Recent literature of the past several years has borne out gas fluidisation phenomena of nano-particle beds and assemblies quite unlike the conventional behaviour observed in fluidisation of micron size or larger particles. A review is presented of the recent publications in the field in comparison with more recent studies of nano-particle assembly fluidisation at Surrey University with the use of high resolution and high speed microtomography techniques. These studies support well the previously published observations in incipiently fluidised 2-D and 3-D beds as well as providing further insight into the highly expanding behaviour of dynamic nano-particle clusters observed at fluidisation velocities much in excess of the incipient fluidisation velocity of a packed bed. It has proved possible to explain the observed behaviour of nano-particle agglomerates in incipiently fluidised beds and those expanding dynamic clusters observed in high gas velocities by extending the established framework of the Geldart Classification to sub-micron particle sizes and to immersed bulk densities as low as 100th of the solid density. Further quantification studies are underway to establish the various long and short range force contributions to the observed dynamic force fields of nano-particle assemblies over a wide range of percolating gas velocities.
A brief review of publications that deal with particle image velocimetry (PIV) and particle tracking velocimetry (PTV) is presented first in this paper. It is followed by a brief review of papers that discuss the applications of PIV and PTV to granular flows. Next, the application of PTV to granular flows is demonstrated in the context of an experimental investigation of free-surface flows of almost spherical, slightly polydisperse, ceramic particles immersed in air. Flows of this granular material down the upper inclined surface of a wedge-shaped static pile of the same material, formed naturally and contained in a narrow channel between two parallel vertical glass plates are considered. Some sample results obtained from PTV measurements of these flows in the statistically steady and fully developed region are presented.
Dry powder inhalation (DPI) is an important means of pulmonary drug delivery for both local and systemic actions. Since drugs of different solid-state chemistry can influence a wide range of physical, chemical and biological properties, control of the solid-state structures and associated behaviours of drug particles is critical for DPI formulation. Current production technology of fine drug particles for pulmonary delivery utilizes sequential batch crystallization and micronization. However, this two-step manufacturing approach often causes unwanted crystallographic damage to the particles and may induce undesirable polymorphic transformation in certain materials. In recent years, spray-drying and supercritical fluid crystallization have emerged as two cost-efficient processing technologies that allow more precise control of the crystal forms and physical properties of the powders produced in a single step operation. This article presents a critical review of these latest technological developments in DPI formulation with focus on the regulation of the physical forms of inhaled drug particles.
Solid-liquid separation processes for dispersions of fine particles continue to present significant challenges in many areas. As an example, in filtration it is usually possible to achieve either fast filtration or a dry cake, but rarely both. To achieve both a compact dry cake and rapid filtration will rely upon an increased ability to control the particle network structure of the filter cake throughout the whole process, with a probable requirement being a controlled structural change from the beginning to the end of the filtration. An obvious pre-requisite is a detailed knowledge of how to control the structure of sediment beds during flocculation processes. Recent advances in measurement technology have provided unique insights of the relationship between the mechanism (bridging, depletion, charge neutralisation) and conditions of flocculation and resultant aggregate structures. As a consequence, the link between aggregate structures and sediment bed properties is also being investigated with renewed interest. Clearly, the link between flocculation, aggregate structure and sediment bed is vital in the understanding and control of solid-liquid separation processes. This paper will present a review of recent research linking aggregate formation and characterisation of solid-liquid dispersions to subsequent physical properties of the sediments and filter cakes that they produce.
Nanostructured films find increasing industrial application for instance in membranes, gas sensors, fuel cells, catalytic layers, biocompatible surfaces, batteries, and electronic components. The performance of these functional layers can be improved by using nanoparticles as building blocks and thereby incorporating their extraordinary physical and chemical properties into the three-dimensional film structure.This article presents an overview of recent research on gas-phase methods for the production of such nanostructured films. Nanoparticle synthesis, methods for gas-phase particle manipulation as well as particle deposition are addressed. Emphasis is placed on flame and hot wall reactors for nanoparticle production along with cluster-beam deposition techniques. Means for gas-phase particle size selection and nanoparticle beam formation by expansion nozzles, aerodynamic lenses or electric charging are introduced. It is highlighted how the deposition process can be controlled to yield either highly porous nanostructured films or precisely ordered arrays of 1D, 2D and 3D nanostructures to fabricate microsensors, catalytic microreactors or of semiconductor nanowires.
