Surface Coating of Nitroamine Explosives and Its Effects on the Performance of Composite Modified Double-Base Propellants

T HE traditional high-energy nitroamine explosives, cyclotrimethylene trinitramine (RDX) and cyclotetramethylene tetranitramine (HMX), have been widely used in many plasticbonded explosives, propellants, and powders due to their high energy performance, smokeless combustion products, and low price [1–4]. The content of nitroamine explosives exceeds 80% in some composite modified double-base (CMDB) and nitrate ester plasticized polyether propellants, respectively [5]. Nitroamine explosives can greatly enhance the specific impulse of propellants. It can, however, degrade the safety, mechanical properties, and processing properties of the propellants, which restricts the application of these highenergy propellants. More recently, much interest has been generated on how to improve the propellant’s overall properties. The main approaches include the following: 1) using advanced binders or plasticizers, such as glycidyl azide polymer [6,7] or 3,3diazidomethyloxetane [8,9]; 2) improving the particle properties of the solid fillers by reducing the particle size [10–13] or changing the particle morphology [14–16]; and 3) optimizing the propellant’s formulation and charge structure [17,18]. An acutely popularmethod to improve the propellant properties is to coat its sensitive fillers. Manning and Thelma [19] used graphite to surface-coat RDX fillers by solvent-evaporation and investigated the application in propellants. Their experimental results showed that, by such surface coating, the drop heightH50 of RDX andRDX-containing propellant increased by 40%and115%, respectively. In addition, some previous researchers have also indicated that the mechanical properties of propellants were improved via coating of the nitroamine fillers with polymer or bonding agent [20–23]. The properties of the coated particles depend on the kind of coating materials. For the nitroamine explosive used in some propellants, the best coating materials should be selected from the propellant ingredients [5]. Nitrocellulose (NC) is necessary for the energy and mechanical properties of double-based propellants. In our previous work, RDX particles coated with NC were prepared by solvent evaporation. These coated samples exhibited par dispersion [24]. Another coating technology, slurry solution distillation (SSD), has also been used to prepare themolding powders [25,26].However, there are two limitation to this method: 1) the energy of the explosive is greatly decreased because the addition of coating materials is higher than 5%; and 2) agglomerates composed of multiple particles can be formed easily, which leads to a change in particle size distribution. Herein, a new method, slurry emulsion distillation (SED), was exploited to coat NC and centralite-1 (C-1) onto the nitroamine particles by introducing a high-shear force in the SSDmethod. Also, the effects of such surface coating on properties of nitroamine explosives and CMDB propellants were investigated.