Fe-Ni Melts Research Articles

Combined Deoxidation of Fe–Ni Melts by Manganese and Aluminum

Combined Deoxidation of Fe–Ni Melts by Manganese and Aluminum

Temperature–Composition Dependence of Thermodynamic Mixing Functions of Co–Cr–Cu–Fe–Ni Melts

Temperature–Composition Dependence of Thermodynamic Mixing Functions of Co–Cr–Cu–Fe–Ni Melts

How do diamonds grow in metal melt together with silicate minerals? An experimental study of diamond morphology

Abstract. The origin and evolution of metal melts in the Earth's mantle and their role in the formation of diamond are the subject of active discussion. It is widely accepted that portions of metal melts in the form of pockets can be a suitable medium for diamond growth. This raises questions about the role of silicate minerals that form the walls of these pockets and are present in the volume of the metal melt during the growth of diamonds. The aim of the present work was to study the crystallization of diamond in a complex heterogeneous system: metal-melt–basalt–carbon. The experiments were performed using a multianvil high-pressure apparatus of split-sphere type (BARS) at a pressure of 5.5 GPa and a temperature of 1500 ∘C. The results demonstrated crystallization of diamond in metal melt together with garnet and clinopyroxene, whose chemical compositions are similar to those of eclogitic inclusions in natural diamond. We show that the presence of silicates in the crystallization medium does not reduce the chemical ability of metal melts to catalyze the conversion of graphite into diamond, and, morphologically, diamond crystallizes mainly in the form of a cuboctahedron. When the content of the silicate material in the system exceeds 5 wt %, diamond forms parallel-growth aggregates, but 15 wt % of silicate phases block the crystallization chamber, preventing the penetration of metallic melt into them, thus interrupting the growth of diamond. We infer that the studied mechanism of diamond crystallization can occur at lower-mantle conditions but could also have taken place in the ancient continental mantle of the Earth, under reducing conditions that allowed the stability of Fe–Ni melts.

Recent studies on thermophysical properties of metallic alloys with PROSPECT: Excess properties to construct a solution model

We have developed the system PROSPECT for measuring thermophysical properties at high temperature. Precise thermophysical measurements provide accurate excess functions, which represent non-ideality of solutions. We use excess functions to discuss solution models on the basis of electronic structure and thermodynamics. Pd-Fe systems show positive excess volume VE with negative excess Gibbs energy GE. The phase diagrams of these systems have common features with those of other Pd-X and Pt-X systems (where X is Fe, Ni, Co, or Cu), which means they all have order-disorder transitions. The correlation between VE and GE is discussed in terms of the electronic structure of the alloys, and an energy diagram is proposed to understand this correlation. The excess heat capacity CpE of Fe-Ni melts is positive over a whole composition range and a wide temperature range. We estimate the temperature dependences of the excess enthalpy HE and excess entropy SE of Fe-Ni melts from CpE. The Lupis-Elliott rule is satisfied for HE and SE with positive CpE.

Thermal Conductivities of Fe-Ni Melts Measured by Non-contact Laser Modulation Calorimetry

A combination of an electromagnetic levitation technique with a static magnetic field and laser modulation calorimetry was used to measure the thermal conductivity of Fe-Ni melts between 1673 K and 1904 K, including the supercooled temperature region. The static magnetic field suppressed convection, translational motion, and surface oscillation of the levitated droplet to reduce the experimental uncertainty in the measurements. High-purity Fe (99.9985 mass pct) and Ni (99.9960 mass pct) were used for the sample of the measurements. For all melt compositions, the thermal conductivity had a positive temperature dependence, except for a sample with a 0.4 mole fraction of Fe. The measured thermal conductivity values of Fe-Ni were larger than those evaluated from the electric conductivity assuming the Wiedemann–Franz law for all composition ranges. It implies that atomic thermal vibration contributes to the thermal conductivity.

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.

Normal spectral emissivity and heat capacity at constant pressure of Fe–Ni melts

The normal spectral emissivity at 807 nm and molar heat capacity at constant pressure of Fe–Ni melts were successfully measured by the combination of an electromagnetic levitation technique and a static magnetic field. The static magnetic field suppressed the surface oscillation and translational motion of the levitated sample droplet to reduce the experimental uncertainty in the measurements. For all compositions of the melts, the normal spectral emissivity values and molar heat capacities showed negligible temperature dependence. The excess heat capacity of the melts was evaluated as a function of composition. This analysis showed a positive deviation from the Neumann–Kopp rule over the entire composition range. Moreover, enthalpy of mixing was calculated from the excess heat capacity up to 2200 K.

