颗粒粒径对尾砂膏体触变性的影响

高浓度尾砂料浆具有复杂的触变性,颗粒粒径是影响料浆触变性的重要因素,颗粒粒径对触变性影响的定量研究尚不丰富.为探究高浓度尾砂膏体的颗粒粒径对触变性的影响,使用同种尾砂制备了不同平均粒径的样品并制成膏体,开展恒剪切速率实验.结果表明,尾砂膏体具有显著的触变性,恒剪切速率条件下呈剪切稀化.稳态条件下,料浆静态屈服应力、动态屈服应力、宾汉姆黏度均与颗粒平均粒径平方的倒数呈线性正相关.瞬态条件下,颗粒平均粒径和相应瞬态拟合参数呈线性关联.推荐的稳态和触变性模型均表现出较高的适用性.通过数据拟合构建了稳态剪切应力和瞬态剪切应力的预测模型,定量表征颗粒平均粒径对触变性料浆稳态和瞬态流变行为的影响.     

基于黏弹性理论液相共烧结模型的建立及应用研究

目前液相共烧结工艺相容性问题是限制功能梯度材料制备技术的关键问题之一,研究其理论模型具有重要的意义。基于现有液相烧结、液相迁移和固相共烧结模型的分析,提出了以颗粒半径、相对密度和液相体积分数为基本参数的液相共烧结模型,模拟预测了液相共烧结两端异种材料致密化和液相迁移的过程,并通过YG类硬质合金实验加以验证。实验结果表明：共烧结试样界面两端材料的密度及Co含量呈现梯度变化,其梯度分布与计算拟合的变化趋势一致,本研究建立的模型较准确地预测了YG8梯度硬质合金Co含量和密度沿梯度方向的变化规律。     

磷含量对铸铁短纤维烧结体组织和性能的影响

研究了合金元素磷对铸铁短纤维烧结体显微组织和性能的影响，结果表明，磷可显著提高铸铁短纤维烧结体的密度、致密化系数，压溃强度和硬变，烧结机理随磷，铜含量的增加逐渐由固相烧结＋瞬态液相烧结转变为液相烧结。     

烧结微孔材料粒径分布形态分析

本文运用定量金相法测量烧结微孔材料之颗粒粒径。根据统计分析原理，验证其粒径分布服从瑞利（Ｒａｙｌｅｉｇｈ）分布律。     

Mo-Cu合金制备及其致密化行为研究

采用高能球磨的方法制备Mo-Cu复合粉末,系统研究了高能球磨对粉末形貌、烧结性能以及烧结坯显微组织的影响,并在此基础上对Mo-Cu致密化机理进行了初步探讨.研究结果表明:Mo-Cu液相烧结不同于传统的液相烧结,而与纯Mo的固相烧结致密化行为相似,Mo-Cu液相烧结致密化过程主要由固态骨架烧结所控制;球磨时间、烧结温度、烧结时间对于粉末烧结性能有很大影响.球磨时间24 h,在1050℃固相烧结60 min并于1300℃液相烧结90 min得到烧结坯致密度最高,相对密度为98.2%,烧结坯显微组织分布比较均匀,Cu相弥散分布于Mo骨架之间,无Cu富集现象,晶粒细小且尺寸相当.     

Mo2 NiB2基金属陶瓷的制备与性能

采用单质硼粉、镍粉和钼粉结合反应硼化烧结法制备了Mo2Ni B2基金属陶瓷,研究了Mo2Ni B2基金属陶瓷在烧结过程中的物相转变和尺寸变化以及烧结温度和保温时间对其力学性能和显微组织的影响.结果发现:随着烧结温度升高,材料物相逐渐由单质相变为二元硼化物相和三元硼化物相,并且材料的尺寸先发生细微收缩,再在硼化反应过程中逐渐增加,最后在液相烧结过程中逐渐减小;随着烧结温度升高,Mo2Ni B2基金属陶瓷的抗弯强度和硬度先增加后减小,在1290℃达到最大,分别为1346.5 MPa和83.7 HRA,并且硬质相颗粒逐渐粗化;保温时间对材料性能的影响与烧结温度一致,但在保温30min时抗弯强度最大(1453.3 MPa),保温60 min时硬度最大(83.7 HRA).     

