二次铝灰烧制镁铝尖晶石固相反应动力学及材料耐水蚀性能

以再生铝行业二次铝灰为主要原料,开展二次铝灰烧结制备镁铝尖晶石材料的研究。材料物相分析表明：二次铝灰可以烧结制备镁铝尖晶石材料。根据适宜的原料配比,在不同温度条件下烧结制备材料,进一步探讨烧结温度对材料耐水蚀性能的影响。二次铝灰烧结制备镁铝尖晶石材料的晶化反应表观活化能E_a=104.54 kJ/mol。在1 200～1 500℃烧结3 h,材料水化反应动力学方程依次为：(1-(1-5.76η)^1/2)²=kt,(1-(1-6.15η)^1/2)²=kt,(1-(1-6.43η)^1/2)²=kt和(1-(1-6.34η)^1/2)²=kt;1 400℃烧结3 h,材料水化率为8.83%,达不到高耐水性材料标准(0.2%)要求。     

铁矿石氧化还原反应动力学实验系统的设计

阐述了铁矿石氧化还原反应实验系统的设计原理、工艺流程、设计思路,包括硬件和软件方面的设计以及系统在实验中的应用情况等。系统可为实验过程物料反应提供等温、非等温的实验温度场和精确的气氛环境。实验结果表明:该系统可实现对200～1 600℃区间内的温度和升温速率的精确控制,控制精度为±1℃,对气体流量的控制精度为±0.01L/min,质量测量精度为±0.001g。     

微波加热高碳铬铁粉固相脱碳动力学

采用微波加热对高碳铬铁粉固相脱碳进行了动力学研究.以碳酸钙粉为固体脱碳剂,按高碳铬铁粉中碳与碳酸钙粉完全分解后产生的CO₂的摩尔比为1︰1和1︰1.4混合,在微波场中对内配碳酸钙高碳铬铁粉加热到不同温度并保温脱碳一定时间,测定其碳含量并计算固相脱碳反应的表观活化能.实验表明:提高内配碳酸钙的比例,物料的脱碳率会相应提高,但混合物料的微波加热升温速率会变小;对于脱碳摩尔比相同的物料,随着脱碳温度的提高和保温时间的延长,物料的脱碳率随之提高.当1200℃保温脱碳60 min时,两种脱碳摩尔比下物料脱碳效果最好,脱碳率分别为65.56%和82.96%.微波场能促进高碳铬铁粉中碳的活化扩散和CO₂的吸附扩散.微波加热内配碳酸钙高碳铬铁粉固相脱碳反应近似为一级反应,脱碳反应的表观活化能为68.43 kJ·mol^-1.     

冶金反应工程学中反应过程动力学的研究方法探究

冶金物理化学中反应动力学的方法已经成功地在冶金学(如黑色冶金、有色冶金等)中得到了应用,并成为传统的冶金学学科体系中一个重要的理论基础,其研究方法已经非常的完善,形成了独自的结构和体系.冶金反应工程学的重要任务之一是要对冶金工程进行模拟,要准确地得到反应过程的机理和不同控制环节转换时间点,因此,冶金物理化学中冶金反应动力学的研究方法和结果并不完全适合于冶金反应工程学.为给在冶金反应工程学中求解传输和化学反应方程的定解条件提供必要的传输与反应过程动力学参数和不同控制环节的转换时间点,提出了用分段尝试法研究冶金反应过程动力学的新思路,并对比了2种方法和得到的结果及对分段尝试法进一步的发展进行了讨论.分段尝试法作为冶金反应工程学中研究反应过程动力学的方法,既可满足冶金反应工程学的自身需要,又能为建立独立的冶金反应工程学学科体系提供必要的保障.     

Solid-state oxidation kinetics of an yttrium-containing AK1M2 alloy

The interaction of an yttrium-modified AK1M2 alloy with atmospheric oxygen in the temperature range 723–823 K is studied by thermogravimetry. The kinetic parameters of oxidation are determined. An yttrium addition is shown to decrease the oxidation rate, which is accompanied by an increase in the apparent oxidation activation energy from 114.9 to 134.6 kJ/mol.     

