Difference between revisions of "Nitrogen triiodide"

Revision as of 06:45, 14 June 2015

Nitrogen triiodide is a touch sensitive explosive often shown in chemistry demonstrations where it is exploded by the touch of a feather. For this reason, it is also known as 'touch powder'.

Properties

Chemical

Originally nitrogen triiodide was originally prepared by reacting boron nitride with iodine monofluoride in trichlorofluoromethane at −30 °C:

BN + 3 IF → NI₃ + BF₃

Chemical reactions with nitrogen triiodide are not done due to its instability.

Physical

Insoluble in water and much the same colour as iodine, a dark purple that can be almost brown or black.

It is a super sensitive explosive once completely dry, yet not so when wet. This is because when wet, there are ammonia molecules in the structure of the compound, which helps to stabilize it. When the NI3 dries, these ammonia molecules evaporate so the NI3 structure is left very unstable, needing only the slightest amount of energy from friction or heat to turn into nitrogen and iodine vapour.

NI3 explodes with a loud cracking a cloud of bright purple smoke is produced. It is not a very powerful detonation, but a very pretty one and the violence of its explosion is often surprising when done from a very light touch.

Availability

NI₃ must be made, and quite often, the iodine crystals need to be made first due to the difficulty and expense of buying pure iodine.

Preparation

Ground iodine is placed into an excess of ammonia solution. The iodine will not dissolve a large amount but the suspension is left to sit before filtering (the time varies between who you ask, but an hour is usually more than enough time for 20 or so grams). The ammonia solution turns a shade of brown.

The solid is usually not transported but the filter paper is moved to the final position where it is left to be dried in the air. It can be hard to tell when it is completely dry by appearance alone but a light tap with a long stick will detonate it if it is dry.There are many Youtube tutorials on this process.

Safety

One must assume NI₃ contains a reasonable amount of elemental iodine as a impurity, due to the method it is created by. So all safety risks that apply to iodine, also apply to this solid.

Skin contact with the wet or dry solid will lead to long lasting unsightly brown stains to your skin.

This chemical carries all the risks associated with sensitive explosives, but due to the explosion creating iodine vapour, carries the risks of the corrosive and somewhat toxic element too. While not a danger in an outside, windy environment, touch powder will quickly erode steel if exploded over it, as well as staining many surfaces like concrete due to the iodine.

The sensitivity of NI₃ once dry cannot be overstated.

References

Relevant Sciencemadness threads