Final Particle Size Distribution Research Articles

Roll compaction/dry granulation: Comparison between roll mill and oscillating granulator in dry granulation

Different experimental factorial designs were employed to evaluate granule properties obtained from oscillating granulator and roll mill. Four oscillating-granulator parameters were varied, i.e. rotor speed, oscillating angle, aperture of mesh screen and rotor type. Six roll-mill parameters that were throughput, speed ratio in both first and second stages, gap between roll pair in both stages and roll-surface texture were also investigated. Afterwards, the granule properties obtained from two milling types with similar median particle size were compared. All milling parameters in both milling types affected significantly the median particle size, size distribution and amount of fine particles (P < 0.05), except the rotor types of oscillating granulator on fines. Only three milling parameters influenced significantly the flowability (P < 0.05). These were the throughput and the gap size in the first stage of roll mill and the sieve size of oscillating granulator. In comparison between milling types, the differences of granule properties were not practically relevant. However, the roll mill had much higher capacity than the oscillating granulator about seven times, resulting in improving energy savings per unit of product. Consequently, the roll mill can be applied instead of oscillating granulator for roll compaction/dry granulation technique.

ChemInform Abstract: Preparation of Aluminum Nitride Powder from Aluminum Polynuclear Complexes.

AIN powder was synthesized from aluminum polynuclear complexes. Basic aluminum chloride and basic aluminum lactate were used as the aluminum polynuclear complexes. These starting materials and glucose were dissolved in water and mixed homogeneously. AIN powder was obtained by calcining after drying and precalcining at 800°C under nitrogen gas flow. Then excess carbon was removed by firing in air. Nitridation in the system was investigated and compared with that in the alumina–carbon black system. It was found that in our reaction system nitridation began and proceeded at lower calcination temperatures above 1200°C than in the alumina–carbon black system. Using aluminum polynuclear complexes, AIN was synthesized through the nitridation of γ-alumina and produced in a very fine and sharp particle size distribution.

Preparation of biocompatible magnetite–PLGA composite nanoparticles using supercritical fluid extraction of emulsions

We report a new strategy for the production via supercritical fluid extraction of emulsion of biocompatible magnetic nanocomposite particles made of magnetite nanocrystals dispersed in a poly(lactic-co-glycolic) acid (PLGA) matrix. Ricinoleic acid-stabilized magnetic nanocrystals have been prepared via coprecipitation of two iron salts in alkaline environment, and subsequently dispersed in a solution of PLGA in dichloromethane. The obtained oil phase has then been dispersed in an aqueous solution of polyvinyl alcohol (PVA) in order to obtain a kinetically stable oil-in-water miniemulsion. The solvent was finally extracted via supercritical fluid extraction of emulsions. The continuous extraction of dichloromethane by means of supercritical CO 2 leads directly to a stable suspension of magnetite–PLGA composite nanoparticles in water. The influence of those parameters affecting the final particle size distribution and morphology, primarily emulsifier amount and magnetite content, has been investigated, so as to optimize the process. Analysis of the products, performed through light scattering and electron microscopy, indicates that narrower size distributions are obtained with larger amounts of emulsifier and lower amounts of magnetite. The morphology of the particles tends to be of Janus type, with the magnetite accumulated on one hemisphere of the particle. The proposed approach is suitable for the preparation of large quantities of high-quality magnetite–PLGA composite nanoparticles for biomedical applications.

