Reduction behaviour of powder mixtures of iron oxide and carbon in reactive atmospheres

Mixtures of fines of iron ore and carbon were kept in hot zone of furnace for various durations under flowing argon or mixture of hydrogen and carbon dioxide. Experiments were conducted at temperatures of 1150, 1250 and 1300 K. Other variables were inlet H₂/CO₂ ratio both oxidising and reducing to wustite, Fe₂O₃/C ratio in sample and sample size. 2 types of carbon were selected, viz. graphite and activated char. The degree of reduction of oxide (F) was determined by subsequent hydrogen reduction of reaction products. F vs. time data did not follow any set pattern due to complex mechanism and kinetics. Equilibrium calculations predict that, inlet H₂+CO₂ mixture which undergoes water gas shift reaction inside the furnace, reduces to wustite at a H₂/CO₂ ratio of 3. As expected, generally it yielded highest value of F. However at 1300 K, even the gas with H₂/CO₂ ratio of 1.5/1, although oxidising to wustite, gave comparably high value of F, presumably due to enhanced gasification rate at higher temperature. Although reactivity of graphite was much lower than that of activated char, they exhibited comparable extents of reduction.     

Catalytic graphitization of carbon/carbon composites by lanthanum oxide

Graphitized carbon/carbon composites were prepared by the process of catalytic graphitization with the rare-earth catalyst, lantha-num oxide (La2O3), in order to increase the degree of graphitization and reduce the electrical resistivity. The modified coal tar pitch and coal-based needle coke were used as carbon source, and a small amount of La2O3 was added to catalyze the graphitization of the disordered carbon materials. The effects of La2O3 catalyst on the graphitization degree and microstructure of the carbon/carbon composites were investi-gated by X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. The results showed that La2O3 promoted the formation of more perfect and larger crystallites, and improved the electrical/mechanical properties of carbon/carbon composites. Carbon/carbon compos-ites with a lower electrical resistivity (7.0 ???m) could be prepared when adding 5 wt.% La2O3 powder with heating treatment at 2800 oC. The catalytic effect of La2O3 for the graphitization of carbon/carbon composites was analyzed.     

Kinetics of metal/slag reactions during spontaneous emulsification

An approach for accommodating the interfacial area changes in kinetic equations for heterogeneous reactions in the presence of spontaneous emulsification has been proposed. The kinetics were analyzed by incorporating time-averaged interfacial areas in the rate equations. The approach was found to be applicable for the experimental data and to satisfactorily describe the reaction kinetics. In the case of a high-temperature reaction between 2.35 g Fe-5 wt pct Al alloy metal droplets with CaO-SiO₂-Al₂O₃ slag at 1650 °C, it was found that the kinetics follow a first-order relationship with respect to aluminum in the metal, and it was concluded that they were controlled by mass transport in the metal phase. The calculated metal mass-transfer coefficient k _m was 1.7×10⁻⁶ m/s.     

Ion/ion reactions for oligopeptide mixture analysis: application to mixtures comprised of 0.5-100 kDa components

Oligopeptide mixtures have been subjected to electrospray ionization, accumulated within a quadrupole ion trap, and subjected to ion/ion proton transfer reactions with anions derived from perfluoro-1,3-dimethylcyclohexane. Various mixtures were studied with approximate molecular weight ranges of 0.5-8.5, 12-30, 45-100, and 0.5-100 kDa. Mixtures of known composition were studied to evaluate the mixture complexity amenable to electrospray combined with ion/ion reactions to reduce spectral complexity associated with multiple charging. Mixture analysis with at least 40 components of low and medium molecular weight and roughly comparable solution concentrations appears to be straightforward. No matrix effects upon ionization were implicated in the data for the low and medium molecular weight mixtures but bovine albumin appeared to inhibit signals from bovine transferrin and chicken conalbumin in the high molecular weight mix. Furthermore, the presence of abundant low mass-to-charge ions appeared to inhibit signals from high molecular weight proteins (> 40 kDa) in the 0.5-100 kDa mix. Such an observation is consistent with dynamic range limitations that can arise from discrimination based on ion space charge effects, although an ionization matrix effect could not be precluded from the data reported here. The results reported here indicate that the limitation to mixture complexity amenable to electrospray mass spectrometry imposed by spectral congestion associated with multiple charging can be significantly reduced via ion/ion reactions. The use of ion/ion reactions can therefore facilitate the study of other factors that can impose limitations to mixture analysis, such as matrix effects upon ionization and differences in ion transmission, accumulation, storage, and detection efficiencies.     

Thermodynamic analysis of self-propagating reaction of alkaline-and rare-earth metal oxide synthesis

A thermodynamic method is proposed to determine the optimal conditions for the synthesis of complex oxides employing self-propagating reactions. This permits estimation of heat effects and changes in Gibbs energy and entropy with the aid of standard thermodynamic functions, and also calculation of the temperatures of synthesized products in the adiabatic approximation.     

