Carbothermic Reduction of MoO3 for Direct Alloying Process

The thermodynamics of Mo-O-C and Ca-Mo-O-C systems was studied in order to understand the carbothermic reduction of molybdenum trioxide, and kinetic studies were also carried out by means of thermogravimetric analysis under argon atmosphere with a heating rate of 10 °C/min. Subsequently, reaction products at various temperatures were identified by X-ray diffraction (XRD) and the results confirmed the previous thermodynamics analysis. Meanwhile, it was found that intermediate products MoO₂ and CaMoO₄ appeared in the process of carbothermic reduction of MoO₃ with or without CaO, which were subsequently reduced to Mo or molybdenum carbide. An experimentally determined reaction mechanism was proposed and discussed. The reduction reaction of MoO₃ with carbon could be divided into two stages. The first stage includes the direct reaction between MoO₃ and carbon and the carbon gasification reaction. The second stage is the gas-solid reaction between CO and MoO₂, and the diffusion of gases through the surface of MoO₂ determines the overall reaction rate. The activation energies of the mixtures with or without CaO were estimated to be 56.6 and 52.9 kJ/mol, respectively.     

1 mm铁碳合金薄带气-固反应脱碳试验

 为了研究1 mm铁碳合金薄带气-固反应脱碳动力学以及探索不同温度对薄带脱碳效果的影响。以初始碳质量分数为4.2%、厚度为1 mm的铁碳合金薄带为研究对象,在气体流量为400 mL/min、[pH2O/pH2]为0.85的Ar-H2-H2O混合气氛条件下,以高温气-固反应形式开展脱碳试验研究。结果表明,提高脱碳温度可以明显提高脱碳效果,在1 413 K温度条件下脱碳30 min可以将碳脱至0.12%。宏观脱碳反应近似为表观一级反应,脱碳反应表观活化能为157.9 kJ/mol。脱碳反应初期主要受控于表面化学反应,后期碳在薄带内部的扩散成为主要限制性环节。     

Analysis of Magnesia Carbothermic Reduction Process in Vacuum

The mechanism of magnesia carbothermic reduction was investigated experimentally in a reduction reaction process in vacuum. The thermodynamic calculation results showed that the initial reduction temperature between MgO and C was 1500 K (1227 °C) at 50 Pa. Other reduction reactions did not occur between the temperature 300 K and 1900 K (27 °C and 1627 °C) and 30 to 100 Pa. Based on the analysis of experimental results, the initial reduction reaction temperature was 1553 K (1280 °C), and it matched well with the thermodynamic calculations. The gas–solid reaction between MgO and CO did not occur at 1723 K (1450 °C), 30 to 100 Pa. Therefore, the main reduction reaction was MgO_(s) + C_(s) = Mg_(g)+ CO_(g) in vacuum. This reaction belonged to the solid–solid reaction type, the condensing product was obtained in the condensation zone, and the main component of the product was metal magnesium. A little magnesia was also obtained in the condensing product due to the reverse reaction.     

真空碳热还原氧化镁脱硫工艺试验

介绍了一种利用真空碳热还原氧化镁对铁水进行脱硫预处理的新工艺。以生铁、氧化镁、石墨为原料,利用真空电阻炉,探讨了真空碳热还原氧化镁对铁水进行脱硫的可行性。氧化镁与石墨的加入比例为1∶2(摩尔比),并加入二者质量分数3%的催化剂CaF2,三者混匀磨细(0.088 mm),加热至800℃后,升温速度由10℃/min降至5℃/min,升温至1 400℃。结果表明,铁中硫含量由0.032%降至0.009%,脱硫率达72%,证明该工艺可行。     

Effect of Nozzle Base Material on the Rate of Clogging during the Continuous Casting of Aluminum‐Killed Steels

