The use of seawater in mining/metallurgical operations seems to be the only sustainable solution in many zones with limited resources of fresh water. This requires new flotation technologies for processes which are to be carried out in highly concentrated electrolyte solutions. This paper reviews fundamental aspects of flotation in aqueous solutions with high concentration of inorganic electrolytes. Salt flotation, the process of flotation of inherently hydrophobic solids in concentrated electrolyte solutions, is especially suitable for theoretical analysis since no other organic agents are used in it. Starting from this example, the case of flotation of sulfide ores (chalcocite, chalcopyrite, pyrite and molybdenite) is discussed. The flotation of Cu-Mo sulfide ores requires the use of flotation agents, which are different for the inherently hydrophobic molybdenite and hydrophilic copper sulfides. The process is commonly carried out in alkaline pH adjusted with lime to depress pyrite, but in seawater depressing effect of Ca ions on molybdenite flotation is augmented, and different pyrite depressants are needed.
Detecting biological threat aerosol is difficult in that a small cloud lasting only a few seconds at a point location may contain sufficient material to infect large numbers of exposed individuals. Clinical analytical methods require relative large amounts of the sample in liquid form to facilitate positive measurements. Biological agents may be fragile because of their lipid membranes that can be susceptible to harsh sample collection treatment. Damaged organisms may render subsequent analyses to be invalid. Virtual impaction (VI) sample collectors have been theorized to provide usable concentration rates yet are sufficiently gentle with the aerosol particles to preserve cellular viability. This review will discuss different implementations of VI technology and examine their merits. Outstanding issues will be outlined to aid future experimentation.
When two different materials are brought into contact and separated, an electrical charge is transferred from one to the other. This phenomenon is called contact electrification, contact charging, or tribocharging. Charged particles cause various secondary phenomena during powder processing, such as deposition, adhesion, and electrostatic discharge. Additionally, charged particles are used in many industrial applications such as electrophotography, electrostatic powder coating, and separation; thus, particle charge control is very important for improving particle performance. However, there are still many unknown effects, and in some cases, inconsistent results have been reported. In this review, the basic concepts and theories of charge transfer between solid surfaces are summarized and a description of particle charging caused by repeated impacts on a wall is formulated. On the basis of these concepts and formulations, novel methods of controlling particle tribocharging are presented. In particular, a method using an applied electric field is expected to be applicable in industrial fields.
Film thin drying is a process to create functional interfaces in solidifying liquids, rather than to separate volatile components from solutions or suspensions. Indeed, recent developments in coating technologies have shed light on self-organization in evaporating complex thin fluids. In particulate coatings, final properties of dried film depend not only on initial liquid compositions but also the imposed drying conditions, which significantly influence local particle distributions, contact area of rigid and/or deformable particles, anisotropic particle orientation, and amounts of adsorbed molecules on particle surfaces. It is of importance to understand how a directional film shrinkage and spontaneous solidification constrain the particle motions, and how they induce particular film structures in a non-equilibrium state. Recently, there has been a great deal of progress in measurement techniques and numerical approaches for analyzing transient structures in evaporating thin liquid films. This article presents an overview of current research activities on local, in-situ determination of (i) fluid properties at air-liquid and liquid-liquid interfaces, and (ii) distributions of particles or solutes in the thickness direction in shrinking films.
A dream in powder technology is to predict the structure and flow of a powder from precise knowledge of the interactions between the particles. The most important interaction is adhesion. In this paper several aspects of adhesion are discussed. First, the influence of humidity and capillary forces is analyzed. To calculate capillary forces the structure of the microcontact needs to be known with an accuracy much better than 1 nm. Determining the structure of a microcontact with such resolution is demanding, if possible at all. Considering that wear can lead to a change of the atomic structure such knowledge is practically impossible. Second, the work to break an adhesive contact depends on the effective spring constant by which the force is applied. Third, adhesion forces depend on the separation speed and not only the surface chemistry and the structure of the particles in the contact region. Fourth, we suggest to distinguish between contact and bridging adhesion.
Despite decades of research, the study of suspension flows still continues to be a subject of great scientific interest. In the development of accurate models for suspension-related processes, prior knowledge of several flow characteristics is essential, such as spatial distribution of phases, flow regimen, relative velocity between phases, etc. Several non-invasive techniques of flow characterisation can be found in the literature, however, electrical tomography offers a vast field of possibilities due to its low cost, portability and, above all, safety of handling. In this paper, a review of the use of electrical tomography for industrial/process monitoring purposes will be presented, giving information about the evolution throughout the years and about the limitations and advantages of the different configurations. Moreover, the signal de-convolution strategies, to obtain the images of the process, will also be discussed. The most recent advances in both fields will be presented. Additionally, information about the strategy adopted by the authors to produce a portable EIT system will be described. Finally, the future challenges for electrical tomography will be addressed.
Segregation negatively impacts the product quality and depends on physical and mechanical properties of particulate materials. Size is the most dominant parameter contributing towards fines percolation segregation from mixtures with size distribution. A continuum theory-based convective and diffusive model was developed and validated to study time-dependent percolation segregation of fines. In addition, to scale-up the results, a mechanistic theory-based dimensional analysis approach was used to incorporate physical and mechanical properties of particulates in a time-independent model. In dimensional analysis model, size, shape, density, size ratio, mixing ratio, strain rate, strain, and bed depth were included. The results showed that the time-dependent convective and diffusive model predicted the segregated mass of fines within the 95% confidence interval of measured fines for size ratios 2.4:1.0 and 1.7:1.0 at strains of 6% and 10%. Dimensional analysis results showed that the Coefficient of Variation (CoV) of the modeled values with respect to the experimental values were 18%, 15%, and 11%, respectively, for binary mixtures of urea and potash at strains of 2%, 6%, and 10% and strain rate of 0.25 Hz.
Rheology plays a major role both in production and application stages of paints. Na-Bentonite, clay based thickening agent, is generally used to modify the viscosity of paints, since it is more economical and environmentally friendly compared to polymer based thickening agents. In solvent based systems bentonite is generally modified with quaternary ammonium salt to obtain appropriate polarity. However it is necessary to improve its thickening character to obtain optimum performance in water based paints. It has been reported that its flow behavior and stability can be improved by additives like MgO and LiCl for use in water based system. In this paper, Na-Bentonite and MgO mixture was evaluated as an additive in water-borne paints. Standard paint tests such as viscosity, density, opacity, gloss, and Bucholz hardness were conducted to characterize the paint quality. It is determined that the bentonite – MgO mixture can perform as well, or better than other thickening agents tested in this study.
The objective of these studies was to evaluate the use of an in silico model for predicting lung deposition of inhaled therapeutic aerosols. A range of input data derived from our own in vitro data and published clinical studies was utilized. The in silico model ran simulations for these propellant driven metered dose inhaler formulations across a range of conditions. Firstly, a range of pressurized metered dose inhaler formulations were evaluated in the in silico model and compared to the in vitro aerosol performance data. Limitations of using in vitro cascade impaction data were observed. Then, using in vivo data from healthy human subjects using metered dose inhalers, lung deposition profiles were compared with the in silico model predictions. Despite differences in oropharyngeal deposition the model predicted lung deposition accurately. We conclude that the in silico model can be applied to various conditions for particulate based inhalation aerosol systems.
For a silo design, it is very important to understand the friction characteristics of bulk solids with silo walls. This so-called wall friction angles were measured in this study with two different testers: Jenike shear tester and Schulze ring shear tester (RST). Soft PE plastic pellets A was used as the tested bulk solids while stainless steel SS 304 and aluminum Al 6061were selected as wall plates. It was found that the most important parameter in this study is wall roughness. With decreasing wall roughness, wall friction angles decrease no matter which tester was used. Wall friction angles for both testers were similar if wall roughness was similar. The only exception is under the testing condition of the low pressure (500 Pa) on a wall plate. In addition, the impact of testing temperatures (22 and 37 °C) has been described in this study.
