The origins of a collaborative project on silo research (CA-Silo) are given, along with some of the background case for support. The activities described include contributions on a state of the art in silo research, and brief descriptions on some collaborative research work that was carried out. The ways in which industry was involved with CA-Silo are explained. Research requirements are identified in terms of both general objectives, and short-term requirements for pre-normative research. Finally, some of the project management issues are raised, and the project outcomes are described.
The paper reviews methods for the electrophysical characterisation of powders and particles and describes in detail many of the laboratory units especially designed for this purpose at the Cagliari University. In particular, the following characteristics can be measured or calculated for powders and particles: (a) electrical conductivity as a function of temperature; (b) thermoelectric potential difference; (c) Seebeck coefficient; (d) electron work function; (e) position of the Fermi level referred to the valence band upper edge; (f) width of the forbidden energy gap; (g) either type of charge carrier concentration (n concentration of electrons in the conduction band, p concentration of free holes in the valence band); (h) either type of charge carrier mobility; (i) electrical charge of powders or single particles; (l) triboelectric charging with different systems. Detailed drawings of the laboratory equipment are provided for each unit used to measure the above-mentioned characteristics, as well as the experimental procedure for both fine powders and single particles. The paper also provides the theory on which the experimental procedure is based and the calculation methods.
Among many attractive effects on physicochemical processes; one of the most promising applications of power ultrasound concerns crystallization. This paper is a review of the previous work on sonocrystallization. Ultrasound has been used in crystallization to initiate primary nucleation by narrowing the metastable zone width. It influences secondary nucleation and crystal growth. It has beneficial effects on crystal habit and crystal size distribution. It can reduce or modify agglomeration and the subsequent liquid inclusions and improve product handling. A description of the available equipment will be given. Finally, from the previous work and the experience gained, the possible future developments in sonocrystallization will be examined.
The powder particle fluidized bed was invented for the processing of fine or very fine particles. In a powder particle fluidized bed, fine powders are continuously fed to a bed in which coarse particles have been fluidized. The fine powders are uniformly dispersed and fluidized in the bed, where they adhere to the surface of the coarse particles. Fine particles are then elutriated from the bed with gas. This study entailed the use of a powder particle fluidized bed to investigate the holdup of fine particles in the bed, the elutriation rate constant of fine particles from the bed, and the average residence time of fine particles in the bed. The holdup of fine particles increased linearly with an increase in the feed rate of fine particles and the holdup of fine particles increased with decrease in gas velocity and the particle size of fine particles. The elutriation rate constant of fine particles increased when fine particle size and gas velocity increased, and decreased when coarse particle size increased. The average residence time of fine particles increased when gas velocity and fine particle size decreased. When fine particle size was smaller than several microns, the average residence time of fine particles in the bed was more than 1,000 times as long as that of the fluidized gas.
The assembly of particles is one of the built-up methods of fabricating an organized structure in the range from micro- to nanometer scales. We proposed a concept for particle assemblage and have been developing a new technique to assemble microscale particles for the fabrication of two- or three- dimensionally controlled micro structures. In this paper, we describe the technique for arrangement of microscale particles that was published in previous papers. This technique is based on colloidal processing and can deposit microscale particles at specific areas on non-conductive substrates. The procedure is as follows: An electrified pattern is formed on a dielectric substrate by scanning of an electron or Ga+ ion beams. The substrate is then dipped into a suspension in which the particles are dispersed. The particles are attracted to the electrified pattern and adhere to the substrate. Spherical silica particles of 5μm diameter were used as model particles in the experiments. Two- dimensional micropatterns were fabricated from the silica spheres by trial. This technique is potentially applicable to fabricate microdevices in electronic, magnetic and optical fields.
Production of high purity aluminum nitride powder which can be processed into electronic packages at a cost competitive with existing lower performance ceramic packages has promoted the development of many different synthesis methods. A survey of the synthesis of ultrafine AIN powders using thermal plasmas is presented. Laboratory scale experiments, applying inductively coupled and transferred-arc plasma systems, have been used to produce nanosize powders by vapour-phase reaction between aluminum vapour and ammonia, using a reduced number of steps. The specific surface area of the powders reported are in the 12 to 280 m2/g range. Sinterability experiments have demonstrated that these powders can be compacted to full density at lower temperatures than powders produced by conventional methods.
