The slag-metal equilibrium in tin smelting

An equilibrium study was undertaken to investigate the effect of the CaO/SiO₂ and Fe/SiO₂ ratios and the SnO and Al₂O₃ contents of slags on the distribution of Fe and Sn between slag and metal in tin smelting. The experiments were performed at 1200 °C by equilibrating Sn-Fe alloys with silicate slags under reducing conditions in closed crucibles. The slag and metal analyses were used to calculate the γ_SnO/γ_FeO ratio in the slags and a multiple-linear regression on these values indicated that, in the range of slag compositions investigated, γ_SnO/γ_FeO is a function only of the CaO/SiO₂ ratio. At 1200 °C, γ_SnO/γ_FeO varies from about 1.1 for CaO-free slags to 3.6 for slags in which the CaO/SiO₂ ratio is 1.0. In practical applications, the slag-metal equilibrium in tin smelting is usually discussed in terms of the variation of the distribution coefficient,k, with the Fe content of the metal, wherek is defined ask = [pct Sn]/[pct Fe] · (pct Fe)/(pct Sn). An equation fork was derived in terms of the atom fraction of iron in the metal, the γ_SnO/γ_FeO in the slag, and the temperature. This equation was used to construct graphs ofk as a function of the iron content over the slag compositions and at temperatures which cover the range of tin smelting practice.     

Thermodynamics of slag-metal equilibrium

In a recent publication Elliott, Lynch and Brown (ELB) have criticized the early Flood and Grjotheim (FG) treatment of slag-metal equilibria. The present paper demonstrates that part of the difference between the ELB and FG treatment is in the different choice of standard state. However, the standard state used by ELB was introduced in 1959³ for the treatment of this type of equilibria. A fundamental thermodynamic error is introduced in the ELB derivation by the use of single ion activity coefficients which invalidates their treatment of experimental data.     

Thermodynamics of slag-metal equilibrium

In a recent publication¹ Elliott, Lynch and Brown (ELB) have criticized the early Flood and Grjotheim (FG) treatment² of slag-metal equilibria. The present paper demonstrates that part of the difference between the ELB and FG treatment is in the different choice of standard state. However, the standard state used by ELB was introduced in 1959³ for the treatment of this type of equilibria. A fundamental thermodynamic error is introduced in the ELB derivation by the use of single ion activity coefficients which invalidates their treatment of experimental data.     

Interfacial phenomena in some slag-metal reactions

In the present work, the change of the interfacial tension at the slag-metal interface for sulfur transfer between molten iron, slag, and gas phases was monitored by X-ray sessile drop method in dynamic mode in the temperature range of 1830 to 1891 K. The experiments were carried out with pure iron samples immersed partly or fully in the slag phase. The slag consisted of 30 wt pct CaO, 50 wt pct Al₂O₃, and 20 wt pct SiO₂ (alumina saturated at the experimental temperatures) with additions of FeO. Metal and slag samples contained in alumina crucibles were exposed to a CO-CO₂-SO₂-Ar gas mixture with defined oxygen and sulfur partial pressures, and the change of the shape of the metal drop was determined as a function of time. The equipment and the technique were calibrated by measurements of the surface tensions of the pure Cu, Ni, and Fe containing two different amounts of dissolved oxygen. A theoretical model was developed to determine the sulfur content of the metal as a function of time on the basis of sulfur diffusion in the slag and metal phases as well as surface tension-induced flow on the metal drop surface. Attempts were made to compute the interfacial tensions on the basis of force balance. 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.     

转炉渣钢间传质的冷态模拟试验

在转炉冶炼过程中,底吹参数对渣钢间传质起着非常重要的作用。为了研究底吹参数如底吹枪支数、底吹强度对传质效果的影响,以100t转炉为原型,根据相似原理,通过冷态模拟试验研究了苯甲酸在油水间的传质规律。试验表明,传质系数随着底吹强度增加呈现先增加后减小的现象;最优底吹流量随底吹枪支数增加而增加,底吹枪由4支逐渐增加到10支时,最优底吹流量由0.08增加至0.25m3/(t·min);最优单支枪供气强度为0.02~0.025m3/(t·min),且随底吹枪支数增加略有增加。     

Enhancing rate of slag-metal reactions involving carbon in liquid iron

Abstract

A series of experiments on decarburisation and iron oxide reduction have been conducted over the past 10 years. Experiments have been recently conducted to demonstrate that the slag-metal reaction between iron oxide and solute carbon is electrochemical, and that the rate of this reaction can be increased by applying a dc voltage across the slag layer. Analysis of this phenomenon has resulted in a deeper understanding of the rate limiting processes. Current research on iron oxide reduction and decarburisation is aimed at studying the effect of reduced pressure and the effect of applied potential on the reaction rate, and the relationship between applied potential and current efficiency. Future research will focus on other oxide reduction reactions, and other reducing agents.     

