KONA Powder and Particle Journal
Online ISSN : 2187-5537
Print ISSN : 0288-4534
ISSN-L : 0288-4534
Volume 30
Showing 1-31 articles out of 31 articles from the selected issue
Front Cover
The Letter from the Editor
Comment of the Cover Photograph
Review Papers
  • Richard Hogg
    Type: Review Papers
    2013 Volume 30 Pages 3-14
    Published: 2013
    Released: December 20, 2013
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    A comprehensive evaluation of flocculation processes is presented with emphasis on physical and engineering aspects. Flocculation by polymer bridging involves three basic sub-processes: mixing of the polymer with the particle suspension, adsorption of the polymer on particle surfaces and the formation and growth of flocs. Each of these is primarily controlled by agitation of the suspension. At the same time, agitation also promotes floc breakage. Since polymer adsorption tends to occur irreversibly, flocculation is a non-equilibrium process and the relative rates of the sub-processes play a critical role. The kinetics of these processes are reviewed and their implications with respect to process design are evaluated. Procedures for controlling the relative rates are shown to provide a basis for the design of efficient flocculation processes in batch systems. Some information on scale-up criteria is presented. Extension of the basic concepts to the design and operation of continuous processes is discussed.
  • Virgil Marple, Dale Lundgren, Bernard Olson
    Type: Review Papers
    2013 Volume 30 Pages 15-21
    Published: 2013
    Released: December 20, 2013
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    A PM1.0/2.5/10 Trichotomous sampler has been developed to determine if the particles in the saddle point between the coarse and fine particle modes (specifically the 1.0 μm to 2.5 μm size range) are primarily coarse or fine mode particles. The sampler consists of a standard high volume sampler with two high volume virtual impactors (one with a cut size of 2.5 μm and the other with a cut size of 1.0 μm) inserted between the PM10 inlet and the 8×10 inch (20×25 cm) after filter. By using nine 47 mm filters, at various locations within the trichotomous sampler, a technique has been developed for subtracting out the effects of particles smaller than the cutsize of a virtual impactor from the minor flow particle collection.
  • Hasan Mandal, Nurcan Calis Acikbas
    Type: Review Papers
    2013 Volume 30 Pages 22-30
    Published: 2013
    Released: December 20, 2013
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    SiAlON ceramics have been known for many years as prime candidate materials in structural applications at ambient and high temperatures involving superior mechanical and/or chemical processes. In spite of their excellent properties, the utilization of SiAlONs has remained limited till today due to the high cost of raw materials and processing. In order to circumvent this problem, low cost refractory grade, coarse, impure, less sinter active β-Si3N4 powder was used to produce SiAlON ceramics with satisfactory mechanical properties.In this article, the processing challenges in the production of SiAlON ceramics with β-Si3N4 powder were discussed. The process parameters obviously affect the phase assemblage, densification, microstructural and mechanical properties of final SiAlON ceramics. Processed β-Si3N4 powder characteristics are majorly investigated by SEM-EDX, XRD, XRF, laser particle sizer and elemental analyser. The existence of undesirable impurities in the β-SiAlON crystal structure because of the use of impure Si3N4 powders has been shown to be tolerable by TEM microstructural analysis. Mechanical properties are in general evaluated by Vickers indentation method. Wear behaviour of the cost effective SiAlONs were compared with commercially available ceramic materials which are commonly being used in wear applications. Initially the use of such powders to produce materials for engineering applications proved challenging, however, satisfactory results have been obtained by the optimization of the initial chemical composition and process parameters.
  • Hyangki Sung, Mansoo Choi
    Type: Review Papers
    2013 Volume 30 Pages 31-46
    Published: 2013
    Released: December 20, 2013
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    Fundamental building block in nanotechnology is the nanoparticle and currently many excellent techniques are available to control its size, morphology and crystalline phase at mass quantity. However, the practical realization of novel nanodevices employing nanoparticles requires the construction of multiscale three-dimensional buildings consisting of the basic building block, nanoparticles, particularly as an ordered array, which remains challenging. In this review, we address various methodology developed for the assembly of nanoparticles by classifying them depending on manipulating force. Methods utilizing electric, capillary, and magnetic forces are discussed. Ion assisted aerosol lithography(IAAL) that utilizes ion induced focusing concept will be described in more detail since it provides an opportunity for multiscale multidimensional assembly of nanoparticles in a parallel fashion at atmosphere.
