malford
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Hottest & Most Heat-Producing Chemical Reaction
The table below was compiled from various sources. For each reaction, the molar mass, enthalpy of formation, and density was entered, allowing the
spreadsheet to calculate the proper stoichiometry, heat per unit of weight, and heat per unit of volume.
My immediate intention is to find the ultimate composition for igniting solid rocket motors with large, complex core geometries. Filling the core with
reaction products as close to instant as possible that have the greatest temperature possible is ideal.
Given the task above, choosing a composition with the greatest heat per unit of volume seems wisest, because the igniter will be limited by space, not
weight.
Lead dioxide and beryllium have an enthalpy of formation of -32.41 kJ/cm^3. If my calculations are correct, that is nearly twice the amount of heat
per unit of volume of the traditional iron oxide and aluminum reaction. Though Be is expensive, only one part of it is required per 13.27 parts of
PbO2, so a small amount will go a long way.
Now, I understand there are many variables that determine the temperature that is produced using the amount of heat generated. That, ultimately, is
what I am after: achieving the highest temperature. This document shows many thermite, metallic, and intermetallic reactions. Each reaction is accompanied by its theoretical maximum density,
adiabatic temperature with and without phase change, total change in enthalpy, etc. What I find confusing about this document, is that it does not
specify what the adiabatic boundary is. How large is this boundary? With what is this space filled? Is it a vacuum with an idealized zero heat
capacity?
Also, for some reason, some of my calculations for heat do not match their calculations.
If anyone has anything to contribute, it would be greatly appreciated. I would love to see some competing enthalpies calculated, thermite or
otherwise, if anyone is so inclined.
[Edited on 9-7-2013 by malford]
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IrC
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"Though Be is expensive, only one part of it is required per 13.27 parts of PbO2, so a small amount will go a long
way."
You are aware of the danger in this reaction? BeO coming from this reaction has to go somewhere, and in your lungs is the last place you want it.
"Science is the belief in the ignorance of the experts" Richard Feynman
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phlogiston
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For your purpose, I think the speed of the reaction is also an important parameter.
You want the core to ignite quickly over its entire surface. Or will you place a small very hot charge at the end of the bore so that the propellant
gasses will ignite the rest of the grain (this is what is done in the space shuttle SRB's)?
Perhaps you can put coarse pellets of a very hot thermite mix in a fast-burning matrix to get the best of both worlds.
According to that document, the I2O5 + 2Ta reaction heats up to 7240 K... wow!
-----
"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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AndersHoveland
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The reaction between Beryllium and Oxygen releases more energy per unit weight (24.36 kJ/g) than any other combination of elements.
The reaction between Lithium and Fluorine is almost as energetic (23.75 kJ/g). Theoretically, burning Be with ozone would yield 26.26 kJ/g.
It is not very practical, but a marginal improvement could be realized by burning a Li-Be alloy with cryogenic liquid OF2, with a lesser amount of
ozone dissolved, as much can be dissolved without posing an explosion hazard.
Because of its slightly positive heat of formation, using oxygen difluoride will yield additional energy. After doing some research, I found three
different entropy values for this compound, which unfortunately do not agree. One source claimed a heat of formation of 23.8 kJ/mol, would translate
into an addition energy of 0.44 kJ/g.
Using a new article: "A New Determination of the Heat of Formation of Oxygen Difluoride" by WARREN R. BISBEE, Rocketdyne Division, North American
Aviation, the heat of formation of OF2, with this newly determined value, was 16.994 kJ/mol. This translates into 0.3147 kJ/g of additional energy.
Wikipedia claims a 24.5 kJ/mol heat of formation, which would translate into 0.454 kJ/g of additional energy.
