9 replies to this topic

[Boffin]

I understand the venerable 65/35 KNO₃/sugar propellant is easy to cast, isn't very hygroscopic and offers a good, stable burn.

65/35 NaNO₃/sugar has a theoretically better performance (due to the lighter Na+ ion compared to the K+ ion, hence better specific impulse) but is more difficult to cast, is hygroscopic and tends to sputter without a burn rate catalyst (e.g. 1-2% Fe₂O₃).

What about Ca(NO₃)₂? The stuff has potentially even better performance than NaNO₃ (20g of Ca++ ions for 1 moles of NO₃, compared to 23g of Na+ ions for 1 mole of NO₃), but its performance as a propellant is poorly documented. Or Al(NO₃)₃?

Also, has anyone had any experience with calcium ammonium nitrate (5Ca(NO₃)₂.NH₄NO₃^.10H₂O) propellant? What happens if you try to heat it to convert it to an anhydrous form to drive off the otherwise inert water molecules that just add mass?

[seymour]

I have a friend who is in to high power experimental rocketry, who looked at those salts and thought the very same thing about the high oxygen content.

He found them to burn badly and be unusably hygroscopic. Indeed, I myself have had a mixture of Sodium nitrate and sucrose dissolve its self in absorbed moisture, and overflow from the dish it was in. (The situation was worsened by impure Sodium nitrate, and high humidity, but you still get the point)

I think the fact that Potassium nitrate is still the pretty much exclusive oxidiser of choice for sugar fuels points out that the alternatives are flawed. There are so many people experimenting with these fuels, that if these other common nitrates workes as well as they look capable of, they would be widely used.

I'm sorry that I have such a pessimistic reply for you. I certainly don't want to prevent you from experimenting.

Good luck, Stay green!

[Boffin]

Have you thought about putting additives to the mix (e.g. 1-2% wax or paraffin to replace some sugar) or sealing the propellant away to try to ameliorate the hygroscopicity? How effective were these?

Also, I note that Ca(NO₃)₂ has an NFPA classification of 3 for instability/reactivity, compared to 0 for KNO₃ and NaNO₃. Does anyone have any experience with the stability of a Ca(NO₃)₂-sugar mixture?

Edited by Boffin, 02 June 2010 - 03:02 PM.

[a_bab]

It won't work. Period.

As everybody said before not only it would have been in use by now if it would, but calcium nitrate needs a higher temperature to start decomposing so the oxigen kicks in burning the heck out of your suncrose. The

Hygroscopicity is so important that even parafine won't do a thing; you'll find dropplets of water on the surface of your fuel rod hours after casting it.

Ca nitrate *may* work with some resin binder system though, but hygroscopicity would still pose a problem.

[Mumbles]

Sodium nitrate can work in rockets if you do it right. A 50:50 mix of sodium nitrate and magnesium is painfully bright. It definitely needs to be protected from moisture though, for more than one reason. There is something about sugar that really exacerbates any hygroscopic nature of potassium or sodium nitrate.

[a_bab]

Mumbles, isn't Mg+NaNO3 the brightest mix available in terms of light output? Or at least close?

I discovered it by accident and it really, really is VERY bright. I even planned to make a kind of "lampare" shell with the mix, that would go "poooof" and create a huge yellow flash. It's so bright that the classical Al+BaNO3 looks like a candle.

As about moisture in this specific mix, you are very right: I kept mine outdoors for a day or so; the Mg turnings all became a crumbly thing, although they apparently looked almost ok. Needless to say, the mix didn't work anymore.

[Potassium chlorate]

NaNO₃+Mg gives a tremendous yellow flash, right. It says "WHOOF!" while going off, if you make the stochiometric 86:14 mix.

[BrightStar]

...if you make the stochiometric 86:14 mix.

5Mg + 2NaN03 —> 5MgO + Na2O + N2

41.6 : 58.4 (Mg : NaNO3)

However, optimum light output is achieved with an excess of Mg burning in atmospheric oxygen. A typical illuminating flare might be:

Magnesium: 58
Sodium Nitrate: 37.5
Binder (usually Laminac): 4.5

Source: Ellern

Edited by BrightStar, 03 June 2010 - 09:51 PM.

[Mumbles]

Of commonly available things, it certainly is up there in terms of maximum brightness. The only thing that comes to mind that might be brighter is armstrong titanium. Extremely fine, and can be extremely bright.

I've never played around with the ratios too much. The 50:50 mix can be used for rockets, gerbes, and stuff, where excess gas is preferable. It might not be at it's brightest, but it still will leave you practically blind.

[vaslop2005]

I also looked at that formula, and was greatly impressed, here are two more compositions I devised

50 NaNO3
20 MgAl (-250#)
20 Charcoal, (airfloat)
10 Sulfer
bound with NC lacquer, produces amazing illumination flares... but they do need priming. (developed to be cheaper than Mg mix)

50 NaHCO3 (yes bicarbonate of soda)
50 Mg granules
This one is quite strange, but even brighter than the NaNO3 version...! and I tested 5g on a brick, and it illuminated the field like an orange sun.

something to play around with, but be weary, I used some 230 mesh magnesium with sodium nitrate, and it scared the crap out of me...!