The purpose of the present study is to develop a new particle classification technique and apparatus to replace centrifugal separation method, where continuous operation for classification is impossible because of the deposition of the coarse particles on the wall of the separator. In our recent research, it was clear that the zeta potential of the silica particles dispersed by a bead mill had size dependency. Hence, the particles were classified using an electrical field flow fractionation (EFFF) system under the condition that the zeta potential of the smaller particles was more negative than that of larger particles. Previous EFFF apparatus utilized horizontal field flow; however, the apparatus designed in this study had vertical field flow and cylindrical channel with length of 350 mm and radius width of 6 mm to reduce the running cost and operation time for classification of particles. About the classification performance of this apparatus, it was found that the silica particles with the size from 50 nm to 400 nm were classified using a low applied voltage. This method prevented deposition of particles on the wall of the apparatus and allowed continuous operation. Results of theoretical calculations supported qualitatively the experimental results obtained in this research.
Spherical nickel particles were prepared by hydrogen reduction assisted ultrasonic spray pyrolysis (USP-HR) method using nickel chloride solution without any additives. Thermodynamic of the hydrogen reduction of the nickel chloride were studied by FactSage software. Particles were obtained at 800°C reaction temperature by hydrogen reduction of aerosol droplets under H2 flow. The effects of the precursor concentration on the particle size and morphology were investigated by scanning electron microscopy. Results showed that nickel particle sizes were decreased from 630 to 270 nm by reducing solution concentration, and also narrower size distribution was obtained using lower concentrated precursor. Nickel particle sizes were theoretically calculated and results indicated that there was a slight difference in the particle sizes compared to experimental values.
The purpose of the present study was to reveal the details of the preparation of CaF2 particles with controllable size (30–900 nm) and shape (spherical, hexagonal, and cubical forms) using a liquid-phase synthesis method, and to demonstrate that a change in the composition of the reactants and crystalline structure of the CaF2 product could improve material performance. The particles were synthesized from the reaction of CaCl2 and NH4F in an aqueous solution in the absence of any additional components (e.g., chemicals, surfactants). Monodispersed particles were achieved by the optimization of the reaction condition parameters: temperature, mixing rate, and reaction time. Control of the particle size was accomplished mainly by changing the concentration of the reactants, which is qualitatively explained by the conventional nucleation theory. Flexibility of the process in controlling particle morphology, from a spherical to a hexagonal and/or a cubical form, was predominantly achieved by varying the concentration of CaCl2. Since the identical XRD pattern was detected in particles with varying morphologies, the shape transformation was due to changes in particle growth. A theoretical background to support how the particles changed was also added and was compared with an analysis of the number of nuclei. In addition, sufficient adjustment of the reactant compositions made it possible to produce a material with an ultralow refractive index (nCaF2 was near to ntheoretical CaF2), which was confirmed by the measurement of the refractive index and the material crystallinity.
The attachment efficiency when nanoparticles contact with a flat smooth wall is investigated by taking the elastic deformation force, van der Waals force and Stokes resistance into account. The equations of interactions between particle and wall are derived and solved numerically to obtain the attachment efficiency for dioctyl phthalate nanoparticles with diameter changing from 100nm to 800nm and for different initial angle of attack. The results show that it is more difficult to attach onto the wall for the particles which attack the wall vertically. The attachment efficiency decreases overall with increasing particle diameter. There exists an abrupt increase in the attachment efficiency when the particle diameter is around 550nm. The attachment efficiency is different with or without considering the elastic deformation force. The difference in the values of attachment efficiency for vertical and horizontal walls is negligible. A new formula for the attachment efficiency is presented to express the relationship between the attachment efficiency and the particle diameter as well as the initial angle of attack.
