Kinetics of the reactions between silica and alumino-silicate refractories and molten iron

The rate of corrosion of silica and alumlno-silicate refractories in Armco iron melts at 1600°C was measured. A standard “immersion” technique was used under both static and dynamic conditions. It was found that the corrosion of the refractories in Armco iron melts was initially controlled by a chemical reaction process but changed rapidly to a steadystate, diffusion-controlled process. A liquid silicate product layer built up at the interface during the induction period. The steady-state rate of corrosion was independent of the oxygen content of the melt and was also found to be a linear function of the peripheral velocity of the refractory specimen. The rate of corrosion for the various refractories was measured and found to be controlled by diffusion of iron and oxygen in the silicate layer.     

Kinetics of desulphurisation of molten pig iron

The analysis of the experimental data obtained in the present work and also of some classical data reported in literature on the basis of simple rate theory, surface renewal theory and the multicomponent mixed transport control theory has shown that in molten pig iron containing silicon the sulphur transfer to slags is controlled by mass transport in the metal phase. In the initial stages the desulphurisation rate is fast but after a few minutes it slows down. In the case of silicon containing iron this second slow stage, as also observed by other workers in the past, is due perhaps to the formation of a micro layer of silica enriched reaction product at the slag-metal interface. On addition of aluminium the silica layer gets reduced and sulphur transfer is enhanced; once again the rate controlling step becomes mass transport in the metal phase. An important conclusion regarding the timing of aluminium is that maximum benefit of aluminium addition can be realised after about 4–5 min of adding the desulphurisation flux.     

Kinetics of the carbon-oxygen reaction in molten iron

The kinetics of carbon monoxide absorption by stagnant liquid iron has been investigated over the first 10 min or so of gas-liquid metal contact. On the basis of experiments conducted at temperatures ranging between 1580° and 1700°C (PCO= 1 atm) and carbon monoxide pressures ranging between 0.1 and 1.5 atm (at 1600†C), it was concluded that the absorption kinetics of CO in liquid iron was diffusion controlled. Mass transfer equations developed to describe the process were adapted to define an “apparent diffusion coefficient” of carbon monoxide. This coefficient is a function of carbon and oxygen binary diffusion coefficients, and also depends on the initial bulk oxygen and carbon concentrations, and on the equilibrium constant for the reaction. CO = C + O Experimental D_COvalues averaged at 9.8 10−⁵cm²s−¹, while binary carbon and oxygen diffusivities were computed to be 41.2 10−⁵ and 5.2 10−T⁵cm²s−¹ respectively. Using the data obtained, the relative influence of carbon and oxygen diffusion on the kinetics of carburization and decarburization reactions is quantitatively considered. Formerly Graduate Student, McGill University, Montreal, Quebec, Canada     

Kinetics of simultaneous reactions between liquid iron-carbon alloys and slags containing MnO

The oxidation rates of carbon, phosphorus, and silicon; the desulfurization rate of liquid iron; and the simultaneous reduction rate of MnO from slag were examined at 1450 °C to 1550 °C by using high carbon iron alloys and CaO-SiO₂-CaF₂ slags containing MnO and FeO. The reaction rates were well reproduced by a kinetic model describing the reaction between the slag and multicomponent iron alloys. The controlling steps applied for the reactions considered in the present kinetic simulation were as follows. The rate of decarburization is controlled by the chemical reaction at the slag-metal interface, and those of the other reactions are controlled by the transport in slag and metal phases. Both observation and simulation results showed that MnO was not a strong oxidizer compared with FeO in the slag, but was an effective component for desulfurization. The simulation results also showed that the interfacial oxygen activity using MnO-based slag was much lower than that using FeO-based slag. The apparent equilibrium constants of phosphorus and sulfur, which were obtained by the kinetic modeling of experimental results, were found to increase with increasing the (MnO + CaO)/SiO₂ ratio of the slag. The controlling step(s) of each element transport across the slag-metal interface was discussed with the aid of the kinetic model.     

Kinetics and mechanism of reactions between iron oxides and iron‐carbon melts

The reaction between iron oxides and iron‐carbon melts was studied in the temperature range 1523–1973 K. Pellets made from three different sources of iron oxides were added onto the melt surface, and the reaction time was measured through the constant volume pressure increase (CVPI) method. The effects of reaction temperature, oxide and melt surface areas, oxide type and weight on reaction time were evaluated. Analysis of partially reduced pellets through SEM was also performed. It has been determined that the reaction time increases as the pellet weight increases, and decreases as the temperature, the contact area between the oxide and the melt and the surface area of the melt increase. Examination of partially reduced pellets had shown that the reduction occurs topochemically. Based on the results, it is proposed that the overall reaction rate is determined by the consecutive reactions of dissociation of FeO and formation of CO.     

