Particle size distribution diameter characteristics

Malvern Insitec) EPCS-F is designed for powders in the size range of 0.2 pm to 1000 pm [202]. Partiele measurements are made at rates up to 500 per second with immediate display of particle size distribution and characteristic diameters. Specific values or points on the particle size distribution are continuously fed back to the user or to a process control system. Particles with different refractive indices and aspect ratios up to 2 1 can be measured. 

The observation of individual AST particles with the hydrodynamic diameter of 10-20 nm (Figure 2.56), i.e., smaller than the average geometrical diameter of primary particles, is untypical for the aqueous suspensions of fumed silica, alumina, titania, or binary oxides (Gun ko et al. 2001e). This result can be caused by a very broad size distribution of primary particles of AST (broad primary particle size distribution is characteristic for nanooxides with a low specific surface area [vide supra Degussa 1997]). Therefore, one can assume that primary AST particles of strongly different sizes are characterized by different contributions of titania, alumina, and silica, since they can be formed in different zones of the flame during the synthesis. 

The electrical low-pressure impactor was used to measure the number concentrations of diesel exhaust particles. The particle size distribution ranges from 30 nm upward were then determined using the aerodynamic diameter as the characteristic dimension. ... 

Glicksman and Farrell (1995) constructed a scale model of the Tidd 70 MWe pressurized fluidized bed combustor. The scale model was fluidized with air at atmospheric pressure and temperature. They used the simplified set of scaling relationships to construct a one-quarter length scale model of a section of the Tidd combustor shown in Fig. 34. Based on the results of Glicksman and McAndrews (1985), the bubble characteristics within a bank of horizontal tubes should be independent of wall effects at locations at least three to five bubble diameters away from the wall. Low density polyurethane beads were used to obtain a close fit with the solid-to-gas density ratio for the combustor as well as the particle sphericity and particle size distribution (Table 6). 

Silica stationary phases display some ion exchange properties, which may also influence the separation characteristics of silica. One of the main disadvantages of the use of silica and silica-based stationary phases is their instability even at slightly alkaline pH, such as 8.0. HPLC stationary phases can be characterized with the average particle diameter and the distribution of particle size. Smaller average diameter and narrow particle size distribution generally enhances the efficacy of separation. The average particle diameter can be calculated with different methods ... 

Early data collection of prototype-blend experiments could be an invaluable tool to successful scale-up. Physical characteristics such as particle size distribution, bulk and tapped density, and flowability and functional characteristics (mainly compactability) are key indicators of possible downsteam scale-up problems. If, for example, the active drug substance has a mean particle diameter... 

Particle deposition velocities depend on a number of factors, including wind speed, atmospheric stability, relative humidity, particle characteristics (diameter, shape, and density), and receptor surface characteristics. Recent studies on dry particle deposition to surrogate surfaces and derived from atmospheric particle size distributions and micrometeorology suggest that a V equal to about 0.5 cm s 1 is applicable to urban/industrial regions [116-120]. 

To give the particles the required momentum, they should be densely packed and rigid and have a well-defined narrow particle size distribution. Friable and oblique particles are not desirable because the penetration depth will increase if the particle characteristic is more variable (Hickey 2001). Studies have been performed with particles ranging from 20 to 40 J,m in size and 1.1 to 7.9 g/cm3 in density impacting human cadaver skin (Kendall et al. 2000). Velocities of up to 260 m/s were applied to particles of this size range. For many applications, smaller particles of about 1 to 4 j,m diameter may be required for an optimized delivery. To deliver particles of this size into the skin, higher densities and impact velocities are required. For this reason, gold particles are used as a carrier material for the delivery of plasmid DNA vaccines (Kendall et al. 2001). 

In this chapter, the basic definitions of the equivalent diameter for an individual particle of irregular shape and its corresponding particle sizing techniques are presented. Typical density functions characterizing the particle size distribution for polydispersed particle systems are introduced. Several formulae expressing the particle size averaging methods are given. Basic characteristics of various material properties are illustrated. 

Figure 6 shows a comparison of the particle size distribution curves for samples 68-B and 8-A obtained by SEM, SFFF, and DCP, those methods directly yielding distribution information. For sample 68-B, based on the SEM number distribution, the sample is unimodal with a small shoulder on the large diameter side. The DCP number distribution curve shows the same characteristics. The SFFF number distribution curve appears to be broader and the small population of larger particles is not discernable. The shoulder on the smaller diameter side in the SFFF distribution appears to be an instrument artifact and occured in the distributions of several samples. 

The shear stabihties of mini- and macroemulsion latexes were compared and quantitatively evaluated with respect to their particle size distributions by Rodrigues and Schork [146]. Although miniemulsion latexes exhibit many of the properties of macroemulsion latexes, there may be subtle differences in particle size distribution and surface characteristics due to differences in their polymerization mechanisms. To study the effects of these differences on the shear stabihties of the miniemulsions, a quantitative approach was developed where changes in the average diameter and total number of particles have been related to the particle size distribution before and after shearing. 

Polystyrene Latex (PSL) Bead Solution Filtration Experiments were conducted to obtain filter retention, flow rate, and Ap data for a DI water based PSL bead mix solution prepared using particles ranging from bead diameters of 0.772 to 20 pm. It is a common practice to use PSL bead challenge solutions (created by mixing different size PSL bead standards in specific volumetric ratio to simulate slurry-like particle size distribution for the bead mix solution) to obtain relative quantitative retention data for various filters. These solutions are expected to retain stable PSD and provide more consistent information compared to real CMP slurries, which may change particle characteristics over time. 

For measurement of particles and gaseous emissions the same equipment and methods were applied for the PDU as for the previously tested commercial wood chip boilers. The patterns of particle size distribution of emissions from the PDU showed similar characteristics as those from commercial boilers. The mode diameters (MD) are at sizes between 80 and 100 nm Figure 8). 

Important issue for urban dispersion modelling is the characteristics of the release, e.g., radiochemical composition, density for gases, size distribution for aerosols, etc. For radioactive aerosols the particle size distribution (e.g., number of modes, distribution type, average diameter and standard deviation for each mode, density, and nuclides) varies significantly for different release types and from one nuclide to another. The particle size spectrum could be very broad, e.g. 0.001-200 fim. 

Thus, Eqs. (2) and (3) enable us to convert the volume-equivalent particle size distribution into aerodynamic-equivalent distribution for any flow regime. The characteristic mean diameters are dy (volume geometric) and (volume aerodynamic). Although dp is numerically close to the mass-median aerodynamic diameter (MMAD) often used for the aerosols, it is better defined for asymmetrical distribution, so often observed for respiratory powders. 

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