Chemistry: Ion Synthesis Makes Better Rocket Fuels

What every rocket designer wants for Christmas is a new and better fuel so that his birds can blast off with extra energy. What every chemical engineer in the business is trying to do is play Santa Claus.

Precision Collision. The standard method for synthesizing high-energy chemical fuels is to mix the ingredients and heat them. The heated molecules move faster, and a few of them move so fast that when they collide they stick to each other, creating new compounds with built-in energy. Instead of this haphazard system, says Vice President Milton Farber of Arizona’s Rocket Power Inc., it is better to slam the molecules at each other with precisely enough energy to make them stick.

Using this system of “ion synthesis.” R.P.I, chemists have taken nitrogen dioxide gas (NO2) and ionized it by squirting it against an electrically charged metal plate at one end of a vacuum tube. As soon as the gas molecules pick up electric charges, they respond to electrical forces and are whisked through a charged grid at a predetermined speed. After traveling a short distance, they hit molecules of vaporized benzene (C6H6) and stick to them, forming nitrobenzene (C6H5NO2). The hydrogen atoms left out of the combination form gaseous hydrogen.

Nitrobenzene is not a desirable rocket fuel; its production was shown only as a demonstration. But R.P.I, chemists are confident that their complex synthesis process can also make exotic high-energy fuels that cannot be manufactured in any other way—fuels with unfamiliar names that are now only whispered because of stringent Air Force secrecy. The big trick is to control accurately the speed of the ions. If they move too slowly, they do not react; if they move too fast, they break up the target molecules and form unwanted products.

Splintering Fragments. At California’s Aerojet-General Corp., another esoteric operation called ”fissio-chemistry” uses the enormous energy of fissioning uranium to slam molecules together. So far, the most promising product of the process is hydrazine, a derivative of which is used as highenergy, self-igniting fuel in the Air Force’s Titan II rockets.

Aerojet scientists mixed liquid ammonia (NH3) with powdered uranium oxide, sealed the mixture in a capsule and stuck the capsule in a nuclear reactor at Livermore Laboratory. When neutrons from the reactor hit uranium atoms in the capsule, they caused the atoms to fission, or split. The atomic fragments shot apart with enormous energy (200 million electron volts per fission), splintering ammonia molecules and knocking them in every direction. The fragments recombined at once. Some formed gaseous hydrogen (H2) or nitrogen (N2). But about half the ammonia that reacted formed the much-desired hydrazine (N2H4).

A capsule is far from a practical factory, but Aerojet is now building a pilot plant that will circulate a mixture of ammonia and uranium oxide through a nuclear reactor. If Aerojet calculations are correct, the plant should produce hydrazine, which now costs $1.50-$2 per lb., for as little as 25¢ per lb.