Inhibition of aluminum dust explosion by NaHCO₃ with different particle size distributions

NaHCO₃ with three particle size distributions was employed to determine the minimum inerting concentration (MIC, g/m³) for the explosion of 5μm and 30μm aluminum dust in a standard 20L spherical chamber and thus examine the effect of particle size on the inhibition efficiency. Results showed that the MIC significantly increases as the aluminum particle size decreases from 30μm to 5μm. For 30μm aluminum, the MIC dramatically decreased with the reduction in the NaHCO₃ particle size. By contrast, for 5μm aluminum, the MIC was nearly independent of the particle size of NaHCO₃ in the range studied. Time-scale analysis indicated that the decomposition of NaHCO₃ must be faster than the aluminum combustion reaction for effective chemical inhibition. Scanning electron microscopy showed that the particles of the explosion residues of a NaHCO₃/Al mixture were considerably larger than those of pure aluminum explosion residues. A diameter ratio β_mix was defined to evaluate the degree of incomplete reaction promoted by NaHCO₃. The composition of the explosion products was analyzed by X-ray photoelectron spectroscopy, and the data revealed that Na₂CO₃ and Al₂O₃ are the major species of the products. An inhibition mechanism was proposed based on these results.