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Author: Subject: HYDRAL - frozen aluminium hydrazine rocket system
deltaH
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[*] posted on 5-11-2015 at 11:10
HYDRAL - frozen aluminium hydrazine rocket system


Building on the ALICE rocket propellant (ice + nano aluminium powder), I have an idea for using frozen hydrazine + aluminium powder.

The combustion reaction being:

2Al(s) + NH2NH2(s) => 2AlN(s) + 2H2(g)

I call it a HYDRAL rocket (or ALAZINE if you preffer).

Some numbers:

HYDRAL:

dHrx° = 8kJ/g propellant (calculated with liquid hydrazine)
V_H2 = 521sccm H2/g propellant

ALICE:

dHrx° = 7.6kJ/g propellant (calculated with liquid water)
V_H2 = 622sccm H2/g propellant

So the HYDRAL system has a slightly higher energy density, but lower gas volume, but the big win comes in with reactivity, in the case of ALICE, nano aluminium has to be used for fast enough burn rates, however, hydrazine is much more reactive than water, so ordinary aluminium powder should suffice... much simpler!

I have not found much on the reaction of aluminium and hydrazine exept for this paper:

http://www.sciencedirect.com/science/article/pii/03682048808...

That attests that hydrazine can be decomposed on the surface of aluminium to hydrogen and nitride (i.e. the all important N-N bond breaking).

Unfortunately, this would require working with anhydrous hydrazine, which is very dangerous, but so too is nano aluminium in the case of the ALICE system.

The freezing point of anhydrous hydrazine is +2°C, so that's easy enough to work with.

Thoughts?




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[*] posted on 5-11-2015 at 22:50


Sounds like a suicide tought :o
Do you have anhydrous hydrazine?
Hydrazine hydrate is alkaline enough to react with Al.
Also,some oxidiser would be great to burn the H2 that is generated.
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[*] posted on 6-11-2015 at 02:29


I am sorry to deviate the topic a little bit from its target but I would like to know how would you reach nano Al powder?
is it possible to reach 80-5 nm using homemade ball mill ? but how much would it take to mill till this size?


I checked the ALICE propellent, I think using water is not the best option, the better reaction would be :
3ZnSO4.7H2O(s)+22Al(s)→11Al2O3(s)+3Zn(s)+3S(s)+21H2(g)ΔH=−9,199 kJ

This is stated in : Method for Manufacturing Energetic Material Composites
US 20120216926 A1

[Edited on 6-11-2015 by ecos]
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[*] posted on 6-11-2015 at 06:05


@Ecos:

Ball milling alufoil flakes for 2-3 weeks in a near airtight drum (and letting it rest for a week before opening!) produces a blueish grey powder that reacts very vigorously. It's like a very dense flour, aluminium oxide content and particle size unknown. It's more reactive though than commercial dark aluminium powder, so I'm guessing you can go sub micron this way. Finest alu powders are made using explosive vaporization in an inert (helium or so) atmosphere (ALEX), that was years ago, maybe more easy production methods have developed by now.

[Edited on 6-11-2015 by nitro-genes]
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[*] posted on 6-11-2015 at 09:50


Quote: Originally posted by ecos  
I am sorry to deviate the topic a little bit from its target but I would like to know how would you reach nano Al powder?
is it possible to reach 80-5 nm using homemade ball mill ? but how much would it take to mill till this size?


I checked the ALICE propellent, I think using water is not the best option, the better reaction would be :
3ZnSO4.7H2O(s)+22Al(s)→11Al2O3(s)+3Zn(s)+3S(s)+21H2(g)ΔH=−9,199 kJ

This is stated in : Method for Manufacturing Energetic Material Composites
US 20120216926 A1

[Edited on 6-11-2015 by ecos]


Interesting, but I think you made a mistake with your equation, it wouldn't make zinc and sulfur but rather zinc sulfide:

3ZnSO4.7H2O(s)+22Al(s)→11Al2O3(s)+3ZnS(s)+21H2(g)

The higher energy content is no surprise, because sulfate is a much stronger oxidant than water, BUT your specific gas volume produced will be much less with this reaction. That's why I always look at both numbers.

