Agglomeration Of Fine Particles Research Articles

On fragmenting, densely mineralised acellular protrusions into articular cartilage and their possible role in osteoarthritis.

High density mineralised protrusions (HDMP) from the tidemark mineralising front into hyaline articular cartilage (HAC) were first described in Thoroughbred racehorse fetlock joints and later in Icelandic horse hock joints. We now report them in human material. Whole femoral heads removed at operation for joint replacement or from dissection room cadavers were imaged using magnetic resonance imaging (MRI) dual echo steady state at 0.23mm resolution, then 26-μm resolution high contrast X-ray microtomography, sectioned and embedded in polymethylmethacrylate, blocks cut and polished and re-imaged with 6-μm resolution X-ray microtomography. Tissue mineralisation density was imaged using backscattered electron SEM (BSE SEM) at 20kV with uncoated samples. HAC histology was studied by BSE SEM after staining block faces with ammonium triiodide solution. HDMP arise via the extrusion of an unknown mineralisable matrix into clefts in HAC, a process of acellular dystrophic calcification. Their formation may be an extension of a crack self-healing mechanism found in bone and articular calcified cartilage. Mineral concentration exceeds that of articular calcified cartilage and is not uniform. It is probable that they have not been reported previously because they are removed by decalcification with standard protocols. Mineral phase morphology frequently shows the agglomeration of many fine particles into larger concretions. HDMP are surrounded by HAC, are brittle, and show fault lines within them. Dense fragments found within damaged HAC could make a significant contribution to joint destruction. At least larger HDMP can be detected with the best MRI imaging ex vivo.

Production of nanocrystalline TiB2 powder through self-propagating high temperature synthesis (SHS) of TiO2–H3BO3–Mg mixture

Nanocrystalline TiB2 powders are produced through self-propagating high temperature synthesis (SHS) technique by igniting the stoichiometric mixture of titanium oxide (TiO2), boric acid (H3BO3) and magnesium (Mg) powder. Different percentages of NaCl are added to the mixture as SHS diluent in order to control the particle size of the TiB2. The synthesised and purified powder is characterised by X-ray diffraction and electron microscopes respectively. The SEM images show the presence of agglomeration of fine spherical particles. The TEM images reveal the formation of nanocrystalline TiB2 particles. The particle size is found to decrease with the addition of NaCl. The TEM images reveal the presence of crystallographic defects in the powder. In order to find out the reaction mechanism of TiO2–H3BO3–Mg system, the synthesis of TiO2–Mg and H3BO3–Mg mixtures is performed in inert atmosphere and phase analysis of TiO2–Mg and H3BO3–Mg mixtures reveal the reaction mechanism.

Synthesis of Ni–Mn ferrite–chromite nanoparticles through plasma arc discharge

Ni–Mn ferrite–chromite was synthesized through plasma arc discharge in an atmosphere of pure oxygen. X53CrMnNiN219 nonmagnetic stainless steel was used in the form of anodic and cathodic electrodes as raw material. Powders were produced at three different currents of 100, 200 and 300A and under three different oxygen pressures of 0.5, 1 and 2atm. The product powders are agglomerates of fine particles whose typical diameters are several tens of nanometers. X-ray diffraction data confirm that nanocrystalline powders with a spinel structure have been formed successfully in all samples. Morphological studies using field emission scanning electron microscopy show agglomerated clusters with an average particle size of 100nm. The saturation magnetization of the produced powders is in the range 31 to 34emu/g, as measured by a vibrating sample magnetometer.

Discrete element modeling of the microstructure of fine particle agglomerates in sheared dilute suspension

The fragmentation and restructuring under shear of agglomerates of fine mineral particles are studied with the Distinct Element Method. The model used takes into account contact forces, van der Waals forces, and hydrodynamic forces computed with the free-draining approximation. A loose initial agglomerate is submitted to a constant shear rate until reaching a quasi-stationary state, where the number, size and structure of fragment of agglomerates can be considered as constant. The influence of shear stress and size of particles on the characteristics of agglomerates at equilibrium is studied. Fragmentation is controlled by a non-dimensional number, depending on the radius of the particles, shear rate and maximal adhesion force.

