Averages of particle size

There are various methods for the determination of the surface area of solids based on the adsorption of a mono-, or polymolecular layer on the surface of the solid. These methods do not measure the particle diameter or projected area as such, but measure the available surface per gram or milliliter of powder. The surface measured is usually greater than that determined by permeability methods as the latter are effectively concerned with the fluid taking the path of least resistance thru the bed, whereas the adsorbate will penetrate thru the whole of the bed as well as pores in the powder particles. These methods appear to be more accurate than surface areas calculated from weight averages or number averages of particle size because cracks, pores, and capillaries of the particles are included and are independent of particle shape and size... 

Averages of particle size, polydisperse particulate 3y3tems, 161-178... 

Needless to say, kinetic parameters established in this way are empirical factors dependent on the definition of other variables,e.g., averaging of particle size distribution to determine R. Nevertheless, the model provides a rational approach to the complex physical and chemical phenomena of multistage, multireaction leaching. It is intended to expand the model to include countercurrent operations. 

The only nearly pure (99+%) form of lead azide used today in the United States is the so-called colloidal lead azide made by quickly mixing dilute solutions of lead and azide salts. Despite the information in reference [5], colloidal lead azide is neither colloidal in particle size (the specification [6] calls for an average of particle size of 5 pm) nor safer to handle, as this form of lead azide is particularly sensitive to electrostatic discharge. It is used in contact with bridge wires in electric detonators (sometimes applied by mixing with a lacquer binder). The process as developed commercially is a proprietary product, and only small amounts are made as needed. 

Specific Surface. The total surface area of 1 g of powder measured ia cm /g is called its specific surface. The specific surface area is an excellent iadicator for the conditions under which a reaction is initiated and also for the rate of the reaction. It correlates in general with the average particle size. The great difference in surface area between 6-p.m reduced iron powder and 7-p.m carbonyl iron powder (Table 3) cannot be explained in terms of particle size, but mainly by the difference between the very inregular-shaped reduced and the spherical carbonyl iron powders. 

Many of the borate chemicals are sold in a variety of particle size distributions, and average size analyses for the various cuts are available from the manufacturer. 

Material and uses Shape"of particles Size range, U.S. standard mesh f Internal porosity, % Bulk dry density, kg/L Average pore diameter, nm Surface area, kmVkg Sorptive capacity, kg/kg (dry)... 

Baldwin (Ref 65) also synthesized a copolymer from acrylic acid and carboranylmethyl acrylate which was used to make the proplnts in Table 36. Composition A has the burning rates shown in the table for the AP particle sizes indicated. Composition B had an average AP particle size of 15 microns and a burning... 

Fig. 33 —SEM images of Si02 particles (a) average Si02 particle size is 15 nm, (b) average Si02 particle size is 30 nm, (c) average SiOj particle size is 50 nm, (d) average SiOj particle size is 160 nm.

Changes in thermal stability and mass due to the formation of CdS nanoparticles in LB films were examined [180]. The LB films were formed onto gold-coated quartz oscillators from monolayers of arachidic acid or nonacosa-10,12-diynoic acid on CdCH containing subphases. The films were exposed to H2S gas until the mass change indicated complete conversion of Cd to CdS. The thermal stability of the H2S-treated films was reduced, with significant mass loss initiating at 55°C, compared to minimal mass loss in the untreated films up to at least 80°C under mild vacuum. The average CdS-particle size... 

As the metal particle size decreases the filament diameter should also decrease. It has been shown that the surface energy of thirmer filaments is larger and hence the filaments are less stable (11,17-18). Also the proportion of the Ni(l 11) planes, which readily cause carbon formation, is lower in smaller Ni particles (19). Therefore, even though the reasons are diverse, in practice the carbon filament formation ceases with catalysts containing smaller Ni particles. Consequently, well dispersed Ni catalysts prepared by deposition precipitation of Ni (average metal particle size below 2-3 nm) were stable for 50 hours on stream and exhibited no filamentous coke [16]. 

It is apparent that the arithmetic average is not a true index of particle size for practical considerations. For example, in a powdered material where particles are classified as 95% at 2 microns and 5% at 0.1 micron, the computed arithmetic average would be on the order of 0.4 micron (5). 

In the chemical preparation of unprotected metal colloids, the metal concentration usually has a significant influence on the particle size of obtained metal nanoclusters. For example, when increasing Pd concentration from 0.1 to 1.0 mM in the preparation of Pd metal colloids by the thermal decomposition of Pd acetate in methyl isobutyl ketone, the average Pd particle size increased from 8 to 140nm [6,7]. However, in the alkaline EG synthesis method, the size of metal nanoclusters was only slightly dependent on the metal concentration of the colloidal solution. The colloidal Pt particles prepared with a metal concentration of 3.7 g/1 had an average diameter of... 

These particle size distributions reveal that the average Pt particle size for all three samples prepared by sputtering was about 1.6 nm and independent of weight loading. 

HRTEM analysis indicates that the two systems have quite different distributions of particle size, the average values being 2.1 nm in the MVS system and 7.1 nm in the commercial sample (Figure 4), thus accounting for their different behavior. 

Many studies have been conducted to look at the effect of particle size on dissolution and the bioavailability of insoluble drugs [69-84], One study looked at the effect of surface area on the bioavailability of griseofulvin, which has an aqueous solubility of 0.014 mg/mL and an average dose of 500 mg. The authors showed that an approximately sixfold increase in the surface area led to a 2.5-... 

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