Solubility of nitrogen in CaO-SiO2-CaF2 slag system

Equilibrium experiments between gas and slag were carried out to understand the thermodynamic behaviour of nitrogen in the CaO-SiO₂-CaF₂ slag system at 1600°C. The solubility of nitrogen in this slag system increased as the oxygen potential decreased and as the reaction temperature increased. The values of the nitride capacity have a minimum at about 2.0 slag basicity, having higher values in both more acidic and basic regions. This may be explained by two mechanisms for nitrogen dissolution; incorporated nitride ion and free nitride ion state. In slag with 2.0 basicity or less, MgO content increased the nitride capacity slightly. At higher slag basicity, however, nitride capacity decreased with MgO content. The effects of BaO to substitute CaO on nitride capacity showed similar behaviour as MgO. This complex relationship between basicity of slag and nitride capacity is explained by using optical basicity. It was found that nitride capacity and optical basicity had a close relationship even in the different basic oxide systems.     

Oxidation state and activities of chromium oxides in CaO-SiO2-CrOx slag system

The activities of chromium oxides in a CaO-SiO₂-CrO _x slag system were determined with the electromotive force (EMF) method by equilibrating with metallic chromium at 1873 K. The effect of slag basicity on the activity coefficients of CrO and CrO_1.5 was analyzed. The results showed that increasing the slag basicity increased the activity coefficient of CrO; however, the effect on that of CrO_1.5 was not significant. The oxidation state of chromium in CaO-SiO₂-CrO _x slags was systematically investigated at both 1873 and 1863 K. It was found that divalent and trivalent chromium coexists in the slags. Divalent chromium oxide is favored, instead of trivalent chromium oxide, because of low slag basicity and low oxygen potential. It was concluded that the oxidation state of chromium in the slag system varied greatly from almost pure “CrO” to a composition corresponding to Cr₃O₄. In addition, the thermodynamic data in the slag system were assessed based on the regular solution model to mathematically describe the activities of chromium oxides in the slags. A group of model parameters were obtained. The calculated activities of chromium oxides were comparable to the measured data.     

Thermodynamic behaviour of carbonate in CaO based slag

Carbonate solubility was measured for CaO bearing slag systems at 1600 °C under different thermodynamic conditions by using equilibration techniques. Carbonate solubility increased with activity of (CaO). The reaction mechanism of the carbonate dissolution in slag can be expressed as a reaction between CO₂ gaseous phase and oxygen ion to form carbonate (CO₃^2-). Carbonate capacities of various slags depended not only on oxygen ion but also activity coefficient of carbonate ion. The activity coefficient of carbonate ion in CaO-SiO₂ slag changed with CaO content, but that of CaO-Al₂O₃ slag did not change remarkably. Substitution of MgO by CaO for solubility of carbonate had a similar effect as in the case of carbide in CaO-SiO₂-MgO slag. The critical oxygen potential for carbide and carbonate stability was found to be 10-¹⁰ bar.     

Thermodynamics of chromium oxides in CaO-SiO2-CaF2 slag

The distribution ratio of chromium between a CaO-SiO₂-CaF₂ slag and liquid silver under the oxygen partial pressure used in practical hot-metal dephosphorization treatment was measured at 1623 K. The distribution ratio was minimal when the basicity index of a slag, wt pct CaO/wt pct SiO₂, was about 2. The redox equilibrium between CrO (Cr²⁺) and CrO_1.5 (Cr³⁺) in the slag was also measured as a function of slag composition. The calculated activity coefficient of CrO had a maximum value at wt pct CaO/wt pct SiO₂=2, whereas that of CrO_1.5 decreased monotonously with the increase in slag basicity.     

CaO-SiO2-FeOx及CaO-SiO2-P2O5-FeOx渣系热力学性质的研究

CaO-SiO2-FeOx三元渣系和CaO-SiO2-P2O5-FeOx四元渣系是转炉脱磷用渣的主要子渣系,研究这两种渣系的热力学性质可为脱磷渣的高效利用提供理论依据。利于相图软件FactSage分别绘制了这两种渣系的相图,并分析了温度和氧分压对体系相平衡关系和液相线的影响规律。分析结果表明:升高温度会使这两种渣系的液相区扩大,初晶相稳定区域显著减小;降低氧分压会导致尖晶石固溶体相的初晶区消失,磷石英(SiO2)、伪硅灰石(CaSiO3)、α’-Ca2SiO4固溶体相减小。     

碱度对CaO-SiO2-Al2O3系熔渣微观结构的影响

为了明确精炼渣冶金功能的微观本质,本文模拟精炼渣的化学组成,采用拉曼光谱测定并解析了CaO-SiO2-Al2 O3系实验渣的熔体结构.结果表明,熔渣中Si4+以[SiO4]-四面体结构形式存在,随着碱度的升高,Q1Si和Q2Si含量减少,Q0Si含量增加;Al3+以[AlO4]-四面体和[AlO6]-八面体结构形式存在...     

