Production Of Fine Particles Research Articles

The β-richness of two detritivore caddisflies affects fine organic matter export

We used stream networks as a model system to test whether the ecosystem function, upstream production, and export of fine organic particles, an important subsidy to downstream habitats, would vary between two stream networks with identical detritivore species but different spatial distributions (i.e. high or low β-richness). Our experiment employed artificial stream networks with two simulated tributaries. We used two species of detritivorous caddisflies, Lepidostoma sp. and Pycnopsyche guttifer, in either sympatry (low β-richness) or allopatry (high β-richness) in the tributaries of each network. The tributaries were given either senesced or green speckled alder (Alnus incana rugosa). In the networks with senesced leaves, particle export was more than twice as great when the detritivores were in allopatry whereas interference competition in sympatry reduced particle export. In the networks with green leaves, particle export did not significantly vary between the allopatric and sympatric distributions because the interference competition was reduced and the two species had similar feeding rates on green leaves. Humans are altering β-richness by homogenizing or differentiating flora and fauna across habitats; however, little is known about how altering this type of biodiversity will affect ecosystem functions. Our experimental manipulation is a simple version of a change in the β-richness of the detritivores in a more complex stream network in nature. These results may indicate that shifts in species distributions across sites may significantly affect ecosystem functions, even when no species are lost from a watershed.

Rapid Precipitation of Magnesite Microcrystals from Mg(OH)2-H2O-CO2 Slurry Enhanced by NaOH and a Heat-Aging Step (from ∼20 to 90 °C)

This study proposes a simple and novel synthesis route for rhombohedral single crystals (<2 μm) of magnesite. This synthesis can be summarized by two main sequential reactions: (1) aqueous carbonation of synthetic brucite (Mg(OH)2) by injection of CO2 in a highly alkaline medium (2 m NaOH) at ambient temperature (∼20 °C), leading to precipitation of platy-compacted aggregates of dypingite (Mg5(CO3)4(OH)2·5H2O) after 24 h, and (2) complete dypingite-to-magnesite transformation after 24 h by a simple heat-aging step from 20 to 90 °C. The dypingite-to-magnesite transformation implies the simultaneous dehydration and carbonation of a brucitic layer of dypingite coupled with instantaneous formation of magnesite crystals. In this study, the NaOH played a catalytic role; that is, it accelerated brucite carbonation by an increase in carbonate ion concentration with time and it promoted the formation of magnesite during the heat-aging step, as illustrated in the following global reaction:At laboratory scale, magnesite is typically synthesized at high temperature (>90 °C) and its synthesis requires several days or weeks depending on experimental conditions. For this reason, industrial-scale magnesite production has been limited. The proposed magnesite synthesis method, requiring only 48 h and moderate temperature, could easily be extrapolated on an industrial scale. Moreover, a simple and novel synthesis route for the production of fine platy particles of hydromagnesite is reported, with synthesis requiring only 5 h. On the basis of their chemical compositions and textural properties, there are potential applications for both minerals, for example, as a mineral filler and/or as a flame retardant.

Use of Supercritical CO2 and N2 as Dissolved Gases for the Atomization of Ethanol and Water

Supercritical dissolved gas atomization (SDGA) is an atomization process in which a gas at temperatures and pressures above the critical point is used as the atomizing medium. The concept of SDGA has been applied mainly using CO2 as atomizing gas in various processes developed for the production of fine particles of pharmaceuticals, polymers, and chemical products and for the atomization of fuels. In this work, SDGA, using ethanol and water as the liquids to be atomized, has been experimentally studied. The spray characteristics, in terms of droplet size and distribution, have been investigated using a laser diffraction analyzer. Ethanol has been chosen due to the large miscibility with CO2 and for its wide use as a solvent in particle formation processes. The use of N2 as an atomizing gas has been also studied. Very narrow droplet size distributions were produced down to 2.5 μm. The properties of the liquid to be atomized (water or ethanol) showed a negligible effect on droplet size. The main parameter t...

Fine Particles of Rubber Cutting Machine Designed to Explore

Tire production of fine particles of powder composition and the mechanical arrangement of tool methods of efficiency of the larger craft. Fine particles of cutting edge cutting machine is a small gap between the edge of the particles produced can not exercise the role of the crowded file. File can not be cut and milled to achieve simultaneously. Multi-blade knife and bevel knife gap between the tool installation form. Between powder particles in the twice cut or ground to reduce the powder particle size cheddar and improve work efficiency results.

