Ceramic fibres for composite applications are discussed. NEXTEL, NICALON, FIBRE FRAX, FIBRE FP and Silicon Nitride processing and properties are discussed. The polymer route to produce ceramic whiskers and fibres is also discussed.

1. Ceramic Fibres for Composite
Applications
Prof. Padmanabhan K
SMEC
VIT University, Vellore.

2. Alumina Whiskers and Fibres
• A whisker is a single crystalline short fibre
normally grown through saturated gas phases,
melts and solutions by chemical
decomposition, electrolysis or by growth from
solids under controlled atmospheres.
• Alumina is also used as flame retardant smoke
suppressive filler.
• Grown normally through tip growth. Can also
be grown through basal growth.

3. Alumina Fibres and Whiskers
• Vapour transport of moist H2 over Al, Al2O3 and
Ti Al 3 powders heated to 1300 to 1500 celsius
deposits acicular sapphire on the cooler part of
the furnace.
• Wettability and bondability at low temperature is
less than that of SiC.
• Fibre FP: alpha alumina fibres ( 1971), du Pont
• Spinning of aqueous base slurry of Al2O3
particles along with organic spinning additives . a
grain size of 0.5 microns is obtained.

4. Alumina Fibres and Whiskers
• Firing process converts to a dense alpha
alumina, dia =20 microns, density=3.9 g/cc.
• Alpha alumina and 20 % partially stabilized
Zr2O3 better than FP by 50 % in mechanical
properties.
• NEXTEL fibres ( alumina, silica, B2O3)
• Sol Gel process: mixing and homogenizing of
solutions ( sol) that gel or condense to a solid
glass or glass/ceramic by catalysis and heat.

5. NEXTEL Fibre
• Spinning through multihole spinnerets
• Fibres are oval with major axis to minor axis
ratio being 2:1
• 62 % alumina, 24 % silica, 14 % B2O3
• Mullite ( 3 Al2O3 2 SiO2), Gamma Al2O3 and
amorphous silica phases are present in other
alumina based fibres
• Strength retention up to 1000 Celsius.

6. Continuous Ceramic Fibres
• Formed by polymer decomposition
• Melt- fibre spinning and heat treatment to
convert to ceramic fibre
• Nicalon is an SiC based fibre processed in
1975 by Yajima and co workers at Tohoku
University of Japan through melt spinning at
350 celsius through quartz spinnerets and
subsequent pyrolysis of polycarbosilane.

7. NICALON
• Nicalon is a fibre with about 10-15 microns in
diameter. It is 61 % SiC, 35 % SiO2 and 3.5 %
free C
• Standard grade and Ceramic grades are
available
• Tensile Strength : 0.3 GPa to 3.6 GPa.
• Tensile modulus : 200 GPa
• Tyranno fibres : Contain Si,Ti,C, O

8. Si3 N4 Whiskers and Fibres
• Crystalline and polycrystalline forms: alpha is low
temperature form and beta is high temperature
form, hexagonal phases are obtained after
sintering at 800 to 1100 celsius , all transform to
beta Si3N4.
• 3Si + 2N2 - Si3N4 ( N2 or NH3 Atmosphere )
• 3SiO2 + 6C + 2N2 - Si3N4 + 6CO ( through
reduction of Silica in N2 atmosphere)
• Strength or Stiffness: more or less SiC, but slightly
tougher.