CONTINUOUS MONITORING OF THE COMPOSITION OF LIQUID PB-17LI EUTECTIC USING ELECTRICAL-RESISTIVITY METHODS

The compsition of liquid Pb-17Li alloys has been continously determined, using an electrical resistivity monitor, during their interaction with nitrogen, oxygen, hydrogen and water vapour. The operation of the monitor depends on the fact that the resistivity of liquid Pb-Li alloys is dependent on their composition. Accurate resistivity-composition isotherms have been derived from resistivity-temperature data for 15 Pb-Li alloys (0 < x(Li) < 18 mol% Li; 625 < T < 775 K). The resistivity of the alloys increases with lithium content with a slightly increasing gradient. Over limited composition ranges, the isotherms are effectively linear; for the Pb-17Li eutectic, the gradient (1.27 x 10(-8) OMEGA-m (mol% Li)-1 at 725 K) is such that a change of 0.05 mol% Li in the alloy composition can be measured. The addition of oxygen and water vapour resulted in a decrease in the resistivity of the liquid alloy. Neither nitrogen nor hydrogen had any effect. The observed changes were shown to be consistent with Li2O formation.