MgO和MnO对CaO-SiO2-Fe2O3-P2O5渣的物相影响

转炉渣中的磷主要存在于n2CaO·SiO2-3CaO·P2O5（以下简记为nC2S-C3P）固溶体的富磷相中。为了深入理解转炉渣的物相,便于有效富集钢渣中的磷,研究MgO和MnO含量的变化对CaO-SiO2-Fe2O3-P2O5渣中nC2S-C3P固溶体的磷含量及渣结晶物相的影响,并对其进行热力学分析。结果表明：在CaO-SiO2-Fe2O3-P2O5四元渣系中加入少量MgO或MnO,可以在一定程度上提高nC2S-C3P固溶体中的磷含量;继续提高MgO或MnO含量,固溶体中的磷含量不再发生变化。随着MgO或MnO的加入,富铁相增多,有利于钢渣的磁选分离。     

Thermodynamic study on the effect of CaF2 on the nitrogen and carbon solubility in the CaO-Al2O3-CaF2 slag system

The nitrogen and carbon solubilities in the CaO-Al₂O₃-CaF₂ slag system at 1723K were measured to understand the effect of CaF₂ on the nitrogen and carbon dissolution behaviour using thermochemical equilibration technique. The nitride capacity in the CaO_satd.-Al₂O₃-CaF₂ system was constant until X_Al2O₃ / X_CaF2 = 0.23, followed by decrease with an increase in X_Al2O₃ / X_CaF2 ratio, and then showed a constant value. The carbide capacity in the CaO_satd.-Al₂O₃-CaF₂ system also showed the similar behaviour to the nitride capacity, however, the effect of CaF₂ on the activity coefficient of nitride and carbide ions showed some differences in case of X_CaF2 = 0.2. The effect of CaF₂ on the activity coefficient of carbide and nitride ions would not be significant in case of CaO-rich region of X_CaO / X_CaF2 = 0.31. However, CaF₂ could be expected to affect the activity coefficient of each ion in case of the Al₂O₃-rich region, causing compensating effect of the incorporated nitride (carbide) mechanism. The relationship between nitride and carbide capacity was also discussed.     

CaO-SiO_2-FeO-P_2O_5-Al_2O_3脱磷渣系中组元活度的计算

2CaO·SiO_2-3CaO·P_2O_5含磷固溶体的生成可提高转炉液相渣的脱磷能力,减少渣量.但目前CaO-SiO_2-FeO-P_2O_5-Al_2O_3渣系中各组元活度的变化规律尚不明确,无法为分析含磷固溶体的形成机理提供理论依据.为此,本文依据分子离子共存理论建立了熔渣组元的活度模型,分析了不同条件下组元活度的变化规律.结果表明:随渣中Al_2O_3含量的增加,2CaO·SiO_2、3CaO·P_2O_5、3FeO·P_2O_5的活度逐渐降低;随着碱度的增大,3CaO·P_2O_5的活度升高,2CaO·SiO_2、3FeO·P_2O_5的活度则呈先升高后降低的趋势;随着渣中FeO含量的增加,2CaO·SiO_2、3FeO·P_2O_5及CaO·Al_2O_3的活度逐渐增大,并在w(FeO)为15%时达到最大值,之后逐渐降低;升高温度会导致CaO、3CaO·SiO_2的活度增大,2CaO·SiO_2的活度降低.     

