Kinetics of oxidation of carbon in liquid iron-carbon-silicon-manganese-sulfur alloys by carbon dioxide in nitrogen

The oxidation of carbon with the simultaneous oxidation of silicon, manganese, and iron of liquid alloys by carbon dioxide in nitrogen and the absorption of oxygen by the alloys from the gas were studied using 1-g liquid iron droplets levitated in a stream of the gas at 1575 °C to 1715 °C. Oxidation of carbon was favored over oxidation of silicon and manganese when cast iron (3.35 pct C, 2.0 pct Si, 0.36 pct Mn, and 0.05 pct S) reacted with CO₂/N₂ gas at 1635 °C. An increase in the flow rate of CO₂/N₂ gas increased the decarburization rate of cast iron. The rate of carbon oxidation by this gas mixture was found to be independent of temperature and alloying element concentrations (in the range of silicon = 0 to 2.0 pct manganese = 0 to 0.36 pct and sulfur = 0 to 0.5 pct) within the temperature range of the present study. Based on the results of a kinetic analysis, diffusion of CO₂ in the boundary layer of the gas phase was found to be the rate-limiting step for the reactions during the earlier period of the reaction when the contents of carbon, silicon, and manganese are higher. However, the limiting step changed to diffusion of the elements in the metal phase during the middle period of the reaction and then to the diffusion of CO in the gas phase during the later period of the reaction when the content of the elements in the metal were relatively low. For the simultaneous oxidation reactions of several elements in the metal, however, the diffusion of CO₂ in the gas phase is the primary limiting step of the reaction rate for the oxidation of carbon during the later period of reaction. Formerly Visiting Assistant Research Scientist, Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109     

Modelling of ferrosilicon smelting in submerged arc furnaces

Abstract

Ferrosilicon alloys are commonly manufactured in submerged electric arc furnaces with little slag. In the presence of iron, silica will be reduced by carbon to give a maximum of ~ 22 wt% silicon in the liquid alloy. The rest of the carbon will be consumed to transform silica to silicon carbide at ~ 1810 K. Higher grades of ferrosilicon alloy may be produced owing to the reactions occurring between silicon carbide and silica at temperatures above 1810 K. Thermodynamic data on the standard free energy of formation of species are used in the study to calculate the required smelting temperatures at various silicon contents of the alloy. The sum of partial pressures of carbon monoxide and silicon monoxide must equal the applied pressure of 1 atm at the smelting temperature. It is important to know the activity coefficient of silicon in the alloy as a function of temperature, and the silicon content of the alloy using literature data. Mass and enthalpy balances are used to determine the carbon and electricity requirements of the process. The recycling of silicon monoxide is promoted by maintaining a bed of a certain height so that evolved gases are cooled owing to heat exchange between the gas and solid phases. It might result in a saving of more than 3000 kWh/t of Fe-80Si alloy. The reduction of silica is found to account for just 47·6% of the total energy that is added via the calorific value of carbon and the electricity in producing the alloy. Further improvement in the performance is visualised by reducing electrical losses and recovering as much as possible the calorific value of outgoing carbon monoxide.     

Si对中碳弹簧钢氧化脱碳行为的影响

试验研究了成分(%)为0.49C-0.29Si-1.65Mn、n53C-0.78Si-1.56Mn和0.54C-1.74Si-0.71Mn(60Si2MnA)3种中碳弹簧钢850℃5～120 min水冷和780～1000℃60 min水冷热处理后的脱碳敏感性和氧化失重行为。结果表明,随钢中硅含量增加,钢的脱碳层深度增加,氧化失重量减少,说明Si能增加钢中碳的扩散系数,促进钢的脱碳。     

Desiliconization and decarburization behavior of molten Fe-C-Si(-S) alloy with CO<Subscript>2</Subscript> and O<Subscript>2</Subscript>

One of the most important problems in the steelmaking process is an increase of the disposal slag mainly discharged from the dephosphorization process. In order to reduce the quantity of the disposal slag, the complete removal of silicon from molten pig iron is considered very effective before the dephosphorization in the pretreatment process. From this point of view, the desiliconization and the decarburization behavior of Fe-C-Si alloy with CO₂ and O₂ has been investigated in the present work. It is thermodynamically calculated that silicon should be oxidized in preference to carbon over 0.60 mass pct Si under the condition of s_SiO2=a _C=1 at 1573 K and is experimentally confirmed that silicon is only oxidized under the condition in actual. Even under the competitive region of desiliconizing and decarbonizing, under 0.60 mass pct Si, silicon is found to be oxidized down to about 0.1 mass pct Si in preference. The overall rate constants for the desiliconization and the decarburization are derived, and the value for the desiliconization is one order of magnitude larger than that for the decarburization. The influence of sulfur is also examined, and the retarding effect is not observed on the oxidation reactions.     

