Effect of particle size and grain composition on two-dimensional infiltration process of weathered crust elution-deposited rare earth ores

The two-dimensional infiltration experiment was carried out by means of digital image technology.The evolution process of the wetting body was described.The wetted front distance and the time show a very significant power function relationship.The horizontal wetted distance is larger than the vertical wetted distance in the initial stage.Then,the vertical distance of the wetted body gradually approaches to the horizontal distance.The infiltration distance decreases as the content of fine particles increases.The wetted front migration rate curve shows a three-stage change law,and it increases with the increase of coarse particle content.The directional velocity ratio is defined.The initial value of horizontal infiltration rate is larger than that of vertical one,and then the vertical infiltration rate is gradually close to the horizontal value.The empirical relationship between the characteristic particle size and the stable infiltration rate is established,which provides a theoretical basis for the prediction of the stable infiltration rate in in-situ leaching.

Modeling for critical state line of granular soil with evolution of grain size distribution due to particle breakage

Determination of the critical state line(CSL)is important to characterize engineering properties of granular soils.Grain size distribution(GSD)has a significant influence on the location of CSL.The influence of particle breakage on the CSL is mainly attributed to the change in GSD due to particle breakage.However,GSD has not been properly considered in modeling the CSL with influence of particle breakage.This study aims to propose a quantitative model to determine the CSL considering the effect of GSD.We hypothesize that the change of critical state void ratio with respect to GSD is caused by the same mechanism that influences of the change of minimum void ratio with respect to GSD.Consequently,the particle packing model for minimum void ratio proposed by Chang et al.(2017)is extended to predict critical state void ratio.The developed model is validated by experimental results of CSLs for several types of granular materials.Then the evolution of GSD due to particle breakage is incorporated into the model.The model is further evaluated using the experimental results on rockfill material,which illustrates the applicability of the model in predicting CSL for granular material with particle breakage.

Grain Size Control of Semisolid A356 Alloy Manufactured by Electromagnetic Stirring

To investigate the possibility of substituting the mechanical stirring system with electromagnetic stirring (EMS) system for aluminum rheo die-casting, the EMS under the different stirring cooling conditions was carried out. It was found that in the early period of solidification, the dendrite breakages led to a fine primary phase. When dendrites grew coarsely, the effect of ripening on grain size overwhelmed that of dendrite breakage. It was also found that the high cooling rate favored large nucleation rate, and led to a fine primary phase. But high cooling rate also made the growth rate of the dendrite arm, which prevented the dendrite arm from being sheared off. Therefore there were a suitable stirring time and suitable cooling rate to obtain the best rheo die-casting structure. Qualified semisolid A356 aluminum alloy was successfully manufactured with short time EMS.

Effect of salt-assisted reduction method on morphologies and size of metallic tungsten particles

A simple method was proposed to produce tungsten(W)particles with controllable shape and size by employing the salt-assisted hydrogen reduction.W particles with controlled shape and size were prepared by adjusting the amount of chlorine salts and the temperature.After adding salt additives,the dispersibility of final particles was obviously improved and more adequate growth of particles was obtained.It was found that the effect of NaCl and LiCl is particularly significant.The average sizes of the obtained W particles at 1038 K after adding 0.1 wt.%NaCl and 0.1 wt.%LiCl were 0.924 and 1.128μm,respectively.With the increase of temperature and amount of chlorine salts,the dispersity of the produced W particles became much better,the size of W sub-particles was increased,and the shape of W sub-particles was changed from spherical to polyhedral.At 1349 K,the addition of chlorine salts even multiplied the particle size,and the average sizes of W particles with 1 wt.%NaCl and 1 wt.%LiCl were raised up to 21.367 and 29.665μm,respectively.Based on the conventional pseudomorphic transformation and chemical vapor transport mechanisms,the effects of adding salts on the reaction mechanism were investigated in detail as well.

