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.     

The kinetics of dephosphorization of carbon-saturated iron using an oxidizing slag

The kinetics of dephosphorization of carbon-saturated iron by oxidizing slags were studied at 1330 °C. Nine slag compositions were investigated in the systems CaO-Fe₂O₃-SiO₂-CaF₂ and CaO-Fe₂O₃-SiO₂-CaCl₂. Increasing Fe₂O₃ up to 50 pct was found to increase the rate and extent of dephosphorization, whereas further increases were found to decrease the rate and extent of dephosphorization. This was explained in terms of two competing effects on the driving force, where increased levels of iron oxide increase the oxygen potential for dephosphorization, hence the driving force, but simultaneously dilute the basic components in the slag, lowering the driving force for dephosphorization. CaF₂ and CaCl₂ were found to decrease the rate and extent of dephosphorization at levels higher than 12 pct. The rate of dephosphorization was found to be first order with respect to phosphorous in the metal and was controlled by mass transport in the slag. The oxygen potential at the slag/metal interface was controlled by the FeO activity in the slag. When the kinetic results were analyzed to take account of different driving forces, Fe₂O₃, CaF₂ and CaCl₂ were all found to increase the mass transfer coefficient of phosphorous in the slag, and a quantitative relationship has been demonstrated between these mass transfer coefficients and the slag viscosity for each system studied.     

Distribution of antimony between carbon-saturated iron and synthetic slags

Author A.F. Kalcioglu is performing national service with the Turkish army.     

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．     

Rate of molybdenum solution in carbon-saturated liquid iron

The rate of solution of molybdenum in molten iron saturated with carbon was studied by rotating cylindrical molybdenum specimens in a stationary graphite crucible containing the iron-base melt. Weight changes were used to determine the solution rate in the temperature range 1315° to 1425°C. Theoretical and experimental correlations of the solution rate coefficient are compared. Molybdenum diffusion in the liquid phase is shown to be rate limiting.     

Reaction mechanism for the CaO-Al and CaO-CaF2 desulfurization of carbon-saturated iron

The desulfurization of carbon-saturated iron with CaO is inefficient due to the formation of solid reaction products on the CaO particles which inhibit sulfur transfer. It has been shown in full scale and pilot plant studies that Al improves desulfurization with CaO. The present results indicate that Al affects the rate at 1450 °C, but not at 1350 °C, and that zirconium, which has a stronger affinity for oxygen than Al, does not increase the rate as much as aluminum. Alternate methods of producing a liquid reaction surface, such as desulfurization with CaO-CaF₂ or a premelted calcium aluminate flux, also increase the rate. From these results, it is concluded that it is critical to have a liquid reaction surface for effective desulfurization. Aluminum in the metal, reacting with oxygen and CaO, provides a liquid calcium aluminate surface. An optimum aluminum level of about 0.1 to 0.3 pct was found. At lower levels, the Al is consumed and eventually solid calcium silicate forms, and at higher levels, possibly an alumina-rich solid phase forms.     

Thermodynamic activity of antimony at dilute solutions in carbon-saturated liquid iron

Activity measurements of Sb are made by equilibrating antimony containing liquid metal,e.g., Pb, Cu, or Ag, with carbon-saturated liquid iron. At low Sb concentrations in Fe-C_sat., γ _° ^sb = 3.2 at 1200 °C increasing to 23.3 at 1550 °C. Previous work onγ _° ^sb in Pb, Cu, Ag, and Fe-C_sat. are reviewed and reassessed in the light of the present work. Formerly a Senior Research Engineer.     

