Extinguishment of sodium fires with Graphite@Stearate core-shell structured particles

Metallic sodium has unique fire hazards for its high chemical reactivity with air and water. Owing to the limitations of existing suppressants for sodium fires, here, a new type of composite particles with expandable graphite as cores and stearate sodium as shells (denoted as EG@SS) was developed for extinguishing sodium fires high efficiently. Laboratory-scale sodium pool fire tests revealed that such graphite powders with stearate sodium coated exhibited much superior performance in comparison to the commonly used raw graphite. The mass ratio (R) of EG@SS composite powders employed over sodium to obtain extinction was 0.7 as opposite to 2.2 of raw EG without surface coating. When applied to sodium fires, the inner expandable graphite would expand rapidly and decrease the flame temperature. Meanwhile the outer stearate sodium would melt and fill the gaps between the loosely packing graphite piles, forming a crust excluding oxygen. Consequently, a fast total extinction was achieved for the combined effects of cooling and suffocation from graphite and stearate sodium. The extinction mechanism was investigated based on experimental results and physicochemical characterizations of the core-shell structured composites.