Showing papers on "Particle-size distribution published in 2004"

Critical Evaluation of the Use of Laser Diffraction for Particle-Size Distribution Analysis

Abstract: Determination of soil particle-size distribution (PSD) by sieving, hydrometer, and pipette methods as well as by laser diffraction (LD) suffers from inherent flaws, mainly due to the difficulty in defining the size of irregularly shaped particles. Therefore these methods yield only estimates of PSD. The objective of this study was to determine whether a functional relationship exists between the PSDs obtained by the combined sieve-pipette method and those obtained by LD. Samples from 42 California soils were analyzed. For the LD measurements a Beckman-Coulter LS-230 apparatus with a 750-nm laser beam that measures particles in the range of 0.04 to 2000 μm was used, employing the Mie theory for the PSD calculations. Values of 1.5 and 0.2 for the real part and the imaginary term of the refractive index (RI), respectively, gave satisfactory results for the optical model calculations. Volume percentage of the clay-size fraction obtained by LD was generally lower than mass percentage of the clay fraction derived by the pipette method. The opposite trend was noted for the silt-size fraction. Coefficients of determination for the regression equations for the day, silt, and sand fractions determined by the two methods were 0.702, 0.689, and 0.821, respectively. Good agreement between measured and calculated LD values for one size class was accompanied by poor agreement between measured and calculated values for the other. The LD method provides a continuous PSD curve, which enables a detailed data analysis and a flexible application of different particle-size dependent classification systems.

High-Resolution Particle Size Analysis of Naturally Occurring Very Fine-Grained Sediment Through Laser Diffractometry

Abstract: In this paper, we present results from a large number of experiments aimed at quantifying method and instrument uncertainty associated with laser diffraction analysis. We analyzed the size distribution of fine-grained sediment ( 24 hours prior to analysis and using 60 seconds of ultrasonication during analysis. (2) Obscuration--a measure of the concentration of the suspension during analysis--produced the most reproducible results at about 20%. (3) Variations in refractive-index settings can significantly alter estimated grain-size distributions. (4) Assumed values for absorption (the degree to which sediment grains absorb the light) can have a profound effect on grain-size results. Absorption settings near 0 resulted in unexpected bimodal grain size distributions for sediments in the < 10 µm size fraction and significantly skewed the fine-grained tail of coarser samples, probably because of sub-optimal diffraction by particles with a diameter similar in size to the laser wavelength. Absorption settings closer to 1 produced very reproducible results and unimodal grain-size distributions over a wide range of refractive indexes. Our study has shown that laser diffraction can measure very fine-grained sediments (< 10 µm) quickly, with high precision ( 5% at 2 standard deviations), and without the need for extensive mineralogical determinations. These results make possible a new generation of studies in which high-resolution time-series data sets of sediment grain size can be used to infer subtle changes in paleohydrology.

Particle size distributions from small-angle scattering using global scattering functions

Abstract: Control and quantification of particle size distribution is of importance in the application of nanoscale particles. For this reason, polydispersity in particle size has been the focus of many simulations of particle growth, especially for nanoparticles synthesized from aerosols such as fumed silica, titania and alumina. Single-source aerosols typically result in close to a log-normal distribution in size and micrograph evidence generally supports close to spherical particles, making such particles ideal candidates for considerations of polydispersity. Small-angle X-ray scattering (SAXS) is often used to measure particle size in terms of the radius of gyration, Rg, using Guinier's law, as well as particle surface area, S/V, from the Porod constant B and the scattering invariant Q. In this paper, the unified function is used to obtain these parameters and various moments of the particle size distribution are calculated. The particle size obtained from BET analysis of gas adsorption data directly agrees with the moment calculated from S/V. Scattering results are also compared with TEM particle-counting results. The potential of scattering to distinguish between polydisperse single particles and polydisperse particles in aggregates is presented. A generalized index of polydispersity for symmetric particles, PDI = BRg4/(1.62G), where G is the Guinier prefactor, is introduced and compared with other approaches to describe particle size distributions in SAXS, specifically the maximum-entropy method.

Model-Based Optimization of Particle Size Distribution in Batch-Cooling Crystallization of Paracetamol

Abstract: The control objectives of batch crystallization processes are often defined in terms of particle size distribution (PSD), or properties related to the PSD, viz. average particle size, product filterability, dry solids flow properties, etc. To achieve these control objectives, a constrained nonlinear model-based optimization strategy has been adopted. This involves the detailed modeling of batch crystallization including model validation and parameter estimation, on-line monitoring of supersaturation and PSD, and the application of optimization strategies. A deterministic population balance model accounting for solution thermodynamics, crystal growth, and nucleation has been developed. State estimation is achieved by the on-line monitoring of temperature, concentrations in the liquid phase, particle density, and PSD. For this purpose, the focused beam reflectance measurement (FBRM) provides an on-line, in-situ information of crystal size and particle concentration in the form of a chord length distribution...

