Spun glass fiber

Typically, air is filtered through spun glass-fiber before and after mixing with ammonia, whereas ammonia liquid is passed through magnetic separators to remove iron and iron oxide particles and ammonia vapor through sintered metal fiber. 

Dry filters are usually deeper than viscous filters. The dry filter media use finer fibers and have much smaller pores than the viscous media and need not rely on an oil coating to retain collected dust. Because of their greater resistance to air flow, dry filters must use lower filtration velocities to avoid excessive pressure drops. Hence, dry media must have larger surface areas and are usually pleated or arranged in the form of pockets (Fig. 17-64), generally sheets of cellulose pulp, cotton, felt, or spun glass. 

Sol-gel preparations of tetraethoxysilane can be spun into fibers once the appropriate viscosity has been achieved. These fibers are only slightly weaker than silica-glass fibers. 

Fiber or Fibre is any tough substance composed of threadlike tissue, especially when capable of being spun or woven. Fibers may be divided into animal (wool or silk), vegetable (cotton, hemp, flax, ramie, esparto, jute, sisal etc), mineral (asbestos, glass fiber) and artificial (Rayon, Nylon, Orion, Vinyon, Saran etc)... 

The chemistries of phosphates and silicates are similar, but the morphology of the crystals of the sparingly soluble phosphates are unsuited for fiber applications. Amorphous phosphate glasses can be easily spun into fibers in a process similar to the manufacture of fiberglass. Unfortunately, amorphous phosphates lack both strength and hydrolytic stability. 

Inorganic Materials. A few inorganic materials form fibers. Fiberglass made of spun glass has excellent insulating properties. Mixed with epoxy resins, fiberglass is an important reinforcing component for use in such products as automobile bodies and boats. Steel fibers can be pressed into steel wool pads, widely used for their abrasive quality, or they can be braided or twisted into ropes. 

Mineral fibers are manufactured from silicate melts of appropriate composition. These melts are converted into fibers with considerably more efficient use of time and space than in the manufacture of textile glass fibers, since the melts are spun at much lower melt viscosities. After solidification the fibers consist of amorphous glasses (according to X-ray diffraction measurements) with... 

Chemically modified cellulose in the form of cellulose nitrate or nitrocellulose was made and tested for commercial applications in Britain in the 1855-1860 period without much success. The discovery by Hyatt, in 1863, that cellulose nitrate could be plasticized with camphor to give moldability to the blend, made this material much more useful. By 1870, celluloid (plasticized cellulose nitrate) was being produced into a variety of commercial products such as billiard balls, decorative boxes, and combs. Nitrocellulose was also soluble in organic solvents, unlike cellulose, and so could be applied to surfaces in solution to form a coating, as in airplane dopes and automobile lacquers. It could also be solution spun into fibers (synthetic silk) and formed into photographic film, or used as a laminating layer in early auto safety glass. It was also used as an explosive. The hazard introduced to many of these uses of nitrocellulose by its extremely flammable nature resulted in an interest to discover other cellulose derivatives that could still be easily formed, like nitrocellulose, but without its extreme fire hazard. 

The smaller the fiber diameter used in the prefilter, the greater the surface area for adsorption of particles and the better the retention of small particles. In the sixties, asbestos fibers were recognized as the best prefilter media. The individual fibrils were smaller than 0.01 ju and they had a positive zeta potential. However, when it was suspected that asbestos fibers presented a health hazard, fine diameter glass and synthetic polymer fibers were substituted. Unfortunately, neither media equals the performance of asbestos. Glass fibers are available in the finest diameters, but some users are fearful they may represent a similar health hazard. The trend has been to use polypropylene or polyester fiber prefilters. Melt blown or spun-bonded fibers are available in diameters near 1 ju. Multilayers of these media with appropriate calendering have resulted in surprisingly efficient prefilters. 

The collection media in this type of filter can be composed of various materials including hair, spun glass, wool, paper and asbestos. (In the past, asbestos has been used in the manufacturing of all types of filters. Since asbestos is cancer causing, be sure to specify a non-asbestos fiber). The ex-Tended surface media filter consists of folds of material woven back and forth. Corrogated aluminum or paper separators are inserted perpendicularly to the filter face and separate the folds to help direct airflow in an even, parallel fashion. 

Oxide fibers find uses both as insulation and as reinforcements. Glass fibers, based on silica, possess a variety of compositions in accordance with the characteristics desired. They represent the biggest market for oxide fibers. Unlike other oxide fibers, glass fibers are continuously spun from the melt and are not used at temperatures above 250°C. Short oxide fibers can be melt blown whilst other aluminasilicate and alumina based continuous fibers are made by sol-gel processes. Initial uses for these fibers were as refractory insulation, up to 1600°C, but they are now also produced as reinforcements for metal matrix composites. Continuous oxide fibers are candidates as reinforcements for use up to and above 1000°C. 

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