Thermodynamics of oxygen solutions in nickel melts containing aluminum and titanium

Thermodynamic analysis of oxygen solutions in nickel melt shows that, as aluminum and titanium are added to the melt, the solubility of oxygen decreases. However, after reaching 0.205% Al and 0.565% Ti, the oxygen concentration in the melt begins to rise with increase in the Al and Ti content. The minimum oxygen concentrations in the reduction of nickel melt by aluminum (1.44 × 10^–4% O) and titanium (2.98 × 10^–4% O) are determined. On that basis, we may propose the optimal approach to alloying nickel melts with aluminum and titanium. First, the melt is reduced by adding sufficient aluminum to minimize the oxygen concentration in the melt (~0.2% Al). Then the oxide formed is removed, so as to prevent repeated oxidation of the melt. Finally, the melt is alloyed with aluminum and titanium to obtain the required alloy composition.     

Cathodic deoxygenation of the alpha case on titanium and alloys in molten calcium chloride

The oxygen-enriched alpha case on titanium and alloys was successfully deoxygenated to satisfactory levels by electrolysis in molten CaCl₂, in which the cathode was made from the metal to be refined. The oxygen distribution in the metal before and after electrolysis was characterized by microhardness tests, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX). The electrolysis has been carried out at voltages sufficiently below that for the decomposition of CaCl₂, and the results obtained suggest that the alpha case deoxygenation follows a simple oxygen ionization mechanism in which the oxygen in the metal is simply ionized at the cathode/electrolyte interface, dissolves in the molten salt, and then discharges at the anode. It is shown that by applying the electrochemical method, the alpha cases on both commercially pure titanium (CP Ti) and the Ti-6Al-4V alloy can be effectively deoxygenated. In particular, due to the removal of oxygen, the original alpha case (single phase) on the Ti-6Al-4V alloy has been converted back to the two-phase microstructure.     

Thermodynamics of molten Li-Sn alloys

The activity of Li in molten Li-Sn alloys was continuously varied and monitored electrochemically in cells of the type Al-LiAl/glass electrolyte/Sn/glass electrolyte/Al-LiAl. The temperature (320 to 380 °C) and compositional dependence of the Li activity coefficient, γ_Li, was found to follow a quadratic expression of the form In γ_Li = A + B(1 − X_Li)² up to 30 mole pct lithium. Further, the liquidus temperature, T_L, was found to follow TL(°C) = 642 X_Li + 188 for 0.20 X_Li 0.44 over the temperature range 320 to 470 °C. The partial and integral molar heats of solution were calculated and the results indicate that strong attractive forces exist between Sn and Li. These forces are strong enough to induce substantial ordering in the melt to an extent that the integral molar entropy of mixing at high Li contents (36 mole pct) is negative.     

含钛废渣熔盐电脱氧法制备钛铁合金

以泡沫镍包裹含钛废渣和Fe2O3混合物为阴极,碳棒为阳极,在900 ℃、3.1 V、CaCl2熔盐电解质中,采用熔盐电脱氧法制备钛铁合金,重点考查阴极成型压力对微观形貌及电解效果的影响.结果表明,烧结后阴极片孔隙率随着成型压力的增加而减小,当成型压力为2 MPa时,烧结后阴极片孔隙率为39.5％,具有良好的电化学活性,...     

Thermodynamics of phosphorus in molten Si-Fe and Si-Mn alloys

The thermodynamics of phosphorus in molten Si-Fe and Si-Mn alloys has been investigated at 1723 K by equilibrating the alloys in a controlled phosphorus partial pressure. The activity coefficient of phosphorus in each alloy shows a maximum value at a certain composition due to a strong interaction between silicon and iron and between silicon and manganese. Interaction coefficients between phosphorus and iron in molten silicon were found to be ε _P ^Fe =7.43 and ρ _P ^Fe =−16.4 (0≦X _Fe≦0.65), and those between phosphorus and manganese were ε _P ^Mn =12.0 and ρ _P ^Mn =−22.2 (0≦X _Mn≦0.5). Further discussion has revealed that the Si-Fe-P and Si-Mn-P systems approximately conform to a regular solution within the composition ranges investigated in the present work.     

Thermodynamic properties of titanium and iron in molten silicon

Titanium and iron in silicon are known as harmful “lifetime killer” impurities, which shorten the lifetime of excited carriers in silicon solar cell and disturb power generation. Therefore, the removal of titanium and iron is one of the most important topics for the production of solar grade silicon. Thermodynamic properties of titanium and iron in molten silicon were determined at 1723 K by equilibrating molten silicon-titanium alloys or molten silicon-iron alloys with molten lead, which has a limited mutual solubility for both alloys. The activity coefficients of infinite dilution, self-interaction coefficients of titanium and iron in molten silicon, and the Gibbs energy change of mixing for silicon-titanium and silicon-iron at 1723 K relative to pure liquid silicon, titanium, and iron were determined.     

Thermodynamics of mixing in molten sodium-potassium silicates at 1100°C: The effect of a calcium oxide addition

A Knudsen cell-mass spectrometer technique has been used to study the thermodynamics of mixing of liquid sodium and potassium metasilicates containing calcium oxide at the composition 0.15 CaO:0.85 (K₂O + Na₂O). It is shown that the CaO addition reduces the maximum excess free energy of mixing of the metasilicates from about 1.9 kJ to about 1.1 kJ per mole of alkali cations. Measurements have been made at the tetrasilicate composition in the absence of CaO, and these results have been combined with previous measurements and a recent thermodynamic relationship due to Wagner to yield the variations in the activities of silica and the alkaline oxides across the disilicate section. All the results are considered to be consistent with cation size effects being the principal cause of positive deviations from ideal silicate mixing in these systems. Dr. CHOUDARY was Formerly a Graduate Student.     

Thermodynamics of titanium and nitrogen in an Fe-Ni melt

The equilibrium solubility of titanium and nitrogen in Fe-Ni melts was measured in the presence of pure solid TiN under various nitrogen pressures in the temperature range of 1843 to 1923 K. The activity coefficients of titanium and nitrogen relative to a 1 mass pct standard state in liquid iron were calculated from the experimental results for Fe-Ni alloys of nickel contents up to 30 mass pct. Nickel decreases the activity coefficient of titanium, but it increases the activity coefficient of nitrogen in an Fe-Ni-Ti-N melt. Therefore, the effect of nickel on the solubility product of TiN is not significant. The first- and second-order interaction parameters of nickel on titanium (e _Ti ^Ni and r _Ti ^Ni , respectively) were determined to be −0.0115 and 0 at 1873 K, respectively. Similarly, the interaction parameters of nickel on nitrogen (e _N ^Ni and r _N ^Ni , respectively) were determined to be 0.012 and 0, respectively, at 1873 K. The temperature dependence of these interaction parameters was also determined.     

碳饱和铁液中钛溶解度测定探讨

介绍了碳饱和铁液中钛溶解度的不同测定方法,对测定结果进行了比较,分析了可能存在的误差原因;当利用含钛物料护炉时,铁液中含钛量应控制在一定的范围内,从而为高炉冶炼钒钛磁铁矿提供指导．     

Thermodynamics and kinetics analyses of ZrB2 formation in molten aluminium alloys

