Moderation of Al dust explosions by micro- and nano-sized Al₂O₃powder

Adding solid inertants to combustible dust is one measure to prevent and mitigate dust explosions. Al₂O₃ at four particle size distributions was used to determine the minimum ignition energy (MIE) and maximum explosion pressure (P_max) of aluminum dust and thus examine the effect of particle size on the inerting efficiency. It was interesting to observe that nano-sized Al₂O₃ powder showed excellent promise as a solid inertant, having inerting efficacy superior to that of micro-sized Al₂O₃. In addition to thermal inhibition, nano Al₂O₃ contributed to explosion moderation by binding Al particles together forming larger-sized aggregates that reduce dispersion in the dust clouds, and thus alleviate explosion hazards. Ignition sensitivity increased when micro-sized Al₂O₃ was admixed at 5 or 10% with 1000-1500 g/m³ Al mixtures, an effect apparently caused by a 20% decrease in effective particle size distribution brought on by the Al₂O₃ addition. Generally, increasing the amount of admixed Al₂O₃ increased MIE and decreased P_max of Al dust clouds, and decreasing the particle size of Al₂O₃ resulted in better inerting performance on moderating both the likelihood of the ignition and the consequence of the explosion.