Improvements in the Chemical Stability of Double-Base Solid Rocket Propellants

Abstract

The effect of copper, compared with lead salt-based ballistic modie ers on the reaction of the propellant stabilizers, para-nitro-N-methylaniline and 2-nitrodiphenylamine, during the aging of nitroglycerin solutions and on the reactions of these stabilizers with the individual reactive species known to be generated during double-base propellant decomposition, namely NO 2, HNO2, and HNO3, have been thoroughly investigated in an attempt to deduce some key parameters that ine uence the reactions that take place in these propellant systems during aging. It was found that copper modie ers greatly differ from lead ones in their effect on the depletion of stabilizers and in their reactivity toward the reactive species. All of the copper salts have a dramatic effect on the reactions of propellant stabilizers. They cause more rapid depletion of stabilizers when compared with that produced by lead salts, the effect of basic copper salicylate being more dramatic than that of copper oxide. The results have shown thattheorganicmoiety oftheballisticmodie erplaysanimportantroleinitsine uenceonthereactionsofstabilizers with propellant degradation species, and that the higher reactivity of copper salts compared with that of lead salts is attributable to the combined effect of both the copper ion and the salt anion. In particular, this investigation has helped contribute information on the propellant compositions that should fule ll the requirements for propellant service use. To overcome the deleterious effect of some copper modie ers on the chemical stability of double-base propellants, the stabilizer system must include resorcinol and the copper salt should be used at a low level. OPPER salts, in combination with lead salt-based ballistic modie ers, are used in nitroglycerin-(NC)-based propellants to modify the combustion characteristics of solid rocket propellants. Nearly all solid propellants based on nitrate esters contain a uniformly distributed stabilizer. The function of the stabilizer is the removal of NO 2, which is formed as a primary decomposition product during the storage of propellants, 1 and which would otherwise autocatalytically accelerate the decomposition. Stabilizer mixture systems are widely used in double-base rocket propellant formulations,wheretheyhavebeenfound 2 tobemosteffectiveinprolonging the crack-free life of the propellant grain during storage. It is generally assumed that the more reactive stabilizer reacts rapidly with the propellantdegradation productsduring theearly stagesofaging, whereas the second stabilizer reacts more slowly. Stabilizerslikeresorcinol,andthe combinationofresorcinolwith other stabilizers, are reported to be useful. 3,4 The effectiveness of resorcinolhasbeenexplained 5 asbeingaresultofactivatedaromatic ring formation, which helps in the absorption of nitrogen oxides quickly and more effectively, resulting in further control of growth of autocatalytic reactions. It was indicated 6 that the chemical stability of double-base propellants is signie cantly ine uenced by different lead-based ballistic modie ers, and that the organic moiety of the ballistic modie er is an important ine uence on the reactions of the stabilizers. In this work, systematic investigations have been carried out to obtain a deeper insight into 1 ) a comparison of the effect of lead and copper salt-based modie ers on the reaction of stabilizers commonly used in the cast double-base (CDB) rocket propellants, namely para-nitro-N-methylaniline (pNMA) and 2-nitrodiphenylamine (2NDPA),duringtheagingofNGsolutionsin acetonitrile-containing identical quantities of the ballistic modie ers that are also commonly used in the propellant matrix, and 2 )a study of the effect of copper modie ers on the reactions of the stabilizers with propellant degradation products (namelyNO2, HNO2, and HNO3). Studying the reaction of these compounds is very impor