Multistep thermal decomposition of energetic NMe4B3H8: insights from combined kinetic and microscopic analyses

Abstract

Tetramethylammonium octahydrotriborate (NMe₄B₃H₈) is a promising high-energy fuel component for solid ramjets due to its high hydrogen–boron content and excellent chemical stability. This study elucidates its physicochemical properties and complex thermal decomposition mechanism. Characterization via SEM, EDS, and FTIR revealed that the synthesized samples comprised high-purity micron-sized spherical particles with an onset decomposition temperature of approximately 227 °C. Non-isothermal decomposition behaviors were investigated using simultaneous TG-DSC. To resolve the severe overlap of exothermic peaks in DSC curves, the Fraser–Suzuki function was employed for deconvolution, isolating three distinct reaction stages. A global fit using Combined Kinetic Analysis based on the Sestak–Berggren (SB) model accurately described the entire process (R2 > 0.99), yielding activation energies of 101.20, 101.05, and 152.07 kJ mol⁻¹ for the consecutive stages. Mechanistic analysis, corroborated by microscopic morphological evolution, indicates that the first two stages follow a three-dimensional random nucleation and growth model (A3). The third stage marks a transition from random chain scission (L3) to a phase boundary-controlled model (R3), corresponding to the degradation of polymer intermediates into a porous skeletal residue. These findings provide a theoretical basis for formulating and predicting the combustion performance of boron-based propellants.