Page 109 - Fiber Fracture

94 M.-H. Berger

2.5 fiNex. 610
Saffil-Safimax Nex. 720. Nex. 440
2 -. m
h Altexm Nex. 480 I
m
Q Nay312
9.
1.5 IPRD166
5
c a FP
1 HAlmax
m
-
.-
a,
m
$ 0.5 --
I-
07
0 5 10 15 20 25 30
Silica Content (wt%)
Fig. 4. Evolution of the room temperature tensile strength as a function of the silica content. The lower
strengths of pure alumina FP and Almax fibres are induced by their larger grain sizes of 0.5 Fm, in contrast
to Nextel 610 and silica-containing alumina fibres.

Fig. 5. Typical room temperature fracture morphology of an alumina fibre containing silica addition.
Fracture has been initiated from a surface flaw, which can not be identified by SEM, located at the centre of
a mirror zone.

a-ALUMINA FIBRES

Single Phase a-Alumina Fibres

To increase the creep resistance alumina fibres, intergranular silicate phases have
to be reduced drastically. This imposes processes other than the addition of silica to
control a-alumina growth. A pure a-alumina fibre was first produced by Du Pont in
1979 (Dhingra, 1980). ‘Fiber FP’ was obtained by the addition, to an alumina precursor,