The reaction:
CaSO4 + 2/3 Al ===> CaO + 1/3 Al2O3 + SO2
... is the only one that can explain SO2 and is poor in heat generation (pitiful, in fact): while that plaster + Al is one of the hottest
'burning' mixtures available to hobbyists.
No, what might be happening is that in Metalresearcher's 'bucket chemistry' an excess of CaSO4 is present in the
mix and undergoes a little decomposition due to T > 2000 C.
Using Nernst it's possible to estimate the partial pressure of SO2 in function of temperature for:
CaSO4(s) < === > CaO(s) + SO3(g)
$$K=\frac{a_{CaS} \times a_{SO_3}}{a_{CaSO_4}}$$
Because of CaSO4's very high Free Energy of Formation, that K is very small but does increase with T. I might have a shot at estimating
pSO3...
Pyrolysis of ionic sulphates has been a past route to SO3 of course but CaSO4 would be an ill-advised choice for that purpose.
[Edited on 29-8-2016 by blogfast25] |