Dispersion Particle Size Distribution Research Articles

Development of dispersed phase size and its dependence on processing parameters

AbstractThrough measurement of phase dimension via laser scattering, phase morphology development in immiscible blends of polyamide 12/poly(ethylene glycol) (PEG) with an extremely high viscosity ratio was investigated. The blends were prepared by melt blending in a batch mixer. The objective was to examine the influence of mixing time, rotor speed, as well as blending temperature on the size distribution of the minor phase. It is of interest that the breakup process of the dispersed PA 12 phase was observed for the blend systems even for extremely high viscosity ratios of ≤ 102–103. Mixing time had a significant effect on the development of dispersed phase size distribution. It was found that the bulk of particle size reduction took place very early in the mixing process, and very small droplets with a diameter of 0.1–10 μm were produced. The number of small particles then decreased, resulting in a larger average particle size. With further prolonged mixing, the particle size levels off. The particle size and its distribution were also found to be sensitive to the rotor speed. The average particle size decreased with increased rotor speed. The effect of blending temperature on size and size distribution, which has seldom been studied, was also examined in this work. When the blending temperature altered from 190°C to 220°C, the size and its distribution of the dispersed phase varied considerably, and the change of viscosity ratio was found to be the key factor affecting the dispersed phase size. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3201–3211, 2006

Power law distribution and self-organized criticality of dispersed particles

Research on particulate characteristics has been an important frontier in physics and chemistry during the past decades. It has however been mostly focused on granular materials with short-range interactions. In this work, it was found that the power law of particle size distribution applied to the long-range interacting system of floating dust in air, from which we deduced that self-organized criticality might hold for floating dust just as granular materials with short-range interactions. This feature may reveal underlying kinetic mechanisms, important in dispersed particle systems. In industry, power law of size distribution of dispersed particles can be used to investigate the change of dust size, and the power law parameter could be taken as an important index for dust separation.

Sedimentary aggregates in the Peoria Loess of Nebraska, USA

Loess grain size data used to infer transport direction or wind strength are generally derived from vigorously disaggregated samples. However, these data may not adequately represent the effective particle size distribution during loess transport, if the transported dust contained aggregates of fine-grained material. Thin sections of minimally altered C and BC horizons in the late Pleistocene Peoria Loess of Nebraska, USA, indicate the presence of aggregates with diameters of 30–1000 μm. The larger aggregates (>250 μm) are unlikely to have been transported, and are interpreted as the result of soil faunal activity and other pedogenic processes after deposition. Aggregates smaller than 250 μm could have a similar origin, but laser diffraction particle size analysis suggests that many are sedimentary particles. Comparison of minimally and fully dispersed particle size distributions from each sampling site was used to estimate the modal diameter of aggregates. The aggregate modal diameter becomes finer with decreasing loess thickness, representing increasing distance from the source. A similar trend was observed in the modal diameter of fully dispersed particle size distributions, which represents the mode of sand and silt transported as individual grains. We interpret both trends as the result of sorting during transport, supporting the interpretation that many of the aggregates were transported rather than formed in place. Aggregate content appears to increase with distance from the source, explaining a much more rapid downwind increase in clay content than would be expected if clay were transported as particles smaller than 2 μm diameter. Although the Peoria Loess of Nebraska contains sedimentary aggregates, many of the coarse silt and sand grains in this loess were transported as primary particles, were thoroughly exposed to sunlight and are potentially well suited for luminescence dating.

Chemical Kinetics in Dispersed-Phase Reactors

Many chemical engineering processes occur under conditions when a dispersed phase undergoes fragmentation (breakup) and/or aggregation (coalescence). It is of considerable interest to model a chemical process that occurs at the interface and therefore depends on the evolving size distribution of the dispersed phase. We apply distribution kinetics to represent the evolution of the dispersed-phase size distribution for simultaneous fragmentation and coalescence. The continuous phase with dissolved reactant enters and exits a continuous-flow stirred-tank reactor. When the dispersed phase contained within the vessel satisfies a similarity solution, several rate expressions, including one for interphase mass transfer, that depend on mass moments of the size distribution allow analytical or simple numerical solutions. The solutions demonstrate how chemical reaction mass balances can be combined with distribution dynamics to extend chemical reaction engineering analysis.

A model for mineral dust emission

In the new dust emission model presented in this paper, the two major dust emission mechanisms are considered, namely, saltation bombardment and aggregates disintegration. The emission of dust generated by the first mechanism is modeled from the perspective of volume removal caused by saltating particles and that arising from the second mechanism is related to the streamwise saltation flux. The dust emission rate is constrained by using the information of minimally and fully dispersed particle size distributions. The performance of the dust emission model is compared with the available field measurements. Despite large uncertainties both in measurements and model parameters, the comparison shows that the model is promising. The accuracy of the model depends on the availability of high‐quality particle size data. It is proposed to establish a detailed database of particle size distributions for various soil types for the purpose of modeling dust emission over large areas.

A contribution towards predicting the evolution of droplet size distribution in flowing dilute liquid/liquid dispersions

There is growing experimental and theoretical evidence that in common flow fields, such as stirred vessels and pipelines, the steady state of the dispersed phase size distribution (including the maximum stable size X m ) may be unattainable over a time period of practical interest. Therefore, computation of the temporal evolution of the dispersion (through the breakage population balance equation) is indispensable. The necessary breakage rate and breakage kernel can be determined from experimental data by solving the so-called inverse problem. To tackle the latter, an improvement of the method originally developed by Sathyagal et al. (Comput. Chem. Eng. 19 (1995) 437) is presented in this paper. The method is based on the concept of self-similarity of size distributions, which is shown here to hold even if the evolving maximum particle size is relatively close to an existing maximum stable size X m . The proposed improved inversion procedure relies on the observation that the form of the breakage kernel can be inferred from the form of the self-similar distribution representing the experimental data. The new method is very stable with respect to noise in the experimental data.

