3
$\begingroup$

I watched this video where fool's gold was heated using a hydrogen torch. The results were surprisingly explosive. I was expecting it to just melt into a puddle.

Is there something special about the pyrite or the hydrogen that caused the explosive actions?

Improve this question
$\endgroup$
6
  • 2
    $\begingroup$ You might want to ask the chemists about that. :-) $\endgroup$
    – CuriousOne
    Apr 3, 2016 at 0:31
  • 5
    $\begingroup$ I'm voting this question as off-topic because it is about chemistry and not physics. $\endgroup$
    – Kyle Kanos
    Apr 3, 2016 at 1:08
  • $\begingroup$ @KyleKanos I wasn't sure if the answer was chemistry-related or physics-related. Feel free to migrate the question if chemistry.SE is a better fit. $\endgroup$
    – David Starkey
    Apr 3, 2016 at 1:33
  • 1
    $\begingroup$ Just migrate questions if they belong somewhere else but otherwise match SE standards. I hate seeing votes to close questions that should be migrated. I feel like there's a meta post on this. $\endgroup$
    – kettlecrab
    Apr 3, 2016 at 4:31
  • $\begingroup$ @JoshuaLamusga: Questions have to be closed as off-topic before they are migrated, as there is no reason to migrate a question that is on-topic here. There is a meta post on this, indeed. $\endgroup$
    – ACuriousMind ♦
    Apr 3, 2016 at 18:13

1 Answer 1

Reset to default
8
$\begingroup$

It's an interesting video but I wouldn't describe what's happening as 'explosions', more like rapid deflagrations. Explosions require prior containment (like in a bomb shell) before violent energy release.

What I suspect is happening is the following. When strongly heated Pyrite undergoes an oxidation reaction, reacting with oxygen in the air and/or the torch's effluent:

$$2 \mathrm{FeS_2} + \frac{11}{2}\mathrm{O_2} \to \mathrm{Fe_2O_3} + 4\mathrm{SO_2}$$

This oxidation reaction was used in the early days of sulphuric acid production, by 'roasting' Pyrite in the presence of air because it generates sulphur dioxide gas (a precursor of sulphuric acid).

A hydrogen torch burns extremely hot (maximum about 2,800 C) and will promote this oxidation strongly. Combined with some thermal shock, the release of high temperature $\mathrm{SO_2}$ on heating could explain the Pyrite 'flying apart'. The oxidation reaction is also exothermic (releases heat), possibly further sealing the fate of the Pyrite lumps.

Improve this answer
$\endgroup$
4
  • $\begingroup$ Great answer. Thanks for the terminology clarification. I always defined it as anytime something split into smaller pieces that travel in several directions at high speeds. $\endgroup$
    – David Starkey
    Apr 3, 2016 at 0:53
  • $\begingroup$ @DavidStarkey: yes, not exactly an explosion. Related but not the same. $\endgroup$
    – Gert
    Apr 3, 2016 at 0:55
  • 3
    $\begingroup$ Explosion does not require containment. It's a (rather informal) term meaning refering to an extremely rapid chemical reaction that releases large amounts of energy and, typically, large amounts of gas. The distinction between deflagration and detonation is the mechanism by which the reaction propagates: deflagration propagates by transfer of heat through the reacting substance; detonation is propagated supersonically by a shock wave. $\endgroup$
    – David Richerby
    Apr 3, 2016 at 3:06
  • 1
    $\begingroup$ Having now watched the video, I agree that "explosion" isn't a very good term for what happens. I'm not sure it's even deflagration: it looks more like thermal shock, to me. The pyrites is burning but it's also expanding due to the heating and the stress of that will eventually cause it to break apart. $\endgroup$
    – David Richerby
    Apr 3, 2016 at 3:14

Not the answer you're looking for? Browse other questions tagged or ask your own question.