Flammability Question

[HoodedHero007]

What material has the highest minimum ignition temperature and what is that temperature?

[Yora]

By ignition you mean the beginning of a self-sustaining exothermic oxydation process?

[Xuc Xac]

Triethylborane spontaneously ignites at -20 C. Look up "autoignition" or "pyrophoricity" on Wikipedia.

[Flickerdart]

Triethylborane spontaneously ignites at -20 C. Look up "autoignition" or "pyrophoricity" on Wikipedia.

That would surely be lowest, not highest as the OP has requested.

[HoodedHero007]

Also, if you have time, the energy needed to make it reach that temp from aprox. 70 degrees F

[cobaltstarfire]

I don't know if has the highest minimum catching on fire points, but tungsten on its own has one of (if not the highest) melting point of any element (it's the reason TIG welders use tungsten alloy electrodes).

Not sure how helpful it is, but it might be a good start?

[Yora]

What exactly do you want to know? There are many things that will never catch fire because they are already oxidated. Ash won't ignite no matter how hot.

[monomer]

Yeah, this is a fairly oddly worded question as stated. I'm assuming the OP means combustion in air causing a reaction with oxygen.

There are some materials that will not normally ignite, like say any of the noble gases, but if you raise the temperature high enough, weird physics things start to happem which would cause a reaction to start.

If we're only looking at materials we know will combust, here is a list of the ignition temperatures of some metals. (http://nuclearpowerradiation.tpub.com/hdbk1081/hdbk10810033.htm). This list has Uranium with the highest ignition temperature at a ridiculously high 3,815 C, but note 5 seems to suggest it is actually lower than this, given that this is the same temperature at which Uranium boils. Another candidate would be Platinum, which I'm almost completely pretty sure does not ignite below its melting point of 1,768 C.

The actual material with the highest ignition temperature is very likely some exotic ceramic that we can only produce in tiny quantities.

So to answer your question, without access to a University Library, this information does not seem to be readily available as you would probably have to dive into some pretty hard to find papers to actually find the answer. That said, if you want to give us a specific use-case, I'm sure we could come up with some suggestions.

[Yora]

Yeah, heavy metal carbides tend to be unbelievably resilient to heat.

[monomer]

Yeah, heavy metal carbides tend to be unbelievably resilient to heat.

Yeap, Boron Nitride, or Boron Carbide are likely good candidates, though I don't have the time, inclination, or resources to look too much more into these.

Diamond, which is normally a great go-to material for exotic properties, is surprisingly pretty bad since it seems to ignite at about 900 C.

[HoodedHero007]

This list has Uranium with the highest ignition temperature at a ridiculously high 3,815 C, but note 5 seems to suggest it is actually lower than this, given that this is the same temperature at which Uranium boils. Another candidate would be Platinum, which I'm almost completely pretty sure does not ignite below its melting point of 1,768 C.
So, since the specific heat of uranium is .12(kG/kJ K) (http://www.engineeringtoolbox.com/specific-heat-metals-d_152.html), room temperature is approximately 294.15 Degrees Kelvin, uranium burns at about 3437.15 degrees kelvin, then it would take how many kJ to heat uranium to the ignition temp?

[monomer]

So, since the specific heat of uranium is .12(kG/kJ K) (http://www.engineeringtoolbox.com/specific-heat-metals-d_152.html), room temperature is approximately 294.15 Degrees Kelvin, uranium burns at about 3437.15 degrees kelvin, then it would take how many kJ to heat uranium to the ignition temp?

Delta T = 3,143 K
Cp = 0.12 kJ/kG K
M = 1 Kg (assumed)
Q = Cp x m x dT = 0.12 x 1 x 3,143 = 377.16 kJ/kg

This is surprisingly low, since it is less than the heat required to bring a litre of water from 0 to 100 C.

[HoodedHero007]

Thanks, on a side note, how much energy (as a rough estimate) would be in the poison spray or acid splash cantrip?
This whole thread was mainly focused on how much energy would you be able to create with a cantrip, then me kinda cheat into being able to do massive damage with minimum spell slots (physics wise)

[Ravens_cry]

Thanks, on a side note, how much energy (as a rough estimate) would be in the poison spray or acid splash cantrip?
This whole thread was mainly focused on how much energy would you be able to create with a cantrip, then me kinda cheat into being able to do massive damage with minimum spell slots (physics wise)
Ye gods, I can hear the catgirls screaming from here . . .:smalleek:

[Brother Oni]

Delta T = 3,143 K
Cp = 0.12 kJ/kG K
M = 1 Kg (assumed)
Q = Cp x m x dT = 0.12 x 1 x 3,143 = 377.16 kJ/kg

This is surprisingly low, since it is less than the heat required to bring a litre of water from 0 to 100 C.

That 377.16 kJ/kg is assuming that there is no heat lost to the environment during the heating process.

