Polycrystalline fiber


These fibers are continuous fibers i.e., fibers having an infinite length with respect to their diameter. The major important fiber in this class is glass fiber. These fibers exhibit high tensile strength, high elastic modulus, and chemical inertness:
The fibers retain their properties even after exposure to high temperatures. However the strength of the fiber is dependent on its microstructure, Presence of pores, defects as well as wide distribution of crystallite size affect the properties of these fibers.

Polycrystalline fiber



Fiber formation

These fibers can be formed by the following methods:

Molten oxide process
In this process, the metal oxide is melted and extruded to form the more.

Extrusion process
In this process, the finely divided and dispersed oxide particles are mixed with plastics and extruded to form continuous fibers,

Precursor process
In this process a solution or suspension of the metal compound is formed into fibers by means of another organic chemical or by burning. The corresponding metal compound is converted into the respective oxide. As per these processes, ceramic fibers, refractory fibers, like silica fibers, are developed. Ceramic fiber is generally prepared by hot extrusion of ceramic oxide particles.
The extrusion process is very suitable for preparing hollow ceramic fibers for special purposes, where porosity is desirable eg, ultrafiltration and fluid separation. 
Ceramic fibers, silica fibers can also be manufactured from the solution of metal compounds. The ceramic fiber consists of 45% alumina, 52% silica and traces of iron oxide, titanium oxide, calcium oxide, etc.
In a similar manner, silica is consists of more than 98% silicon oxide with traces of aluminum oxide and calcium oxide. Alternately normal glass fibers can be acid bleached to extract all the oxides other than silica, then washed to get a silica fiber.

Application of Polycrystalline fiber

These fibers are mostly used tor insulation and reinforcement purpose, The probable field of applications is aircraft. the aerospace industry, rocket engines, jet engines, high-rotating turbine blades, springs, shafts, battery plates, acoustic insulation, high-temperature resistant components, nuclear industry, electrical machinery, super-conductors


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