Soft- and hard-agglomerate aerosols made at high temperatures.

Abstract: Criteria for aerosol synthesis of soft-agglomerate, hard-agglomerate, or even nonagglomerate particles are developed on the basis of particle sintering and coalescence. Agglomerate (or aggregate) particles are held together by weak, physical van der Waals forces (soft agglomerates) or by stronger chemical or sintering bonds (hard agglomerates). Accounting for simultaneous gas phase chemical reaction, coagulation, and sintering during the formation and growth of silica (SiO2) nanoparticles by silicon tetrachloride (SiCl4) oxidation and neglecting the spread of particle size distribution, the onset of hard-agglomerate formation is identified at the end of full coalescence, while the onset of soft-agglomerate formation is identified at the end of sintering. Process conditions such as the precursor initial volume fraction, maximum temperature, residence time, and cooling rate are explored, identifying regions for the synthesis of particles with a controlled degree of agglomeration (ratio of collision to prima...

Modeling the optical properties of mineral particles suspended in seawater and their influence on ocean reflectance and chlorophyll estimation from remote sensing algorithms.

Abstract: The optical properties of mineral particles suspended in seawater were calculated from the Mie scattering theory for different size distributions and complex refractive indices of the particles. The ratio of the spectral backscattering coefficient to the sum of the spectral absorption and backscattering coefficients of seawater, b(b)(lambda)/[a(lambda) + b(b)(lambda)], was analyzed as a proxy for ocean reflectance for varying properties and concentrations of mineral particles. Given the plausible range of variability in the particle size distribution and the refractive index, the general parameterizations of the absorption and scattering properties of mineral particles and their effects on ocean reflectance in terms of particle mass concentration alone are inadequate. The variations in the particle size distribution and the refractive index must be taken into account. The errors in chlorophyll estimation obtained from the remote sensing algorithms that are due to the presence of mineral particles can be very large. For example, when the mineral concentration is 1 g m(-3) and the chlorophyll a concentration is low (0.05 mg m(-3)), current global algorithms based on a blue-to-green reflectance ratio can produce a chlorophyll overestimation ranging from approximately 50% to as much as 20-fold.

Multicomponent aerosol dynamics model UHMA: model development and validation

Abstract: . A size-segregated aerosol dynamics model UHMA (University of Helsinki Multicomponent Aerosol model) was developed for studies of multicomponent tropospheric aerosol particles. The model includes major aerosol microphysical processes in the atmosphere with a focus on new particle formation and growth; thus it incorporates particle coagulation and multicomponent condensation, applying a revised treatment of condensation flux onto free molecular regime particles and the activation of nanosized clusters by organic vapours (Nano-Kohler theory), as well as recent parameterizations for binary H2SO4-H2O and ternary H2SO4-NH3-H2O homogeneous nucleation and dry deposition. The representation of particle size distribution can be chosen from three sectional methods: the hybrid method, the moving center method, and the retracking method in which moving sections are retracked to a fixed grid after a certain time interval. All these methods can treat particle emissions and atmospheric transport consistently, and are therefore suitable for use in large scale atmospheric models. In a test simulation against an accurate high resolution solution, all the methods showed reasonable treatment of new particle formation with 20 size sections although the hybrid and the retracking methods suffered from artificial widening of the distribution. The moving center approach, on the other hand, showed extra dents in the particle size distribution and failed to predict the onset of detectable particle formation. In a separate test simulation of an observed nucleation event, the model captured the key qualitative behaviour of the system well. Furthermore, its prediction of the organic volume fraction in newly formed particles, suggesting values as high as 0.5 for 3–4 nm particles and approximately 0.8 for 10 nm particles, agrees with recent indirect composition measurements.

