMA. The experimental data are compared with a thermodynamic model based on the free energies of formation of end-member spinels, free energy of solution of oxygen in liquid nickel, interaction parameters, and the activities in liquid Ni-Mn alloy and spinel solid solution. Mixing properties of the spinel solid solution are derived from a cation distribution model. The computational results agree with the experimental data on oxygen concentration, potential, and composition of the spinel phase.     

Thermodynamics of the oxygen solutions in Fe-Ni-Ti melts

The oxygen solutions in Fe-Ni melts containing up to 3% titanium are analyzed thermodynamically. The results of the works that determined the fields of the oxide phases in iron and nickel deoxidized by titanium are generalized. The proposed calculation model is shown to adequately describe the titanium deoxidation of iron-nickel alloys. The deoxidizing capacity of titanium decreases as the nickel content in the melt increases to 40% and, then, increases sharply as the nickel content increases further. The oxygen solubility curves pass through a minimum, whose position changes from 0.5644% Ti for pure iron to 0.6332% Ti for pure nickel. The points of equilibrium between the TiO₂, Ti₃O₅, and Ti₂O₃ oxide phases are determined for six alloy compositions at 1873 K. The titanium deoxidation of Fe-40% Ni melts is experimentally studied, and the calculated and experimental results are in good agreement.     

Study of the surface properties of nickel-based melts by the constrained drop method: I. Surface tension

The constrained drop method is used to study the surface tension σ of the following melts at 1773–1923 K and p _Ar = 0.1 MPa: nickel of various grades (with various oxygen contents), binary Ni-Al (Re) alloys, and a complex Ni-Re-(W, Mo, Co) alloy. The value of σ of liquid nickel is shown to decrease with increasing oxygen content in it. The additions of aluminum (6%) and rhenium (3–7%) to nickel in binary alloys weakly change its surface tension. Alloying elements (W, Mo, Co) in Ni-Re-(W, Mo, Co) alloys insignificantly affect σ of their melts.     

Thermodynamic studies of oxygen behavior in tantalum-based alloys

An experimental study of equilibrium thermodynamic properties of oxygen in pure tantalum and tantalum alloyed with V, Nb or Mo was made by EMF measurements on solid electrolytic cells over the temperature range of 873–1373 K (600–1100°C). The solubility of oxygen in pure tantalum in equilibrium with Ta₂O₅ was determined to be C_s = 12.4exp[−(16 kJ/mol)/(RT)] over the experimental temperature range. It was concluded that oxygen obeys Henry's law for concentrations up to the terminal solubility in tantalum for the temperature range 873–1373 K (600–1100°C). The oxygen activity coefficient increased with Mo content in TaMo alloys and decreased with V content in TaV alloys. The equilibrium results showed virtually no change in thermodynamic behavior of the oxygen solution by adding Nb to TaO alloys. The positive deviation of the oxygen activity coefficient in TaMo alloys is evidence of a repulsive interaction between molybdenum and oxygen atoms. The interaction energy was calculated assuming that the interaction extends to third nearest neighbors. It may, in fact, extend to fourth or higher neighboring shells of atoms.     

Structure and stability of the precipitates in melt spun ternary Al-transition-metal alloys

The decomposition of supersaturated solid solution of ternary, melt spun Al-transition-metal alloys has been examined using analytical transmission electron microscopy. It has been found that the presence of small amounts of iron in AlV, AlMo and AlCr alloys can give rise to a fine dispersion of P-phase precipitate in the grain centres. It has been shown that the P-phase is quasicrystalline phase and has an orientation relationship with Al matrix as: i2|〈001〉_Al, 〈τ²τ1〉_Al, i3|〈111〉_Al, 〈τ²10〉_Al; i5|〈τ10〉_Al, τ = (1 + √5)/2. The stability of quasicrystals is significantly improved by the presence of iron in A1-transition-metal alloys. The effect of iron on stabilising the quasicrystal precipitates is believed to be due to the fact that iron replaces the oversized transition metal (TM) atoms V, Cr and Mo in the smaller TM sites, resulting in a reduction of structural stress of quasicrystalline phase. The significance of these observations on the structure and stability of quasicrystal precipitates is discussed in terms of the development of high temperature dispersion strengthening Al-based alloys with transition metals.     

