Particle size definitions

Taking into account the concepts presented above, it is obvious that the measurement of particle size results dependent on the conventions involved in the particle size definition and also the physical principles employed in the determination process (Herdan, 1960). When different physical principles... 

Only four of the above particle size definitions are of general interest for applications in packed beds and fluidized beds. They are the sieve diameter, d, the volume diameter, d, the surface diameter, (f, and the surface-volume diameter, d. The most relevant diameter for application in a fluidized bed is the surface-volume diameter, 4v For applications in catalytic reactors with diflferent isometric catalyst shapes. Rase (1990) suggested that we use the equivalent diameters summarized in Table 1. 

An important characteristic of the log-normal distribution is that the transformation among the various particle size definitions and the statistical diameters can be performed analytically and graphically (Smith et al., 1929). The Hatch-Choate (1929) transformation... 

Coke breeze and limestone particle size definitely have an effect on the sintering productivity. Sinter with the coarse coke breeze and limestone particle size produces larger pore and gives a high performance of sintering productivity due to good permeability of the sinter bed. 

Isobutyhdene diurea [6104-30-9] is a nonhygroscopic white crystalline soHd available in fine (0.5—1.0 mm), coarse (0.7—2.5 mm), and chunk (2.0—3.0 mm) particle sizes. The AAPFCO official definition requires a minimum nitrogen content of 30% with 90% of the nitrogen in water-insoluble form prior to grinding (3). 

When a process is continuous, nucleation frequently occurs in the presence of a seeded solution by the combined effec ts of mechanical stimulus and nucleation caused by supersaturation (heterogeneous nucleation). If such a system is completely and uniformly mixed (i.e., the product stream represents the typical magma circulated within the system) and if the system is operating at steady state, the particle-size distribution has definite hmits which can be predic ted mathematically with a high degree of accuracy, as will be shown later in this section. 

The definitions coarsely chopped to finely powdered , which formerly in the pharmacopoeias were given as mesh sizes, are mostly nowadays indicated without such a requirement in the DAB 10, V. 4.N6, only coarsely chopped (4000 to 2800 sieve), finely chopped (2000 sieve), and powdered (710 to 180 sieve) are distinguished. The wide particle-size ranges have rightly been criticized [1, 2], partly on the basis of extensive investigations. 

ISO i) I 992) Air Quality—Particle Size Fraction Definitions for Health-Related Sampling. ISO/ Cl) 7708 International Standardization Organization, Geneva. 

The complete mathematical definition of a particle size distribution is often cumbersome and it is more convenient to use one or two single numbers representing say the mean and spread of the distribution. The mean particle size thus enables a distribution to be represented by a single dimension while its standard deviation indicates its spread about the mean. There are two classes of means ... 

Smoke is taken as having a particle size of less than one pm. Dust consists of particles I-76 pm in diameter. Grit can be interpreted as particles larger than dust. These definitions were taken from the Beaver Report of November 1954 which formed the basis for the 1956 Act. 

Discussion. The turbidity of a dilute barium sulphate suspension is difficult to reproduce it is therefore essential to adhere rigidly to the experimental procedure detailed below. The velocity of the precipitation, as well as the concentration of the reactants, must be controlled by adding (after all the other components are present) pure solid barium chloride of definite grain size. The rate of solution of the barium chloride controls the velocity of the reaction. Sodium chloride and hydrochloric acid are added before the precipitation in order to inhibit the growth of microcrystals of barium sulphate the optimum pH is maintained and minimises the effect of variable amounts of other electrolytes present in the sample upon the size of the suspended barium sulphate particles. A glycerol-ethanol solution helps to stabilise the turbidity. The reaction vessel is shaken gently in order to obtain a uniform particle size each vessel should be shaken at the same rate and the same number of times. The unknown must be treated exactly like the standard solution. The interval between the time of precipitation and measurement must be kept constant. 

Many emulsion polymerizations can be described by so-called zero-one kinetics. These systems are characterized by particle sizes that are sufficiently small dial entry of a radical into a particle already containing a propagating radical always causes instantaneous termination. Thus, a particle may contain either zero or one propagating radical. The value of n will usually be less than 0.4. In these systems, radical-radical termination is by definition not rate determining. Rates of polymerization are determined by the rates or particle entry and exit rather than by rates of initiation and termination. The main mechanism for exit is thought to be chain transfer to monomer. It follows that radical-radical termination, when it occurs in the particle phase, will usually be between a short species (one that lias just entered) and a long species. 

The term particle and particle size are so highly ambiguous as to require precise definition. As used in this article particles will.be limited by size to those distinct entities which have physically detectable boundaries in any direction within the limits of 0.05 and 10 microns (1 micron, p -0.001mm). This size range covers those particles which can be directly measured without magnification down to those which exhibit colloidal behavior... 

Attempts to determine how the activity of the catalyst (or the selectivity which is, in a rough approximation, the ratio of reaction rates) depends upon the metal particle size have been undertaken for many decades. In 1962, one of the most important figures in catalysis research, M. Boudart, proposed a definition for structure sensitivity [4,5]. A heterogeneously catalyzed reaction is considered to be structure sensitive if its rate, referred to the number of active sites and, thus, expressed as turnover-frequency (TOF), depends on the particle size of the active component or a specific crystallographic orientation of the exposed catalyst surface. Boudart later expanded this model proposing that structure sensitivity is related to the number of (metal surface) atoms to which a crucial reaction intermediate is bound [6]. 

For code R8 it commences with a solid with the help of AFNOR standards NF T 20-035 . Handling consists in preparing mixtures of variable compositions of an oxidant to be classified as cellulose. Both substances have to have a definite particle size distribution. The composition which gives the fastest combustion on a moulding of the mixture at a distance of 20 cm is established. This speed is compared with the one of the mixture used as a reference, which has an imposed composition of barium nitrate and cellulose. If the combustion speed of the particular substance is higher than that of the reference, it will bear R8. 

Chemists have been working for a long time with particles having sizes of nanometers. The novelty of recent developments concerns the ability to make nanostructured substances with uniform particle sizes and in regular arrays. In this way it becomes feasible to produce materials that have definite and reproducible properties that depend on the particle size. The development began with the discovery of carbon nanotubes by Ijima in 1991 (Fig. 11.15, p. 116). 

Flow Experiments. A "critical velocity," vc, is defined as that velocity at which a "measurable" release of particles is observed above this critical velocity, release of particles is continuous. Specifically, it is taken to be the velocity at which 10% of the particles have been released. Based on this definition, vc is a function of particle size--the larger the particle, the smaller is vc (Figure 5). 

This property is readily established from the definition of Fourier transform and convolution. In scattering theory this theorem is the basis of methods for the separation of (particle) size from distortions (Stokes [27], Warren-Averbach [28,29] lattice distortion, Ruland [30-34] misorientation of anisotropic structural entities) of the scattering pattern. 

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