Product and formulation engineering of emulsions

Abstract: The physical properties of emulsions such as stability, rheology, sensory and optical characteristics or mass-transfer kinetics are largely influenced by their characteristic microstructure. The interrelationship between properties and microstructure is called the property function. The desired microstructure may be attained by establishing suitable process conditions; the link between the two is described as the process function. Essential structure parameters, besides the dispersed phase fraction, are droplet size and droplet size distribution of the internal phase. The distribution of the dispersed phase of an emulsion, for example, depends on the intensity and mechanism of droplet disruption and on the extent of superimposed or subsequent coalescence in the apparatus. Droplet disruption is a function of equipment characteristics and energy input per volume. This concept of energy density, an example of an explicit process function, may serve as a useful tool for those concerned with the designing and scaling-up of mechanical emulsification processes in practice. The rate of droplet coalescence, determined using a novel method, depends on the stabilizing properties of the emulsifier, but may also be influenced by process parameters. Various examples are presented to show how to change emulsion properties by property and process functions. By the example of formulating solubilized free phytosterols poorly soluble in water and oil, the significant effect of a properly adjusted microstructure will be demonstrated.

Size-related vaporisation and ionisation of laser-induced glass particles in the inductively coupled plasma

Abstract: Ongoing discussions about the origin of elemental fractionation occurring during LA-ICP-MS analysis show that this problem is still far from being well understood It is becoming accepted that all three possible sources (ablation, transport, excitation) contribute to elemental fractionation However, experimental data about the vaporisation size limit of different particles in the ICP, as produced in laser ablation, have not been available until now This information should allow one to determine the signal contributing mass within the ICP and would further clarify demands on suitable laser ablation systems and gas atmospheres in terms of their particle size distribution The results presented here show a vaporisation size limit of laser induced particles, which was found at particle sizes between 90 nm and 150 nm using an Elan 6000 ICP-MS Due to the fact that the ICP-MS response was used as evaluation parameter, vaporisation and ionisation limits are not distinguishable The upper limit was determined by successively removing the larger particles from the aerosol, which was created by ablation of a NIST 610 glass standard at a wavelength of 266 nm, using a recently developed particle separation device Various particle fractions were separated from the aerosol entering the ICP The decrease in signal intensity is not proportional to the decrease in volume, indicating that particles above 150 nm in diameter are not completely ionised in the ICP Due to the limited removal range of the particle separation device, which cannot remove particles smaller than 150 nm, single hole ablations were used to determine the lower vaporisation limit This is based on measurements showing that larger particles occur dominantly during the first 100 laser pulses only After this period, the ratio of ICP-MS counts and total particle volume was found to be constant while most of the particles are smaller than 90 nm, indicating complete vaporisation and ionisation of these particles To describe the influence of different plasma forward powers on the vaporisation limit, the range 1000–1600 W was studied Results indicate that optimum vaporisation and ionisation occurs at 1300 W However, an increase of the particle ionisation limit towards larger particles was not observed within the accuracy of this study using the full range of parameters available for optimisation on commonly used ICP-MS instruments

Generation of Ultrafine Particles by Spark Discharging

Abstract: Ultrafine carbon, metal, and metal oxide particles were generated with a commercially available spark generator designed for the production of carbon particles. Aerosols with number concentrations up to 107 cm−3 were produced at flow rates up to 150 lpm. Lognormal size distributions with modal diameters in the range of 18–150 nm and geometric standard deviations of about 1.5 were obtained. The chemical composition, size, number concentration, morphology, and surface area of the particles were varied, and the generation of particles with fixed characteristics could be maintained over many hours. The particle characteristics, however, could not be varied independently. For a certain chemical composition only size and number concentration were variable; morphology and surface area were fixed regardless of particle size. The particles grow by coagulation of primary particles formed by nucleation. The coagulated particles can either stick together and maintain their identity or fuse together and lose their ide...

Inkjet recording medium

Abstract: An inkjet recording medium comprising an ink-receiving layer containing kaolin, synthetic amorphous silica and a binder formed on one surface or both surfaces of a base paper mainly containing a wood pulp, wherein the kaolin has a particle size distribution in which a percentage of particles having a size of from 0 4 µm or more to less than 4.2 µm which account for 60% or more of the total as the cumulative value of the volumetric basis by a laser diffraction particle size distribution measurement, and the synthetic amorphous silica has a mean secondary particle diameter of from 0 5 µm or more to 4 µm or less measured by a coulter counter method.