This paper focuses on the review of research works contributed by Thai researchers over the last two decades. It surveys research works available in domestically issued journals, which are therefore inaccessible to any international database. Based on our survey, the spectrum of researches involving Particle Technology in Thailand covers three major categories which are 1) Fundamental research in particle synthesis and production, 2) Research and development in particle processing and handling, and 3) Research and development in particle application and utilization. It could clearly be seen that fundamental research works have continuously been conducted while there are increasingly strong policies from governmental and funding agencies to encourage Thai researchers to pay more attention to applied research and development because there have been few successful cases of commercialized research outcomes. This is attributable to imperfect linkages among universities, industries and governmental agencies, which still lack a systemic supporting mechanism from the government, thereby resulting in research projects not amenable to commercialization.
A novel particle processor was designed and built for the production of flake-shaped powders. 300 μm magnesium and 140 μm iron particles processed for 1 and 2 minutes were analyzed for dimensional, ductile, and morphological characteristics. Particle diameter distributions tended to broaden towards higher size ranges after 2 minutes of processing; the mean particle size was in the range of 400 μm for magnesium and 300 μm for iron. The flake thickness decreased over time, leading to a mean-thickness of 12 μm for the magnesium particle sample processed with 2 × 6.0 mm milling ball media after 2 minutes. The effect of particle medium showed that the milling operation had greater influences on the more ductile material. Surface morphology also became smoother as the milling time increased. Larger ball media tended to produce samples with larger particle sizes with wider size distributions, while smaller ball media produced smaller particles with narrower size distributions. Loading weights also tended to have similar trends. The novel process was demonstrated as an effective and efficient method for the production of flake-shaped metal particles which greatly reduced the amount of milling time and energy required for flake particle production.
The change in bulk density or solids fraction that occurs when a vessel of granular materials is vibrated is an important, industrially-relevant process. In this paper, we present findings from experiments and discrete element simulations on the relaxation behavior of assemblies of uniform spheres that are vertically oscillated. Physical measurements of the bulk solids fraction, qualitatively reproduced in the simulations, reveal noticeable trends in the data dependent on the vibration amplitude and frequency. By carrying out extended simulations, a ‘phase’ chart depicting the percentage improvement in bulk density in terms of amplitude and frequency is obtained. Our results suggest that the behavior revealed in this chart may be characteristic of density relaxation in bulk solids.
The effects of aeration on the discharge of silos loaded with initially segregated particles have been evaluated. Experiments were carried out on a two-dimensional laboratory-scale aerated silo, loaded according to either ideal or controlled natural segregation patterns. Two different systems of powders made up of two size cuts were tested, one system belonging to group A and the other to group B of the Geldart classification. One of the two cuts was colored to visualize the segregation changes and the solids flow during discharge. Time variations of the discharged solids discharged were evaluated by means of a rotating sample. Results of aerated discharge were compared with mass flow discharge. From analysis of the experimental results, it is possible to conclude that aerated discharges can effectively promote the uniform solids discharge of horizontally segregated solids of group A powders. In contrast, further segregation occurs for aerated discharges of group B powders below the minimum for fluidization.
An overview of three studies on seeded precipitation in a fluidised bed reactor (FBR) is presented. The objective of using the FBR is to remove dissolved metals as precipitated metal salts onto a seed surface. For the nickel hydroxy-carbonate system (S =±105), particle enlargement was found to occur by a combination of growth and aggregation. The concentration of fines correlated with the degree of supersaturation in the reactor, which suggests that fines formation was due to homogenous nucleation, attrition of rough growth precipitate, or a combination of the two. Reducing the local supersaturation by multiplying the feed points was found to be a successful fines control strategy. For the mixed nickel/cobalt sulphide system, (S =±1011 for nickel and ± 1012 for cobalt), a significant quantity of fines was formed but these eventually aggregated onto the seeds. In contrast, for the copper sulphide system(S =±1034), the fines formed immediately but never aggregated onto the seed material and it was not possible to control the supersaturation levels to the extent that fines formation was avoided.