One approach to solving the problem of nozzle clogging during the continuous casting of aluminum‐killed steels is through careful selection of nozzle materials. In this study, the rate of clogging was measured while casting steel through simulated nozzles produced from alumina, zirconia, magnesia, zirconia‐graphite, and alumina‐graphite ‐ three common base materials and two common carbon‐containing nozzle materials. Spent nozzles were characterized using optical and cathodoluminescence microscopy. Interactions between the nozzles and steel were not observed in the alumina, zirconia, and zirconia‐graphite nozzles. Slight interactions were observed in the magnesia nozzles as alumina inclusions within the steel interacted with the nozzle to produce alumina‐magnesia spinel. Greater amounts of interaction were observed with alumina‐graphite nozzles. No statistical differences in the mean rate of clogging were observed between all of the pure oxide nozzles and zirconia‐graphite nozzles. However, the alumina‐graphite nozzles clogged at a much higher rate than the other nozzles. The higher rate of clogging is thought to be due to refractory‐steel interactions.     

A model for the role of carbon on carbochlorination of TiO2

The carbochlorination of TiO₂ is characterized by two successive reaction stages, named the first and the second stage. In both stages, reaction rate increases as carbon mass fraction increases. This kinetic effect of carbon was interpreted on the basis of a model developed to describe the rate of each reaction stage as a function of carbon mass fraction in TiO₂-C powder mixture. The model considers, for both reaction stages, two global steps: [I] the formation of gaseous intermediates at the carbon surface and [II] the reaction of these intermediates with TiO₂ to form the reaction products. The mathematical treatment from these steps involves the adaptation of the general model applied to catalytic gas-solid reactions. The first reaction stage occurs, for high carbon contents, under strong external chlorine transport control and, for low enough carbon content, under internal mixed control. The second reaction stage occurs out of external gaseous influence and a net chemical control operates, both at low temperatures and for the lowest carbon content. The intrinsic activation energies for the first and second reaction stages are 40 and 117 kJ-mol⁻¹, respectively.     

The Reaction Behavior of Direct Reduced Iron (DRI) in Steelmaking Slags: Effect of DRI Carbon and Preheating Temperature

An experimental study was conducted to quantify the rate of direct reduced iron (DRI) decarburization in a steelmaking slag using the constant volume pressure increase technique. Experiments were conducted by dropping DRI pellets into molten slag at temperatures from 1773 K to 1873 K (1500 °C to 1600 °C). Subsequent experiments were carried out in which the DRI pellets were preheated while the slag temperature remained constant. The effect of the initial carbon content and the preheating temperature of the DRI on the reaction rate was investigated. The decarburization of DRI seems to comprise two stages, a reaction between the FeO and DRI followed by decarburization through the iron oxide of slag. Carbon has a significant effect on the kinetics of both stages, whereas the preheating temperature mainly influences the rate of decarburization between FeO and carbon inside the pellet.     

An experimental investigation of the gasification of graphite by carbon dioxide

The gasification of graphite by carbon dioxide was studied under atmospheric pressure in a fixed bed reactor in the temperature range of 1173–1773?K, CO₂ partial pressures 2–10?kPa and gas flow rate 0·5–2·0?L?min^?1. Iron presented in a small amount in graphite ash had a catalytic effect on the gasification reaction at 1373?K; this effect was weaker at 1473?K due to the melting of iron saturated with carbon. The gasification rate increased with increasing CO₂ partial pressure and total gas flow rate.     