Densities of Fe–Ni melts and thermodynamic correlations

The densities of liquid Fe–Ni alloys were measured accurately by combination of an electromagnetic levitation technique and a static magnetic field. The static magnetic field suppressed the surface oscillation of the levitated sample droplet, which reduced the experimental uncertainty in the density measurement. Densities were determined over a wide temperature range and included a supercooled region. The densities of all Fe–Ni alloys investigated vary linearly with temperature over the range of measurements. The excess volumes were slightly positive over the entire composition range. The results were discussed within a thermodynamic framework using relationship between excess volume and thermodynamic properties such as excess Gibbs energy and enthalpy of mixing. The excess volume is correlated positively with excess Gibbs energy and enthalpy of mixing for various binary alloy systems.

Thermodynamics of oxygen solutions in Fe-Ni, Fe-Co, and Co-Ni melts

By thermodynamic analysis of oxygen solutions in Fe-Ni-O, Fe-Co-O, and Co-Ni-O melts, the composition of the oxide phase is established for the first time. In addition, the equilibrium oxygen concentrations in these melts are determined over the whole range of alloy compositions. In Fe-Ni-O and Fe-Co-O melts, the oxide phase mainly contains FeO over a relatively broad of alloy compositions. Sharp increase in NiO content is only observed when the molar fraction of nickel exceeds one; sharp increase in CoO content is only observed when the molar fraction of cobalt exceeds 0.8. In the Co-Ni-O system, the oxide phase contains both CoO and NiO over the whole range of alloy compositions. In the Fe-Ni system, adding nickel to the melt reduces the solubility of oxygen as a result of weakening of the oxygen bonds in the melt by nickel and consequent increase in oxygen’s activity. With further increase in nickel content in the melt, the oxygen content rises at first slowly and then very sharply. In the Fe-Co system, analogously, adding cobalt to the melt reduces the solubility of oxygen as a result of weakening of the oxygen bonds in the melt and consequent increase in oxygen’s activity. With further increase in cobalt content, the oxygen content rises at first slowly and then relatively rapidly. In the Co-Ni system, adding nickel to cobalt increases the solubility of oxygen over the whole range of alloy compositions, on account of the significantly greater solubility of oxygen in nickel than in cobalt.

Deoxidation Equilibrium of Niobium in the Iron-Nickel Melts

The oxygen solubility in iron-nickel alloys with niobium was experimentally studied in Fe-40 pct Ni melt at 1823 K (1550 °C). It was shown that the presence of niobium decreases the oxygen solubility in this melt. The equilibrium constant of interaction of niobium with oxygen dissolved in the Fe-40 pct Ni ( $$ \log K_{{(1)({\text{Fe - }}40\% {\text{Ni}})}} = {-}4.619 $$ ), the Gibbs energy of this reaction ( $$ \Delta {\text{G}}_{{(1)({\text{Fe - }}40\% {\text{Ni}})}}^{ \circ } = 161 ,210\,{\text{J}}/{\text{mol}} $$ ), and the interaction coefficients characterizing these solutions ( $$ e_{{{\text{Nb}}({\text{Fe - }}40\,{\text{pctNi}})}}^{\text{O}} = {-}0.630 $$ ; $$ e_{{{\text{O}}({\text{Fe - }}40\,{\text{pctNi}})}}^{\text{Nb}} = {-}0.105 $$ ; $$ e_{{{\text{Nb}}({\text{Fe - }}40\,{\text{pctNi}})}}^{\text{Nb}} = 0.010 $$ ) were determined. In the wide concentration range, the equilibrium constants and Gibbs energy of interaction of niobium and oxygen dissolved in the Fe-Ni melts and the interaction coefficients for these solutions were calculated for 1823 K (1550 °C). For this temperature, the oxygen solubility in the niobium-containing Fe-Ni melts was also determined. With an increase in the nickel concentration in the alloy the niobium affinity to oxygen rises appreciably. This appears to be associated with a decrease in the bond strength between metal and oxygen in the melt as the nickel concentration increases ( $$ \gamma_{\text{O(Fe)}}^{ \circ } = 0.0084;\;\gamma_{{{\text{O}}({\text{Ni}})}}^{ \circ } = 0.297 $$ ).

