Interesting chemicals

[ceptimus]

A thread for posting occasional chemistry factoids.

Chlorine trifluoride ClF3 Is generally too dangerous to consider using. It's a green liquid at room temperature, and a colorless gas when warmed (though warming it isn't really a good idea). It's an incredibly strong oxidizing agent - much more so than boring old oxygen. It self-ignites and burns most materials, most of them explosively. It also corrodes things generally considered non-corrodible: iridium, platinum, and gold.

It burns most materials that oxygen can't: sand, asbestos, glass, tungsten, water, most fire retardants, concrete, the ashes of materials already burnt in oxygen, living flesh, ...

It can be stored in vessels made from steel, copper, nickel or quartz - but the vessels must be scrupulously cleaned and passivated. The only reason the metal vessels can contain the chemical is because it reacts with the metals forming a thin layer of insoluble metal fluoride - but any contamination allows the chlorine trifluoride to burn through the passivation layer faster than it can re-form, and so the container is quickly turned into a non-container.

The reaction with water is particularly violent and the products of the reaction include hydrogen chloride and hydrogen fluoride - in themselves fairly potent and alarming chemicals - and these are given off in the form of a steam or vapor due to the highly exothermic reaction.

In a nasty chemical accident at Shreveport, Louisiana, nine hundred kilograms of ClF3 were being moved across a factory in a sealed metal cylinder, kept very cold to reduce the risk of reaction. Unfortunately the cold made the metal brittle, and it cracked spilling the ClF3 everywhere. It burned through the one-foot thick concrete floor, and a further three feet of gravel beneath. The remains of the man moving the cylinder were found about a hundred-and-fifty yards away, blasted there by the force of the explosion - official cause of death was a heart attack.

Uses: It was tried in the 1940s as a rocket propellant, but kept setting fire to the rockets themselves, so was abandoned. The nazis tried to use it as a weapon, but it killed too many of their own chemists, and cost too much to produce. It is used (carefully, in small amounts) by the semiconductor industry to clean chemical vapor deposition chambers - it reacts with any slight contaminants on the walls of the chambers, burning them away: its high reactiveness is an advantage here as other lesser chemicals need to be activated by high temperature plasma to do the same work. It's used in the nuclear fuel processing industry during the production of uranium hexafluoride.