Sciencemadness Discussion Board

High-temperature flames.

The WiZard is In - 7-4-2010 at 17:04

This is "energetic" enough for me. I hope it doesn't annoy the moderator(s).

The late Herbert Ellern, Military and Civilian Pyrotechnics. 1968 sez — Chapter 27 High-Temperature Flames. Page 230

... cyanogen (CN)2 and carbon subnitride C2N2 ... furnish, with oxygen, flames measured at 4800 and 5300oK, respectively—higher than any other measured.

... since between 5500 and 6000oK one reaches "the limits of chemistry," [490] this means also that pyro hemically-created heat cannot raise above this limit.

John D Clark **
Igntion! An Informal History of Liquid Rocket, Propellants
Rutgers University Press. [I have misplaced the publication date.]

P. 36-7. The climax of unsaturation came with butyne di-nitrile, or dicyano-acetylene, N [triple bond] C [single bond] C [triple bond] C [single bond] C [triple bond] N which had no hydrogen atoms at all, but rejoiced inn the possession of three triple bonds. This was useless as as a propellant — it was unstable, but one thing, and its freezing point was too high — but it has one claim to fame. Burning with ozone in a laboratory experiment, Professor Grosse of Temple University [no citation] (who always liked living dangerously) attained a steady state temperature of some 6000 K, equal to that of the surface of the sun.

[490] B. Lewis, "High Temperatures : Flame," Sci. American, special issue on heat, 191, No. 3, p. 84 (Sept. 1954)

Anyone care to suggest an improved mixture?

** An eminently readable and interesting book. Used copies cost "HOW MUCH!" One would think it would be scanned and posted somewhere on La Net.

---------
But detonation traps [in the fuel line] aren't always the complete answer. We discovered that when, in the summer of 1960, we tried to fire a 10,000 pound Cavea B* motor. We didn't have Mike's trap at that time, so we inserted a battery of sixteen
0.25-inch loop traps in the line. Well, through a combination of this and that, the motor blew on startup. We never discovered whether of not traps worked - we couldn't find enough fragments to find out. The fragments from the injector just
short-circuited the traps, smashed into the tank, and set of the 200 pounds of propellant in that. (Each pound of propellant had more available energy than two pounds of TNT.) I never saw such a mess. The walls of the test cell - two feet of concrete - went out, and the roof came in. The motor itself - a heavy, workhorse job
of solid copper - went about 600 feet down range. And a six-foot square of armor plate sailed into the woods, cutting off a few trees at the root, smashing granite boulder, bouncing into the air and slicing off a few treetops, and finally, coming to rest some 1400 feet from where it started. The woods looked as though a stampeding herd of elephants had been through.

* 2-Methy - 1,4, diaza, 1,4 dimethyl, bicycle 2,2,2 octane dinitrate

a_bab - 7-4-2010 at 21:14

Another very hot flame I know would be from burning hydrogen in fluorine (with resulting HF fumes as a bonus). Ouch!
There are plenty of studies on the 'net concerning the H+F flame system.

But burning something in ozone, that's plain insane...

[Edited on 8-4-2010 by a_bab]

chief - 8-4-2010 at 00:22

H + F in optical resonator gives chemical Laser ... with high output !

bquirky - 8-4-2010 at 01:12

man Imagen the mirrors you would have to use for that ! :)

hissingnoise - 8-4-2010 at 03:25

Gah! Fuck Kelvin - why did he have to complicate things!
6000K is I believe, still 273*C short of the sun's surface!
But WiZard, you've obviously got up to some fun derring-dos in your time!
A stoichiometric mixture of airfloat charcoal or amorphous graphite in liquid O3 intitiated by a strong booster might on detonation produce a 'fairly' hot fireball.
Or spongy Al saturated with liquid O3?



[Edited on 8-4-2010 by hissingnoise]

Formatik - 8-4-2010 at 14:18

The below might be of interest. The file has been edited and some values added.

[Edited on 9-4-2010 by Formatik]

Attachment: high temperature chemistry.txt (6kB)
This file has been downloaded 1159 times

Mr. Wizard - 8-4-2010 at 16:36

Nobody ever mentions the simple but technically difficult mono atomic H flame. This is the combination of mono atomic H combining to form diatomic H2.

It can be made, but not easily.
http://www.science.uva.nl/research/quant/sph.html

The energy available per mole is unmatched. Short of atomic reactions, it is the most energetic chemical combination by weight.

unionised - 9-4-2010 at 03:26

Quote: Originally posted by hissingnoise  
Gah! Fuck Kelvin - why did he have to complicate things!
6000K is I believe, still 273*C short of the sun's surface!
But WiZard, you've obviously got up to some fun derring-dos in your time!
A stoichiometric mixture of airfloat charcoal or amorphous graphite in liquid O3 intitiated by a strong booster might on detonation produce a 'fairly' hot fireball.
Or spongy Al saturated with liquid O3?



[Edited on 8-4-2010 by hissingnoise]


If you want stuff to end up hot cooling it down to start with is not very helpful. Why use liquid O3 when you can use the gas and start a couple of hundred degrees hotter?

hissingnoise - 9-4-2010 at 03:39

Quote:
Why use liquid O3 when you can use the gas and start a couple of hundred degrees hotter?

Because the increased density more than makes up for the lowered temperature, obviously!



a_bab - 9-4-2010 at 07:50

In terms of the maximum reachable temperature, liquid of gaseous O3 won't change much. In liquid form it will "saturate" the reaction, thus maximizing the chances of getting the highest possible temperature from the combustion of something. The difference of a few hundreds degrees lower initially won't change too much the overall thermodynamics; I bet that if you manage to sink a hot coal in liquid O3 it will burn very well under "LOZ*" (actually the LOZ will likely explode).

We should never forget the old video featuring "how to light up a bbq with LOX", in which the coals are consumed in seconds, in a blazing hot hellish flame, melting everything in the path: now that's heat output!

As Mr. Wizzard said, the Langmuir's atomic hydrogen torch is no joke either: http://www.lateralscience.co.uk/AtomicH/atomicH.html

____________________________________
LOZ = Liquid OZone. Just made it up.


[Edited on 9-4-2010 by a_bab]

The WiZard is In - 9-4-2010 at 10:37

Quote: Originally posted by a_bab  
Another very hot flame I know would be from burning hydrogen in fluorine (with resulting HF fumes as a bonus). Ouch!
There are plenty of studies on the 'net concerning the H+F flame system.

But burning something in ozone, that's plain insane...

[Edited on 8-4-2010 by a_bab]


Attachment: Explosives Detonation velocity table.doc (615kB)
This file has been downloaded 1240 times


Google turned up this interesting XLS spread sheet

www.dcr.net/~stickmak/JOHT/propella.xls

Formatik - 9-4-2010 at 11:11

Liquid ozone explodes for no reason, so it has to be diluted with liquid air, N2, O2, etc. Even those are only partly suitable diluents, since they evaporate much easier leaving behind pure concentrated ozone, e.g. Gmelin mentions explosions easily occurring when O2 as a diluent evaporates.

chief - 9-4-2010 at 13:03

A higher temperature can also be achieved by pre-heating the reactants: So some Extra-1000 Kelvin are possible ...

bquirky - 10-4-2010 at 06:10

wow. that had never crossed my mind. so if you preheat air and propane (say to 800 degrees) the flame temprature go's up 800degrees acordingly ?

is there an upper limit to that ? so chould you use your preheated flame to preheat some more gas to get another 800degrees ?

unionised - 10-4-2010 at 06:11

Quote: Originally posted by hissingnoise  
Quote:
Why use liquid O3 when you can use the gas and start a couple of hundred degrees hotter?