Micromagnetic studies of perpendicular recording FePt media with controllable grain size distributions

A 3-dimensional(3D)micromagnetic model combined with Fast Fourier Transform(FFT)method was built up to study the writability in the L1_(0)FePt perpendicular medium.The effects of controllable grain size distributions were studied by grain growth simulation.It is found that the cross-track-averaged magnetization changes little between the L1_(0)FePt medium with uniform or non-uniform grain size distribution.

Particle breakage of sand subjected to friction and collision in drum tests

This paper presents a laboratory experimental study on particle breakage of sand subjected to friction and collision,by a number of drum tests on granular materials(silica sand No.3 and ceramic balls)to investigate the characteristics of particle breakage and its effect on the characteristics of grain size distribution of sand.Particle breakage increased in up convexity with increasing duration of drum tests,but increased linearly with increasing number of balls.Particle breakage showed an increase,followed by a decrease while increasing the amount of sand.There may be existence of a characteristic amount of sand causing a maximum particle breakage.Friction tests caused much less particle breakage than collision tests did.Friction and collision resulted in different mechanisms of particle breakage,mainly by abrasion for friction and by splitting for collision.The fines content increased with increasing relative breakage.Particle breakage in the friction tests(abrasion)resulted in a sharper increase but with a smaller total amount of fines content in comparison with that in the collision tests(splitting).For the collision tests,the fines content showed a decrease followed by an increase as the amount of sand increased,whereas it increased in up convexity with increasing number of balls.The characteristic grain sizes D_(10) and D_(30) decreased in down convexity with increasing relative breakage,which could be described by a natural exponential function.However,the characteristic grain sizes D50 and D60 decreased linearly while increasing the relative breakage.In addition,the coefficients of uniformity and curvature of sand showed an increase followed by a decrease while increasing the relative breakage.

CHARACTERISTIC GRAIN SIZE: PART Ⅱ MEASURING PRINCIPLES

The principles for measuring characteristic grain sizes of materials, such as fully-dense single phase materials, porous materials and materials with isolated second phase particles, are developed on the basis of its definition associated closely with the surface area per unit volume, Sv, of grain. The focus of the measuring principles of the characteristic grain size is put on determining Sv of grains. Unlike the measurement of average grain size commonly used, G, correcting factors such as grain shape and grain size distribution factors, will not be applied to the determination of the characteristic grain size, Gc, due to its unique geometric meaning and the measure precision of Sv being guaranteed by quantitative stereological technique and gas adsorption method. The measurement of Gc can be directly carried out on the polished and etched cross section of materials, similar to the measuremernt of the average grain size using the Heyn intercept method.

A NEURAL NETWORK-BASED MODEL FOR PREDICTION OF HOT-ROLLED AUSTENITE GRAIN SIZE AND FLOW STRESS IN MICROALLOY STEEL

For the great significance of the prediction of control parameters selected for hot-rolling and the evaluation of hot-rolling quality for the analysis of prod uction problems and production management, the selection of hot-rolling control parameters was studied for microalloy steel by following the neural network principle. An experimental scheme was first worked out for acquisition of sample data, in which a gleeble-1500 thermal simolator was used to obtain rolling temperature, strain, stain rate, and stress-strain curves. And consequently the aust enite grain sizes was obtained through microscopic observation. The experimental data was then processed through regression. By using the training network of BP algorithm, the mapping relationship between the hotrooling control parameters (rolling temperature, stain, and strain rate) and the microstructural paramete rs (austenite grain in size and flow stress) of microalloy steel was function appro ached for the establishment of a neural network-based model of the austeuite grain size and flow stress of microalloy steel. From the results of estimation made with the neural network based model, the hot-rolling control parameters can be effectively predicted.

Influence of Block Copolymer on Formation and Acid Resistant Properties of Hybrid CaCO_3 Particles

Block copolymer polystyrene-b-poly（acrylic acid）（PS-b-PAA） was used as structural template for the synthesis of CaCO3 microparticles. Through this procedure, acid resistant hybrid CaCO3 micro- spheres were obtained. Acid resistant properties of this type of hybrid CaCO3 were studied. Size measurement shows that the acid resistant properties of the hybrid particles are different in different solutions, such as HCl, EDTA, and H2SO4 solutions.

