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.     

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.     

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.     

Equilibria between silica-saturated iron silicate slags and molten Cu-As,Cu-Sb,and Cu-Bi Alloys

The solubilities of copper, arsenic, antimony, and bismuth in silica-saturated iron silicate slag, equilibrated with molten copper which included the corresponding element, were measured at temperatures 1473 and 1523 K under oxygen pressures ranging from 10⁻¹ to 10⁻⁷ atm. The results confirm that copper is dissolved as CuO^0.5 in silica-saturated fayalite slag. Dissolution of As, Sb, and Bi was found to be dependent upon the oxygen potential, suggesting oxidic rather than atomic dissolution. The data obtained also support models in which these elements exist in the slag mainly as two different types of oxides, but occasionally these oxides coexist with neutral atoms. Based on these models, equations were obtained that related the solubilities of these elements in the slags to the oxygen potential in them. The knowledge obtained in this investigation will be helpful in eliminating deleterious minor elements in copper smelting.     

Equilibria between ferrous and ferric chlorides in molten chloride salts

Equilibria between ferrous and ferric chlorides in molten salts have been studied for improving magnesium electrolysis and molten salt chlorination. The apparent equilibrium constants,K, of reaction FeCl_2(melt)+0.5Cl_2(gas)=FeCl_3(melt) were obtained. Measured values ofK were in good agreement with computed ones from regression equations. The composition of the melts, the partial pressure of chlorine, and the temperature were found to have important effects onK, and the effect of dissolved iron was smaller than that of other factors. At identical other conditions, the largest values ofK were observed in system 3, which suggested that the current efficiency for electrolysis of MgCl₂ should be lower when carnallite was used as electrolyte and that catalysis of iron species in molten salt chlorination would be better when molten salt systems containing high potassium chloride were used.     

Hydrogen transport in stagnant molten iron

A new experimental method is described for the study of gas absorption in liquid metals. The technique involves the sudden admission of the gas into a previously evacuated tube containing a column of stagnant liquid metal. Following a short initial period of pressure instability (< 10 sec), absorption rates can be accurately followed by monitoring changes in gas pressure (or volume) using a differential pressure transducer. In the present work, the solution of hydrogen in pure liquid iron was studied and confirmed to be a diffusion controlled process. The mean diffusion coefficient measured for hydrogen absorption in pure iron at 1 atm pressure over the temperature range 1550° to 1720°C was 8.76 x 10⁻⁴ sq cm sec⁻¹. This figure is about 35 pct lower than previously reported values by Parlee and coworkers.⁹⁻¹⁰     

高碳铁液中的Al-C-O平衡

为了促进铁水脱硫,在铁水预处理过程中加Al脱氧,由于铁水中C含量很高,Al、C同时存在于铁水中.研究了铁水中生成Al₄C₃的判定条件,分析了Al₄C₃的生成对Al脱氧的影响.利用热力学方法,计算了a_Al⁴·a_C3的值,从而对Al-C-O三相平衡进行了分析,通过得出的a_Al⁴·a_C3值绘制了Al-C平衡曲线,并进行了相关讨论,以确定Al₄C₃的生成范围.     

The solubility of tungsten in molten iron

The solubility of tungsten in iron has been determined at 1560–1620°C by successively saturating molten iron with tungsten while ensuring a uniform distribution of the content over the height. The temperature dependence of the solubility over that temperature range is described by a Schröder equation: C_s=(3.94±0.11)×10³e-(84.4±0.4)/RT.     

Solutions of iron oxides in molten cryolite

All the iron oxides (FeO, Fe₃O₄, Fe₂O₃, and FeAl₂O₄) dissolve in cryolite-alumina melts to give solutions containing both Fe(II) and Fe(III). The factor controlling the Fe(II)/Fe(III) ratio is the oxygen pressure, and experimental results are interpreted on that basis. Predictions are made of the variation of solubility with oxygen pressure, and the standard potential of the Fe²⁺/Fe³⁺ redox couple is calculated. The anode and anode gas of an industrial Hall-Heroult cell appear to be insufficiently oxidizing to cause significant conversion of Fe(II) to Fe(III). An anomaly in the liquidus diagrams for FeF₂ – Na₃AlF₆ and FeO – Na₃AlF₆ is accounted for in terms of solid solution of FeF₂ in cryolite. This article is based on a presentation made at “The Milton Blander Symposium on Thermodynamic Predictions and Applications” at the TMS Annual Meeting in San Diego, California, on March 1–2, 1999, under the auspices of the TMS Extraction and Processing Division and the ASM Thermodynamics and Phase Equilibrium Committee.     

Activity coefficient of antimony and arsenic in molten iron and carbon saturated iron

In connection with removal of tramp elements from molten iron and steel, activity coefficients of arsenic and antimony in carbon saturated iron and in pure iron were determined between 1473 to 1923 K and between 1823 to 1923 K, respectively, by measuring the distribution of those elements between the metals and silver. The following activity coefficients are observed: for carbon saturated iron: log γ_As = 3560/T + 1.14, log γ_Sb = 6890/T + 5.06; and for molten iron: log γ°_As = - 198/T - 1.41, log γ°_Sb = - 7030/T + 4.38, respectively. The possibility of the removal of arsenic and antimony from molten iron by using a BaO-BaF₂ flux is discussed.     