If you are wondering why not just dissolve the ozone in liquid oxygen, that is because ozone has its own unique hazards, which takes a little bit of
explaining. The boiling point of oxygen is 90 K, while the boiling point for is ozone is 161 K. The liquid oxygen boils out from a mixture of ozone
much faster, gradually increasing the concentration of ozone. When the concentration approaches 30 percent, below 93 K, the mixture separates into two
distinct liquid layers, the first containing 30% ozone, and the second containing 75%. As more oxygen boils off, the volume of the 30% concentrated
ozone layer decreases, while the volume of the 75% layer increases. This creates an unusual danger of explosion when trying to enrich liquid oxygen
with ozone. However, addition of either 5% oxygen difluoride or of 9% liquid fluorine prevented layers from separating out in the liquid oxygen and
ozone mixture, thus reducing danger of explosion.
Energy density is not the same thing as temperature, however, and so I suspect some other chemical could attain a higher temperature.
[Edited on 9-7-2013 by AndersHoveland]
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woelen
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@AndersHoveland: I think that malford has another requirement as well (although he did not state explicitly) and that is that the reaction should be
practically possible and that the reagents required for it should be available. What you mention does not seem anything practical at all.
@malford: I think that you need to search for a combination of reagents, which gives solid or liquid products only, keeping all heat inside the
reaction mix and not allowing for pressure buildup due to production of gas.
@phlogiston: I2O5 is quite volatile and decomposes above a few hundred C. I have a few tens of grams of this chemical and I noticed that it is not
really stable, it easily decomposes on heating, giving oxygen and iodine (with the lower oxide I4O9 as intermediate product). One of the reaction
products (Ta2O5) is a refractory solid, but I2 will be a gas at the reaction temperature. How can this in practice work? Doesn't it lead to explosion,
due to pressure buildup?
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Fantasma4500
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well in a nuclear bomb the heat is around if not higher than 500000*C or was it several million *C? cant remember
blackpowder is said to be able to reach 6000*C in a amount of 100g or some, in the very core
no clue how they measured it tho
i believe that if you have a HE, that goes fast enough, and gives off enough heat in the reaction, and you use ENOUGH there will be much more heat
generated than what numbers you would get from theoretical calculations
this video is about thermite / thermate
skip the political parts of it if you want, SM isnt a place for political debates anyways
http://www.youtube.com/watch?v=LNOM_U5UM6Q
this is pretty much increasing reaction speed, with a super hot reaction thereby having a much higher reaction temperature
nano thermite should work nicely also, as its ofcourse very fast burning
the data, is that just for curiosity or do you have some actual appliance you would want to have the best of the best put in?
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blogfast25
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Malford:
Regardless even of whether some of the stated values of adiabatic temperature are correct or not, once it goes over, say (arbitrary) 4,000 K or so, it
becomes almost impossible to contain because one or both of the reaction products will vaporise. I don’t think that is what you want in your solid
rocket motors but I could be wrong on that (please clarify). And having to contain the reaction in a shell would slow things down because the heat
then needs to conduct through the shell before it hits the material to be ignited.
In that respect it would be useful to look at oxidisers that are reduced to high melting/boiling materials and reducers that are oxidised to high
melting/boiling materials.
Earth alkali sulphates are powerful oxidisers that meet that requirement, e.g.:
CaSO4 + 8/3 Al === > CaS + 4/3 Al2O3 burns extremely hot, much hotter than Thermite ™.
Other reducing agents like Mg could be used here:
CaSO4 + 4 Mg === > CaS + 4 MgO
… because MgO has an insanely high BP. If my calculation is correct that gives a value of about - 14 kJ/cm3 (or better: - 1452 kJ/mole). But I don't
like those units in this context: at the end of the day one really needs to calculate adiabatic end temperature for a fair comparison.
CaS and MgO have very high boiling points compared to lead (a measly 1750 C, a recipe for flash powder!)
Be could give a marginal improvement but it's very expensive and Be powder is very toxic.
Bear in mind also that your ignition mix will of course also have to be ignited… presumably electronically? As with Classic Thermite considerable
local heat has to be applied to get things going.
Earth alkali carbonates could also be considered.