Catalytic Mechanism of KCl during Carbothermic Reduction of Pre-Oxidized Ilmenite

The carbothermic reduction is one of the mainmethods used in pyrometallurgy.It has been widelyused in both ferrous and nonferrous metallurgy.　　 As confirmed by experimental works,suitableamount of alkali additives can effectively catalyze thecarbothermic reduction[1] ,reduce the apparent acti-vation energy and the reaction start tempera-ture[2— 7] .It is generally believed that the catalyticeffect of alkali additives is to catalyze the Boudouardreaction and consequently accelerate the overa…     

Gas-solid reaction-rate enhancement by pressure cycling

An experimental study and mathematical modeling of the effects of external pressure cycling on gas-solid reactions have been conducted using the reduction of nickel oxide pellets by hy-drogen. Experiments were carried out in two phases: In the first phase, the intrinsic kinetic parameters were measured, and in the second phase, the gas-solid reaction was carried out under a constant or cycling external pressure. The effects of the frequency and amplitude of pressure cycling were studied at various reaction conditions. Pressure cycling substantially increases the overall rate of the reaction. A mathematical model was developed from the first principles to establish the extent of the overall reaction-rate enhancement and subsequently to analyze the experimental observations. The calculated values from the mathematical model are in good agreement with the experimental results. The effects are most pronounced when the overall rate under a constant pressure is controlled by diffusion. Depending on the reaction condition, a very large degree of rate enhancement could be achieved. Furthermore, low-amplitude pressure waves, like acoustic waves, could significantly increase the rates of gas-solid reactions. M.B. ABOUKHESHEM, formerly Graduate Student, Department of Metallurgical Engineering, University of Utah.     

真空感应熔炼AerMet100超高强度钢脱氮实验研究

摘要：通过取样检测并结合热力学和动力学计算研究了氧化镁质（MgO）、镁铝尖晶石质（MgO·Al2O3）和氧化钙质（CaO）3种坩埚和2种真空压力（50~100Pa和5~10Pa）对AerMet100超高强度钢脱氮的影响。实验结果表明：随着精炼时间增加,3种坩埚在2种真空压力下的钢液中N质量分数都逐渐减少。相比之下,CaO坩埚脱氮效果最佳,2种真空压力下30min时N质量分数均减少到0.0005%。动力学计算结果表明：MgO和MgO·Al2O3坩埚在2种真空压力下的钢液中O和S活度较高,脱氮反应均服从2级,即钢液脱氮受界面化学反应控制;而CaO坩埚在2种真空压力下的钢液中O和S活度较低,脱氮反应均服从1~5级,即钢液脱氮由液相边界层传质和界面化学反应共同控制。此外,减小真空压力,脱氮速率加快,有利于钢液脱氮。     

Nonisothermal gravimetric investigation on kinetics of reduction of magnesia by aluminum

An investigation of the reduction of magnesia by aluminum was carried out using a nonisothermal gravimetric technique under an argon atmosphere, in the temperature range from 1273 to 1873 K. The mixture of magnesia and aluminum powders was formed into a pellet under various isostatic pressures. It was found that magnesia is reduced by aluminum to form magnesium and spinel at first, and then the excess aluminum reacts with spinel slowly. The temperature at which the reaction starts increases with an increasing heating rate. The reaction rate is also affected by pellet-forming conditions. A kinetic model is proposed to explain the experimental results. The activation energy of the reduction of magnesia by aluminum is 151.2 kJ/mol. Good agreement between calculated and experimental results is obtained.     

碳热还原法制取Ti(C,N)的热力学原理

分析了以TiO2为原料，用碳热还原法制取Ti（C，N）的热力学原理。结果表明钛氧化物的还原是逐级进行的，反应过程伴随着相变，当TiO2粉末和C粉末均匀混合时还原碳化反应主要依赖于CO／CO2传质的气固反应，当TiO2颗粒表面被C包膜时主要是碳和钛氧化物之间的固固反应，当TiO2粉末和C粉末混合压球时则两种反应机理均有。升高温度有利于还原进行，钛氧化物的开始还原温度随气相中的CO分压降低而降低。Ti（C，N）中的C，N含量取决于温度和N2压力。     