Ternary alloying study of MoSi2

Ternary alloying of MoSi₂ with adding a series of transition elements was investigated by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). Iron, Co, Ni, Cr, V, Ti, and Nb were chosen as alloying elements according to the AB₂ structure map or the atomic size factor. The studied MoSi₂ base alloys were prepared by the arc melting process from high-purity metals. The EDS analysis showed that Fe, Co, and Ni have no solid solubility in as-cast MoSi₂, while Cr, V, Ti, and Nb exhibit limited solid solubilities, which were determined to be 1.4±0.7, 1.4±0.4, 0.4±0.1, and 0.8±0.1. Micro-structural characterization indicated that Mo-Si-M_VIII (M_VIII=Fe, Co, Ni) and Mo-Si-Cr alloys have a two-phase as-cast microstructure, i.e., MoSi₂ matrix and the second-phase FeSi₂, CoSi, NiSi₂, and CrSi₂, respectively. In as-cast Mo-Si-V, Mo-Si-Ti, and Mo-Si-Nb alloys, besides MoSi₂ and C40 phases, the third phases were observed, which have been identified to be (Mo, V)₅Si₃, TiSi₂, and (Mo, Nb)₅Si₃.     

A thermodynamic model of nickel smelting and direct high-grade nickel matte smelting processes: Part II. distribution behaviors of Ni, Cu, Co, Fe, As, Sb, and Bi

A thermodynamic model has been developed to predict the distribution behavior of Ni, Cu, Co, Fe, S, As, Sb, and Bi in nickel smelting and direct high-grade nickel matte smelting processes. The model has been validated by numerous experimental data and industrial data with a wide range of operating conditions. The effect of operating conditions on the distributions of Ni, Cu, Co, As, Sb, and Bi among the gas, matte, and slag phases has been investigated. It was found that the distribution behavior of Ni, Co, Cu, As, Sb, and Bi in the nickel smelting furnace depends on process parameters such as the smelting temperature, matte grade, oxygen enrichment, Fe/SiO₂ ratio in the slag, Cu/Ni ratio in charge, and oil/air ratio. The parameters also have an influence on the behavior of Fe₃O₄ in the slag.     

Oxygen activities in Cr-containing Fe and Ni-based melts

Plug-type, ZrO₂-based oxygen sensors have been used for long-term measurements of oxygen activity in Fe–O–Cr and Ni–O–Cr melts. In these melts, equilibrated with chromium oxide, oxygen activities a_O were determined as a function of Cr content. From the experimental results, data were derived for activity coefficients f_O and of 1st and 2nd order interaction parameters e_O^Cr and r_O^Cr. Cr₂O₃ has been identified as the oxide phase in equilibrium with the metal melt at ≥ 5 wt.% Cr in the case of iron and at ≥ 0.2 wt.% Cr in the case of nickel. Oxygen activities and oxygen contents in Cr-containing iron melts are lowered with increasing additions of nickel. Further investigations were directed to a_O determination in Fe–O–Cr–C and Fe–O–Cr–Al melts.     

Spinel deoxidation equilibria in the Fe—Mn—Al—O system – experiment and computation

The concentration and chemical potential of oxygen in liquid Fe—Mn alloys equilibrated with the spinel solid solution, (Fe, Mn)Al_2+2xO_4+3x, and α-Al₂O₃ have been determined at 1873 K as a function of manganese concentration. The composition of the spinel phase has been determined using electron probe microanalysis. The results are compared with data reported in the literature. The deoxidation equilibrium has been computed using data on free energy of solution of oxygen in liquid iron, free energies of formation of hercynite and galaxite, and interaction parameters reported in the literature. The activity-composition relationship in spinel solid solution was derived from a cation distribution model. The model is in excellent agreement with the experimental data on oxygen concentration and potential and the composition of the spinel phase.     

Transfer of iron to Cu–Ni alloys from the lining of the vacuum induction furnace

In Ni–Cu alloys, iron must be excluded in many cases. Iron may enter the alloy from the batch or the furnace lining. Since the Fe₂O₃ content in refractories may be as much as 2.5%, it is important to assess the increase in iron content in alloys on account of interaction with the furnace lining. In the present work, the influence of the Fe₂O₃ content in the crucible and the volume of the crucible on the iron content in the final alloy is studied. Thermodynamic analysis and experimental data indicate that the nickel and copper in Ni–Cu alloys may reduce iron that is present in the lining. When using low-iron batch, iron from the crucible is transferred almost completely to the melt. The increase in iron content in Ni–Cu alloys is investigated as a function of the capacity of the vacuum induction furnace and the Fe₂O₃ content in the periclase crucibles, with complete transfer of the iron from the lining to the melt. With increase in furnace capacity, less iron enters the melt from the crucible. With more than 200 kg of metal, the increase in iron concentration mainly depends not on the furnace capacity but on the Fe₂O₃ content in the refractory. In order to produce Ni–Cu alloys with <0.01% Fe, refractories with Fe₂O₃ content no higher than 0.5% must be used. To produce Ni?Cu alloys with <0.05% Fe, the use of lining refractories with Fe₂O₃ content no higher than 2.5% is recommended.     

