Posted: 2/18/2004 7:05:00 PM EDT
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Ok, time for one of those random weird questions. I don't know why I thought of it, and I don't know why it keeps bugging me... But what's the lowest temperature a fire can exist at? Or should I say, what will burn with the lowest amount of heat? (and what temperature is it?) anyone...? Oh... and just to contradict my title... there's no such measurement as "cold". It would be lack of heat... just like you can't measure darkness. (No, I'm not stoned) 
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It's a difficult question to answer because you would need to define 'burn'. Are you talking about common substances that combust with oxygen such as charcoal, gasoline, alcohol? Are you using oxygen under pressure (rocket) or air under reduced pressure? Does the oxidizer have to be oxygen? For instance, the liquid di-tert-butylperoxide or DTBP will burn in an internal combustion engine with air, but can continue to 'burn' ie. decompose exothermically without oxygen to ethane and acetone. The liquid was proposed for use in chainsaws used by firemen so that they would continue to work in an atmosphere with reduced or absent oxygen. The combustion temperature is [b]much lower[/b] without oxygen. (Ref: H.O. Pritchard and P.Q.E. Clothier, "Anaerobic Operation of an Internal Combustion Engine", Journal Chem. Soc., Chem. Commun. (1986), p.1529 In the CRC Handbook of Chemistry and Physics, you can look up the heats of combustion for many organic compounds. Those that already contain oxygen will release less heat when burned with oxygen than if they do not. Therefore, methanol will burn at a lower temperature than gasoline (octane) all variables being equal. To partially answer your question, I know that lycopodium powder (IIRC the spores of club moss) burns with a bright but [b]very low[/b] temperature flame, certainly lower than the combustion of organic liquids, carbon, sulfur, phosphorous, metal powders, etc. Now if you had asked what was the [b]hottest[/b] flame, that would be the combustion of carbon subnitride (C4N2) with oxygen at 5300 Kelvin. |
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so far i found sulfer with an ignition temperature of 93 degrees. my shift is over and i get to leave, so , at least this is a starting point for you. long article, scroll to the red if you want to cut to the chase. Pyrophoric Materials Handbook Flammable Metals and Materials By Charles R. Schmitt, P.E., C.H.C.M. Edited By Jeff Schmitt Chapter 1 Table of Contents 1. Definitions Next Back -------------------------------------------------------------------------------- 1. Definitions According to Webster's dictionary, "pyrophorc"[1] means "igniting spontaneously, as certain finely divided materials". The word "pyrophoric" has also been defined[2] as "producing sparks, when rubbed, or burning spontaneously in air, e.g. finely divided metals". Thus, a pyrophoric material is any material that ignites spontaneously or emits sparks when rubbed, scratched, or struck. Chambers' technical dictionary [3] defines pyrophoric powders as "finely divided powders which take fire or oxidize extremely rapidly when exposed to the air; usually a metal or a mixture of a metal and its oxide". By another definition, [4] a pyrophoric material is "any liquid or solid that will ignite in air below 130°F (54.4°C)." In consideration of the many fire and explosion incidents that have occurred involving the handling, transportation, and shipment of many materials in such diversified physical forms as metal machine turnings, chips, pellets, derbies, massive metal, etc., any definition of pyrophoric material should not be restricted to finely divided powders. "Pyrophoricity" (spontaneous ignition or rapid oxidation) as used in its broadest sense, therefore, must also include massive pieces of material, pure metals, alloys, carbides, hydrides, non-metallic materials, and even liquids such as the aluminum alkyls. A simplified definition of "ignition" is the initiation of combustion, [5] and combustion may be defined as the process by which materials are oxidized at a rapid rate. [6] Combustion may also be defined as "an exothermic, self-sustaining reaction involving a fuel (condensed or gas phase) and an oxidant". Old newspapers tend to turn yellow and brittle with age because of a relatively slow oxidation rate. Since paper is a carbohydrate, the yellowing is a result of the oxidation or slow burning of carbon and hydrogen. Oil is another carbon compound that oxidizes in contact with air. When oily rags are left to accumulate around the house, for example, the heat of oxidation may not be able to escape and after enough heat accumulates, the oily rags may be set aflame. This process is known as spontaneous combustion. Ignition is the process of initiating self-sustained combustion. If the ignition is caused by the introduction of some small external flame, spark, or glowing object, it is called "pilot-ignition". If ignition occurs without the assistance of an external pilot source, it is termed "autoignition" or "spontaneous ignition". In a chemical context, all elements that are not in their highest oxidation state can undergo oxidation. Some metals oxidize so slowly that the heat generated during oxidation is dissipated so that the ignition temperature is never reached. Under appropriate conditions, some metals oxidize rapidly in the presence of air, oxygen, and/or moisture, and can generate sufficient heat to reach ignition temperatures. Certain metals, such as zirconium and uranium, are described as combustible metals because of their potential for rapid oxidation under appropriate conditions. The use of magnesium as a flashlight powder for photography is a common example of a combustible metal. Ignition is accomplished by raising the temperature of a substance or material to the "ignition temperature". This temperature may be defined as the lowest temperature