Mechanochemical-hydrothermal preparation of crystalline hydroxyapatite powders at room temperature

Crystalline hydroxyapatite (HAp) powders were prepared at room temperature from heterogeneous reaction between Ca(OH)2powders and (NH4)2HPO4 solutions via the mechanochemical-hydrothermal route. X-ray diffraction, infrared spectroscopy, thermogravimetric characterization, and chemical analysis were performed, and it was determined that the room temperature products were phase-pure, thermally stable HAp with a nearly stoichiometric composition. Dynamic light scattering revealed that the dispersed particle size distribution of the room temperature HAp powders was in the range of 0.15–3.0 μm with a specific surface area of ≈90 m2/g. Both specific surface area measurements and scanning electron microscopy confirmed that the HAp powders consisted of agglomerates containing hundreds of ≈20 nm HAp crystals.

Gas disengagement technique in a slurry bubble column operated in the coalesced bubble regime

The gas disengagement technique is discussed in detail and is applied in a two-dimensional bubble column and slurry bubble column to obtain the bubble size distribution. Flow characteristics including velocities of each phase and dispersed phase size distribution during the gas disengagement process are obtained by using an advanced image analysis tool including a particle image velocimetry technique. It is shown that in the coalesced bubble regime, the bubble and flow characteristics during the gas disengagement process are complex, i.e., there are strong bubble–bubble interactions as well as interactions between the liquid flow and bubbles. Several different analogies of the disengagement processes assuming a bimodal bubble size distribution are discussed in terms of the behavior of large and small bubbles and their influence over one another. The small bubbles, which disengage within the fast bubble flow region, must be taken into account to evaluate the bimodal bubble size distribution. The applicability of the gas disengagement technique to obtain a multimodal bubble size distribution is also elaborated upon.

Influence of melting icebergs on distribution, characteristics and transport of marine particles in an East Greenland fjord

A detailed study of distribution of suspended sediments in an East Greenland fjord with a high iceberg production rate reveals the existence of intermediate nepheloid layers (INLs). Observed INLs extended from the head to the mouth of the fjord at water depths between 100 and 400 m. Particulate organic carbon and nitrogen, chlorophyll a, and nutrient measurements and observation by microscope and energy dispersive X‐ray analyses were used to characterize marine particles. Particles in the INLs are composed of glacial flour including >50 μm quartz and feldspar grains with angular and sharp edges, considered to be released from melting icebergs. In situ photographs show large aggregates (>1 mm) at high concentration (>300 particles per liter) in and below INLs. These aggregates, in comparison with the dispersed particle size distribution, demonstrate that smaller size particles (e.g., clay) settle effectively along with larger single size grains. In Kangerlugssuaq Fjord, the mass transport of marine particles was governed by the subsurface iceberg melting, producing observed INLs, rather than the surface meltwater plume. This suggests that the subsurface water temperature controls release of iceberg debris and the existence of warm subsurface water, as well as the spread of cold and fresh water in the surface layer, needs to be considered to evaluate the occurrence of ice‐rafted debris layers, including Heinrich layers. This study provides the field evidence of a modern analogue on ocean conditions that could form iceberg‐rafted layers.

The determination of particle size distribution of submicrometer particles by capillary hydrodynamic fractionation (CHDF)

Capillary tubes have been used to separate submicrometer colloidal particles by size. When dispersed colloidal particles of different sizes are transported through the open capillary tube by a fluid, they fractionate, emerging in order of decreasing diameter. This paper shows, for the first time, that the particle size distribution of polydisperse mixtures of submicrometer colloidal particles can be obtained from the separation achieved by flow through small-bore open capillary tubes. The integrated, computerized capillary hydrodynamic fractionation (CHDF) described here determines the particle size distribution of the sample containing submicrometer particles in suspension. An iterative numerical method was used to obtain the particle size distributions from the fractograms obtained. Several mixtures of well-characterized standards were injected into the CHDF system in order to illustrate the resolution of the separation. The high resolution of the separation achieved in a 4-μm-diameter capillary tube allows analytical fractionation of mixtures of particles with diameters of 234 and 357 nm in less than 200 s; the difference between their peak elution times is only 8 s. Particle size distributions of multimodal distributions obtained by CHDF were compared to those obtained by transmission electron microscopy (TEM) in order to determine the accuracy of the calculated particle size distributions. Our results demonstrate that CHDF can be used to obtain particle size distributions of dispersions, regardless of the breadth of the distribution of submicrometer particles.

Nondiffusive coagulation of microparticles in solid-state dispersions

An expression is derived for the size distribution of dispersed particles and other relations are derived as well, on the basis of a more general equation for the rate of change of the upper and lower limits of the size spectrum. An analysis of these relations reveals the characteristics of transition between two processes, namely from formation of a dispersed phase (crystallization) to coagulation of particles through a disperse system where no coagulation of microparticles occurs. It is shown that in many real disperse systems (dispersion-hardened alloys) microparticles grow by the mechanism of nondiffusive coagulation, the latter being limited by the rate at which atoms build up at the boundaries of particles.

Determination of Particle Size Distributions of Dispersions of Small Superconducting Particles from Magnetic Measurements

Determination of Particle Size Distributions of Dispersions of Small Superconducting Particles from Magnetic Measurements