Production of Fine Organic Crystalline Particles by Using Milli Segmented Flow Crystallizer

In the pharmaceutical production field, it is required to produce organic fine crystalline particles having a monodispersed crystal size distribution (CSD). Anti-solvent crystallization is one method for producing crystal particles. In order to produce fine crystalline particles and/or crystals having a monodispersed CSD, several methods such as segmented flow in the tubular crystallizer, ultrasound irradiation, and modulated operation in batch cooling crystallization have been studied in previous studies. In this study, integrated operation of ultrasound irradiation and temperature modulation at a milli-sized segmented flow has been carried out to produce organic fine crystalline particles having a monodispersed CSD in the anti-solvent crystallization. Taurine (solute)–water (solvent)–EtOH (anti-solvent) system is employed. The effect of segmented flow on mixing solution has been observed with a high-speed microscope. Fine crystalline particles which have tens of microns average size are obtained with the integration of ultrasound irradiation and temperature modulation on a milli-sized segmented flow. Furthermore, crystals of 10 µm size are produced under controlled supersaturation condition. Additionally, it is suggested that the CSD could be improved by introducing temperature modulation after nucleation.

The attrition behaviour of oxygen-carriers under inert and reacting conditions

The attrition of two potential oxygen-carriers for chemical-looping, 100wt% mechanically-mixed, unsupported iron oxide (400–600μm diameter) and 25wt% copper oxide impregnated on alumina (600–900μm diameter), has been studied. The rates of attrition of batches of these particles whilst they were being fluidised and subjected to successive cycles of reduction and oxidation were determined by measuring the rate of production of fine particles elutriated from the bed, as well as progressive changes in the distribution of particle sizes retained in the bed. The ability of the particles to withstand impacts was also investigated by examining the degree of fragmentation of 1g of reacted particles of known size on projecting them at a target at various velocities. It was found that the mechanical strength of the iron oxide particles deteriorated significantly after repeated cycles of oxidation and reduction. Thus, the rate of elutriation increased ∼35-fold between the 1st and 10th cycle. At an impact velocity of 38m/s, the amount of fragmentation in the impact test, viz. mass fraction of particles after impact having a size less than that before impact, increased from ∼2.3wt% (fresh particles) to 98wt% after the 10th cycle. The CuO particles, in comparison, were able to withstand repeated reaction: no signs of increased rates of elutriation or fragmentation were observed over ten cycles. These results highlight the importance of selecting a durable support for oxygen-carriers.

Effect of gas and liquid flowrates on the size distribution of barium sulfate nanoparticles precipitated in a two phase flow capillary microreactor

Production of fine particles by precipitation is a relatively simple process but the control of product particle size distribution can be difficult. In recent years microreactors are being seen as effective devices to achieve this aim and in that the two-phase flow microreactor is a promising alternative. In the present work, fine (nano/micro) particles of barium sulfate have been produced by reacting barium chloride and sodium sulfate solutions in a 30 cm long and 830 μm inner diameter glass capillary microreactor. The T-inlet section has all three limbs 15 mm long and 1 mm in diameter. Particle sizes produced ranged from about 200 nm to 1100 nm, with mean sizes between 300 nm and 670 nm. Results show that an increase in the flowrate of any of the three streams, the two reactant liquid streams and one inert gas stream, led to a decrease in the mean particle size of the precipitated barium sulfate product. Increased mixing and higher Ba 2+ ion concentrations in the small microreactor (liquid slugs) are believed to shift rates in favour of nucleation as compared to agglomeration, yielding smaller particles in the product. Size variation results show a trend similar to that reported in earlier researches on BaSO 4 precipitation in single (liquid) phase microreactors but the actual sizes obtained in the present work are bigger. Other geometries and flow conditions may yield smaller particles, hence the need for further investigation of the two-phase flow system.

Characterisation of pharmaceutical materials produced by electrospraying

Electrospraying of solutions or suspensions provides a method for production of fine particles, in certain conditions even down to nanometer size. In the present study, electrospraying was used in drug particle production. The most important properties of the produced particles in a pharmaceutical sense are size distribution, degree of crystallinity and porosity. The size of the produced particles can easily be tailored by varying the concentration of the dissolved material, electric field strength or liquid flow rate. Most experiments on electrospraying are performed at atmospheric pressure. In the present study, the produced particles were dried under atmospheric or reduced pressure, the latter in order to improve the drying process. The effect of pressure reduction on the degree of crystallinity of the produced drug particles was studied by XRD and DSC. Also the porosity of the particles depends mainly on the drying conditions. The porosity and size of the produced particles was studied by SEM imaging.