PaRMAC is a newly developed evaluation method for the particle size distribution in agglomeration. The particle number distribution is divided into three size categories: 1-10 μm ("sand"), 10-40 μm ("stones") and 40-100 μm ("block"). The "stones" form the basic framework of the pellets. The "sand" is needed to fill in the voids. The relationship between the size categories is quantified by comparing each smaller size to the next larger. Two ratio factors are obtained and used as x-y coordinates. The obtained point defines the status of the sample. By following changes in the position of this point, changes in the original size distribution can be traced. The PaRMAC method allows us to visualise and compare hundreds of samples at the same time. Changes in the particle size distribution of LKAB iron ore concentrates are tracked as the agglomeration process advances. The magnetite concentrates begin to agglomerate as early as during filtration. The bentonite binder redisperses the agglomerates. The dispersion grade varies due to changes in the efficiency of the bentonite mixer.
Particle mass spectrometry has been shown to be an effective diagnostic technique to determine particle size and size distribution of charged nano-particles originating from different reactive sources. In the present paper, the principle of the PMS is described in detail and examples of application to various particle formation systems are presented. A spark generator, a microwave reactor, and a low-pressure premixed flame burner were used to produce particles of different materials in different size ranges between 1 and 10 nm. The resolution and sensitivity of the PMS has been improved by the adaptation of a preamplifier consisting of a secondary electron multiplier coupled to an external conversion dynode. The particle mass – being the main parameter of the measurements – is not influenced by the additional acceleration due to the conversion current. The use of a secondary electron multiplier leads to a signal gain of 104 compared with measurements without the preamplifier.
Paste extrusion is an important process used for manufacturing products based on particulate materials. From a theoretical viewpoint, paste extrusion resembles solid metal extrusion, for which extensive theory has been developed. In particular, exact solutions are available for many extrusion processes involving plane strain deformations, allowing extrusion pressures to be accurately determined in these situations. However, axisymmetric extrusion is more common in a paste flow context, and in this case simple alternative methods for estimating extrusion pressures are desirable. In this article, we describe how exact solutions for plane strain extrusion can be applied empirically to axisymmetric geometries, to provide accurate estimates for extrusion pressures. The nominal extrusion pressures for plane strain and axisymmetric extrusions with equal area reductions appear to be similar, for both smooth- and rough-walled square-entry dies. The axisymmetric extrusion pressure can be estimated directly in the smooth wall case, while for rough walls, the contribution due to rigid sliding, away from the deforming zone, must also be considered. Some new correlations describing combined results from slipline field solutions for plane strain extrusion are also presented.
The term nanoparticle is used nowadays to indicate particles with diameters smaller than 100 nm. The reduced size of nanoparticles is responsible for changed electronic, optical and magnetic properties of nanoparticles and nanostructured materials in comparison with the bulk material. This can be used for new applications such as quantum dots, luminescent materials, gas sensors, conductive films, and capacitive, resistive, magnetic and optical materials. An overview is given of the different synthesis processes used to provide nanoparticles with the required properties for functional applications, especially electronic and optical ones. We will concentrate on gas-phase processes to show their advantages. Apart from the synthesis techniques, handling techniques are described. Some examples from our own research are given, in which the use of electrical forces plays a central role: size fractionation, deposition and mixing can all be controlled by using charged particles.
The generation of fine solid particles by heterogeneous desublimation of succinic acid vapor is investigated experimentally and theoretically. In the experimental investigations, a gas mixture consisting of air and succinic acid vapor is cooled by means of subsonic nozzle expansion and is directly cooled by mixing. As a result of the cooling process, the gas mixture is supersaturated and the succinic acid vapor desublimes to fine particles. The number concentrations and particle size distribution of the powders generated are measured with an optical particle counter. The particle growth by desublimation is calculated with an Eulerian-Eulerian approach in a two-dimensional flow field. The population balance for the particle size distribution is solved and the mass and energy balance equations for each particle class are implemented in a CFD program (CFX 4.2).