You can always get more heat by adding an oxidant with aluminium, in fact, zinc sulfate is a little puzzling, why not use calcium nitrate tetrahydrate (a far better 'wet' oxidant) and get even more heat. and make calcium aluminate as the product etc.

As is being discussed in another thread, aluminium + H2O2 produces much more thrust than ALICE because again, it's a much better oxidant than water. Hydrazine is a compromise, it has a high hydrogen content but also energetic, so you get the best of both worlds.



[Edited on 6-11-2015 by deltaH]




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[*] posted on 6-11-2015 at 14:18


Hi DeltaH,

This is not my equation , I got it from this patent : Link

I think you are right regarding ZnS , I think this is also a propellent with Isp=50 :).

H2O2 would be a better oxidizer but it has high cost and safety precautions is needed. (I am not sure about stability)

Hydrazine would be superior but the same probls : higher cost and very toxic.

Thats why I like the idea of the patent regarding hydrated compounds. There exist a table inside the patent for different compounds.

do you plan to make any experiments or just logical thinking ?





[Edited on 6-11-2015 by ecos]
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[*] posted on 7-11-2015 at 01:38


Hi ecos,

Thanks for that, yes the hydrates are an interesting twist. I will think on it some more. Never realised Na2S had so many crystal waters :o

For now, HYDRAL is out of my reach for testing, but hydrates are more amateur friendly, so only a thought experiment for the time being and for others if they're interested in it.

The HYDRAL notion has a far more exotic parent: https://www.sciencemadness.org/whisper/viewthread.php?tid=56...

That being a DARPA-style idea for a super gun (light gas cannon) propellant. You gotta love that Isp of 1300/s :D Funny nobody said that it's impossible? :o



[Edited on 7-11-2015 by deltaH]




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[*] posted on 7-11-2015 at 02:04


Hi DeltaH,

Na2SO4.10H2O has many water crystals but reacts fast with Al which make it not a good choice. it also would make it sensitive to any heat !

the patent stated :
Quote:

Some hydrates, such as Glauber's salt (Na2SO4.10H2O), can be melted (at 32° C.). This allows the fuel powder to be mixed in directly without the need for a solvent. When nanoaluminum is mixed in at room temperature (25° C.), it begins to release hydrogen within a few minutes, making it impractical without some pH buffering of the solution or coating of the particles.


I hope to see your results for your experiments on hydrates :) . I am still investigating how to reach nano Al. it would take more than 1 month in a ball mill to reach 5 nano :(

for DARPA-style idea , I think it would make super gun for sure :D
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[*] posted on 7-11-2015 at 03:55


I was talking about sodium sulfide, not the sulfate... but the mix up is all too easy to make. According to wiki and the patent, the sulfide comes in a low melting nonahydrate that has an impressive water density.

Ideally you want something that passivates aluminium nicely, the sulfides might just do that, sulfur bonds on very firmly to metal surfaces.

[Edited on 7-11-2015 by deltaH]




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[*] posted on 7-11-2015 at 17:19


I found the clue for nano Al. You should use planetary ball mill for this

video : https://www.youtube.com/watch?v=5ShOAS3EGGU

from Wikipedia :

Quote:

Aside from common ball mills there is a second type of ball mill called a planetary ball mill. Planetary ball mills are smaller than common ball mills and mainly used in laboratories for grinding sample material down to very small sizes. A planetary ball mill consists of at least one grinding jar which is arranged eccentrically on a so-called sun wheel. The direction of movement of the sun wheel is opposite to that of the grinding jars (ratio: 1:-2 or 1:-1 or else). The grinding balls in the grinding jars are subjected to superimposed rotational movements, the so-called Coriolis forces. The difference in speeds between the balls and grinding jars produces an interaction between frictional and impact forces, which releases high dynamic energies. The interplay between these forces produces the high and very effective degree of size reduction of the planetary ball mill.