  • Masayoshi Fuji, Yong Sheng Han, Chika Takai
    Type: Review Papers
    2013 Volume 30 Pages 47-68
    Published: 2013
    Released: December 20, 2013
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    Hollow particle is a promising material with the special properties of low densities, thermal insulation and distinct optical activity. Due to their potential promising applications in the fields of drug delivery, catalysis and optics, a great effort has been devoted to develop new preparation methods which are collected and reviewed in this paper. All these methods are classified into three groups, namely sacrificed template method, in-situ template method and device-based method based on the characteristics of the methods. The advantage and disadvantage of each method are compared and the trends for preparation are pointed out. In light of the wide applications of hollow particles, the later part of this paper focuses on their potential applications in industry. Their applications are not limited in the fields of papermaking, rubber processing and plastic improvement, but also expanded to electronic, catalytic and biological areas.
  • Duu-Jong Lee, Sachin Jangam, Arun S. Mujumdar
    Type: Review Papers
    2013 Volume 30 Pages 69-83
    Published: 2013
    Released: December 20, 2013
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    Thermal drying is a highly energy-consuming process found in almost all industries accounting for between 10–20% of national industrial energy consumption in the developed economies of the world. It is arguably the oldest unit operation and yet R&D in this area is only a few decades old. Over 50% of products consumed by humans are in particulate form so that drying of wet particulates as well as feedstock such as solutions, suspensions or pasty solids is of great industrial interest. Efficient drying technologies must produce engineered dry particulates of desired quality at minimum cost, low carbon footprint and little environmental impact. This article attempts to provide a global overview of recent advances in drying technologies most of which represent evolutionary innovations. In order to reduce investment costs one needs to enhance drying rates within limits imposed by the product properties and end product quality requirements. Several novel gas-particle contactors for example have been evaluated for drying. Combined modes of heating and hybrid dryers can improve drying performance in some cases. Recent interest in production of nanoparticles by wet processing also has stimulated interest in drying to produce nanoparticles. Drying of heat sensitive biotech and pharmaceutical products also pose new challenges. A capsule overview is presented of recent developments including enhancements in conventional drying technologies as well as more innovative new technologies.
  • Olukayode I. Imole, Nishant Kumar, Vanessa Magnanimo, Stefan Luding
    Type: Review Papers
    2013 Volume 30 Pages 84-108
    Published: 2013
    Released: December 20, 2013
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    Stress- and structure-anisotropy (bulk) responses to various deformation modes are studied for dense packings of linearly elastic, frictionless, polydisperse spheres in the (periodic) triaxial box element test configuration. The major goal is to formulate a guideline for the procedure of how to calibrate a theoretical model with discrete particle simulations of selected element tests and then to predict another element test with the calibrated model (parameters).Only the simplest possible particulate model material is chosen as the basic reference example for all future studies that aim at the quantitative modeling of more realistic frictional, cohesive powders. Seemingly unrealistic materials are used to exclude effects that are due to contact non-linearity, friction, and/or non-sphericity. This allows us to unravel the peculiar interplay of stress, strain, and microstructure, i.e. fabric.Different elementary modes of deformation are isotropic, deviatoric (volume-conserving), and their superposition, e.g. a uniaxial compression test. Other ring-shear or stress-controlled (e.g. isobaric) element tests are referred to, but are not studied here. The deformation modes used in this study are especially suited for the bi- and triaxial box element test set-up and provide the foundations for understanding and predicting powder flow in many other experimental devices. The qualitative phenomenology presented here is expected to be valid, even clearer and magnified, in the presence of non-linear contact models, friction, non-spherical particles and, possibly, even for strong attractive/ adhesive forces.The scalar (volumetric, isotropic) bulk properties, the coordination number and the hydrostatic pressure scale qualitatively differently with isotropic strain. Otherwise, they behave in a very similar fashion irrespective of the deformation path applied. The deviatoric stress response (i.e. stress-anisotropy), besides its proportionality to the deviatoric strain, is cross-coupled to the isotropic mode of deformation via the structural anisotropy; likewise, the evolution of pressure is coupled via the structural anisotropy to the deviatoric strain, leading to dilatancy/compactancy. Isotropic/uniaxial over-compression or pure shear respectively slightly increase or reduce the jamming volume fraction below which the packing loses mechanical stability. This observation suggests a necessary generalization of the concept of the jamming volume fraction from a single value to a “wide range” of values as a consequence of the deformation history of the granular material, as “stored/memorized” in the structural anisotropy.The constitutive model with incremental evolution equations for stress and structural anisotropy takes this into account. Its material parameters are extracted from discrete element method (DEM) simulations of isotropic and deviatoric (pure shear) modes as volume fraction dependent quantities. Based on this calibration, the theory is able to predict qualitatively (and to some extent also quantitatively) both the stress and fabric evolution in another test, namely the uniaxial, mixed mode during compression. This work is in the spirit of the PARDEM project funded by the European Union.