This work is concerned with the development of a computational fluid dynamics model for a two-phase, turbulent, swirling flow produced by stationary guide vanes. The swirling flow causes separation of particles in the air stream and hence the device is called swirler separator. The Reynolds-averaged continuity and Navier-Stokes equations are solved along with the Boussinesq hypothesis to describe the stress distribution throughout the flow field in a body-fitted coordinate system. The κ-ε model is used to determine turbulent viscosity. Finite volume methodology is adopted to discretize the system of governing partial differential equations and the semi-implicit method for pressure linked equations consistent to deal with the pressure-velocity coupling. The dilute phase is accounted for by following a Lagrangian methodology in which a Newtonian force balance tracks the particles throughout the flow field. A stochastic method is employed to model the dispersion of particles due to turbulence of the fluid-phase. The phenomenological model is then successfully used to predict velocity and pressure fields created by the guide vanes as well as particle classification curves brought about by the swirler separator.
Thermal pretreatment can significantly improve industrial comminution operations by reducing energy requirements. The effect of pretreatment using conventional and dielectric heating followed by quenching on the microstructure and on the fracture characteristics of selected single-phase and multiphase materials has been investigated using single-particle fracture experiments, crack density measurements and indentation fracture. It was shown that measurements of the crack density from polished sections correlated very well to a parameter related to material integrity, called damage, which makes the latter a very good tool to assess pretreatment. It has been observed that very significant reductions in both fracture energy and material integrity were achieved by heating followed by water quenching.
A wide range of advanced technology for existing and emerging products based on high temperature metal-ceramic composites used in aircrafts, cutting tools, lithium-ion based rechargeable batteries, superconductors, field emission based flat-panel displays, etc. employ micron to submicron sized (0.1-10 microns) particulate precursors in their manufacturing process. Although there has been a significant emphasis given to control of the particle characteristics (shape, size, surface chemistry, adsorption, etc.), relatively little or no attention has been paid to concomitant designing desirable surface and bulk properties at the particulate level, which can ultimately lead to enhanced properties of the product. By attaching atomic to nano-sized inorganic, multi-elemental clusters either in discrete or continuous from onto the surface of the core particles, i.e. nano-functionalization of the particulate surface, materials and products with significantly enhanced properties can be obtained. In this paper, we demonstrate for the first time the synthesis of artificially structured, nano-functionalized particulate materials with unique optical, cathodoluminescent, superconducting and electrical properties. In this paper, we show the feasibility of the pulsed laser ablation technique to make very thin, uniformly distributed and discrete coatings in particulate systems so that the properties of the core particles can be suitably modified. Experiments were conducted for laser deposition of Ag nano particles on Al2O3 and SiO2 core particles by pulsed excimer laser (wavelength =248 nm and pulse duration =25 nanosecond) irradiation of a Ag, Y2O3:Eu3+, and TaSi2 sputtering targets. Analytical techniques using scanning electron microscopy (SEM), wavelength dispersive x-ray mapping (WDX) , transmission electron microscopy (TEM) , scanning transmission electron microscopy with z contrast (STEMZ), and photoluminesence (PL) were utilized to examine the structural, chemical, and morphological characteristics of the nanometric coatings. Qualitative surface uniformity measurements by WDX mapping techniques showed a high degree of coating uniformity on the core particulate. Structural TEM and STEMZ imaging showed both continuous and discrete polycrystalline, multiply twinned nano particle coatings ranging from 5-40 nm in thickness.
The main objective of granulation processes is to produce granules with specific physical properties based on the end usage. The numerous disturbances associated with most granulation processes causes significant variations in first pass yield. Development and application of a yield based on-line control strategy is essential to maintaining consistent product quality. This paper highlights the problems associated with, and the need for, the development and online implementation of a yield based control scheme that controls appropriate physical properties of the granules exiting the granulator. A multi-level control scheme using process models of varying complexity is proposed. This paper discusses some of the results from online implementation of a section of this control scheme on a continuous granulation unit.
This paper deals with particle formation by homogeneous nucleation in a system containing seed particles. A model of homogeneous nucleation previously developed by the present authors (Kousaka and Nomura, 1997) is here extended to include the effect of the presence of seed particles. To this end, the cell model upon which the original model was based has been modified to account for the random distribution of the interparticle distances in the medium. Liquid-phase experiments, in which particles have been generated by a chemical reduction method with varying number concentrations of seed particles and generation rates of precursor monomers, have confirmed the validity of the model. The proposed model enables determination of the operating conditions where 1) homogeneous nucleation is predominant, 2) particle growth is predominant, and 3) homogeneous nucleation and particle growth coexist.
