The nanoparticle technology, relating to the preparation, characterization, processing, and applications of nano-sized particles, plays an increasingly important role in the emerging nano-technology. Although the nanoparticles have many unique functional properties superior to the coarser particles, they also suffer from dispersion and stability problems because of their strong cohesiveness and high specific surface areas. To make the best use of nanoparticles and solve their application problems, the development of nanomaterial processing techniques is essential. New chemical synthesis methods for producing nano-sized oxides particles in the gas phase and producing biocompatible polymeric nano-composite particles in the solution phase were elucidated in the paper. In addition, mechanical breakdown method (e.g. nano-grinding) was briefly discussed. Furthermore, newly developed dry particle processing systems for making high performance nanocomposites as well as their applications in Fuel Cells, Drug Delivery Systems, and Cosmetics were introduced.
We review models and numerical methods used in flame synthesis of organic and inorganic nanoparticles. We discuss a general model in which particles form in the gas phase and grow through mass-adding surface reactions, condensation, and coagulation. They shrink or reshape by sintering and mass-abstracting surface reactions. The model is formulated in terms of a population balance which can incorporate a range of levels of detail, i.e. a varying number of internal coordinates. These coordinates can not only describe the geometry of a particle but also its chemical composition or age. In the simplest version a particle is modelled as a sphere whereas in the most complicated form a particle is modelled as an agglomerate of smaller or primary particles where the geometrical shape is known exactly. For these population balance models a number of different numerical approaches exist. We review the method of moments, sectional, finite element, and Monte Carlo methods and give examples of their applications in flame synthesis. Different strategies for coupling a population balance to laminar and turbulent flows are reviewed. For turbulent flows the closure problems arising from chemical reactions and the population balance are briefly discussed. We then summarize the literature on nanoparticle modelling from laboratory to industrial scale and highlight important areas for future research.
The majority of drug products are solid dosage forms, most of which contain the drug substance in the crystalline state. This review considers the forces responsible for crystal packing, the various types of pharmaceutical crystals, and the methods used to determine the structure of pharmaceutical crystals. These topics provide background for the main thrust, which focuses on the importance of studying the structure of pharmaceutical crystals with particular stress on phase changes of crystal forms of drugs during pharmaceutical processing and implications of different solid forms of drugs on its mechanical properties. The present review does not consider pharmaceutical co-crystals, which could be the subject of another review.
Gas-solid flow systems are found in many industrial applications such as catalytic reactions, pneumatic conveying, granulation, crystallisation, mineral classification, etc. The operational hydrodynamics can vary depending on the operation method from fast dilute flow, which is dominated by collisional particle-particle contacts, to dense slow flow, which is dominated by sustained frictional contacts. For many years, the former has been successfully modelled using the classic kinetic theory for granular flow, while the latter has been modelled based on soil mechanics principles. At the intermediate-dense regime, three different modelling approaches are identified: (1) the kinetic-frictional model using an ad hoc patching together of the stress from the two limiting regimes at a specific solid fraction (Johnson and Jackson, 1978; Ocone et al., 1993; Syamlal et al., 1993); (2) the switching from one regime to another using different solid stress formulations (Laux, 1998; Makkawi and Ocone, 2005); and (3) the new emerging fluid mechanic approach which allows for a smooth transition from one regime to another using a unified model (Tardos et al., 2003, Savage, 1998). In this study, a one-dimensional fully developed gas-solid flow model for horizontal flow will be used to review the various treatments of solid stresses, and the sensitivity of the flow predictions to the frictional stress will be assessed.
On August 13, 2003, the Cabinet of Thailand approved the setup of National Nanotechnology Center (NANOTEC) under National Science and Technology Development Agency (NSTDA), Ministry of Science and Technology (MOST). One of its urgent tasks is the preparation of the 10-year National Strategic Framework in Nanotechnology for submission to the Cabinet via the recently established National Nanotechnology Policy Committee. The task and framework are in line with the National Strategic Framework in Science and Technology approved by the Cabinet in 2004. What follow is an overview of the recent status and development of nanotechnology in Thailand and a brief introduction of the Nanotechnology Framework, including the R&D direction and human resources development (HRD) of Thailand.