  • Driss Oulahna, Romain Collet, Alain de Ryck
    Type: Review Papers
    2013 Volume 30 Pages 109-118
    Published: 2013
    Released: December 20, 2013
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    Mixing granular media with a given amount of liquid is an operation conducted and used intensively for the preparation of concrete. The power and time required to obtain good homogeneity of the granular paste are known to have a complex relationship with the physical properties of the particles, with the liquid and with the mixer design. In this paper some of these issues are addressed by evaluating the shear resistance of a granular paste. Using model spherical materials (glass beads) and ground and sieved minerals (calcite CaCO3), we investigate experimentally the impact of the particle size, liquid amount and morphology of the particles.From quasi-static experiments in shear cells, different regimes of shear resistance are revealed. In dry conditions, van der Waals’ forces dominate. In wet conditions, a capillary or consolidation regime where shear resistance is dominated by capillary forces is strongly impacted by the morphology of the particles and by the formation of texture. These regimes are qualitatively observed in a bowl mixer for which the variation of the current intensity correlates with the shear resistance observed in quasi-static experiments.
  • Amor Sayari
    Type: Review Papers
    2013 Volume 30 Pages 119-124
    Published: 2013
    Released: December 20, 2013
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    In this research, nanocrystalline ZnO flakes were synthesized via a simple reaction process by using zinc acetate dihydrate, diethyl amine and sodium hydroxide. It is confirmed by scanning electron microscopy analysis that nanocrystalline ZnO flakes are flat, irregular in shape, have a high thickness and their average dimension is about 300 nm. The X-ray diffraction (XRD) and FT-IR results indicated that the synthesized ZnO product has the pure wurtzite structure with lattice parameters a and c of 3.253 and 5.210 Å, respectively. The average crystallite size of the ZnO nanostructures deduced from the Scherrer formula is ∼31 nm. Raman scattering exhibits a sharp and strong E2H mode at 438 cm−1 which further confirms the good crystallinity and wurtzite hexagonal phase of the prepared ZnO nanostructures. The synthesized powder exhibited the UV absorption at around 370 nm with the estimated direct band gap energy of 3.278 eV. The particle size was also deduced by using the Brus equation and the estimated band gap energy of the ZnO nanopowder sample. The obtained value is in agreement with the calculated one from the Scherrer formula. The strain in the ZnO nanoparticles was also calculated.
  • Frank M. Etzler, Mohammad Nasir Uddin
    Type: Review Papers
    2013 Volume 30 Pages 125-143
    Published: 2013
    Released: December 20, 2013
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    Both the FDA (U.S. Food and Drug Administration) and ICH (International Conference on Harmonisation) have urged the incorporation of Quality by Design (QbD)1) into the manufacture of pharmaceutical products2).The performance of many pharmaceutical manufacturing processes and the performance of some pharmaceutical products requires a knowledge of powder properties. Under the principles of QbD it is possible to adjust processes to account for variations in powder properties. These adjustments, in turn, require knowledge of the relation between powder properties and manufacturing performance. This relation between powder properties and performance is often not well understood; thus, the required information is not collected.In this paper, particle-particle and particle-surface interactions are considered to be a source of product variability. As particle size effects are intertwined with particle adhesion effects this topic is also considered. From the discussion below, it can be seen that the surface chemistry of particles can vary due to mechanical treatment, crystallization solvent, and surface contamination. Variations in surface chemistry affect interparticle adhesion and thus may lead to process or product performance changes. Issues concerning the role of interparticle adhesion that are related to tableting and dry powder inhalers are discussed in some detail.It is clear that a deeper understanding of the powder state and the establishment of appropriate analytical tools will be required to fully implement QbD. Improvements in particle sizing technologies, improvements powder sampling procedures and measurements of particle surface properties will be required. It is hoped that this paper will stimulate thought on this issue.