Because the increased density more than makes up for the lowered temperature, obviously!




Sorry, but it's not obvious to me that starting colder is a good way to end up hotter.
Also, since temperature is a matter of heat per molecule, rather than heat per gram, the density won't affect the final temperature.

It's already been pointed out that preheating the reactants will increase the final temperature so, as I say, it's far from obvious why cooling them would help.

hissingnoise - 10-4-2010 at 06:28

Well, it's pretty obvious to me that the difference in potential energy between liquid and gaseous O3 is great. . .

unionised - 10-4-2010 at 08:18

Indeed, and the energy difference is that required to separate the ozone molecules (held together by dipole dipole interactions) and then to heat those molecules up to room temperature.
All of this energy is provided from the heat of reactions and so it's not there to raise the temperature of the reaction products. That's why, as far as I can see, the flame won't be as hot.

hissingnoise - 10-4-2010 at 08:53

Quote:
That's why, as far as I can see, the flame won't be as hot.

What I said was; 'a stoichiometric mixture of charcoal in liquid ozone'.
It will, on detonation, produce a much hotter flame than any oxidation by gaseous ozone. . .
That really should be obvious to anyone!



[Edited on 10-4-2010 by hissingnoise]

unionised - 10-4-2010 at 11:18

No.
A stoichiometric mix of gaseous ozone and charcoal will release more heat (because it doesn't have to waste energy boiling the ozone) and it will start off hotter so it will end up much hotter.
Admittedly it would be tricky to disperse the charcoal evenly through the gas but that's just a technicallity.

What should be obvious to anybody is that cooling stuff down doesn't make it hotter.

watson.fawkes - 10-4-2010 at 11:26

Quote: Originally posted by hissingnoise  
What I said was; 'a stoichiometric mixture of charcoal in liquid ozone'. It will, on detonation, produce a much hotter flame than any oxidation by gaseous ozone. . .
That really should be obvious to anyone!
It's not obvious to me. Enthalpy density is what you are seeking to optimize, but it's not obvious that always translates into high temperature. The outward-directed kinetic energy released by detonation isn't regarded as "high temperature" but rather "high velocity". So you have two kinetic energy terms, one microscopic for temperature and the other macroscopic for velocity. Since energy is conserved, you have to make the argument that the partition between these two energy modes gives you the high temperature you're claiming.

a_bab - 10-4-2010 at 11:36

Noobody said that fact of having a cold oxidizer will result in a hotter flame. It's the fact that if you start with concentrated reactants, the results are better. And it happends that in order to get liquid ozone, oxygen whatever you need to such energy from the molecules, energy that will be paid back at the reaction time. A simple thermodynamics calculation will reveal the amounts for those who are curious.

It's like comparing a butane flame in air: it's better tu use pure oxygen instead. The resulted flame melts steel and such.

In an ideal world, if you can supply a continous stream of ozone over your "porous Al" the resulted temperature will be higher then using oxygen (ozone already has more energy in the molecule and it's more chemical active). Also, if the ozone will be streamed at 1000 degrees C, the reaction will become explosive due to the speed, and the surplus of energy.

Neither of these are practical in our world, so why fighting?

unionised - 10-4-2010 at 11:51

It's not a "fight" it's a request for scientific information.
Specifically, I want to know why starting with something colder, and then making it do more work will give a hotter flame.
Incidentally, while nobody said that "having a cold oxidizer will result in a hotter flame", hissingnoise has repeatedly said that liquid ozone will give a hotter flame than the gas would.
Unless you plan to liquefy the ozone by compression alone then it's bound to be colder. (Some brave soul has measured the critical point and it's 12 degrees below freezing. You can't get liquid ozone unless it's cold)

The point is that, even if I'm wrong, saying "That really should be obvious to anyone! " without offering any sort of explanation is unhelpful.

Incidentally, the reason a butane flame is hotter in oxygen than in air is because it doesn't have to waste energy heating up nitrogen. Nobody is proposing to add a diluent here so that's a red herring.



[Edited on 10-4-10 by unionised]

hissingnoise - 10-4-2010 at 14:48

Quote:
It's not a "fight" it's a request for scientific information.

What we have is a simple difference of opinion.
But I still maintain that the detonation of liquid ozone/fuel will be more energetic than that of ozone gas/fuel.
Ozone is liquid at -120*C, but as I said already, the density-difference should more than make up for the low temperature.



Formatik - 10-4-2010 at 16:45

I don't think it will be more energetic, but more exothermic. An example is given in the chart above comparing LOX/C2N2 detonation against combustion of C2N2 in oxygen.

unionised - 11-4-2010 at 01:22

Hissingnoise,
I don't see why the volume that the reactants occupy makes a difference to the energy released, and you have made absolutely no attempt to explain why it might do so.

The temperature is a measure of the energy per molecule, it doesn't depend on the volume.
If you have the same reaction i.e. 3 C +2 O3 ---> 3 CO2 then the energy released is the same per molecule more or less independently of the volume or initial temperature so the rise in temperature will be the same.

However if some of that energy is used converting the liquid to a vapour then there will be less left over.
Also it will have started colder so all things being equal it will end up colder.

As I have said there's a phase change that takes place when the ozone boils and you need energy to do that. Where do you think that energy comes from if not from the heat of the reaction?
If that heat goes into boiling the ozone why do you not think this will reduce the final temperature?

You keep restating that you believe it will get hotter if it starts colder, but you don't provide any explanation at all. To make this into a scientific discussion you need to explain your opinion rather than repeating it.

If I'm wrong then fair enough, but don't just say I'm wrong; say why.

chief - 11-4-2010 at 01:43

Quote: Originally posted by bquirky  
wow. that had never crossed my mind. so if you preheat air and propane (say to 800 degrees) the flame temprature go's up 800degrees acordingly ?

is there an upper limit to that ? so chould you use your preheated flame to preheat some more gas to get another 800degrees ?



Of course. This is used in the steel-industry, where the exhaust-gasesd heat up alternatingly 2 heat-exchangers:
==> Every now and then one of the heat-exchangers is hot: Then it's switched, so that the incoming air goes through that hot exchanger, while the exhaust gases go through the other one, heting it up ...

That's how steel can be melted with coal ..., up to 1700 Cels or even hotter ...

======================

The amateur can eg. get himself an electric hot-air-gun and burn charcoal in th 600-Cels-Air of it, reaching temperatures beyond 1400 or 1500 Cels ... :D

======================

The pre-heating can go as far as the raectants allow; like in a pyramid-construction there are even multi-stage processes possible, depending on what the materials used can withstand ...; it just costs more fuel, so a lot of fuel would form the basement of the temperature-pyramid, for a quit hot flame on the top ...

=====================

Since cheap materials exist for up to 2000 Cels: Those 2000 Cels can somewhat easily be set onto the top of eg. a Hydrogen-Oxygen flame ...

[Edited on 11-4-2010 by chief]

[Edited on 11-4-2010 by chief]

bquirky - 11-4-2010 at 02:25

very interesting...


