Resulting Particle Size Distribution Research Articles

Influence of particle shape on size distribution measurements by 3D and 2D image analyses and laser diffraction

Abstract This paper highlights the fact that particle size distribution (PSD) is not unique for the same product, and is dependent on the chosen measurement technique, especially for asymmetric shapes. Laser diffraction and 2D image analysis are commonly used PSD measurement techniques. However, the results may not be representative of the true physical dimensions of the particles. The influence of particle shape on PSD results obtained from 2D/3D image analysis and laser diffraction was investigated. Two metallic powders presenting extreme shape properties (round and elongated particles) were analyzed, as well as a blend of the two pure products. 2D image analysis and laser diffraction results were compared to 3D image analysis (measuring the true particle size). This paper compares the PSD results obtained from the three methods. Some commonly used size parameters in image analysis software did not give meaningful results in regard of the true physical dimensions of the particles. The existence of the two populations (products with extremely different shape and size characteristics) could not be identified with such size parameters, and laser diffraction also performed poorly. The PSD obtained from more precise size parameters (image analysis) better corresponded to the true dimensions of the particles. This study highlights the strengths and weaknesses of particle size analysis techniques when studying products presenting diverse particle shapes, and points out that caution is required in the choice of the size parameters, and in the interpretation of PSD results.

Study on Measuring Particle Size Distribution of a Nanodiamond Powder

Particle size distribution (PSD) of a nanodiamond powder in a high concentration suspension was measured by a new dynamic light scattering (DLS) technique based on the Doppler frequency shifting effect. Influence of dispersing pre-treatment, distribution bases and materials’ properties on DLS results was analyzed, and PSD results were validated by TEM analysis. It was found that the optimized ultrasonic dispersing time of the diamond powder in a sodium hexametaphosphate (SHP) solution was about 5 minutes. And median sizes of the nanodiamond powder were 115.6 nm, 53.0 nm and 32.6 nm, based on light intensity, volume and number respectively. PSD results of the nanodiamond based on number accorded well with results from TEM analysis. And PSD results were affected hardly by refractive indices of the diamond and the dispersing medium, while they were affected markedly by viscosity of the medium. It is concluded that this new DLS technique could measure PSD of the nanodiamond powder in high concentration suspensions which has been dispersed properly.

Bayesian parameter estimation for a jet-milling model using Metropolis–Hastings and Wang–Landau sampling

Bayesian parameter estimates for a computationally expensive multi-response jet-milling model are computed using the Metropolis–Hastings and Wang–Landau Markov Chain Monte Carlo sampling algorithms. The model is accompanied by data obtained from 74 experiments at different process settings which is used to estimate the model parameters. The experimentally measured quantities are the 10th, 50th and 90th quantiles of the resulting particle size distributions. Parameter estimation is performed on a population balance jet-milling model composed of three subprocesses: jet expansion, milling and classification. The model contains eight parameters requiring estimation and can compute the same quantities that are determined in the experiments. As the model is computationally expensive to solve, the sampling algorithms are applied to a surrogate model to establish algorithm specific parameters and to obtain model parameter estimates. The resulting parameter estimates are given with a discussion of their reliability and the observed behaviour of the two sampling algorithms. Comparison of the autocorrelation function between samples generated by the two algorithms shows that the Wang–Landau algorithm exhibits more rapid decay. Trace plots of the parameter samples from the two algorithms appear to be analogous and encourage the supposition that the Markov Chains have converged to the distribution of interest. One- and two-dimensional density plots indicate a unimodal distribution for all parameters, which suggests that the obtained estimates are unique. The two-dimensional density plots also suggest correlation between at least two of the model parameters. The realised distribution generated by both algorithms produced consistent results and demonstrated similar behaviour. For the application considered in this work, the Wang–Landau algorithm is found to exhibit superior performance with respect to the correlation and equivalent performance in all other respects.

Physical and geotechnical characterization of unconsolidated sediments associated with the 2005 Mbonjo landslide, Limbe, Cameroon

