Deoxidation equilibria of molten nickel by Mg-Al and Mn-Al

The deoxidation equilibria of aluminum-magnesium and aluminum-manganese in liquid nickel equilibrated with Al₂O₃-saturated MgAl₂O₄ and MnAl₂O₄, respectively, were investigated in the temperature range of 1773 to 1873 K. At 1773 K, the oxygen levels could be reduced to 5.8 to 6.6 ppm with 2.5 to 10 ppm magnesium and 0.05 to 0.9 mass pct aluminum in the Ni-Mg-Al-O system, and to less than 20 ppm with more than 1.5 mass pct manganese and 30 ppm aluminum in the Ni-Mn-Al-O system. With the experimental results mainly obtained in the present work, the interaction parameters, e _Mg ^Al , e _Mn ^Al , e _O ^Mg , e _O ^Mn , and e _O ^Al , and the equilibrium constants, log , log , log K _Mg(Ni), log K _Mn(Ni), and log K _Al(Ni), were estimated using a multiple regression analysis.     

Calcium desulfurization equilibrium in liquid iron

Sulfur distribution ratios between CaO-Al₂O₃ slags and liquid iron were measured at 1873 K as a function of aluminum content using an alumina or a lime crucible. Activity coefficients of CaS relative to a solid standard state were obtained as 52&2.6 and 23&1.7 for the CaO-Al₂O₃ slags saturated with an Al₂O₃ and a CaO crucible, respectively, in the concentration range up to the CaS solubility limit. From these results, logarithm of the equilibrium constant, log K_CaS, for the calcium desulfurization reaction CaS(s) = Ca + S and the first-order interaction parameter e_S^Ca (e_S^Ca) were estimated to be –8.72&0.27 and –269&28 (–336&35), respectively.     

Kinetics of deoxidation of liquid Cu-O alloys by rotating graphite cylinders under argon

The rate of deoxidation of liquid Cu-O alloys by graphite cylinders rotating at about 250, 580, and 860 rpm was studied at 1400, 1482, and 1582 K under argon at 30, 58, and 99 kPa. Those at 1400 and 1482 K with about 580 and 860 rpm and at 1582 K do not depend on rotational speed. Under each argon pressure with these rotational speeds, at 1400 K, the apparent deoxidation-rate constantK _e defined by first order kinetics increases and then approaches a constant value with a decrease in the concentration of oxygen in the melt and at 1482 K,K _e is constant. At 1582 K,K _e is approximately constant. A plot of log₁₀ K _e at 1482 K and in very low oxygen concentration at 1400 and 1582 Kvs 1/T gives an apparent activation energy of 146 kJ · mol⁻¹. The dependence ofK _e on the concentration of oxygen can qualitatively be explained on the basis of a mechanism involving the chemisorption of oxygen from liquid copper onto the graphite surface, the release of carbon monoxide from the surface, and the interfacial reaction between oxygen in the melt and the carbon monoxide. This mechanism indicates that the activation energy is that for the chemisorption. The rate of deoxidation of liquid Cu-O alloys in graphite crucibles also was studied at 1473, 1573, and 1673 K under argon at 100 or 60 kPa by use of an induction furnace and is much smaller than that by the rotating graphite cylinders. The values ofK _e under both pressures of argon at 1473 K appear not to differ from each other and are close to theK _e value at 1573 K under argon at 100 kPa.     