Solid-state diffusion-based processing kinetics for uniaxial self-propagating high-temperature synthesis of MoSi2

An analysis is presented for self-propagating, high-temperature synthesis (SHS) of MoSi₂ from a mixture of silicon and molybdenum powders compacted into a semi-infinite, uniaxial bar and ignited at one end. The kinetics of reacting molybdenum grains are controlled by solid-state diffusion through the interposing product shell of MoSi₂ that surrounds each shrinking molybdenum grain. The previously determined temperature-dependent microkinetics of this solid particle reaction are coupled with one-dimensional (1-D) heat transfer and storage to describe the time-dependent macrokinetics of the synthesis reaction sequencing through a perfectly insulated bar. The resulting equations are solved numerically to provide computed results of temperature and conversion as a function of time and distance. Preignition time, propagation velocity, and thickness of the reaction front are also determined. Results depend primarily on the initial temperature at the end of the bar, which affects preignition time, and the molybdenum grain radius. The perfectly insulated model was relaxed by limiting the maximum temperature to arbitrary values corresponding with lateral heat dissipation, and these results compare favorably with experimentally measured propagation velocities and maximum temperatures during SHS of MoSi2. The model presented, with MoSi₂ as the prototype, is expected to be applicable to the SHS of many other refractory materials. This article is based on a presentation made in the “In Situ Reactions for Synthesis of Composites, Ceramics, and Intermetallics” symposium, held February 12–16, 1995, at the TMS Annual Meeting in Las Vegas, Nevada under the auspices of SMD and ASM-MSD (the ASM/TMS Composites and TMS Powder Materials Committees)     

铁酸镁生成反应非等温动力学

为了研究镁铁质材料中粘结相铁酸镁的生成反应过程,使用轻烧镁粉和分析纯试剂Fe₂O₃粉混合料,在静态空气中分别以10,15,20 K·min^-1的升温速率进行了铁酸镁合成反应的DSC实验研究,并用Kissinger、Flynn-Wall-Ozawa和Achar-Brindley-Sharp-Wendworth三种方法进行了反应动力学特征参数计算.研究结果显示,铁酸镁生成机理满足随机形核与长大机理模型,反应的活化能介于626.83~652.60 kJ·mol^-1之间.     

Morphology and kinetics of the hamster sperm acrosome reaction

The morphology and kinetics of the normal acrosome reaction were examined in vitro using hamster sperm incubated in detoxified sera. The reaction involved either swelling and elevation or crenulation and fragmentation of the acrosomal cap. Swelling and elevation occurred during both normal and degenerative reactions, as reported by others. Crenulation with subsequent fragmentation of the cap was observed during normal reactions. Early crenulation of the acrosome could be induced by cold shock (5 degrees C, 25 minutes), but this did not decrease the incubation time required (at 37 degrees C) for completion of the normal reaction. In appropriate sera, the occurrence of normal and degenerative acrosome reactions in motile sperm was significantly separated in time to study the reactions independently. The duration of the normal reaction, i.e., the time between the first morphological change in the acrosome (initiation)until the actual detachment of the cap (termination) was estimated to be 20 minutes. Saline dilution of these sera delayed initiation of the reaction and increased the duration of the reaction once it had started. Data from cold-shock and serum dilution experiments indicate that the mechanisms which govern the initiation and termination of the normal reaction are independently variable, and further suggest that initiation involves a change in membrane permeability and that termination includes membrane vesiculation.     

Solid-state reaction synthesis and chemical stability studies in Nd-doped zirconolite-rich ceramics

In this study, Nd-bearing zirconolite-rich ceramics were prepared by solid-state reaction process using CaF_2,ZrO_2, Ti,TiO_2, Fe_2 O_3 and Nd_2O_3 as the raw materials. Neodymium was used as trivalent actinide surrogate and designed to substitute the Ca and Zr sites of zirconolite with general stoichiometry of Ca_(1-x)Zr_(1-x)Nd_(2 x)Ti_2O_7(0≤x≤0.3). Density of Fe-Nd-O sample reaches a maximum value of 4.13 g/cm~2 after being sintered at 1325 ℃ for 42 h. Three major phases, namely zirconolite, perovskite and pseudobrookite, are observed in all these samples. The EDX result shows that Nd_2O_3 can be successfully incorporated into the lattice structure of the prepared zirconolite-rich minerals and replace the Ca sites of zirconolite and perovskite with Fe~(3+) as the charge-compensating ion. Furthermore, the thermal conductivities are all in the range of 1.51-1.67 W/(m·K). The normalized elemental leaching rates of Ca and Nd in the Fe-Nd-0.2 sample keep in low values of 6.20 × 10~(-2) and 4.86 x 10~(-4) g/(m~2·d) after 42 d.     

固相法合成锂离子电池正极材料LiFePO4

橄榄石型LiFePO4是近年发展起来的一种锂离子电池正极材料,它的理论容量为170 mA·h/g,具有价格便宜、环境友好、无毒、无吸湿性、热稳定性好等优点,越来越受到人们的重视.通过固相法制备LiFePO4,分别考察了锂铁摩尔比与烧结时间对于LiFePO4的电化学性能的影响.结果表明,最佳的锂铁摩尔比为1.05,最佳的烧结时间应为24h,在0.1C倍率下放电,初始放电容量为140.4mA·h/g.     

微生物催化大洋多金属结核和黄铁矿共同浸出及反应动力学模型

为了直观地表征大洋多金属矿微生物浸出过程中各因素的相互关系,进行了微生物催化MnO₂-FeS₂-H₂SO₄体系的好氧和厌氧浸出实验,利用DLVO理论建立厌氧条件下微生物催化浸出氧化锰矿物中有价金属的动力学模型——收缩核模型.微生物在厌氧条件下催化大洋多金属矿和黄铁矿的氧化还原反应,浸出锰的机理是细菌催化铁离子在二价和三价的循环转化;微生物吸附在矿物表面加速反应的进程,矿物颗粒在反应中不断缩小.进一步实验表明收缩核模型曲线与实验曲线拟合较好,验证了模型的可靠性.     

The kinetics of the nitrogen reaction with liquid iron-Sulfur alloys

An experimental apparatus was designed and constructed which permits utilization of both the modified Sieverts' technique and the isotope exchange technique for study of the kinetics of ni-trogen reaction with liquid iron alloys. Experimental results from the two techniques are used in con-junction with the current knowledge in the field to readdress several persisting questions dealing with the nitrogen reaction. Results from this study have confirmed that N₂ dissociation is the rate lim-iting step in the intrinsic chemical reaction mechanism of nitrogen absorption. In addition, the ex-istence of a residual nitrogen absorption rate at high sulfur concentrations has been reaffirmed and possible reasons for the phenomenon are discussed. Lastly, results of an investigation into the in-fluence of carbon on the nitrogen reaction rate in liquid Fe-C-S alloys indicate that carbon has a negligible effect on the rate. Formerly with the Department of Metallurgical Engineer-ing and Materials Science, Carnegie-Mellon University, Pittsburgh, PA     

A contribution to the theoretical description of metal-slag reaction kinetics

In this paper the main aspects of a theoretical model of mass transfer through liquid-liquid interfaces under non-turbulent flow conditions are described. The model is based on the general boundary layer theory of momentum and mass transfer. Expressions for calculation of the mass transfer coefficients on the metal and slag side of the phase boudary are presented. It is shown that the model comprises as limiting cases the mass transfer through free surfaces and at solid walls.     

The kinetics of the nitrogen reaction with liquid iron-chromium alloys

The isotope exchange technique was employed to study the interfacial reaction kinetics of nitrogen with liquid iron-chromium and iron-chromium-sulfur solutions. Chromium was found to increase the rate of the nitrogen exchange reaction. The increase in the rate occurs, at least in part, through promotion of N₂ dissociation on the chromium surface sites. Although mass transport effects in the liquid are eliminated through the use of the isotope exchange technique, it was found that a correction for gas phase mass transfer was required for the determination of the interfacial reaction rate constant due to the faster exchange rates encountered in liquid iron solutions containing chromium. Formerly with the Department of Metallurgical Engineering and Materials Science, Carnegie-Mellon University, Pittsburgh, PA     

Intrinsic kinetics of the reaction between zinc sulfide and water vapor

The reaction between zinc sulfide and water vapor is a component reaction in a new reaction scheme recently developed to transform zinc sulfide to zinc oxide through the use of lime and water vapor. The intrinsic kinetics of this reaction for ultrafinely ground (<1 μm) ZnS particles was determined by carrying out measurements in the absence of heat- and mass-transfer effects. The reaction products were identified to be ZnO and H₂S. The kinetics of the reaction can be represented by and 3.94<C _H2_O <9.84 mol/m³ withn=1.28 andk ₁=45.3 exp(−14600/T) m³·mol⁻¹·s⁻¹, whereX _B is the fractional conversion. DAESOO KIM, formerly Granduate Student at the University of Utah     

The reaction kinetics of gastric intrinsic factor and IgG intrinsic factor blocking antibody: a soluble system

Three cases of high jugular bulb are presented. On of these occurred as a mass in the external auditory canal simulating an osteoma, and to our knowledge is the first reported case of a high jugular bulb presenting in the external canal. The clinical manifestations are described, and the value of polytomography as an aid to diagnosis is stressed.