I wonder how I would build such mill. It seems very complex ! :(
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[*] posted on 7-11-2015 at 22:51


Building is not that simple. My school dont even has one :o (Chemical enginier)
Has a good price too. Imagine the black powder made there :)
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[*] posted on 7-11-2015 at 23:42


I think if you move away from using water, then you can get away with conventional pyro-aluminium powders. Granted, hydrazine might be too toxic and hard to work with for the amateur but there might be other pseudo-fuels to use, for example, what about urea?

You probably wondering what an aluminium powder and urea would react to form... that's a good question!

Initially upon heating just above its melting point, urea decomposes to form cyanuric acid and ammonia. We might assume that aluminium would react to form aluminium cyanurates and aluminium nitride from these, releasing hydrogen and heat. But at high temperature, metal cyanurates decompose further to liberate CO2 and form metal cyanamides. CO2 might be reduced by aluminium at high temperature to CO and aluminium oxide? So all in all, you might expect the formation of aluminium cyanamide, aluminium oxide, aluminium nitride, carbon monoxide and hydrogen gas.

Idealised hypothetical stoichiometry for an aluminium-urea reaction:

6(NH2)2CO(s) + 10Al(s) => Al2(CN2)3(s) + Al2O3(s) + 6AlN(s) + 3CO(g) + 12H2(g)

The nice thing about urea is that you might cast it by carefully melting at 135C (but no hotter!). There is, of course, the danger of self-ignition, so this would need to be experimented with under very controlled conditions and safety methods in place and small amounts.

Cyanuric acid that starts to form upon melting urea (also ammonia) is a very weak acid, so I doubt it would etch the passivating aluminium oxide layer over the aluminium powder at those temperatures, but still... I'm not *sure* about it.

The resulting casting would be very dense and hard, which would be great for a rocket engine.

Bert, where are you?

Reference:

Cyanuric Acid and Cyanurates
www.sciencemadness.org/talk/files.php?pid=185660&aid=112...

[Edited on 8-11-2015 by deltaH]




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[*] posted on 8-11-2015 at 01:32


Okay, I did some back-of-the-envelope thermodynamics.

I couldn't find any standard heats of formation for aluminium cyanamide, so I modified the equation by adding more aluminium and assuming this would react with aluminium cyanamide to form aluminium carbide and more aluminium nitride, so that I can use known values of standard heats for aluminium carbide and nitride:

6(NH2)CO(s) + 18Al(s) =>Al4C3(s) + Al2O3(s) + 12AlN(s) + 3CO(g) + 12H2(g)

The specific enthalpy of reaction is a paltry -4.7kJ/g for such a fuel :(

Specific gas volume is also only a paltry 397sccm/g fuel mix.

So performance would be shitty, but then it's so easy to make, possibly very safe and cheap, so I don't know...

[Edited on 8-11-2015 by deltaH]




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[*] posted on 8-11-2015 at 02:07


Some more thermodynamics, I thought I might compare the heats with another low melting fuel, like xylitol. The equation considered:

3C5H12O5 + 30Al => 5Al4C3(s) + 5Al2O3(s) + 18H2(g)

I was surprised to find that xylitol performs slightly worse than urea theoretically:

Specific standard heat of reaction: -4.6 kJ/g reagents
Specific gas volume: 318sccm/g reagents

I suppose this is because the xylitol is acting as an oxidant in this case and xylitol is a better fuel (reductant) than urea, so a worse oxidant.

But it's nevertheless still surprising to see that you might launch a candy rocket that contains no oxidant at all :o

Xylitol melts at 92C, so a xylitol-aluminium powder mix should also be readily castable.

