Modelling of heterogeneous gas-solid reactions

A general modelling is presented of the heterogeneous gas-solid reactions relevant to the field of extractive metallurgy. The unreacted core shrinking (topochemical) and the homogeneous model are presented as the limiting cases between a reaction taking place on a sharp interface and one taking place in a diffuse manner throughout a pellet-matrix. Analysis shows that under certain conditions of temperature, porosity, and grain size, the reaction interface may spread out over a definite width and thus make the topochemical model an unrealistic one. Also for cases where the spread factor is large and intragranular resistance is important, the homogeneous model becomes inadequate. Two models are discussed and developed. The first one which neglects intragranular resistance takes into consideration the diffuse character of the interface by incorporating spread and effectiveness factors into the reaction scheme. The second model, which assumes intragranular resistance, includes important variables such as porosity, grain size, solid reactivity, and gas-solid diffusivities in the overall reaction system; in this respect it gives a better insight on a quantitative basis as to the effects of each variable upon the rate of reaction. Formerly with The International Nickel Formerly with The International Nickel     

Calorimetric studies and kinetic parameters of solid state reactions in 7017 Al-Zn-Mg alloy

Differential scanning calorimetric (DSC) studies have been carried out at different heating rates to examine the solid state reactions in a 7017 Al-Zn-Mg alloy of water-quenched (WQ) state and artificial aged tempers. All the exothermic and endothermic peaks of the thermograms indicating the solid state reaction sequence have been identified and discussed. The shifting of peak temperatures of all the reactions to higher temperatures with increasing heating rates suggests that the reactions are thermally activated and kinetically controlled. The variations of hardness with aging time at an artificial aging temperature have also been studied to obtain the under-, peak- and over aged tempers. The fraction of transformation (Y), the rate of transformation (dY/dt), the transformation function f(Y) and the kinetic parameters such as activation energy (Q) and frequency factor (k₀) of the solid state reactions in the alloy have been determined by analyzing the DSC data i.e. heat flow involved with the corresponding DSC peaks. It has been found that the kinetic parameters of the solid state reactions are in good agreement with the published data.     

The rate of movement of the topochemical interface during gas-solid reactions

The rate of recession of the topochemical interface between a porous core and the product layer is shown to be given by wherer _c is radial position of the interface,R(r_c) the rate of the chemical reaction at the interface and (dC _s/dr)|_{r s} is the gradient of concentration profile of solid reactant in the porous core at the interface. The integration of the above equation can sometimes be achieved analytically but can always be done numerically for even highly complex reaction mechanisms. The equation correctly reduces to previously known solutions when the inner core is impervious to gas diffusion. The utility of the equation is demonstrated by applying it to the industrially important multistage reduction process Mn₃O₄ → MnO — > Mn. The predictions from the theoretical model are compared successfully with experimental data for this reaction. Formerly Student in Department of Metallurgy, University of Strathclyde, Scotland.     

高温烧结矿气-固换热过程数值模拟及参数分析

在详细分析了高温烧结矿冷却过程传热机理的基础上,根据能量守恒定律建立了高温烧结矿气-固换热过程的一维非稳态热过程数学模型,并利用现场实测数据对所建立的数学模型进行了验证.结果表明:所建立的数学模型是正确可信的.在此基础上,重点研究了冷风风速和台车移动速度等主要热工参数对环冷机内冷却过程的影响,并针对某环冷机的实际生产情况提出了具体的操作建议.     

The effect of environment and grain size on the creep behavior of a ni-6 pct w solid solution

The effects of environment and grain size on the steady-state creep and creep rupture properties of a Ni-6 pct W solid solution are examined by testing in vacuum and commercial purity argon at 5000 psi and 900°C. The steady-state creep rate is found to decrease with increasing grain size at small grain sizes, both in vacuum and argon, owing to the effects of grain boundary sliding. At large grain sizes the creep rate is independent of grain size in vacuum and increases with grain size in argon. It is suggested that the increase in creep rate with increasing grain size is associated with fact that large-grained samples tested in argon do not reach steady-state before rupture occurs. Formerly Graduate Student, Stanford University, Stanford, Calif.     

