Explosion characteristics of aluminium and silver particles in various sizes and concentrations for a confined and vented system / Khairiah Mohd Mokhtar

Khairiah , Mohd Mokhtar (2021) Explosion characteristics of aluminium and silver particles in various sizes and concentrations for a confined and vented system / Khairiah Mohd Mokhtar. PhD thesis, Universiti Malaya.

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Abstract

The rising metals applications in electronics, aerospace, and solar cell industries could potentially lead to a destructive dust explosion. To assess the associated hazard and appropriate preventive and mitigation measures against the accidental metal dust explosion, it is crucial to identify the physicochemical properties particularly on kinetic reaction mechanism and explosion characteristics of metal powder. Thus, in this work, the explosion characteristics of two metals powder viz; aluminium (Al) and silver (Ag) were explored in a 0.0012 m3 cylindrical vessel, by varying the particle sizes and the powder concentrations. It was found that the Minimum Explosion Concentration (MEC) for both aluminium and silver was 300 g/m3. The experimental results showed that the maximum explosion pressure (Pmax) and maximum rate of pressure rise (dP/dtmax) increase with the increasing powder concentration from 300 g/m3 to 500 g/m3, however, the decreasing trend was observed when the concentration values exceeding ~ 700 g/m3. The shortened inter-particle distance and oxygen deficiency at higher powder concentrations give a significant reduction in the heat transfer rate, and hence, it lowers the explosion severity. Further, the decrease values of both Pmax and dP/dtmax were also shown when the agglomeration effect occurred at smaller particle size. The lower particle weight gaining of Al 40 nm in the thermogravimetric (TG) curve, than Al 70 nm, reflects on the slower oxidation reaction of the particles due to the agglomeration effect. In contrast to aluminium powder, sluggish oxidation was shown in the TG curve of silver powder corresponding to the smaller specific surface area of silver powder, and this condition justifies the lower explosion severity of silver powder than that of aluminium powder. Further experimental works were conducted on the aluminium and silver (Al-Ag) mixtures which can be encountered in the passivated emitter and rear contact (PERC) solar cell industry. The finding demonstrates that the explosion severity of Al-Ag mixtures is lower than the pure aluminium powder explosion, with the most significant effect was observed when the silver powder is in excess. The Pmax and dP/dtmax of 40:60 mixing weight ratio of Al-Ag mixtures is approximately one-fifth of the values obtained in the pure aluminium powder. It can be depicted that the silver powder disrupts the aluminium oxidation reaction, hindering the heat transfer among the metal particles which leads to the reduction of the mass burning rate, and hence, lowering the explosion severity of the aluminium. Based on the kinetic mechanisms, it can be suggested that the reduction of aluminium explosion severity in 50:50 and 40:60 mixing weight ratio of Al-Ag mixtures corresponds to the amount of unreacted aluminium. In addition to the role of silver powder, the magnitude of aluminium explosion severity was also decreased in the vented explosion. However, the venting effectiveness reduces as the static burst pressure (Pstat) of the venting membrane increases. The explosion pressure of Al 70 nm was reduced by about 60% when Pstat of 0.5 bar was applied, gave approximately 30% lower value than the pressure obtained at the 0.1 bar Pstat.

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