Fused alumina or electric
fused alumina is made by fusing
aluminous raw materials
electrically. The fused product
from an electric arc furnace is
cooled in ingots, crushed and
classified in different grades.
Fused alumina includes brown
fused alumina and white fused
alumina. Brown fused alumina
(BFA) is produced by using
bauxite as the starting
material, whereas, white fused
alumina (WFA) is produced
by using calcined alumina, from
the Bayer’s process, as the
starting material. Both are
being used as refractory raw
materials and also as grinding
materials.
In brown fused alumina, the
impurities in bauxite are
reduced and separated by
allowing them to precipitate as
Fe-Si-Ti system iron alloys, but
some titanium oxides form a
solid solution together with
alumina and accounts for the
brown colour of the product.
This alumina is frequently used
as a grinding material due to
its high degree of toughness. As
a refractory raw material, its
use is limited to non-critical
grades of alumina bricks and
monolithics.
White fused alumina is the
principal fused alumina used
for making refractories. It
is obtained by simply fusing
calcined alumina. Some white
fused alumina contain a trace of
chromium oxide accounting for
ruby colour.
Fused alumina, with its perfect
crystallization, is difficult to
sinter. In addition, it is
inactive and does not readily
react with other raw materials.
Compared to sintered alumina, it
is less liable to deformation at
high temperatures. It is also a
material with excellent
strength, considerable
resistance to abrasion and
corrosion. As a result, it is
often selected as an aggregate
for refractories in severe
conditions.
The used of white fused alumina
has grown in absolute terms,
even after continuous, decline
in relative consumption of
refractories in steel industry,
worldover. The increased use of
continuous casting in steel
making, the steadily increasing
share of unshaped refractories
and the strong trend to improved
steels with more stringent
specifications are
major drivers for white fused
alumina refractories.
Fused bubble alumina is used as
the raw material for high
temeprature insulating
refractories. When blown by
using a stream of high pressure
air into molten alumina forms
bubble.