The Rate of reduction of MgO by carbon

The rate of reduction of MgO by carbon within a carbon-bearing MgO refractory material was investigated by measuring the rate for an actual refractory material as well as for various powder mixtures of MgO and carbon in atmospheres of Ar, He, and CO from 1475 to 1600°C. The effective gas diffusivities within the brick were also determined in order to interpret the results. For small samples, for which gas-diffusion processes do not affect the rate, the rate is controlled by a slow chemical reaction. Indications are the slow reaction is the oxidation of carbon however, the exact mechanism is not known. The temperature dependence of the rate of reaction is large 157 kcal (657 kJ). For larger samples the initial rate is controlled by the diffusion of the products (Mg and CO) through the gas film boundary layer near the surface and in the later stages by diffusion through the pores of the reacted MgO. To model the actual geometry in a BOF an experiment in which the reaction products would be removed from a single surface was conducted and indicated that after a short period of time the rate is controlled by diffusion through the pores of the brick. It was concluded that in actual practice a pseudosteady-state thickness for the reacted decarburized zone will develop because of the balance between the diffusion-limited layer growth and normal refractory wear and that the layer would be relatively small (0.1 to 0.4 cm).     

The kinetics of nickel oxide reduction by hydrogen; Measurements in a fluidized bed and in a gravimetric apparatus

The suitability of a batch fluidized bed laboratory reactor for measuring the rates of gas-solid reactions was investigated. Experiments were carried out on the reduction of Falconbridge nickel oxide by hydrogen in a batch fluidized bed reactor within the tem-perature range 550 K to 650 K using particles in the range of 60 to 100 mesh. The reactor was operated at approximately atmospheric pressure and gas flow rates were in the range of two to four times the minimum fluidization velocity at temperature. The results showed internal consistency and rough agreement with the results of previous workers. The re-sults were interpreted and correlated by means of a structural model for gas-solid reac-tions. As a check on the fluidized bed measurements, experiments were also carried out using the conventional gravimetric technique to measure the rate of reduction of compac-ted pellets of nickel oxide by hydrogen. When due allowance was made for the change of surface area of the oxide during compaction, the results were in close agreement with the fluidized bed results. Rate measurements using hydrogen-nitrogen mixtures revealed that the reaction is not first order with respect to hydrogen, as usually assumed, but is ap-proximately of order two-thirds at one atmosphere hydrogen partial pressure. Formerly Graduate Student at Berkeley     

30MVA直流电弧炉冶炼钛渣配碳比研究

工业生产中,为生产出合格的钛渣必须加入适量的碳作为还原剂,将高价氧化物还原为低价氧化物。云南某公司30 MVA大型密闭直流电弧炉(DC炉)生产运行过程中,通过控制无烟煤用量与钛精矿用量之比——配碳比(ratio of anthracite to ilmenite,简称AIR),使生产在输入能量一定、钛精矿成分稳定的条件下力求获得良好的产品品质。生产通过中空石墨电极将钛精矿和无烟煤加入DC炉内,熔炼温度控制为1973～2023 K;熔炼输入功率为15 MVA;入炉钛精矿粒度为0.1～0.33 mm;入炉无烟煤粒径为5～25 mm的比例大于85%。理论上熔炼还原1 t钛精矿,将会产出526 kg渣和368 kg金属铁,O/I比率约为89.4%,理论配碳比约为7.895%。通过生产物料衡算得出,一定熔炼周期内的AIR平均值为12.228%,O/I比率平均值为81.317%。在配碳量不足的情况下,钛精矿中的FeO易于离解出氧并与碳结合,使FeO还原反应优先于TiO2等氧化物,碳最大可能的消耗在FeO的还原上;配碳量越高,则碳将用于还原难还原的氧化物(如MgO,CaO,MnO等)上,使FeO的还原受到抑制。配碳比还会影响DC电炉熔渣流动性和挂渣层。试生产熔炼周期内,通过调整AIR,实现了钛渣中TiO2品质的提高,其含量可从82%提高到89%以上。     