I must meditate on the possibility's, I might be able to do things with air that I had assumed i neaded oxygen for.

hissingnoise - 11-4-2010 at 04:01

Quote:

If I'm wrong then fair enough, but don't just say I'm wrong; say why.

Well, I try to avoid exerting myself (simple laziness!) but I came up with this; an explosive uncompressed will detonate with an appreciably slower velocity than the same explosive compressed to high density.
It seems safe to assume that the reaction taking place in a smaller timeframe will produce an appreciably hotter flame.
An awkward analogy but you see my point?


unionised - 11-4-2010 at 05:01

"It seems safe to assume that the reaction taking place in a smaller timeframe will produce an appreciably hotter flame."
Not to me it doesn't.
You still end up with the same energy shared between the same molecules so you get the same final temperature.

hissingnoise - 11-4-2010 at 05:41

Well then, we'll have to agree to disagree.
I'd like to go into it more deeply but I haven't time right now. . .

unionised - 11-4-2010 at 07:32

Does anyone else out there have any ideas about this?

chief - 11-4-2010 at 07:50

Higher pressure in a detonation can be calculated to be some sort of equivalent with higher Temperature ...
==> ... but the calories per mole are still the same ...

So it depends on the conditions the temperatures are given for ...

hissingnoise - 11-4-2010 at 09:16

Yes, but I believe the faster reaction will attain a higher temperature, however momentarily.

Formatik - 11-4-2010 at 10:36

Quote: Originally posted by unionised  
Does anyone else out there have any ideas about this?


That's what I was pointing at with the cyanogen example. Explosions are hotter than respective combustions. The energy of explosions tend to be less than combustions (compare enthalpies to see the difference).

It has to do with the kinetics of explosion as to why explosions are hotter (not more energetic). Like the pressure generated in an explosion, this wouldn't be able to be so high if the reaction were not so instantaneous. The velocity and pressure are also directly dependent on loading density. It seems like this is also the case for temperature.

FederoffD596.png - 5kB

unionised - 11-4-2010 at 12:32

There may be a bit of talking at crossed purposes here.
Initially in this thread the conditions were not specified for any of these flame temperatures. In those circumstances the usual value quoted is the adiabatic flame temperature. (It's the hottest the reaction can get and it assumes a start at room temp and pressure)
On the other hand if you have a relatively small quantity of material in a container of some sort then the temperature rise will depend, among other things, on how much energy goes into heating the container.
It seems to me that the temperature measured for TNT etc depends on the packing density because the more of it you pack in the more heat is available to warm up the container.
In that case you are not really talking about "what combination of materials gives the highest temperature" but "what design of furnace / device gives the higher temp."
In the limit of an infinitely large blob of premixed fuel/oxidant it doesn't matter- the stuff gets to the adiabatic limit.
That will be higher for gaseous ozone, rather than the liquid; if you are looking for a "world record" the gas phase wins for the reasons I gave earlier.

chief - 11-4-2010 at 13:15

A faster detonation will set free more caloric power: More mass will be heated, but to the same temperature ...

Maybe at the high pressures some sort of phase-changes could come into account:
Such phase-changes would probably eat up energy, thereby lower the temperature ...

Molcular-dynamically Temperature halfway is defined via a medium-velocity-distribution of the particles, and pressure via the force exerted by the particles onto a surface ... ...
==> A higher pressure can come from a higher number of particles ...
==> but a higher temperature must mean a higher medium velocity of the particles ...

There's the difference: Quicker detonation means more particles, at the same speed, pressing against the environment ... higher pressure ; but the speed would be the same, so: Same Temperature ....

===============================
But on the other hand:
==> Detonations take place at velocities way above any usual molecular speeds ...
The medium molecular speed even for the lightest Atoms (Hydrogen) is only maybe 2-3 km/s (which limits the muzzle-velocity in guns)

==> Then again the speed of sound in eg. steel is around 5000 m/s, in other solids as well, which is often _higher_ than the molecular speed in gases for any of the atoms involved ...
==> For compressed explosives this speed is even higher ... in the zone where the shockwave runs ...


So: If the velocity of sound in a shockwave, namely 8000 m/s or anything like that, could be directly converted to a temperature, than by molecular velocity this would mean a _very_ high temperature ..., above the caloric possibilities ...
==> so either the molar heat-content, in calories per mol and Kelvin, is lower at high temperatures than at standard-conditions ...
==> or there is a mechanism in the shockwave that momentarily sucks heat ("temperature") away from most of the material and stores it in the shockwave ..., i.e. overheats the shockfront at expense of already detonated material ... (then a necessary symptom for that would be that the shockwave would have to build up speed, not start at full speed ... )
=====================

Well: I'm quite lazy now, lets see what anyone else thinks ... :D

[Edited on 11-4-2010 by chief]

Panache - 12-4-2010 at 20:37

i tend to side with hissingnoises' rational on this one, temperature is only relevant when measurable, ie the effect/change it bears upon on some other matter, unionised is absolutely correct in asserting that the calorific value of the combined reactions remains constant, however this is not temperature as we understand it practically, temperature to be relevant for lab use has to be defined in the context of the effect that reaction will have on your measuring device. This is very related to surface area of the device and the area of effect (aoe lol) of the reaction. If you had 1kg of reactant spread out in space over hundreds of km3 its ludicrous to believe it would raise the temperature of a small thermocouple very much at all, even though it was within the area of effect, compress that same amount of reactants down into a cubic meatre and place the thermocouple within it and the temperature rise will be appreciably larger than that for the former situation.

Detonation and comparisions with it i think confuse the discussion, as chief has already pointed out (actually he/she also pointed out everything else i have said, i just dumbed it down, my god we're a committee, anyone else want to restate this information in another way, rofl)

Panache - 12-4-2010 at 20:44

Quote: Originally posted by chief  
[


That's how steel can be melted with coal ..., up to 1700 Cels or even hotter ...

======================

The amateur can eg. get himself an electric hot-air-gun and burn charcoal in th 600-Cels-Air of it, reaching temperatures beyond 1400 or 1500 Cels ... :D

======================

The pre-heating can go as far as the raectants allow; like in a pyramid-construction there are even multi-stage processes possible, depending on what the materials used can withstand ...; it just costs more fuel, so a lot of fuel would form the basement of the temperature-pyramid, for a quit hot flame on the top ...

=====================

Since cheap materials exist for up to 2000 Cels: Those 2000 Cels can somewhat easily be set onto the top of eg. a Hydrogen-Oxygen flame ...


apparently back in the day (middle ages) it used to take a few days to setup the pyre for their blast furnaces, carefully cutting and stacking the fuels to produce this effect exactly.

Nasa recently lit the first flame in space after all these years, its on utube (crap video though you really have to use your imagination). I think it was butane, a small blob the size of a hazenut. When lit it produced a perfectly spherical flame that as it heats and the butane expands increases then suddenly as no fuel remains it dies, strange, but obvious how the shape of our flames are completely determined by gravity.

chief - 13-4-2010 at 01:10

The Boltzmann-treatment of temperature is quite interesting; everything derived from molecular dynamics ...
==> I once read his original books, when I had access to them ... (still have) ; recommending this !

unionised - 13-4-2010 at 11:03

Quote: Originally posted by Panache  
i tend to side with hissingnoises' rational on this one, temperature is only relevant when measurable, ie the effect/change it bears upon on some other matter, unionised is absolutely correct in asserting that the calorific value of the combined reactions remains constant, however this is not temperature as we understand it practically, temperature to be relevant for lab use has to be defined in the context of the effect that reaction will have on your measuring device. This is very related to surface area of the device and the area of effect (aoe lol) of the reaction. If you had 1kg of reactant spread out in space over hundreds of km3 its ludicrous to believe it would raise the temperature of a small thermocouple very much at all, even though it was within the area of effect, compress that same amount of reactants down into a cubic meatre and place the thermocouple within it and the temperature rise will be appreciably larger than that for the former situation.