Inclusion control of ferritic stainless steel by aluminum deoxidation and calcium treatment

A thermodynamic equilibrium between aluminum and oxygen and inclusion morphology in the Fe-16Cr stainless steel were investigated to understand the fundamentals of the aluminum deoxidation technology for ferritic stainless steels. Further, the effect of calcium addition on the changes in chemistry and morphology of inclusions was discussed. The measured results for the aluminum-oxygen equilibria exhibit relatively good agreement with the calculated values, indicating that an introduction of the first-and second-order interaction parameters, recently reported, is reasonable to numerically express the aluminum deoxidation equilibrium in a ferritic stainless steel. In the composition of dissolved aluminum content greater than about 60 ppm, pure alumina particles were observed, while the alumino-manganese silicates containing Cr₂O₃ appeared at less than 20 mass ppm of dissolved aluminum. The formation of calcium aluminate inclusions after Ca treatment can be discussed based on the thermodynamic equilibria among calcium, aluminum, and oxygen in the steel melt. In the composition of steel melt with relatively high content of calcium and low aluminum, the log ( ) of inclusions linearly increases by increasing the log [a _Ca/a _Al ² ·a _O ² ] with the slope close to unity. However, the slope of the line is significantly lower than the expected value in the composition of steel melt with relatively low calcium and high aluminum contents.     

Calcium deoxidation equilibrium in liquid iron

Calcium-oxygen equilibrium was studied at 1873 K under normal pressure by the method of immersing a pure iron capsule containing calcium metal into liquid iron, which was equilibrated with CaO-Al₂O₃ slags in Al₂O₃ and CaO crucibles. On the basis of these and previous results obtained in the equilibrium experiments between liquid iron and CaO-containing slags, the equilibrium constant,K _Ca, for the reaction, CaO (s) =Ca +O, and the first-order interaction parameter,e ₀ ^Ca , were estimated. The measured value forK _Ca reported in previous experiments, which was found to be significantly different from that calculated from the reliable thermodynamic data, was discussed. Nitrogen distribution ratios between CaO-Al₂O₃ slags and liquid iron were also measured. Formerly Graduate Student, Department of Metallurgical Engineering, Tohoku University     

Aluminum deoxidation equilibrium in liquid Fe-16 pct Cr alloy

For thermodynamic prediction, the deoxidation equilibrium of aluminum in liquid Fe-16 pct Cr alloy was studied by employing the electromagnetic levitation technique with a cold crucible in an Ar gas atmosphere at 1923 K. The interaction parameters were determined to be e _Al(Fe) ^Cr =0.0001 (0.19/T, 1823 K≤T<1923 K) and r _Al(Fe) ^O,Cr =−0.001. The calculated relationship between aluminum and oxygen contents in Fe-16 pct Cr alloy by thermodynamic data obtained in this study is in good accordance with the experimental results of the present study and other research.     

Thermodynamic assessment of Mg deoxidation reaction of liquid iron and equilibria of [Mg]‐[Al]‐[O] and [Mg]‐[S]‐[O]

The deoxidation reaction of magnesium was investigated thermodynamically employing the equilibrium system between magnesium vapour and liquid iron in the molybdenum chamber sealed with an iron cover at 1873 K as a fundamental study to address the clean steel production technology in the steelmaking process. The previously reported thermodynamic data for magnesium deoxidation reaction are limitedly in good agreement with only their respective specific Mg concentration range, but fail to explain the thermodynamic equilibria generally over the wider range of magnesium concentration beyond the limited range. Therefore, the equilibrium constant, K_Mg for the magnesium deoxidation reaction as well as the first and second‐order interaction parameters between magnesium and oxygen were determined over the extensive magnesium mass content range covering up to 0.04 %. Furthermore, the phase stability diagram based on the equilibria of [Mg]‐[Al]‐[O] in liquid iron for the purpose of controlling the oxide inclusions in the steelmaking process was accomplished using the determined thermodynamic parameters. The equilibria of [Mg]‐[S]‐[O] were also discussed in order to evaluate the utilisation of Mg as a desulphurizing agent as well as deoxidizer in the production process of low carbon steels.     

