FIB-Nanotomography of Particulate Systems—Part II: Particle Recognition and Effect of Boundary Truncation

The focused ion beam-nanotomography (FIB-nt) technique presented in Part I of this article is a novel high-resolution three-dimensional (3D) microscopy method that opens new possibilities for the microstructural investigation of fine-grained granular materials. Specifically, FIB-nt data volumes allow particle size distributions (PSD) to be determined, and the current paper discusses all the processing steps required to obtain the PSD from 3D data. This includes particle recognition and the subsequent PSD estimation. A refined watershed approach for 3D particle recognition that tolerates concavities on the particle surfaces is presented. Particles at the edge of the 3D data volume are invariably clipped, and because the data volume is of a very limited size, this effect of boundary truncation seriously affects the PSD and needs to be corrected. Therefore, two basic approaches for the stereological correction of the truncation effects are proposed and validated on artificially modeled particle data. Finally, the suggested techniques are applied to real 3D-particle data from ordinary portland cement and the resulting PSDs compared with data from laser granulometry.     

Separation Based on Shape Part I: Recovery Efficiency of Spherical Particles

The use of an inclined rotating disc apparatus, employed to separate spherical from non-spherical particles, is studied theoretically and experimentally. The effects of feed rate F_s, speed of rotation of the disc n, angle of inclination of the disc θ, angular co-ordinate of the feed point α, and the feed point position on the efficiency of recovery of spherical particles η_s are investigated. A rate-type equation is proposed to describe the variation of η_s with F_s and n. The ‘rate constant’ K is theoretically related to θ by a linear equation. The experimental results generally confirm the features of the model. The results indicate F_s, n and θ to be critical variables. Further, it is found that η_s is critically affected by the angular co-ordinate of the feed point α, whereas the radial co-ordinate of the feed point is a non-critical variable.     

Particle Technology: Design of Particulate Products and Dispersed Systems

There are currently a number of subjects related to particle technology, i.e., to particle formation processes and the design of particulate products and disperse systems, that still require further investigation, including the characterization and experimental determination of various particle properties, the simulation and modeling of process operation involving dispersed products and, in particular, the relationship between product properties and the properties of dispersed systems and particles. This work discusses example methods for creating particles and presents a method for the indirect detection of the inner structure of dispersed systems.     

颗粒粒度粒形测量的新技术

关于材料的研究和生产过程经常会涉及到颗粒状材料的物理特性，例如粒度大小，比表面积等参数。颗粒的粒度分布以及颗粒的形状对于最终产品的宏观物理性能．例如抗冲击性能、强度、流动性等有着非常重要的影响。此外．面向材料宏观物理性能发展的数学模拟和仿真也要求在数学建模之前得到关于颗粒大小和形状的实际信息．所有这些都要求对颗粒的粒度和粒形进行准确分析。     

Heating/Drying Using Particulate Medium : A Review Part I. General and Heat transfer parameters

ABSTRACT

This paper presents an Overview of particulate medium drying and heat treating of cereal grains. While the conventional air drying of grains is well documented, studies on the drying of grains using heated granular medium do not appear to exist. The scientific study of the different aspects of drying with a heated granular medium began in the early 1970's. Progress on the utilization of particle-to-particle heat transfer was slow as evidenced by the fact that there is no commercial dryer using the method as of today.

The first section of this paper deals with conduction heating and how it led to the use of granular medium in heating the grain. Starting with the earliest work on conduction heating reported by Kelly ( 1939), the developments in the heating of grain using granular media is discussed. For decades since Kelly's report, work in the subject area dealt mostly with the theoretical aspects of solid-to-solid heat transfer. Thus, in the succeeding section of the paper, heat transfer parameters and mechanisms involved in the process are thoroughly investigated.     

Heating/Drying Using Particulate Medium : A Review Part I. General and Heat transfer parameters

This paper presents an Overview of particulate medium drying and heat treating of cereal grains. While the conventional air drying of grains is well documented, studies on the drying of grains using heated granular medium do not appear to exist. The scientific study of the different aspects of drying with a heated granular medium began in the early 1970's. Progress on the utilization of particle-to-particle heat transfer was slow as evidenced by the fact that there is no commercial dryer using the method as of today.

