Graphite
Chemical
Formula: C, CARBON
CAS number: 7782-42-5
Refractories:
This end-use begins
before 1900 with
the graphite crucible
used to hold molten
metal; this is now
a minor part of
refractories. In
the mid 1980s, the
carbon-magnesite
brick became important,
and a bit later
the alumina-graphite
shape. Currently
the order of importance
is alumina-graphite
shapes, carbon-magnesite
brick, monolithics
(gunning and ramming
mixes), and then
crucibles. Crucibles
began using very
large flake graphite,
and carbon-magnesite
brick requiring
not quite so large
flake graphite;
for these and others
there is now much
more flexibility
in size of flake
required, and amorphous
graphite is no longer
restricted to low-end
refractories. Alumina-graphite
shapes are used
as continuous casting
ware, such as nozzles
and troughs, to
convey the molten
steel from ladle
to mould, and carbon
magnesite bricks
line steel converters
and electric arc
furnaces to withstand
extreme temperatures.
High-purity monolithics
are often used as
a continuous furnace
lining instead of
the carbon-magnesite
bricks.
Steelmaking:
Natural graphite
in this end use
mostly goes into
carbon raising in
molten steel, although
it can be used to
lubricate the dies
used to extrude
hot steel. A carbon
raiser is added
to increase the
carbon content of
the steel to the
specified level.
Expanded
graphite:
Expanded graphite
is made by immersing
natural flake graphite
in a bath of chromic
acid, then concentrated
sulfuric acid, which
forces the crystal
lattice planes apart,
thus expanding the
graphite. The expanded
graphite can be
used to make graphite
foil or used directly
as "hot top"
compound to insulate
molten metal in
a ladle or red-hot
steel ingots and
decrease heat loss,
or as firestops
fitted around a
fire door or in
sheet metal collars
surrounding plastic
pipe, (During a
fire, the graphite
expands and chars
to resist fire penetration
and spread.), or
to make high-performance
gasket material
for high-temperature
use.
Brake linings:
Natural amorphous
and fine flake graphite
are used in brake
linings or brake
shoes for heavier
(nonautomotive)
vehicles. This use
has been important
for quite some time,
but nonasbestos
organic compositions
are beginning to
cost graphite market
share.
Foundry
facings and lubricants:
A foundry facing
or mold wash is
a water-based paint
of amorphous or
fine flake graphite.
Painting the inside
of a mold with it
and letting it dry
leaves a fine graphite
coat that will ease
separation of the
object cast after
the hot metal has
cooled. Graphite
lubricants are specialty
items for use at
very high or very
low temperatures,
as a wire die extrusion
lubricant, an antiseize
agent, a gear lubricant
for mining machinery,
and to lubricate
locks. Having low-grit
graphite, or even
better no-grit graphite
(ultra high purity),
is highly desirable.
It can be used as
a dry powder, in
water or oil, or
as colloidal graphite
(a permanent suspension
in a liquid).
Other uses:
Natural
graphite has found
uses as the marking
material ("lead")
in common pencils,
in zinc-carbon batteries,
in electric motor
brushes, and various
specialized applications