An assessment of the CaO-SiO2 system

An evaluation of the CaO-SiO₂ system has been made using a newly developed model, a two-sublattice model for ionic solutions. Two alternatives were tested. In the first one, three anions were assumed, O⁻², SiO₄ ⁻⁴, and SiO₃ ⁻². In the second one, SiO₃ ⁻² was omitted. A set of parameter values describing the Gibbs energy of the liquid phase and solid phases was fixed for each alternative by a computer-operated optimization procedure called PARROT. Satisfactory assessments were achieved over the whole phase diagram range with both alternatives. The main difference between them occurs at the monotectic point. A comparison between calculated properties and experimental data is given. Formerly Research Associate, Royal Institute of Technoloy     

Some observations on the draining of CaO-SiO2-Al2O3 slag bubble films

Fundamentals of slag foaming were investigated by withdrawing slag bubble films from pools of CaO-SiO₂-Al₂O₃ slags using platinum wire frames in order to measure their draining rate and lifetime before rupture. Studies were carried out using a series of developed gravimetric and optical techniques. The results showed that increasing the temperature increased the rate of draining of the slag films; however, the influence of SiO₂ concentration for a given slag temperature appears rather complicated. Measurements of the thickness of bubble film plateau borders as a function of time showed slag temperature to be very important in influencing their draining behavior, i.e., the activation energy for the plateau-border thinning was found to be ∼ 150 kJ/mol, very close to that required for viscous flow in the system studied (∼60 kJ/mol). A lowering of the slag surface tension by addition of surface-active oxides (such as P₂O₅ and Na₂O) profoundly decreased the rate of draining of the films, irrespective of the slag temperature. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS.     

Phase relations in the system CaO-SiO2-ZrO2 at 1573 K

Zirconia-based solid electrolytes with zircon (ZrSiC₄) as the auxiliary electrode have been suggested of sensing silicon concentrations in iron and steel melts. A knowledge of phase relations in the ternary system MO-SiO₂-ZrO₂ (M = Ca, Mg) is useful for selecting an appropriate auxiliary electrode. In this investigation, an isothermal section for the phase diagram of the system CaO-SiO₂ZrO₂ at 1573 K has been established by equilibrating mixtures of component oxides in air, followed by quenching and phase identification by optical miroscopy, energy disperse analysis of X-rays (EDAX) and X-ray diffraction analysis (XRD). The equilibrium phase relations have also been confirmed by computation using the available thermodynamic data on condensed phases in the system. The results indicate that zircon is not in thermodynamic equilibrium with calcia-stabilized zirconia or calcium zirconate. The silica containing phase in equilibrium with stabilized zirconia is Ca₃ZrSi₂O₉. Calcium zirconate can coexist with Ca₃ZrSi₂Og and Ca₂SiO₄.     

Thermodynamic behaviour of zinc in Fe‐C and CaO‐FeO‐CaF2 slag at high temperatures

The distribution ratio of zinc between Ag‐Zn and Fe‐Zn alloys was measured to clarify the thermodynamic behaviour of zinc in Fe‐C melt at high temperatures. Also, the distribution ratio between Ag‐Zn alloy and CaO‐FeO‐CaF₂ slag was measured to understand the dissolution mechanism of zinc in molten slags. The activity coefficient of zinc in Ag‐Zn alloy was preliminarily measured as a fundamental thermodynamic data for the activity of zinc in Fe‐C melt. From the dependence of the activity coefficient of zinc in Fe‐C melts on temperature and carbon content, the following equation could be obtained at 1473 ‐ 1623 K: The distribution ratio of zinc between Ag‐Zn alloy and CaO‐FeO‐CaF₂ slag increased by increasing both the oxygen potential and slag basicity. The stoichiometric coefficients of the dissolution reaction were obtained by considering the relationship between zinc distribution ratio and slag basicity or oxygen partial pressure, when one of these two independent variables was fixed. The dissolution reaction of zinc into the slags could be described as follows:      

Activity model of CaO-SiO2-AleO3-V2O3 quaternary system

根据熔渣结构的分子离子共存理论建立了CaO-SiO2-Al2O3-V2O3四元系活度模型。应用该模型计算出的活度数据,对用钒氧化物矿代替钒铁直接合金化冶炼高速钢的工艺过程进行了热力学计算和分析。用此活度数据计算了Al作还原剂时渣的平衡成分。计算结果表明,渣中V2O3的质量分数极低,直接合金化的热力学条件好,钒的理论最大还原率高。通过计算钢中或渣中的各种还原剂还原渣中V2O3的ΔG和LV,表明在炼钢工艺常用的所有还原剂中,Al的还原能力最强。     

Thermodynamic study of MnO-SiO2-Al2O3 slag system: Liquidus lines and activities of MnO at 1823 K