Vertically-resolved particle size distribution within and above the mixing layer over the Milan metropolitan area

Abstract. Vertical aerosol profiles were directly measured over the city of Milan during three years (2005–2008) of field campaigns. An optical particle counter, a portable meteorological station and a miniaturized cascade impactor were deployed on a tethered balloon. More than 300 vertical profiles were measured, both in winter and summer, mainly in conditions of clear, dry skies. The mixing height was determined from the observed vertical aerosol concentration gradient, and from potential temperature and relative humidity profiles. Results show that inter-consistent mixing heights can be retrieved highlighting good correlations between particle dispersion in the atmosphere and meteorological parameters. Mixing height growth speed was calculated for both winter and summer showing the low potential atmospheric dispersion in winter. Aerosol number size distribution and chemical composition profiles allowed us to investigate particle behaviour along height. Aerosol measurements showed changes in size distribution according to mixing height. Coarse particle profiles (dp&gt;1.6 μm) were distributed differently than the fine ones (dp&lt;1.6 μm) were, at different heights of the mixing layer. The sedimentation process influenced the coarse particle profiles, and led to a reduction in mean particle diameter for those particles observed by comparing data above the mixing height with ground data (−14.9±0.6% in winter and −10.7±1.0% in summer). Conversely, the mean particle diameter of fine particles increased above the mixing height under stable atmospheric conditions; the average increase, observed by comparing data above the mixing height with ground data, was +2.1±0.1% in winter and +3.9±0.3% in summer. A hierarchical statistical model was created to describe the changes in the size distribution of fine particles along height. The proposed model can be used to estimate the typical vertical profile characterising launches within pre-specified groups starting from: aerosol size and meteorological conditions measured at ground-level, and a mixing height estimation. The average increase of fine particle diameter, estimated on the basis of the model, was +1.9±0.5% in winter and +6.1±1.2% in summer, in keeping with experimental findings.

Rapid removal of fine particles from mine water using sequential processes of coagulation and flocculation

The processes of coagulation and flocculation using high molecular weight long‐chain polymers were applied to treat mine water having fine flocs of which about 93% of the total mass was less than 3.02 µm, representing the size distribution of fine particles. Six different combinations of acryl‐type anionic flocculants and polyamine‐type cationic coagulants were selected to conduct kinetic tests on turbidity removal in mine water. Optimization studies on the types and concentrations of the coagulant and flocculant showed that the highest rate of turbidity removal was obtained with 10 mg L−1 FL‐2949 (coagulant) and 12 mg L−1 A333E (flocculant), which was about 14.4 and 866.7 times higher than that obtained with A333E alone and that obtained through natural precipitation by gravity, respectively. With this optimized condition, the turbidity of mine water was reduced to 0 NTU within 20 min. Zeta potential measurements were conducted to elucidate the removal mechanism of the fine particles, and they revealed that there was a strong linear relationship between the removal rate of each pair of coagulant and flocculant application and the zeta potential differences that were obtained by subtracting the zeta potential of flocculant‐treated mine water from the zeta potential of coagulant‐treated mine water. Accordingly, through an optimization process, coagulation–flocculation by use of polymers could be advantageous to mine water treatment, because the process rapidly removes fine particles in mine water and only requires a small‐scale plant for set‐up purposes owing to the short retention time in the process.

Particle dynamics simulation of nanoparticle formation in a flame reactor using a polydispersed submicron-sized solid precursor

Formation of nanoparticles from polydispersed, non-spherical submicron-sized particles via a gas-phase route in a flame reactor was investigated using tungsten oxide particles as a model material. Nanoparticles were formed by the evaporation of non-spherical powder, followed by nucleation, coagulation and surface condensation. The effects of both the flame temperature profile and the carrier gas flow rate on particles formation were studied numerically, and the results were validated by experimental data. The simulation was initiated by the use of computational fluid dynamics (CFD) to obtain the temperature distribution in the flame reactor. Then, evaporation of the feed material was modeled, taking into account both the polydispersity and the shape of the non-spherical particles. A nodal method was selected to solve the general dynamics equation (GDE), which included nucleation, coagulation, and surface condensation terms, for the prediction of particle dynamics. Results of the simulation were consistent with the experimental data, indicating that the selected model adequately predicts the final particle size distribution.

