Thermal degradation behaviour of sodium fire extinguishant powder

Abstract

Although liquid sodium has proved to be a technologically superior and economically viable coolant in the heat-exchange circuit s of fast reactors, it is fraught with the serious problems of fire hazards in the event Of accidental leakages into the ambient air. For the rapid and effective suppression of sodium fires, sodium bicarbonate has emerged as a potential extinguishant. This paper attempts a description of the thermal decomposition behaviour of sodium bicarbonate fine powder in vacuum on the basis of thermogravimetry and differential thermal analysis. The analog percentage mass change data, transformed into dimensionless extents of reaction and calculated rates of reaction, are then analysed by a generalized computational technique. The results indicate that the most probable rate-controlling step is a process of three-dimensional contraction of the bq-lcarbouate particle surface, with activation energy E = 82.94 kJ mol-1 and frequency factor A = 34.73 x 104 s-1. The decomposition temperature of sodium bicarbonate shows an upward trend with increasing heating rate.