[Edited on 8-11-2015 by deltaH]




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[*] posted on 8-11-2015 at 04:35


Quote: Originally posted by kecskesajt  
Building is not that simple. My school dont even has one :o (Chemical enginier)
Has a good price too. Imagine the black powder made there :)


I read some documents about this machine.
I can build similar one that can do the same functionality but I miss some parameters here.
I don't know what should be the optimum speeds for the both moving parts. I also miss the size of the jar ,the circular moving disk,..... !.

If i have all parameters I think I can build similar one. :)
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[*] posted on 8-11-2015 at 04:38


Quote: Originally posted by deltaH  
Some more thermodynamics, I thought I might compare the heats with another low melting fuel, like xylitol. The equation considered:

3C5H12O5 + 30Al => 5Al4C3(s) + 5Al2O3(s) + 18H2(g)

I was surprised to find that xylitol performs slightly worse than urea theoretically:

Specific standard heat of reaction: -4.6 kJ/g reagents
Specific gas volume: 318sccm/g reagents

I suppose this is because the xylitol is acting as an oxidant in this case and xylitol is a better fuel (reductant) than urea, so a worse oxidant.

But it's nevertheless still surprising to see that you might launch a candy rocket that contains no oxidant at all :o

Xylitol melts at 92C, so a xylitol-aluminium powder mix should also be readily castable.

[Edited on 8-11-2015 by deltaH]


I think Erythitol would be better than xylitol. it has higher H/C ratio.
do you have any estimate about the Isp for the above mixtures?
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[*] posted on 8-11-2015 at 04:57


The difference between erythritol and xylitol would be very minor, BUT xylitol has a lower melting point, which is safer. There is also an erythritol/xylitol eutectic with an even lower melting point. I have the paper on the xylitol calcium oxide putty thread.

But really the candy versions are pointless IMHO seeing as though the urea version has better specs and is MUCH cheaper,

I don't have an Isp calculated because I would need an adiabatic flame temperature which would be just too much of a pain to calculate for these complex mixtures without some software that gives shortcuts.

If anybody has such software, I would greatly appreciate some values, particularly for the urea one.




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[*] posted on 8-11-2015 at 12:16


Why not simply hydrazine hydrate (NH2-NH3OH = H2N-NH2.H2O or 80% hydrazine solution) sprayed on porous Al sponge?
So you get a little Al2O3, a lot of H2 and N2.

In place of urea maybe using H2N-NH-CO-NH-NH2...
or salts like ammonium, hydrazinium or hydroxylamonium sulfate or carbonate

(NH4)2CO3/Al should be good!




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[*] posted on 8-11-2015 at 14:43


How much aluminium powder do you guys need for a planetary size ball mill?! :) Seriously though, never heard of them before, guessing it creates way more friction than a tumbler.

Regarding the urea/sorbitol + nano aluminium powder propellants, is there a burn rate or pressure exponent known for similar kind of propellants? I'm guessing slow burnrates (if any at atmospheric pressure) and very small pressure exponent, meaning you would have to run ridiculously high chamber pressures with something that burns exceedingly hot, without much gas production. Im picturing a thermite rocket or similar. :)

An epoxy style amateur friendly propellant using AN would be a good use of the nano Al IMO, maybe hard to get reliable as avg. particle size and oxide content can be different between batches. :)

[Edited on 8-11-2015 by nitro-genes]
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[*] posted on 10-11-2015 at 04:57


planetary ball mill is classified as high energy mill. It depends on the centrifugal force rather than the gravity as other in ball mills.
if the rotation speed is high the media would have enough energy to strike the Aluminium with more power. This is nice idea which would save much but but the probability of hazards would increase since the sparks might exist.
it would take time to make a similar one. I found many patents for designs on google.

AN+Al+epoxy is not that good propellent, it has a lot of challenges. you will find experiments here : http://www.nakka-rocketry.net/anexp.html
AN tend to cake and is very hygroscopic :( ....blah blah.

