ABSORPTION OF METALLIC SODIUM IN CARBON CATHODE MATERIALS

The absorption of sodium vapour in commercial cathode materials for al uminium electrolysis has been studied within the range 1020-1227 K and 3-600 Torr. The absorption increases strongly with decreasing degree of graphitization. The absorption of sodium in the commercial material s can be described as a BET isotherm with calculated surface area betw een 9 and 124 m(2)/g. The measured surface area by helium absorption, however, is less than 1 m(2)/g. Pure synthetic graphite behaves differ ently and a minimum sodium pressure is needed before absorption starts .