Experimental Insight into the Catalytic Mechanism of MFe₂O₄(M = Ni, Zn and Co) on the Thermal Decomposition of TKX-50

Synthesized dihydroxylammonium 5,5’-bistetrazole-1,1’-diolate (TKX-50) owes its outstanding application prospects in the field of insensitive solid propellants not only to its high energetic performance but also to its low mechanical sensitivity. Based on the excellent catalytic activity of bimetallic iron oxides for the thermal decomposition of TKX-50, the catalytic mechanism of bimetallic iron oxides (NiFe₂O₄, ZnFe₂O₄and CoFe₂O₄) for TKX-50 pyrolysis has been explored. For this study, the decomposition process of TKX-50, before and after mixing with the bimetallic iron oxides NiFe₂O₄, ZnFe₂O₄and CoFe₂O₄was monitored by in-situ FTIR and gas-phase MS-FTIR instruments. Of the different catalysts, ZnFe₂O₄gave the best result for reducing the initial decomposition temperature of TKX-50. Additionally, the activation energy of functional group cleavage of TKX-50, before and after mixing with ZnFe₂O₄, was also calculated for mechanism analysis from the results of the in-situ FTIR measurements. The results showed that the condensate and the gas-phase decomposition products of TKX-50 remained unchanged after mixing with different catalysts, while the activation energy of tetrazole ring cleavage was significantly reduced. The results of this study will be helpful for the rational design of insensitive solid propellant formulations containing TKX-50, and for understanding the pyrolysis mechanisms of TKX-50 before and after mixing with the efficient catalyst ZnFe₂O₄.