METALLURGY
METALLURGY
OF
OF
ALUMINUM
ALUMINUM
METALLURGY
METALLURGY
OF
OF
ALUMINUM
ALUMINUM
PROPERTIES
PROPERTIES
the lightest of the common metals
(except with Mg) with density = 2.7
g/cc (
1
/
3
the density of Cu).
soft and malleable at ordinary
temperature (becomes brittle when
heated to above 150
o
C).
silvery white in color
an amphoteric metal
good conductor of heat and electricity
an active metal but it does not corrode
OCCURENCE
OCCURENCE
Aluminum is the most abundant and the 3
rd
plentiful element on the earth’s crust.
The elemental form does not occur in
nature, its principal ore is bauxite. The
major sources of aluminum are:
bauxite, Al
2
O
3
.
H
2
O
cryolite, Na
3
AlF
6
corundum, Al
2
O
3
orthoclase, KalSi
3
O
8
beryl, Be
3
Al
2
Si
6
O
18
USES
USES
its chief use is in automobile and
aircraft construction.
kitchen utensils, aluminum foil and
beverage cans
high voltage transmission line
used as solid propellant for rockets
in the welding of iron and steel.
PREPARATION
PREPARATION
Aluminum is usually prepared from
bauxite.
Hall Process reduces bauxite to
aluminum.
The cell contains a series of carbon
(graphite) anodes.
The cathode is also made of carbon
and constitutes the lining inside the
cell.
HALL PROCESS
HALL PROCESS
The aluminum oxide from bauxite is melted with
cryolite to form 5% solution. The oxide dissociates as
follows:
Al
2
O
3
2Al
+3
+ 3O
-2
The mixture is electrolyzed to produce aluminum and
oxygen gas:
Anode : 3 [2O
-2
- 4e
-
O
2
]
Cathode : 4 [Al
+3
+ 3e
-
Al]
The overall reaction is:
2Al
2
O
3
4Al + 3O
2
Oxygen gas reacts with the carbon anodes to form
monoxide, which escapes as a gas. The liquid aluminum
metal (m.p. 660.2
o
C) sinks to the bottom of the vessel
from which it can be drawn from time to time.