Morphological evolution mechanism of copper-based azide during gas-solid azidation process: Experiment and thermodynamic analysis

Copper-based azide (CA) synthesized by in-situ gas-solid azidation and utilized as preferred material for miniaturized explosive systems has attracted extensive attention from researchers. This work aims to reveal the morphological evolution mechanism of CA during gas-solid azidation processes. The morphological evolution processes of CA under different reaction conditions were observed and corresponding reaction stages were divided by the characteristics of product morphology. The morphology of product islands possesses a significant impact on the final morphology. To further reveal the morphological evolution mechanism, the continuous product layer and product islands core-shell thermodynamic equilibrium models were derived and studied to explain experimental findings. The energy properties of Cu(111), CuN₃(220), Cu(N₃)₂(110) surfaces and corresponding interfaces were studied by first principle calculation to perform the thermodynamic equilibrium analysis. Based on the calculation results, the equilibrium thermodynamics analysis of Cu-CuN₃, Cu-Cu(N₃)₂ and CuN₃-Cu(N₃)₂ core-shell systems were performed and the corresponding dependence was discussed. The reaction modes were divided into thermodynamic-dominated and kinetic-dominated modes based on the different orders of product generation and the results of thermodynamic equilibrium analysis. The morphological evolution mechanism was proposed based on thermodynamic analysis and different reaction modes, which provides a fundamental perspective to regulate CA morphology and enhance corresponding performance.