Acoustic Coagulation of Fine Particles from WFGD

The objective of this study is employing acoustic coagulation to induce agglomeration of fine and ultrafine particles after wet flue gas desulfurization (WFGD) and analyzing its effectiveness and characteristic based on numerical simulation. Matters such as calcium sulfate and calcium sulfite in WFGD can form very fine particles. Smoluchoski’s equation is employed as the simulating model. Orthokinetic coagulation, hydrodynamic coagulation and Brownian coagulation are taken into account to form the agglomeration kernel. An improved sectional arithmetic is introduced to achieve sectional size adjusting automatically according to the mass concentration of particles, so that section size is fine where the mass concentration is large to guarantee computational accuracy, but coarse where the mass concentration is small to save computation time. Besides, mass conservation rate is introduced to estimate the calculation error in the compute of mass concentration. Simulation results show that the overall number concentration decreased more than 40% after acoustic wave acting on the flue gas for 2 second; Increasing sound intensity level (SIL) is more effective to coagulation than increasing frequency; There exists an optimal acoustic wave frequency within 1500~2000Hz; Coarse particles are more sensitive to acoustic wave frequency than fine particles.

Numerical modelling of breakage and adhesion of loose fine-particle agglomerates

In this study, discrete element method (DEM) simulations are used to examine the breakage and capturing behaviour of loose fine-particle agglomerates on impact with a target particle. The model system is an agglomerate composed of 5µm fine particles and a 200µm target particle. The cohesion between fine particles was modelled using the Johnson, Kendall and Roberts (JKR) theory. In contrast to the breakage of hard agglomerates which break in large fragments, as commonly investigated, loose agglomerates break in finer fragments. Impact velocity was found to be a significant parameter not only for the adhesion strength but also for the structure of the particles captured on the target. The capture ratio of the agglomerate as well as the thickness of the particle layer covering the target decreases with increasing impact velocity. High impact velocity results in finer fragments attached to the target with greater tensile strength due to the re-structuring mechanism that occurs during impact. Accordingly, impact velocity is one of the critical parameters governing the structure resulting after collision. However, the effect of material properties, e.g. surface energy, material hardness and plasticity, on adhesion behaviour should be investigated to obtain a full picture of the breakage-adhesion regime map.

Experimental research on acoustic agglomeration of fine aerosol particles in the standing-wave tube with abrupt section

There is great concern about air pollution caused by fine aerosol particles, which are difficult to be removed by conventional removal system. Acoustic agglomeration is proved to be a promising method for particle control by coagulating the small particles into larger ones. Removal efficiency was grown rapidly as acoustic intensity increased. A standing-wave tube system with abrupt section was designed and built up to generate high intensity sound waves above 160 dB and avoid strong shock waves. Extensive tests were carried out to investigate the acoustic field and removal characteristics of coal-fired inhalation particles. For the development of industrial level system, a high power air-modulated speaker was applied and an insulation plate was used to separate flow induced sound. Separate experiments to determine the difference of plane standing-wave field and high order mode were conducted. The experimental study has demonstrated that agglomeration increases as sound pressure level, mass loading, and exposure time increase. The optimal frequency is around 2400 Hz for attaining integral removal effectiveness. The agglomeration rate is larger (above 86%) as much greater sound level is achieved for the pneumatic source and high order mode. The mechanism and testing system can be used effectively in industrial processes.