The first section of this paper deals with conduction heating and how it led to the use of granular medium in heating the grain. Starting with the earliest work on conduction heating reported by Kelly ( 1939), the developments in the heating of grain using granular media is discussed. For decades since Kelly's report, work in the subject area dealt mostly with the theoretical aspects of solid-to-solid heat transfer. Thus, in the succeeding section of the paper, heat transfer parameters and mechanisms involved in the process are thoroughly investigated.     

In Situ X-Ray Radiography and Tomography Observations of the Solidification of Aqueous Alumina Particle Suspensions—Part I: Initial Instants

This paper investigates by in situ high-resolution X-ray radiography and tomography the behavior of colloidal suspensions of alumina partic les during directional solidification by freezing. The combination of these techniques provided both qualitative and quantitative information about the propagation kinetic of the solid/liquid interface, the particle redistribution between the crystals and a particle-enriched phase, and the three-dimensional organization of the ice crystals. In this first part of two companion papers, the precursor phenomena leading to directional crystallization during the first instants of solidification are studied. Mullins–Sekerka instabilities are not necessary to explain the dynamic evolution of the interface pattern. Particle redistribution during these first instants is dependent on the type of crystals growing into the suspension. The insights gained into the mechanisms of solidification of colloidal suspensions may be valuable for the materials processing routes derived for this type of directional solidification (freeze-casting), and of general interest for those interested in the interactions between solidification fronts and inert particles.     

Particulate processes in freshly prepared silver iodide hydrosols Part I. Radiometric and electron-microscopic investigations

Ageing of negative, stable AgI sols prepared in statu nascendi was investigated utilizing radiometric (heterogeneous exchange) and optical (electron microscopy) methods. AgI sols with different molar concentrations C_o, of AgI have shown that the examined sols age by two processes of different speed. The duration interval Δt_A, of the faster ageing process is approximately inversely proportional to the molar concentration of the sols. Results of a comparative analysis of the heterogeneous exchange process obtained by two different exchange procedures in identically prepared and aged sols revealed that primary particles of the sols approximately double their volume during the faster ageing process. This result is confirmed by analysing electron micrographs of differently aged stable sols. On the basis of data obtained by two different exchange procedures and the results of electron-microscopy analysis respectively, a new structural form of silver iodide is predicted. Such an up to now unknown form of silver iodide transforms spontaneously and gives a mixture of well-known cubic and hexagonal modifications of silver iodide during the aggregation of primary particles into secondary ones. This transformation is markedly accelerated during electrolytic coagulation of the sols.     

Preventing Segregation during Centrifugal Consolidation of Particulate Suspensions: Particle Drafting

Dilute, dispersed, multicomponent suspensions containing Ce-ZrO₂, Al₂O₃, and varying Al₂O₃-platelet contents were centrifugally consolidated. Despite the favorable conditions for segregation, phase and size segregation did not occur in the highest Al₂O₃-platelet content suspension. The suspension properties did not consist of agglomeration, high solids fractions, or high suspension viscosities typically attributed with segregation prevention. Thus, a new mechanism is suggested, considering the effects of hydrodynamic particle interactions (interference drag or "drafting") on particle arrangement during consolidation. Particle drafting is proposed and supported as a mechanism for preventing segregation, and the importance of hydrodynamic particle interactions in ceramic processing is discussed.     

Effect of Particle Shape on Inline Particle Size Measurement Techniques

The influence of the particle shape on the results of different measuring techniques was investigated. Considered were single‐frequency ultrasound technique, 3D optical reflectance measurement (advanced particle analyzing system with multi capture signal technology), and focused‐beam reflectance measurement probes as techniques which are usable inline and in suspension density ranges usually present in industrial crystallization processes. Advantages and shortcomings of these techniques are compared and discussed.     