On-line investigation of anatase precipitation from titanyl sulphate solution

Precipitation of concentrated titanyl sulphate is an important step in the Sulphate Process used for manufacturing titanium white in which titanium dioxide particles are formed and the particles size as well as its distribution is determined. This study investigated the transient changes of TiO 2 precipitation process by using two on-line particle measurement techniques, turbidimeter and focused beam reflectance measurement (FBRM), in order to explore the mechanism of particles formation. Induction period as well as primary nuclei formation of the precipitation process was calculated by turbidity value changes and the influence of feeding rate on primary nucleation, primary crystal sizes and final product particle size distribution (PSD) were also investigated. FBRM was employed for detecting the transient variations of PSD during the process. It was found that the process was divided into four stages: induction, rapid hydrolysis and aggregation, aggregation balance with further reaction, and ripening. The Sigmoidal–Boltzmann model is used to describe these transient phenomena and describes well the formation of TiO 2 particles.

The effect of an organic ion-exchange resin on properties of heterogeneous ion-exchange membrane

This case study deals with relationships between characteristic properties of organic ionexchange resins and heterogeneous ion-exchange membranes. At first chemical and temperature stability, humidity and particle size distribution of different types of ion-exchange resins was analyzed. Subsequently, membranes were prepared by using different filler/polymer matrix ratio or by using milled resins with different particle size distribution. Finally, different ion-exchange resins were used for preparing of heterogeneous ion-exchange membranes at fixed filler/polymer matrix ratio. We analyzed many characteristic properties of raw materials, intermediate and final products and we paid attention to process parameters during preparing of membranes too. It was proved that there are important relationships between properties of a membrane and the type of resin used for its preparation and the process of membrane preparation. The results show that most of ion-exchange resins can be used for ion-exchange membranes preparation but with different impact on characteristic properties of membranes. We also proved that increasing of filler/polymer matrix ratio or using very fine particle size distribution of milled resin improve electrochemical properties of membranes at the expense of worst mechanical properties and more complicated membrane preparation. On the basis of these results we are able to modify composition of heterogeneous ion-exchange membranes to reach required properties.

Slurry Particle Agglomeration Model for Chemical Mechanical Planarization (CMP)

AbstractIn this work we propose a particle agglomeration model for chemical mechanical planarization (CMP) under the primary motivation of understanding the creation and behavior of the agglomerated slurry abrasive particles during the CMP process, which are a major cause of defectivity and poor consumable utility due to sedimentation.The proposed model considers the slurry composition as a colloidal suspension of charged colloidal silica in an electrically neutral aqueous electrolyte. First, a theoretical relationship between the measurable chemical parameters of the slurry's aqueous electrolyte, the surface potential of the abrasive particles, and corresponding zeta potential between the agglomerated abrasive particles is presented. Secondly, this zeta potential is used in a modified DVLO interaction potential model to determine the particle interaction potentials due to both the attractive van Der Waals forces and repulsive electrostatic interactions. Finally, the total interaction potential created is then used to define a stability ratio for slow versus fast agglomeration and corresponding agglomeration rate equations between particles; these are used in a discrete population balance framework to describe the final particle size distribution with respect to time and agglomerate composition.The proposed model will provide both a qualitative and quantitative description of agglomeration of abrasive slurry particles during CMP that can be extended to account for slurry composition or abrasive particle type, enabling more accurate process control, increased consumable utility, and possible defectivity reduction.

Effects of H2O and Particles on the Simultaneous Removal of SO2 and Fly Ash Using a Fluidized-Bed Sorbent/Catalyst Reactor

This study investigated the potential of a fluidized-bed sorbent/catalyst reactor for the simultaneous removals of SO2 and fly ash from a simulated flue gas containing different H2O and particles. Experimental results showed that the removal efficiency of particles and SO2 was 85%−96% and 5.75−2.97 mg SO2/g, respectively, as the H2O content was 1.5−5.3%. The activities of sorbent/catalysts for simultaneous removals of SO2 and particles were inhibited by H2O and particles, and the inhibition effects increased with the content of H2O. As the H2O content increased, the particle size distribution (PSD) of fine particles shifted to the coarse particles. The results of BET analysis show that the obstruction phenomenon of the sorbent/catalyst caused by the particles was diminished with the increased content of H2O. The results showed this aggregation phenomenon of fine particles shifted to the coarse particles may cause increased water vapor content in fluidized-bed sorbent/catalyst reactor.