[Edited on 9-7-2013 by blogfast25]
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bbartlog
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I don't know exactly what OP's goal is (maybe it's some for-it's-own-sake noodling around), but I just want to point out that maximizing *temperature*
of the reaction is not useful per se. Much more relevant to the goal of pushing a rocket around is the maximization of the velocity of the molecules
produced by the reaction. Since the temperature is proportional to the kinetic energy of individual molecules, there is an inverse relationship
between the molecular mass and the velocity at a given temperature. As a consequence rocket fuel tends towards small, lightweight elements.
Secondary to this, the use of lightweight molecules allows for acceptable exhaust velocities at temperatures that are still (barely) manageable with
suitable nozzle construction. Even if you have a chemical reaction that allowed for Mn + MgO vapors to be ejected at 4000 degrees C, I don't see how
you can contain or channel the resulting exhaust.
The less you bet, the more you lose when you win.
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blogfast25
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bbart: the goal here is not to use the reaction as a propellant but as a super-hot, super-fast igniter for the solid fuel propellant. BIG difference!
For CaSO4 + 4 Mg I get an adiabatic end temperature of well over 4000 K, using NIST Shomate Equations. Unfortunately the NIST Shomate Equations for
CaS only run up to 3000 K, so the vaporisation enthalpy of CaS (assuming it does boil off, I don't have a BP for CaS) is not taken into account. But
that's a relatively small error, IMHO.
[Edited on 9-7-2013 by blogfast25]
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malford
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Quote: Originally posted by IrC  | You are aware of the danger in this reaction? BeO coming from this reaction has to go somewhere, and in your lungs is the last place you want it.
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Thank you for the heads-up. Testing would be done in a booth with 1500 cfm exhaust.
| Quote: Originally posted by phlogiston | Or will you place a small very hot charge at the end of the bore so that the propellant gasses will ignite the rest of the grain (this is what is done
in the space shuttle SRB's)?
Perhaps you can put coarse pellets of a very hot thermite mix in a fast-burning matrix to get the best of both worlds. |
Allowing the solid rocket fuel to ignites the rest of itself is a great option, but I would like try and ignite it all nearly instantaneously, when
the button is pressed. It seems that a material hotter and more energetic than the fuel itself would be able to ignite the core faster than a small
area of the fuel itself. Addressing your second point, that is exactly what I had in mind! I was leaning towards nitrocellulose or binder like HTPB.
| Quote: Originally posted by AndersHoveland | The reaction between Beryllium and Oxygen releases more energy per unit weight (24.36 kJ/g) than any other combination of elements.
The reaction between Lithium and Fluorine is almost as energetic (23.75 kJ/g). Theoretically, burning Be with ozone would yield 26.26 kJ/g.
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I believe for my purposes, reactants that are liquid or solid at room temperature would greatly increase the convenience, however, thank you for the
input. Perhaps, you have helped me narrow the choices a bit. What is the best oxygen donor to use with Be? Would it be the compound that has a lot of
oxygen and low enthalpy of formation?
| Quote: Originally posted by woelen | @malford: I think that you need to search for a combination of reagents, which gives solid or liquid products only, keeping all heat inside the
reaction mix and not allowing for pressure buildup due to production of gas.
@phlogiston: I2O5 is quite volatile and decomposes above a few hundred C. I have a few tens of grams of this chemical and I noticed that it is not
really stable, it easily decomposes on heating, giving oxygen and iodine (with the lower oxide I4O9 as intermediate product). One of the reaction
products (Ta2O5) is a refractory solid, but I2 will be a gas at the reaction temperature. How can this in practice work? Doesn't it lead to explosion,
due to pressure buildup? |
I have thought much about this issue. I currently do not believe that the products need to be solid or liquid. The reaction will take place in the
core of a solid rocket motor. This provides a level of confinement that allows most of the heat in the escaping product gasses to be absorbed by the
fuel which is at a much lower temperature. The core would be open to the atmosphere through the nozzle, preventing an explosive build up of gasses.