Silicon Carbide Ceramic Particulate Reinforced AA2024 Alloy Composite - Part I: Evaluation of Mechanical and Sliding Tribology Performance

In this research work, a master batch (comprising of AA2024 alloy, Silicon Nitride (Si3N4) and Graphite particulates) was reinforced by Silicon-Carbide (SiC) ceramic particulates (0–6 wt.-%; at steps of 2%; i.e. four composites samples viz. ASC-0; ASC-2; ASC-4; ASC-6) with the aim of enhancing mechanical and sliding tribology performance. The semi-automatic stir-casting fabrication process was followed as per standard industrial practice in-order-to fabricate the sample plates of the said alloy composites as per design. Thereafter, the sample specimens were prepared via wire EDM cutting followed by polishing over emery paper; as per ASTM standard dimensions and various physical (density and void content), mechanical (tensile strength, flexural strength, impact strength, hardness etc.), sliding tribology performance (steady state sliding wear; ASTM G-99; Pin-on-Disc tribo-meter), thermal (thermal conductivity, Thermo-Gravimetric Analysis (TGA)); thermo-mechanical (Dynamic Mechanical Analysis (DMA)), fracture-analysis, X-ray diffraction (XRD) etc. characterisation were performed and discussed. In Part-1: Physical, mechanical and sliding tribology performances were discussed. The Taguchi design of experiment technique was employed for designing of experimental runs having input controlling parameters like sliding velocity (0.654–2.616 m/s), sliding distance (784.8–3139.2 m), normal load (5–50 N), reinforcement content (0–6 wt.-%) and environment temperature (20–50 °C). The worn surface morphology studies were performed to understand prevalent wear mechanism using Field Emission Scanning Electron Microscope (FESEM) along with Energy-dispersive X-ray spectroscopy (EDS) that reveals elemental composition and its dispersion on the surface. In Part-2: evaluation of characterizations like thermal, thermo-mechanical, fracture-analysis, X-ray diffraction (XRD) etc. were discussed in correlation with mechanical and sliding wear performance. In Part-3: the entire performance data are analysed using hybrid AHP-TOPSIS technique (an MCDM technique; computationally simple and easy to understand) in-order-to rank the composites formulations.     

在催化过程中不同形状和尺寸的固体颗粒的磨损规律

应用圆盘碾磨器对制得的七种不同形状和尺寸的固体颗粒进行了系统的磨损试验和研究。验证了Ｇｗｙｎ的固体颗粒磨损动力学方程能在较广泛的范围内适用于颗粒的磨损；并推导出了颗粒的磨损速率与颗粒床层所受到的正压力大小之间关系的数学模型；研究了颗粒的平均粒径的变化与颗粒受磨损的时间（转角）之间的关系，并得出了表达它们之间关系的数学方程式；比较了不同形状和尺寸的固体颗粒的磨损规律，初步掌握了固体颗粒被磨损的因素。     

Influence of Particle Shape on Filtration Processes

The influence of particle shape on filtration processes was investigated. Two types of particles, including spherical polystyrene latex (PSL) and iron oxide, and perfect cubes of magnesium oxide, were examined. It was found that the removal efficiency of spherical particles on fibrous filters is very similar for corresponding sizes within the range of 50–300 nm, regardless of the fact that the densities of PSL and iron oxide differ by a factor of five. On the other hand, the removal efficiency of magnesium oxide cubic particles was measured, and found to be much lower than the removal efficiency for the aerodynamically similar spheres. Such disparity was ascribed to the different nature of the motion of the spherical and cubic particles along the fiber surface, following the initial collision. After touching the fiber surface and before coming to rest, the spherical particles could either slide or roll compared to the cubic ones, which could either slide or tumble. During tumbling, the area of contact between the particle and the fiber changes significantly, thus affecting the bounce probability, whilst for the spheres, the area of contact remains the same for any point of the particle trajectory. The extra probability of particle bounce by the cubes was derived from the experimental data. The particle kinetic energy was proposed to be responsible for the difference in removal efficiency of particles with alternative shapes, if all other process parameters remain the same. The increase in kinetic energy is shown to favor the increase of the bounce probability.     

Particle Shape and Purity in Membrane Based Crystallization

Well‐controlled crystallization is the best method for preparing materials that are uniform in shape, size, structure and purity. The driving forces for crystallization are local gradients of supersaturation as the source and desupersaturation as the drain. Very high local supersaturation causes a high growth rate and represents a limiting factor for unstable modifications and product impurities. Hybrid membrane technology provides an interesting tool for controlling and limiting the maximum level of supersaturation due to defined mass transfer across the membrane. In this paper, the level of crystal growth rate in the system NaCl/KCl/water is varied by using different crystallization techniques. Vacuum evaporation crystallization (high growth rate) is compared to membrane based evaporation crystallization (low growth rate) and the results are interpreted in terms of product purity, particle shape and size. Membrane based crystallization in combination with effective solid/liquid separation as well as high performance analytics is suggested as a significant ultrapurification methodology.     