Size distributions of fine silicate and other particles in Masaya's volcanic plume

Direct‐sampling and remote‐sensing measurements were made at the crater rim of Masaya volcano (Nicaragua) to sample the aerosol plume emanating from the active vent. We report the first measurements of the size distribution of fine silicate particles (d &lt; 10 μm) in Masaya's plume, by automated scanning electron microscopy (QEMSCAN) analysis of a particle filter. The particle size distribution was approximately lognormal with modal d ∼ 1.15 μm. The majority of these particles were found to be spherical. These particles are interpreted to be droplets of quenched magma produced by a spattering process. Compositional analyses confirm earlier reports that the fine silicate particles show a range of compositions between that of the degassing magma and nearly pure silica and that the extent of compositional variability decreases with increasing particle size. These results indicate that fine silicate particles are altered owing to reactions with acidic droplets in the plume. The emission flux of fine silicate particles was estimated as ∼1011 s−1, equivalent to ∼55 kg d−1. Sun photometry, aerosol spectrometry, and thermal precipitation were used to determine the overall particle size distribution of the plume (0.01 &lt; d(μm) &lt; 10). Sun photometry and aerosol spectrometry measurements indicate the presence of a large number of particles (assumed to be aqueous) with d ∼ 1 μm. Aerosol spectrometry measurements further show an increase in particle size as the nighttime approached. The emission flux of particles from Masaya was estimated as ∼1017 s−1, equivalent to ∼5.5 Mg d−1 where d &lt; 4 μm.

Physical and electrochemical properties of LiFePO4/C composite cathode prepared from various polymer-containing precursors

The goal of this research was to study the effect of various polymer-containing precursors on the performance of LiFePO4/C composite. A coprecipitation method was applied to prepare a series of LiFePO4/C materials by calcinating amorphous LiFePO4 with various polymer compounds at 600 °C. The materials were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, particle size analysis, thermal analysis, BET specific surface area, Raman spectral analysis and electrochemical methods. The results showed that the structure of polymer precursors played an important role in improving the performance of LiFePO4/C composites. The residual carbon produced by the pyrolysis of polymers with functionalized aromatic groups exhibited a better capacity in the LiFePO4/C composites. A polyaromatic compound, e.g. polystyrene, with more functionalized aromatic groups displayed improved performance because its decomposition temperature was close to the temperature of the LiFePO4 phase transformation, which resulted in fine particle size and uniform carbon distribution on the composite surface. According to Raman spectral analysis, polystyrene with more aromatic groups has a lower ID/IG and sp3/sp2 peak ratio indicating more highly graphite-like carbon formation during polymer pyrolysis and exhibited a better capacity.

Applying traceability to grinding circuits by using Particle Texture Analysis (PTA)

LKAB has started a new pelletizing plant at Malmberget, where the raw material will be a mix of ores from Kiruna and Malmberget. The new plant necessitated an investment in a new grinding section in the concentrator. As usual, the new section has larger mills. It also lacks the wet cobbing stage present in the old sections. Comparing the analysis data from the new grinding section with the old grinding sections it shows that they give similar results. There are slight variations; the older mills produce a steeper final particle size distribution. Also, it appears that the new mills are more efficient, since they have higher calculated grindability indices. To better understand the differences between the sections, and the process implications of the new grinding section, a combination of Particle Texture Analysis (PTA) and the statistical method multivariate data analysis (MVDA) is used. It shows that it is possible to identify and follow systematic changes in the particle morphology of the mill products. Also, that there are differences in process mineralogical aspect between the old and new grinding sections.

