Hacker News Reader

Comment by ocfnash | Hacker News Reader

This is a good piece but I have one nit: it is incorrect to say "thermite [...] will not detonate."

I was shocked to discover this first hand some years ago: http://olivernash.org/2009/11/12/fun-with-thermite/index.htm...

I can still recall the echoing boom of that (copper) thermite.

View on HN

Thank you for this correction. Do you know whether Al + Fe2O3 thermite as normally prepared (meaning, not ground up into nanoparticles) will detonate? I'll update the piece accordingly.

Moreover, are you sure this was a detonation (shock wave) rather than a deflagration?

Given that ocfnash's page never uses the term detonate, never discusses the difference between detonation and deflagration, and doesn't describe the experiments that would distinguish them, I'm pretty sure they were not in fact performed, and the (informal) explosion he witnessed was not a (formal) detonation.

That's not to say it isn't worth a footnote to explain that "doesn't detonate" does not mean "won't go pop and propel burning material everywhere." Even a campfire can do that, but I could understand if someone heard "doesn't detonate" and drew the wrong conclusion.

Thanks for these helpful words of clarification!

As I commented above, I was rather sloppily using the words "explosion", "detonation" to mean flash and boom.

On the two occasions on which I witnessed this event, it was stunningly powerful but I now believe most likely just a deflagration.

From a practical point of view, the only semi-common thermites that can actually explode are copper and silver. However, these thermites do not "detonate" as in the definition. They merely deflagrate extremely quickly, quickly enough to fool an observer but not in the true physical sense.

Very interesting, thanks!

I carried out two rounds of thermite "experiments", both times using oxides of iron, manganese, and copper. I witnessed two "explosions" (I now presume deflagrations) and they occurred with the copper oxide. I've occasionally wondered if that was a coincidence that it was the same metal that "exploded" both times. Mystery solved: apparently not!

I am sure of nothing except that there was a sudden big flash and boom :)

From the clarifying comments below it seems likely it was a deflagration but I confess I've been using the words "explosion", "detonation" rather sloppily to mean "flash and boom" till now.

Thanks again for a marvelous article.

I recall a high school chemistry demonstration where they made flour "explode". (From _vague_ 35 year old memories, a coffee tin with a spark plug and an assembly that blew compressed air in through the flour to distribute it in a mist...)

I'd stop short of claiming that flour "detonates" or that flour purchases are terrorist indicators...

https://en.wikipedia.org/wiki/Dust_explosion

Yep - that all seems strangely familiar...

(We must now put all bakers on terrorist no fly lists...)

Reply on news.ycombinator.com