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.
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.
