Dry powder inhalers may be employed for the delivery of drugs to the lungs for the treatment of pulmonary and systemic diseases. Dry powder inhalers consist of a formulation, metering system and delivery device. The formulation consists of small drug particles (median aerodynamic diameter < 5 μm) usually combined with large excipient particles (30-125 μm). The physico-chemical properties of particles influence flow, fluidization and dispersion. An aerosol is passively inhaled by means of the inspiratory effort of the patient. Active devices use independent energy sources to deliver the aerosol. The aerodynamic particle size of an aerosol significantly effects lung deposition. Inertial deposition of particles, as a function of their aerodynamic diameter, allows measurement of the drug mass in a specific size range. The fine particle dose, or fine particle fraction (FPF) of the metered dose, is the simplest expression of the aerosol particle size. Passive inhalers have been reported to administer up to 50% FPF and active inhalers up to 70% FPF. The criteria for optimal inhaler performance must be defined to facilitate the rapid growth in research and development in this field.

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This review describes the modification of fine particles by the formation of an inorganic coating. It shows how a technology, which has been developed in, but mainly confined to, the titanium dioxide pigment industry, has considerable potential in other areas. Inorganic coatings may be used to encapsulate a solid or modify its dispersion properties. They may also be used to impart desired properties, e.g. electrical conductivity or to obtain specific optical effects. In ceramics, inorganic coatings offer a way of distributing minor components, such as stabilisers for zirconia or toughening agents for alumina, in a way that does not depend on the vagaries of mixing. Examples of different coating procedures are presented, and for two of these – dense silica and silica-alumina – the mechanism is briefly described. The uses and limitations of gas adsorption, electron microscopy, electrophoresis, ESCA and SIMS for coatings characterisation are summarised. It is shown that each is useful for coating characterisation but none can unambiguously differentiate between uniform and patchy coating. Finally, specific examples of improved dispersion, improved barrier performance and beneficial powder properties are presented.

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The paper deals with the design and operation of cooling and evaporation crystallizers and precipitators for reaction crystallization. It will be shown that the median crystal size L₅₀ of a crystalline product and the Crystal Size Distribution (CSD) mainly depend on the crystallization kinetics, e.g. the rates of nucleation and crystal growth, and that this kinetics is controlled by supersaturation. Therefore, the main objective in crystallization and precipitation is to choose and to maintain the optimal supersaturation with respect to product quality at all times and all locations in the crystallizer or precipitator.

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Particle characteristics affect porosity mainly via three factors: dimensionless particle size distribution, particle shape and absolute particle size, giving various packing systems from the simple coarse spherical particle packing to the complicated fine and nonspherical particle packing. Consequently, the modelling of the relationship between porosity and particle characteristics may be carried out by considering these three factors, either successively or simultaneously. This paper presents a review of the work in this area since the early 1980s. The dependence of porosity on particle size, shape and their distributions is examined from typical examples for different packing systems. The need for further development is also discussed.

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Aerosol research in Korea started in the beginning of 1970's in various fields of hygiene, air pollution control, inhalation toxicology, atmospheric physics, clean room and powder manufacturing. The first aerosol related association in Korea was established in 1984 under the name of Subcommittee of Powder Technology (SCPT) of the Korea Institute of Chemical Engineers (KIChE).
The aerosol science research has grown continuously with various application fields in science and engineering. The importance of the aerosol science was recognized in newer technology fields such as clean room for semi-conductor, manufacturing for material science, and combustion for diesel engines in 1980's. The Korean Association for Particle and Aerosol Research (KAPAR) was founded in September 1994 with various background of aerosol science researches. The main purpose of KAPAR is to exchange the knowledge of aerosol science and let public recognize the importance of particle technologies.
The KAPAR started to promote the aerosol research through advancing the arts and sciences in the fields of aerosol science and particle technology with various science and engineers backgrounds. In four years, KAPAR has more than 200 individual members of scientists and engineers from research institutions, universities and private companies. These two associations of SCPT and KAPAR promote mutual understanding and technology exchange.

