decompose and react with the semiconductor material. Rocket propellant Chlorine trifluoride has been investigated as a high-performance storable oxidizer in rocket propellant systems. Handling concerns, however, severely limit its use. John Drury Clark summarized the difficulties: 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 that 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. Chlorine pentafluoride (ClF5) has also been investigated as a potential rocket oxidizer. It offered improved specific impulse over chlorine trifluoride, but with all of the same difficulties in handling. Neither compound has been used in any operational rocket propulsion system. Proposed military applications Under the code name N-Stoff ("substance N"), chlorine trifluoride was investigated for military applications by the Kaiser Wilhelm Institute in Nazi Germany not long before the start of World War II. Tests were made against mock-ups of the Maginot Line fortifications, and it was found to be an extremely effective incendiary weapon and poison gas. From 1938, construction commenced on a partly bunkered, partly subterranean munitions factory, the Falkenhagen industrial complex, which was intended to produce 90 tonnes of N-Stoff per month, plus sarin (a deadly nerve agent). However, by the time it was captured by the advancing Red Army in 1945, the factory had produced only about 30 to 50 tonnes, at a cost of over 100 German Reichsmark per kilogram. N-Stoff was never used in war. Hazards ClF3 is a very strong oxidizer and fluorinating agent. It is extremely reactive with most inorganic and organic materials, and will combust many otherwise non-flammable materials without any ignition source. These reactions are often violent, and in some cases explosive, especially with flammable materials.