Xinjian Zhou,Ruixuan Xu,Hongqi Nie,Qilong Yan,Jun Liu,Yunlan Sun
Burning rate modulation is a crucial but challenging technology for designing solid propellants. The core–shell structured Al@AP and Al@AP/CuO were prepared and their thermal reaction properties were investigated at different pressures. The precise catalytic mechanism of doped CuO in oxidizer and the key reason for its burning rate modulating effect on solid propellants were elucidated by combining DFT calculations. The *NH 4 ClO 4 on the CuO (1 1 1) surface is more likely to undergo a dehydrogenation reaction first. The large difference in activation energy between *NH 4 ClO 4 →*NH 3 +*ClO 4 +*H and *NH 4 ClO 4 → NH 3 + HClO 4 explains the reasons that CuO can reduce the ignition delay of the Al@AP. CuO promotes the decomposition of the AP@Al at the low- and high-temperature decomposition (LTD and HTD) stage. For the Al@AP-CuO, the temperature of the high-temperature decomposition peak (THTD) does not shift to the lower temperature range with increasing pressure. These results are responsible for a reduction of pressure exponent in the presence of minor CuO as reported in the literature. CuO can facilitate the transformation process *NH 3 →*NH 2 on the CuO (1 1 1) surface at low-temperature and low-pressure conditions. However, at high-temperature and high-pressure conditions, it can inhibit the reaction *NH 2 →*NH→*N, so the burning rate of solid propellants can be controlled.
Burning rate modulation is a critical but challenging technology for solid propellants’ design. Great efforts have been made to synthesize and utilize catalysts to modify the pressure exponent ( n ), but poor catalytic efficiency and lower energy level of conventional catalysts limit their further applications. In this research, interfacial control of Al@AP together with precise catalysis of CuO is represented for the purpose of pressure exponent reduction and combustion performance improvement. The core-shell structured Al@AP and Al@AP/CuO composites were prepared and applied into HTPB/Al/AP composite propellants. These prepared propellants have the same formula but different micro-structures of ingredients, leading to varied combustion performance, in terms of the burning rates, combustion wave structures, flame spectra, agglomeration processes of Al particles and condensed combustion products . The investigation results show that by using interfacial control of Al@AP and precise catalysis of CuO, the n of involved propellants over 1–4 MPa can be greatly decreased from 0.42 to 0.21 and the agglomeration of Al could be effectively inhibited. In addition, propellants based on Al@AP and Al@AP/CuO interfacial controls of this research are summarized and compared together with those based on Al@RDX published recently, to present overall characteristics of interfacial control techniques, which could lead to the development of new smart controllable propellants.
As a strong oxidizer, ammonium perchlorate (AP) is one of the most paramount raw materials in composite solid propellants (CSP) formulations, and the thermal decomposition features of AP would directly impact the energy release and the impulsion performance of CSP. CuNCN as an example of metal carbodiimides is explored as a burn rate modifier for AP decomposition, given their oxide counterpart belonging to typical burn rate modifiers. Our results reveal that the as-prepared CuNCN can effectively accelerate the thermal decomposition of AP. The CuNCN as additive in AP mixture can reduce the activation energy of decomposition of AP and bring down the HTD of AP decomposition by 84°C. The present study highlights on the effective application of metal carbodiimides in the thermally enhanced decomposition of AP.
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