Solubility of oxygen in zirconium-containing iron-nickel melts

The oxygen solubility in zirconium-containing Fe-Ni melts is for the first time studied experimentally at 1873 K using the Fe-40% Ni alloy as an example. It is shown that the deoxidizing ability of zirconium in this melt is very high, but it is slightly lower than pure iron. This is due to the fact that, when the nickel content in the melt increases, the bond strengths of zirconium with the melt base (γ Zr(Fe) ∘ = 0.043; (γ Zr(Ni) ∘ = 0.00007) rise to a considerably greater degree than the bond strengths of oxygen weaken (γ O(Fe) ∘ = 0.0105; (γ O(Ni) ∘ = 0.357). The equilibrium constant of interaction of zirconium and oxygen dissolved in the Fe-40% Ni melt (K (Fe-40% Ni) = 6.011 × 10−7) and the interaction parameters characterizing these solutions (e Zr O = −7.16; e O Zr = −1.25; e Zr Zr = 2.16) were determined.

Solubility of oxygen in niobium-bearing iron-nickel melts

The solubility of oxygen in niobium-bearing iron-nickel melts is studied experimentally, for the example of Fe-40% Ni alloy at 1823 K. Niobium reduces the solubility of oxygen in this melt. Values are determined for the equilibrium constant of the reaction between niobium and oxygen dissolved in the given melt (logK(1)(Fe-40% Ni) = −4.619), the Gibbs energy (ΔG(1)(Fe-40%Ni)o = 161210 J/mol), and the interaction parameters (eNb(Fe-40% Ni)O = −0.630; eO(Fe-40% Ni)Nb = −0.105; eNb(Fe-40% Ni)Nb = 0.010). Over a wide range of concentrations, the Gibbs energy of the reaction between niobium and oxygen dissolved in Fe-Ni melts, the equilibrium constants, and the interaction parameters at 1823 K are determined. The solubility of oxygen in Fe-Ni melts of different composition containing niobium is determined at 1823 K. With increase in nickel content in the Fe-Ni melts, the oxygen affinity of niobium increases significantly, on account of the decrease in oxygen binding forces with increase in nickel content in the melt (γO(Fe)∘ = 0.0084, γO(Ni)∘ = 0.297).

Structural, Thermodynamics and Dynamics Properties of Fe-Ni Melts with Different EAM Models

Molecular dynamics (MD) simulation has been performed to explore the microstructure, thermodynamics and dynamics properties of liquid Fe-Ni alloy based upon two different embedded atom method (EAM) models. The calculated PCFs with two EAM models are good agreement with the experimental values. While the calculated Scc (q) of Bhatia-Thornton (B-T) structure factor (SF) shows different behavior: a sharp increasing and a small one at lower q from G. Bonnys model and Zhous model respectively. The mixing of enthalpy with G. Bonnys EAM is positive in the whole concentration range. While the different mixing behavior with a slightly negative mixing of enthalpy based on Zhous model, which is consistent with the experimental results, is observed. Density and diffusion coefficients of liquid Fe-Ni as a function of composition show the same tendency based on both G. Bonnys model and Zhous model. In this work, Fe-Ni melts show different mixing behavior based on the two different EAM models.

Thermodynamics of the oxygen solutions in niobium-containing Fe-Ni melts

A thermodynamic analysis is performed for the oxygen solutions in niobium-containing Fe-Ni melts. The deoxidizing capacity of niobium in iron—nickel melts is shown to be low. It decreases slightly as the nickel content in a melt increases to 40% and then increases insignificantly as the nickel content increases to 60%; a further increase in the nickel content leads to a marked increase in the deoxidizing capacity. The solubility curves of oxygen in iron—nickel melts passes through a minimum, whose position shifts toward higher niobium concentrations with increasing nickel content. Subsequent niobium additions increase the oxygen concentration in the melt. The equilibrium constants of the reactions of niobium deoxidizing of iron—nickel melts, the activity coefficients, and the interaction parameters characterizing Fe-Ni-Nb-O melts are determined.