Simultaneous desulfurization and dephosphorization reactions of molten iron by soda ash treatment

Desulfurization and dephosphorization reactions of molten iron by soda ash has been studied on laboratory heats of Fe-C, Fe-C-S, Fe-C-P, and Fe-C-S-P alloys at 1573 and 1623 K. The alloys were melted in helium gas flow and preheated soda ash was added; metal samples were taken at certain time intervals and analyzed for sulfur, phosphorus, and carbon. Evolved gas samples were also taken at certain time intervals and analyzed. The phosphorus and sulfur contents in metals decreased rapidly, reaching the lowest values two to four minutes after the soda ash addition. The degree of desulfurization was generally greater than that of dephosphorization, and both degrees were higher at lower reaction temperature. The major component of evolved gas was CO with small amounts of CO₂. Phosphorus appeared to form a stable phosphate compound with Na₂O, possibly 3Na₂O-P₂O₅, in the slag phase. Soda ash reacts with carbon resulting in decarburization of molten iron and vaporization of sodium; this reaction may cause the fading of soda ash and can be expressed as: Na₂CO₃(1) + (1 +x)C = (1 -xNa₂O(1) + 2xNa(g_ + (2 +xCO(g). For the phosphorus containing melt, the reaction can be expressed as: Na₂CO₃(l) +yC + 2x/3P =x(Na₂O · 1/3P₂O₅)(1) + (2 −y − 8x/3)Na₂O(l) + 2(−l + y + 5x/3)Na(g) + (1 +y)CO(g) and for the sulfur containing melt: Na₂O(l) +C +S = Na₂S(l) + CO(g). Katsumi Mori, Formerly Visiting Associate Research Scientist, University of Michigan, Ann Arbor, MI     

Kinetics of removal of bismuth and lead from molten copper alloys in vacuum induction melting

An investigation was made of the rates of removal of bismuth and lead from molten copper alloys stirred differently under vacuum at 1403 K. The heating conditions, which corresponded to highest, intermediate, and lowest stirring, were referred to as HC-A, HC-B, and HC-C, respectively. The rates of removal were described by a first-order rate equation involving the final concentration of the impurity. The overall mass-transfer coefficient for bismuth or lead (i),K _i, was determined, and it was found that K_i(HC-A) > K_i(HC-B) but K_i(HC-B) < K_i(HC-C) in Cu-Bi, Cu-Pb, and Cu-Bi-Pb alloys. In general, it was found that K_i(Cu-Bi-Pb) > K_i(Cu-Bi) or K_i(Cu-Pb). Oxygen reducedK _i more than sulfur. The reducing effect of oxygen and sulfur was weakened when stirring rate increased. In vacuum melting of Cu-Bi-Pb-O and Cu-Bi-Pb-S alloys under HC-C,K _i tended to decrease with increasing oxygen and sulfur concentrations. The loss of copper indicated that the rates were determined by liquid-phase mass-transfer and evaporation. The liquid-phase mass-transfer coefficient,K _L, was calculated, and it was found thatK _L(UC- A) > K_L(HC-B) but K_L(HC-B) < K_L(HC-C). The last relation was contrary to current theoretical prediction. A new model was assumed to account for this fact. The observed relative volatility coefficients of bismuth and lead were much smaller than their respective theoretical coefficients. Oxygen and sulfur adsorbed on the surface of the melt were considered to be close to equilibrium with their respective bulk concentrations, and their effects on the evaporation mass-transfer coefficients for bismuth and lead were estimated to be fairly small. This result means that the observed reduction ofK _i is due mostly to the decrease inK _L and made possible the calculation ofK _L. Oxygen decreasedK _L more than sulfur. In vacuum melting of Cu-Bi-Pb-O and Cu-Bi-Pb-S alloys under HC-C,K _L decreased linearly with increasing oxygen or sulfur concentration. The final concentrations of bismuth and lead in these alloys under HC-C tended to increase with increasing oxygen and sulfur concentrations and tended to decrease with increasingK _i andK _L.     

Equilibria between cerium or neodymium and oxygen in molten iron

Autoradiographs show that there is an obvious reaction between Ce and Nd in liquid iron and the MgO/CaO crucible wall. For reaching the Ce-O, Nd-O equilibrium, a long melting period and the addition of rare earth elements (RE’s) in several batches were needed to ensure the full reaction between the RE’s in the melt and crucible wall. The dissolved Ce or Nd content in iron was measured by means of radioactive isotopes¹⁴¹Ce or¹⁴⁷Nd and electrolysis in the organic electrolyte. The oxygen activity was measured by solid electrolyte sensors made of ZrO₂(MgO) tube. The relationships between the equilibrium constants and the temperatures for reactions Ce₂O₃ (s) = 2[Ce] + 3[O], CeO₂ (s) = [Ce] + 2[O], and Nd₂O₃ (s) = 2[Nd] + 3[O], as well as the corresponding thermodynamic parameters, have been determined. Formerly Graduate Student at the University of Science and Technology Beijing     

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.     