Modeling of sequential reactions during micropyretic synthesis

A numerical model for a two-step sequential micropyretic reaction is reported. Such multiple reactions can take place during micropyretic synthesis of composite materials. The model was developed for the aluminothermic reaction between molybdenum oxide, aluminum, and silicon, which react to give molybdenum disilicide and aluminum oxide. The model was used to obtain the solution for the propagation of the combustion front. The melting of various constituents of reactants and products was incorporated into the model. The effect of the pre-exponential factor and the amount of diluent on the nature of propagation and temperature profile was investigated. Other conditions of propagation and synthesis for general two-step reactions were explored by changing the activation energy and heat release of each sequential reaction. A mapping procedure to characterize the types of sequential reactions is proposed and studied for several aluminothermic type reactions. Formerly Graduate Research Assistants, Department of Materials Science and Engineering     

Kinetics of solid vanadium-nitrogen reactions at high temperatures

Thermogravimetric studies were made to determine the kinetics of the reaction between 99.83 pct vanadium sheet and purified nitrogen gas in the temperature range of 1173 to 1723 K, at pressures of 9.3 × 10⁴ to 9.3 Pa (700 to 7 × 10^-2 torr) and times up to 160 h. Metallographic and X-ray diffraction techniques were used to examine the reaction products. The data followed either parabolic, cubic, or linear kinetics. In general it was observed that the initial kinetics were parabolic. At high temperatures and near atmospheric pressures, the reaction kinetics changed from parabolic to cubic at longer times. At the lowest pressure the preparabolic kinetics were linear. Weight gains in the parabolic region were mainly due to solution and diffusion of nitrogen in vanadium with the weight gain shown by the equation (ΔW/A)² = 3.2 × 10^-4 Te162-000/RT _t. The cubic region was related to the formation of an outer layer of VN over an intermediate layer of V₃N and a core of the saturated solution of nitrogen in vanadium with the approximate weight gain shown by the equation (ΔW/A)³ = 1.24 × 10^-3 Te- ^208,000/RT _t Linear weight gains at low pressure were presumed to be controlled by the rate of nitrogen adsorption.     

Role of bulk and mass effects of reactions in reaction sintering processes

Peculiarities of the fabrication of ceramic porous and dense composite materials based on compounds of the Si–C–O–N system with the participation of chemical reactions and the formation of new phases are discussed. An analysis of comparatively new technologies is attempted in terms developed in earlier studies on the reaction sintering of silicon nitride, carbide, and oxynitride. It is shown that the approach to reaction sintering that includes the selection of promising reaction systems allowing for the bulk effect of reactions accompanying material formation can be extended to the fabrication of porous and highly porous materials. In contrast to the fabrication of dense materials, when reaction systems with positive bulk effects are used, the reaction systems with negative bulk effects can be used in the fabrication of highly porous materials.     

铁索体/贝氏体多相组织钢硬化行为表征参数

摘要：为了研究大变形管线钢应变硬化行为及其表征参数之间关联性,采用TMCP工艺调控制备了9种不同贝氏体体积分数的铁素体/贝氏体（F/B）多相组织钢。通过力学性能及应变硬化行为分析,对应变硬化指数、应力比、屈强比和伸长率等大变形管线钢应变硬化能力表征参数之间的关联性及其机制、内涵和适用范围进行了研究。结果表明,F/B多相钢中,应力比Rt20/Rt10和均匀伸长率与应变硬化指数呈线性正比关系,屈强比与应变硬化指数呈非线性反比关系,应力比Rt50/Rt10在一定条件下与应变硬化指数存在线性关系,应力比Rt15/Rt05、总伸长率、应变硬化指数之间不具备明显的关系。通过应变硬化行为分析合理阐释了以上参数之间的关联机制,并阐释了其内涵和适用范围。硬化指数、均匀伸长率和应力比Rt20/Rt10应作为描述F/B多相钢塑性形变阶段应变硬化能力的主要参数,屈强比和应力比Rt50/Rt10则应作为次要参数。采用工业化生产数据对上述结论进行了验证,与所得结论吻合良好。     

Studies in gas-solid reactions: Part II. An experimental study of nickel oxide reduction with hydrogen

Experiments are reported on the rate of reduction of nickel oxide pellets with hydrogen over the temperature range 200° to 900°C. Measurements were also made of the pore size distribution of the reacted and unreacted specimens, by mercury porosimetry. In addition, the size of the individual grains was also determined by X-ray diffraction techniques and by electron microscopy. These physical measurements supplied most of the information required for the comparison of reduction rates with the predictions made in Part I of this study. It was found that the trends predicted by the structural model were consistent with measurements, thus the, structural model shows promise both for the interpretation of experimental data and for the semiquantitative prediction of experimental behavior.     