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This paper reviews methods of producing particles using supercritical fluids. First it explains the properties of supercritical fluids, phase behaviors of supercritical solutions, and reaction equilibrium and reaction rate in supercritical fluids. Next it explains the principles of new crystallization methods using supercritical fluids. These explanations cover the RESS method, GAS method, retrogressive crystallization, supercritical drying, and hydrothermal synthesis in SCW. The use of rapid expansion of supercritical solutions (RESS) through a nozzle obtains extremely high supersaturation, which brings about rapid nucleation.
This leads to the formation of ultrafine particles. Changing the expansion conditions allows one to control particle morphology and size. Using two nozzles makes it possible to coat particles with other materials. Supercritical CO₂ can be used as an antisolvent. This gas anti-solvent (GAS) method is used to recrystallize the solute, which is thermally or chemically unstable. The solubility of a solute in a supercritical fluid is largely dependent on temperature and pressure, and this temperature and pressure dependence differs from one substance to another. Thus, manipulating temperature makes it possible to precipitate only one solute from a mixture solution. This method is called retrogressive crystallization. Supercritical fluid extraction can be used for drying particles. Using this method eliminates capillary force among particles because there is no gas-liquid interface during drying, thereby inhibiting particle coagulation. Hydrothermal synthesis in supercritical water is an attractive method for producing metal oxide fine particles while controlling particle size, morphology, and crystal structure. Since SCW is miscible with O₂, H₂, or CO gas, these gases can be used to control the oxidizing or reducing atmosphere. The reaction equilibrium for hydrothermal reactions varies greatly around the critical point by slightly varying pressure and/or temperature, which brings about change in the morphology of the produced particles. This paper also considers the possibilities of creating new powder processing processes.

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Coercivity in hexa-ferrite magnets originates in the magnetic behavior of so-called "single domain particles" with uniaxial magneto-crystalline anisotropy. The critical diameter, below which a single domain is stable, is estimated at around 1 micrometer (10^-6 m) for M-type Sr-ferrite, which means that control of grain size to under a micron is significant for achieving high coercivity. For this reason studies were performed on a process for obtaining submicron powder and sintered grains, as well as on techniques for obtaining high orientation under magnetic fields when using submicron powder. For analytical purposes, Particle size distribution, magnetic properties, and lattice defects of Sr-ferrite particles were investigated to explain the observed behavior.

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We describe experimental observations of slugging bed dynamics with passive acoustic sensors. Our results indicate that acoustic signals contain both similar and complementary information relative to dynamic pressure signals. We find that selective preprocessing of acoustic signals is a key step in separating information about microscale and macroscale processes. With such preprocessing, both linear and nonlinear dynamical features are apparent. Nonlinear features appear to be especially useful for practical diagnostics.

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The authors describe their experience with organic binders in pelletization plant. It started with carboxi-methyl-cellulose and hematite concentrates. The addition of sodium tri-poli-phosphate (TPP) was demonstrated to be essential. In pelletizing limestone fines, it has been shown to be possible to use dispersants like soda ash, for this particular case, it was possible to make use of no binder and to work only with the dispersant. This fact has been understood as a consequence of the dispersing effect of the chemicals. To check this hypothesis, a set of different kinds of organic dispersants were prepared to test on pellet feed, with the interesting results described herein.
The conclusion is a model for the behaviour of these binders as: 1 – the dispersion of colloidal particles on the surface of the particles to pelletise increases the viscosity in the liquid film between the particles, and 2 – it provides the physical way to link then by bridging. As a practical consequence, in principle, any dispersant may become the binder for pelletization and there is potential to achieve greater mechanical values than by using the conventional binders, bentonite and lime.