which will cause a flame or glow, to start and spread through the substance or material. The substance or material need not be a solid, but could be a gas or mechanical mixture of combining substances such as carbon and oxygen. The ignition temperature varies considerably with the substance. Some typical values are: [red]Substance Ignition Temperature °F Phosphorus 93 Sulfur 470 Carbon 750 Hydrogen 1090 Carbon Monoxide 1250 [/red] Ignition has been defined by Setchkin [7] as a "self-perpetuating exothermic reaction that is initiated at the temperature of incipient oxidation, and that increases the temperature of the reactants above the initial air temperature until an explosion, flame, or sustained glow occurs." In actuality, ignition can occur without an accompanying visible flame, sustained glow, or explosion, such as in metal powers where this type of ignition is termed "thermal ignition". The ignition temperature of a metal has been defined by Pitts [8] as "the temperature at which the exothermic oxidation reaction becomes self sustaining at such a rate as to cause a significant temperature increase above ambient conditions". editted to say that i had to chop off well over half the article as it was too long. |
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Quoted: so far i found [s]sulfer[/s] phosphorus with an ignition temperature of 93 degrees. Good post, but the question is the [b]lowest burning temperature[/b] rather than [b]ignition temperature[/b]. White phosphorus is definitely the most easily ignitible substance. A small piece will ignite in your hand (and cause a horrific/toxic burn[:D]). [red]If you slightly rub a piece against wood, it will ignite much more easily than even a strike-anywhere match.[/red] White phosphorus was used in the igniter in Napalm bombs along with a bursting charge of TNT. |
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Well… Back to when I had a Chemistry set when I wert young…. You can have alcohol burning on your hands without getting hurt. I once spilled some alcohol for the alcohol lamp once and my hands got covered with the fluid. The fluid got lit somehow. Some of my fingers glowed with a blue fire. Yeah, the alcohol on my fingers was burning. I quickly put the fire out. But the fire never felt hot. So I guess you can say that Alcohol can burn at a very low temperature. By the way, it was in the basement on a concrete floor. So stop wondering about it. |
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Its not that the alcohol burns with such a low temperature, its that when the alcohol ignited while on your hand...only the alcohol was burning...not your hand. All of the heat energy was (semi) safely escaping upwards. Quoted: Well… Back to when I had a Chemistry set when I wert young…. You can have alcohol burning on your hands without getting hurt. I once spilled some alcohol for the alcohol lamp once and my hands got covered with the fluid. The fluid got lit somehow. Some of my fingers glowed with a blue fire. Yeah, the alcohol on my fingers was burning. I quickly put the fire out. But the fire never felt hot. So I guess you can say that Alcohol can burn at a very low temperature. By the way, it was in the basement on a concrete floor. So stop wondering about it. |
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Ahhh... now we're getting somewhere. Yeah, I have had a few discussions with friends about different temp fires (and their colors), and wondered just what the coolest burning flame could be... I guess that would eventually lead to what color it is, heh. So, when one brings up that the ignition temp of phosphorus is 93F, does that mean its flame will continue to burn 93F? It sounds to me like that's just where it gets set off... So, for instance... can a flame exist that only puts out 93F temp? C-4 (sounds like your name fits the discussion pretty well): I was actually just trying to figure out what the least ammount of heat or temperature that any known substance could actually put out when it is "on fire". AFAIK, fire itself isn't a substance... just a reaction, so I think I worded that properly. So, even with your examples... whatever of those can create a flame (fire) that puts out the least ammt of heat. I've heard many people before discuss how HOT some flames are, but never heard anyone comment on this side... just thought I'd ask. |
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Quoted: Its not that the alcohol burns with such a low temperature, its that when the alcohol ignited while on your hand...only the alcohol was burning...not your hand. All of the heat energy was (semi) safely escaping upwards. Uh, isn't that the liedenfrost effect? (Like dunking your wet hand into a pot of molten lead...no pain, no burn, way cool). |
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Particle radiation. Each atom of flame product (often elemental carbon, but it could be any reaction product) will radiate energy. The radiation wavelength and the temperature are correlated. Therefore, you can (in theory) have a flame of any color, including infrared (heat only - no "light" for your eye to detect) and ultraviolet (get a tan from it). Though an [b]ultraviolet[/b] flame would be AWFUL hot. [edited] Anyway, the rather low flame temperature of methyl alcohol (Indy car fuel) can make the flame very hard to find. Therefore, the technical crew working an Indy car wreck will, every time, "put out" the [b]entire[/b] car. If by "flame" you mean a kind of exothermic convective (e.g. moving air) burning reaction, then flame temperature could be anything. If by "flame" you mean an optically perceptible reaction, then the minimum flame temperature would be around 1000 Fahrenheit (a dark red). I don't know of any reaction which actually can make a flame like that, but I can't think of anything which would prevent it. |