Laboratory analyses of unconsolidated sediments from the ruptured zone of the 2005 Mbonjo Landslide scar were carried out to characterize and evaluate their role as contributory factors in enhancing the slide. Colour, particle size (PS) and particle size distribution (PSD), Atterberg limits [liquid limit (LL), plastic limit (PL) and plasticity index (PI)] and basic geotechnical properties [bulk density (ρ), dry bulk density (ρd), dry unit weight (γd), moisture content (Mc), specific gravity (Gs), void ratio (e) and porosity (n)] were determined. Colour ranged from reddish brown to yellowish brown. Texturally, samples were classified as loam, silty clay loam and silty clay. Liquid limit ranged from [56 to 74 weight percentage (wt%)], PL (37 to 50 wt%) and PI (15 to 36 wt%). Values for geotechnical properties were ρ (2 to 2.25 g/cm3), ρd (1.75 to 1.95 g/cm3), Mc (14 to 15 wt%), Gs (2.67 to 2.69 g/cm3), e (0.37 to 0.52) and n (0.27 to 0.34). From results of colour, PS and PSD, Atterberg limits and geotechnical analyses, the samples were reflective of clay-rich sediments with high plasticity and sliding potential. Based on the interpretative data, the studied sediments were qualified as landslide prone with clay interbeds serving as the slide surface. Key words: Cameroon volcanic line, clay interbeds, geotechnical properties, ruptured zone, slide surface.

Performance study of a twin-head electrospray system

A twin-head electrospray (THES) aerosol generation system with one spray head producing positively charged particles and the other producing negatively charged ones has been constructed and its performance has been experimentally evaluated in this study. The charge-enhanced coagulation between oppositely charged droplets generated by the THES was verified by the measuring the resultant particle size distributions via a scanning mobility particle sizer (SMPS), the imaging of dye-labeled coagulated particles via a fluorescence microscope and the chemical composition characterization of generated particles via high-efficiency liquid chromatography (HPLC). The characterization time of charge-enhanced coagulation in our study's generator was estimated to be in the order of 10−5s under the tested operational conditions. The size evolution due to charge-enhanced coagulation was studied for particles with initial sizes ranging from 10 to 710nm. Compared with those prior to the coagulation, the size distributions of particles upon coagulation became broader. Further, regardless the initial charge levels, the peaks of resultant particle size distributions were about 1.3 times larger than the corresponding ones before coagulation, indicating the collision of two oppositely charged particles. As expected, the number of charges on the resultant particles was significantly reduced in the THES generation system. However, only a small fraction of resultant particles carried zero electrical charge. Our study also evidenced that a maximal 70% transmission efficiency can be achieved for the THES system. It is therefore concluded that the twin-head ES technique makes it feasible to take unique advantage of electrosprayed particles without any charge reduction scheme.

The crystal growth kinetics of alpha calcium sulfate hemihydrate in concentrated CaCl2–HCl solutions

The crystal growth kinetics of calcium sulfate α-hemihydrate (α-HH) in nearly constant supersaturated HCl–CaCl2 solutions were investigated. Two types of solutions were used, the first had a low HCl (1.4mol/L) and high CaCl2 (2.8mol/L) concentration and the second had a high HCl (5.6mol/L) and low CaCl2 (0.7mol/L) concentration. These conditions were chosen to represent the first and last stage of a newly developed stage-wise HCl regeneration process. The seeded growth experiments were carried out in a stirred, temperature controlled semi-batch reactor in which supersaturation was kept constant by simultaneous addition of CaCl2 and Na2SO4 solutions. The influence of the following parameters on α-HH crystal growth was studied: temperature (70–95°C), specific power input of stirring (0.02–1.29W/kg) and equimolar inflow rate of CaCl2 and Na2SO4 (0–0.6mol/h). The crystal growth rate was derived from particle size distribution measurements made with the laser light diffraction technique. It was found that the surface area normalized crystal growth rate increased linearly with the molar inflow rate up to 0.3mol/h, at higher inflow rates no further increase of the growth rate was observed. Temperature and specific power input, within the investigated ranges, did not show a marked effect on the growth rate, attributable to a diffusion/adsorption controlled growth process. An interesting finding of the present research is the establishment of a positive relationship between the narrowing of the width of the particle size distribution with increasing crystal growth rate. The results show that the resulting particle size distribution is positively related to the reagent inflow rate, a finding that can be applied to the industrial design and scale-up of the α-HH crystallization/HCl regeneration process.

Size-Controlled Flow Synthesis of Gold Nanoparticles Using a Segmented Flow Microfluidic Platform

Segmented flow is often used in the synthesis of nanomaterials to achieve narrow particle size distribution. The narrowness of the distribution is commonly attributed to the reduced dispersion associated with segmented flows. On the basis of the analysis of flow fields and the resulting particle size distribution, we demonstrate that it is the slip velocity between the two fluids and internal mixing in the continuous-phase slugs that govern the nature of the particle size distribution. The reduction in the axial dispersion has less impact on particle growth and hence on the particle size distribution. Synthesis of gold nanoparticles from HAuCl(4) with rapid reduction by NaBH(4) serves as a model system. Rapid reduction yields gold nuclei, which grow by agglomeration, and it is controlled by the interaction of the nuclei with local flow. Thus, the difference in the physical properties of the two phases and the inlet flow rates ultimately control the particle growth. Hence, a careful choice of continuous and dispersed phases is necessary to control the nanoparticle size and size distribution.