Acoustic and Ultrasonic Methods for Particle Characterisation have many advantages. They are generally non-invasive, can be non-contact, are safe and often are economic. However, it can be difficult to interpret data, and the expertise and commercial equipment necessary may be in short supply and inappropriate to commercial requirements. Nevertheless the potential for these techniques is immense, particularly with regard to the newly emerging field of nanotechnology. A less well-recognised but just as important requirement is the ability to characterise systems on length scales between the molecular and the macroscopic. It is not so well known that acoustics can provide information over a huge range of length scales, from a few nanometres (ultrasound spectrometry) up to geological scales. Commonsense approaches to the understanding of acoustics obscure the potential of the modality. Scattering theory underpins all the theory of acoustic propagation, and adopting this initially theoretical approach indicates a world of new information. At one level particles and structures may be sized, at another their molar compressibility obtained, at another their shape determined. Acoustic methods are complementary to light scattering techniques offering advantages where light scattering does not work? optically opaque systems, mixtures with small refractive index differences, for example. So ultrasound spectrometry is uniquely well-suited to the characterisation of nanoparticle concentrates. In this article the theory of ultrasound propagation is outlined simply for a general audience, emphasising those aspects which provide the greatest potential for adoption of the modality in the particle characterisation community and briefly describing the relevant current commercial and laboratory equipment.
The main objective of this work was the study of the fluidisation behaviour of a glass powder in order to allow its application by electrostatic pulverisation. The high density and the small diameter of the original product lead to bed channelling and slugging. To avoid these inconsistency problems, different fluidisation-aid techniques were experimented with: incorporation of easy-to-fluidise large spherical glass particles into the glass powder, the use of mechanical agitation and the addition of four different types of flow conditioners (or glidants). Four batches containing 1 w/w% of different fluidisation additives (two containing hydrophilic additives and two hydrophobic additives) were tested. Fluidisation additives were Aerosils®, which are nano-sized silica products. The quality of fluidisation was determined by monitoring the pressure drop through the bed during fluidisation experiments at decreasing air velocities. Two sizes of spherical glass particles were used as easy-to-fluidise particles. Nevertheless, the fluidisation was not obtained by means of this technique. Using the stirring system, a better but still poor fluidisation was achieved, although its quality was improved by adding flow conditioners. An insignificant influence of the stirring speed on fluidisation was observed when using the fresh powder or batches containing hydrophilic fluidisation additives. Moreover, the influence of the proportion of additive was tested in six batches containing 0.1, 0.2, 0.3, 0.4, 0.5, and 1 w/w% of the agent, which led to the most satisfactory improvement in fluidisation behaviour of the glass powder.
Flowsheeting program packages are now commonly used in chemical engineering for the design of processes involving fluids. The simulation of processes which involve solids or solids and fluids is not as advanced. In solids processing it is still common practice to design one apparatus separately from the other. There is a lack of suitable methods to combine single apparatus models to form a process and to treat this process as a whole. With the program package ‘SolidSim’, a simulation system especially designed for the simulation of processes including solids has been developed. At the present state of development, modules are available for classification, particle size reduction, crystallisation and dissolution, liquid-solid separation, gas-solid separation, agglomeration, reaction, drying, conveying and different general modules. The structure of the system is explained in detail and the application to a process for the treatment of contaminated sludge is shown.
Recently, many biochemists have identified that chitosan is not rejected by the body and that it can improve the effective and safe delivery of drugs and vaccines with its absorptive power. Also, it has been known that chitosan is suitable for controlled drug release thanks to its advantages of biodegradability and bio-compatibility. As the interest into the extension of human life and personal health has been increased, the pharmaceutical and medical worlds have been making efforts to develop more sustained and effective drug release property in a body. This study investigated the individual drug characteristics and drug release behavior by manufacturing the chitosan patch using insulin, a drug used for treating diabetes, at a low temperature, and further tried to find the optimal condition by adding the skin activating agent to the chitosan patch using NOD (Non Obese Diabetic) mice. According to the analysis using the chitosan-insulin drug and the skin-activating agent, a dramatic decrease in the blood glucose level was achieved. An experiment was performed in vivo by utilizing chitosan nanoparticles as a biopolymer to control the drug delivery rate at an optimal concentration, pH and temperature. It was also observed that the experiment of the drug delivery by nanoparticles containing insulin could effectively lower the blood glucose of the mouse.
We have released a colloid simulator named KAPSEL implemented the “Smoothed Profile (SP) method” which has been developed by ourselves for direct numerical simulations of particulate flow providing a way to couple continuum fluid dynamics with rigid-body dynamics through smoothed profile of colloidal particle. KAPSEL enables us to simulate multi-component fluids, such systems as charged colloids in electrolyte solutions. Dynamics of colloidal dispersions is solved as much computational cost as required for solving non-particulate flows. KAPSEL computes the fluid velocity and the electrostatics potential by solving both Navier–Stokes and Poisson equations directly. The time evolutions of the colloidal particles and the density of counter ions are then determined by solving Newton’s equation of motion and advection-diffusion equation, respectively, in a consistent manner so that the electro-hydrodynamic coupling can be fully taken into account. The electrophoretic mobility of spherical colloidal particles is calculated in several situations including those in concentrated dispersions. The comparisons with theories show excellent quantitative agreements.
