Phase Stabilization of Ammonium Nitrate

Abstract

Abstract : Ammonium nitrate (AN) as an ingredient for solid propellants has problems caused by a large volume phase change in normal operational temperature range, difficulty in keeping dry at relative humidities above 30%, 91 degrees F phase change making smaller AN particles causing propellant grain growth during temperature cycling, and caking behavior that creates a need for processing into propellant relatively soon after grinding to retain small particle sizes. Interference of propellant cure using isocyanate curatives commonly occurs due to moisture content in the AN. AN phase stabilization is typically accomplished by introducing another substance into the ammonium nitrate crystal structure. Salts containing ions larger or smaller than either ammonium or nitrate ions have been used. Since the U.S. military has decided not to use nickel or copper phase stabilizing agents, our laboratory has been looking for new materials for phase stabilizing ammonium nitrate for use in solid propellants. Use of N,N,N',N'-tetramethyl hexane-1,6-diamine appears to solve many AN problems. That is, elimination of phase changes, elimination of propellant grain growth during temperature cycling, lack of moisture for cure interference, and lack of caking in 50% relative humidity environments. How AN can be transformed into a well behaved oxidizer ingredient will be discussed.