Modelling wheat breakage during roller milling using the Double Normalised Kumaraswamy Breakage Function: Effects of kernel shape and hardness

The effects of wheat properties on breakage during First Break roller milling, as described by the Double Normalised Kumaraswamy Breakage Function (DNKBF), were investigated. A set of 45 wheats from nine varieties representing the range of commercial varieties grown in the UK, and grown over three harvest years at several nitrogen fertiliser levels, were milled at five roll gaps under Sharp-to-Sharp and Dull-to-Dull dispositions. The resulting particle size distributions were fitted with a DNKBF in order to understand the physical significance of the DNKBF parameters and to relate them to shape and hardness. The DNKBF parameters related strongly to hardness as measured using either the Single Kernel Characterisation System or Particle Size Index, allowing the particle size distribution over the range 0–4000 μm to be predicted solely from wheat hardness. A residual analysis showed that the remaining variation was correlated with kernel mass, and that more elongated kernels break to give slightly larger particles than more spherical kernels of equivalent hardness. Two types of breakage are identified, one of which principally produces many small endosperm particles along with large bran particles, while the other tends to produce mid-sized particles. The former dominates under Dull-to-Dull milling and for soft wheats, while the latter becomes more prominent under Sharp-to-Sharp milling and for harder wheats.

Multiangle dynamic light scattering analysis using angular intensity weighting determined by iterative recursion

Multiangle dynamic light scattering (MDLS) can provide better results for particle size distribution (PSD) determination than single-angle dynamic light scattering. Proper analysis of MDLS data requires data from each measurement angle to be appropriately weighted according to the intensity scattered by the particles at each scattering angle. The angular weighting coefficients may be determined by measuring the angular dependence of the scattered light intensity or estimated in various ways. In either case, any noise on the weighting coefficients will adversely affect the PSD determination. We propose a new iterative recursion method for estimating the weighting coefficients and demonstrate its effectiveness for recovering PSDs from both simulated and real experimental data. The new method gives better PSD results than those found using other weighting estimates.

Overcoming challenges in analysis of polydisperse metal-containing nanoparticles by single particle inductively coupled plasma mass spectrometry

Detection and sizing of metal-containing engineered nanoparticles (ENPs) was achieved at concentrations predicted for environmental samples (part-per trillion levels) using single particle inductively coupled plasma mass spectrometry (SP-ICP-MS). Silver nanowires, titanium dioxide and cerium oxide nanoparticles were found to be detectable by this technique, while zinc oxide dissolved too quickly for analysis at these concentrations. In addition to the potential dissolution of particles, other considerations affecting ENP analysis include: instrumental background, mass interferences, percent metal in a nanoparticle, and isotopic abundance of the analyte element. Sizing of these metal-containing nanoparticles was done by correlating ICP-MS response (pulses) from ENPs entering the plasma to mass of metal in dissolved standards. The resulting particle size distributions compared well with results from sedimentation field-flow fractionation. Coincidence in ENP pulses may be difficult to detect in the broad size distributions that arise from polydisperse samples. Comparison of data obtained by combination of multiple analyses of dilute solutions to single analyses of higher concentration allowed discrimination between coincidence and polydispersity. The ratio of ENP pulse detections to the total number of readings during analysis was optimized at 2.5% or less to minimize coincident pulses while still allowing definition of a size distribution.

Key characteristics of hydride–dehydride titanium powder

Titanium powders produced via the hydride–dehydride process are described with reference to the markets that they serve, on the basis of more than 20 years of operating experience at Reading Alloys. Raw material selection and downstream finishing play important roles in determining key characteristics of the finished powder. Resultant chemistry, morphology and particle size distributions are discussed.

The Truncated Geometric Approximation and the Size Distribution of Small Atmospheric Particles

Abstract This paper describes a simple relationship between the slope of particulate optical depth as a function of wavelength and the size distribution of spherical particles. It is based on approximating extinction using a truncated geometric optics relationship and is applicable when optical depth decreases with wavelength. The new relationship suggests that extinction versus wavelength measurements are most sensitive to particles that are comparable in size to the wavelength. When optical depth is expressed as a power-law function of wavelength, the resulting particle size distribution is also a power-law function of size, with the two exponents reproducing the well-known relationship between the Ångström and Junge exponents. Examples of applying the new relationship are shown using both numerical calculations based on Mie theory and measurements from the Aerosol Robotic Network (AERONET) sun photometer at NASA Goddard Space Flight Center (GSFC). Since the truncated geometric approximation makes no assumptions per se concerning the form of the particle size distribution, it may find application in supplementing solar aureole profile measurements in retrieving the size distributions of particles in thin clouds—for example, cirrus—or when they are present.