†This report was originally printed in Kagaku Kogaku Ronbunshu, 23(5), 673-678 (1997) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Chemical Engineers, Japan.
Fluidized bed granulation is used widely in the manufacturing processes for solid drug products. It is known that optimum granulation conditions are not determined simply by the complexity of the operation factors. This study investigated the effects of manufacturing factors on the physical properties of granules in order to understand the granulation mechanism. Experiment results indicated that granule moisture content determines average particle size. A granulation model is proposed in accordance with a theoretical consideration of the physical properties of granules. The model was found to simulate granule density and bulk density. Also discussed is the scale effect of the experimental apparatus on the physical properties of granules.
†This report was originally printed in J. Soc. Powder Technology, Japan. 34(8), 586-591 (1997) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
We studied coarse particle behavior in a laterally vibrated vessel under microgravity. Vibration conditions were a frequency of 75-150 Hz and a displacement amplitude of 86-310 μm. The two dimensional displacement distribution of particles moving in three dimensions was measured by particle image sampling within the depth of field. Observations revealed a saddle-shaped distribution in which concentration was higher at the center in the lateral direction and the ends in the longitudinal direction. This tendency became distinct with increasing total particle concentration. The round corners of the vessel made the distribution more uniform due to enhanced circulation. We also found that particle concentration increased with velocity amplitude.
†This report was originally printed in J. Soc. Powder Technology, Japan. 34(11), 834-839 (1997) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
The authors investigated a compounding process in which fine WC powder is uniformly dispersed into particulate Ag-Ni alloy with a high-speed elliptical-rotor-type powder mixer. The growth of composite particles is observed as processing time elapses. A model for the growth phenomenon is constructed on the basis of the theory of powder grinding with a ball mill, and of the dynamics of the plastic deformation of metal particles. In the model, a function of the probability that composite particles grow is expressed in terms of three factors that include the compounding conditions as parameters: (1) the probability that particles are caught between a pair of medium balls (zirconia beads), (2) that they have undergone plastic deformation, and (3) the frequency with which the mixture of composite particles and beads is compressed by the elliptical rotor at the minimum clearance per unit time. Temporal change in the size distribution of composite particles has been calculated by using model equations. Comparison of calculated values with the experimental data for particle median diameter shows that they agree closely. It was demonstrated that the model is valid and that it is possible to accurately estimate and control particle size.
†This report was originally printed in J. of Soc. of Powder and Powder Metallurgy, 45(4), 362-367 (1998) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Japan Society of Powder and Powder Metallurgy.
The grinding rate constant is one of the important factors needed to measure or evaluate a grinding process. It has been found that the decreasing rate of the feed size is described by a first-order equation in the initial grinding stage of various mill types. In this study we conducted grinding tests on silica glass using a ball mill, and measured the grinding rate constant of the feed size decrease. We investigated the effects of ball diameter and feed size on the rate constant when the ball mass, feed mass, and the mill's rotational speed were constant. The results indicated that the grinding rate constant can be expressed by modifying the equation that was proposed by Snow as the function of ball diameter and feed size.
†This report was originally printed in J. Soc. Powder Technology, Japan. 35(1), 12-17 (1998) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
The authors propose a new granulation technique employing a spray fluidized bed granulator that directly produces granules from liquid materials. Instant coffee dissolved in water was used as the liquid material. In order to elucidate the agglomeration mechanisms in the granulator, changes in the physical properties of granules were measured at various liquid material feed rates. We proposed an index R that is related to the liquid feed rate and is capable of quantitatively evaluating the conditions of drying in the granulator. Experimental results showed that granule formation depends on the R value in accordance with the following three mechanisms: 1) generation of fine particles by the spray drying effect, 2) agglomeration of fine particles, and 3) layering of fine particles onto the surface of individual agglomerates. Spherical granule products with high bulk density were obtained especially with layering granulation in a stable fluidized bed. Further, an equation derived from the mass balance for coffee solids in the granulator accurately described the growth of granules during layering granulation.
†This report was originally printed in J. Soc. Powder Technology, Japan. 36(5), 368-377 (1999) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.