So, in other words, even if the products are gasses, as long as they are very high temperature gasses, they will ignite the fuel, the core of which
they are being forced through. In theory, this might even be better than solid or liquid products because the gas will have the ability to uniformly
ignite the highly irregular core shape.
| Quote: Originally posted by blogfast25 | Regardless even of whether some of the stated values of adiabatic temperature are correct or not, once it goes over, say (arbitrary) 4,000 K or so, it
becomes almost impossible to contain because one or both of the reaction products will vaporise. I don’t think that is what you want in your solid
rocket motors but I could be wrong on that (please clarify). And having to contain the reaction in a shell would slow things down because the heat
then needs to conduct through the shell before it hits the material to be ignited.
In that respect it would be useful to look at oxidisers that are reduced to high melting/boiling materials and reducers that are oxidised to high
melting/boiling materials.
Earth alkali sulphates are powerful oxidisers that meet that requirement, e.g.:
CaSO4 + 8/3 Al === > CaS + 4/3 Al2O3 burns extremely hot, much hotter than Thermite ™.
Other reducing agents like Mg could be used here:
CaSO4 + 4 Mg === > CaS + 4 MgO
… because MgO has an insanely high BP. If my calculation is correct that gives a value of about - 14 kJ/cm3 (or better: - 1452 kJ/mole). But I don't
like those units in this context: at the end of the day one really needs to calculate adiabatic end temperature for a fair comparison.
CaS and MgO have very high boiling points compared to lead (a measly 1750 C, a recipe for flash powder!) |
Please see above regarding containment and vaporization of products. Thank you for the tip on CaSO4. I will research this more.
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blogfast25
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Malform:
If containment is of no great concern, look at potassium chlorates/perchlorates/nitrates. As oxidisers, these would be almost as powerful as I2O5 (for
instance) but perfectly stable at RT, as well as easy to handle, size reduce or even bind in a nitrile binder or such like. Chlorates and perchlorates
boil off KCl, nitrates elementary K and N.
I've worked with all of them, as well as CaSO4, and if these don't work I don't really know what would.
[Edited on 9-7-2013 by blogfast25]
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malford
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Here is an updated chart with more reactions and one error corrected.
After observing the results, I have hypothesized that since Be and O is the most exothermic reaction physically possible, the quest now is simply to
find the best O donor to react with Be, because I cannot have O solid at room temperature. The idea of a liquid could at least be entertained, because
it could sealed in a capsule with the Be powder. Based on the chart and logic, a compound that has the most O with the lowest enthalpy of formation
will make the best oxidizer. It gives the most oxygen to the fuel while robbing little heat. I tested this hypothesis with the last entry on the chart
(N2O5, a white powder) and it rang spectacularly true. Basically, the A column under formation enthalpy should be low while the D column should be as
high as possible.
The entirety of my chemistry background extends 3 weeks and inevitably that shows, but am I barking up the right tree with the above statements?
Also, I am mainly concerned with kJ/cm3, because for a given igniter size, which is restricted by the opening in the rocket nozzle, I want the most
heat. I am not restricted by weight.
Update: I added KClO4 + Be to the list and the H kJ/g is -13.52 and the H kJ/cm3 is -33.58. Stoich is 15.37:1
[Edited on 10-7-2013 by malford]
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blogfast25
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Malford:
I believe substances like N2O5 simply won’t work, at least not without containment, because they aren’t stable enough and are too volatile. I
could be wrong on that.
Reactions between a solid oxidiser and a solid reducer tend to proceed via a reaction front: a layer that burns from the ignition point right through
the whole mass. If the reaction front is very hot and the oxidiser volatile/unstable, fizzling can occur. Jeffrey Schwartz (AmazingRust.com)
encountered that problem with an Ag2O/Al thermite: despite the promise of massive ΔH, the mixture couldn’t be lit and fizzled because the Ag2O
fell apart prematurely (on ignition). In the case of an N2O5/Be reaction only experiment can tell whether fizzling would occur, of course.
