Enhanced fire-extinguishing performance of struvite powder through modulation of its thermal-decomposition characteristics

Struvite (MgNH 4 PO 4 ·6H 2 O) exhibits strong fire-extinguishing properties due to its chemical structure, which resembles that of the widely used ammonium dihydrogen phosphate (ADP). The crystalline water within struvite contributes to its enhanced cooling effect. However, its relatively low pyrolysis temperature range (60 °C–300 °C) restricts its efficiency in high-temperature fires (e.g., 600 °C), where pure struvite struggles to penetrate the flame base. To overcome this limitation, a composite powder was developed by coating struvite with ammonium polyphosphate (APP), a compound known for its high thermal stability. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and TGA-IR were used to investigate the fire-extinguishing mechanism. Results showed that the incorporation of APP extended the thermal decomposition range of struvite, with the 15 wt% APP composite demonstrating optimal performance. This composite exhibited a multifaceted fire-extinguishing action: releasing water vapor for cooling, ammonia for flame suppression, and solid residues that formed a protective layer to isolate the flame from the fuel. Consequently, the composite powder demonstrated superior fire-extinguishing performance, outperforming traditional ADP powder in oil pool fire tests, demonstrating its potential for practical fire suppression applications.