Morphology of steel electrofurnace dust

The size distribution and morphology of steel electrofurnace dust is studied by optical and scanning electron microscopy. Mechanical mixing in water is investigated as a means of isolating ultradisperse particles and splitting up large particles. By suspension in water, the dust particles are separated into three fractions. The characteristics of the particles in each fraction are determined.     

The kinetics of reduction of hematite by carbon

Reduction kinetics of mixtures of hematite and carbon powders were investigated in the temperature range of 850° to 1087°C. Experiments were carried out under argon atmosphere and the isothermal weight loss of the samples was determined as a function of time. The effects of carbon particle size, hematite/carbon ratio of the mixture, and addition of promotive or inhibitive reagents were also investigated. The results were summarized in the form of fractional reaction vs time plots. A kinetic model developed on the basis of carbon solution-loss reaction as rate-controlling represented the results fairly well. An enthalpy of activation of 72 kcal/per mole was calculated, within the range of 957° to 1087°C. The observed effects of Li₂O and FeS on the reduction kinetics are consistent with the influence these reagents are known to exercise on the solution-loss reaction.     

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).     

Studies on the reduction of hematite by carbon

Single pellet experiments have been carried out in a nitrogen atmosphere to study the reduction of hematite by graphite in the temperature range 925 to 1060°C. The effect of variables such as c/Fe₂O₃ molar ratio, pellet size, and so forth, has been investigated. Gas analysis data show a continuous decrease in CO₂/CO ratio during reduction, the values being far away from Fe/FeO equilibrium for wustite reduction by CO. The activation energies associated with different degrees of reduction appear to be widely different suggesting a possible changeover in reaction mechanism during the progress of reduction. X-ray diffraction studies confirm the stepwise nature of hematite reduction. Formerly Research Scholar in the Department of Metallurgy, Indian Institute of Science, Bangalore-560012, India,     

Kinetics of manganese ore reduction by carbon monoxide

A step has been made in the direction of understanding the fundamental chemical processes taking place inside electric are furnaces producing manganese alloys. The reduction of higher manganese oxides to MnO by carbon monoxide has been studied in the temperature range 700 °C to 1100 °C. A topochemical pattern with a single shrinking core inside the ore particles has been observed in most cases. It has been found that the reduction of some manganese silicates (braunite minerals) is influenced by reaction interface kinetics, whereas the reduction rate of manganese oxides (bixbyite and hausmannite) is mostly determined by product shell pore diffusion. Sintering kinetics and the extent of natural porosity determine the product shell pore diffusivity. As the melting point of the reaction product is approached, rapid sintering leads to a decrease in diffusivity.     

活性炭选择性催化还原NOx

采用活性炭作催化剂,NH3为还原剂,进行活性炭脱硝机理的实验研究.分别考察了烟气组分、温度、活性炭的比表面积及不同材质对NOx去除率的影响.结果表明:活性炭作为单纯的吸附剂,其NO吸附容量较小,O2的加入使吸附容量增大,NH3与O2同时存在则可达到最佳去除效果,H2O的存在不利于活性炭的催化作用;温度在200℃时,活性炭催化活性达到低谷;煤质活性炭催化效果优于木质;在一定范围内,比表面积的增大有利于催化活性的提高.利用SEM对所用不同样品进行扫描,进一步分析活性炭表面结构对吸附催化效果的影响.     

Solid-phase carbothermic reduction of the components of chrome-iron ore raw materials

The procedure and results of laboratory studies of the solid-phase reduction of chromium and iron from chrome-iron ore raw materials are presented.     

The rate of reduction of iron oxides by carbon

The rate of reduction of Fe₂O₃ and FeO by coconut charcoal, coal char and coke, in an inert atmosphere within the temperature range 900 to 1200°C was investigated. The effects of pressure, particle size, and the amount of carbon were determined. The results indicate that the reaction takes place by means of the gaseous intermediates CO and CO₂, and that the overall rate is controlled by the oxidation of the carbon by CO₂. The rates of reduction of FeO and Fe₂O₃ by CO are relatively fast, and the CO₂/CO ratio for the oxidation of carbon is determined by their equilibria. The reduction of Fe₂O₃ by carbon is accomplished in two stages, with FeO forming first. The reduction of Fe₂O₃ to FeO is faster than that of FeO to Fe because its CO₂/CO equilibrium ratio is higher and hence the rate of oxidation of carbon is faster. A direct comparison was made between the rate constants for the reduction of FeO by carbon and those for the oxidation of carbon in the appropriate CO₂-CO gas mixtures, and they are in good agreement. Apparently the iron formed by the reduction does not significantly catalyze the oxidation of carbon; whereas for the reduction of NiO by carbon, the Ni formed does catalyze the oxidation of carbon.     

