Synergistic suppression of magnesium dust explosions by montmorillonite/ammonium polyphosphate composites: Experimental and kinetic modeling insights

Magnesium (Mg) dust in metal processing and energy settings exhibits high explosion sensitivity and strong destructiveness, readily triggering cascading accidents. To precisely control this risk, this study mechanochemically prepared montmorillonite (MMT) and ammonium polyphosphate (APP) composite inhibitors, established a vertical combustion duct platform, evaluated its suppression efficacy for Mg dust explosions, and combined residue characterization, thermal analysis, and Chemkin simulations to elucidate the synergistic suppression mechanism. The MMT/APP composite outperformed single components; at an inerting ratio (α) = 1.25, the 1:1 formulation fragmented the flame, prevented the formation of a continuous front, and self-extinguished at mid-duct. Relative to pure Mg dust, the maximum flame velocity (V_max) decreased by 91.5%; the peak flame front pressure (P_max) and the maximum rate of pressure rise ((dP/dt)_max) were reduced by 97.6% and 98.0%, respectively; and the peak temperature (T_p) fell to 236°C. Mechanistically, MMT provides endothermy alongside heat and mass transfer shielding. At elevated temperature, MMT forms refractory SiO₂ and Al₂O₃ phases and lamellae that suppress O₂ diffusion and interparticle heat conduction. Gas phase reaction kinetics simulations indicate that APP decomposes endothermically to generate nitrogen and phosphorus-containing intermediates that markedly deplete the O radical, manifested as rapid chain termination along the nitrogen pathway and sustained suppression along the phosphorus pathway. This study provides quantitative guidance for the formulation of efficient Mg dust inhibitors and supports improvements in the inherent safety of Mg processing.