Reactive phosphide inclusions in commercial ferrosilicon

The goal of this work was to determine the origin of phosphine gas (PH₃), which has been reported to be generated from wet, commercial ferrosilicon alloys containing ∼75 wt pct Si. Based on previous work, it is suspected that PH₃ evolves when phosphides present within the alloy react with atmospheric moisture or water. Reactive phosphides have been identified in synthetic ferrosilicon alloys, which contain higher amounts of phosphorus than are typically present in commercial alloys. Therefore, reactive phosphides in commercial FeSi75 alloys are expected to be important to the evolution of PH₃ from these alloys. To identify the role of reactive phosphides in the evolution of PH₃ from commercial FeSi75 alloys, the microstructures of four commercial and two synthetic FeSi75 ferrosilicon alloys were investigated. Reactive phosphides were observed in each of the commercial alloys and characterized with respect to composition, morphology, and location within the microstructure. The phosphides observed in all of the commercial alloys contained aluminum, calcium, and magnesium. The phosphides had inclusion-like morphologies and were located on the silicon/ζ (high-temperature FeSi₂) interfaces at microcracks. The microstructural features observed support the hypothesis that atmospheric moisture penetrates ferrosilicon, reacting with the phosphide inclusions to produce PH₃. A possible mechanism describing the spontaneous crumbling sometimes observed in ferrosilicon alloys is also presented.     

碳、硅铁及碳化硅对白钨矿还原动力学的影响

在实验室用15 kW碳管炉进行碳粉、硅铁粉(75％Si)、碳化硅粉对白钨矿粉(67．25％WO3)还原动力学影响的研究。结果表明,碳还原白钨矿的反应级数为二级,反应表观活化能为234．6 kJ／mol;碳在较低温度下,反应性能差,当温度达到1 400℃时,反应剧烈;随温度升高,硅铁的还原性能比较平稳,反应产生SiO₂,使渣量增加;碳化硅高温反应性能好(≥1 400℃);碳和硅铁适合较低合金化率(3％W),碳化硅适宜用于较高的合金化率(≥5％W)。     

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.     

Oxidation kinetics of iron alloy drops in oxidizing slags

The kinetics of reactions between drops of Fe-C, Fe-C-P and Fe-C-S alloys and synthetic oxidizing slags at 1550°C have been studied. The reaction kinetics are obtained either from chemical analysis of quenched samples, or, for decarburization, * by continuous measurement of the flow rate of evolved gas. The marked effect, on the kinetics, of the metal emulsification during carbon removal is evidenced. A decrease in slag oxygen potential results in the slow-down of decarburization. Sulfur shows a tendency to limit interfacial reactions, but it enhances metal emulsification. Both mass transfer processes and interfacial reactions, as well as nucleation, are believed to play their part on the rate of decarburization.     

Decarburlzation of silicon melt for solar cells by filtration and oxidation

In studies on the decarburization of liquid silicon, two types of carbon were identified in a silicon melt containing more carbon than the solubility. One was in the form of silicon carbide particles and the other was in the form of dissolved carbon. The silicon was filtered to remove the carbide particles. Using silica or silicon carbide as the material for the filter, the carbon content was reduced from 100 to 30 to 60 ppmw. Oxidation was done under reduced pressure to eliminate the rest of the carbon as carbon monoxide, and the final carbon content was as low as 10 ppmw. Silica was chosen as oxidizing reagent. To avoid a reverse reaction, Ar was introduced on the surface to expel extraneous CO or CO₂ gas evolved. The thermodynamics of the oxidation of carbon in silicon melts is also discussed. Formerly with the Graduate School of the University of Tokyo     

直接氧化法制备陶瓷基复合材料的动力学研究

对直接氧化法制备Al2O3/Al复合材料动力学及反应机理进行了研究，实验分析Al-3Mg-4Si合金在不同温度下和不同时间内的氧化增重速度，通过对烧结材料的成分分析来研究直接氧化法制备材料的反应机理。     

Internal oxidation of NiAl and NiAlSi alloys at the dissociation pressure of NiO

NiAl and NiAlSi alloys were internally oxidized at temperatures of 1073–1273 K by the Rhines Pack method. For the NiAl alloy, the oxidation process follows parabolic law and the oxidation front was flat with severe integranular oxidation occurring at 1073 K and extensive grain boundary sliding at 1273 K. As for NiAlSi alloys, the oxidation rate increased with increase of Si content at 1073 K but the rate decreased at higher temperatures due to total or partial continuous oxide layer formation at the internal oxidation front. The depth of intergranular oxidation was also greatly reduced. For all samples, nickel was found to be transported out to the surface with the amount proportional to the Si content. Lattice diffusion (Nabarro-Herring creep) was believed to be the main cause for nickel transport in the NiAl alloy while dislocation pipe diffusion is the mechanism for NiAlSi alloys.     