Effects of NaOH concentration on the crystal structure and the reaction rate of the zeolite synthesized from fly ash with a hydrothermal treatment method was investigated. The fly ash or the mixture of fly ash and silica powder was hydrothermal treated using NaOH aqueous solutions of various concentrations. As a result, a decrease in the NaOH concentration raises the selectivity of phillipsite to the generated zeolite, and lessens that of hydroxysodalite. The reaction rates of them increase consistently with the NaOH concentration. It is clarified that the dependence of crystal structure of generated zeolite on NaOH concentration is not only induced by the dependence of the dissolution rates of silicate ion and aluminate ion from fly ash on it. The fraction of additive silica powder required to synthesize phillipsite selectively increases with increase in the NaOH concentration, and the required treatment time decreases with it.
†This report was originally printed in J. Soc. Powder Technology, Japan, 40, 497-504 (2003) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
This paper presents the effect of frictional force between colloidal particles and a solid substrate on the formation of particle monolayer by a numerical simulation. Discrete Element Method is employed to simulate the dynamics of colloidal particles trapped in liquid film. Forces such as capillary immersion force, van der Waals force and frictional force are included in the simulation model. Isotropic ordering factor and non-dimensional boundary length are introduced to quantify the structures of colloidal particles. In the case where the diameter of colloidal particles ranges from 100nm to 1000nm, the monolayer structures depend strongly on the frictional constant between a particle and a solid substrate. On the other hand, in the case where diameter is about 10nm, large domains of hexagonal close-packed structures are formed because of the Brownian force.
†This report was originally printed in J. Soc. Powder Technology, Japan, 41, 465-472 (2004) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
For crystallization in solution, the method of changing particle shape by adding the impurities called habit modifiers has been attracted attention as a fabrication process of functional particles. The method is complicated due to many controlling parameters, such as supersaturation, concentration, kinds of impurities, etc. It needs to clarify the mechanism of crystal growth for the control of crystal shape. Therefore, the influence of impurities on crystal growth has been examined by experiments and simulations. In the experiment, the technique by differential scanning calorimeter (DSC) was used for measuring the properties of clusters with changing the habit modifiers. In adding habit modifiers, the number of clusters increased. The formation of clusters was investigated by molecular dynamics (MD) simulation. This simulation result agreed with the experiment result and then the formation of clusters which assembled remarkably around impurities was demonstrated by simulation.
†This report was originally printed in J. Soc. Powder Technology, Japan, 41, 431-439(2004) before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
The effect of liquid additives such as alcohol and glycol on the ultrafine grinding of limestone was investigated by using a vibration rod mill. Liquid additives used in the present work were three alcohols and two glycols with different alkyl groups. The experiments were carried out by a batch operation, and the change in specific surface area of limestone with grinding time was measured by BET adsorption method. The behavior of methanol molecules added as an additive was traced by monitoring the temperature and pressure in the grinding pot during grinding. The results showed that alcohols and glycols promote the ultrafine grinding of limestone, and that the maximum specific surface area of limestone obtained with additives is proportional to the amount of the additive. The stepwise addition of a small amount of additive was more effective rather than adding the whole amount at once in increasing the grinding rate of limestone. It was also found that the degradation of crystal structure of limestone was controlled by the addition of alcohol. The grinding status of limestone could be traced by monitoring the temperature in the grinding pot, and the measurement of pressure change in grinding pot revealed that the additive molecules are chemisorbed on fresh surface of limestone created by the grinding.
†This report was originally printed in J. Soc. Powder Technology, Japan, 42, 178-184 (2005) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
Carbon microcoils (CMCs) have an interesting 3D-helical/spiral form with a coil diameter of micrometer orders and a coil length of mm orders. Pulverized CMCs are generally embedded into polymer matrix to form CMC/polymer composites for various applications. The CMCs are very interested as a possible candidate for electromagnetic absorbers, remote microwave heating elements, microwave visualization materials, tactile and nearness sensors, chiral catalyst, etc. In this review, the preparation conditions, morphology, some properties and possible applications of the CMCs are briefly introduced.
†This report was originally printed in J. Soc. Powder Technology, Japan, 42, 715-720 (2005) in Japanese, before being translated into English by KONA Editorial committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.