Thermodynamic properties of titanium and iron in molten silicon

Titanium and iron in silicon are known as harmful “lifetime killer” impurities, which shorten the lifetime of excited carriers in silicon solar cell and disturb power generation. Therefore, the removal of titanium and iron is one of the most important topics for the production of solar grade silicon. Thermodynamic properties of titanium and iron in molten silicon were determined at 1723 K by equilibrating molten silicon-titanium alloys or molten silicon-iron alloys with molten lead, which has a limited mutual solubility for both alloys. The activity coefficients of infinite dilution, self-interaction coefficients of titanium and iron in molten silicon, and the Gibbs energy change of mixing for silicon-titanium and silicon-iron at 1723 K relative to pure liquid silicon, titanium, and iron were determined.     

焦炭床内铁水渗碳行为

摘要：高炉冶炼过程中铁水最终渗碳量接近饱和,相比而言,闪速炉中没有固体炉料的压迫作用,无法发生像高炉炉缸内死料柱根部与铁水之间的渗碳反应,最终渗碳量难以预料。为此,以电解铁和化学纯石墨为原料,利用管式电阻炉升温到1855K熔化铁块,以高纯Ar作为保护气体研究焦炭床内铁水渗碳行为,并对铁水渗碳行为进行数值模拟,为闪速炼铁工业化打下基础。实验结果表明,终铁C含量随焦炭粒度增大和渗碳床高度降低而减小,且铁水初始C含量对终铁C含量具有较大影响。对于不同条件下铁水渗碳反应中C元素的迁移规律,基于VB编程技术进行了数值模拟,模拟结果与高温实验结果较吻合,相对误差在3%以内。渗流速度控制因子始终控制在05左右,即铁水在焦炭床中的平均速度为初始滴落速度的一半左右。     

Kinetic experiment of dissolving coke in molten iron

The liquid iron carburization in the blast furnace process can almost come to a saturation state, while, that in flash ironmaking process is unexpected, since there is no solid charge that will press the hot metal and no carburization reaction that occurs between the bottom deadman. In order to study the kinetics of coke dissolution into the molten iron in flash iron- making process, a series of experiments were carried out. Reduced iron powder and chemically pure graphite were used as raw materials, and the tubular resistance furnace was employed to heat the samples up to 1855K and melt them, and the high- purity N2 was injected as the protective gas throughout the experiments. The experimental results show that without regard to the factor kt of dissolution rate, the values of kt under natural convection condition are 4. 20??m/s in group 1, 5. 28??m/s in group 2 and 6. 50??m/s in group 3. On the contrary, when taking this factor into account, kt decreases with time increase and only can be controlled by the mass transfer. Besides, when there is sulfur in the iron- carbon melts, it shows that kt also decreases with the increase of sulfur content.     

COREX用焦在铁水中的渗碳特性

 钢铁工业是支撑国民经济发展的基础产业,同时也属于资源和能源密集型行业,随着国家严格的环保政策的逐渐实施,其面临的资源和环保要求日益增加。传统高炉炼铁生产工艺由于存在能耗高、污染物排放多的弊端,发展受到了限制,因此非高炉炼铁工艺的研究和应用日益受到钢铁行业的重视。系统研究了COREX熔融还原非高炉炼铁工艺使用的顶装焦、捣固焦和气煤焦在铁水中渗碳特性,并分析了3种不同样品在铁水中的渗碳动力学行为。研究结果表明,高温铁水与碳原子接触时发生渗碳反应的吉布斯自由能远小于Fe₃C生成反应的吉布斯自由能,焦炭与高温铁水接触被消耗的过程以渗碳反应为主。顶装焦、捣固焦和气煤焦3种焦炭样品与高温液态铁水接触后迅速发生渗碳反应,铁水中碳含量快速增加,但铁水中碳含量增加的幅度随着铁水中碳含量的升高而快速降低,在渗碳反应时间超过120 min后铁水中的碳含量基本保持恒定。3种焦炭在铁水中的渗碳速率由高到低分别为气煤焦、顶装焦和捣固焦,铁水温度对渗碳过程具有明显的影响,随着温度的升高,渗碳速率和最终铁水中的碳含量增加。动力学分析表明,捣固焦在铁水中的渗碳活化能最高,顶装焦次之,气煤焦最小。     

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．     

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     

Viscosity measurement and prediction model of molten iron

In order to explore effects of element content and temperature on the viscosity, viscosities of molten iron were precisely measured by the oscillating crucible method. The results obtained are summarised as follows: The viscosity of molten iron rises first and then decreases with the decreasing temperature; the viscosities before and after the turning point are the viscosity property and the solidification property, respectively. The temperature of the turning point decreases with the increasing carbon content. The viscosity increases with the increasing silicon and titanium content; on the contrary, the viscosity shows a downward trend with the increasing manganese, phosphorus, and sulphur content. The mechanism of various elements on the viscosity was analysed; the quantitative relationship between the viscosity and element content was obtained. The prediction model of the viscosity was established based on the co-existence principle; the calculation results of the model were in accordance with the measurement.