Detonation and comparisions with it i think confuse the discussion, as chief has already pointed out (actually he/she also pointed out everything else i have said, i just dumbed it down, my god we're a committee, anyone else want to restate this information in another way, rofl)


The problem you mention, that the temperature reached depends on how much stuff you have, is precisely the reason why adiabatic flame temperatures are used.
Otherwise it's simply meaningless to talk about the temperature of a flame, because it depends on how big the flame is.

Unless you are going to specify the details of the system very precisely there's only one meaningful way to answer the question "how hot will the reaction of A and B get?" and that's to quote the upper limit which will be obtained for a large enough flame.
On that basis, starting with the stuff cold means it ends up cold (in accordance with common sense too, though I accept that's not always a good guide).

Incidentally, if temperature were only relevant when it were measurable then, in the heart of a brutal explosion which will, among other things, alter the electron density and, therefore, the thermoelectric coefficients of the metals in your thermocouple, how do you measure it?

It's impossible to measure it in those circumstances so, by your logic it's not relevant.


I take the view that a temperature exists (in some cases several temperatures exist simultaneously) whether you can measure it or not and also whether or not you can get the ozone and charcoal properly mixed before it explodes anyway.

hissingnoise - 13-4-2010 at 11:37

As The WiZ said; carbon sub-nitride burning in ozone produces a continuous high-temperature flame - now imagine a hypothetical mixture of liquid ozone and liquid carbon sub-nitride being detonated by shock.
Common sense(?) tells me that the temperature of the fireball will far exceed that of the continuous flame. . .
And the detonation of large quantities would be expected to produce higher temperatures than that of smaller quantities.



unionised - 13-4-2010 at 13:03

Why?
I keep asking where you think the energy comes from to raise the temperature further and you keep not answering.

The WiZard is In - 13-4-2010 at 13:25

Quote: Originally posted by hissingnoise  
As The WiZ said; carbon sub-nitride burning in ozone produces a continuous high-temperature flame - now imagine a hypothetical mixture of liquid ozone and liquid carbon sub-nitride being detonated by shock.
Common sense(?) tells me that the temperature of the fireball will far exceed that of the continuous flame. . .
And the detonation of large quantities would be expected to produce higher temperatures than that of smaller quantities.






Well delta Hf is delta Hf... so comes now the question is there
a difference in the Hf of ozone gas and ozone liquid?

I ran a quick check and cannot find the Hf of ozone liquid.

Any rate this would only yield the theoretical high temp. Real
world ....


djh
-----------
... Your sickness appears to be a specific illness
of chemists. One could call it Hysteria Chemikorum,
which originates from the combined damaging
influence of mental exertion, ambition, and the
vapors and fumes. Davy suffered from it,
Mitscherlich, I -- on the whole probable all
great chemists."

Friedrich Wöhler to Justus von Liebig

hissingnoise - 13-4-2010 at 14:12

Temperatures attainable by chemical reactions are limited primarily by the exothermicity of the reactions, not by some arbitrary 'theoretical limit of chemistry'. . .


The WiZard is In - 13-4-2010 at 17:24

Quote: Originally posted by hissingnoise  
Temperatures attainable by chemical reactions are limited primarily by the exothermicity of the reactions, not by some arbitrary 'theoretical limit of chemistry'. . .





Exactly.

The way we obtain our heat is by breaking old and forming new chemical bonds. If the energy produced by the new bonds is greater than used to break the old, we have a net gain in energy, and this gain is output as heat.

Shidlovskii points out that the maximum gain will be obtained by breaking weak bonds and forming strong new ones. He also says that the strongest bonds are formed by the combination of elements of opposite properties. As a guide to bond strength we can compare electronegativity. Electronegativity being the ability of an element to attract electrons. In this race there is one clear winner, fluorine, with a value of 3.98. However, while there are fluorine compounds with weak bonds the majority are either gases [BF3, CIF3, NO3F, F2O, F2O3, FCI04] or low boiling point liquids [BrF3, F202], most are more than a little toxic! Next in the electronegativity contest is, you guessed it! Oxygen, with a value of 3.44. Followed by chlorine 3.16, and nitrogen 3.04.

These elements to produce the largest amount of energy should be combined with elements with low values of electronegativity. Values for some of the more useful elements are listed below:

K 0.82 Ti 1.54 Ba 0.89 Mn 1.55 Na 0.93
Al 1.61 Sr 0.95 Zn 1.65 Si 1.90 Li 0.98
Cr 1.66 Mg 1.31 Fe 1.83 Zr 1.33 Cu 1.90

No matter how good a chemist one do be, you do be limited .... delta Hf reactants vs delta Hf products.


Physics is different. Think Star-Trek's Matter/Antimatter.

Like you cannot boil water at 760mm Hg above 100o
(no microwaves please) I suspect the limit of chemistry
is where the gas produced, nitrogen for instance, disassociates, suckling up a lot of energy.

Where solids are produced the limit is the solid with the lowest boiling point. Assuming your reactants can produce that much heat.

12AX7 - 14-4-2010 at 00:28

I expect the equilibrium temperature is the point where they become a soup of dissociated atoms, i.e. the temperature where the reaction could "go either direction" and therefore is unable to proceed any further at that temperature due to the balance of energy gained in reaction vs. lost in dissociation.

Incidentially, such a state of matter will have high apparent heat capacity, since the reactants basically haven't reacted; as the mixture cools, it delivers significant amounts of heat, far more than the amount expected from an ideal gas at the same temperature and pressure.

The funny thing about physics, actually, is that it *isn't* different. The energy scale is higher, but the principle is the same. For instance, the equilibrium temperature of a fusion reaction will be on the order of 7MeV, which is around the energy yield of D-D fusion, and also the binding energy per nucleon of the byproduct, helium. Helium is not well known to fission or spall, and maybe it simply doesn't; but, as a reversible reaction, it should be possible to add that amount of energy and smack it back into deuterons. And concerning matter-antimatter, a plasma of matter, antimatter and photons at the same energy (~GeV for protons) will easily have self interactions where photon pairs produce matter just as well. Indeed, at high energy scales, most matter turns into energy, and one of the early epochs in the Big Bang cosmology is the point when matter condensed out of energy as it expanded and cooled. (The hard part is, how in the hell we apparently managed to get ordinary matter only, without antimatter!)

Tim

JohnWW - 14-4-2010 at 01:10

Quote: Originally posted by 12AX7  
(cut)
The funny thing about physics, actually, is that it *isn't* different. The energy scale is higher, but the principle is the same. For instance, the equilibrium temperature of a fusion reaction will be on the order of 7MeV, which is around the energy yield of D-D fusion, and also the binding energy per nucleon of the byproduct, helium. Helium is not well known to fission or spall, and maybe it simply doesn't; but, as a reversible reaction, it should be possible to add that amount of energy and smack it back into deuterons.(cut)

Helium nuclei - alpha particles - are VERY difficult to spall by means of nuclear collisions, because it is a "doubly magic" nucleus, having "closed shells" of 2 neutrons and 2 protons (which are spin-paired). This also means that fusion leading to it gives off a particularly large amount of radiant energy. "Hydrogen bombs" contain LiD as the fusionable material.