The effect of particle agglomeration and attrition on the separation efficiency of a Stairmand cyclone

The influence of material properties on the separation grade efficiency of cyclones has long been ignored by researchers. This experimental study investigates the behaviour of two powders of similar density, Kaolin and SAE, in a small scale Stairmand cyclone with inlet velocities of 15, 30 and 45ms−1. Initially evidence of agglomeration of fine particles occurring within the cyclone body is observed; however, as the inlet velocity increases, particle attrition dominates the behaviour of fine particles in the grade efficiency graphs. Both powders respond similarly to increased flow rates; however, Kaolin exhibits a greater tendency to agglomeration and attrition, which is manifested in the difference between the respective grade efficiency curves, thus demonstrating the complex effect of material properties on cyclone efficiency.

Single and mixed oxide and clay particle agglomeration: Influence of feed mineralogy and percent drum volume loading

Agglomeration of fine particles into coarse and robust product with desired attributes is a key precursor to a number of industrial processes and unit operations. This study investigates isothermal, batch, drum agglomeration behaviour and agglomerate attributes of model, single and mixed oxide (hematite and quartz) and clay (kaolinite and smectite) minerals, the nature of which reflects mineral feed ore preparation for heap leaching. Particularly, the influence of per cent drum volume loading and feed mineralogical composition on agglomeration behaviour and product structural properties was examined. 5–40mm size agglomerates produced with 30% w/w H2SO4 solution as a binding medium displayed drum volume loading and mineralogy dependent structure and properties. Increasing the per cent drum volume loading from 2.9 to 8.6 led to the formation of larger agglomerates due to a concomitant increase in particles' collision frequency. Furthermore, clay-rich (single and mixed minerals) feeds exhibited slower growth rates than the oxide-rich ones, despite the higher binder dosages used in the agglomeration of the former. For mineral type (clay vs. oxide) particle–binder interactions during agglomeration, NMR analysis showed that H2SO4 adsorption by kaolinite was considerably greater than that of quartz. On equivalent feed masses, the differences in agglomerate growth rates of the oxide and clay minerals can be attributed to the differences in their intrinsic properties (e.g., plasticity, ore mineralogy/chemistry). Dry agglomerates' compressive strengths for kaolinite and hematite were quite similar and greater than those for quartz and smectite. Their re-wetting stability, however, decreased in the order: kaolinite>quartz>hematite=smectite. Oxide and clay minerals mixing and synergistic particles' interactions resulted in agglomerates which displayed markedly enhanced compressive strength and re-wetting stability.

Ion-irradiation effects on dissimilar friction stir welded joints between ODS alloy and ferritic stainless steel

Friction stir spot welding (FSSW) is an advanced technique for the joining of materials to prevent agglomeration of fine oxide particles, grain coarsening, and stress corrosion cracking etc. In this study, the dissimilar FSSW joint of stainless steel 430/ODS was irradiated with a Fe+/He+ dual ion beam. Irradiation damage can cause deterioration in the mechanical properties especially in the welding zones. The joint quality therefore plays a decisive role in the life expectancy of nuclear reactors. The effect of irradiation on different zones in the joint (the thermo-mechanically affected zone, the heat affected zone and the base material) was investigated by TEM and nanoindentation. Irradiation causes a hardness increase in all welding zones with a characteristic hardness maximum. The relative hardness increase and the related microstructure are discussed. The formation of He bubbles at chromium carbide precipitates and the homogeneous distribution of He filled vacancies in the mixture region of the 430/ODS FSSW joints was observed.

Improved microstructure and performance of Ni-based anode for intermediate temperature solid oxide fuel cells

Three kinds of anodes prepared by NiO impregnation, (Ni, Mg)O impregnation and conventional sintering methods are investigated under the conditions of anodic current polarization and redox cycling. The optimized NiO loading in the NiO-impregnated anode is 40 wt%; and the minimum polarization resistance is 1.40, 0.71 and 0.60 Ω cm2 at 700, 750 and 800 °C, respectively, due to the increased triple phase boundary and conductivity that promote the charge-transfer process of H2 oxidation reaction. The conventional Ni–YSZ cermet anode is less sensitive to the current polarization at 200 mA cm−2; however, its polarization resistance is much higher than those of the impregnated anodes. (Ni, Mg)O impregnation improves the performance durability and redox-ability at 800 °C, with a low polarization resistance of 0.93 Ω cm2 after 48 h of current polarization and of 0.71 Ω cm2 after 10 redox cycles. The addition of Mg lowers the reducibility of (Ni, Mg)O particles; and its improved electrochemical performance and redox cycling resistance are attributed to its stabilized microstructure consisting of nano-scale Ni particles distributed on the surface of the pre-sintered YSZ scaffold. The agglomeration of fine Ni particles is suppressed by the unreduced (Ni, Mg)O in the anode.