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Phase Doppler technique is a non-intrusive optical device for in-situ measurement of single particles. In the case of an irregular particle, it provides a deterministic measure of particle velocity and statistical information about the particle size in the form of a phase shift signal. By collecting sufficient signals, velocity-resolved particle size distributions can be reconstructed. This is demonstrated by comparing phase Doppler measurements of irregular particles with an aerodynamic particle sizer. Preliminary measurements in a crystallizer are also presented. The present device is shown to work with near back-scatter collection of scattered light; hence, leads to a robust setup that can be used under the conditions of limited optical access.

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The filling of particulate material into confined spaces such as dies (typical volume a few cubic centimeters) presents problems that affect the quality of the final product. Some researchers have studied the effects of filling method on fundamental particulate, properties, and load distribution in large storage systems such as bins and silos. However, there is a lack of quantitative analysis of the process of deposition of particulates into small storage systems such as dies. A low-cost tester capable of acquiring real-time data has been developed for experimental analysis of the process of filling of dies. A literature review and preliminary study of the effect of die filling methods (funnel fill and sieve fill) impact on spatial fill distribution (for spray-dried Alumina) in a cylindrical die have been carried out. Cumulative mass profile plots show that the load cells record a flatter profile in the case of sieve fill than the funnel fill case. This suggests a more uniform powder fill for the sieve filling method compared to the funnel fill method.

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The effect of an ultrasonic field on the precipitation process of barium sulphate has been investigated. Experiments in a semi-batch precipitator showed that small crystal sizes with narrow distribution are obtained with ultrasound in a very reproducible way; however, this effect could not be assigned to an improvement in micromixing.
Experiments on continuous precipitation of barium sulphate in two reactors in series were carried out in order to characterise the effect of ultrasound on precipitation, by separating the nucleation and growth processes. It was concluded that the main effect of ultrasound is an enhancement of secondary contact nucleation by acoustic cavitation.
This change in the precipitation process allows small crystals with uniform size and shape to be obtained without effect of mechanical mixing. It is only necessary to sonicate the mixing volume of the reactants with a low level of ultrasonic power: this is very promising for industrial applications.

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Acoustic chemometrics is an interdisciplinary approach covering diverse fields including applied engineering, electronics, signal analysis and chemometrics. The applications of acoustic chemometrics are manifold, but quantitative analysis (chemical/physical) and process monitoring and physical characterisation of products are areas in which it can be beneficially used. Potential applications in many industry sectors abound. In one particular sense, acoustic chemometrics is simple: Acoustic signals from any process or equipment, followed by some form of pertinent signal analysis, are subjected to chemometric data analysis. In this context it is often the power of multivariate calibration that comes to the fore. Here, we give one major example of the use of applied acoustic chemometrics – non-invasive monitoring of a pneumatic transport line. Noise and acoustics have been defined as follows: noise – Irregular fluctuations accompanying, but not relevant to, a transmitted signal (Concise Oxford Dictionary), acoustics – science of sound (Scribner Bantam Dictionary). The irregular fluctuations referred to above contain much valuable information, and it is the line acquisition, conditioning and analysis of such fluctuations that we are concerned with in this paper.

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The paper summarises recent developments of the Euler/Lagrange approach for the prediction of particulate two-phase flows. Based on detailed experiments, the modelling of particle-wall collisions, including the effect of wall roughness, could be considerably improved. Moreover, a stochastic approach was developed for modelling inter-particle collisions which were found to be quite important even for low particle mass loading. Model calculations with inter-particle collisions were validated based on large eddy simulations for a homogeneous isotropic turbulence field. The effect of inter-particle collisions on the development of a particle-laden horizontal channel flow was analysed in detail by varying particle size and mass loading. Numerical predictions were performed for pneumatic conveying in a horizontal pipe and compared with measurements by phase-Doppler anemometry in order to further validate the developed models.