This special stability of the He-4 nucleus or alpha particle also accounts for the mode of decay of many heavy nuclei, from Po-210 upwards to a limit where spontaneous fission is more probable, and also a number of long-lived naturally-occurring alpha-emitters from about Pr to Re, being spallation by means of alpha-emission. It also explains why the isotope Be-8, which one would think would be stable, decays almost instantly into two alpha particles (the one stable isotope of Be being Be-9). It is also the reason why the stable isotopes of Li, Li-6 and 7, are so cosmically rare compared to neighboring elements; while they are produced in large amounts in stars by fusion, the extra proton and neutrons are relatively loosely-held, and both isotopes tend to be largely destroyed in supernova explosions in favor of either He-4 or heavier elements than Li.

The WiZard is In - 14-4-2010 at 09:59

Quote: Originally posted by 12AX7  


The funny thing about physics, actually, is that it *isn't* different.

Tim



To paraphrase Arthur C Clarke.

Sufficiently advanced chemistry is indistinguishable from physics.

djh
--------

unionised - 14-4-2010 at 10:41

Quote: Originally posted by unionised  
Why?
I keep asking where you think the energy comes from to raise the temperature further and you keep not answering.

hissingnoise - 14-4-2010 at 11:37

Oh yeah, liquid ozone vs. gaseous ozone. . .
The liquid ozone will react faster than gaseous ozone.
The faster reaction will produce the higher temperature.



[Edited on 14-4-2010 by hissingnoise]

The WiZard is In - 14-4-2010 at 12:28

Quote: Originally posted by hissingnoise  
Oh yeah, liquid ozone vs. gaseous ozone. . .
The liquid ozone will react faster than gaseous ozone.
The faster reaction will produce the higher temperature.



[Edited on 14-4-2010 by hissingnoise]



You dobe assuming liquid O3 @ -113o will react at all!

hissingnoise - 14-4-2010 at 13:47

Well yes, certainly - with the right conditions; it isn't, after all, noted for its stability. . .

The WiZard is In - 14-4-2010 at 14:07

Quote: Originally posted by hissingnoise  
Well yes, certainly - with the right conditions; it isn't, after all, noted for its stability. . .



I have not great faith in generalities. That said I would note
that the temperature of detonation is usually greater than
that of combustion for the same chemical. The difference is attributed to ....
different reaction products/reaction product ratio's between combustion
and detonation. I, however, am not sure this applies to chemical mixtures vs.
explosive chemical compounds where the heat is the result or the rearrangement
of the explosives elements as opposed to redox reactions.

hissingnoise - 14-4-2010 at 14:58

A dispersion, in gaseous ozone, of finely divided carbon can be expected to explode on ignition.
If, that is, such a mixture isn't hypergolic to start with?
But the explosion produced by LOZ/carbon will have a considerably higher velocity and temperature.



[Edited on 14-4-2010 by hissingnoise]

unionised - 14-4-2010 at 21:58

You still have not said where the extra energy comes from.
You just keep repeating the "mantra" that it's faster so it will be hotter.

Formatik - 14-4-2010 at 22:50

With rapidly occurring exothermic reactions the energy liberated can not dissipate, this results in an increase in temperature and reaction velocity. This is a fundamental difference between combustion and detonation.

unionised - 15-4-2010 at 10:04

"With rapidly occurring exothermic reactions the energy liberated can not dissipate,"
Now look up the meaning of adiabatic.

hissingnoise - 15-4-2010 at 11:22

Are you sure you're not the one having difficulty with 'adiabatic processes'?

unionised - 15-4-2010 at 13:05

from
http://hyperphysics.phy-astr.gsu.edu/Hbase/thermo/adiab.html

"An adiabatic process is one in which no heat is gained or lost by the system."


It's the whole reason why flame temperatures are calculated for the adiabatic condition- it saves having to estimate how much energy is lost because that depends on the experimental design.

Formatik - 16-4-2010 at 13:25

Quote: Originally posted by unionised  
Now look up the meaning of adiabatic.


Yeah, and? Adiabatic flame temeprature isn't even the highest flame temperature. That is the theoretical flame temperature. An example is stoichiometric combustion of methane in oxygen, which has a theoretical flame temperature several thousand degrees higher than the adiabatic flame temperature. The difference between those two is dissociation. This is also why burning combustibles in oxygen gets hotter than burning in air even with the same amount of oxygen, which latter dilutes with nitrogen.

unionised - 17-4-2010 at 08:24

I'd still like to know where the extra energy comes from.

Also, since it is never possible in practice to ensure that no heat is lost from a reaction all adiabatic temperatures are theoretical. You are therefore saying that the theoretical temperature is higher than the theoretical temperature. That seems odd.

The adiabatic temperature is what you calculate id you share out the energy released from the reaction among all the products of that reaction. Obviously that means finding (or calculating) the heat capacity of those products as a function of temperature. In doing that you have to take account of dissociation and other effects like electronic excitation. It's tot a trivial exercise but, if you say it doesn't give the highest temperature possibel then you are saying, in effect, that letting the heat out (i.e. not running the reaction adiabatically) makes it get hotter.
Again, that seems odd.

[Edited on 17-4-10 by unionised]

Formatik - 17-4-2010 at 10:26

The explanation earlier was one that I saw it was from an inorganic chemistry book by Erwin Riedel. Even in a closed container, if we burn something the energy release is much more gradual, but in a detonation this energy release is abrupt and rapid. Since temperature is due to kinetic energy movement in a material, and detonations are much more kinetic in nature than combustions, it seemed to make sense.

Dissociaton in the products could play a role. Detonations develop very high pressure. And it is known high pressure reduces dissociation in combustions (flame temperatures are known to be higher under high pressure). This could account for thousands of degrees in difference.

After looking around a little, it turns out even for the flame temperature, adiabatic is not the theoretical limit. Described in Fuels and Combustion by Samir Sarkar. According to him, there are four categories of flame temperatures:

Theoretical flame temperature: maximum value of fuel and oxidant at stoichiometric amounts. Not enough oxidant dilutes and incomplete combustion results. Too large of an amount dilutes the products and takes away heat. Those both lower flame temperature. Degree of dissociation reactions increase with temperature and an endothermic effect results (e.g. CO2 = CO + 0.5 O2 + 67,636 kcal). Example: CH4 with O2: 5050 C.
Adiabatic flame temperature: flame temperature at adiabatic conditions. Example: CH4 with O2: 2740 C.
Actual flame temperature: This is practical combustion under regular conditions (non-adiabatic).
Maximum adiabatic flame temperature (also called maximum flame temperature): realized when the fuel is in slight excess of stoichiometric amounts. Examples: H2 in 78.0% oxygen: 2660 C. C2H2 in 44.0% oxygen: 3137 C. C2N2-oxygen (CO, N2 as products): 4580 C. Hydrogen-fluorine flame: 4300 C.

unionised - 17-4-2010 at 11:14

That theoretical maximum is a weird flame temperature; it's how hot you have to get the mixture before the forward and reverse reactions are equally fast.