熔剂颗粒在烧结过程中的特征演变及影响

 对烧结现场生产进行全流程取样,分析熔剂颗粒在烧结过程中的演变规律,及其对烧结过程的影响。结果表明,在烧结混合料制粒过程中,小于0.5 mm熔剂颗粒较铁矿粉颗粒更容易黏附至核颗粒表面形成新的颗粒,从而相对均匀地分布至混合料各粒级中。大于0.5 mm粒级熔剂颗粒作为核黏附一定厚度的黏附层形成新的颗粒,黏附层厚度均小于1 mm,因此,新颗粒直径仅在原始颗粒粒径基础上增大不超过2 mm。同时由于熔剂原始颗粒粒级较细,导致制粒后大于5 mm粒级混合料中熔剂含量较少。而在烧结台车布料过程中粒级存在偏析,大颗粒向下分布,最底层大于5 mm粒级颗粒分布最多,从而导致熔剂的偏析,混合料中大于5 mm粒级颗粒增多加大了熔剂的偏析,混合料中3~5 mm粒级颗粒增多减弱了熔剂的偏析。料层粒级偏析使烧结料层,最底层混合料中熔剂总量变少,大颗粒熔剂增多,熔剂颗粒数量减少,导致熔剂分布点变少,熔剂分布不均匀程度增加,局部高碱度环境变少,液相产生的难度增加。同时,由于颗粒的偏析,最底层混合料中大颗粒铁矿粉增加,出现更多的未熔原矿,最终导致烧结料层最底层烧结矿质量变差。     

纳米氧化铝弥散强化铜的放电等离子体烧结动力学及机制

利用经典热压模型,系统研究纳米氧化铝颗粒弥散强化铜的放电等离子烧结(SPS)致密化过程与机理。结果表明,放电等离子烧结初期,氧化铝弥散强化铜的致密化过程由晶界滑移和晶界扩散共同控制。随保温时间延长,烧结机制转变为由晶界滑移所主导。烧结后期致密化主要以塑性变形的方式进行。纳米氧化铝颗粒抑制了铜的烧结致密化,导致材料的密度降低。抑制机理为氧化铝颗粒阻碍晶界和位错运动,导致晶界滑移和塑性变形的激活能提高,从而增大致密化抗力。在外力和纳米氧化铝颗粒的共同作用下,塑性变形的主要形式为孪生。     

升温速率对金红石型二氧化钛颜料性能的影响研究

以工业偏钛酸为原料,经过漂白、洗涤、盐处理和煅烧制备金红石型二氧化钛,考查了煅烧过程升温速率对二氧化钛颗粒晶体结构和颜料性能的影响,并对样品进行XRD、SEM、激光粒度及颜料性能测试分析。结果表明:升温速率对二氧化钛颗粒的相转变、表面形貌、粒子大小及分布和颜料性能有显著影响,升温速率越快,有利于促进二氧化钛颗粒相转变和粒子成长,但易出现烧结,导致粒径过大且分布宽。适宜的升温速率为1.2℃/min,所得二氧化钛粒径为252 nm,分布最窄,球形度好,颜料性能最佳。     