钢中钛含量对连铸结晶器内渣金反应的影响

 高钛钢在浇铸过程中发生渣金反应易出现结鱼现象,恶化铸坯质量,严重时引发漏钢。采用扫描电镜对现场浇铸中出现的结鱼物进行分析,结合高温真空压力烧结炉对不同钛含量的高钛钢和保护渣之间的渣金反应进行研究,并利用旋转黏度仪、熔点熔速测试仪、XRD和OPA金属原位分析仪对渣金的综合性能进行深入探讨。结果表明,随着高钛钢中钛含量的增加,渣金界面反应程度增加;高钛钢钛质量分数为0.05%时,未发生渣金反应;高钛钢钛质量分数为0.10%和0.20%时,发生渣金界面反应,钢中钛质量分数分别减少0.02%和0.04%,钢中硅质量分数分别增加0.02%和0.03%,保护渣中SiO₂质量分数分别减少0.36%和0.8%,TiO₂质量分数分别增加2.17%和4.3%。渣金反应发生后熔渣碱度增大。钛以氧化物的形式进入熔渣中未溶解,导致熔渣黏度和熔点增大。     

Model study of mixing and mass transfer rates of slag-metal in top and bottom blown converters

Water model experiments have been conducted to clarify mixing rates of molten steel and mass transfer rates between slag and metal in LD and Q-BOP furnaces using six different circular tuyere arrangements. Splashing and ‘spitting’ were also examined with a view to finding a quiet bath with minimum mixing time and maximum mass transfer rate. Froude’s similarity criterion was fulfilled to determine gas flow rate and bath depth. Complete mixing time of water determined by tracer technique had been 0.9 second to 1.8 seconds for Q-BOP as compared to 6 seconds to 13 seconds for LD. This shows that the stirring intensity in Q-BOP is remarkably larger than that of LD. A simple relationship τ = 5.9(Q/N) ^−0.49 was obtained with gas flow rateQ and number of tuyereN. This indicates that flow rate of gas per tuyere should be intensified to realize better mixing. Mass transfer coefficient K_Ba for bottom blowing was found to be almost double that for top blowing. Of all the tuyere configurations studied for Q-BOP’s, a half circular tuyere arrangement was found to be the best considering all aspects of mixing, mass transfer, and bath agitation.     

Effect of fluorspar and other fluxes on slag-metal equilibria involving phosphorus and sulfur

The effect of additions of fluorspar-and potential substitutes such as borate, manganese ore, and ilmenite—to basic steelmaking slags on the equilibrium phosphorus and sulfur distribution ratio has been studied at 1550δC. From laboratory slag-metal equilibrium studies it was found that the presence of CaF2 in concentrations between 1.5 and 5 wt pct in the slag (equivalent to 2 and 6 kg of fluorspar per ton of steel) lowered the equilibrium phosphorus content in the metal by about a factor of three. The use of B₂O₃, manganese ore, or ilmenite (the active ingredient in Sorel flux) did not affect the equilibrium phosphorus content of the metal. The effect of CaF₂ is ascribed to a lowering of the activity of P₂O₅ in the slag. Good agreement was found between the metal phosphorus content obtained from open-hearth plant data (no fluorspar added) and the present laboratory data for slags not containing CaF₂. None of the fluxes studied in this work, including CaF₂, improved the equilibrium sulfur distribution between metal and slag. The present results indicate that the choice of a substitute for fluorspar in an actual steelmaking operation, except when phosphorus presents a problem, should be based primarily on the cost of using the fluorspar substitute, including any change in refractory costs resulting from using the substitute.     