On the mechanism of iron oxide reduction by carbon

A theoretical analysis has been made to determine the conditions under which the reduction of iron oxide by carbon takes place according to the 2 step mechanism involving the Boudouard reaction. This is based on the concept of minimum temperature of reduction (T _min) below which the Boudouard reaction does not affect the reduction process. The effect of variables such as carbon reactivity, total pressure and so forth onT _min has been studied. TheT _min can be used to determine if metallization is possible under a given set of conditions.     

CO还原烧结矿过程中的析碳行为

高炉中CO 还原烧结矿过程中会发生析碳反应,对高炉操作产生不利的影响。采用 CS-8800型高频红外碳硫分析仪分析CO 还原烧结矿过程中的析碳行为,并采用 Nova400NanoSEM型场发射扫描电子显微镜分析还原后烧结矿微观结构。研究结果表明：随着温度的升高,析碳反应 CO 的平衡浓度越高,反应越难发生。在低温下析出的碳较多,析出的碳主要分布在烧结矿表面和气孔中,而在温度较高时只有微量碳析出;体系中 CO2对析碳反应有明显的抑制作用;析碳量随着还原时间的增加而增加。     

碳热FeO反应过程的控速环节分析

为了探讨煤基还原FeO在试验过程可能出现的控速环节,分多种条件进行了理论计算及分析。在不考虑传热条件下(加热方向物料很薄时),同一种还原剂在不同的温度段表现出不同的控速环节。气煤作为还原剂时,1 273 K以下碳的气化反应为控速环节,1 273～1 523 K为混合控速;温度超过1 523 K,则CO还原FeO转为反应的控速环节。不同煤种在同一温度下,可能表现出不同的控速环节。如1 373 K,气煤作为还原剂时,碳气化与FeO间接还原混合控速,而兰炭作为还原剂时,碳气化为控速环节。煤粉粒度与FeO粒度之比不同会使控速环节发生变化。如果物料厚度小于1 mm,则可忽略传热影响;如果物料厚度不小于4 mm,则传热将成为限制性环节;如果试验时的物料厚度介于两者之间,就有可能出现传热与反应混合控速情况。     

Reaction mechanism of FeO reduction by solid and dissolved carbon

The reduction reactions of FeO by carbon have been studied in order to be able to understand the fundamental phenomena occurring in smelting reduction process. The reduction of pure FeO by solid carbon proceeds mostly according to the same reaction mechanism as that by dissolved carbon in iron, the rate of which was experimentally determined to be controlled by the interfacial chemical reaction between Fe-C melt and intermediate CO₂ gas. Hence, the reduction rate of pure FeO by solid carbon is also chemically controlled by the Boudouard reaction between the dissolved carbon and CO₂ at the interface of by-product Fe droplet/gas phase, the activation energy of which was found to be about 193.2 kJ/mol. In addition, the reduction reaction of FeO in CaO-SiO₂-Al₂O₃-FeO slags by the dissolved carbon in Fe melt was also investigated over the FeO mass content less than 20 %. The reduction rate shows first order dependence with respect to FeO concentration. The surface active sulphur content in iron does not affect the reduction rate, and the temperature dependence of reduction rate gives the activation energy of 24.78 kJ/mol. Therefore, the reduction rate of FeO in slags by the dissolved carbon can be safely mentioned to be controlled by the liquid phase mass transfer of FeO through the slag phase diffusion-resistant boundary layer over the limited FeO concentration range. The empirical expression for the mass transfer controlled reactioe, deren Aktivierungsenergie ca. 193.2 kJ/mol beträgt. Außerdem wurde die Reduktion von FeO in CaO-SiO₂-Al₂O₃-FeO-Schlacken mit dem in der Eisenschmelze gelöstem Kohlenstoff fär FeO-Massengehalte von weniger als 20% untersucht. Die Reduktionsgeschwindigkeit weist hinsichtlich der FeO-Konzentration eine Abhängigkeit 1. Ordnung auf. Der Anteil an oberflächenaktivemn rate was determined as r = 5.94(±0.07).10^?6.exp(-24780/RT).(%FeOP)^0.96 over the reaction conditions employed.     

还原碳化法制备超细碳化铬粉末

以纳米Cr_2O_3和乙炔黑为原料,经高温还原碳化制备超细Cr_3C_2粉末,研究反应温度、反应时间以及配碳量对Cr_3C_2粉末的粒度与游离碳含量的影响。通过热力学计算,只有当温度高于1 350 K时还原碳化反应才有可能进行,采用纳米Cr_2O_3可显著降低反应温度,在1 573 K下焙烧6 h碳化率即达到98.20%;Cr_3C_2粉末的游离碳含量随配碳量增加而显著提高,配碳量(质量分数)为理论配碳量的1.05倍时制得游离碳含量为0.23%、氧含量为0.91%(均为质量分数)、平均粒度为1μm的Cr_3C_2粉末,该粉末达到硬质合金及热喷涂应用的要求。