The liquid MnO-SiO₂-Al₂O₃ system was studied at 1823 K by equilibrating MnO-SiO₂-Al₂O₃ melts of different compositions with Pt-Mn alloys and an oxygen-bearing gas phase. Liquid compositions for cristobalite saturation were determined at 1823 K. A new liquidus for the cristobalite primary field is proposed. The activity of Mn in the Pt-Mn alloy at 1823 K can be represented by the following equation:

CaO-SiO_2-Al_2O_3-V_2O_3四元系活度模型

根据熔渣结构的分子离子共存理论建立了CaO-SiO2-Al2O3-V2O3四元系活度模型。应用该模型计算出的活度数据,对用钒氧化物矿代替钒铁直接合金化冶炼高速钢的工艺过程进行了热力学计算和分析。用此活度数据计算了Al作还原剂时渣的平衡成分。计算结果表明,渣中V2O3的质量分数极低,直接合金化的热力学条件好,钒的理论最大还原率高。通过计算钢中或渣中的各种还原剂还原渣中V2O3的ΔG和LV,表明在炼钢工艺常用的所有还原剂中,Al的还原能力最强。     

高铅渣还原过程渣性能及其还原特性的热力学分析

液态高铅渣的还原过程中炉渣物理化学性能变化对其还原特性至关重要。本文在分析高铅渣的主要物化性能指标及其研究方法及分析检测手段基础上,对目前铅渣物理化学性能及还原特性的研究现状进行了概述。并运用热力学软件分析计算了高铅渣还原过程的热力学特性,结果表明,在高铅渣还原反应中,从热力学角度,渣系的所有物相中,无论是和C反应还是和C0反应,Pb_8ZnSi_6O_(21)都是最容易被还原的。在温度700℃条件下,Pb_8ZnSi_6O_(21)和Pb_4SiO_6与C直接还原反应比与C0还原反应更容易进行,但是对Pb_2SiO_4和Pb0没有明显的趋势。     

Thermodynamic aspects of steel reoxidation behavior by the ladle slag system of CaO-MgO-SiO2-Al2O3-Fe t O-MnO-P2O5

The reoxidation behavior of steels by slag in the secondary steelmaking process was addressed by investigating the thermodynamic equilibria between the liquid iron containing Mn and P and CaO-MgO-SiO₂-Al₂O₃-P₂O₅-MnO-Fe _t O ladle slag at 1873 K. The activity coefficient of Fe _t O shows a maximum value in the vicinity of the basicity ((X _CaO + X _MgO + X _MnO)/(X _SiO2 + X _Al2O₃ + X _P2O₅)) = 2.5 at the specific mole fraction range of Fe _t O, while that of MnO seems to increase gradually with increasing the basicity. However, the values of and γ _MnO showed minima with respect to P₂O₅ content of slag. In addition, the values of and γ _MnO increased as (pct CaO)/(pct Al₂O₃) ratio increased at given SiO₂, MgO, and P₂O₅ contents. The conversion equations between the Fe _t O and MnO activities and their calculated activities via regular solution model were derived by the correlation between the measured and calculated activities over the limited ranges of Fe _t O and MnO contents. The regular solution model was used to estimate the oxygen potential in the slag. For MgO saturated slags, . For Al₂O₃ saturated slags, .     

Kinetics of chromite ore reduction from MgO-CaO-SiO2-FeO-Cr2O3-Al2O3 slag system by carbon dissolved in high carbon ferrochromium alloy bath

Abstract

Kinetic experiments were performed in an induction furnace to investigate the reduction of chromite ore by carbon dissolved in a high carbon ferrochromium alloy melt under conditions of varying Cr₂O₃ concentration, slag basicity, and temperature. The results obtained show that chromite reduction by dissolved carbon in slag systems of the type MgO-CaO-SiO₂-FeO-Cr₂O₃- Al₂O₃ occurs principally by a stagewise process encompassing an intermediate reaction in which the divalent chromium oxide species is involved. During the fast period, Cr₂O₃ reduction is controlled by the diffusion of oxygen species in the slag for which a mass transfer coefficient of 0·003 cm s^-1 was calculated. An activation energy value of 117 kJ mol ^-1 obtained for the reduction of Cr₂O₃ implies the rate controlling step is mass transfer of Cr₂O₃ from the slag to the slag/metal interface, since activation energies for metal phase control are typically <70 kJ mol ^-1. The second period represents a pseudo-equilibrium condition with respect to Cr₂O₃ reduction that is probably under thermodynamic control by a step or mechanism involving the reduction of divalent chromium oxide to chromium.