  • Alexandra Teleki, Andrea Hitzfeld, Manfred Eggersdorfer
    Type: Review Papers
    2013 Volume 30 Pages 144-163
    Published: 2013
    Released: December 20, 2013
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    Micronutrients and nutraceuticals such as vitamins, carotenoids, polyunsaturated fatty acids and polyphenols are classes of food ingredients that are essential for human health and well-being. These compounds are rarely added purely to the targeted food application but rather in encapsulated, solid, dry product forms with added functionalities such as improved stability, bioavailability or handling. This review presents some of the industrially most relevant particle technologies, as well as emerging ones, for synthesis and formulation of micronutrients and nutraceuticals. The influence of technological process parameters on product particle physicochemical properties such as size, morphology and structure are highlighted as well as their importance for end-use applications.
  • Raimundo Ho, Jerry Y.Y. Heng
    Type: Review Papers
    2013 Volume 30 Pages 164-180
    Published: 2013
    Released: December 20, 2013
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    Surface properties can profoundly impact the bulk and interfacial behavior of pharmaceutical solids, and also their manufacturability, processability in drug product processes, dissolution kinetics and mechanism in drug delivery. Variation in the inter- and intra-molecular interactions gives rise to anisotropic surface properties of crystalline solids which display direction-dependent characteristics relative to the orientation of the crystal unit structure. Despite its establishment since the 1950s, inverse gas chromatography (IGC) is still an evolving technology in the field of pharmaceutical R&D. In this review, the principles behind IGC as a physicochemical technique to measure the surface properties of solids are presented. The introduction is followed by an overview of its utility in pharmaceutical R&D, spanning a variety of applications including batch-to-batch variability, solid-solid transitions, physical stability, interfacial behavior in powder processing, and more. For anisotropic materials, IGC has been utilized to characterize the heterogeneity of materials using adsorption and energy distribution functions. Recent development and applications of IGC at finite concentration (IGC-FC) to determine the surface heterogeneity distribution of solids are presented. This methodology overcomes a number of limitations associated with traditional experiments.
  • Wiwut Tanthapanichakoon, Tawatchai Charinpanitkul, Suracha Udomsak, Bu ...
    Type: Review Papers
    2013 Volume 30 Pages 181-192
    Published: 2013
    Released: December 20, 2013
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    First we survey the scope and level of research activities in nanoparticle technology (NPT) in ASEAN by looking at relevant international journal publications (2006–2012) in terms of absolute numbers (AN), numbers of publications per million population (PMP) and per billion USD GDP (PBG). Obviously, the statistics show that, within ASEAN, the strength of Singapore covers a wide range of nanotechnology fields and applications, including carbon materials, biosensors, bioelectronics, and pharmaceutics. Malaysia places emphasis on alloys & compounds, carbon materials, and separation technology. Thailand’s emphasis is on molecular modeling, carbon materials, and biosensors. When classification is made on the morphology of nanoparticles mentioned in the titles, the topmost are nanotubes (including CNT, SWCNT, MWCNT) at 392 out of 612 (64.1%), followed by generic nanoparticle/nanopowder and nanofiber (including nanowire, nanorods). Next we look closer at 2 nanoparticle R&D organizations in Thailand, namely, CEPT (CU) and NANOTEC together with their alliances. The interest in nanotechnology of SCG (Siam Cement Group), a leading Thai industrial conglomerate, will also be briefly introduced. .
Original Research Papers
  • Pradip, Charles C.H. Li, Douglas W. Fuerstenau
    Type: Original Research Papers
    2013 Volume 30 Pages 193-200
    Published: 2013
    Released: December 20, 2013
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    A procedure is described for synthesizing cerium fluorcarbonate. This synthetic bastnaesite was characterized through X-Ray diffraction, chemical analysis and thermogravimetric studies. The solubility product of Ce-bastnaesite was determined to be 10−10.1. The stability constant pK CeHCO32+ complex was experimentally determined to be 3.04 ± 0.21. Based on the thermodynamic data available in the literature, a speciation diagram has been prepared for the synthetic cerium bastnaesite.