LF精炼渣对镁碳质基片的润湿性和渗透性

 采用座滴法测定固液间接触角,分别对镁碳质基片及基片中的两种主要组元与LF精炼渣之间的润湿性进行了研究,并从润湿性角度研究了镁碳砖损毁机理。研究表明,在精炼温度下,熔渣对石墨均呈不润湿状态,温度越低越不容易润湿。而熔渣对MgO组元呈完全润湿状态。熔渣与镁碳质基片间的接触角在温度为1 460～1 480 ℃时存在明显转折,在转折点温度以下,MgO和碳的反应受到抑制,熔渣对基片保持不润湿状态。在转折点温度以上,镁碳质基片中的MgO和碳发生反应生成镁蒸汽和CO气体。该反应导致基片内碳质量分数减少,熔渣对基片的接触角迅速下降,最终呈完全润湿。当熔渣与基片间的接触角小于90°时,熔渣将对基片产生明显渗透作用。MgO与碳反应形成的孔隙成为熔渣渗透的主要通道。熔渣渗透到镁碳质基片内部的未反应层时,由于两者之间的不润湿性及较少的孔隙阻碍了熔渣的进一步渗透。     

微孔MgO耐火材料对钢液洁净度的影响

摘要：通过浸泡实验研究了3种镁质（致密镁质、微孔MgO质、镁碳质）耐火材料与超低碳钢液(1560℃)的相互作用,考察了不同浸泡时间(0～35min)钢中O、N、C和Al、Si、Mn含量及钢中夹杂物的成分、数量、分布等特征的变化,并对耐火材料与钢的界面层进行了观测和分析。结果表明,随着浸泡时间的延长,3组钢中氧含量均先升高再降低,均对钢液有一定的污染,钢中夹杂物的数量增加,夹杂物种类由Al2O3-MnO夹杂逐渐转变为Al-Mg-Si-Mn-O复合夹杂。与致密镁质耐火材料相比,微孔MgO质和镁碳质耐火材料与钢的界面处分别能形成连续的镁铝尖晶石层和致密的MgO层,有助于降低耐火材料的侵蚀以及对钢液的污染。此外,与不含碳的镁质耐火材料相比,镁碳质耐火材料对钢液增碳严重。因此,微孔MgO质耐火材料不仅对钢液的二次污染小、不会向钢液增碳,而且还可以吸附钢中氧化铝夹杂,更有利于超低碳洁净钢的生产。     

Corrosion mechanism of commercial doloma refractories in contact with CaO–Al2O3 –SiO2 – MgO slag

Abstract

The dissolution of three doloma based refractories in liquid CaO–Al₂O₃–SiO₂–MgO slag was studied. Cylindrical refractory specimens of doloma, carbon bonded doloma, and magnesia doloma were rotated in a stationary crucible of molten slag under forced convection conditions. Slag composition, temperature, rod rotation speed and rod immersion time were varied. The refractory dissolution rate was determined from the change in diameter of the cylindrical specimens. The corrosion rate was found to increase with temperature and rod rotation speed and decrease when the slag was nearly saturated with MgO. The findings of the study substantiate the assumption that the diffusion of magnesium oxide through the slag boundary layer controls the corrosion process. The results indicated the overall corrosion process to be the dissolution of refractory material into the slag, followed by slag penetration of the pores and grain boundaries and finally, dispersion of the grains into the slag.     

The kinetics of dissolution of sphalerite in ferric chloride solution

The dissolution of sphalerite in acidic ferric chloride solution was investigated in the temperature range 320 to 360 K. Both sized particles from three sources and polished flat surfaces were used as samples. The effect of stirring rate, temperature, ferric and ferrous ion concentration, purity, and particle size on the dissolution rate were determined. During the initial stages of the process chemical reaction at the mineral surface is rate controlling while during the later stages diffusion through the product sulfur layer is rate controlling. Overall the process follows the mixed-control model embodying both chemical reaction and diffusion. The activation energy for the dissolution of sphalerite particles was found to be 46.9 kJ/mol.