Modeling and simulation of polyacrylic acid/protamine nanoparticle precipitation

In this study a model for the prediction of polyacrylic acid/protamine nanoparticle precipitation was developed, which constitutes the first numerical approach for modeling the precipitation of organic nanoparticles. Due to the complexity of the process, a spatial resolution (i.e., a simulation via computational fluid dynamics) was not the target. For the description of the precipitation process, population balance equations, accounting for nucleation, growth and aggregation were used and coupled with the engulfment model for mixing. Furthermore, experiments have been carried out by turbulent mixing of precursors in a vortex mixer. Measurements of the resulting particle size distributions and of the final concentrations in the liquid were performed. Finally, by selecting unknown parameters, it was possible to achieve a good agreement of experimental and numerical results. It was found that the formation of the electrostatic surface charge, caused by a layer of protamine on the particle surface, cannot be described instantaneously. Small deviations in the final liquid concentrations and particle size distributions are probably caused by the significant simplifications introduced by the engulfment model and by the description of the solid/liquid equilibrium. However, the presented model may serve as a basis for further development, i.e., by replacing the engulfment model by more sophisticated approaches, e.g., via computational fluid dynamics.

Using laser diffraction data to obtain accurate particle size distributions: the role of particle composition

Suspended particle composition has a large influence on light scattering by small (<20 µm) particles. Inorganic particles and organic phytoplankton cells, both common in natural waters, have very different indices of refraction. This can affect results from laser diffraction particle size analyzers, which measure light scattering and assume an index of refraction to calculate the particle size distribution. Here we examine the effect of the assumed index of refraction on laser diffraction data. A Laser In‐situ Scattering and Transmissometry (LISST) 100X instrument is used to record scattered light distributions from glass microspheres, phytoplankton monocultures, and natural particle samples of mixed composition. The scattering distributions are processed with kernel matrices, derived using Mie theory, assuming either organic or inorganic compositions. Resulting particle size distributions are compared against microscope images. Processing with an assumed inorganic index of refraction was found to produce the most accurate results over the majority of the samples tested. The effect of scattering by particles having diameters outside the instrument inversion range was also assessed. The presence of significant concentrations of particles exceeding the upper limit of the LISST range (>250 µm) produced little effect; however, particles smaller than the lower limit (<1.25 µm) influenced concentrations over the entire LISST size range and produced counterintuitive effects, such as increased concentrations in the largest size bins.

Preparation of Spherical Titania Nanoparticles by CO2 Laser Evaporation and Process‐Integrated Particle Coating

The CO2 laser vaporization (LAVA) method was used to prepare titania nanopowders. Because this versatile method does not require special precursors, a coarse anatase raw powder was applied as starting material. Powder samples produced under varied process parameters were characterized by transmission electron microscopy (TEM), X‐ray diffraction measurements, and Brunauer–Emmett–Teller surface area measurements. The laser‐generated powders consist of spherical, single crystalline and pure anatase nanoparticles, merely softly agglomerated by weak van der Waals forces. Using TEM analysis, the influence of the process parameters on the resulting particle size distribution was investigated. The results are discussed with respect to the particle formation by gas phase condensation. The potential of a process integrated, i.e. in situ, coating procedure for the surface modification of the anatase nanoparticles is demonstrated. As an exemplary representative of organic layer materials stearic acid was chosen. The organic coating was characterized by TEM and Raman spectrometry. Because of the unavoidable soft agglomeration the coating covers entire agglomerates rather than individual primary particles. Thus, the influence of the LAVA process parameters on the agglomerate sizes was systematically studied using a scanning mobility particle sizer.

Measurement of the floating particle size distribution by a buoyancy weighing-bar method

The particle size distribution of cylinder-shaped solid particles was measured using a buoyancy weighing-bar method where the liquid phase density was adjusted to settle or float the particles. The particle size distribution obtained in our experiment agrees with the particle size measured by other method. The present study demonstrates that a buoyancy weighing-bar method, a novel method for measuring the particle size distribution, is suitable for measuring the particle size distribution of a floating solid. The precision of the resulting particle size distribution is comparable to that of a laser diffraction/scattering method as well as a direct measurement with a micrometer. Moreover, this buoyancy weighing-bar method can measure the particle size distribution even in a mixture of two particles with different sizes.