  • Zhen Xu, Anthony J Hickey
    Type: Original Research Papers
    2013 Volume 30 Pages 201-210
    Published: 2013
    Released: December 20, 2013
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    This paper reviews scientific understandings relevant to the dry powder inhaler (DPI) development including turbulent airflow characteristics in the inhaler, microparticle entrainment and deaggregation within the airflow and device. Using standardized entrainment tubes (SETs) and powder aerosol deaggregation equation (PADE), the aerosol performance profile in a shear stress range defined by SETs can be predicted. However, such predictions are based on the hypothesis that the shear stresses characterized from SETs are readily translatable to those of the DPIs’. Two selected model DPIs (Rotahaler and Aerolizer) with either gelatin or HPMC capsules were used to evaluate the FPF at the DPI shear stresses. The performance result using DPIs was close to the predicted FPF using SETs and PADE method. The application of SETs and PADE method can be used for performance prediction of these DPIs.
  • Anuranjan Pandeya, Virendra M. Puri
    Type: Original Research Papers
    2013 Volume 30 Pages 211-220
    Published: 2013
    Released: December 20, 2013
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    Compaction is a key unit operation in many particulate industries. Accordingly, this study addresses a research question of considerable importance concerning compact (or tablet) formation, i.e., the feasibility of using mechanical properties of powder formulations in low to medium pressure regime (<10 MPa) as predictors of tablet (i.e., compact) quality parameters. For the feasibility study, mechanical properties, i.e., elastic and elastoplastic, of dry powder formulations at three binder contents were determined using a flexible boundary cubical triaxial tester in low to medium pressure regime. For the same formulations, tablets formed at two pressing pressures (70 and 90 MPa) were tested for four physical quality parameters, i.e., diametral strength, axial penetration strength, indentation hardness, and friability. Some of the key findings were: bulk modulus increased with pressure and binder; shear modulus increased with confining pressure; tablet hardness increased with binder content upto a point and thereafter decreased or remained constant. All the powders' properties related with tablet qualities, i.e., had R2>0.80; i.e., demonstrating the feasibility of using powder properties as initial predictors of tablet quality for formulations tested. In particular, the spring-back index, compression index, and bulk modulus were found to be most correlated with tablets' diametral strength, axial penetration strength, indentation hardness, and friability. An elastic energy based hypothesis was proposed to provide a fundamental basis for mechanical properties of powder formulations vs. tablet quality relationships. The positive outcome of this feasibility study suggests that the approach could be used for other similar powder formulations.
  • Aarthi Narayanan, Parvesh Sharma, Brij M. Moudgil
    Type: Original Research Papers
    2013 Volume 30 Pages 221-235
    Published: 2013
    Released: December 20, 2013
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    The development of nanotechnology for advances in various sectors like health, consumer products has paved way for possible applications in agriculture and food industries. Antimicrobial agents (e.g., silver, titanium dioxide), nano-bio pesticides (hydrophobic silica), smart delivery systems (polymeric nanoparticles) provide promising enhancement or alternatives to the conventional crop protection strategies, which are primarily based on applying chemicals in solid, liquid or suspension forms. Nanotechnology approaches in food industry can impart properties such as resistance to gas penetration, increased tensile strength and enhanced absorption of nutrients leading to novel food packaging and processing materials. Despite these features, the usage of nanotechnology is still limited, owing to the lack of proper toxicity evaluation data. Understanding the risks and taking appropriate measures to mitigate them will significantly enable nanotechnology advances targeting to agriculture and food industries. In this paper, we have reviewed some of the recent research and development efforts that have been carried out in nanotechnology for its potential applications in agrifood sector. More specifically, nanotechnology approaches mediated by particle technology advances are reviewed.
  • Aleksey Alekseevich Gusev, Vitaliy Petrovich Isupov, Evgeniy Grigoriev ...
    Type: Original Research Papers
    2013 Volume 30 Pages 236-243
    Published: 2013
    Released: December 20, 2013
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    It is demonstrated by means of XRD, IR spectroscopy, electron microscopy, laser light scattering and measurements of the specific surface area that mechanical activation of a mixture of lithium carbonate, niobium pentoxide and copper oxide in the planetary centrifugal activator AGO-2 involves mixing, dispersion and amorphization of the components, as well as the phase transition of the monoclinic form of niobium (V) oxide into its orthorhombic form. Subsequent mechanical treatment results in the partial formation of a lithium-niobate phase. Thermal treatment of the compacts prepared from mechanically activated powders, at a temperature above 400°C, leads to the appearance of the structure-forming trigonal phase based on LiNbO3. The data obtained provide evidence that the mechanochemical method is promising for the synthesis of solid solutions based on lithium niobate.
