Micron classification

The jet pulverizer (jet Pulverizer Co.) is another mill of the shallow-pan, angle-jet, and radial-inward-classification type, hke the Micronizer. 

Figure 49 shows a set of bed collapsing curves for a Geldart Group A-A (for Geldart s classification of solid particles, see Geldart, 1972, 1973) binary solids mixture, two closely sized alumina powders, of average particle diameter 104 and 66 microns, respectively. The curve on the extreme left with 0% fines represents the pure coarse component, which is... 

Figure 8. Figure (a) after Clayton et al. (1976, 1977). The scales are as in Figure 1. The O isotopic compositions of the different meteorite classes are represented ordinary chondrites (H, L, LL), enstatite chondrites (EFl, EL), differentiated meteorites (eucrites, lAB irons, SNCs) and some components of the carbonaceous chondrites. As the different areas do not overlap, a classification of the meteorites can be drawn based on O isotopes. Cr (b) and Mo (c) isotope compositions obtained by stepwise dissolution of the Cl carbonaceous chondrite Orgueil (Rotaru et al. 1992 Dauphas et al. 2002), are plotted as deviations relative to the terrestrial composition in 8 units. Isotopes are labeled according to their primary nucleosynthetic sources. ExpSi is for explosive Si burning and n-eq is for neutron-rich nuclear statistical equilibrium. The open squares represent a HNOj 4 N leachate at room temperature. The filled square correspond to the dissolution of the main silicate phase in a HCl-EIF mix. The M pattern for Mo in the silicates is similar to the s-process component found in micron-size SiC presolar grains as shown in Figure 7.

Figure 8.3 Fluidized bed jet mill with classification. (Photo courtesy of Hosokawa Micron Powder Systems.)...

The crospovidone monograph of Ph.Eur. 5 requires a functional classification into Type A (= non-micronized product) and Type B (= micronized product) by means of a particle size measurement in identification test D. 

This classification was developed by the laboratory of Ph.Eur. measuring samples of different crospovidones as agueous suspensions in water and observing the swollen particles under the microscope. It was found that in the case of the tested micronized product almost 100% of the particles were finer than 50 pm (= definition of Type B) and that in the case of the non-micronized product more than 50% (= the majority) were coarser than 50 pm (= definiton of Type A) [631]. 

Current legislation in most developed countries classifies as hazardous most fine and all ultrafine particulate solids separated and collected from fluids with environmental control devices of any kind. In many cases, the mere fact that solids are micron or submicron sized, constitutes a reason for this classification. Owing to their fineness, dusts and slurries or moist residues from pollution abatement that are or become dry particulate matter easily become airborne causing a renewed threat to the environment and to human and animal or plant life (secondary pollution). Also, the large surface area of fine particulate solids results in high solubility so that toxic or otherwise undesirable substances may leach out and spill into surface water or end-up in aquifers if such fines are stored outside or deposited in unprotected landfills. 

Some new developments in impactor design include a parallel stage impactor a micro-orifice impactor for sub-micron aerosol size classification and an eight stage, low pressure impactor... 

Classification. Extenders are mainly natural minerals that are converted into a usable form by working natural deposits, separating secondary constituents, and comminution (micronization). Synthetic products such as precipitated carbonates [e.g., calcium carbonicum praecipitatum (ccp), precipitated sulfates (e.g., blanc fixe), precipitated and pyrogenic silica, and silicates are used for optical brightening. Synthetic fibers (generally organic) are used for reinforcement. The classification of extenders used in surface coatings is summarized in Table 4.1. 

This classification scheme may be extended to a fifth case [3]. In Case 5, the experimental time scale is very long (very slow scan rate) so that diffusion to the entire substrate is convergent, giving sigmoidal voltammetry. This behaviour is most readily observed experimentally when the supporting substrate itself is of microscale and the electroactive particles are of sub-micron size. 

Ideally such a formulation should be universally applicable. This was achieved by the invention of the drug nanocrystals. " With the nanocrystals one went one step beyond micronization in fact to "nanonization". Drug nanocrystals dissolve very fast and thus they can overcome oral bioavailability problems in which the dissolution velocity is the rate limiting step for absorption (e.g. drugs of class II of the Biopharmaceutical Classification System (BCS)). Meanwhile five products for oral administration are on the market. Because of their small size drug nanocrystals can also be injected intravenously. With a size below 1 fim, typically between 200-600 nm, they are much smaller than the smallest blood capillaries being in the range of 5-6 tm. Intravenous products are under development. 

Units are available in stainless steel or protected mild steel, often prefabricated, up to 12.5 m in diameter, capable of processing up to 5m /s or more depending on the separation efficiency required. When the separator is used for classification of granular solids, smaller diameter units are used, up to 4m in diameter, separating nearly all particles coarser than about 150 microns. 

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