That’s about it, really.
Just for clarification, which of these questions are you asking: “What is the lowest temperature that a flame can be ignited?” or “What is the lowest temperature I could find a sustained flame to have?”
With the first question, the temperature would probably rise significantly after the ignition.
Uh…both? I assumed that they would be the same temp. If they wouldn’t be, I would like the answer to both questions.
Uh . . . That’s not a flame. That’s plasma, ionized gas.
'm sure if you introduced some Caesium into a Fluorine atmosphere, it would burn merrily at a pretty low temperature (it wouldn’t remain cold for very long though).
I’m not sure about the lowest temperature you can create a flame at (I would have thought that, with creative use of fuels and oxidants, you could get significantly below 75C). However, on a university course I am currently taking, it was mentioned (without elaboration), that you can create flames which give a temperature rise of as little as 100C. A sustained flame temperature of around 200C was also mentioned.
Chairman Pow, you will get a rise as burning releases chemical energy which then heats the environment (it is exothermic).
Plenty of things will spontaneously ignite if exposed to moisture at room temperature. Obviously they won’t stay at room temp for long though.
Sodium, for one, and red phosphorus. Silane gas will spontaneously combust in the presence of air, at room temperature, too, so you have to be pretty careful when handling it.
Well, it was around -15 C the other day when someone flamed me…
Maybe I’m thinking too hard about the OP (never mind a query ending in a proposition). Creation of a flame is one thing-sustaining a flame is another. Are we speaking only of ordinary Class A combustibles, or can we open up the chemical bag of tricks?
Sustaining a “flame” is more a matter of heat transfer than an absolute matter of temperature. Open up whatever bag of tricks you think you have. :rolleyes:
The image in my mind was of a demonstration when a lecturer poured some liquid oxygen onto cookies and stuff, which went “whoof”. That must have been at minus a lot.
Wouldn’t that simply have been the l’oxygen’s boiling very quickly, rather than its burning?
Well, what is a flame, then? If we’re going to look for extreme situations, we have to carefully define our terms and delineate when something doesn’t count as a flame anymore.
I was under the impression that a luminescent region of ionized gas in a large volume of unionized gas would be a flame.
Well it looked like a flame. There was orange glowing stuff coming off it making it spin like a catherine wheel iirc.
I am also interested in this question, and have no answers, but…
Does pressure effect the temperature of a flame? Would cool flames exist that don’t radiate light in the visible spectrum but still would have the typical flame appearance if viewed in microwave or IR? Is there a flame that you could place an unprotected finger in without getting harmed?
Exothermic oxidation can occur at low temperatures - rusting of steel is exothermic oxidation, as is the slow congealing of vegetable oil into crusty goo around the top of the bottle. Neither gives a flame though.
luminous flames such as the good old candle are nice and visible because they contain soot particles that are hot enough to glow. Treating these soot particles as black bodies, the lower temperature limit to produce them would be about 500 deg C, which is a dull red glow. As to whether anything exists that gives a barely “red hot” flame like this, I’m not sure.
Alcohol flames are not very luminescent because they don’t contain a lot of soot. They are often described as “cool flames” but this is misleading. They can be quite as hot as luminous flames. The trick of holding burning lighter fluid in the hand works because of evaporative cooling - the flames themselves are not cool.
There is allegedly a neat “cool flame” experiment you can do with phosphorus. If phosphorus is heated in a vessel with an inert gas (carbon dioxide will do) flowing through it, the outflow will contain traces of phosphorus vapour which will spontanously combust with a spooky green flame when it mixes with the air. This is allegedly cool enough to hold your hand in, and will not light a match held in it.
There’s a diagram of the equipment on this page:
I find this experiment to be highly dubious safety-wise! Technically there is a real flame there. I don’t know by what mechanism phosphorus gives a green glow as it oxidises though - it clearly isn’t black body radiation like the soot in a candle flame.