Preparation of poly(vinyl chloride) latexes using a dual surfactant system: The effect in the particle size distribution

AbstractThe control of the average particle size and size distribution in the emulsion polymerization of vinyl chloride monomer is an important parameter to determine, not only the latex characteristics, but also the properties of the final dispersion powder in several industrial applications. It is possible to manipulate the particle size distribution (PSD) by applying a mixture of an anionic surfactant‐fatty alcohol before the start of the free radical polymerization. Contrary to the procedures of the miniemulsion and the derivative diffusional swelling techniques, no kind of high shear is applied to the monomer and/or surfactant mixtures. In fact, the concentration and selection of the anionic surfactant, together with the fatty‐alcohol, can play an interesting role on the final PSD of the polymer's particles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

RAFT-Mediated Emulsion Polymerization of Styrene in Water using a Reactive Polymer Nanoreactor

We have demonstrated a nanoreactor methodology to produce polystyrene nanoparticles with narrow molecular weight distributions (MWD) and control over the final particle size distributions. Our reactive thermoresponsive diblock copolymer nanoreactor is an ideal setting to carry out otherwise difficult reversible addition–fragmentation chain transfer (RAFT)-mediated polymerizations, resulting in surfactant-free nanoparticles that can be tuned to size and MWD. By confining the MacroRAFT agent within the nanoreactor, the poor P(DMA68-b-NIPAM73)-SC(=S)SC4H9 (PNIPAM) leaving group on the MacroCTA behaves as a highly active MacroCTA through kinetic rather than thermodynamic control. The Mn was close to theory with low polydispersity indices (PDIs) (&lt;1.2). The particle size increased with the ratio of styrene to nanoreactors and with very narrow particle size distributions. However, we found that there was a limited amount of styrene monomer that can be encapsulated into the nanoreactor, leading to polymerizations stopping well before full conversion. This problem was overcome through the addition of a non-reactive thermoresponsive diblock copolymer, which resulted in Mns close to 340 K and low PDIs. Manuscript received: 15 April 2009. Manuscript accepted: 15 July 2009.

Influência da técnica de dispersão nas propriedades de sílica ativa

A sílica ativa tem sido empregada em composições de materiais cimentícios com o intuito de aumentar a compacidade e/ou a resistência devido à sua atividade pozolânica e à sua atuação como filler promovida por sua granulometria muito fina. Contudo, para alcançar esses efeitos a sílica ativa deve se encontrar desaglomerada e dispersa, expondo assim toda a sua superfície reativa, além de possibilitar que suas partículas preencham os espaços vazios no empacotamento. No entanto, devido ao processo de densificação a que normalmente são submetidas, suas partículas se encontram fortemente unidas, podendo resultar, inclusive, em aglomerados macroscópicos que não se rompem com facilidade mesmo após cisalhamento intenso. Nesse caso, os benefícios esperados pelo uso da sílica ativa não são alcançados em sua plenitude. Desta forma, foram avaliadas as características de dispersão em água de duas sílicas ativas comerciais, as quais foram submetidas a condições de cisalhamento brando e intenso em um misturador convencional de baixa energia e em um dispersor de alta energia de cisalhamento, respectivamente.

Large Eddy Simulation of mixing and reaction in a Confined Impinging Jets Reactor

Confined Impinging Jets Reactors have recently found many interesting applications. Their ability to provide very efficient mixing performances is of paramount importance in the production of very fine particles. In fact, in many particle precipitation processes mixing plays a crucial role in determining the final particle size distribution and therefore the final product quality. Relevant examples are the production of polymeric nano-particles for pharmaceutical applications through solvent displacement, the production of many oxides through sol–gel processes, as well as standard reactive crystallization processes. In order to develop reliable design and scale up rules and in order to understand and master the interaction between mixing and particle formation, it is of crucial importance to resort to modeling and simulation tools. In this work mixing and reaction in these devices is studied with Computational Fluid Dynamics (CFD) by using the Large Eddy Simulation (LES) approach coupled with a subgrid-scale mixing model, to take into account the effect of molecular mixing. The performance of the model is investigated through a sensitivity analysis and eventually predictions are compared with experimental data and with simulations obtained by using the Reynolds-Averaged Navier–Stokes equations (RANS) approach.

