It happens every year doesn’t it? You are teaching about the production of aluminium, you say that cryolite is used to lower the melting point* and some bright spark starts asking you about cryolite. What is it? Where is it from? and so on.
Well todays positng is aimed at keeping that inquisitive student quiet. All his or her questions can now be answered. Read on….
….. Cryolite is sodium aluminium fluoride (NaAlF6) and is actually a synthetic substance.
In the Hall – Heroult cell (that’s the standard electrolytic cell that we teach) only 5% of the mixture is aluminium oxide. Cryolite is responsible for 95% of the mixture, the other 5% coming from calcium fluoride.
* Contary to popular belief / teaching, cryolite does NOT reduce the meltinfg point of aluminium oxide, more so it reduces the meltinmg point of the mixture.
That should keep those inquisitive minds busy!