The construction of a sodium beta alumina probe for the determination of the sodium activity in molten aluminum alloys is
described. It was found that the emf at a given sodium concentration was a strong function of the silicon content. Henry’s
law was obeyed in super purity aluminum and the activity coefficient of 350 at 998 K agrees with other determinations.
Formerly Graduate Student in the Department of Metallurgy and Materials Science, University of Cambridge