  • Anna Jackiewicz, Albert Podgórski, Leon Gradoń, Jakub Michalski
    Type: Original Research Papers
    2013 Volume 30 Pages 244-255
    Published: 2013
    Released: December 20, 2013
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    The main objective of this study was to present one of the possibilities of increasing the initial efficiency of aerosol particle removal from the gas stream, i.e. the application of nanofibers in the filter structure. The modified melt-blown technique of producing such thin fibers is hereby presented. During this work, various filter media with fiber diameters from micro- to nanosized made of selected polymers differing in melt flow index were obtained via this method. Their morphology was precisely analysed using high-resolution equipment. The crucial parameters characterizing those fibrous materials were determined: an initial pressure drop across the filters and an initial filtration efficiency. The behavior of clean filters composed of microfibers were compared with the behavior of those made of nanofibers. An attempt was made to decrease the diameter of fibers to the nano range by using different materials for their formation. Collected data of penetration for melt-blown fibrous media were described via experimentally verified realistic models for better simulation of the air filter’s performance. Additionally, the obtained results were compared with predictions of the classic filtration theory predominating in the literature on the subject.
  • Jing Wang
    Type: Original Research Papers
    2013 Volume 30 Pages 256-266
    Published: 2013
    Released: December 20, 2013
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    The rapid development of nanotechnology brings new challenges to aerosol filtration, which plays a critical role in controlling pollution and protecting the environment and human health. The filtration of airborne nanoparticles is becoming an important issue as they are produced in large quantities from material synthesis and combustion emission. Recent studies indicate that the filtration efficiency increases as the particle size decreases down to 2 – 3 nm. Thus the conventional filters are working well against the nanoparticles. The filtration of non-spherical nanomaterials, such as carbon nanotubes and nanoparticle agglomerates, possesses different filtration characteristics compared to spherical particles. The interception effect for elongated particles is stronger than for spheres with the same mobility, thus higher filtration efficiency is achieved. Modeling results based on the single-fiber theory are compared to experimental data and then used to predict the difference between the filter penetrations for agglomerates and spheres. The effects of the filtration velocity, filter fiber size, solidity and thickness are systematically investigated.
  • Alexander Stepuk, Karl W. Krämer, Wendelin J. Stark
    Type: Original Research Papers
    2013 Volume 30 Pages 267-275
    Published: 2013
    Released: December 20, 2013
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    Recent improvements in precursor chemistry, reactor geometry and run conditions extend the manufacturing capability of traditional flame aerosol synthesis of oxide nanoparticles to metals, alloys and inorganic complex salts. As an example of a demanding composition, we demonstrate here the one-step flame synthesis of nanoparticles of a 4-element non-oxide phosphor for upconversion applications. The phosphors are characterized in terms of emission capability, phase purity and thermal phase evolution. The preparation of flame-made β-NaYF4 with dopants of Yb, Tm or Yb, Er furthermore illustrates the now available nanoparticle synthesis tool boxes based on modified flame-spray synthesis from our laboratories at ETH Zurich. Since scaling concepts for flame synthesis, including large-scale filtration and powder handling, have become available commercially, the development of industrial applications of complex nanoparticles of metals, alloys or most other thermally stable, inorganic compounds can now be considered a feasible alternative to traditional top-down manufacturing or liquid-intense wet chemistry.
  • Stefan Zigan, Amit Patel
    Type: Original Research Papers
    2013 Volume 30 Pages 276-283
    Published: 2013
    Released: December 20, 2013
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    The generalisation of scientific findings between differently sized silos is a challenge faced across many industries. One obstacle is the scaling of material properties (e.g. particle size), process parameters (e.g. the powder feeding rate) and dimensions (e.g. silo diameter and height) to obtain significant results1). The second issue for a meaningful scaling law is maintaining the dynamic similarity between two differently sized silos. A common phenomenon observed when filling alumina storage silos is called air current segregation (ACS,) and was investigated in detail in Zigan et al.2). This paper is now a continuation, exposing the developed scaling rule to a challenging test by replacing alumina with sand particles and the continuum air with water. Results of the scaling tests show that the proposed dimensionless groups do not capture the complete physics. One reason is that using terminal velocity in the scaling law as a physical parameter to lump in fluid and material properties over-simplifies the problem. Another finding is that the particle dynamics in the water model is somehow different from experiments in the air silo.
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