“Ignition! An Informal History of Liquid Rocket Propellants”

I am currently reading “Ignition! An Informal History of Liquid Rocket Propellants” by John D. Clark. (The work is currently out of print, but a PDF copy is available here)

As its title says, the work constitutes a summary of the early history of  liquid rocket propellant research. While maintaining an informal tone, it contains vast amounts of interesting technical information,as well as many anecdotes of experimental blunders and tales of testing gone awry.

One of my favorite quotations so far is Clark’s description of the compound Chlorine Trifluoride, which was at one point under study for use as part of a hypergolic (or self-igniting) propellant mixture. He describes the compound thusly:

Chlorine trifluoride, ClF3, or “CTF” as the engineers insist on calling it, is a colorless gas, a greenish liquid, or a white solid. It boils at 12° (so that a trivial pressure will keep it liquid at room temperature) and freezes at a convenient —76°. It also has a nice fat density, about 1.81 at room temperature.

It is also quite probably the most vigorous fluorinating agent in existence—much more vigorous than fluorine itself. Gaseous fluorine, of course, is much more dilute than the liquid ClF3, and liquid fluorine is so cold that its activity is very much reduced.

All this sounds fairly academic and innocuous, but when it is translated into the problem of handling the stuff, the results are horrendous. It is, of course, extremely toxic, but that’s the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water —with which it reacts explosively. It can be kept in some of the ordinary structural metals — steel, copper, aluminum, etc. —because of the formation of a thin film of insoluble metal fluoride which protects the bulk of the metal, just as the invisible coat of oxide on aluminum keeps it from burning up in the atmosphere. If, however, this coat is melted or scrubbed off, and has no chance to reform, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes.