Since more than a century aluminum is produced by the Hall Heroult process which is very energy intensive. Alternatives are under development such as direct reduction from Al2O3 to Al metal by carbon
at very high temperatures which costs considerably less energy per kg of Al than Hall-Heroult, despite the much higher working temperature (> 2000C
vs 1000C).
The problem is however to get a reaction vessel, but why not just using the 'unmeltable' graphite ? Maybe because C is a participant in the reaction ?
And Hall-Heroult has more problems: F2 and HF in the electrolysis fumes which have to recovered and the preprocessing of alumina and the need for
cryolite which is just used as a solvent for Al2O3 to get much lower working temperatures.
Why not electrolyzing just molten Al2O3 in a graphite vessel under an Ar atmosphere ? This should work well even under the extreme temperatures.
But there should be a reason for this why this is not used. High temperatures ? Well, there are some commercial large scale processes using temps >
2000C, such as the synthesis of CaC2 and SiC. unionised - 19-11-2017 at 02:55
SiC is made at temperatures near 2300 C
CaC2 at temps a little lower.
Alumina doesn't melt until near 3000 C
Those extra 700 degrees or so make a big difference.
Also, the melt isn't a good conductor.metalresearcher - 19-11-2017 at 08:47
SiC is made at temperatures near 2300 C
CaC2 at temps a little lower.
Alumina doesn't melt until near 3000 C
Those extra 700 degrees or so make a big difference.