Desenvolvimento de pó à base de gesso e binder para prototipagem rápida

Foram desenvolvidas formulações de pó à base de gesso e binder para aplicação em equipamento de prototipagem do tipo 3D Print. Na técnica de impressão tridimensional, impressoras denominadas 3D Print são baseadas em cabeçotes de impressão de impressoras comerciais a jato de tinta, que depositam um binder sobre camadas sucessivas de pó e, em cada fatia, o binder reage com o pó e consolida o formato bidimensional da seção, que somadas às fatias subsequentes, consolidam um modelo tridimensional. Embora este modelo de impressora tridimensional esteja se popularizando pelo baixo custo, ainda tem em seus insumos o pó e o binder o seu maior empecilho devido ao custo elevado. Neste projeto foram desenvolvidas formulações de pós, obtidos pela moagem do gesso em meio alcoólico com ligantes e aditivos, seguido de aglomeração das finas partículas de gesso, e formulações de binder baseadas na reação com o gesso. Foram avaliadas as condições do pó aglomerado para a uniformidade da deposição das camadas e os requisitos mínimos do binder para a operação do cabeçote de impressão. Corpos de prova no formato de barras foram produzidos em equipamento comercial e analisados com relação à resistência a flexão, densidade e metrologia. Foram obtidos corpos a partir de pó com adição de 5 vol.% de PVB e binder com 90 vol.% de água destilada e resistência de 290 kΩ, que apresentaram resistência média à flexão de 0,33 MPa, suficiente para o manuseio inicial dos prototipados, com manufatura simplificada e a um custo muito econômico.

Numerical study of the gas–solid flow characteristic of fibrous media based on SEM using CFD–DEM

The Computational Fluid Dynamics (CFD)–Discrete Element Method (DEM) coupled method was applied to simulate the gas–solid flow characteristic within the fibrous media, and then to study the influences of the fiber structure and particle properties on particle deposition and agglomeration characteristics in the filtration process. In addition, six fibrous structures with different sizes were designed in this study to analyze the impact of the structural parameters on the filtration performances (including pressure drop and filtration efficiency). The results show that it is convenient and feasible to investigate the fine particle deposition and agglomeration process on the surface of the media using CFD–DEM, and the simulation results are identical with the former experimental observations, numerical simulation and empirical correlation results. In the filtration process, the particles may stack together to form the dendritic structure on the surface of the fibrous media. The pressure drops of all fibrous structures increase relative to those of the gas flow field, and show the trend of the exponential growth. Meanwhile, the total pressure drop of the fibrous media increases with the fiber diameter df, and when df and the length of fibrous media (H) are constant, the pressure drop increases with decreasing the distance that the fiber deviates from the former cross section (L). The pressure drop decreases with the increase of H when df and L keep unchanged; The filtration efficiency decreases with increasing L, and changing H has basically no effect on the filtration efficiency.

