26 replies to this topic

[newtoolsmith]

Hi friends,

sitting here and reading a lot stuff about rocket motors, I noticed the many times there were questions about the use of ammoniumnitrate as an oxidizer in rocket fuels.

The biggest disadvantage seems to be the hygroscopicity.

Cant this problem be solved by using paraffin as the fuel?

I think it should be possible to mill the nitrate down to dust and add a slight excess of molten paraffin. Just enough to ensure that all nitrate particles are fully covered by the fuel.

The high ignition temperature is a further disadvantage but I think we can even let this work for us...

Now we have to ask: are there advantages?

Yes, there are some.

Ammonium nitrate is very easy available even in tons because it is a common used fertilizer.

Ammonium nitrate is very cheap, mmuch less expensive than KNO3.

The mixture would be easier to produce than BP and it should be possible to press or ram it into motor casings very similar to BP.


Did anyone try this?

Does anyone agree or disagree?

Any errors in reasoning?


MfG
newtoolsmith

[pyrotrev]

I've never tried this but know that NH4NO3 (AN) and polyurethane/polybutadiene derived resin mixtures have been used sucessfully by HPR amateurs. Don't know about the burning rates, but AN theoretically has an advantage over NH4ClO4 (AP) as an oxidiser in that the molecular weight of the combustion products are smaller (no HCl) leading to a higher exhaust velocity and more power. However an AN/paraffin wax mixture is worryingly similar to a HE mix used by people of evil intent, so I would tend to be very afraid and stay well clear of it!!!! For some references see [url=http://rocketsciencebooks.home.att.net/set3-an.html], or rec.models.rockets.
PS Maybe this should be in the rocketry section???

Edited by pyrotrev, 06 January 2007 - 12:58 PM.

[newtoolsmith]

Another advantage would be that all reaction products will be gases.

When KNO3 is used, K2O will be formed wich is a solid at low Temperatures. Im not sure, if the K2O will be gasified at the temperature we reach.

The higher potential following thereof will allow to lift payloads with less motor weight or greater payloads with the same motor weight.

Of course handling Ammonium nitrate makes one think about NH4NO3/petrol mixtures and other high explosives. On the other hand, we all promised not to produce such materials and we should keep this promise!

I should do some tests to ensure I didnt post how to make a expolsive comp.

Maybe this post should be in the rocketry section because its for rocketry use only.

MfG
newtoolsmith

[.:HAMMER:.]

correct me if im wrong, but nh4no3 serves as the oxidixer. i use ammonium perchlorate (NH4CLO4). it yelds four oxygen molecules to the nitrates three. it pretty cheep too.

[spanner]

Ammonium nitrate is a viable oxidiser, but it's used with a binder like HTPB. This takes the use of AN from the "easy and cheap" to the opposite end of the spectrum real quick.

If you are going to the trouble and expense of casting grain for composite motors, you might as well just use ammonium perchlorate from the get go, and take advantage of the assets it offers.

[newtoolsmith]

@.:HAMMER:. :

I didnt know that NH4ClO4 is cheap!!

PLease PM me and tell me more - I really want some!

Where I come from its not available at all.

MfG
newtoolsmith

[TzaRocket]

Let me tell you a recepi made by me and works good.This is a recepi for thoseho dont have sulfur.Just replace the sulfur whit powdered sugar (the formula is the same:75/15/10).Itworks well and gives a color diferent from the orinal black powder.Try it if you want and dont be disapointed is it doesnt burn wery well ,just make a rocket whit it and see how it flys

[pyrotrev]

@.:HAMMER:. :

I didnt know that NH4ClO4 is cheap!!

PLease PM me and tell me more - I really want some!

Where I come from its not available at all.

MfG
newtoolsmith

It's not easy to get in the UK - if only ....... I'd love to make some stars with it.

Edited by pyrotrev, 18 January 2007 - 12:49 AM.

[alex000]

It's not easy to get in the UK - if only ....... I'd love to make some stars with it.

well if anyone can get it I will be willing to buy some.
Thanks

[selwyndog]

Ammonium nitrate based fuels have exhaust gas velocities in the region of 2200m/s compared to GP 800m/s odd. A good formulation is ammonium nitrate 240g aluminium powder 40g and styrene/peroxide binder 14g. The mixture is quite sticky and has to be placed into the rocket casing before the styrene/peroxide cures.
Ammonium Perchlorate exhaust gas velocity is about 2400m/s so only a 10% increase in impulse over ammonium nitrate formulations.
NH4NO3 burns fairly cool, produces very little toxic exhaust and is dirt cheap realitivly availible and very stable. To be used as an explosive it requires a detonator/booster and large charge size to perpetuate the detonation wave.

[leosedf]

Can you give more info on styrene/peroxide binder ?

[selwyndog]

Can you give more info on styrene/peroxide binder ?

It's the resin used for fibre glass repairs. The fibre glass repair kits are availble from halfords for a few quid. They're styrene based, the peroxide is just the polymerisation initiator, low levels of peroxide lead to slower curing rates, as does keeping the mixture cool. The end product is quite brittle but presents few problems if cast into a tube. Stronger formulations can be prepared by altering the ratio of binder to other fuel components. The addition if fibres also reinforces the material. Hope this is of use.

[leosedf]

Can't we use a different binder?

[selwyndog]

Can't we use a different binder?

Other binders work well, I like using strene based ones as there is a place which makes fibreglass parts by me where I can get gallons of the stuff real cheap.

[BrightStar]

A good formulation is ammonium nitrate 240g aluminium powder 40g and styrene/peroxide binder 14g.

Interesting that you can use ordinary polyester / styrene fibreglass resin. Looks like the Al is the main fuel here if the proportions are correct, as opposed to the dual purpose fuel/binder resin used with AP. Do you have a web reference for more info on this AN based formula or similar ones?

Edited by BrightStar, 07 February 2007 - 09:36 AM.