As has been mentioned, if you pre heat the starting materials you get a higher temperature but, even then there is a limit- if you heated the fuel and oxygen to over 5050C then mixed them, they wouldn't react much because the reaction products would decompose back into the starting materials.
OK, that's a maximum temperature- but it's never going to have a meaningful realisation.

In particular, it's not going to be obtained by cooling the starting materials.

The adiabatic temperature is the highest temperature you can reach from any given starting temperature (usually STP). Of course, it depends on the fuel: oxidant ratio but, for any given pair there will be a limit.

franklyn - 17-4-2010 at 14:27

What exactly constitutes flame ?

If ultra high temperature is desired it is acheived by a thermic lance.
http://www.wisegeek.com/what-is-a-thermal-lance.htm

Heat generated at the burning end of the steel clad magnesium tube
into which oxygen is fed , can be enhanced by providing an electric
current from an arc welding tranformer.

Something close to 11000 ºF has been attained.

_ _ _ _ _ _ _ _ _

Tempeartures acheived by particle collision in accelerators made
for the purpose generate transient peaks of billions of degrees.

.

Formatik - 17-4-2010 at 20:13

Quote: Originally posted by unionised  
That theoretical maximum is a weird flame temperature; it's how hot you have to get the mixture before the forward and reverse reactions are equally fast.

As has been mentioned, if you pre heat the starting materials you get a higher temperature but, even then there is a limit- if you heated the fuel and oxygen to over 5050C then mixed them, they wouldn't react much because the reaction products would decompose back into the starting materials.
OK, that's a maximum temperature- but it's never going to have a meaningful realisation.

In particular, it's not going to be obtained by cooling the starting materials.

The adiabatic temperature is the highest temperature you can reach from any given starting temperature (usually STP). Of course, it depends on the fuel: oxidant ratio but, for any given pair there will be a limit.


Sakir attributes the whole difference between theoretical and adiabatic flame temperature in methane and oxygen to dissociation. I take it then that the adiabatic flame temperature is a calibration of the theoretical flame temperature. Resistance of reaction products to dissociation (and high reaction enthalpy) is the reason e.g. hydrogen and fluorine flames reach such high temperatures.

While it's true pre-temperature has a role in flame temperature, in a detonation (which can be thousands of degrees higher) this effect doesn't seem appreciable as a mixture of charcoal and liquid oxygen (23/73) has an estimated detonation temperature of about 6600 K.

unionised - 18-4-2010 at 05:02

Franklyn, could you translate that temperature into Rankine please?


Anyway, I'd still like to know where the energy comes from to give hotter products if you start with something colder. I have an idea of what it might be, but I'm not sure.

[Edited on 18-4-10 by unionised]

Formatik - 19-4-2010 at 11:07

What is your idea?

franklyn - 20-4-2010 at 10:30

@ unionised

Rankine is degrees Farenheit minus ~ 460 ( approximately , actual absolute zero is very slightly less )

Kelvin is degrees Celsius minus ~ 273 ( again approximately , actual value is very slightly more )

See => http://en.wikipedia.org/wiki/Rankine_scale

____________________


The incandescent plasma being electrically conductive can be heated to higher temperature than
from the combustion of the metal by the supplemental current from an arc welder. The energy
provided is additive.


Attachment: phpzm0BMi (12kB)
This file has been downloaded 835 times

[Edited on 20-4-2010 by franklyn]

unionised - 20-4-2010 at 10:30

Imagine I dispersed a cloud of charcoal in some ozone and lit it, the product would be a a much larger volume of very hot gas.
Now imaging that I took that gas and adiabatically squashed it to the volume of a lump of charcoal soaked in liquid ozone.
Doing so would need me to do a lot of work and (like the air in a diesel engine) heat the gas mixture.
I'm not sure if that would get it to 6600K or whatever, but I can see it getting rather hot.
At least it's a possible answer- it's the energy not lost pushing back the atmosphere.

franklyn - 20-4-2010 at 10:34

Well yes free expansion of a gas does not reduce it's temperature unless it has done work ( pushing something ).

True of the individual particles ( molecules , atoms , ions )
The average apparent temperature factors in the volume.
The solar wind is a very high temperature rarified gas the
apparent temperature of a volume of space is near
absolute zero.

.

[Edited on 20-4-2010 by franklyn]

Justin - 26-6-2010 at 05:57

Quote: Originally posted by franklyn  
@ unionised

Rankine is degrees Farenheit minus ~ 460 ( approximately , actual absolute zero is very slightly less )

Kelvin is degrees Celsius minus ~ 273 ( again approximately , actual value is very slightly more )

Degrees Kelvin is Celsius PLUS 273 since 0 kelvin is absolute zero




[Edited on 20-4-2010 by franklyn]


[Edited on 6/26/2010 by Justin]

[Edited on 6/26/2010 by Justin]

Anders Hoveland - 26-6-2010 at 16:21

Probably F2 burning with B(CN)3 would be super hot.
By the way, B(CN)3 probably polymerizes under heat and pressure to make a superstrong ceraminc armor.

Or SF6 burning with magnesium

White Yeti - 3-8-2011 at 07:37

A simple hydrogen flame can be brought up to temperatures exceeding 5000C if an electric arc is maintained between two tungsten electrodes. The energy from the arc is absorbed by diatomic hydrogen and then released again when the hydrogen radicals strike a cold metal surface. This is the theory behind AHW or atomic hydrogen welding.

Can you top this?

The WiZard is In - 3-8-2011 at 09:36

Can you top 6500o K?

The experimental combustion phase was aimed at producing the highest, possible temperature
by varying the metal, the oxidizer ant he pressure of the reaction. It was found, both theoretically
and experimentally that higher temperatures, were achieved with higher pressures. Two techniques,
were used to achieve higher pressures: (a) Dynamic pressurizing of metal powder and solid, oxidizer:
and (b) pre -pressurizing metal wool with gaseous oxygen The results achieved with these two
techniques are shown graphically in Figure 1. This snows that the pressurized oxygen system
produces brightness temperatures equivalent to those of dynamic pressurization, but at, lower
pressures. The highest brightness temperature 6500o K, was obtained by the, reaction of hafnium
powder and potassium perchlorate under a pressure of approximately 40,000 psi. However, it can,
be seen from Figure 1 that temperatures -greater than, 6000o K are achieved at the much lover
pressure of 1450 psi by pressurized oxygen.



Accession Number : AD0443158
Title : SPECTRAL EMISSIVITY OF FLASH COMBUSTION REACTION STUDY PROGRAM
Descriptive Note : Final technical rept. 1 Jun 1963-31 May 1964
Corporate Author : NORTH AMERICAN AVIATION INC LOS ANGELES CA
Personal Author(s) : Gerhauser, J. M.
Handle / proxy Url : http://handle.dtic.mil/100.2/AD443158
Report Date : 06 JUL 1964
Pagination or Media Count : 178

Abstract : This study was initiated to provide the additional data required on maximum intensity,
spectral distribution, duration, and efficiency of radiation emitted by high energy metal-oxygen
reactions and the degree of control that might be achieved over these characteristics. In brief, the
study has shown: (1) several reactions produce brightness temperatures above the approximate
threshold temperatures for neodymium (3500 to 5000 K) and ruby (5200 K) with a maximum of 600 K
achieved; (2) the brightness temperatures are a strong function of pressure with highest temperatures
achieved between 2000 and 50,000 psi; (3) except in the early stages of unpressurized reactions
where line and band emission are present, the spectral distribution is a continium, but not necessarily
a black body distribution; (4) the time duration of the flash can be controlled to within 1/2 to
3 milliseconds; and (5) that these reactions can be effectively used to pump high energy density
laser systems.

