Experimental study of sodium reignition behavior

Reaction residue of sodium combustion has possibility of reignition in an air atmosphere even at 50deg-C when the sodium pool fire was extinguished by nitrogen (N2) gas. Thus we carried out an experimental study of this behavior for the purpose to clarify the cause of the reignition and to make a suggestion for a preventive measure. The sodium burning and extinguishing experiments were performed changing fraction of oxygen (O2), carbon-dioxide (CO2) and humidity in the atmosphere, using 1g sodium and a glass-made chamber of 70mm inner diameter and 300mm length. By the observation of phenomena, measurement of reignition temperature, and analyses of reaction residue, the following results and conclusions were obtained. i) When the burning was distinguished by pure N2 gas, reignition did not occur at 50deg-C. However, reignition occurred at 50deg-C when the distinguishing N2 gas contained over 1% O2. ii) Reignition temperature became higher by supplying humidity and CO2 after cooling down the residue, even when the distinguishing N2 gas contained O2. iii) The reaction residue consisted mainly of Na2O and Na, partly of NaOH, Na2CO3, and Na2O2 depending on the experimental condition. No peculiar compound was detected. The reignition might be attributed to the sharply projecting-shaped gray-white-colored reaction products which contains Na2O. (author)