Activities in liquid Fe-V-O and Fe-B-O alloys

The activities in liquid Fe-V-0 and Fe-B-O alloys have been determined using the following galvanic cells Cr-Cr₂O₃(s) | ZrO₂(CaO) | Fe-V-O (l, saturated with oxide) Cr-Cr₂O₃(s) | ThO₂(Y₂O₃) | Fe-V-O (l, saturated with oxide) Cr-Cr₂O₃(s) | ZrO₂(CaO) | Fe-B-O (l, B₂O₃ saturated with Al₂O₃) The solubility of oxygen in Fe-V alloys at 1600°C decreases with increasing vanadium content to a minimum of about 180 ppm at 3 wt pct V, and then increases to over 4000 ppm at 36.3 wt pct V. Vanadium was found to decrease the activity coefficient of oxygen and the value of the interaction coefficient e_o ^V at infinite dilution of vanadium is -0.14. The activity of vanadium was calculated from the measured electromotive force, and log γ_v was found to be represented well by the quadratic formalism for N_v < 0.4: log γ_V = -0.70N ² _Fe -0.30 At 1550°C boron decreases the solubility of oxygen down to about 80 ppm at 0.67 wt pct B in Fe-B melts in equilibrium with B₂O₃ saturated with A1₂O₃ (N_{Al 2} O₃ = 0.087). The boron deoxidation product, ’K′ = (wt pct B)²(wt pct 0)³ at infinite dilution of boron is 4.4 × 10_-9 and 1.5 × 10^-8 at 1550° and 1600°C, respectively. Boron decreases the activity coefficient of oxygen in liquid iron, and the value of the interaction coefficient e_o ^B is -2.6 at infinite dilution of boron. The activity coefficient of boron at infinite dilution (γ^° _B) is 0.083 at 1550°C relative to solid boron.     

Solubility and thermodynamic properties of oxygen in solid molybdenum

The solubility of oxygen in solid Mo, determined in the range 1400 to 1900°C by equilibrating rods of zone-refined Mo with mixtures of Mo and MoO₂ powders, can be expressed as ln Χ_O ^α(sat) (atom fraction) = 5.86 - 27,900/T Using the known value of the free energy of formation of MoO₂, the chemical potential of oxygen in the dilute solid solution is calculated to be μ^α _O1/2μ^o _O2 = ΔG ^α _O = -10,760 + (6.92 +R ln χ^μ _O)T ± 1000 cal/g-atom oxygen The heat of solution of oxygen in Solid Mo, ΔH_Oα = -10,760 ± 3000 cal/g-atom oxygen, and the excess entropy for the interstitial solid solution ΔS_Oα(xs, i) =- 9.10 ± 1.5 cal/degree, g-atom oxygen, assuming that the oxygen atoms reside in the octahedral interstices of bcc Mo.     

Distribution of nickel between copper-nickel and alumina saturated iron silicate slags

The solubility of nickel in slag was determined by equilibrating copper-nickel alloys with alumina-saturated iron silicate slags in an alumina crucible at 1573 K. The experiments were carried out under controlled oxygen partial pressures in the range of 10^-10 to 10^-8 atm by use of suitable CO-CO₂ gas mixtures, and at Fe/SiO₂ ratio 1.34. The results showed that nickel dissolves in slag both as Ni²⁺ (nickel oxide) and Ni‡ (nickel metal), and the relation obtained was: (Wt pct Ni in slag) = (ie33-01) The activity coefficient of nickel oxide (γ^dgNio) and distribution coefficient of nickel (A_Ni) is calculated to be 0.375 and 233.3, respectively. γ^dgNio and A_Ni are found to be independent of oxygen partial pressures. The presence of alumina increases the solubility of nickel in slags.     

Study of the surface properties of nickel-based melts by the sessile drop method: II. Density

The density of melts based on nickel of various grades (i.e., with various oxygen contents) is experimentally studied at 1500–1650°C and p _Ar = 0.1 MPa, and the effect of alloying elements (Al, Re, W, Mo, Co) on this density is analyzed. As compared to liquid nickel, the density of a Ni-6% Al melt decreases and that of Ni-(3–7)% Re and Ni-7% Re-(W,Mo,Co) melts increases. The difference between the molar volume of the melt calculated from the experimental data and using the additivity rule is determined, and the structures of the melts at 1823 K are found to have a low density.