I was wondering if anyone knows what the shelf life of ammonium nitrate is?

In my Improvised C-4 book, it says to only use fresh AN. It is getting harder and harder to find AN so I would like to stock some assuming it will last awhile.

AN is quite hygroscopic and I have had it mess up my 'experiments' because I did not dry it first. After drying it, it seems to behave the same as a brand new bag.

So I'm wondering if as long as I dry it out before hand, will it last a reasonable amount of time, or will it start breaking down into a unuseable composition fairly quickly? If it breaks down, what does it turn into?

Thanks!

Pure ammonium nitrate can be considered stable at room temperature. Even at elevated temperatures (upto 100°C) there won't be any significant decomposition. I don't see any problem storing it for several years.

However, that is for pure AN. There are several substances that catalyze the decomposition. Most notably chlorides, nitrites, chromium and manganese compounds. Even with small amounts of such catalysts present in the AN the decomposition will be rather slow at room temperature. It is still stable for storage.

An interesting observation is that coated AN seems more stable than uncoated. That means it's best stored unprocessed.

At low temperatures the reactions contributing to a decomposition are most likely:
NH4NO3 <=> NH3 + HNO3
NH4NO3 --> N2O + 2 H2O

All of the decomposition products are easily evaporated and will not contaminate your AN. I think what your book suggests is to only use freshly processed (dried) porous AN. The age of the actual AN doesn't matter.

Thanks sprocket.

That was the kind of info I was looking for.

I mainly use it for my exploding targets so a couple bags will last me quite awhile. Just didnt want to buy it if I'm going to end up throwing it out in a year.