Both producers and users of divided solids regularly face the problem of caking after periods of storage and/or transport. Particle agglomeration depends not only on powder water content, temperature and applied pressure, but also on the interactions between the solid substance and water molecules present in the atmosphere, i.e. on relative humidity (RH) at which the product is stored. Ambient humidity plays an important role in most events leading to caking: capillary condensation of water at contact points between particles, subsequent dissolution of a solid and formation of a saturated solution eventually followed by precipitation of the solid during the evaporation of water. Here, we focus on the kinetics of dissolution followed by evapo-recrystallization of a hygroscopic sodium chloride powder under controlled temperature and RH, with the aim of anticipating caking by predicting rates of water uptake and loss under industrial conditions. Precise measurements of water uptake show that the rate of dissolution is proportional to the difference between the imposed RH and deliquescence RH, and follows a model based on the kinetic theory of gases. Evaporation seems to be governed by more complex phenomena related to the mechanism of crystal growth from a supersaturated salt solution.
High-shear wet granulation is commonly used in many industries such as in the pharmaceutical industry to convert fine cohesive powders into dense and round granules. The purpose of this work was to determine the effects of some important powder properties (crystalline or amorphous nature, hygroscopicity, solubility and particle size) and process variables (liquid addition rate, impeller speed) on the early stages of the granulation process and on drug distribution in granules obtained by high-shear wet granulation. The glass transition concept coupled with on-line impeller torque monitoring and measurements of the time evolution of the particle size distribution were used to study mixtures of pharmaceutical excipients and some common active ingredients. In particular a formulation map for estimating the minimum amount of liquid binder required to induce appreciable granule growth is presented, thus outlining a new method to considerably increase the predictability of the behaviour of different formulations on the basis of the physical properties of each single component. The description of the effects of the wetting condition on drug uniformity content in some formulations with hydrophobic active ingredients is given as well.
The silicon age that started in the 60s of the last century has changed the world profoundly, mainly related to the invention and development of microprocessor technology. Meanwhile, the demand for silicon is driven by the photovoltaics industry that consumes about 80% of the high-purity silicon produced worldwide. Independent of the final product, all high-purity silicon has passed through a couple of gas-phase reactions for purification. The most important gaseous species within this production chain are chlorosilanes and monosilane. We will discuss the direct formation of crystalline silicon by homogeneous gas-phase reactions as a direct and highly economical way to produce the required high-purity raw material for silicon solar cells. The direct formation of solid silicon particles from monosilane requires only a fraction of the energy compared to the established Siemens process based on the chemical vapor deposition of silanes. We have developed a method to synthesize nanocrystalline silicon powder using a hot-wall reactor, and the technology was scaled up to the pilot-plant scale. While an economical production strategy is decisive for solar cell production, the structure of the gas-phase product allows for additional, highly promising applications benefiting from the specific properties of the nanoscale particulate material. Both, thermoelectric generators as well as lithiumion batteries benefit from the nanocrystalline structure of the gas-phase product due to high phonon scattering and short diffusion lengths, respectively. First successful examples with regard to these two topics will be discussed. In these fields, silicon finds potential new markets for sustainable energy technology because of its abundant availability and low-cost production.