Reaction mechanism for the CaO-Al and CaO-CaF2 desulfurization of carbon-saturated iron

The desulfurization of carbon-saturated iron with CaO is inefficient due to the formation of solid reaction products on the CaO particles which inhibit sulfur transfer. It has been shown in full scale and pilot plant studies that Al improves desulfurization with CaO. The present results indicate that Al affects the rate at 1450 °C, but not at 1350 °C, and that zirconium, which has a stronger affinity for oxygen than Al, does not increase the rate as much as aluminum. Alternate methods of producing a liquid reaction surface, such as desulfurization with CaO-CaF₂ or a premelted calcium aluminate flux, also increase the rate. From these results, it is concluded that it is critical to have a liquid reaction surface for effective desulfurization. Aluminum in the metal, reacting with oxygen and CaO, provides a liquid calcium aluminate surface. An optimum aluminum level of about 0.1 to 0.3 pct was found. At lower levels, the Al is consumed and eventually solid calcium silicate forms, and at higher levels, possibly an alumina-rich solid phase forms. Formerly a Graduate Student with the Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University     

Influence of chromium and nickel on the dissociation of CO2 on carbon-saturated liquid iron

At 1600 °C, under conditions where the rate was not significantly affected by liquid-phase or gasphase mass transfer, the rate of dissociation of CO₂ was determined from the rate of decarburization of iron-based carbon-saturated melts containing varying amounts of chromium and nickel. The rate was determined by monitoring the change in reacted gas composition with an in-line spectrometer. The results indicate that neither chromium nor nickel had a strong effect on the kinetics of dissociation of CO₂ on the surface of the melt. Sulfur was found to significantly decrease the rate, as is the case for alloys without chromium or nickel, and the rate constant is given by $$k = \frac{{k^0 }}{{1 + K_s a_s }} + k_r $$ where k ⁰ denotes the chemical rate on pure iron, K _s is the adsorption coefficient of sulfur, a _s is the activity of sulfur corrected for Cr, and k _r represents the residual rate at a high sulfur level. The rate constants and adsorption coefficient were determined to be: $$\begin{array}{*{20}c} {k^0 = 1.8 \times 10^{ - 3} mol/cm^2 s atm} \\ {k_r = 6.1 \times 10^{ - 5} mol/cm^2 s atm} \\ {K_s = 330 \pm 20} \\ \end{array} $$ Experiments run at lower carbon contents showed that only a very small quantity of chromium was oxidized, immediately forming a protective layer. However, this oxidation occurred at a higher carbon content (2 pct) than what was expected from the thermodynamics.     

Phosphorus distribution between carbon-saturated iron at 1350 °C and lime-based slags containing Na2O and CaF2

The Corex process is capable of consistently producing hot metal with very low silicon contents (<0.1 pct), and as a consequence, its hot metal is ideally suited for the external removal of phosphorus. Various studies have shown that small additions of Na₂O significantly enhance the ability of lime-based slags to dephosphorize liquid iron. Additions of fluxes (such as CaF₂) may be required to ensure that the slags remain fluid during treatment. The aim of the present investigation was to study the dephosphorization capabilities of lime-based slags from the CaF₂-CaO-Na₂O-SiO₂ system. Phosphorus containing slag and carbon-saturated iron was equilibrated in carbon crucibles at 1350 °C under a carbon monoxide atmosphere. It was confirmed that additions of Na₂O increase the phosphate capacity of silicate and lime-based slags considerably. Additions of CaF₂ to Na₂O containing lime-based slags increase the activity coefficient of P₂O₅ and, therefore, decrease the phosphate capacity thereof. These slags have high phosphate capacities and low melting points, yielding them suitable as effective reagents for dephosphorization, and even desulphurization, of hot metal at relatively low temperatures. However, CaF₂ additions to these slags should be limited.     

Kinetics of reactions between gases and molten alloys of iron

Abstract

Under conditions where transport in the gas phase is rate determiiling, a unified concept of reactions between gases and solutes dissolved in liquid metals may be based on the equilibrium constant for the reaction. Examples are given for reactions between the gases hydrogen or oxygen and the solutes carbon, sulphur and oxygen dissolved in liquid iron.

Résumé

Quand le transport en phase gazeuse détermine le taux de réaction, un concept unifié de réactions entre des gaz et des solutés dissouts dans un métal liquide peut être basé sur les constants d'équilibre de la réaction. Nous présentons des exemples pour la réaction de l'oxygène ou de l'hydrogène gazeux avec du carbone, du soufre ou de l'oxygène dissouts dans du fer liquide.     