Water has a ridiculous SHC due to the hydrogen bonding and the majority of life on this planet has adapted to this (hence why animals sweat to lose heat).


Thanks, on a side note, how much energy (as a rough estimate) would be in the poison spray or acid splash cantrip?
This whole thread was mainly focused on how much energy would you be able to create with a cantrip, then me kinda cheat into being able to do massive damage with minimum spell slots (physics wise)

The SRD20 doesn't state how much matter is generated with either spell, and I haven't a clue how to calculate spontaneous matter generation outside of using data generated by the LHC (plus that's assuming you're fusing air together, rather than creating matter out of nothing, which breaks thermodynamics), plus since hit points are an abstraction, you can't quantify how much acid is required to deal 1-3 points of damage.

I suppose if you asked your DM of how many Acid Splash cantrips you'd need to dissolve a fixed volume of matter, then with making some assumptions on the type of acid, we could start crunching some numbers and slaughtering catgirls.

Looking at the other cantrips available, Ray of Frost puts thermodynamics over its knee and spanks it until it cries, while Mage Hand is the easiest calculation of energy generation since it moves a 5lb object, 15 feet in 1 round (I'll crunch the numbers when I get more time).

Edit: Assuming a linear velocity and that a round is still 10 seconds from my time with D&D, it accelerates the object to its final velocity of 1.5 f/s after the first second, giving an acceleration of ~0.07 m/s2.
Force = mass x acceleration, so 2.27kg x 0.07 m/s2 = ~0.16N
Work = force x distance, so ~0.16N x 4.572m = 0.7J

I suppose you could factor in its vector, in which case Mage Hand would be capable of maximally generating a force against gravity when going straight up, but I don't think it's going to be significant (and my physics fails me).

[The Great Wyrm]

A round is 6 seconds, but you don't even need the time to calculate energy (you do to calculate power, though). The maximum energy would be 5 lbs * 15 ft = 75 foot-pounds = 101.686 J. Doing that in 6 seconds would be 16.95 W. This would be the power required to lift 5 pounds 15 feet straight up in 6 seconds.

Alternatively, if the spell can be thought of as accelerating the 5 lb object to 2.5 ft/s (so it would have a final velocity of 15 feet in 6 seconds), the energy would be given by 1/2 * (2.268 kg) * (0.762 m/s)^2 = 0.658 J

Very different results for different interpretations of the spell.

[ace rooster]

What exactly do you want to know? There are many things that will never catch fire because they are already oxidated. Ash won't ignite no matter how hot.
Never is a strong word, and oxygen is not the strongest oxidising agent (http://blogs.sciencemag.org/pipeline/archives/2008/02/26/sand_wont_save_you_this_time).

Delta T = 3,143 K
Cp = 0.12 kJ/kG K
M = 1 Kg (assumed)
Q = Cp x m x dT = 0.12 x 1 x 3,143 = 377.16 kJ/kg

This is surprisingly low, since it is less than the heat required to bring a litre of water from 0 to 100 C.

Temperature can be thought of as the average energy per degree of freedom, so the Cp can be thought of as a measure of the degrees of freedom of a material per unit mass. For every uranium atom there will be about 13 water molecules, and each of those water molecules has two hydrogens that behave as though they are on a spring (for a total of 3 DoF per molecule). Nieve assumptions made, this suggests that the Cp of water should be a bit less than 40 times that of uranium.


Fire is wierd, so ignition temperature is tricky. Fire is a hot self sustaining reaction, so lets break that down. Firstly, it is a chemical reaction, generally between a fuel and air. Secondly, the reaction must be exothermic, obviously. Thirdly, the reaction must be self sustaining, and this is where it gets complicated. Assuming the material will not just burn at ambient temperatures; for it to be self sustaining, enough of the energy liberated by the reaction must be retained within the system to keep the reaction going. In other words, energy production must excede loss rate, and enough energy must get to the next bit of fuel to raise it to ignition.

Lets consider energy production first. Thermodynamics insists that the same reaction will always produce the same energy, so energy production is a measure of rate of reaction. Often our reaction rate will increase dramatically with temperature, so the point of 'ignition' is pretty well defined with big bounds on loss rate. The other major factor is how big the reaction interface is. For solids this is the surface area, and for fluids how well they mix. This is where things get funny, and I will use aluminium as an example.

Aluminium gives off tons of energy when it reacts with air, but it is near impossible to get a lump of the stuff to burn. This is because a thin layer of aluminium oxide forms, rapidly reducing the interface to 0. If you start with a high surface area powder and you try to light that, generally it will melt into a blob, reducing the surface area and then forming the layer of oxide. For it to burn you need conditions that keep the surface area high, which rarely happen naturally. Fire suppressants work this way, and for many materials the temperature at which these sort of effects break down is the ignition temperature.