含钛中碳钢中钛氧化物析出热力学分析

以含钛中碳钢为研究对象,从热力学的角度分析了含钛中碳钢中钛氧化物析出行为,结果表明:浇注温度为(1535±10)℃且钢中溶解氧含量大于0.003％(质量分数,余同)时,低钛中碳钢中的溶解Ti可与钢中的溶解氧反应生成Ti3O5、Ti2O3,生成TiO2、TiO夹杂的可能性较小;高钛中碳钢中的溶解Ti可与钢中的溶解氧反应生...     

Toxicity of metal mixtures to chick embryos

A method of incorporating vertical and horizontal tissues in an obturator impression using an open palate impression tray is presented. The laboratory technique of obturator construction from this impression allows for a definitive (heat-cured) or interim (cold-cured) prosthesis for an edentulous or dentulous patient.     

吡咯/炭黑氧化物复合氧阴极材料的制备及催化性能

氧还原反应(ORR) 是碱性燃料电池和金属-空气电池的重要阴极反应.由于常见的铂基氧阴极材料存在价格昂贵、稳定性较低等问题, 因此, 开发低成本、高效率的非贵金属基氧阴极材料具有重要的研究意义和应用价值.氮掺杂碳材料是目前氧阴极材料研究的热点, 炭黑中碳原子的排列方式类似于石墨, 由于其价格低廉、来源广泛, 在碳材料的研究中具有独特的优势.本文基于炭黑, 采用化学法制备了氮掺杂炭黑氧阴极材料, 研究了其氧还原反应催化活性, 并进行了相关表征.结果显示炭黑-吡咯复合材料具有极好的氧还原反应活性, 700℃热处理后性能最优, 在1 mol·L-1KOH中其起峰电位约为0. 9 V, 极限扩散电流密度为2. 6 m A·cm-2, 转移电子数高于3. 5, 这些特性使得这类材料具有广阔的应用前景.      

Atomistic modelling of the metal/oxide interface with image interactions

We calculate the interfacial energy and lowest energy relative position for an Ag (001)/MgO (001) interface. The dominant image terms and short-range repulsions are included in full, and the MgO ions are relaxed to equilibrium using the MIDAS code. An essential new feature is the suppression of charge density fluctuations with wave-vectors greater than a (Fermi wavevector) cutoff. Our results show that the powerful methods based on interatomic potentials, widely used for ionic systems, can be extended to metal/ionic interfaces.     

Solubility of magnesium oxide in calcium oxide-calcium chloride mixtures

Measurements and theoretical calculations of the solubility product of magnesium oxide in calcium chloride-calcium oxide mixtures at 1133 K are reported. A filtration technique in an inert atmosphere was used to obtain samples for analysis by atomic absorption for magnesium content. At low concentrations of O^-2, the data are in consonance with the very low solubility product of 10^-6.2 predicted by a simple thermodynamic cycle first proposed by Flood, Fϕrland and Grjotheim. Work performed under the auspices of the U.S. Energy Research and Development Administration.     

Mixed transport control in gas-liquid metal reactions

The calculation of the rate of gas-liquid metal reactions of the typeA(gas) +B(dissolved) =AB(gas) is described, assuming that the rates are controlled by transport. Mixed control is shown to occur in a number of important gas-liquid metal reactions. This leads to slow rates which may be erroneously ascribed to control by a chemical step. The definition of parameters which can be calculated to indicate without ambiguity whether control is mixed or lies in the gas or liquid phases is discussed.     

Effects of rare earth oxide on hardfacing metal microstructure of medium carbon steel and its refinement mechanism

The electrodes for hardfacing medium carbon steel with six additions of rare earth oxide were developed in this work. By means of optical microscopy and scanning electron microscopy, the microstructure, inclusion and the fractograph of the hardfacing metal were observed. Then, the effects of rare earth oxide on microstructure and inclusions in hardfacing metal were analyzed. The effectiveness of rare earth oxide as heterogeneous nuclei of δ-Fe was calculated with the misfit theory. The results showed that, the microstructure of hardfacing metal was composed of ferrite and small amount of pearlite. The microstructure was refined at first and then coarsened with the increase of rare earth oxide addition. The fractograph was changed from brittle to equiaxed dimples, then became quasi-cleavage and cleavage gradually. The calculated results showed that, the ferrite grain size could be refined because that LaAlO3 as heterogeneous nuclei of δ-Fe was moderately effective, and the ferrite grain size was coarsened because the misfits between Ce2O3 and δ-Fe, Ce2O2S and δ-Fe were increased with futher increase of rare earth oxide addition.