Effect of engine load on diesel soot particles

Abstract: This study concentrates on characterization of nonvolatile fraction of diesel particles. These particles have an impact on earth's radiation balance as well as on health effects of vehicle emissions. In addition to composition and size distribution of particles, an important factor affecting their health effects and properties and lifetimes in the atmosphere is their morphology. The effect of engine parameters on soot particle size distributions and also on particle morphology has been studied. It was found that the shape of the size distribution and also the structure of diesel particles depend on engine load. The number distributions were found to obey log-normal assumption. The width of the distribution increased with increasing engine load. The geometric standard deviations of measured distributions varied from 1.7 to 2.1. Simultaneously, the fractal dimension of particles decreased with increasing engine load. The values for mass fractal dimensions based on sealing of particle mass and mobility size were between 2.6 and 2.8. Both electron microscopy and measurements of aerodynamic size versus mobility size suggest that the morphology of particles in different size regimes vary, with the large particles being less compact than the small ones.

Initiation of movement of quartz particles

Abstract: A theoretical description of the initiation of movement of sediments consisting of uniform-size, quartz particles is developed. These sediments behave in a noncohesive manner for coarse-grained particles but show cohesive behavior for fine-grained particles, i.e., as the particle size decreases, the critical shear stress increases and also becomes strongly dependent on the bulk density. The analysis includes gravitational, lift, drag, and cohesive forces as well as changes in bulk density and is uniformly valid for the range of particle sizes investigated, from fine-grained, cohesive particles to coarse-grained, noncohesive particles. Excellent agreement between theory and experiments is obtained. The analysis is also extended to quartz particles with small amounts of an added clay, bentonite, which makes the mixture more cohesive. This increase in cohesivity is greatest for intermediate size particles. An additional binding force due to the bentonite must then be included in the analysis.

Rapid soil particle size analyses using laser diffraction

Abstract: Soil particle size analyses (PSA) are needed to relate soil texture to soil performance or behavior. Standard analyses of dry soils usually include dispersion of the soils followed by particle size determination by a variety of time-consuming methods. Clay- and silt-sized particles are usually measured by sedimentation using a hydrometer or pipette method. Sands are then measured by sieving. Recent advances in laser diffraction technology have led to the production of devices specifically designed to rapidly measure the particle distribution of dispersed particles. This study compares the PSAs of 43 soil samples collected from the Southern High Plains of Texas measured by the pipette method and sieving with results obtained using a laser diffraction particle size analyzer (LDPSA). No pretreatment to remove organic matter or salts was used. The LDPSA required about 300-mg soil sample and overnight dispersion while shaking in a sodium hexametaphosphate solution. Each sample was analyzed in about 10 min, including device clean up. The correlation of the laser analyses with pipette analyses varied by particle size and mineralogy. Better correlations were obtained when non-calcareous soils were separated from calcareous soils. Regression analyses relating laser with pipette methods for non-calcareous soils yielded coefficients of determinations of 0.97, 0.99, and 0.99 for the <2-, <50-, and <100-.m fractions, respectively. Use of the laser particle size analyzer greatly reduced the time and labor required for soil PSAs. Since a relatively small sample size is required, care must be taken to ensure a representative sample is selected for analysis.

Growth of zirconia particles made by flame spray pyrolysis

Abstract: The growth of ZrO2 particles in spray flames is studied at production rates of 100 and 300 g/h by thermophoretic sampling (TS) and image analysis of transmission electron microscope (TEM) micrographs. At each TS location, the corresponding temperature of the particle-laden spray flame is measured along the centerline by Fourier transform infrared (FTIR) spectroscopy. The product powder is analyzed by nitrogen adsorption and TEM. The measured evolution of primary particle size distribution is presented and quantitatively explained, accounting for aerosol coagulation and sintering. The evolution of the average agglomerate size and number of primary particles per agglomerate is calculated and compared to TEM micrographs. © 2004 American Institute of Chemical Engineers AIChE J, 50: 3085–3094, 2004

Scaling of energy dissipation in crushing and fragmentation: a fractal and statistical analysis based on particle size distribution

Abstract: An extensive experimental investigation on concrete specimens under crushing and fragmentation over a large scale range (1:10) - exploring even very small specimen dimensions (1 cm) - was carried out to evaluate the influence of fragment size distribution on energy density dissipation and related size effect. To obtain a statistically significant fragment production as well as the total energy dissipated in a given specimen, the experimental procedure was unusually carried out up to a strain of approximately −95%, practically corresponding to the initial fragment compaction between the loading platens. The experimental fragment analysis suggests a fractal law for the distribution in particle size; this simply means that fragments derived from a given specimen appear geometrically self-similar at each observation scale. In addition, clear size effects on dissipated energy density are experimentally observed. Fractal concepts permit to quantify the correlation between fragment size distribution and size effect on dissipated energy density, the latter being governed by the total surface area of produced fragments. The experimental results agree with the proposed multi-scale interpretation satisfactorily.