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7a. Nitrogen Tri-Iodide, NI3.NH3 (Pyrotechnics)




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This article is from the Pyrotechnics FAQ, by Hans Josef Wagemueller zoz@cs.adelaide.edu.au with numerous contributions by others.

7a. Nitrogen Tri-Iodide, NI3.NH3 (Pyrotechnics)

Nitrogen Tri-Iodide is a very unstable compound that decomposes
explosively with the slightest provocation. It is too unstable to have
any practical uses, but is often made for its novelty value. Some books
describe uses for it in practical jokes etc. but in my experience it has
been far too unstable for this to be a feasible idea. Despite its common
name, the explosive compound is actually a complex between nitrogen
tri-iodide and ammonia, NI3.NH3 (nitrogen tri-iodide monoammine).

Reagents:

Solid Iodine (I2)
Ammonia solution (NH4OH) - Use only pure, clear ammonia. Other solutions,
such as supermarket 'cloudy' ammonia, will not
give the desired product.

Place a few fine crystals of iodine in a filter paper. The best way to
make fine iodine crystals is to dissolve the iodine in a small quantity
of hot methanol (care: methanol is toxic and flammable. Heat on a steam
bath away from open flame. Use in a well-ventilated area.), and then pour
the solution into a container of ice-cold water. This will cause
extremely fine iodine crystals to precipitate out. Drain off the liquid
and wash the crystals with cold water. If this method is not possible,
crush the iodine as finely as possible.

Then filter ammonia through the iodine crystals. Use a small amount of
ammonia and refilter it, to reduce wastage. The smaller the pieces of
iodine the better the result, as more iodine will react if it has a
greater surface area. You will be able to recognise the NI3.NH3 by its
black colour, as opposed to the metallic purple of the iodine.

Reaction:       3I     +  5NH OH     --->  3NH I     +  NI .NH    +  5H O
                  2(s)       4  (aq)          4 (aq)      3   3(s)     2 (l)

When the NI3.NH3 decomposes it will leave brown or purple iodine stains.
These are difficult to remove normally, but can be removed with sodium
thiosulphate solution (photographic hypo). They will fade with time as
the iodine sublimes.

Safety aspects:

NI3.NH3: Despite the common misconception presented in many articles
on NI3.NH3, it is NOT safe when wet. I have personally witnessed
NI3.NH3 exploding while at the bottom of a 1000Ml plastic beaker
full of water. NI3.NH3 can not be relied on not to decompose at
any time. Even the action of air wafting past it can set it off.

If you want to dispose of some NI3.NH3 once you have made it, it
can be reacted safely with sodium hydroxide solution. NI3.NH3 is
a potent high explosive, and should be treated with respect. Its
power, instability and unpredictability require that only small
batches be made. Do not make more than you can immediately use.
Never attempt to store NI3.NH3.

The detonation of NI3.NH3 releases iodine as a purple mist or
vapour. This is toxic, so avoid breathing it. Toxicity data on
NI3.NH3 is unknown, but I think it is safe to assume that eating
or touching it would be a bad idea anyway.

Iodine: Iodine sublimes easily at room temperature and is toxic -
ingestion of 2-4g of iodine can be fatal. Make sure you are in a
well-ventilated area, and avoid touching the iodine directly.

Ammonia: Again, use in a well-ventilated area as ammonia is not
particularly pleasant to inhale. Ammonia is corrosive, so avoid
skin contact, especially if using relatively concentrated
solution. If skin contact occurs, wash off with water. Don't
drink it.

 

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