Effect of crude oil ageing on low salinity and low salinity surfactant flooding

Injection of brine with lower salinity than the connate brine has proven to give a moderate increase in oil recovery in sandstones. Recent research has shown that this process will significantly benefit from introducing surfactant optimised for low salinity environment. The mechanisms underlying increased recovery by low salinity brine injection are not yet fully understood. However, research to date suggests that they are related to complex crude oil/brine/rock interactions. With this in mind, the present paper investigates primarily how the extent of oil recovery from Berea sandstones subjected to long term exposure of crude oil is influenced by (1) low salinity water injection and (2) combined process low salinity water injection with surfactant flooding. Core displacement tests were conducted on four Berea cores (30 cm), two in a natural state and two that had been subject to extensive crude oil ageing at high temperature. Results obtained from different flooding steps are discussed in terms of oil recovery and effluent properties including turbidity, pH- and ion analysis (Na +, Mg 2+, Ca 2+). The results effectively illustrate that oil recoveries from the aged cores are higher during both low salinity water injection and low salinity water injection combined with surfactant flooding. An assessment of how tertiary oil recovery in aged and unaged cores varies with surfactant concentration is also presented. Effluent ion analysis from low salinity water floods showed that Mg 2+ ions were strongly retained in the aged core while Ca 2+ ions were being produced from both aged and unaged cores. The latter was attributed mainly to calcite dissolution. Results obtained from pressure profiles, effluent ion analysis and turbidity tests suggest higher production and elution of fine particles from the unaged core.

Novel aspects of wet milling for the production of microsuspensions and nanosuspensions of poorly water-soluble drugs

Micronization and nanoparticle production of poorly water-soluble drugs was investigated using single wet milling equipment operating in the attritor and stirred media modes. The drug particles in the median size range of 0.2–2 µm were prepared by changing the milling mode and operating conditions of a Micros mill with a purpose of elucidating the dynamics of the wet milling process. It was determined that particle breakage due to mechanical stresses and aggregation due to insufficient stabilization are two competing mechanisms which together control the wet milling dynamics of the poorly water-soluble drugs. The study in the attritor mode using four different classes of stabilizers with six drugs indicated that steric stabilization worked better than electrostatic stabilization for the drugs studied. In addition, the existence of different minimum polymer concentrations for the stabilization of microsuspensions and nanosuspensions was indicated. The major role of a non-ionic polymer during the production of fine particles is its stabilization action through steric effects, and no experimental evidence was found to support the so-called Rehbinder effect. Periodic addition of the polymer as opposed to the addition of the polymer at the start of milling process was introduced as a novel processing method. This novel method of polymer addition provided effective stabilization and breakage of drug particles leading to a narrower and finer particle size distribution. Alternatively, it may allow shorter processing time and lower overall power consumption of the milling process for a desired particle size.

DEM Simulation of Autogenous Grinding Process in a Tumbling Mill

We have investigated on size reduction process in an autogenous (AG) grinding a solid in a tumbling mill with 12.1 cm in inner diameter and 14.7 cm in length. The model solid samples were two kinds of cubic shaped sugar particles, having 15 mm x 15 mm x 15 mm. The size reduction process of these samples was monitored by using DEM simulation as well as the experiment, both of which were conducted in ambient condition. As a result, the motion of the samples simulated has been shown by surface grinding model, and this grinding behavior explains fairly well the phenomena observed by the experiment. The fine particle production ratio observed by the experiment is in agreement quantitatively with that shown by the DEM simulation. Consequently, we have confirmed that the AG grinding process of the solid samples in the mill can be promoted by surface grinding under the present condition.

Analysis of Dissolved-Gas Atomization: Supercritical CO2 Dissolved in Water

Supercritical dissolved-gas atomization is an atomization process in which carbon dioxide at temperature and pressure above its critical point is used as the atomizing gas. The spray characteristics in terms of droplets size and distribution have been experimentally studied using a laser diffraction method based on a Malvern apparatus. The main parameter that influences the droplets size is the gas-to-liquid mass ratio (GLR); the injection pressure in the range of 7.4−13 MPa has a minor effect. Upon variation of the GLR from 0.5 to 3, the droplet mean diameter changes from about 8.0 to 2.0 μm; very narrow droplet size distributions are also produced. From the point of view of the atomization mechanism, the mean droplet diameter is mainly influenced by the sudden release of the gas dissolved in the liquid. The overall analysis of the experimental data confirms that dissolved-gas atomization allows for the formation of micrometric droplets that can produce precipitates with controlled sizes and distributions that are useful in several fine-particles production processes.