Organic crystals grown from solution are known to exhibit multiple morphology as well as habits which are of great importance to the end-use property of the product such as the bioavailability and the downstream processing such as in filtration and drying. The crystal morphology can also dictate other quality measures such as the size. Compared with the great amount of research work that has been done on the on-line measurement of other quality measures such as the size and concentration using various spectroscopy techniques, the literature on the on-line measurement and manipulation of crystal morphology is scarce. Attempts were made in the past to use laser diffraction and ultrasound spectrometry for shape monitoring. These methods have not proved to be very successful due to the difficulty in extracting detailed shape information from the signals corrupted by noise and multiple scattering. In this paper, we describe a new approach for on-line crystal morphology measurement and control which is based on the integration of online imaging, multi-scale image analysis and crystal morphology modelling, and present the results obtained on applying the approach to the batch crystallisation of (L)-glutamic acid. Online imaging proved capable of capturing high fidelity crystal shapes and polymorphic transitions in real time. A multi-scale image analysis method was proposed to extract the crystals from the image background and to calculate shape descriptors which were then used for shape recognition and to derive monitoring charts showing the ratios of different polymorphs in real time as well as the relative average growth rates of facets of crystals. Calculating crystal growth rates and estimating kinetics parameters for needle-shaped crystals was also investigated. Finally, a methodology called ‘camera model’ for integrating on-line imaging and crystal morphology modelling was presented.
The potential of inorganic polymeric materials – silica aerogels – as tailor-made drug carriers is discussed. It is shown that the dissolution rate of poorly soluble drugs can be significantly changed through the adsorption on silica aerogels. Adsorption takes place in supercritical CO2 and allows distribution of the drugs inside the aerogel matrix on the molecular level. The drug concentration in the aerogel is explicitly determined by the temperature, bulk concentration of the drug in the supercritical phase and the properties of the aerogel (density, pore size distribution and surface area). The release rate of the drug depends on the hydrophobicity of the aerogel. In the case of hydrophilic aerogels, an extremely fast release – even compared with nanocrystals – of drugs is achieved, which is especially advantageous for poorly water-soluble drugs. Hydrophobic aerogels exhibit a slower release which is governed by diffusion. In addition, the possibility of generating organic microparticles inside the pores of the aerogels by precipitation from supercritical solutions is discussed.
In this work we demonstrate that it is possible to create new optical and magnetic materials based on metal-containing nanoparticles stabilized on the surface of polytetrafluoroethylene (PTFE) nanogranules. The magnetic and optical properties of these materials have been investigated. The materials were prepared by a method of thermal decomposition of metal compounds in the heated polytetrafluoroethylene-oil system. Transmission electron microscopy data show that the diameter of the particles is 3–6 nm. Magnetic studies show that for the obtained nanoparticles, the blocking temperature and the magnetic anisotropy is highest for homometallic nanoparticles; this fact makes it promising material for the different magnetic applications. The optical properties of nanomaterials CdS/nanogranules of PTFE are specified. The size and core-shell structure of the nanomaterials has been confirmed by TEM and X-ray diffraction.
The aim of the study was to investigate the specific influence of force control agents (FCAs) (leucine, lecithin and magnesium stearate) on the interfacial properties of a salbutamol sulphate-lactose dry powder inhaler formulation. The influence of FCAs on the cohesive and adhesive force balance was directly assessed via an atomic force microscopy (AFM) colloid probe technique, with a recently developed cohesive-adhesive balance (CAB) graphical analysis procedure. Co-processing of constituent particles was conducted by a novel dry mechanical fusion method (Mechanofusion). The in vitro deposition profile of the model salbutamol sulphate formulations was investigated using a Monohaler® DPI device with a next generation impactor (NGI) apparatus. The CAB-graph analysis of a salbutamol sulphate-lactose binary system suggested a predisposition for an interactive mixture. However, the reduced intermixing coefficient (Fdrug-lactose/Fdrug-drug) suggested that a significant amount of energy would be required to overcome the strong adhesive interaction for efficient dispersion of the drug from a lactose surface. The processing of lactose with leucine, lecithin or magnesium stearate, prior to formulating with the drug, significantly reduced the adhesive interactions of the salbutamol with modified lactose samples. The CAB analyses indicated that the reduced intermixing coefficients shifted to such an extent that cohesive drug interactions dominated. These dramatic shifts in the balance of forces were shown to lead to poor blend homogeneity and potential for significant segregation between drug and carrier particles. Conversely, the conditioning of salbutamol sulphate with leucine, lecithin and magnesium stearate, which modified both the adhesive and cohesive interactions, formed homogenous interactive blends with advantageously weaker drug-lactose interactions. Formulations with pre-conditioned drug, in contrast to conditioned lactose, offered the best drug delivery performances. The use of the colloid AFM technique in combination with the cohesive-adhesive balance (CAB) approach provided a very accurate means of predicting dry powder formulation behaviour and the specific influence of particulate interactions on aerosol performance.