Effects of Si and Cr on Complete Decarburization Behavior of High Carbon Steels in Atmosphere of 2 vol.% O2

The effects of chemical compositions,especially silicon and chromium contents,on the complete decarburization behaviors of steels in atmosphere of 2 vol.% O_2 and 98vol.%N_2 were investigated by using a simultaneous thermal analyzer.Complete decarburization was observed at both 750 and 800 ℃ for 60Si2 Mn A steel,while 750 ℃ only for 92 A steel.For GCr15 steel,no decarburization was found at 750 or 800 ℃,and only partial decarburization was observed at 850 ℃.It indicates that silicon promotes while chromium prevents the complete decarburization of steels in atmosphere with 2 vol.%O_2.The main reason is that silicon increases while chromium reduces the equilibrium concentration of ferrite at the interface of ferrite and austenite,which results in the complete decarburization.     

Thermodynamic and Kinetic Behavior of B and Na Through the Contact of B-Doped Silicon with Na2O-SiO2 Slags

Boron (B) is the most problematic impurity to be removed in the processes applied for the production of solar grade silicon. Boron removal from liquid silicon by sodium-silicate slags is experimentally studied and it is indicated that B can be rapidly removed within short reaction times. The B removal rate is higher at higher temperatures and higher Na₂O concentrations in the slag. Based on the experimental results and thermodynamic calculations, it is proposed that B removal from silicon phase takes place through its oxidation at the slag/Si interfacial area by Na₂O and that the oxidized B is further gasified from the slag through the formation of sodium metaborate (Na₂B₂O₄) at the slag/gas interfacial area. The overall rate of B removal is mainly controlled by these two chemical reactions. However, it is further proposed that the B removal rate from silicon depends on the mass transport of Na in the system. Sodium is transferred from slag to the molten silicon through the silicothermic reduction of Na₂O at the slag/Si interface and it simultaneously evaporates at the Si/gas interfacial area. This causes a Na concentration rise in silicon and its further decline after reaching a maximum. A major part of the Na loss from the slag is due to its carbothermic reduction and formation of Na gas.     

Fe-Si-B非晶带材高温氧化行为及回收工艺

??In order to reduce the oxidative burning loss of Fe78Si9B13 amorphous ribbon in the recovery process?? the oxidation behavior of Fe78Si9B13 amorphous ribbon was studied. The results show that the oxidation of Fe78Si9B13 amorphous ribbon at high temperature is related to the heating rate. The oxidation weight gain of Fe78Si9B13 amorphous ribbon at 5 and 10K/min from room temperature to 1223K are 44% and 31% respectively. There is an oxide layer with loose texture and a small amount of microcrack at the interface between the sample and atmosphere by SEM. The oxide layer contains a large amount of Fe2O3 and a little SiO2 by XRD. Oxidation kinetics curve shows that the oxidation weight gain of the samples follows a linear rule within 5hours at 1073 and 1173K?? then a parabolic rule. At 1273K?? however?? it only follows a linear rule?? meanwhile the oxidation speed is very fast?? with the oxidation weight gain reaches 40% in 12min. The oxidation weight gain in the amorphous ribbon recycling process can be reduced through cutting down the furnace gas temperature?? compressing the waste ribbon and unqualified products in the packaging process and blowing argon to reduce the partial pressure of oxygen in the furnace. Thus the slag decreases to 9-10g when 1kg waste ribbon is recovered?? and the Si content of liquid alloy increases to 8. 9%.     

硅溶胶粘结SiC预制件的烧结特性研究

本文以硅溶胶为粘结剂,采用粉末冶金工艺制备SiC预制件,探讨煅烧温度以及引入钠离子对预制件强度、氧化增重和SiO2总含量的影响.结果表明:硅溶胶含量为1.55％～3.88％的SiC预制件在空气中高温煅烧时的氧化增重随温度的升高而增大,与硅溶胶的含量无关.当煅烧温度在1 050℃以上时才能获得足够的强度,此时预制件中SiO2的总含量不低于4.61％.当硅溶胶中引入钠离子(模数为2.5～20),可将SiC预制件的煅烧温度降至750～850℃,SiC的氧化增重随煅烧温度的升高和钠离子含量的增加而增大;预制件获得足够强度对应的SiO2的总含量降至1.35％.     