Particle size distribution dynamics during precipitative softening: Declining solution composition

Particle removal is a critical step in the treatment of surface water for potable use, and the majority of drinking water treatment plants employ precipitative coagulation processes such as alum and iron “sweep-floc” coagulation or lime softening for particle pre-treatment. Unfortunately, little is quantitatively known about how particle size distributions are shaped by simultaneous precipitation and flocculation. In an earlier paper, we demonstrated the effects of the saturation ratio, the mixing intensity and the seed concentration on the rates of homogeneous nucleation, precipitative growth and flocculation during precipitation of calcium carbonate at constant solution composition using electronic particle counting techniques. In this work, we extend those findings to systems more closely emulating the conditions in actual softening processes ( i.e., declining solution composition). Key findings include the strong dependence of the rate of flocculation on the initial saturation ratio and demonstration of the benefits of seeding precipitative softening from the perspective of optimizing the effluent particle size distribution. The mixing intensity during precipitation was also shown to strongly influence the final particle size distribution. Implications of the findings with respect to softening practice are discussed.

El Chichón volcano, April 4, 1982: volcanic cloud history and fine ash fallout

This retrospective study focuses on the fine silicate particles (<62 µm in diameter) produced in a large eruption that was otherwise well studied. Fine particles represent a potential hazard to aircraft, because as simple particles they have very low terminal velocities and could potentially stay aloft for weeks. New data were collected to describe the fine particle size distributions of distal fallout samples collected soon after eruption. Although, about half of the mass of silicate particles produced in this eruption of ~1 km3 dense rock equivalent magma were finer than 62 µm in diameter, and although these particles were in a stratospheric cloud after eruption, almost all of these fine particles fell to the ground near (<300 km) the volcano in a day or two. Particles falling out from 70 to 300 km from the volcano are mostly <62 µm in diameter. The most plausible explanation for rapid fallout is that the fine ash nucleates ice in the convective cloud and initiates a process of meteorological precipitation that efficiently removes fine silicates. These observations are similar to other eruptions and we conclude that ice formation in convective volcanic clouds is part of an effective fine ash removal process that affects all or most volcanic clouds. The existence of pyroclastic flows and surges in the El Chichon eruption increased the overall proportion of fine silicates, probably by milling larger glassy pyroclasts.

Composition‐resolved size distributions of volcanic aerosols in the Mt. Etna plumes

Particle size distributions for soluble and insoluble species in Mt. Etna's summit plumes were measured across an extended size range (10 nm &lt; d &lt; 100 μm) using a combination of techniques. Automated scanning electron microscopy (QEMSCAN) was used to chemically analyze many thousands of insoluble particles (collected on pumped filters) allowing the relationships between particle size, shape, and composition to be investigated. The size distribution of fine silicate particles (d &lt; 10 μm) was found to be lognormal, consistent with formation by bursting of gas bubbles at the surface of the magma. The compositions of fine silicate particles were found to vary between magmatic and nearly pure silica; this is consistent with depletion of metal ions by reactions in the acidic environment of the gas plume and vent. Measurements of the size, shape and composition of fine silicate particles may potentially offer insights into preemission, synemission, and postemission processes. The mass flux of fine silicate particles from Mt. Etna released during noneruptive volcanic degassing in 2004 and 2005 was estimated to be ∼7000 kg d−1. Analysis of particles in the range 0.1 &lt; d/μm &lt; 100 by ion chromatography shows that there are persistent differences in the size distributions of sulfate aerosols between the two main summit plumes. Analysis of particles in the range 0.01 μm &lt; d &lt; 0.1 μm by scanning transmission electron microscopy (STEM) shows that there are significant levels of nanoparticles in the Mt. Etna plumes although their compositions remain uncertain.