Effects of concentration of dispersions on particle sizing during production of fine particles in wet grinding process

Stirred media milling is a prospective technology for producing colloidal dispersions by means of wet grinding process. In the past, many researchers have studied the effects of different operating parameters such as size, shape, nature and quantity of grinding medium, the speed of agitator in grinding chamber, the feed rate of dispersions, etc. in stirred media mills. However, it is still less known how particle sizing which generates valuable information of particle size of the product to interpret, control and optimize the grinding process, is influenced by the concentration of the dispersion during stirred media milling where particles change their size from micron to colloidal range rapidly. One of the reasons of this lack had been our incapability in the past to study the particle size distribution of dispersions without dilution. The recent advent of acoustic attenuation spectroscopy is known to be capable of studying dispersions without dilution, under real process conditions and on line. The study employs acoustic attenuation spectroscopy to investigate the effects of concentration of dispersions of CaCO 3 on its particle sizing during size reduction process in a stirred media mill (LabStar manufactured by NETZSCH). The dispersions of CaCO 3 at 5%, 10%, 20% and 30% (m/m) were studied about six hours under a selected set of operating conditions. Contrary to the existing knowledge obtained through other techniques of particle sizing that are based on the principle of dilution, acoustic attenuation spectroscopy shows that, under certain grinding time at given operating conditions, increase in concentration of dispersion results in better grinding results yielding smaller particles. The causes behind the differences in results of acoustic attenuation spectroscopy and dynamic light scattering have been thoroughly investigated. We find certain limitations of acoustic attenuation spectroscopy in particle sizing. A typical phenomenon which causes misleading trends in particle sizing is multiple scattering in acoustic measurements. Multiple scattering, particularly, influences acoustic results when particles approach to fine size range during size reduction process.

Influence of dry and wet grinding conditions on fineness and shape of particle size distribution of product in a ball mill

The influence of grinding conditions on the production of fine particles and the width of the particle size distribution produced during ball mill grinding was investigated. The grinding experiments were carried out varying the grinding ball diameter under dry and wet conditions. The relation between the weight passing size observed in an arbitrary cumulative undersize fraction and the grinding time was expressed by modifying Tanaka’s semi-theoretical equation for the grinding limit. The fineness of the product was evaluated by the median particle size in undersize distribution, and the shape of the particle size distributions by three different size ratios calculated using 10%, 20%, 50%, 80% and 90% cumulative weight passing sizes, that showed the width of the particle size distribution. The median particle sizes of product obtained for the grinding limit in wet and dry conditions were around 0.5–0.6 μm and 2 μm, respectively. The width of the particle size distribution in wet grinding decreased with decreasing median particle size of the ground product, and the size distribution in dry grinding became nearly constant. The particle size distribution width was lowered by using smaller grinding balls in wet condition and larger grinding balls in dry condition.

Loess and dust on Earth and Mars: particle generation by impact mechanisms

Abstract Impact between windblown quartz grains as a source of desert dust is consistent with laboratory abrasion experiments and has received some field confirmation in the Negev. The suggestion is that an important process on Mars now gains support from laboratory studies; even though their geochemical interpretation is controversial, they show that dust generation by impact is tenable even for quartz. A simple mechanism for small dust production from sand seas is proposed; internal stresses can be mobilized by impact energy. A speculative mechanism (the andesite scenario) is proposed for fine particle production by particle impact on Mars. The internal stress range in terrestrial sand grains may vary, depending on the nature of the source rock, and this may influence particle production by impact processes.

Finer Silver Nano-Particle Producing in Water Utilizing a Dielectric Bed

An fine silver particle has a variety of uses, such as in killing micrograms and as catalysts. Many techniques have been used for the production of the fine particles. Faraday cell, consisting of two silver electrodes in an electrolyte, is unique, but it is hard to get a very fine particle by this method. A finer silver nano-particle producing cell, utilizing a dielectric bed as a lower electric current and higher field controlling means, has been proposed and investigated. The I-V characteristics of the cell and effect of the dielectric bed on the producing finer silver nano-particles have been investigated. The I-V characteristics of the cell with the dielectric bed were different from that of the same system without the bed, due to the increased cell resistance and elevated electric field intensity. It is found that the proposed cell with the dielectric bed can produce finer silver nano-particles effectively, which, however, can be used as one of effective fine silver nano-particle producing means.