Improvement and Application of Grain Size Distribution Characteristics Calculation of Bed Material

Grain size distribution of bed material is an important characteristic for studying evolution of natural river channel by means of experimental ways and numerical modeling of flow and sediment process.In this study,the fractal characteristic of sediment particle has been defined by means of fractal theory based on ana- lyzing the property of grain size distribution of bed material in the river channel.Furthennore,the fractal prop- erty of sediment particle has been applied to judge the process of armorin...

Grain size refinement of magnesium composite alloys by addition of B_2O_3

The high performance magnesium alloy was investigated by adding B2O3 in magnesium and magnesium alloys. Experiments include adding B2O3 in Mg, Mg-Al and Mg-RE alloys, respectively, studying the effects of B2O3 on the microstructure, were studied measuring the change of grain size and microhardness of the materials, discussing the change of grain size, morphology and distribution. The results show that adding 3% or 6%(mass fraction) B2O3 in Mg can bring twinning in Mg, adding B2O3 in Mg-Al alloys and Mg-RE alloys can refine the alloy grain size. Adding 3%B2O3 in Mg-6Al alloys can refine the average grain size by about 5μm, with the average hardness increased by 13.3% (53.3-60.4 HV0.03); adding 6%B2O3 in Mg-6Al alloys can refine the average grain size by about 13μm, with the average hardness increased by 15.8% (53.3-61.73 HV0.03); adding 3% and 6%B2O3 into Mg-6RE alloys can refine the grain size by about 5 and 9μm, respectively, with the average hardness decreased to HV0.03 64.66 and HV0.03 57.86, respectively from HV0.03 88.57. In the Mg-6Al alloy the content of aluminum is increased, while in the Mg-6RE alloy the content of oxygen is decreased. It can be concluded that it is beneficial to develop Mg-Al-B-O particle reinforce composite alloys, and it is feasible to develop nanometer crystallization of block material by Mg-B-O-RE.

Grain size control in quasi-two-dimensional perovskite thin film via intermediate phase engineering for efficient bound exciton generation

Quasi-two dimensional(2D)perovskites have emerged as a promising class of materials due to their remarkable photoluminescence efficiency,which stems from their exceptionally high exciton binding energies.The spatial confinement of excitons within smaller grain sizes could enhance the formation of biexcitons leading to higher radiative recombination efficiency.However,the synthesis of high-quality quasi-2D perovskite thin films with controllable grain sizes remains a challenging task.In this study,we present a facile method for achieving quasi-2D perovskite thin films with controllable grain sizes ranging from 500 to 900 nm.This is accomplished by intermediate phase engineering during the film fabrication process.Our results demonstrate that quasi-2D perovskite films with smaller grain sizes exhibit more efficient bound exciton generation and a reduced stimulated emission threshold down to 15.89µJ cm^(−2).Furthermore,femtosecond transient absorption measurements reveal that the decay time of bound excitons is shorter in quasi-2D perovskites with smaller grain sizes compared to that of those with larger grains at the same pump density,which is 230.5 ps.This observation suggests a more efficient exciton recombination process in the smaller grain size regime.Our findings would offer a promising approach for the development of efficient bound exciton lasers.

Effect of TiN Particles and Grain Size on the Charpy Impact Transition Temperature in Steels

The toughness of ferritic steels is influenced by the grain size distribution, second phase, precipitates and coarse inclusions. In this work an examination of the effect of coarse TiN particles （〉0.5 μm） and ferrite grain size on the Charpy impact transition temperature in high strength low alloyed steels has been carried out. Steels with high Ti content （up to 0.045 wt%）, have been heat-treated and furnace cooled to obtain a ferrite-pearlite microstructure with different ferrite grain sizes. Coarse TiN particle size and ferrite grain size distributions have been measured and Charpy impact testing has been carried out. Scanning electron microscopy （SEM） analysis has been used to measure the grain boundary carbide thickness and to determine if the coarse TiN particles are acting as cleavage initiation sites by fractographic analysis. The Charpy ductile-brittle transition temperatures （DBTT） have been predicted using standard literature equations, and compared to the measured values. The relationship between the ferrite grain size and coarse TiN particle size and number density in terms of whether the coarse TiN particles act as effective cleavage initiation sites is discussed in this paper.