Thermodynamics of iron alumino-chromite spinel inclusions in steel

The effect of chromium on the oxygen concentration of iron melts in equilibrium with various spinel reaction products has been determined. Alumina crucibles were used and experiments were performed at 1550, 1600, and 1650°C. Thermodynamic relationships between the equilibrium concentrations of chromium and oxygen in the iron melts have been established for chromium concentrations ranging up to 20 wt pct. Results from X-ray and electron microprobe analyses for the composition of the deoxidation products, together with solute activity relationships, indicate that the composition of the equilibrium spinel phase changes progressively from iron aluminate in the absence of chromium, through a series of aluminate-chromite solid solutions, FeO (Al _x Cr_1−x )₂O₃, (<0.5 pct chromium), to a complex chromite spinel, Fe₂Cr₇O₁₂, (0.5 to 3 pct chromium), and finally chromium oxide, Cr₃O₄ (>3 pct chromium). Deoxidation diagrams have been constructed and the effects of small amounts of alloying elements on the deoxidation behavior of aluminum interpreted in terms of buffered reactions which maintain oxygen concentrations in the melt at levels in excess of those normally associated with aluminum killed steel in equilibrium with alumina alone.     

Thermodynamics of O,N, and S in liquid Fe equilibrated with CaO-AI2O3-MgO slags

Nitrogen and S distribution ratios between CaO-Al₂O₃-MgO slags and liquid Fe were measured at 1873 K as a function of Al (or Mg, Ca) content in metal, using CaO, MgO, and A1₂O₃ crucibles. Based on the results for the solubility product of MgO, the equilibrium constant,K _Mg , for the reaction MgO =Mg +O and the first-order interaction parameter,e _O ^Mg (e _Mg ^O ), were estimated to be logK _Mg = -7.8 ± 0.2 ande _O ^Mg = -190 ± 60 (e _Mg ^O = -290 ± 90), respectively. The activities of A1₂O₃ at the slag compositions double-saturated with CaO/MgO, MgO/ MgO A1₂O₃, and MgO Al₂O₃/CaO 2A1₂O₃ components were obtained from the S distribution ratios between slag and metal, coupled with the reported values of sulfide capacities. Nitride capacities were also estimated from the N distribution ratios and the activities of A1₂O₃.     

The effect of zirconium,cerium, and lanthanum on the solubility of oxygen in liquid iron

The effect of zirconium, cerium, and lanthanum up to about 1 wt pet on the solubility of oxygen in liquid iron in equilibrium with an oxide phase at 1680°C was measured. All three elements are strong deoxidizers of iron, and the oxygen solubility minimums were 10 ppm or less at 0.05 to 0.1 wt pet of the alloying element. The interaction coefficients were estimated from the results giving e_o ^zr = −3, e_o ^Ce = −3, and e_o ^La = −5. When the concentration of the alloying element is expressed in wt pet, the effect of each of the three elements (Zr, Ce, and La) on the activity and solubility of oxygen in liquid iron is similar to that of aluminum.     

Equilibria between rare earth elements and sulfur in molten iron

The equilibrium constants of Ce-S, La-S, and Nd-S in molten iron and the related interaction coefficients were determined experimentally and the following results obtained: K_CeS = 2.80 × 10^-6 e_S ^Ce = −1.88 K_LaS = 7.41 × 10^-7 e_S ^La= −1.51 K_NdS = 2.57 × 10^-6 e_Nd ^S= −1.51 In these experiments a radioactive isotope technique was used to determine the extremely low contents of the rare earth elements in the metal phase at equilibrium. In order to avoid errors caused by any partial inclusion of RE content of nonmetallic inclusions in the analytical results for the dissolved RE, the metal samples were electrolyzed in an organic electrolyte at low temperature, and the dissolved rare earth contents determined by measuring the radioactivity of the electrolyte. The dependence of the equilibrium values (concentration products) Ce-S on [pct C] in the system Fe-Ce-S-C was also determined. The interaction coefficient e_Ce ^C was determined to be −0.43. Earlier workers have obtained higher values for the Ce-S and La-S equilibrium constants than the present authors. Some explanation is offered for the difference.     

