Abstract
In this paper, the dependences of the morphology, particle sizes, and compositions of the condensed combustion products (CCP) of modified double-base propellants (1,3,5-trimethylenetrinitramine (RDX) as oxidizer) on the chamber pressure (<35 MPa) and nickel inclusion have been evaluated under a practical rocket motor operation. It has been shown that higher pressure results in smaller average particle sizes of the CCPs. The CCPs of Ni-containing propellants have more diverse morphologies, including spherical particles, large layered structures, and small flakes coated on large particles depending on the pressure. The specific surface area (SSA) of CCPs is in the range of 2.49 to 3.24 m2 g−1 for propellants without nickel are less dependent on the pressure, whereas it is 1.22 to 3.81 Ni-based propellants. The C, N, O, Al, Cu, Pb, and Si are the major elements presented on the surfaces of the CCP particles of both propellants. The compositions of CCPs from Ni-propellant are much more diverse than another one, but only three or four major phases have been found for both propellants under any pressure. The metallic copper is presented in CCPs for both propellants when the chamber pressure is low. The lead salt as the catalyst has been transformed in to Pb(OH)Cl as the most common products of lead-based catalysts with pressure lower than 15 MPa. When pressure is higher than 5 MPa, the nickel-based CCPs has been found to contain one of the following crystalline phases: Pb2Ni(NO2)6, (NH4)2Ni(SO4)2·6H2O, C2H2NiO4·2H2O, and NiO, depending on the pressure.
Highlights
In spite of great advancements in the field of new energetic materials (EMs), the 1,3,5trimethylenetrinitramine (RDX) and ammonium perchlorate (AP) are still the most widely used ingredients as oxidizers in solid propellants [1]
The particles in micron sizes are collected by sedimentation in ethanol, whereas the upper suspended part containing nano-sized particles are subject to the Transmission Electronic Microscopy (TEM) analyses in a later section
The morphologies of the micron-sized condensed combustion products (CCP) are investigated by the Scanning Electronic Microscopy (SEM) technique, which are shown in Figures 4 and 5
Summary
In spite of great advancements in the field of new energetic materials (EMs), the 1,3,5trimethylenetrinitramine (RDX) and ammonium perchlorate (AP) are still the most widely used ingredients as oxidizers in solid propellants [1]. It has been shown that the catalysts could largely increase the burn rate and combustion efficiency of the solid propellants by changing the solid-state and gas-phase reaction mechanisms of between the oxidizers and fuels generated by the main ingredients such as binders, RDX, and AP. The effects of catalysts on the decomposition kinetics, reaction mechanisms, and burning rates, combustion characteristics have been widely investigated in the past decades. In the presence of extra oxidizer, such as potassium chlorate, the major gaseous decomposition products of RDX could be changed to CO, CO2, HCN, NO2, and H2O due to instant consumption of CH2O through the gas-phase transformation CH2O + O2 → HCO +HO2, resulting in higher reaction rate [3]
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