This article describes the research leading to the development of a new process for flotation deinking of waste paper, including old newsprint (ONP), magazines, etc. The technique involves a simple reagent scheme (ammonium hydroxide or sodium bicarbonate) that can be used at room temperature to generate fine bubbles at the ink/fiber/water interface that help in the ink particle detachment as well as in rendering ink particles hydrophobic. The reagents also act on desorbing organic species (oil) from oil-based ink, thereby stabilizing the bubbles. A self-aeration flotation machine could be used to enhance flotation kinetics. Experimental studies have been conducted to evaluate different operating conditions, including reagent dosage, flotation time, recycling flotation water, etc. The efficiency of the process is evaluated in terms of yield of clean pulp, brightness, and reagent consumption.
Abrasive powders are used in fine grinding and polishing applications many of which require defect-free surfaces. Scratching is a primary defect that can be caused by very low levels (less than 10 ppm) of large, oversize particles in the powders. Powders containing low levels of oversize particles can escape the scrutiny of quality control efforts because particle size analysis techniques have detection and sensing limits that prevent detection and quantification. This paper describes several common size analysis techniques with special regard to the limits of detecting oversize particles. Recommendations are described for measuring and quantifying low levels of oversize particles in powder size ranges of greater than and less than 10 microns.
On-board hydrogen storage is an important obstacle to the development of a sustainable, ultra-low emission transportation system. A dry particle coating technique was used to coat micron-sized magnesium powders with Ni nanoparticles for hydrogen storage. Three parameters were explored in this study: powder size, nickel loading, and processing time. The composite materials were evaluated based upon a number of criteria, including the degree to which the nanoparticles were distributed over the Mg surface, the improvement in kinetics for hydrogen absorption, and the increased amount of hydrogen absorbed and desorbed. Comparisons were made between the bulk Mg powders and those coated with Ni. Due to the high shear forces it created, the dry particle coating system effectively distributed Ni nanoparticles onto the Mg powder surface. A coating process that required 48 hours using traditional ball milling was reduced to 90 minutes with the dry particle coating system. Magnesium powder with a mean diameter of 44 microns and a nickel loading of 2 atomic weight percent was the most kinetically active for hydrogen absorption under the conditions studied. Hydrogen absorption began at 150°C, and desorption started at 250°C. The dry particle coating system, however, did not alter the magnesium microstructure during 90 minutes of processing and did not produce the large surface areas generated by ball milling.
Modeling of Mechanical Alloying (MA), which is a solid-state powder processing technique, is carried out by examining one widely used laboratory scale milling device, the SPEX 8000 shaker mill. It is a vibratory mill; its vial is agitated at a high frequency in a complex cycle that involves motion in three orthogonal directions. In this work, a popular dynamic simulation technique, Discrete Element Modeling, is applied to examine dynamics of a SPEX 8000 shaker ball mill based on the movement of milling balls. The computational results for energy dissipation rate inside the mill are calculated for different ball sizes and varied total ball to powder mass ratios (charge ratios). The computational results are well correlated with the experimental results tracking milling dose (used to define the degree of milling) as a function of ball sizes and charge ratios. Moreover, the numerical (theoretical) milling dose that correlates well with its experimental analog was found to depend on the energy dissipation rate of the head-on ball collisions. The numerical simulations also indicated that the milling progress is most significantly affected by milling media collisions with the energy within a specific threshold, while the collisions with smaller and greater energies are less effective. Finally, discussion shows how this novel approach of correlating specific scaling terms between experiments and simulations can be applied to other powder processing equipment.