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Quoted: Yeah, I have had a few discussions with friends about different temp fires (and their colors), and wondered just what the coolest burning flame could be... I guess that would eventually lead to what color it is, heh. Ultimately, it would help us if I knew [b]why[/b] you wanted to know, and what you were trying to accomplish. For instance, if you are trying to create a ghostly glow effect, you can burn methanol and add small amounts of different chemicals to achieve different colors ie. boric acid for green, strontium chloride for red, sodium salts for yellow. They are [b]not[/b] very bright, but for indoor 'theatrical' purposes, they are fine. Quoted: So, when one brings up that the ignition temp of phosphorus is 93F, does that mean its flame will continue to burn 93F? [red]It sounds to me like that's just where it gets set off...[/red] Correct. White phosphorous (as opposed to red which ignites at about 300 Celcius) will ignite at 93F, but it will burn at a much higher temperature (which I could look up). Ironically, and as a sidenote, when white phosphorus burns, it produces beautiful copious white clouds of phosphorus pentoxide. If you try to light a match above burning phosphorus, these clouds will cover the match, absorb moisture from the air (to make phosphoric acid), and then make it difficult to ignite the match. OTOH, phosphorus grenades when thrown into a room will create intense heat and chemical burns. It will burn up most of the oxygen in a small room. Quoted: So, for instance... can a flame exist that only puts out 93F temp? A [b]flame[/b], by definition, indicates that particles are incandescent, and this can only occur at high temperatures. Quoted: So, even with your examples... whatever of those can create a flame (fire) that puts out the least ammt of heat. Either alcohol or sulfur. Both burn with relatively low heat in air. |
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Quoted: Iron will oxidize into rust, Aluminium will corrode as well. These are the same reactions that occur in Thermite and the Shuttle engines, but with much less heat. This is the response I was going to give. Or cellular respiration, which is combustion. Rusting of iron releases substantial heat and is the reaction used in "hot hands" You know, remove the pouch from the bag and it keeps your hands warm while deer hunting? |
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Quoted: Quoted: Yeah, I have had a few discussions with friends about different temp fires (and their colors), and wondered just what the coolest burning flame could be... I guess that would eventually lead to what color it is, heh. Ultimately, it would help us if I knew [b]why[/b] you wanted to know, and what you were trying to accomplish. For instance, if you are trying to create a ghostly glow effect, you can burn methanol and add small amounts of different chemicals to achieve different colors ie. boric acid for green, strontium chloride for red, sodium salts for yellow. They are [b]not[/b] very bright, but for indoor 'theatrical' purposes, they are fine. I don't actually have any particular application... just one of those curiosity things. I started thinking about how hot different flames are, and wondered what the coolest (relatively) one could be. Quoted: So, when one brings up that the ignition temp of phosphorus is 93F, does that mean its flame will continue to burn 93F? [red]It sounds to me like that's just where it gets set off...[/red] Correct. White phosphorous (as opposed to red which ignites at about 300 Celcius) will ignite at 93F, but it will burn at a much higher temperature (which I could look up). Ironically, and as a sidenote, when white phosphorus burns, it produces beautiful copious white clouds of phosphorus pentoxide. If you try to light a match above burning phosphorus, these clouds will cover the match, absorb moisture from the air (to make phosphoric acid), and then make it difficult to ignite the match. OTOH, phosphorus grenades when thrown into a room will create intense heat and chemical burns. It will burn up most of the oxygen in a small room. Quoted: So, for instance... can a flame exist that only puts out 93F temp? A [b]flame[/b], by definition, indicates that particles are incandescent, and this can only occur at high temperatures. Ahh. So, combustion could be lower, but to have an actual "fire" or "flame" it would be in the red spectrum and thus have to be a certain temperature... which trachnload pointed out above to be in the 1000F range. Everyone agree with that? Quoted: So, even with your examples... whatever of those can create a flame (fire) that puts out the least ammt of heat. Either alcohol or sulfur. Both burn with relatively low heat in air. So... there's not really any "fire" that will be a low temperature reaction (that's relative, I know), but there could be other things that aren't technically considered fire/flames that would be lower temperature combustion. Does that sound like it's correct? Or am I way off? |
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Quoted: The radiation wavelength and the temperature are correlated. Therefore, you can (in theory) have a flame of any color, including infrared (heat only - no "light" for your eye to detect) and ultraviolet (get a tan from it). Though an infrared flame would be AWFUL hot. Soooo... if I said someone was flamingly gay, it'd be best to tack on "untraviolet" somewhere into that to indicate the high level of gayness? [:D] |
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Quoted: Quoted: The radiation wavelength and the temperature are correlated. Therefore, you can (in theory) have a flame of any color, including infrared (heat only - no "light" for your eye to detect) and ultraviolet (get a tan from it). Though an infrared flame would be AWFUL hot. Soooo... if I said someone was flamingly gay, it'd be best to tack on "untraviolet" somewhere into that to indicate the high level of gayness? [:D] LOL! And a pat on the back for correctly interpreting my error (infrared/ultraviolet). |