The above demonstrates the difficulties with getting liquids to burn, (petrol vapor is flammable, but try lighting paraffin without a wick) they simply will not maintain a large surface area naturally. This is why the ignition temperature of many materials is the minimum of their boiling point, or the boiling point of their oxide. This is moot if you have an oxidising agent that is non volitile even at high temperatures, which is how thermite works.

Loss rate is generally dominated by radiation, which increases with the fourth power of temperature. This means that most high temperature fires have huge loss rates, and so must either have very high reaction rates, or have the radiation contained to be considered a fire.

Getting enough energy to the next bit of fuel can also be a bit interesting, particularly in gas fires. With solids about (carbon dust in the exhaust counts) the usual dominant factor is radiation, which is very geometry dependent. This is why building fires is a skill. In gasses though, conduction is usually how the flame spreads, unless the gasses are preheated somehow.

Generally the flammability of a material has more to do with the mechanical properties of the various fuels and products than the energy released, and the geometry of the system will play a massive factor on whether something will keep burning.(small scale geometry too, so foams can behave differently from bulk solids).

I like fire.:smallbiggrin:


Anyway, I don't think you can do much better than uranium, though a carbon skeleton within it could also make it solid at high temperatures and possibly increase the boiling point of the uranium (?). Uranium carbide would be my bet currently, but if there is a heavy metal oxide with higher boiling point I would switch to that carbide.

[Max™]

Convection is still really freaking important in a liquid like the atmosphere, even when things begin to radiate really effectively at higher temperatures because without convection you don't actually get the flame part of a fire, and kudos for mentioning FOOF.

[Brother Oni]

Convection is still really freaking important in a liquid like the atmosphere, even when things begin to radiate really effectively at higher temperatures because without convection you don't actually get the flame part of a fire, and kudos for mentioning FOOF.

FOOF is terrifying to me; the closest I've gotten to that many fluorine atoms in a compound is trifluoroacetic acid (CF3CO2H) and that caused my skin to peel off 3 days after I spilled a small amount on my hand.

[Peelee]

As to the original question, Peeleenium would be your answer. It's really high on the periodic table.

[factotum]

Never is a strong word, and oxygen is not the strongest oxidising agent (http://blogs.sciencemag.org/pipeline/archives/2008/02/26/sand_wont_save_you_this_time).

Technically CF3 is a fluorinating agent, not an oxidising one, although I admit the difference would be largely academic when the flames start... :smallsmile:

[Max™]

Technically CF3 is a fluorinating agent, not an oxidising one, although I admit the difference would be largely academic when the flames start... :smallsmile:

The difference being that you learn how flammable academics are--plus sand, concrete, grad students, burner hoods, rubber gloves, you get the idea--and discover who the REALLY smart people are: the ones two miles away upwind.

[ace rooster]

Convection is still really freaking important in a liquid like the atmosphere, even when things begin to radiate really effectively at higher temperatures because without convection you don't actually get the flame part of a fire, and kudos for mentioning FOOF.

Yeah, though it is more important as a mixing mechanism than a heat transfer one. It is really cool what happens when you turn it off (https://www.youtube.com/watch?v=BxxqCLxxY3M). In particular, if air is not being vigerously whiped about by some mechanism, your only mixing mechanism is diffusion, which is quite slow. Slow mixing means slow reaction rates, but at relatively low temperatures radiation is a very minor factor, not least because the dust forming reactions are less favoured. What is really interesting is that hydrocarbons can have a second stable combustion mode at these lower temperatures, though it is quite easily disturbed.

Lots to say, but I'll stop rambling on about it (unless you particularly want me rambling about gunpowder, thermite, and blast furnaces :smalltongue:). I've been doing a fair bit of reading on rocketry recently, which is why I regard flourine as an oxidiser, and convection is not overly special in my mind. Convection is a special case of fluid flow, and not the one I have been working with.


My favourite bit of the ClF3 spill story (the one where they spilled a ton of it) is what happened to the guy who was steadying the tank at the time. He survived, but was hospitalised from a heart attack having run 400ft at olympic speeds. Still sucks to be him, but in his position I would take that outcome.

[Max™]

Convection being set aside for pure radiative models is just a pet peeve of mine, it's more relevant in regards to weather and climate than rocketry for sure.

I don't blame the guy for running that hard, I used to be a hell of a sprinter in my teenage years and nothing quite makes you move as fast as having a really good reason behind you.

Got vague memories of being like 18, drinking, skinny dipping at a high school pool, then cops showing up, whipping my pants on, then as I was running across the track I saw headlights from where they drove out onto it trying to catch us.

Then I remember running up a chainlink fence and vaulting over the barbed wire in one smooth motion.

They probably gave up the chase at that point, I just know I woke up with scratches on my palms and had to think back to where they came from.

You spill a half ton of FOOF or anything remotely as... interesting as it?

I'm not even bothering going over the fence, you can come find me and get the fence back if you want it. :D