I think any compound that has hydrate + Al might be a very good propellent. I think if urea hydrate exists it would be better than urea alone

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[*] posted on 10-11-2015 at 07:49


It was nakka's experiments indeed that I had in mind, I was thinking that the disadvantages of normal aluminium powder in these types of propellants may be overcome by the use of nano aluminium, but perhaps not. :)

Other idea might be urea-peroxide adduct for use in propellant, don't know if it has been mentioned before and possible compatibility issues with aluminium powder (wouldn't directly think so), it is rather easy to make though. May need some down-tuning to prevent explosion instead of burning though.

https://en.wikipedia.org/wiki/Hydrogen_peroxide_-_urea

[Edited on 10-11-2015 by nitro-genes]
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[*] posted on 10-11-2015 at 11:12


Carbamate peroxide (urea hydrogen peroxide) might be a fantastic idea... if it won't explode or spontaneously ignite, but it might well not. Pity you won't be able to melt cast it though :(

[Edited on 10-11-2015 by deltaH]




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[*] posted on 11-11-2015 at 00:53


Quote: Originally posted by nitro-genes  
It was nakka's experiments indeed that I had in mind, I was thinking that the disadvantages of normal aluminium powder in these types of propellants may be overcome by the use of nano aluminium, but perhaps not. :)

Other idea might be urea-peroxide adduct for use in propellant, don't know if it has been mentioned before and possible compatibility issues with aluminium powder (wouldn't directly think so), it is rather easy to make though. May need some down-tuning to prevent explosion instead of burning though.

https://en.wikipedia.org/wiki/Hydrogen_peroxide_-_urea

[Edited on 10-11-2015 by nitro-genes]


I checked Nakka experiments and found him using : Aluminum (atomized powder <60µm from Axson Technologie)

if he would use nano Al he would have better performance and the results might change but this won't solve the challanges of AN :
1-hygroscopic nature
2-known to be very hard to ignite
3-experiences phase change at room temperature which means that it cannot be stored it in an easy way


Hydrogen peroxide urea would explode because of the very high temperature and pressure generated inside the rocket motor !

hmmm :) I was thinking now in a funny way. since Al and water is a propellent then AN+Al+water would be better propellent. the hygroscopic nature might be an advantage here :)

[Edited on 11-11-2015 by ecos]
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[*] posted on 11-11-2015 at 03:40


Very good idea, compared to ALICE, a flash frozen (liquid N2 or something) ammonium nitrate/nano aluminium propellant might be even better! In case of a flash-frozen ammonium nitrate emulsion type composition (used in mining) +aluminium, the propellant may have increased storage stability as well, even at RT and could be moulded into the shape and then flash-frozen before launch.

The hygroscopic nature is also something encountered for regular RC propellant, although sucrose is non-hygroscopic, the heat treatment leads to formation of mono saccharides, which do absorb moisture from the air (rel. humidity over here us usually around 80-90%), when corn syrup is used to control crystal size, the propellant is incredibly hygroscopic. I used to store it in sealed glass jar with silica gel to prevent this, same way I store my finely powdered AN. According to some patents, the phase change of ammonium nitrate can be prevented by a small percentage of zinc salts IIRC, something I have never tried.

I would think that a nano aluminium/AN propellent instead of 60 um atomized would lead to better ignitability and higher burnrates. Though these guys probably had a good reason to use atomized, thinking flake Al may lead to very unpredictable propellant behaviour, depending on the batch of aluminium used. :)

[Edited on 11-11-2015 by nitro-genes]
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[*] posted on 11-11-2015 at 10:16


I think some here are underestimating the power of nano-aluminium.

If you want to see just what these nanometals can do in combination with oxidants, see our very own dornier335a:

https://www.youtube.com/channel/UC6SItJwaTE3jawp-wGNKPBQ

Urea and pyroaluminium... ok
Urea and nanoaluminium... ehhh... maybe ok?
Peroxide or AN and nanoaluminium... BOOM!

[Edited on 11-11-2015 by deltaH]




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