Kinetic and thermodynamic studies on partitioning of polychlorinated biphenyls (PCBs) between aqueous solution and modeled individual soil particle grain sizes

The significance of soil mineral properties and secondary environmental conditions such as pH, temperature, ionic strength and time in the partitioning of eight selected polychlorinated biphenyl(PCB) congeners between aqueous solution and soil particles with different grain sizes was studied. The mineral properties of a model soil sample were determined, and Brunauer–Emmett–Teller(BET) adsorption–desorption isotherms were employed to observe the surface characteristics of the individual modeled soil particles.Batch adsorption experiments were conducted to determine the sorption of PCBs onto soil particles of different sizes. The results revealed that the sorption of PCB congeners onto the soil was dependent on the amount of soil organic matter, surface area, and pore size distribution of the various individual soil particles. Low pH favored the sorption of PCBs,with maximum sorption occurring between pH 6.5 and 7.5 with an equilibration period of 8 hr.Changes in the ionic strength were found to be less significant. Low temperature favored the sorption of PCBs onto the soil compared to high temperatures. Thermodynamic studies showed that the partition coefficient(K_d) decreased with increasing temperature, and negative and low values of ΔH° indicated an exothermic physisorption process. The data generated is critical and will help in further understanding remediation and cleanup strategies for polluted water.

Critical points in the formulation of pharmaceutical swellable controlled release dosage forms——Influence of particle size

Swellable matrix represents one of the most employed controlled release systems. These dosage forms provide slow release of drugs to reduce the fluctuation of drug concentration in plasma in order to improve the efficiency of treatment and/or to reduce adverse effects. The application of the concepts of statistical physics has allowed discovering the existence of critical points in the formulation of swellable matrices. These points, representing the volume fractions of the tablet components where the properties of the matrix diverge or change suddenly, provide important knowledge of how to rationalize the design of swellable matrices. The critical points are generally related to the percolation threshold of one of the components of the formulation, which corresponds to a geometrical phase transition of this component, passing from isolation to spanning the whole system. The last section of the paper is devoted to more recent findings concerning the influence of particle size of the components on the percolation threshold of the matrix forming polymer, and therefore on the release behaviour of the matrix. Knowledge of the excipient percolation threshold allows a more rational design of swellable matrices, according to the guidelines of the regulatory authorities concerning science-based formulation and quality by design.

Reduction Process of Blue Tungsten Oxide and its Microcomputer Process Control

Grain size control of tungsten powder is essential for high quality tungsten products. Based on studies on the hydrogen reduction process of tungsten oxide, a microcomputer system is described for reduction process control. The system, now running in Zhuzhou Tungsten and Molybdenum Materials Plant, controls the temperature of the reduction furnace and hydrogen pressure. It also controls a mechanical pusher which pushs the boats charged with blue tungsten oxide into the furnace tubes. Some of the technical problems in the process are analysed.

Experimental study on specific grinding energy and particle size distribution of maize grain,stover and cob

Reducing the particle size of biomass is of great significance for rational and efficient utilization of biomass.In this study,maize grain,stover,and cob were comminuted at different speeds(2000-2800 r/min)by hammer mill with a mesh size of 2.8 mm.The mechanical energy for smashing three selected samples was obtained directly through the sensor and data testing system.Experimental results demonstrated that the maize cob had the highest total specific energy while the maize grain had the lowest(135.83-181.10 kW·h/t and 27.08-36.23 kW·h/t,respectively).In addition,for the same material,higher hammer mill speed generated more specific energy consumption.And the effective specific energy of maize stover had a similar trend to the total specific one.However,the effective specific grinding energy of maize cob and grain increased initially and then decreased with the increase of rotating speed.The fitting curves of the specific energy to mill speeds were determined,and the range of determination coefficients of the regression equation was 0.933-0.996.Particle size distribution curves were drawn by sieving the pulverized particles of the three samples based on a series of standard sieves.Fourteen relevant parameters characterizing the particle size distribution were calculated according to the screening data.Calculation results demonstrated that larger rotational speed leads to smaller particle sizes.Combining the size parameters,distribution parameters,and shape parameters,it was found that the distributions of the three samples all exhibit a distribution of“well-graded fine-skewed mesokurtic”.The Rosin-Rammler function was considered to be suitable for characterizing the particle size distribution of maize grain,stover,and cob particles with a coefficient of determination between 0.930 and 0.992.

