Inhibition effect and mechanism of APP/ZB composite suppressant on coal dust explosion

APP/ZB composite suppressant prepared via mechanochemical treatment (1:1). • Pmax reduced by 90.7% and (dp/dt)max by 88.3% at 30 wt% addition. • Flame propagation distance and velocity reduced by 47.5% and 62.5%. • APP/ZB decomposes earlier (256.1 °C) with higher heat absorption (65.6 J/g). • P–B–Zn inorganic barrier layer formed on coal particle surface. • Synergistic inhibition via endothermic cooling, dilution, char promotion, and barrier. To enhance coal dust explosion suppression, an APP/ZB composite suppressant (1:1 mass ratio) was prepared via mechanochemical treatment. Its performance was evaluated using a 20 L explosion sphere and a transparent pipe system. Mechanochemical treatment promoted adhesion of ZB fines onto APP surfaces, improving interfacial contact. APP/ZB exhibited a lower initial decomposition temperature (256.1 °C) than the individual components, while its heat absorption (65.6 J/g) was approximately 9.61% higher than the theoretical value (59.85 J/g) calculated for a simple 1:1 physical mixture of APP and ZB. At 30 wt% addition, the maximum explosion pressure decreased by 90.7% (from 0.54 to 0.05 MPa), the maximum pressure rise rate by 88.3% (from 46.2 to 5.4 MPa/s), and K St from 1.25 to 0.14 MPa·m/s; induction and combustion times were significantly prolonged. At 20 wt%, flame propagation distance and velocity dropped by 47.5% and 62.5%, respectively, with the flame front becoming discontinuous. Residue characterization revealed that polyphosphates from APP crosslinked with boron- and zinc-species from ZB, forming a dense inorganic protective layer (P O P, Zn O P, Zn O B) on coal particle surfaces. APP/ZB acts synergistically through early endothermic decomposition, inert gas dilution, char promotion, and a P B Zn barrier that restricts heat, oxygen, and volatile transfer, interrupting the pyrolysis–combustion feedback loop. These findings offer a useful reference for designing phosphorus‑nitrogen/borate composite suppressants for coal dust explosions. Download: Download high-res image (245KB) Download: Download full-size image