Study on the ignition and hydrogen evolution characteristics of wet magnesium powder under strong ignition conditions

Abstract

Magnesium powder has extensive industrial applications, but its production and material processing release combustible dust clouds. Under humid conditions, these particles readily react with water vapor through hydrolysis, generating hydrogen gas that creates significant explosion hazards when encountering ignition sources. This study introduces a bidirectional dust injection system for 20L spherical explosions, enabling controlled moisture regulation (0–5 % water content) during dispersion to mitigate particle agglomeration artifacts inherent in conventional single-nozzle configurations. The system quantitatively characterizes explosion dynamics of magnesium powder (20–105 μm) under precisely maintained moisture conditions through simultaneous pressure-imaging diagnostics. The experimental results reveal a dual-effect mechanism of moisture content on explosion behavior. At lower moisture levels (below 3 %), humid magnesium powder demonstrates enhanced explosion severity due to hydrogen generation through the magnesium-water reaction. However, when moisture content surpasses the critical threshold (≈3%), the combined cooling effect and inerting action of water suppress explosion intensity. Particle size analysis demonstrates an inverse correlation between explosion severity and particle dimensions. The minimum explosive concentration increases with particle size (1000 g/m³ for 20.7 μm, 1200 g/m³ for 41.8 μm, and 1400 g/m³ for 104.1 μm), while finer particles exhibit greater explosion intensity. Microstructural examination of explosion residues reveals a marked increase in cubic crystalline magnesium oxide particles under high humidity conditions, confirming the critical role of hydrogen generation and oxide decomposition in explosion mechanisms. This mechanistic investigation delineates the humidity-dependent duality in magnesium dust explosions: moisture can enhance explosion intensity through hydrogen generation, while under high moisture content conditions, it suppresses explosions via endothermic and inerting effects. The findings provide crucial insights for optimizing safety protocols in magnesium-related industrial processes, particularly emphasizing the necessity for strict humidity control during storage and handling. The identified dual-effect mechanism of moisture content offers theoretical support for developing explosion prevention strategies in high-risk environments where magnesium powder is exposed to both elevated temperatures and humidity conditions.