Blue Flamethrowers (Hypothetical physics/chemistry thingy)

[sktarq]

A bit more on-topic, what would you 'package' the powdered copper compounds in? It needs to be liquid, and probably flammable (at least it can't extinguish the burning copper), but that won't overpower the blue from the copper.

It's not really the copper compound which is doing the majority of the burning here--you can use any regular fuel for the flamethrower you like. That's why they use things like that in pyrotechnics, because a small amount dissolved in your fuel goes a long way.

Well the blue colour would come from a dopant of petrochemicals most likely. As factorum pointed out something similar already works for doping black powder based fireworks. So doing something similar for the diesel or fuel oil based flamethrower should be simple enough.

That said there are a few things that do come up.

Firstly is solubility. In many cases you may actually want to burn a solid fragment of the material. So an actual solution could be bad as there could be lots of messy reactions between the fuel and the dopant that both lower the damage potential from the fuel and disrupt the pretty blue colour that is the point of the copper in the first place. So you may even NEED particles of the stuff mixed into your fuel....but you want to avoid settling of such particles in the holding tanks. So really you're going to want micro or even nano particles in a suspension. So you may need some sort of bondable-to-the-dopant combustible lipid coating similar to what you want on a ferrofluid. I recommend the youtube channel NileRed for their videos on ferrofluid for a good demonstration of this process.

Also several of the best copper dopants actually burn their best blue with a chlorine instead of oxygen combustion or at least with the availability of a chlorine donor. So the pressurized gas tank (normally filled with Nitrogen) in a flame thrower may end up being significantly more toxic depending on the Evil Overlord's views on OHS/OSHA equivalent regulations...also gives a good excuse for very intimidating gas masks on the Evil Overlord's minions faces.

[Peelee]

US-ite here (nearly everyone on two continents get twitchy when I call myself an "American")

Eh, the non-Americans can say what they want. Doesn't bother me as an American.

and I'd love to cast a stone at the US.

I ain't throwing 14 lbs at nothin'!

Fat Rooster is apparently British, and over here a pint is the Imperial one, which is 20 fluid ounces or 568ml. So, no, half a litre *would* be a downgrade from a pint here.

I was actually planning a witty retort but double-checked beforehand, which is why I didn't - couldn't come up with something once the gears changed (or, at least, couldn't come up with something within like ten seconds, after which I moved on).

But yeah, Imperial and American Customary Units are super close to each other, except when they're not (notably, volume).

[druid91]

Perhaps something similar to this guy's process?

Green Flamethrower.

[Fat Rooster]

Perhaps something similar to this guy's process?

Green Flamethrower.

Wow, I did not expect methanol to work as well as that as a base. Copper chloride in methanol should just work, and is even soluble enough that we don't need to worry about suspensions.

Don't expect it to be particularly effective as a military flamethrower. That video is shot at night because those flames are still very dim compared to standard black body dust yellow flames, which makes setting things on fire that are not in direct contact with the flame far less likely. Heat is concentrated on objects directly above the strike point, which may not be do anything and in the worst case the heat simply escapes. The low boiling point of methanol actually prevents damage to where the liquid is sitting. You can set methanol on fire in your hand safely. Heat transfer back into the liquid is also much reduced, so it would be far easier to put out. Concrete is not permeable and quite a good insulator, but there are many materials where the flame might just go out if you shot at them.

I'm surprised they are not used regularly for special effects, given how impressive they are compared to how ineffective (and hence relatively safe to work with) they actually would be.

Edit: blue alone might not be particularly impressive, but you can vary the dopants to get any colour, and with a mixing nozzle you can have it changing colour mid stream! An RGB flamethrower isn't much harder.

[factotum]

Edit: blue alone might not be particularly impressive, but you can vary the dopants to get any colour, and with a mixing nozzle you can have it changing colour mid stream! An RGB flamethrower isn't much harder.

Now I'm just imagining some sort of automated flamethrower that creates a multicolour image out of flames...

[Bohandas]

Possibly relevant:

https://m.youtube.com/watch?v=5ZNNDA2WUSU