Optical properties of nanometric TiO 2 clusters deposited on thin films by high pressure sputtering

Titanium dioxide thin films have been prepared by using a magnetron sputtering source placed inside a high pressure aggregation chamber. This preparation technique allows the production of fine particles from a target material through sputtering after cluster aggregation inside a high pressure (10 − 1 mbar) He/Ar gas atmosphere. After that process, by channelling the clusters to a low pressure main deposition chamber, it is possible to prepare films made up by nanometric clusters. The distribution of the cluster size can be changed controlling the residence time within the aggregation zone. Films of clusters with different sizes have been deposited after varying the Ar/He atmosphere ratio and its pressure in the aggregation region. Cluster size distribution has been characterized by Atomic Force Microscopy as a function of different preparation parameters. Finally, the crystalline degree, structural phase and band-gap of the titanium oxide were obtained by means of optical spectroscopies to study the size dependence of the nanometric clusters properties.

Photocatalytic Reduction of Silver Ions on Ferric Oxides and Ferric Hydroxides

Irradiation of an aerated aqueous suspension of silver nitrate and catalysts (ferric oxides and ferric hydroxides) with UV light (wavelength λ≥320 nm) led to the production of fine silver particles. On these catalysts, all the adsorption isotherms of silver ions fitted well to the Langmuir adsorption equation and the initial rate of Ag(I) reduction increased linearly with the increase in the initial amount of adsorbed Ag(I). The slope decreased according to the following order: α-Fe2O3 α-FeOOH γ-Fe2O3 γ-FeOOH δ-FeOOH. However, for the first three catalysts the reduction of Ag(I) only occurred when the amount of adsorbed Ag(I) reached about half the maximum coverage and also the reaction rate was nearly unaffected by N2 purging. The reduction of Ag(I) on δ-FeOOH and TiO2 upon degassing with N2 was significantly accelerated. This implies that O2 competes with silver ions for adsorption sites and reducing species on the catalyst, which is dependent on the catalyst′s properties. X-ray diffraction (XRD) analysis showed that α-Fe2O3 and δ-FeOOH were well and poorly crystallized, respectively. This indicates that the high crystallinity of the hydroxides is beneficial to the separation of photogenerated charge carriers and thus to their redox reactions with target substrates on the surface.

The critical importance of the grinding environment on fine particle recovery in flotation

This paper examines published and new experimental evidence on the effect of the grinding environment on fine (−10 μm) value mineral recovery in flotation. Reasons for increases in fine value mineral recovery from ores with fully electrochemically inert grinding media are discussed in relation to reduced surface contamination by iron hydroxide emanating from the grinding media. The application of stirred milling technology, which allows the use of fully inert grinding media, to primary grinding applications may lead to increased fine value mineral recovery in flotation rougher applications. It is suggested that the effect of the grinding media, which is important for fine particles and progressively becomes more important as the grind size becomes finer, is principally due to the abrasion mechanism of the minerals with the grinding media in the production of fine particles. Opportunities for research and industry application are discussed.

粉砕方式を変えた転動ミル粉砕によるＳｒフェライト微粒子の生成

The processes for obtaining fine Sr-ferrite particles have direct efects upon the crystallite size and distribution of sintered Sr-ferrite specimens. The influence of grinding conditions on the production of fine Sr-ferrite particles during ball mill grinding was investigated. The grinding experiments were carried out under dry and wet conditions, and dry condition with methanol as a grinding aid. Particle size distributions of the ground products were measured by the microscopic method, and could be expressed accurately as described by a modified Gaudin-Schuhmann equation. The fine grindability of Sr-ferrite particles was evaluated by the median particle size in undersize distribution, and the ratio of 10% and 90% cumulative weight passing sizes that showed the broadness of the size distribution. Sr-ferrite particles with a median particle size of 0.8-1.0μm were produced. The broadness of the size distribution increased with decreasing median particle size of the ground products. The broadness of the size distribution by wet grinding and dry grinding with a grinding aid was lowered using larger grinding media.