The concentration-dependent diffusion of chromium in nickel oxide

A theory has been developed to describe the diffusion of trivalent impurities in a divalent metal oxide and has been evaluated for the diffusion of trivalent chromium in NiO. The theoretical model developed by Lidiard to describe the diffusion of divalent impurities in alkali halides was revised to describe the migration of chromium-vacancy complexes in the divalent NiO crystal. A radioactive⁵¹Cr tracer and NiO single crystals were used and the concentration profiles were analyzed by sectioning and counting. The diffusion coefficient of chromium as a function of chromium concentration was determined at 1000°, 1100°, 1200°, and 1300°C and at oxygen pressures of 1.0, 10^-2, and 10^-5 atm using a modified Matano analysis of the concentration profiles. A reasonable fit of the theory to the experimental concentration dependence of chromium diffusion was obtained which indicates that, at 1000°C and above, chromium diffuses in NiO by a mechanism involving chromiumvacancy two-member complexes. The energy of association of a chromium-vacancy couple was found to increase from approximately -3000 cal at 1000°C to about -600 cal at 1300°C. The diffusivity of chromium (Dcr) in NiO saturated with chromium increases from approximately 2 x 10^-12 cm²/s at 1000°C to 2 x 10^-10 cm²/s at 1300°C.     

The magnetic susceptibility of chromium silicides

Summary Faraday's method was used to investigate the effect of temperature on the magnetic susceptibility of CrSi₂ CrSi, Cr₅Si₃, and Cr₃S'i in the range 20–800°C. It is shown that the Curie-Weiss law is valid for chromium monosilicide, while the susceptibility of the other suicides depends on temperature. Hypotheses are put forward regarding the possible interpretation of the experimental data obtained.     

Transformation behaviour of the high temperature martensitic steels with 8 – 14% chromium

Comprehensive development work on martensitic steels belonging to the so-called 12% Cr steel group were performed at the Institute for Materials Research (IMF) of Forschungszentrum Karlsruhe on martensitic steels, the so-called 12% Cr steel group, in order to meet the various requirements in nuclear and conventional energy technology. The transformation characteristics of 29 different grades of steel and 38 heats have been determined and continuous cooling transformation (CCT) diagrams have been prepared. The diagrams are first described by groups of subjects in a chronological order because the change in the chemical composition cannot be correlated in all cases with the change in transformation behaviour. The quenching hardness can be satisfactorily described as a function of the C+N content if, taking into account the Nb, Zr, Ta, Hf fractions, a common effectiveness factor is calculated. This effectiveness factor is also integrated in the calculation of the M_s point by modifying accordingly the equation proposed by Steven and Haynes for low-alloy steels and supplemented by the summands for V and W. An equation is introduced for the calculation of the critical cooling rate for pearlite transformation which takes into account the special influence exerted by elements Cr, V, Mo, W, Ge. The comparison between calculated and measured values for Ms and Vcrit is satisfactory, except for some steels.     

The effect of chromium in high carbon bearing steels

Chromium is present in the 52100 bearing steel composition in the range 1.30 to 1.60 wt pct. Chromium has a significant influence on the spheroidization of cementite, finer carbides being formed due to chromium additions. The ferrite to austenite transformation temperatures are increased due to chromium. The microchemistry of the cementite in 52100 changes during heat treatment; the chromium content of secondary carbides is generally lower than that in the spheroidal (FeCr)₃C produced by soft annealing. The rate of carbide dissolution is controlled by the rate of chromium diffusion from the carbide-matrix interface. Also, the chromium content of the residual, spheroidal (FeCr)₃C increases during austenitization. The effect of substitution of chromium in bearing steel compositions is discussed. In view of the beneficial effect of chromium, only substitution by similar strong carbide forming elements should be considered for bearing steels.     

二溴对甲基偶氮磺褪色光度法测定铬青铜中铬

基于0.6 mol/L硝酸介质中,显色剂二溴对甲基偶氮磺与铬(Ⅵ)的褪色反应,建立了测定铬青铜中铬(Ⅵ)含量的褪色光度分析方法。讨论了吸收光谱、酸度、试剂用量、时间、络合物组成、干扰离子等因素的影响,确定了反应的最佳条件。在25 mL溶液中,铬(Ⅵ)量在0.8~12μg范围内符合比尔定律,表观摩尔吸光系数为4.34×104L.mol-1.cm-1。方法可用于直接测定铬青铜中铬(Ⅵ)的含量,结果与二苯基碳酰二肼光度法(DPC)相符,其相对标准偏差(RSD)在0.97%~1.02%之间。