Descriptors : *LIGHT, *LASERS, *COMBUSTION, *PYROTECHNICS, LASER PUMPING, MAGNESIUM,
BRIGHTNESS, ALUMINUM, CHEMICAL REACTIONS, ZIRCONIUM, PERCHLORATES, CHLORATES,
LINE SPECTRA, POTASSIUM COMPOUNDS, EMISSIVITY, TRANSFORMATIONS, BAND SPECTRA,
NEODYMIUM, ABSORPTION SPECTRA, RUBY, SODIUM COMPOUNDS, THORIUM, PRESSURE,
LIGHT PULSES, PUMPING(ELECTRONICS), HAFNIUM, HIGH TEMPERATURE, ENERGY, INTENSITY
Subject Categories : PYROTECHNICS

----------
Actually - the Analogue Guy has found a ref
to higher temp's if'n I can relocate it I'll
post it.


djh
----
If I have seen further…. it is by
standing on the shoulders of giants.

Isaac Newton,
letter to Robert Hooke,
Feb. 5, 1675/6

The WiZard is In - 3-8-2011 at 10:07

Extracted from
High-Temperature Research
By means of "liquid containers," liquid metals can be studied at
much higher temperatures than heretofore.
Aristid V. Grosse
Science Volume 140 781-789.
17 May 1963

because La PDF is a bit over
3 meg thus toooo large to post here.



Methods were developed at our institute to
burn many metals at atmospheric pressure.
The metals were burned in the solid state (as rods, pipes,
balls, sheets, and powders), in the liquid
state, and in the vapor state. The
expected adiabatic temperatures in the
range of 3000o to 5000°K were reached
(2). The highest temperature, close to
5000oK, was attained (3) through
burning zirconium powder in a torchtype
apparatus. Beryllium, at pressure
of 1 atmosphere, in oxygen produces a
temperature of 4300oK, and aluminum
and magnesium, temperatures of 3800o
and 3350oK, respectively.

Fluorine is the most electronegative element
known, and thus many fluorine compounds
are more stable than the corresponding
oxides, because of the
greater strength of the fluorine bond.
A good example is hydrogen fluoride.
When it is formed from hydrogen and
fluorine a flame temperature of 4000°K
is reached (6, 7). At a total pressure
of 5 atmospheres the temperature is
raised to 4200oK (6). In contrast, the
maximum temperature of the hydrogenoxygen
flame is only 2930°K at atmospheric
pressure.

When a mixture of cyanogen and
oxygen was burned according to the
equation (CN)2 + 02 > 2CO + N2,
one of the highest flame temperatures
so far attained, 4800°K (at atmospheric
pressure), was produced (8). By burning
the same mixture under a total
pressure of 100 pounds per square
inch, a temperature of 5050°K was attained
(9).

It was found that the unstable colorless
liquid, carbon subnitride, C4N2-
the first member of the dicyanoacetylene
series-can be burned with oxygen
(J0) in either a diffusion flame or a
flame of premixed type, according to
the equation C4N2 + 202 - > 4CO
+ N2. The calculated flame temperature
is 5260°K at atmospheric pressure.

Since the flame temperature calculated
for the cyanogen-oxygen flame
has been checked experimentally (8),
the enthalpy data for CO and N2 may
be used with confidence. The accuracy
of the calculated flame temperatures is
+2°. In all these combustion studies
ordinary oxygen, 02, was used. It was
recognized that significantly higher
temperatures could be obtained if ozone,
03, were substituted for 02. The heat
of formation of ozone from oxygen
is +33.98 kilocalories per mole of
ozone; thus, the amount of heat liberated
is increased, and, provided the
stoichiometry of the combustion is adjusted
to produce the same reaction
products as with oxygen, the flame
temperature is also increased.
However, pure ozone in either gaseous,
liquid, or solid form may detonate
with great violence to molecular oxygen,
although with proper handling it
can be made to burn in a regular, but
faint and nonluminous, blue flame (11)
to oxygen, according to the equation
203 >- 302. Because of the experience
we had gained in handling and
burning 100-percent ozone we were
able to premix and burn various mixtures
of hydrogen (12) and cyanogen
(13) with ozone. The mixture 3(CN)2
+ 203 burns uniformly, noiselessly, as
brightly as an electric arc, and with a
pink-violet color: 3 (CN)2 + 203 -*
6CO + 3N2. At pressures of 1 and 10
atmospheres, its calculated temperatures
are 52080 and 55060K (±20), respectively.
The temperatures of the corresponding
oxygen flame, 3 (CN)2 +
302 -- 6CO + 3N2, are 48560 and
5025 OK, respectively.
The cyanogen-ozone and the carbon
subnitride-oxygen flames, with temperatures
of 52080 and 5260°K, respectively,
produce the highest chemicalflame
temperatures achieved to date at
pressure of 1 atmosphere. Calculations
indicate (10) that substitution of ozone
for oxygen in the carbon subnitrideoxygen
flame, provided explosions and
detonations could be avoided, particularly
under pressure, would produce a
temperature higher than 6000°K (see
Table' 2). These flame temperatures
represent the ultimate goals with chemical
reactions.

Use of the noble gases helium and
argon makes it possible to produce a
chemically inert "flame" of temperature
up to 25,000oK.

The first ionization potential of
argon is 15.68 volts, equivalent to 362
kilocalories per gram atom; that of
helium is 24.46 volts or 565 kilocalories
per gram atom. Helium begins to
ionize appreciably only in the 20,000o
to 25,000oK range, and therefore its
heat content is lower than that of argon.
Up to 10,000o Another problem relates to the nature
of chemical substances that can be
heated to extremely high temperatures.
As I have said, the highest temperature
attainable through ordinary chemical
reaction is in the range 5000° to
6000°K. This is the limit of existence
of chemical compounds. At these temperatures
all chemical bonds break and
all molecules are dissociated into transient
radicals or atoms. Thus, flame
temperatures higher than these cannot
be produced through chemical reaction.
The temperature above which no
known solid can exist has been reached.
The metal with the highest melting
point is tungsten, which melts at
36430K, and the oxide with the highest
melting point is thorium dioxide,
which melts at 3300°K. Tantalum
carbide, which melts at 4200°K, has
the highest melting point of any known
substance. For purposes of containment,
in practice at our laboratories,
these maxima are attained and used
only rarely, because of (i) chemical
reaction between the high-melting substance
and any other substance being investigated; (ii) the occurrence of
eutectic mixtures, which lower the melting
point; and (iii) thermal shock.

And it is not likely that substances
will be found with melting points many
hundreds of degrees higher. Thus, we
are compelled to find, if possible, thermally
stable liquids if we want to contain
higher temperatures in some useful
way.

Fortunately for the future development
of high-temperature research and
technology there are substances which
will exist as liquids up to very high
temperatures-much higher than any
at which we had thought liquids could
exist. These substances are the refractory
metals, which will eventually be
useful in our rocket and space technology.
Some of them remain as rather
dense liquids even up to temperatures
of 20,000°K. Since they are
elementary monatomic liquids they cannot
undergo any chemical change (except
for ionization), even at extremely
high temperatures.

niertap - 6-8-2011 at 10:21

ATOMIC HYDROGEN

The WiZard is In - 6-8-2011 at 12:06

Quote: Originally posted by niertap  
ATOMIC HYDROGEN


Why? Does it have some magic Hf?

