Synthesis Of Energetic Complexes Based On Bis 1,2,4-oxadiazole-bitetrazole Ligand And Study On Thermal Catalysis Of Ammonium Perchlorate

Ammonium perchlorate（AP）composite propellants,with AP as oxidant component,have always been a workhorse in the field of solid rocket propulsion.The thermal decomposition performance of AP greatly affects the combustion performance of propellant.Its disadvantages of high decomposition temperature and insufficient decomposition can be improved by adding combustion catalyst.So far,additives mainly include zero-valent metal,metal oxides,metal and carbon-based composites,energetic complexes,etc.Among them,energetic complexes stand out,for which the energy of the propellant system will not be reduced with their addition.The nitrogen-rich ligands bis1,2,4-oxadiazole-bitetrazole compounds possess the characteristics of high nitrogen content,high energy and good oxygen balance.A range of energetic complexes were constructed and prepared by combining these ligands with transition metal ions.Their catalytic effect on the thermal decomposition of AP as catalysts was also studied.The main contents are as follows:（1）Preparation and characterization of two energetic ligands of bis1,2,4-oxadiazole-bitetrazole.The ligand[3,3’-bi（1,2,4-oxadiazole）]-5,5’-bistetrazole（BODT）and 5,5’-{[3,3’-Bi（1,2,4-oxadiazole）]-5,5’-diyl}bis（1H-tetrazole-1-ol）（BODTO）were synthesized from glyoxal by polystep reactions.The two ligands were tested by nuclear magnetic resonance spectroscopy（NMR）,mass spectrometry（MS）,infrared spectroscopy（IR）,single crystal XRD and which confirmed that the structures were as designed.（2）Preparation and characterization of 11 energetic complexes based on two ligands.Among them,two complexes,[Zn（BODT）（H₂O）₄]_n（1）and[Cd（BODT）（H₂O）₄]_n（2）,were prepared based on BODT ligand.Using BODTO as the ligand,nine complexes were prepared,namely[Mn（BODTO）（H₂O）₄]_n（3）,[Zn（BODTO）（H₂O）₄]_n（4）,[Co（BODTO）（H₂O）₄]_n（5）,[Co（BAFTO）（H₂O）₄]_n·2H₂O（6）,[Cu（BODTO）（H₂O）₄]_n（7）,[Cu（BAFTO）（H₂O）₄]_n（8）,[Ni（BODTO）（H₂O）₄]_n（9）,[Pb（BODTO）（H₂O）₄]_n（10）,[Fe₂（μ₂-CH₃O）（μ₃-OH）（μ₂-O）（BODTO）（H₂O）]₄（11）.Among them,the complexes 6 and 8 are energetic complexes based on the isomer BAFTO of BODTO ligand.The structures of them were tested by SC-XRD.Except for complex 11,which has zero-dimensional octagonal iron cluster structure,the other complexes are one-dimensional chain structure.Among them,the complexes 1～5,7,and 9 all belong to the triclinic P-1 space group.Besides,the average local ionization energy（ALIE）of the two ligands was calculated by Multiwfn.The BODT^2-and BODTO^2-after deprotonation were calculated.Their ALIE minimum points appear on the connected N and O atoms where the proton lost,indicating that it is easier to coordinate with metal ions,and explaining why the complexes 1～5,7,and 9 are likely to form the same one-dimensional chain structure.（3）The thermal stabilities,energetic properties,and mechanical sensitivities of 11 complexes were studied,respectively.The DSC results show that the thermal decomposition peak temperature（T_p）of these complexes is higher than 490 K.The complexes are of good thermal stabilities,and the maximum T_p is 576.1 K for complex 1.The energetic characteristic parameters of the complexes show that eleven energetic complexes have high energy,i.e.,detonation velocity（D）≥8.81 km·s^-1,detonation pressure（P）≥37.45 GPa.The safety performance of the series of complexes was evaluated by BAM sensitivity instrument.The test results show that these complexes have low mechanical sensitivity,i.e.,impact sensitivity（IS）≥15 J,friction sensitivity（FS）≥288 N.（4）Study on the catalytic performance of energetic complexes for the thermal decomposition of AP.The DTA results show that these complexes can reduce the T_p of the high temperature decomposition（HTD）stage and reduce the activation energy of AP thermal decomposition.Among them,complex 8 has the best catalytic performance,which can advance the decomposition peak temperature of HTD by 103.5 K,and E_a is reduced to 139.3 k J·mol^-1.Based on the test data and the existing literature,the possible catalytic mechanism of energetic complexes on the thermal decomposition of AP was deduced.