Thermodynamics of iron-manganese aluminate spinel inclusions in steel

The effect of manganese on the residual oxygen concentrations of liquid iron in equilibrium with alumina saturated iron-manganese aluminate spinel solid solutions was investigated at temperatures of 1550, 1600, and 1650°C. The relationship between the equilibrium concentrations of manganese and oxygen in iron melts containing up to 6 wt pct manganese has been established. The compositions of the spinel deoxidation products, (Fe _x Mn _j-x ) O · Al₂O₃, which were formed during equilibration with the iron melts were determined with electron microprobe and neutron activation analysis. From these results, new thermodynamic data pertaining to galaxite formation reactions have been derived and their implications with respect to the deoxidation of aluminum semikilled, silicon free, steels have been discussed.     

Thermodynamics on the formation of spinel (MgO·Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) inclusion in liquid iron containing chromium

The stability diagram of MgO, spinel solid solution (MgO·(Al _X Cr_1−X )₂O₃), and sesquioxide solid solution ((Al _Y Cr_1−Y )₂O₃) as a function of Mg, Al, and O contents at a constant chromium content (18 mass pct) in liquid iron is drawn at 1873 K. The interaction parameters between Mg and other solutes (Al, Cr, Ni, Ti, Si, and C) are determined by the experimental method, which assures equilibrium between Mg vapor and liquid iron, were applied to calculate the diagram. Titanium deoxidation is not recommended for the prevention of spinel formation, because Ti accelerates Mg dissolution from refractory or slag due to its high affinity for Mg (e _Mg ^Ti = − 0.64). The standard Gibbs free energies of formation for the three inclusions (periclase, spinel, and sesquioxide solid solutions) and the tielines between two solid solutions were calculated with the aid of the regular solution model and the thermochemical F*A*C*T database computing system, respectively. The phase stability regions and oxygen content in steel for the current Fe-Mg-Al-Cr (18 mass pct)-O system are compared with those of the previous non-Cr system. Detailed information on the spinel composition according to Mg and Al contents is also available from the present stability diagram.     

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.     

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.     

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 (e _{Nb(Fe-40% Ni)} ^O = ?0.630; e _{O(Fe-40% Ni)} ^Nb = ?0.105; e _{Nb(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 (γ _O(Fe) ^° = 0.0084, γ _O(Ni) ^° = 0.297).     

Thermodynamics of calcium and oxygen in molten titanium and titanium-aluminum alloy

The deoxidation equilibrium of molten titanium and titanium-aluminum alloys saturated with solid CaO has been measured in the temperature range from 1823 to 2023 K. The equilibrium constant of reaction CaO (s)=Ca (mass pct in Ti,Ti-Al)+O (mass pct in Ti,Ti-Al) and the interaction parameter between calcium and oxygen were determined for Ti, TiAl, and TiAl₃. The standard Gibbs energy of reaction for TiAl was obtained as follows: $$\Delta G^\circ = 279,000 - 103TJ/mol$$ The possibilities for the deoxidation of titanium and titanium-aluminum alloys by using calcium-based fluxes are discussed.     

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.     

Equilibria between the rare earth elements,oxygen and sulfur,in molten iron

The values ofK _ce2o2s andK _ce2S3 reported in the literature are greater than they should be. Such a situation has arisen because in the calculation of the respective equilibrium constants, the total amount of Ce, O, and S each contained in the samples has been used instead of only the dissolved amounts. The relationships between equilibrium constants and temperatures of Ce-O-S, Y-O-S, Nd-O-S, La-O-S, and Ce-S in pure liquid iron have been determined by using a previously developed experimental method. The activity interaction coefficients,e _-S ^/Nd,e _-S ^/Y, ande _-S ^/La at different temperatures have been determined. The standard free energies of formation of Nd₂O₂S, Y₂O₂S, and Ce₂S₃ have been calculated by using the relevant experimentally derived parameters.