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Two different optical methods for the determination of particle size distributions in the nanometer range are described. One method uses the scattering of polarized light at different angles and applies a regularized inversion algorithm and is applicable for arbitrary materials. In the other method, light-absorbing particles are heated by a short laser pulse up to evaporation temperature, and the temperature of the particles is determined by the measurement of the thermal radiation. This method has been applied since many years; the detailed analysis, however, shows that one has to be careful with interpretation of the measured data.

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The electrification of fine particles in a gas-solids pipe flow is investigated theoretically and experimentally. Flowing particles are charged through their collisions with a pipe wall. When a part of the pipe is electrically isolated and grounded, the charge transferred from the particles to the wall is detected as an electric current from the wall. The current generated and the electric charge of fine particles (fly-ash: Dp₅₀=3.4 and 12 μm) and relatively large particles (quartz sand: Dp₅₀=320 μm) are measured. The relationship between the current per unit powder flow rate I/W_p and charge-to-mass ratio (q/m_p)₀ is represented by a linear equation irrespective of particle diameter as long as the mass flow ratio is below 0.0058. However, the absolute value of l/W_p of fine particles decreases with increasing mass flow ratio m when m exceeds 0.011. It is found that the current I/W_p is represented by a quadratic equation of (q/m_p)₀. The fact is readily explained by introducing the concept of electrification efficiency.

^† This report was originally printed in J. Soc. Powder Technology, Japan. 34(2), 91-96 (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.

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The electrostatic force between a uniformly charged dielectric particle and a conducting plane was carefully calculated including the effect of higher-order polarizations. The potential distribution problem was solved using spherical coordinates by considering the symmetry of the image and using a re-expansion technique of the Legendre functions. On the basis of the results, the electrostatic force was calculated using the orthogonality of the Legendre terms. In this method, numerical calculations are required for each condition, such as the contact gaps and the dielectric constants of the particle. This would be avoidable if an approximate formula was available. Thus, for convenience, an approximate formula was searched for by trial and error, and F_e=F_e(d=0)/{1 + (d/a) ^α}^β was found to be a good approximation. This was the simple expansion of the contact gap dependence of the particle with a relative dielectric constant ε = 1, i. e., with no effect of polarization.

^† This report was originally printed in J. Soc. Powder Technology, Japan. 34(3), 154-159 (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.

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To ascertain the stress inside silos we developed several kinds of sensors with specific applications: (1) pressure cells, (2) two-directional stress cells, (3) slipping velocity detectors, (4) surface temperature detectors, and (5) internal temperature and slipping velocity detectors.
The detecting sections of pressure cells and two-directional stress cells comprise a parallel plate structure and strain gauges that can detect pressure, and pressure and frictional stress, respectively.
Measurements of physical phenomena in silos lead to the following conclusions: Pressure cells and two-directional stress cells (1) work as designed, and (2) they are capable of elucidating the fundamental physical phenomena in silos.

^† This report was originally printed in J. Soc. Powder Technology, Japan. 34(5), 312-323 (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.

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A new granulation method by a tumbling fluidized bed granulator equipped with opposed pulsed air-jet assembly applied to produce the microgranules having the size distribution in less than 100μm region was investigated. Powdered remedy material, consisting of diclofenac sodium as the main component was microgranulated by the granulator to investigate the effects of the pulsed air-jet on the microgranule properties, and also discuss its growth model. It was confirmed that the microgranules produced by the new method have not only the smaller granule size but the remarkably larger surface area, better solubility and higher compressibility compared with those of the granules made by conventional tumbling fluidized bed granulation. The microgranule growth mechanism was characterized by the following three steps. The first step was the formation process of smaller granules by the agglomeration of feed particles. The smaller granule size depended on the spray mist size. The next step was the successive coating process of the smaller granules. The final was the coalescence of the smaller granules into final microgranules.

^† This report was originally printed in J. Soc. Powder Technology, Japan. 35(4), 256-264 (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.

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