Step-Energy Barriers and Particle Shape Changes during Coarsening

Models of particle shape changes usually do not account for the step-energy barrier associated with adding or removing additional atomic planes from a faceted surface. However, the step-energy barrier can be a substantial limitation when the free energy changes that drive particle shape changes are relatively low. A good example of this is particle coarsening. The analysis presented in this article describes dislocation-free particles with surfaces that have faceted and nonfaceted regions. When the chemical potential differences responsible for shape changes are too small to overcome the step-energy barrier, atomic layers cannot be added or removed from the facets. Even with this constraint, it is possible to add or remove atoms from the particle surface; however, this can cause the particle shape to differ substantially from the traditional equilibrium shape.     

机制砂颗粒形状的评价方法及其特征研究

为研究机制砂粒形表征方法及特点,采用集料图像测量系统(AIMS)和数字图像处理(DIP)技术测试了5种机制砂的颗粒形态。基于现有研究存在的不足提出了一种改进的粒形测试方法,并研究了不同粒形表征参数之间的关系。结果表明:随着粒径范围从大到小,机制砂的棱角性呈先增大后减小的趋势,而二维形状值无明显变化规律;0.3~0.6 mm的机制砂可以反映整体粒径范围的棱角性;通过单次投影进行图像处理获取的粒形参数有较大的波动范围,无法准确判断机制砂的颗粒形状;纵横比与凹凸度有较强的相关性,粗糙度与纵横比、圆度、凹凸度的相关性较强,而分形维数与其他几种参数都不具有相关性;通过改进的DIP技术得出的粒形评价结论与AIMS得出的评价结论一致,具有一定的可行性和推广价值。     

Influences on the Particle Size Distribution of Diesel Particulate Emissions

Particulates give great concern for mankind health. Especially the nano size particles are under discussion. Therefore, the particle size distribution from the combustion chamber to tail pipe emissions are of great interest. With the aim of scanning mobility particle sizer the number weighted particle size distributions were measured in the combustion chamber as well as in the exhaust gas up and downstream of aftertreatment systems. Using the identical particle measurement technique results can be compared without changing the particle size definition. The particles in the cylinder of a modern serious DI diesel engine were sampled with a time resolved fast gas sampling valve. The Soot particles formed in the cylinder during the early combustion phase are oxidized by about 99% in the late combustion/early expansion phase, whereas the soot particle sizes distribution in the cylinder at the end of the expansion phase are equal to that in the tail pipe. DI diesel engines with high pressure injection system emit less numbers of particle with in tendency greater sizes compared to IDI diesel engines. Oxidation catalysts do not influence particle size distribution but particulate traps reduce particle number by up to two orders of magnitude. Detail analysis shows that an increase of nano size particle number downstream of an aftertreatment device results from artifacts.     

Anisotropic Shrinkage in Tape-Cast Alumina: Role of Processing Parameters and Particle Shape

Aqueous suspensions of alumina and other powders containing no visible morphological anisotropy were tape cast under different conditions to study the role of processing parameters and powder characteristics in the origin of in-plane sintering shrinkage anisotropy. High anisotropic shrinkage, with the typical shrinkage in the transverse direction exceeding that in the casting direction by more than 10%, was observed for tape-cast alumina cast at high solids loading and high shear rates. Tape casting without any binder also resulted in similar anisotropy. Lower solids loading with increased agglomeration resulted in a drastic reduction of shrinkage anisotropy. Under similar casting conditions, BaTiO₃ did not show any shrinkage anisotropy unlike alumina. Cubic zinc ferrite and titania powders also showed some consistent shrinkage anisotropy. A correlation was found between in-plane particle orientation and anisotropic shrinkage proving that powder characteristics, particularly particle shape, control anisotropic shrinkage even in apparently equiaxed powders.