加拿大铁精粉对烧结体固结强度的影响及其改善方法

 加拿大铁精粉由于具有铁品位高、脉石及有害元素含量低等优点，其在烧结过程中使用具有有利条件。采用微型烧结法考察了该铁精粉配比对烧结体固结强度的影响及其机理，并研究了4种富矿粉的细粉液相流动性和粗颗粒吸液性。在此基础上，通过固结试验，探究并验证了烧结体固结强度的改善方法。研究结果表明，将该铁精粉配入混匀料中，大幅降低了黏附粉偏析碱度，减弱了液相流动性，因此恶化了烧结体的固结强度。在固定碱度的条件下，高硅铁矿粉有较高的细粉液相流动性，低气孔率铁矿粉有较弱的粗颗粒吸液性。在配加该铁精粉的条件下，选择高液相流动性铁矿粉、弱吸液性铁矿粉、强吸液性铁矿粉粗颗粒分加制粒均能有效改善烧结体的固结强度。     

Transient Head Development due to Flood Induced Seepage under Levees

The purpose of this study was to predict the uplift force during floods on confining layers that overlay extensive horizontal confined aquifers that intersect a large river in response to the water level changes that occur with time in a flooding river. Transient flow of water through the confined aquifer was described by a diffusion type of equation with a boundary condition at the river in which the river head varied with time. The transient head distribution developed from the unsteady flow model applied to the aquifer was compared with the hydraulic head distributions obtained from U.S. Army Corps of Engineers steady-state flow model and a finite-element seepage model. This study concluded that the transient flow model has the potential to analyze time lag in head development, and to predict the seepage condition and heaving potential at various times and distances landside of a levee during a flood cycle, but additional case histories are needed to justify widespread use of the model.     

应用波理论预测旋转盘离心雾化膜状分裂区的粉末尺寸

应用平面和圆柱液膜破碎的波理论研究了旋转盘离心雾化膜状分裂区的粉末尺寸的预测方法;推导了最快增长的液膜破碎的波数方程,建立了旋转盘外液膜厚度与液膜径向位置的关系,并用数值方法进行了求解;计算的液膜破碎长度和粉末粒径与文献中的实验数据基本吻合,表明本文所提出的预测方法是可行的。     

Cold shock: biological implications and a method for approximating transient environmental temperatures in the near-field region of a thermal discharge

Biological data on the temperature preferences of fish indicate that, in general, they will be attracted to thermal discharges in the winter. This attraction to warmer temperatures increases their vulnerability to cold shock if the discharge heat source is discontinued. A scheme is proposed to predict the near-field thermal plume environmental temperatures during a power transient. This method can be applied to any jet discharge for which a steady-state model exists. The proposed transient model has been applied to an operating reactor. The predicted results illustrate how very rapidly the maximum temperatures decrease after an abrupt shutdown. This model can be employed to help assess the impact where cold shock may be a problem. Such predictions could also be the basis for restrictions on scheduled midwinter plant shutdowns.     

Particle size determination of a flocculated suspension using a light-scattering particle size analyzer

Microscopy is a useful and direct method for measuring the particle size of a suspension because, in addition to the particle size and size distribution, it provides visual detection of the shape and state of aggregation of the particles in the suspension. However, this method suffers from the shortcomings of being tedious and time consuming. In this study, a light-scattering particle size analyzer was used to determine the particle size and size distribution of a flocculated suspension. The sonication of the sample prior to and during measurement was found to be critical in ensuring that data are representative of the size distribution of the primary particles of the suspension. The light-scattering results were further confirmed by data generated using a polarized light microscope equipped with an image analyzer.     

Modeling Immune Building Systems for Bioterrorism Defense

This paper presents the results of research on the performance of air-cleaning and air-disinfection systems used for protecting buildings against intentional releases of biological agents. The air-cleaning technologies addressed include dilution ventilation, filtration, and ultraviolet germicidal irradiation. A 40-story commercial office building is modeled using typical occupancy levels and leakage rates for doors, walls, and floors. A steady-state single-zone model is used to predict steady-state conditions resulting from the use of various levels of air cleaning. A transient single-zone model is used to predict transient indoor concentrations from which inhaled doses and estimated casualties are predicted. A transient multizone model is used to evaluate contaminant dispersion and estimate potential casualties. Three design-basis attack scenarios are simulated using various biological weapon agents. Predicted casualties are estimated using an epidemiological model of the dose response curves for each of the agents. The effect of increasing levels of air cleaning is examined under the attack scenarios to evaluate their effectiveness. Results indicate that high levels of protection are possible for building occupants with moderate and affordable levels of air cleaning when filtration is combined with ultraviolet germicidal irradiation. Results also suggest that diminishing returns occur when increased levels of air cleaning are applied. It is hypothesized that the maximum useful size of any air-cleaning system is defined and limited by building physical characteristics alone.     