冶金用耐火材料与铁水相际间运动的电现象

钢铁冶炼过程中,耐火材料与钢液(铁水)界面间存在的电场将影响两相间的润湿、溶解以及化学反应等界面作用.为明确钢液(铁水)与耐火材料间因相对运动所引起的摩擦起电行为,进行低温流体流动带电试验和热态模拟试验.由低温流体流动带电试验可知,随着搅拌速度的增加,流体与石墨容器因摩擦起电所产生的静电电压逐渐增大;不同种类的流体因其...     

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.     

Dephosphorization and desulfurization of molten Fe-Cr-C alloys

Thermodynamic calculation of phosphorus-chromium and sulfur-chromium relationships in molten Fe-Cr-P-C and Fe-Cr-S-C alloys at 0 to 18 wt. % Cr and 0 to 6 wt. % C. Experiments to prove the potentiality of dephosphorization and desulfurization of Fe-Cr alloys at 18 wt. % Cr and elevated carbon contents using highly basic FeO_n-CaO-CaF₂-BaF₂ slag.     

Density and viscosity of molten Zn-Al alloys

Different Zn-Al alloys were applied in various hot-dip coating processes, such as galvanizing, GALFAN, GALVALUME, and aluminizing, for corrosion protection. Density and viscosity are two important parameters of the molten alloys in many studies, especially those involving fluid mechanics. However, the experimental data of these two important properties are scarce. Interpolation and extrapolation of experimental data are often necessary. Models that can describe the entire system are needed for the prediction of these properties at different temperatures and with different alloy compositions. Various thermodynamic models were examined in the current study, and the one that provided the best fit to the experimental data of the Zn-Al binary system was introduced.     

Interfacial tension between low pressure argon plasma and molten copper and iron

The interfacial tension between the molten metal and the surrounding plasma environment affects the circulation of molten metal in the weld pool, heat transfer, and the eventual structure and properties of the weld metal. Since the effect of plasma on the interfacial tension of molten metals is not known, interfacial tension values between low pressure argon plasma and pure copper and iron were measured. The variables studied were temperature and the intensity of plasma emission.     

Solidification of undercooled molten Ni-based alloys

The effect of undercooling on grain structure is investigated in pure nickel, Ni₇₅Cu₂₅, and DD3 singlecrystal superalloy by employing the method of molten salt denucleating combined with thermal cycling. Meanwhile, a comparison of factors that may be related to structure formation is performed and the difference in the refined structure between Ni₇₅Cu₂₅ alloy and DD3 single-crystal superalloy is explained. Only one grain refinement occurs at the critical undercooling in pure nickel, whereas two take place at both low and high undercoolings in Ni₇₅Cu₂₅ and DD3 single-crystal superalloy melts. The first grain refinement at low undercoolings mainly originates from dendrite remelting driven by the chemical superheating produced in recalescence, and the second one at high undercoolings is due to the recrystallization process as a result of the high stress provided in the rapid solidification after high undercooling. Dislocation morphology evolution in as-solidified structure is also provided by the transmission electron microscopy (TEM) technique to further verify the recrystallization mechanism.     

Gaseous oxygen absorption by molten iron and some Fe-AI,Fe-Si,Fe-Ti,and Fe-V alloys

An experimental investigation of the initial rates of oxygen dissolution in molten iron and some Fe-(≤9 pct Al), Fe-(≤6 pct Si), Fe-(≤1 pct Ti) and Fe-(≤1 pct V) alloys was carried out in pure oxygen. Two experimental techniques were employed in this study: a modified constant-volume Sieverts method and a falling droplet technique. It was found that the oxidation behavior of liquid iron-based alloys in gaseous pure oxygen as a function of alloy composition was similar under conditions of the falling droplet and modified constant volume Sieverts methods. Marked declines in the oxygen absorption rates were observed for Fe-Al and Fe-Si alloys when the initial alloy compositions reached 6 wt pct Al and 3 wt pct Si in iron, respectively. This behavior indicated a change in mode of oxidation from a burning to a passive type. Fe-Ti and Fe-V alloys initially containing up to 1 wt pct solute in iron exhibited only a burning type behavior. The sudden decline in oxygen absorption rate in molten iron-aluminum and iron-silicon alloys is discussed in terms of changes in the nature of the surface oxide film with increasing amounts of alloying element in the metal.