Somewhere (I at the moment cannot put hands on it)
I came across a ref to 10 000o with O3 and Zr (?)
Hf (?) at 100 000 psi or some such.

Here is something to keep you busy.

MISSION IMPROBABLE
by
The WiZ (Donald J Haarmann)

You have been chosen lead pyrotechnist for the first peopled mission to Dubious 7. Your mission, should you choose to accept, is: supply a pyrotechnic compound as a source of heat for cooking purposes. Because of the limited weight carrying capacity of the launch vehicle the reaction you choose must have the highest possible ratio of heat produced to weight of reactants, i.e., kilo calorie/gram (K/cal/gm) of reactants. There are no restrictions on the state of the reactants; they may be either solids, liquids or gases.

For those not familiar with the method of calculating the amount of heat produced by a reaction, the following explanation is provided.

The amount of heat in kilo calories is calculated by subtracting the heat(s) of formation [heat of formation is now called “standard enthalph of formation”] (Hf°) of the reactant(s) from the heat(s) of formation of the products. This value is then divided by the weight of the reactants to obtain heat per gram in kilo calories per gram.

Hf° prod (K/cal) Hfo react (K/cal) = Heat (K/cal)

K/cal
-------------
gms of reactants = K/cal/gm

The heat of formation is the amount of heat required to form one gram MOLEcular weight (mole) of a compound from its constituent elements. If heat is liberated by the reaction the heat of formation has a negative value, i.e., the heat of formation of aluminium oxide Ai2O3 is 400.5 K/cal per mole (102 grams) of aluminium oxide. That is, if we were to react sufficient oxygen and aluminium to produce 102 grams of aluminium oxide we would also produce ( )400.5 K/cal of heat. Elements have a heat of formation of zero. Remember a negative value means heat has been produced.


Let us look at a simple reaction, such as the
burning of titanium in oxygen.

Ti + O2 = TiO2

One mole of titanium (47.9 gms) reacts with one mole of oxygen (32 gms) to produce one mole of titanium dioxide (79.9 gms). The heats of formation for titanium and oxygen are 0, while the Hf° of titanium dioxide is 225 k/cal mole.


47.9 gms + 32 gms = 79.9 gms

Ti + O2 = TiO2

0 k/cal 0 k/cal = 225 k/cal

.

Hf° products Hf° reactants
------------------------------------- = heat produced per gram weight of
reactants
weight of reactants



( 225) (0 + 0) = 225 K/cal
-------------------------------------------------------------------- = 2.82 k/cal per
gram
(47.9 gms) + (32 gms) = 79.9 gms



A more complicated reaction:

3998.94 gms

1960.8 gms + 2038.14 gms

(16)(122.55gms) + (6)(339.69gms)

16KCIO3 + 6SbS3 --> 16KCI + 18SO2 + 3Sb2C4,

(16)( 93.5k/cal) (6)( 43.5) --> (16)( 51.6) + (18)( 71.0) + (3)(214)
( 1496 k/cal) + ( 261) --> ( 825.6) + ( 1278) + ( 642)

( 1757 K/cal) --> ( 2745.6 K/cal)
[reactants] [products]

988.6 k/cal

[products] [reactants]


( 2745.6 k/cal) ( 1757 k/cal)
-------------------------------------- = 0.25 k/cal gm
3999 gms of reactants



Now looking at these reactions and the way the results were obtained, two things will be obvious; first because the Hf° of the products is subtracted from the Hf° of the reactants it will be useful to produce products with high Hf° using reactants with the low Hf°. Indeed the best results will be obtained using reactants with either a low Hf° (small negative value), 0 (elements) or compounds with a positive ( + ) Hf°'s, of which there are not many. (Remember minus a minus is a plus.) There are only few inorganic compounds with positive values of Hf° and are some what exotic e.g., fluorine perchlo¬rate CIOF4, Hf° + 18.5, BrCI, + 14.6, N2O, + 19.49. Secondly, because the heat pro¬duced must be divided by the molecular weight of the reactants, it would be wise to use products with low molecular weights. The reaction between hydrogen and oxygen or fluorine comes to mind, however, these reactions produce only 3.2 K/cal/gm of heat despite their low molecular weights. These two reactions do, however, produce high specific impulse, which makes these reactions useful in rockets, and such.

Heats of formation can be found in the CRC Handbook among other references [my reaction was obtained using products in the CRC Handbook. Most libraries have a copy.

A final note; heat does not mean temperature, e.g., the reaction of oxygen with aluminium produces 3.9 K/cal/gm of heat vs. 3.6 for magnesium/oxygen, the magnesium reaction is capable of producing a temperature of 3600°C, whereas aluminium can only produce a temperature of 3000°C. Indeed the reaction between hydrogen and fluorine while only producing 3.21 K/cal/gm results in a temperature of 4030°C. In general the highest temperature produced by a reaction can never exceed the boiling temperature of the most refractory reaction product when the reaction products are solids. The highest value being approximately 4500°C (thorium oxide). The highest flame temperature for a reaction using gases is 4500°C for the reaction between cyanogen (C2N2) and oxygen. For comparison the flame temperature for oxy/acetylene is 3140°C.

Originally published in PGII Bulletin 21. May/June 1987

Scanned 21vi97


The best result I have been able to obtain is -- 6 K/cal per gram of reactants. Can you do as well or even better? Using boron and ozone


2B + 2O3  3B2O2

(6) (10.8gms) (2) (48gms) --> 160.8 gms


-906 - (+68) = -974 K/cal

-974 K/cal
160.8

= 6.05 K/cal


Added [Well… I see in the late Dr. Ellern’s book a better reaction! One that will yield -13.4 K/cal per gram!!]

[I have doubts about cyanogen and oxygen producing a 4500oC flame temperature. I believe this is base on an old value for the boiling point of carbon, e.g., 4500oC. 3600 oC is more likely.]



Bert - 27-11-2017 at 20:12

Darn. Can't ask the WiZ what he found in Ellern now, and my copy is in storage 80 miles away.

In reference to the odd chemicals that were (or are being) offered at Skylighters going out of business sale, I've come across something interesting:

Attachment: Ti, Zr & Hf compounds as pyrotechnic fuels.pdf (1.1MB)
This file has been downloaded 386 times

Zirconium diboride, Hafnium carbide, etc. All are usually considered highly refractive ceramics for extreme environments... But they burn.

Merely mixed straight out of the jar from chemical supplier with stoichometric ammounts of Potassium nitrate, these ceramics BURN. Not quite as hot as the pure metals, but then, they don't go off from minor static discharges, bumps or mere dirty looks as the finely powdered metals do. I do not enjoy handling fine Zr powders in particular, I have had a couple of near misses.

From a quick look at the tables in the attached paper- Hafnium carbide has a density around 12 g/cc, and burns somewhere upwards of 3,000 C? Al is only around 2.7 g/cc. And it looks like the HfC is often supplied as particles verging on sub micron range? I can think of possible uses.

[Edited on 28-11-2017 by Bert]

[Edited on 28-11-2017 by Bert]