铁矿粉与CaO同化反应性能的表征方法

为解决在研究铁矿粉与CaO进行同化反应时通常采用最低同化温度这一终点体系指标来表征,而没有考虑同化反应速度和升温速率的缺陷以及采用多个指标来表征同化反应温度和速度在使用上的不便,本文充分利用铁矿粉在高温同化反应过程中获得的数据和范特霍夫规则,提出了量纲为1的同化反应特征数.该特征数包括同化反应速度、升温速率、同化温度和温度对同化反应速度的影响,可用来表征铁矿粉与CaO的同化过程中铁矿粉的同化温度、同化反应时间、同化反应结束温度等性能,并以烧结过程中的实际温度作为基准.该特征数综合了铁矿粉与CaO在同化反应过程中各重要信息,可以更全面地反映铁矿粉与CaO的同化反应性能.对两种方法得到的结果进行了比较,发现仅考虑最低同化温度这一终点指标时得到的结果相近,而采用同化反应特征数可以进一步细分出不同铁矿粉同化反应性能的差异.     

New refractories for closing iron notches and ramming troughs

Karaganda Metallurgical Combine. Chemico-Metallurgical Institute, Academy of Sciences of the Kazakh SSR. Translated from Metallurg, No. 12, p. 36, December, 1990     

Influence of ash on interfacial reactions between coke and liquid iron

Interfacial reactions occurring between molten iron and carbonaceous materials are of great significance in the steel industry, and specifically, the reaction of iron with metallurgical coke is one of the key phenomena occurring during blast furnace ironmaking. Major operating parameters such as hot metal composition will be directly influenced by the reactions occurring between liquid iron and coke. In the current investigation, the interfacial reactions occurring between coke and liquid iron were studied at a temperature of 1550 °C using the sessile drop method to further the understanding of the fundamental reactions occurring at the interface between coke and iron. The formation of interfacial reaction products was observed, and time-dependent reactions were identified. The transfer of elements such as carbon, sulfur, and silicon was determined. The reduction of silica was determined as having a major influence on the transfer of both silicon and carbon into liquid iron. This article is based on a presentation given in the Mills Symposium entitled “Metals, Slags, Glasses: High Temperature Properties & Phenomena,” which took place at The Institute of Materials in London, England, on August 22–23, 2002.     

CaO-FeO-SiO2-Al2O3/Na2O/TiO2渣系与碳饱和铁水间磷分配行为

 为了研究Al2O3、Na2O和TiO2作为铁水预处理渣的助熔剂对铁水预处理脱磷的影响,借助FactSage热力学软件绘制了CaO-FeO-SiO2渣系1 573 K液相区。随着Al2O3和Na2O质量分数的增加,该渣系液相区明显扩大,TiO2对渣系液相区影响不大。实验室研究采用纯铁箔替代碳饱和铁水进行热力学平衡试验,间接测定了1 573 K时铁水预处理脱磷渣与碳饱和铁水间的平衡磷分配比。结果表明,渣铁磷分配比随渣中Al2O3和TiO2质量分数的增加而减小,TiO2对磷分配比的影响相对较小;渣铁磷分配比随渣中Na2O质量分数和碱度的增加而增加,Na2O可显著提高渣的脱磷能力;渣铁磷分配比随渣中FeO质量分数的增加先增加后减小,最合适的FeO质量分数为35%～40%。     

Slag formation during high temperature interactions between refractories containing SiO2 and iron melts with oxygen

