Electrostatic precipitation particle shape

Aluminium and Precipitator Ash. In some Victorian brown coals significant quantities of acid-soluble aluminium are found. This is believed to be present as aluminium hydroxide which is dispersed throughout the water phase of the coal. During combustion of this coal, the refractory aluminium oxide formed takes the shape of the relics of the plant material present in the coal, thus forming an extremely low density ash (approximately 100 kg/m ). Whilst the collection of these particles by electrostatic precipitation is possible, the problem of reentrainment on rapping has necessitated the use of larger sized units than would otherwise be required. It is therefore important to determine the acid soluble aluminium fraction in the coal to determine if precipitation of fly ash is likely to be a problem. 

Particles can be captured directly on a glass slide by sedimentation, electrostatic precipitation, or thermal precipitation and viewed directly in a microscope. Powders or bulk dust samples can be spread out on a slide by gentle smearing with a toothpick. The procedure for viewing particles captured on a filter is to cut out a small pie-shaped piece of the filter and place it on a clean glass microscope slide. A drop of immersion oil is allowed to saturate the filter to make it transparent. The filter is covered with a glass coverslip and examined in the microscope. The immersion oil must have fiie same refractive index as the filter material. The most common type of filter for optical microscope examination of aerosol particles is a cellulose ester membrane of 0.45-pm pore size. These filters have a refractive index of I.SIO. Unfortunately, particles having exactly this refractive index are also made transparent and cannot be observed by this method. 

The equivalent spherical particle diameter of an aggregate of irregularly shaped particles can be found by studying the inertial motion of particles in a medium. This inertial motion behavior is used in many applications, such as sedimentation vessels, electrostatic separators and precipitators, and particle collectors. The various forces that affect particle motion, shown in Figure 4, are briefly discussed below. 

A sol-gel process is an important method to synthesize many materials in a variety of shapes and forms such as particles, films, and bulks. This method is especially suited for the synthesis and preparation of ultrafine rare earths oxide particles at relatively low temperatures. A sol is a stable colloidal dispersion of small particles suspended in a liquid. The particles are amorphous or crystalline and particle aggregation is prevented by electrostatic repulsion. The particles in some sols interact to form a continuous network of connected particles called a gel, instead of aggregating to form larger particles (precipitates). 

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