我国冶金固废大宗利用技术的研究进展及趋势

我国钢渣、赤泥、铜渣和部分铁合金渣年排放量在千万吨甚至亿吨级,难以大量用于传统的水泥、混凝土或道路工程领域,是难利用的大宗冶金固废。本文分析了以上典型冶金固废大宗资源化利用的现状,指出了制约大宗资源化利用的瓶颈问题;进一步提出砂石骨料、陶瓷材料、人造石材在我国具有年亿吨级乃至百亿吨级的市场需求,适合作为冶金固废利用的大宗量出口,并综述了这一领域冶金渣低成本制备烧结陶粒、冶金渣制备陶瓷和烧结砖、熔渣调质制备骨料以及熔渣人造石材制备等方面研究取得的进展,包括在新建年10万吨基于带式焙烧机原理的固废陶粒生产线上进行了赤泥掺加质量分数50%～65%的烧结陶粒工业化生产试验;分别掺入质量分数40%～60%的赤泥,30%～50%的钢渣,50%～80%的铜渣,先后完成了陶瓷砖和烧结砖的工业化中试以及工业化生产实验;加入质量分数12.96%的砂子对熔融电炉渣进行调质并制备砂石骨料、基于“Petrurgic”工艺的利用熔渣制备石材技术也完成了工业化和中试试验。在此基础上提出了固废的大宗量利用、协同利用、节能减碳利用和与智能化结合的资源化利用是这一领域技术发展的主要趋势。      

多单元多步骤阶段矿房采矿法参数优化

在缓倾极厚破碎矿体中，进行多单元多步骤阶段矿房采矿法试验研究，通过理论手试验实践确定，并优化了单元的结构凿岩爆破参数，得出了简易、实用的参数计算公式。     

微米球光催化剂在环境净化及能源转化的研究进展

光催化在污染物降解及能源转化应用方面前景宽广。然而,大部分光催化剂因本身物理结构的缺陷而难以广泛运用。微米球光催化剂具有显著的优点,如低密度、高光捕获能力和载流子分离效率、优异的电子和光学性能、高比表面积、易回收、优良的传递性能和表面渗透能力。这些结构有利于提高光催化性能和实际运用,因而受到广泛关注。重点介绍并讨论了一些典型的微球光催化剂（TiO₂, ZnO, Bi₂WO₆, PbWO₄,BiFeO₃, BiOX (X = Cl, Br, I)等）的制备及这类光催化剂在环境净化和能源转化方面的研究进展,并展望了微米球光催化剂的发展方向。      

The effect of small deformation on abnormal grain growth in bulk Cu

The effect of small deformation below the level (about 8 pct) required for primary recrystallization on abnormal grain growth (secondary recrystallization) has been investigated in bulk polycrystalline Cu. The starting microstructure, without any texture and with a nearly uniform grain size of 168 μm, has been obtained by compressing a cylindrical Cu specimen and recrystallizing at 800 °C. The fully recrystallized specimen shows distinct abnormal grain growth (AGG) after heat treatment at 800 °C for 12 hours. Most of the grain boundaries are faceted when observed under transmission electron microscopy (TEM), and most of the faceted segments are expected to be singular. A singular grain boundary free of defects will migrate by two-dimensional nucleation of new layers, with its velocity varying nonlinearly with the driving force arising from the grain-size difference. Such a growth mechanism is analogous to the well known process for the growth of crystals with singular surfaces from liquid or vapor. The grains slightly larger than the average size will hardly grow, because the driving force for their growth is not sufficient for nucleation of new crystal layers at the boundaries. Those grains larger than a certain critical size will, however, grow at ever-increasing rates with their increasing size, because of the sufficient driving force for two-dimensional nucleation. Such a selective accelerated growth of large grains results in overall AGG behavior. The specimen deformed to 2 pct shows AGG after heat treatment for only 5 minutes at 800 °C, and after 1 hour, large impinged grains are obtained. The grain boundaries show many extrinsic dislocations even after the heat treatments. As proposed earlier by Gleiter, Balluffi, Smith, and their colleagues, the extrinsic grain-boundary dislocations increase the grain-boundary mobilities even at low driving forces, and, hence, even those grains slightly larger than the average size can rapidly grow at the early stages of the heat treatment, in agreement with the observation. In the specimens deformed to 4 to 8 pct, below the level for primary recrystallization, all grains grow steadily without producing distinct AGG. With high densities of extrinsic dislocations at the grain boundaries even after long heat treatments, all grains can readily grow, resulting in overall growth patterns resembling the normal growth. When deformed to 20 and 50 pct, primary recrystallization occurs, and the subsequent AGG behavior depends on the grain size obtained at the completion of the primary recrystallization. Similar small-deformation effects are observed with heat treatment at 600 °C.