Particles and Particle Dispersoids

Characteristics of particles and particle dispersoids, (Courtesy of the Stanford Research Institute prepared hy C. E. Lapple.)... 

Fig. 2-2. Characteristics ui particles and particle dispersoids Reprnduci d by penni >-ien of SRI International, Menlo Park, California, 1959-...

Table 13.1 covers general information for different particulates, liquids in gas, typical particles and gas dispersoids, behavior of particles in the human body, charging mechanisms, principles of particle size analysis, methods for particle size analysis, and an estimation of the general collection efficiency of available commercial particle removal equipment. 

The particle sizes of liquid and solid dispersoids will vary markedly depending upon the source and nature of the operation generating the particular particles. For design of equipment to reduce or eliminate particles from a fluid stream, it is important either to know from... 

Inversions tend to inhibit mixing of air below the inversion with that above the inversion. The combination of the Pacific high pressure, tbpograpy and generally clear sky conditions found in the Pacific Northwest during the summer months results in multilevel inversions (e.g. subsidence, marine air, valley and canopy inversions). All of these could affect a particular site. However, the valley and canopy inversions are the most common. These, in combination with slope and valley winds, greatly affect the distribution of particle and gaseous dispersoids. 

Aluminum alloy microstructures are developed as a result of alloy composition and thermomechanical treatment. From a corrosion perspective, the dominant features of alloy microstructure are grain structure and the distribution of second phase (intermetallic) particles as constituent particles, dispersoids, or precipitates. Such particles have electrochemical characteristics that differ from the behavior of the surrounding alloy matrix, making alloys susceptible to localized forms of corrosion attack that has been termed microgalvanic corrosion. 

Once the precipitates grow beyond a critical size they lose coherency and then, in order for deformation to continue, dislocations must avoid the particles by a process known as Orowan bowing(23). This mechanism appHes also to alloys strengthened by inert dispersoids. In this case a dislocation bends between adjacent particles until the loop becomes unstable, at which point it is released for further plastic deformation, leaving a portion behind, looped around the particles. The smaller the interparticle spacing, the greater the strengthening. 

The primai y distinguishing charac teristic of gas dispersoids is particle size. The generally accepted unit of particle size is the micrometer, [Lm. (Prior to the adoption of the SI system, the same unit was known as the micron and was designated by 1.) The particle size of a gas dis-persoid is usually taken as the diameter of a sphere having the same... 

Small particles can be introduced into metals or ceramics in other ways. The most obvious is to mix a dispersoid (such as an oxide) into a powdered metal (aluminium and lead are both treated in this way), and then compact and sinter the mixed powders. 

If the diameters of the disperse particles, supposed spherical, lie between the limits of 1 and 100 /x/z (/r/x=icr6mm.) the particles are of colloid dimensions, and the flame is colloidal. It is termed a stationary, but not a stable dispersoid system by von Weimarn.4 In a stable system the particles would not change, whereas in a flame they constantly disappear and are as frequently renewed. 

Dioxin A family of chemicals with related properties and toxicity. There are 75 different dioxins, or polychlorinated dibenzodioxins (PCDDs) 135 different furans, or polychlorinated dibenzofurans (PCDFs) and 209 different polychlorinated biphenyls (PCBs). Each different form is called a congener, a member of a family of compounds known chemically as dibenzo-p-dioxins. Concern about them arises from their potential toxicity as contaminants in commercial products. Tests on laboratory animals indicate that it is one of the more toxic anthropogenic (man-made) compounds a term used interchangeably with 2,3,7,8-tetrachlorodibenzo-p-dioxin or TCDD Disease prevention Measures used to prevent a disease or reduce its severity Dispersoids The particles of a dispersion... 

---