Subject: Re: Rocketfuel
From: glhurst@onr.com (Gerald L. Hurst)
Date: Nov 16 1996
Newsgroups: rec.pyrotechnics

In article <56jp16$qna@bashir.peak.org>, billn@PEAK.ORG (Bill Nelson) says:

>John H. Cato, Jr. (jcato@almatel.net) wrote:
>
>: Ammonium Nitrate (AN) based fuels typically don't equal AP based fuels (from
>: what I've seen).  I'm guessing here - maybe as low as 100 up to 150 seconds 
>: (Bill Nelson, can you elaborate??).  However, AN can be dangerous to work 
>: with (and is hygroscopic to boot) - but there is a Phase Stabilized version 
>: (PSAN) that I hear is safer and better.
>
>The Isp range is correct - and possibly slightly higher in very large motors.
>However, such motors are theoretical, because of the phase change problem
>you mention - even if using the stabilized version.
>
>The hygroscopicity is not a real problem, if using a binder that protects
>the oxidizer. AP is also hygroscopic, and the fuel grains made using it are
>stable for years - and probably decades.

Bill, AP is not hygroscopic to any significant level; its molar 
solubility is lower than that of table salt. It has been my
experience that organic coatings such as oils, waxes, tar and the like
are ineffective in protecting AN from ambient moisture.  Admittedly, 
most of the combinations I worked with were not dead-pressed, which 
would help to limit the ingress of water and temporarily inhibit its
deleterious effects to the surface of a compressed grain.

If you carefully mix AN with a stoichiometric amount of tar and then 
lower the mix into a bucket of water, you quickly wind up with a layer 
of pure tar floating on a concentrated solution of AN. This is a very
discouraging observation when you are trying to make water-resistant 
ANFO.

Jerry (Ico)