硼对高强度弹簧钢脱碳敏感性的影响

弹簧表面形成脱碳层将恶化其疲劳性能,因此要求弹簧钢具有低的脱碳敏感性。研究了不同硼含量(0．0006％～0．0027％)对中碳高强度弹簧钢脱碳敏感性的影响。采用等温处理和等时处理研究了含硼中碳弹簧钢和作为对比的60Si2Mn钢的脱碳层深度和氧化失重量的变化情况。结果表明：实验钢的脱碳层深度和氧化失重量均随硼含量的增加而减少。这表明,钢中添加微量硼能够抑制弹簧钢的氧化和脱碳。硼的这种良好作用主要与其在原奥氏体晶界的偏聚有关。含硼中碳弹簧钢的氧化和脱碳敏感性明显低于所对比的60Si2Mn钢,这除了与硼抑制钢的氧化和脱碳的作用有关外,前者较低的碳含量也是一个主要原因。     

Mathematical modeling of the argon-oxygen decarburization refining process of stainless steel: Part I. Mathematical model of the process

Some available mathematical models for the argon-oxygen decarburization (AOD) stainless steelmaking process have been reviewed. The actual situations of the AOD process, including the competitive oxidation of the elements dissolved in the molten steel and the changes in the bath composition, as well as the nonisothermal nature of the process, have been analyzed. A new mathematical model for the AOD refining process of stainless steel has been proposed and developed. The model is based on the assumption that the blown oxygen oxidizes C, Cr, Si, and Mn in the steel and Fe as a matrix, but the FeO formed is also an oxidant of C, Cr, Si, and Mn in the steel. All the possible oxidation-reduction reactions take place simultaneously and reach a combined equilibrium in competition at the liquid/bubble interfaces. It is also assumed that at high carbon levels, the oxidation rates of elements are primarily related to the supplied oxygen rate, and at low carbon levels, the rate of decarburization is mainly determined by the mass transfer of carbon from the molten steel bulk to the reaction interfaces. It is further assumed that the nonreacting oxygen blown into the bath does not accumulate in the liquid steel and will escape from the bath into the exhaust gas. The model performs the rate calculations of the refining process and the mass and heat balances of the system. Also, the effects of the operating factors, including adding the slag materials, crop ends, and scrap, and alloy agents; the nonisothermal conditions; the changes in the amounts of metal and slag during the refining; and other factors have all been taken into account. []—metal phase; ()—slag phase; {}—gaseous phase; and 〈〉—solid phase     

硅铁合金中金属钙元素对铝脱氧钢中夹杂物的影响

大尺寸CaO?Al₂O₃类夹杂物容易引起轴承钢疲劳失效,大尺寸CaO?Al₂O₃类夹杂物的控制是生产高端GCr15轴承钢的关键因素之一。精炼过程中合金引入杂质元素、渣精炼和精炼过程中卷渣是铝脱氧轴承钢中大尺寸CaO?Al₂O₃类夹杂物的主要潜在来源。硅铁合金通常用来提高轴承钢的淬火和抗回火软化性。本文通过实验室实验、样品分析和热力学计算,研究了硅铁合金中金属钙元素对铝脱氧钢中夹杂物的影响。硅铁合金主要由深色的硅相和浅色的硅铁相组成,钙元素在硅相和硅铁相的界面处以金属化合物形式存在。研究发现,加入硅铁合金后,钢中总钙（T.Ca）含量增加,钢中的Al₂O₃和MgO·Al₂O₃夹杂物被改性为CaO?Al₂O₃类夹杂物,夹杂物尺寸随着夹杂物中CaO含量增加而减小,钢中并未生成大尺寸CaO?Al₂O₃类夹杂物。随着钢中T.Ca含量增加,夹杂物平均尺寸降低,钢中T.O含量增加,表明硅铁合金中金属钙元素不会直接引起钢中大尺寸CaO?Al₂O₃类夹杂物的生成。但是生成的小尺寸固相CaO?Al₂O₃类夹杂物在水口处粘附结瘤,结瘤物脱落后会成为钢中大尺寸CaO?Al₂O₃类夹杂物的来源之一。      

高炉炮泥中氮化物的组成与结构分析

为了改善高炉炮泥的烧结性能,提高其抗侵蚀能力,在炮泥配料中加入了氮化硅或氮化硅铁。对加人氮化物的炮泥组成与结构以及氮化物的作用机理进行了分析。结果表明：氮化硅存在由氮氧化物转化为氧化物的反应过程,而氮化硅铁则氧化为硅铁的氧化物。氮化物的氧化过程伴随着结构致密化反应,能减缓碳的氧化,从而改善炮泥的耐用性能。