Constrained sintering of a substrate with a sandwich structure, which was the laminated inner-constraining alumina layer between the glass-alumina mixed layers, has been studied. The influence of specific surface area of the particles and porosity of inner constraining particle layer upon sintering shrinkage was investigated. Specific surface area of the alumina powder for the inner constraining particle layer could be changed by grinding and blending two different particle size powders. As for the debinded sheet used with ground alumina powder, the pore distribution was sharp, and the bending strength was proportional to the specific surface area. In the case of inner constraining particle layer used with ground alumina powder, penetration length of molten glass from glass-alumina mixed layers obeyed Kozeney-Carman’s equation. On the other hand, as for the debinded sheet with particle size blended powder, the effects of specific surface area on the bending strength and the penetration length of molten glass differed from the results of the grounded one. Sintering shrinkage in X-Y direction of the sandwich substrate was basically related to the bending strength of debinded alumina powder sheet for inner constraining particle layer in both cases.
†This report was originally printed in J. Soc. Powder Technology, Japan, 41, 730-737 (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.
Size classification of ultrafine particles is one of the most difficult techniques in materials processing. We developed a novel ultrafine particle classification method based on heterocoagulation phenomena of colloidal particle. In this paper, rapid size classification of silica particles (median diameters of 100nm and 300nm) from their mixed suspension was examined in various solution chemistries by column bed packed with ferro-nickel slag (FS) as a fibrous collector medium. Many of 100nm-silica particles selectively attached to the FS surface during passing through the FS-packed column, while 300nm-silica remained in an outlet suspension. Newton’s efficiency depended on pH and ionic strength; optimal classification was attained at pH3.5 in 10mM KNO3. These results were qualitatively explained by DLVO-type interaction energy curve, indicating that interfacial interaction of both particle and collector determined the classification efficiency. Furthermore, particle concentration and superficial velocity had an influence on classification efficiency. This method proved to be simple, rapid and cost-effective for classifying ultrafine particles in aqueous media.
†This report was originally printed in J. Soc. Powder Technology, Japan, 39, 175-182 (2002) 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 discrete element method (DEM) takes enormous calculation time because it requires a very small time step, one small enough to represent the large frequency in the contact dynamic model. In general, the equations of motion of particles are solved using the second-order Adams-Bashforth method, which estimates the values of contact force in the following calculation time by linear extrapolation, or by multi-step methods such as the predictor-corrector method. Inspired by these two conventional methods, we propose a Contact Force Prediction Method that makes a larger time step possible. Our method uses the predicted values of contact force at every contact point, which are exact solutions or numerical solutions of differential equations that represent two particle contacts. It has been confirmed experimentally that the proposed method gives reasonable results of packing and discharge simulations, and accelerates DEM calculation 3–8 times.
†This report was originally printed in J. Soc. Powder Technology, Japan, 40, 236-245 (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 study investigates the development of new technology for particle transportation in pipes with cyclic pressure waves. The flow is not steady because progressive and reflective pressure waves do exist in pipes and as a result, the flow in pipes is a pulsating one. The particles are continuously supplied into a horizontal pipe and are transported by the cyclic pressure waves. In this experiment, the loading ratio corresponds to a general high-pressure force feed system, and as a result the main flow pattern is plug flow. The properties of the plug are clarified by measuring the characteristic length and velocity of the plug, and the mean number of pressure waves between successive plug passages. Then, the properties of particle transportation are explained using the calculated apparent loading ratio.
†This report was originally printed in Japanese J. Multiphase Flow, 17, 276-284 (2003) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Society of Multiphase Flow.
Among photo-functionalized materials, photocatalysts in particular have been researched and developed by many researchers in various fields. After the discovery of the Honda-Fujishima effect, their effectiveness became apparent, not only in water decomposition but also in sanitation and purification of the environment, for example, through antibacterial, self-cleaning, and deodorizing effects as well as NOx removal. Recently, novel nano-size photocatalysts, with performance superior to that of conventional types, have been developed, and examples include nitrogen-doped photocatalysts responsive to visible light and brookite-type photocatalysts with higher photocatalytic activity. Moreover, when applying a photocatalyst, it must be fixed to a substrate and blocking of the latter avoided. When photocatalysts with high photocatalytic performance are fixed to plastics, papers and textiles, the substrate can be decomposed and may be prone to peel off when exposed to irradiation with light, owing to the oxidation action of the photocatalysts. To prevent damage to the substrate resulting from photocatalytic oxidation, we have developed a photocatalyst whose particles are coated with inorganic compounds that can be blended with organic substances.
†This report was originally printed in J. Soc. Powder Technology, Japan, 41, 750-756 (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.