Abstract

Refractory–metal interactions and associated reactions are important during casting as they can lead to the formation of inclusions. High temperature interactions between aluminosilicate refractories and molten steel were studied in the present investigation using the sessile drop method. Changes in the contact angles between molten iron with well defined oxygen levels and substrates of silica, mullite (3Al₂O₃.2SiO₂) as well as commercial refractories, were measured in the dynamic mode. In all cases, the reaction led to slag formation. The experiments were performed under isothermal conditions at 1823 and 1873 K. A known and constant oxygen partial pressure was imposed above the iron drop, through appropriate CO–CO₂–Ar mixtures. For all substrates, the contact angles started decreasing due to lowering of the surface tension of iron, as oxygen was imposed onto the system. When a critical level of oxygen was reached, slag started forming at the drop/substrate interface and at this stage, the contact angle dropped suddenly. Subsequent behaviour of silica and mullite was observed to be different, with SiO₂ showing a non-wetting behaviour. In the case of SiO₂ substrate, there were also deep erosions along the periphery of the drops and there was slag accumulation at the sides of the metal drop, probably due to Marangoni flow and/or SiO_(g) formation. SEM and EDS analysis of the substrates revealed that the formed slag was fayalite. The thermodynamic criteria for slag formation and possible mechanisms of the reaction are discussed in the light of the experiments.     

Coarsening kinetics of silica in copper

Coarsening experiments have been conducted in the copper-silica system to study the aging behavior of compound precipitates in metallic systems under various conditions of temperature and atmosphere. Most of the experiments were conducted in a two-zone heating furnace, wherein a copper-cuprous oxide mixture was heated in one zone and the copper-silica sample was heated in the other zone, all enclosed in a quartz capsule. The temperature of the former zone determined the oxygen partial pressure in the system and the temperature of the latter zone determined the coarsening temperature. The silica particles from the coarsened samples were extraction-replicated and photographed in an electron microscope. The average radii obtained from these photographs were used to determine coarsening rate constants and activation energies. Isothermal coarsening kinetics followed the γ^-3 vs t law, indicating volume diffusion control. Activation energies were obtained for four different sets of experimental conditions. In each case the activation plot was linear. For coarsening under variable oxygen pressure the experimental activation energy of 530 kJ (127 Kcal) agrees fairly well with the predicted value of 514 kJ (123 Kcal) which takes into consideration the heats of solution and dissolution, as well as the activation energy for diffusion. For coarsening under constant oxygen pressures the experimental activation energies do not compare well with the predicted values, calculated on the basis of complete equilibration of oxygen between the gaseous phase and the sample. However, the experimental activation energies of 524 kJ (125 Kcal) and 447 kJ (107 Kcal) lie in the predicted range calculated on the basis of fixed amounts of oxygen in solution in copper. In no case is the activation energy for coarsening equal to that for diffusion of either species in the matrix as is sometimes assumed. Formerly DSR Staff Member.     

Coarsening kinetics of silica in copper

Coarsening experiments have been conducted in the copper-silica system to study the aging behavior of compound precipitates in metallic systems under various conditions of temperature and atmosphere. Most of the experiments were conducted in a two-zone heating furnace, wherein a copper-cuprous oxide mixture was heated in one zone and the copper-silica sample was heated in the other zone, all enclosed in a quartz capsule. The temperature of the former zone determined the oxygen partial pressure in the system and the temperature of the latter zone determined the coarsening temperature. The silica particles from the coarsened samples were extraction-replicated and photographed in an electron microscope. The average radii obtained from these photographs were used to determine coarsening rate constants and activation energies. Isothermal coarsening kinetics followed the γ^-3 vs t law, indicating volume diffusion control. Activation energies were obtained for four different sets of experimental conditions. In each case the activation plot was linear. For coarsening under variable oxygen pressure the experimental activation energy of 530 kJ (127 Kcal) agrees fairly well with the predicted value of 514 kJ (123 Kcal) which takes into consideration the heats of solution and dissolution, as well as the activation energy for diffusion. For coarsening under constant oxygen pressures the experimental activation energies do not compare well with the predicted values, calculated on the basis of complete equilibration of oxygen between the gaseous phase and the sample. However, the experimental activation energies of 524 kJ (125 Kcal) and 447 kJ (107 Kcal) lie in the predicted range calculated on the basis of fixed amounts of oxygen in solution in copper. In no case is the activation energy for coarsening equal to that for diffusion of either species in the matrix as is sometimes assumed.