The influence of fullerene additives on the combustion behaviour of cyclotrimethylene trinitramine/ammonium perchlorate composite modified double-base (RDX/AP-CMDB) propellants are investigated by thermogravimetricdifferential thermogravimetric (TG-DTG) analysis, burning rate tests, and scanning electron microscopy observations. The difference between lead salicylate (F-Pb) and bismuth citrate acid (CP-Bi) as combustion modifiers has also been examined. TG-DTG investigations show that the addition of all additives advanced and accelerated the evaporation of nitroglycerin (NG). The addition of Extracted Fullerene Soot (EFS), C 60 and carbon black (CB) additives obviously accelerated the liquid phase decomposition of NG. Also, the solid phase decomposition of nitrocellulose (NC) and the liquid phase decomposition of RDX were accelerated by 0.5 per cent Fullerene Soot (FS)/2.5 per cent CP-Bi/0.5 per cent copper adipic acid (J-Cu) composite catalyst. The addition of all composite catalysts promoted the decomposition of ammonium perchlorate (AP) except 0.5 per cent EFS/2.5 per cent CP-Bi/0.5 per cent J-Cu composite catalysts. It is well known that there exists dark zone in the flame structure of RDX-CMDB propellant, but in our observation, the dark zone vanished with the addition of 10 per cent AP to the forenamed propellant. The burning rates were increased at low pressure but reduced at high pressure by all catalysts except 0.5 per cent EFS/2.5 per cent CP-Bi/0.5 per cent J-Cu and 0.5 per cent C 60 /2.5 per cent CP-Bi/0.5 per cent J-Cu which reduced the burning rates at every tested pressure. The pressure exponents of tested propellants were reduced by 0.5 per cent FS/2.5 per cent CP-Bi/0.5 per cent J-Cu with a factor of 17 per cent . The quenched surface observations significantly differed with the additions of diverse composite catalysts, which were consistent with the burning rate results.
Energetic additives can effectively increase the heat release of ammonium perchlorate (AP) decomposition to prevent nonenergetic additives from decreasing the energy density of composite solid propellants. However, the roles of energetic additives are unclear due to their complex changes in the decomposition process. Using ZIF-67 as a model energetic additive, we investigate its roles and catalytic processes in the decomposition of AP, especially the effect on heat release. We find that the decomposition process includes two periods: low-temperature oxidation of ZIF-67 by AP and high-temperature catalytic decomposition of excess AP. The oxidation of ZIF-67 can release a mass of heat and provide oxidation products for catalytic decomposition of excess AP. Meanwhile, the heat release of excess AP is increased to 2.33 times compared with pure AP (1.83 vs 0.78 kJ•g −1 ), and the relationship between heat release and the content of ZIF-67 is quantified. Our results provide new insights into the roles of MOFs in enhancing the thermal decomposition of AP.
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