激光粒度仪在特殊土颗粒分析试验中的应用

采用激光粒度仪对膨胀土、黄土和红土进行了颗粒分析试验,研究了取样质量和超声波分散时间对试验结果的影响,发现遮光率与取样质量呈现很好的线性正相关,给出了特殊土在激光粒度仪法试验中适宜的遮光率范围(15%~25%)、取样质量(膨胀土取0.1~0.2 g,黄土取0.4~0.8 g,红土取0.2~0.4 g)和超声波分散时间(膨胀土取6 min,黄土和红土取2 min);激光粒度仪法试验结果的离散性,对于黄土和膨胀土较小,但对红土相对较大,红土平行试验中粒组含量极差的最大值为10.1%;与密度计法相比,激光粒度仪法测得的胶粒(0,0.002]mm含量偏小,而黏粒(0.002,0.005]mm或更大粒组的含量则偏大,可能是因为两者试验原理的不同而导致的;2种方法对红土的测试结果差异较大,与红土的特殊性质有一定关系。研究成果为激光粒度仪在特殊土颗粒分析试验中的应用提供了借鉴。

IN718高温合金的新型热控凝固工艺优化

针对高温合金复杂薄壁铸件易出现欠铸、晶粒粗大和疏松等问题,开发了一种以“低温浇注、高温充型、顺序凝固”为特征的新型热控凝固工艺,研究了在1 380℃浇注温度下模壳温度(1 260~1 350℃)和抽拉速度(6~48 mm·min^(-1))等工艺参数对IN718高温合金圆柱试样组织的影响,并在优化工艺下进行了复杂薄壁特征结构件的成形试验。结果表明:随着模壳温度升高,试样的晶粒尺寸从2.33 mm增加到7.46 mm,且组织均匀性变差,断面等轴晶比例由98%降低到41%,疏松数量减少,尺寸减小。随着抽拉速度增大,晶粒尺寸从3.66 mm减小到2.69 mm,疏松数量增加,尺寸增大;当抽拉速度不小于24 mm·min^(-1)时,组织均匀性较好。最优工艺为模壳温度1 290℃、抽拉速度24 mm·min^(-1),采用该工艺可制备得到晶粒尺寸为0.81 mm、疏松面积分数仅为0.2%、最小壁厚为1.8 mm的IN718高温合金大面积薄壁特征结构件。

抓斗式散粮卸料过程逸尘机理探究

为探究抓斗卸料过程中的逸尘机理,解决当前港口物料转运过程中存在粉尘外逸严重的难题,搭建抓斗卸料逸出气流在线测试实验平台。采用试验与数值计算相结合的方式,以典型主粮散体颗粒为卸料对象,基于气固两相流理论,探究卸料高度和卸料质量流量对料斗内逸出气流速度的影响映射耦合关系,结合粉尘颗粒逸出过程的运动特性和规律推导出粉尘逸出的临界粒径。结果表明:逸出气流速度峰值与卸料高度成正相关,同一卸料高度下,逸出气流峰值与质量流量成幂函数关系;基于粉体颗粒受力,推导出粉尘颗粒逸出的临界粒径计算公式,并验证公式的计算误差在11%以内;大豆、玉米和小麦卸料时,粉尘颗粒逸出的临界粒径范围分别为160.9~292.5,182.6~359.6,95.1~196.1μm。研究为抓斗式散粮卸料过程中的粉尘控制和抑尘装置设计提供理论支撑。