Effective Performance Modifications for a Composite Rocket Propellant via Coagglomerates of Cyclic Nitramines

Area of Science:

• Propellant combustion chemistry and energetic materials science.
• Solid rocket propellant formulation and performance evaluation.

Background:

• Ammonium perchlorate (AP) is a common oxidizer in composite propellants.
• Novel combustion modifiers are sought to enhance propellant performance and safety.
• cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]-imidazole (BCHMX) is a new combustion modifier.

Purpose of the Study:

• To investigate the effect of substituting ammonium perchlorate (AP) with BCHMX-based formulations on propellant characteristics.
• To analyze the relationships between BCHMX content and propellant properties like burning rate, ignition temperature, and sensitivity.
• To characterize the structure of HMX/BCHMX coagglomerates (CACs).

Main Methods:

• Preparation of propellants with varying weight percentages (10, 20, 30 wt %) of AP substituted by HMX, mechanical mixture (PM), and coagglomerate of HMX/BCHMX (CACs).
• Characterization of CACs using powder X-ray diffraction, FTIR, and Raman spectroscopies.
• Measurement of propellant burning rate, heat of combustion (Qc), ignition temperature, thermal decomposition rate, impact sensitivity, hardness, and specific impulse.

Main Results:

• CACs were confirmed to be a mixture of cocrystal β-HMX/BCHMX with excess β-HMX.
• Increasing CACs content reduced the propellant's pressure exponent, unlike pure HMX or PM.
• A significant positive effect on burning rate was observed with CACs, particularly at 20 wt % AP substitution.

Conclusions:

• BCHMX, especially in CAC form, is a promising combustion modifier for HMX/HTPB/AP propellants.
• CACs enhance burning rate and reduce the pressure exponent, offering improved propellant control.
• Further research into the relationships between combustion properties and sensitivities is warranted.