You need to ask yourself whether it is really worth pursuing a few extra kJ/cm3 with very exotic materials (like Be and N2O5) when you can reach a
theoretical 4000 K with very standard materials… BTW: the stable equivalent of N2O5 is... nitrate. Stoichiometrically speaking: 2 KNO3 = N2O5 + K2O
[Edited on 10-7-2013 by blogfast25]
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woelen
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| Quote: | | You need to ask yourself whether it is really worth pursuing a few extra kJ/cm3 with very exotic materials (like Be and N2O5) when you can reach a
theoretical 4000 K with very standard materials… |
Exactly, you precisely hit the nail. This also was my
remark when I responded to the post of AndersHoveland. Of course, if you search long enough then there certainly will be some super-efficient and
super-hot composition which does what you want, but in the end you may not come further than a lot of theory. Availability and cost of reagents is one
concern. Construction and dealing with exceedingly corrosive and toxic materials is another concern. For example, how would you handle stuff like
N2O5, which decomposes in a matter of weeks at room temperature, is insanely corrosive (fuming nitric acid is a children's toy compared to this) and
is very volatile? If you really want to pursue perfect ignition properties, then I would try to find a nice solution, which is very hot (but not the
hottest imaginable) and uses common, easy to get, cheap reagents. Next, I would try to search in other directions, such as physical construction, how
is the igniter embedded in the fuel and that kind of things. Most likely you know much more about that than I do, I just want to add some new
directions of thought.
This is a typical example of dimishing returns on increased effort. Getting the last 10% of improvement requires 90% of the effort (and cost, and
risk). Once you reach this point, it is time to step back, and try to think in other directions.
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ScienceSquirrel
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The combustion of cyanogen 4795 °K or dicyanoacetylene 5260 °K in pure oxygen produces extremely hot flames.
However cyanogen is a toxic gas and dicyanoacetylene has a nasty habit of exploding spontaneously.
http://en.wikipedia.org/wiki/Cyanogen#Safety
http://en.wikipedia.org/wiki/Dicyanoacetylene
[Edited on 10-7-2013 by ScienceSquirrel]
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malford
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My goal here is to find the theoretically most exothermic composition physically possible, then I will do a cost analysis and see if it is worth the
extra performance. First, however, I must have these data to analyze!
So, by fizzling, you mean one of the reactants boiling away from the reaction from prior to being reacted? This could probably be remedied by the used
of a binder like nitrocellulose or HTPB. Further, mixing in with the binder a small amount of something that burns fast such as KClO4+Al along with
something like I2O5 + Be would probably allow the reaction front to proceed quickly enough to complete the reaction before the heat of the reaction
has time to convect through the material and boil off unreacted reactants.
What I will do now to test the overall heating ability of these compositions, is create an igniter with an amount by volume, seal it with an
ultra-thin plastic wrapper (think Saran wrap), immerse it in, say, 500 ml of water, then measure the change in temperature of the water. I understand
this will not be an indication of the total energy produced by the reaction, as much of it will escape with the gasses produced, but it will be an
excellent indication of which compositions are most capable of heating the material around them. Thoughts?
[Edited on 10-7-2013 by malford]
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blogfast25
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| Quote: Originally posted by woelen | | Next, I would try to search in other directions, such as physical construction, how is the igniter embedded in the fuel and that kind of things. Most
likely you know much more about that than I do, [...]. |
Hear, hear! Of course practical implementation is as important as theoretical considerations. Hot but stable igniters that could, perhaps
Semtex-style, be embedded in the solid rocket fuel would probably be a bonus, compared to hard-to-handle, short shelf-life but potentially
hotter devices.
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blogfast25
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By fizzling here has to be understood premature decomposition/volatilisation of the oxidiser: if your mixture starts flying apart before full
combustion has been achieved you won't realise the full enthalpy potential of the igniter.
Make sure you have enough water and strong stirring there to avoid steam explosions! I'm not sure whether water based calorimetry is really what you
want to be doing here. Sounds more like something for a bomb type calorimeter, possibly with pressure vent or without if you only test very small
amounts of mixture.
Before any calorimetry I'd run a few select mixtures, just for a visual: much can often be deduced from naked eye observation.
[Edited on 10-7-2013 by blogfast25]
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