Compositional Fragmentation Model for the Oxidation of Sulfide Particles in a Flash Reactor

A mathematical model to predict the size distribution and chemical composition of a cloud of sulfide particles during high-temperature oxidation in a flash reactor is presented. The model incorporates the expansion and further fragmentation of the reacting particles along their trajectories throughout the reaction chamber. A relevant feature of the present formulation is its flexibility to treat a variety of flash reacting systems, such as the flash smelting and flash converting processes. This is accomplished by computing the chemical composition of individual particles and the size distribution and overall composition of the particle cloud in separate modules, which are coupled through a database of particle properties previously stored on disk. The flash converting of solid copper mattes is considered as an example. The model predictions showed good agreement with the experimental data collected in a large laboratory reactor in terms of particle size distribution and sulfur remaining in the population of particles. The cumulative contribution and distribution coefficients are introduced to quantify the relationship between specific particle sizes in the feed and those in the reacted products upon oxidation, the latter of which has practical implications on the amount and chemical composition of dust particles produced during the industrial operation.     

Directional dendritic solidification of a composite slurry: Part II. Particle distribution

The present work attempts to form an understanding of particle distribution during dendritic solidification of a composite slurry. It is shown that the magnitude and nature of the forces involved between a foreign particle and a growing dendrite are distinctly different from those during plane front solidification. A particle distribution map, based on theoretically evaluated forces, is proposed to predict the conditions under which engulfment, entrapment, or pushing of particles occurs during dendritic solidification. Directional solidification experiments have been conducted to study particle distribution, and comparison of these results with theoretical predictions based on the map agree well with a large number of experimental observations reported to date.     

Influence of particle size distribution on coarsening

This study has examined the evolution of the particle size distribution and the effect of the initial and transient distributions on coarsening kinetics and the path of evolution. A numerical procedure has been employed to simulate the coarsening process statistically. It was found that the distribution passes through a continuous range of forms from the initial distribution towards the asymptotic state, with initially narrow distributions widening and wide distributions narrowing. Experimental studies using liquid phase sintered Cu-20 Co alloy with different initial distribution widths agreed with the above simulation results qualitatively. The simulated coarsening rate was found to be related to the width and shape of particle size distribution. A rate constant has been derived relating the instantaneous coarsening rate and the transient moments of the distribution. The effect of the initial distribution on coarsening rate was found to be particularly significant in the early stage of coarsening when rapid distribution changes occur. After these early rapid transients but still far from the asymptotic state, the instantaneous coarsening rate was closely related to the instantaneous geometric standard deviation of the distribution.     

Image-Based System for Particle Counting and Sizing

A procedure is developed to provide measurements of particle size by adapting parts of a commercially available particle image velocimetry system to obtain in situ digital images of the particles. The procedure is nonintrusive and is able to capture images of the particles as they are mixed, thus avoiding the need for disturbing the flow or withdrawing samples for later analysis. Measured size distributions are shown to compare closely with manufacturer's values for standard polystyrene spherical particles, and particles with diameters as small as 6 μm are resolved. The system also is shown to track changes in particle-size distribution during an aggregation test. In addition, information on particle geometry is obtained, which should be useful for improving the ability to model aggregation processes. A simple modeling framework based on the Smoluchowski equation is presented to demonstrate the use of data obtained with this procedure in particle aggregation modeling.