Effect of nickel laterite agglomerate properties on their leaching performance

Heap leaching is a widely used extraction method for low-grade minerals including nickel and cobalt. Agglomeration of fine mineral particles as a precursor to heap leaching is an important means of enhancing leaching rates and metal recoveries. Single pellet leaching behaviour of three nickel laterite ores, namely siliceous goethitic (SG), goethitic (G) and saprolitic (SAP) was investigated to assess the effect of pellet properties (binder type, binder content, porosity and dryness) on its stability, initial leaching rate and maximum Ni recovery. The column leaching performance of agglomerates of the same ores was also investigated. Both single pellet and column leaching tests showed that the ore mineralogy played a major role in the Ni extraction rate, with G-type of ore the lowest. The Ni extraction rate was also found to be directly related to the pellet/agglomerate dryness and the highest rate was obtained at an intermediate degree of dryness due to the better wetting and diffusion of acidic lixiviant into the pores in between the particles. However, no significant effect of drying on the stability of the agglomerates (measured by agglomerate slump in the column) was found in column leaching. For G type of ore, mixing it with high clay ores during agglomeration is recommended to enhance its robustness during leaching process.

Discontinuous addition of small volumes of liquids in an intensive mixer to animal supplement feed with different particle size distributions

Abstract Animal compound and supplement feed can generally be characterised as dispersible multi-ingredient mixtures in which particles differ in size, density and shape and tend to segregate. The segregation of animal compound and supplement feed is frequently a reason for customer and official complaints. To avoid segregation, usually small volumes of liquids – e.g. molasses or vegetable oils – are added in the main mixer of a feed production line to cause fractional agglomeration of fine particles. The presence of small volumes of liquids will affect the distribution behaviour of particles during mixing and it may also influence the material and technological properties. However, the mixing homogeneity of typical compound feeds that can be achieved when small volumes of liquids are present is not adequately characterised at the moment. There is insufficient knowledge of the process design and specifically the time of the liquid application in the mixing sequence. This study aimed to investigate the effect of adding liquids in customary amounts to animal supplement feed on the achievable mixing homogeneity as well as its dependency on the time of the liquid application in the mixing sequence. Major material properties, namely flowability and dusting potential, were determined to evaluate both the results and the product quality. An intensive mixer equipped with a feed pipe for liquid application was used as test facility. The results show that, under certain conditions, the addition of liquids in an intensive mixer may have a positive effect on the achievable mixing homogeneity of mineral feeding stuffs.

Carbothermal synthesis of Si3N4 powders using a combustion synthesis precursor

Si3N4 powders were synthesized by a carbothermal reduction method using a SiO2 + C combustion synthesis precursor derived from a mixed solution consisting of silicic acid (Si source), polyacrylamide (additive), nitric acid (oxidizer), urea (fuel), and glucose (C source). Scanning electron microscopy (SEM) micrographs showed that the obtained precursor exhibited a uniform mixture of SiO2 + C composed of porous blocky particles up to ∼20 μm. The precursor was subsequently calcined under nitrogen at 1200–1550°C for 2 h. X-ray diffraction (XRD) analysis revealed that the initial reduction reaction started at about 1300°C, and the complete transition of SiO2 into Si3N4 was found at 1550°C. The Si3N4 powders, synthesized at 1550°C, exhibit a mixture phase of α- and β-Si3N4 and consist of mainly agglomerates of fine particles of 100–300 nm, needle-like crystals and whiskers with a diameter of about 100 nm and a length up to several micrometers, and a minor amount of irregular-shaped growths.

Characterization of nanocrystalline Mg0.6Zn0.4Fe2O4 soft ferrites synthesized by glycine-nitrate combustion process

In this study, Mg–Zn ferrite with the chemical formula of Mg0.6Zn0.4Fe2O4 is synthesized through a modified combustion synthesis using glycine as fuel and metal (Mg, Zn and Fe) nitrates as reactants. The technique, known as glycine-nitrate process, involves exothermic decomposition of a viscous liquid, prepared by thermal dehydration of an aqueous solution containing metal nitrates and glycine. The product powders produced at seven different molar ratios of glycine to nitrate (G/N ratio), varying from 0.37 to 0.75, are agglomerates of fine particles whose typical diameter are several tens of nanometers. Thermodynamic modeling of the combustion reaction indicates that as the fuel-to-oxidant ratio increases, the amount of gases produced and the adiabatic flame temperature rise. X-ray diffraction shows that samples crystallize in a spinel-type structure in all reactions. The morphology of the powders is examined using field emission scanning electron microscopy and transmission electron microscopy. Through magnetic measurements conducted by a vibrating sample magnetometer, the maximum saturation magnetization (46emu/g) is found to occur at the highest G/N ratio.