Smelter grade aluminium can be used as a source for electrical conductor grade aluminium after the transition metal impurities such as zirconium (Zr), vanadium (V), titanium (Ti) and chromium (Cr) have been removed. Zirconium (Zr), in particular, has a significant effect on the electrical conductivity of aluminium. In practice, the transition metal impurities are removed by adding boron-containing substances into the melt in the casthouse. This step is called boron treatment. The work presented in this paper, which focuses on the thermodynamics and kinetics of Zr removal from molten Al–1?wt-%Zr–0.23?wt-%B alloy, is part of a broader systematic study on the removal of V, Ti, Cr and Zr from Al melt through boron treatment carried out by the authors. The thermodynamic analyses of Zr removal through the formation of ZrB₂ were carried out in the temperature range of 675–900°C using the thermochemical package FactSage. It was predicted that ZrB₂ is stable compared to Al–borides (AlB₁₂, AlB₂) hence would form during boron treatment of molten Al–Zr–B alloys. Al–Zr–B alloys were reacted at 750?±?10°C for 60 minutes, and the change in the chemistry and microstructure were tracked and analysed at particular reaction times. The results showed that the reaction between Zr and AlB₁₂/B was fast as revealed by the formation of boride ring at the early minutes of reaction. The presence of black phase (AlB₁₂), i.e. the original source of B, after holding the melt for 60 minutes advocated that the reaction between Zr and AlB₁₂/B was incomplete, hence still not reached the equilibrium state. The kinetics data suggested a higher reaction rate at the early minutes (2 minutes) of reaction compared to at a later stage (2–60 minutes). Nevertheless, a simple single-stage liquid mass transfer controlled kinetic model can be used to describe the overall process kinetic. The analysis of integrated rate law versus reaction time revealed that the mass transfer coefficient (k_m) of Zr in molten alloy is 9.5?×?10^?4?m?s^?1, which is within a typical range (10^?3 to 10^?4?m?s^?1) observed in other metallurgical solid–liquid reactions. This study suggests that the overall kinetics of reaction was predominantly controlled by the mass transfer of Zr through the liquid aluminium phase.     

Kinetics of oxygen dissolution in molten lead

An electromotive force cell employing the ZrO₂-CaO solid electrolyte has been set up to investigate the kinetics of dissolution of oxygen in molten lead under various oxidizing conditions. The cell may be written as The cell has been so designed that the electrode chambers are completely isolated from each other. The oxygen in lead is first reduced to a very low value by bubbling hydrogen. subsequently, oxygen dissolution is achieved through gas diffusion across the free surface or through bubble metal interaction. During all these reactions the electromotive force of the cell changes continuously and is automatically recorded. The diffusion coefficient of oxygen in lead, as calculated from the experimental data, is 1.29×10⁻⁵ sq cm per sec and the liquid phase mass transfer coefficient is estimated to be 0.035 cm per sec at 750°C.     

Thermodynamics of oxygen solutions in Fe-Mn melts

Oxygen solutions in Fe-Mn melts are analyzed thermodynamically. The composition of the oxide phase is determined, and the equilibrium oxygen concentrations in Fe-Mn melts are calculated over a wide composition range. The oxide phase mainly contains MnO: even at a molar fraction of manganese of 0.02 in the melt, the molar fraction of manganese oxide in the slag is more than 0.9. This is due to a much higher oxygen affinity of manganese as compared to iron; that is, manganese additives to iron considerably decrease the oxygen solubility. When the manganse content in the melt is 19.32%, the oxygen solubility curve has a minimum corresponding to an oxygen concentration of 5.136 × 10^?3%. However, a further increase in the managanese content results in an increase in the oxygen concentration in the melt. In liquid manganese, the oxygen saturation concentration at 1873 K is 0.0472%. The interaction parameter e _o(Mn) ^o (?0.207) and the activity coefficient γ _o(Mn) ^o (1.131 × 10^?4) have been calculated for the first time.     

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.     

Thermodynamics of oxygen behaviour in cobalt-nickel alloys

In this study the concentration and chemical potential of oxygen in liquid Co-Ni alloys equilibrated with cobalt-nickel aluminate spinel solid solutions and alumina have been determined at 1773, 1823 and 1873K as a function of nickel concentration. The oxygen content of the melt has been measured by suction sampling and inert gas fusion analysis. The corresponding oxygen potential has been determined with the following solid state cell: Mo, Mo+MoO₂ | (MgO)ZrO₂ | (Co, Ni) melt + AI₂O₃ + (Co, Ni)O·(1+x)Al₂O₃, Mo. The effect of nickel on the activity coefficient of oxygen in Co-Ni alloys has been determined. The results for the activity coefficient have been modelled with Wagner's interaction parameters and also the more recent exponential method of St. Pierre et al. at the three temperatures.