Diffusivities of an Al–Fe–Ni melt and their effects on the microstructure during solidification

A systematical investigation of the diffusivities in an Al–Fe–Ni melt was presented. Based on the experimental and theoretical data about diffusivities, the temperature- and composition-dependent atomic mobilities were evaluated for the elements in Al–Ni, Al–Fe, Fe–Ni and Al–Fe–Ni melts via an effective approach. Most of the reported diffusivities can be reproduced well by the obtained atomic mobilities. In particular, for the first time the ternary diffusivity of the liquid in a ternary system is described in conjunction with the established atomic mobilities. The effect of the atomic mobilities in a liquid on microstructure and microsegregation during solidification was demonstrated with one Al–Ni binary alloy. The simulation results indicate that accurate databases of mobilities in the liquid phase are much needed for the quantitative simulation of microstructural evolution during solidification by using various approaches, including DICTRA and the phase-field method.

Thermodynamics of the oxygen solutions in iron-nickel melts

The oxygen solutions in Fe-Ni melts containing chromium, manganese, vanadium, carbon, silicon, titanium, or aluminum are studied thermodynamically. The equilibrium constants of the deoxidation of the melts by these elements are determined, and the activity coefficients for infinite dilution and the interaction parameters in alloys of various compositions are found. The oxygen solubilities in the alloys are calculated as a function of the nickel and deoxidizer contents. The deoxidizer contents at the minima in the oxygen solubility curves for the melts are determined, and the corresponding minimum oxygen concentrations are calculated. As the nickel content in the system increases, the deoxidizing capacities of chromium, manganese, and silicon are shown to increase substantially, and the deoxidizing capacity of carbon increases most strongly. As the nickel content in the melt increases, the deoxidizing capacities of vanadium and titanium first decrease insignificantly and then increase substantially. As the nickel content in the melt increases to 50%, the deoxidizing capacity of aluminum first decreases and then increases; in pure nickel, it is identical to that in pure iron.

Deoxidation Equilibrium of Vanadium in the Iron–Nickel Melts

Thermodynamic analysis of oxygen solutions in the Fe–Ni melts with vanadium has been carried out. The deoxidizing ability of vanadium decreases slightly with the nickel content up to 20% but it considerably rises with a further increase in its concentration. The oxygen solubility curves pass through a minimum, which shifts to the lower vanadium concentrations with a rise in the nickel content, i.e., from 2.32% for pure iron to 0.77% for pure nickel. The further vanadium addition causers an increase in the oxygen concentration in melt. For pure nickel or alloys with the nickel concentration higher than 60%, the deoxidizing ability of vanadium is lower in comparison with that of manganese and is close to the deoxidizing ability of chromium. This can be explained by the fact that although the bond strength of oxygen with nickel is appreciably weaker as compared to that with iron (γ°O(Fe)=0.0105; γ°O(Ni)=0.357), but the vanadium bond strength with nickel is much stronger than that with iron (γ°V(Fe)=0.1; γ°V(Ni)=0.011). The deoxidation of iron–nickel melts with vanadium was experimentally studied by the example of the Fe–40%Ni alloy.

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.

Thermodynamics of oxygen solutions in iron-nickel, iron-cobalt and iron-manganese melts

The oxygen solubility in Fe-Ni, Fe-Co, and Fe-Ni melts has been calculated. The calculation of oxide phase composition over Fe-Ni, Fe-Co and Fe-Mn melts was carried out at 1873 K. The FeO oxide is mainly contained in the oxide phase of the Fe-Ni system; the NiO content rapidly increases only when the Ni mole fraction is close to unit. In case of the Fe-Co system, the FeO also is contained mainly in the oxide phase and the CoO content rapidly increases as the Co mole fraction increases above 0.8. The MnO oxide is contained mainly in oxide phase of the Fe-Mn system; in this case, when the Mn mole fraction is more than 0.02, the MnO mole fraction in oxide phase is more than 0.9.

Suppression of peritectic reaction in the undercooled peritectic Fe–Ni melts

Peritectic Fe–Ni alloys were undercooled using glass fluxing. When subjected to an undercooling (ΔT) beyond a critical value (ΔT∗ ≈ 130 K), the peritectic reaction, L + δ → γ, normally occurring after primary recalescence, was found to be suppressed. This can be ascribed to a longer incubation time for the occurrence of the peritectic reaction than the time required for solidification of δ phase during post-recalescence, for ΔT > ΔT∗.