Drum agglomeration behavior of nickel laterite ore: Effect of process variables

Heap leaching is a promising, economically viable processing pathway for extracting nickel (Ni) and cobalt (Co) from complex, low grade laterite ores. Producing a stable heap with high permeability and sustainable lixiviant percolation rate is a key requirement to ensure efficient leaching operation for maximum value metal recovery. Agglomeration of fine ore particles to produce robust granules with desirable attributes (e.g., size distribution and strength and porosity) is a critically important precursor to the heap leaching process. In this study, the effect of binder type/composition and dosage, drum speed, temperature and batch time on drum agglomeration behavior of siliceous goethite (SG) Ni laterite ore was investigated. Isothermal, batch agglomeration performed with tap water and 30, 44 and 98%w/w H2SO4 solutions as binders revealed the key role of binder dosage and acidity in controlling ore particle wettability, granule nucleation and growth behavior. Increasing the binder acidity from zero (tap water) to 30, 44 and 98%w/w H2SO4 led to a higher binder dosage to initiate and maintain a moderate rate of agglomeration. This accordingly reflected decreasing growth rates with increasing binder acidity where 98%w/w H2SO4 resulted in complete suppression of granule growth. At a fixed binder acidity and dosage, both higher temperature and drum speeds led to faster agglomeration rates. The impact of binder acidity and dosage on agglomerates' wet strength appeared to be insignificant. Acid-bound, wet agglomerates' integrity/stability in solution was, however, greater at lower binder dosage and/or binder acidity. The findings foster our understanding of how various, primary process variables may be prudently controlled to produce Ni laterite agglomerates with desirable properties and behavior, as a key step to enhance heap leaching.

Frequency comparative study of coal-fired fly ash acoustic agglomeration

Particulate pollution is main kind of atmospheric pollution. The fine particles are seriously harmful to human health and environment. Acoustic agglomeration is considered as a promising pretreatment technology for fine particle agglomeration. The mechanisms of acoustic agglomeration are very complex and the agglomeration efficiency is affected by many factors. The most important and controversial factor is frequency. Comparative studies between high-frequency and low-frequency sound source to agglomerate coalfired fly ash were carried out to investigate the influence of frequency on agglomeration efficiency. Acoustic agglomeration theoretical analysis, experimental particle size distributions (PSDs) and orthogonal design were examined. The results showed that the 20 kHz high-frequency sound source was not suitable to agglomerate coal-fired fly ash. Only within the size ranging from 0.2 to 0.25 μm the particles agglomerated to adhere together, and the agglomerated particles were smaller than 2.5 μm. The application of low-frequency (1000–1800 Hz) sound source was proved as an advisable pretreatment with the highest agglomeration efficiency of 75.3%, and all the number concentrations within the measuring range decreased. Orthogonal design L16 (4) 3 was introduced to determine the optimum frequency and optimize acoustic agglomeration condition. According to the results of orthogonal analysis, frequency was the dominant factor of coal-fired fly ash acoustic agglomeration and the optimum frequency was 1400 Hz.

Population balance based modelling of nickel laterite agglomeration behaviour

Agglomeration of fine mineral particles as a precursor to heap leaching is an important means of enhancing leaching rates and metal recoveries, particularly in processing low grade ores. In this paper, the modelling of a batch drum agglomeration process applied to nickel laterite using population balance model is explored. The coalescence kernels which are linked to feed material and agglomerator operating conditions are reviewed. The use of a physically based coalescence kernel which relates agglomerate layer thickness to binder content and agglomerate consolidation shows great promise for the modelling of the agglomerate size distribution of nickel laterite ore. The model parameters were then used to predict the effect of operating parameters such as binder content on agglomerate size distribution.