Phase stabilization of Ammonium Nitrate

[holthof]

Dear people,

 

First of all: I'm just new to this forum, I hope someone can help me out with this.

 

As an amateur rocketeer, I have quite a lot of experience with solid propellant rocket motors. I have designed and built several myself, up to a class O motor. Normally, I use potassium nitrate as oxidizer and Sorbitol as fuel/binder. The problem with this propellant, however, is it's relatively low specific impulse. Therefore, I would like to try and use ammonium nitrate as oxidizer. This chemical has the unwanted property of forming a new crystal structure at elevated temperatures, causing cracks in the propellant grain. This can be resolved by phase-stabilizing it. My question now is: does anyone know of a procedure for this, that I can follow in my home lab?

 

Thanks in advance.

[imp]

I cannot help with your quest for "phase-stabilization", but would point out that due to several physical qualities, ammonium nitrate is an undesirable and difficult compound.

 

Extremely hygroscopic, the material quickly becomes a wet and pulpy mass if exposed to the air. It then is relatively useless for anything but plant fertilizer. Indeed, when sold as fertilizer, it usually is made in the form of "prills", small, coated spheres, to resist absorption of water until used.

 

It's somewhat unpredictable ability to dissociate instantaneously adds danger to use as fuel, I should think. This quality has made procurement of the material a scrutinized activity. imp

[holthof]

These are properties I am fully aware of. However, ammonium nitrate has also some obvious advantages: high specific impulse, non-toxic. Therefore, it would be nice to control the high hygroscopy and temperature instability, to make this a useful oxidizer. It has been done by people before, by using an metal oxide (zinc- or cupric oxide), but the process itself seems to be quite a mystery.

Thanks for the quick reply anyway! I will keep searching for a method, and in the mean time stick with the potassium nitrate as oxidizer.