Powder handling operations can give rise to the tribo-electrification of particles, causing a number of problems such as risk of fire and explosion, particle adhesion to the walls of processing equipment and segregation. Current methods available for measuring the dynamic charging of bulk powders are unsuitable for testing/handling small quantities of powders, some of which are highly active. Furthermore, very little work has been reported on the effect of tribo-electrification on the segregation of components of mixtures. A methodology has recently been developed for investigating the tribo-electrification of small quantities of bulk powders using a shaking device. Two common pharmaceutical excipients, namely α-lactose monohydrate (α-LM) and hydroxypropyl cellulose (HPC) were used as model materials. The electric charge transferred to the particles was quantified as a function of shaking time, frequency and container material. The temporal trend follows a first-order rate process. Using numerical simulations based on the Distinct Element Method (DEM), the charge accumulation of an assemblage of alumina beads inside the shaking device was analysed based on the single particle contact charge obtained from the experiments. It was shown that the inclusion of electrostatic mechanisms into the DEM model leads to an improved prediction of the charge buildup, but the difference with experimental data is still notable. Using the above method, segregation induced by tribo-electric charging was characterised for binary mixtures comprising α-LM and HPC. The bulk and wall-adhered particles were analysed for the mass fraction of each component using selective dissolution of one component and filtration of the non-dissolving component, followed by a gravimetric analysis. The findings reveal that a considerable level of segregation can take place on the wall-adhered particles. The method described here has the potential to be used to characterise small quantities of pharmaceutical powders including active pharmaceutical ingredients (API), which are sparse in the early development stages.
The modelling of experimental distributions of breakage energy by compression and impact was carried out. In terms of our model, the part of the particle that is directly contacted with the stressing tool is admitted into the equation as a hemispherical asperity with known breakage energy distribution. The main contribution of stressing energy is accumulated by this hemispherical asperity that is responsible for crack generation and particle breakage. The breakage probability distribution of particles is calculated as a superposition of the breakage probabilities of asperities. Based on geometrical similarity, one can assume the same normalized log-normal size distribution of asperities for all tested particles of a given material. As a result, all experimental distributions of normalized breakage energy can be fitted with the same log-normal function for all particle sizes.
The synthesis of silicon quantum dots is performed in the [3–5 nm] range using CO2 laser pyrolysis of SiH4. This size range is particularly relevant for potential applications in photovoltaic devices and biomedical imaging. The laser pyrolysis technique offers convenient control of the synthesis parameters in the case of nanoparticle production. However, controlling the size of small silicon objects remains difficult. The original approach consists here in a time-control of the energy injected into the reaction by gating the laser. The laser gate-on duration is adjusted in the range of 10 to 80 μs while keeping the average power constant. In parallel, supersonic expansion and on-line time-of-flight mass spectrometry are performed for on-line size characterization. A monotonic increase of the size as a function of the gate-on duration is observed for several SiH4 volume concentrations. The results are discussed qualitatively.
With the rapid advancement of nanotechnology and with nanoparticles beginning to enter into products, the demand for production-level quantities of advanced nanopowders such as multi-component or coated oxides is rising. Such advanced nanoparticles can be effectively made by flame spray pyrolysis (FSP), and research with laboratory reactors yielded a spectrum of new nanomaterials for catalysis, pigments, ceramics, optics, energy and biomaterials, among others. Here, the transfer of FSP nanopowder synthesis from gram-level lab-scale to pilot reactors with up to 10 metric tons annual production rate is investigated by the example of FSP pilot plants that were realized in industrial-oriented settings. Design considerations for such pilot-scale systems are addressed and guides to production cost estimates are given. Special attention is brought to safe and contained nanoparticle manufacture in order to address the growing awareness of the potential health and environmental effects of nanoparticles.
We present in this paper a generic multiscale methodology for the characterization and crystallization of eflucimibe polymorphs. The various characterization techniques used have shown that eflucimibe polymorphism is due to a conformational change of the molecule in the crystal lattice. In addition, the two polymorphs are monotropically related in the temperature range tested and have similar structures and properties (i.e. interfacial tension and solubility). Consequently, it was found that for a wide range of operating conditions, the polymorphs may crystallize concomitantly. Induction time measurements and metastable zone width determination allow to infer the origin of the concomitant appearance of the polymorphs. A predominance diagram has been established which allows to perfectly control the crystallization of the desired polymorph. However, even if the stable form can be produced in a reliable way, the crystal suspension went toward a very structured gel-like network which limits the extrapolation process. Based on microscopic observation of the crystallization events performed in a microfluidic crystallizer, we propose a range of operating conditions suitable for the production of the stable form with the desired handling properties.