Focus on nanoscience and nanotechnology

Focus on nanoscience and nanotechnology

The Characteristics of Heavy Metals and Particle Size Distribution from Hydrodynamic Vortex Fine Filter Chamber for Treatment of Urban Stormwater Runoff

Hydrodynamic vortex fine filter chamber has gained in popularity as a viable system to improve water quality in urban combined sewer overflows (CSOs) and surface runoff. This paper reports on analysis of particle size distribution (PSD) and analysis of removal efficiency of TSS and total metals from sediment captured by hydrodynamic vortex fine filter (HVFF) chamber modified by the KIST and Seoul National University. In this study, the sediment samples are collected from urban roadway, parking lot and resident/constructed area storm runoff. For the result of PSD, the particle sizes are variously distributed and coarser on the residential/constructed area storm, while total metal concentration is low. For the result of the metal concentration, the metal concentration on urban roadway storm runoff is higher than on the parking lot and resident/constructed area storm runoff. The metal concentration on the 3 urban land-use types is listed from most to least as follows: Urban roadway > Parking lot > Resident/constructed area. For the result of removal rate of TSS and total metal, TSS removal is strongly correlated to total metal removal because solid-associated metals may be adsorbed primarily to particulates. The efficiency of removal on the 3 land-use types is listed from most to least as follows: Parking lot > Urban roadway > Resident/constructed area.

De-agglomeration mechanisms of TiO2 aerosol agglomerates in PWR steam generator tube rupture conditions

A steam generator tube rupture (SGTR) in a pressurized water reactor (PWR) might be a major source of accidental release of radioactive aerosols into the environment during severe accident due to its potential to by-pass the reactor containment. In the ARTIST program, tests were carried out at flow conditions typical to SGTR events to determine the retention of dry aerosol particles inside a steam generator tube. The experiments with TiO2 agglomerates showed that for high velocities in the range of 100–350 m/s, the average particle size at the outlet of the tube was significantly smaller than at the inlet due to particle de-agglomeration. Earlier, particle de-agglomeration has not been considered significant in nuclear reactor severe accidents. However, the tests in ARTIST program have shown that there is a possibility that TiO2 aerosol particles de-agglomerate inside a tube and in the expansion zone after the tube exit under SGTR conditions. In this investigation, we measured TiO2 aerosol de-agglomeration in the tube with very high flow velocities with two different TiO2 aerosols. The de-agglomeration was determined by measuring the size of the agglomerates at the inlet and outlet of the test section. The test section was composed of tubes with three different lengths, 0.20, 2.0 and 4.0 m, followed by an expansion zone. The main results were: (i) the de-agglomerate process was relatively insensitive to the initial particle size distribution, (ii) the agglomerates were observed to de-agglomerate in all the tubes, and the resulting particle size distributions were similar for both TiO2 aerosols, (iii) at high flow rates, increasing the gas mass flow rate did not produce further de-agglomeration, and (iv) the agglomerates did not de-agglomerate to primary particles. Instead, after de-agglomeration the particles had a median outer diameter Dc = 1.1 μm. Based on analysis using computational fluid dynamics (CFDs), the de-agglomeration was caused by the turbulent shear stresses due to the fluid velocity difference across the agglomerates in the viscous subrange of turbulence. It has to be noted that the particles used in this investigation were TiO2 agglomerates, and not prototypical nuclear aerosols with significantly different characteristics. Therefore, the results of this investigation cannot be directly used to determine whether the nuclear aerosol particles may de-agglomerate in SGTR sequences. However, this investigation highlights the possibility of particle de-agglomeration under SGTR conditions, and identifies the mechanism of the de-agglomeration inside the broken tube and when the aerosol is discharged to an open space.

Modeling of Particle Size Distribution for Semibatch Precipitation of Barium Sulfate Using Different Activity Coefficient Models

Our recent experiments with precipitation of barium sulfate (Steyer et al. In BIWIC 15th International Workshop on Industrial Crystallization; Shaker VerlagAachen, Germany, 2008; pp 73−80. Steyer and Sundmacher J. Cryst. Growth 2009, 311, 2702−2708) showed that an excess of barium or sulfate ions in the crystallizer has a strong impact on the resulting particle size distributions (PSDs). Theoretically, this effect is not well understood, as most kinetic models in the literature are valid only for stoichiometric conditions. The aim of this work was, therefore, to investigate the influence of detailed thermodynamically well formulated activity coefficient models on the PSDs in a one-dimensional population balance model of a semibatch continuous stirred-tank reactor (CSTR). The nonsymmetry of these models with respect to an excess of barium or sulfate ions was studied. It was found that the effect on the supersaturation is too weak to explain the experimental results in terms of supersaturation-dependent kin...