REACTIONS BETWEEN SODIUM POLYSULFIDE AND MATERIALS FOR CURRENT FEEDS IN SODIUM-SULFUR BATTERIES

In order to measure corrosion rates of potential materials for current feeds in the sodium polysulfide melt of sodium-sulfur batteries changes with time of the thicknesses of thin films were measured using the 4-point resistance method. At the free corrosion potential the steady state corrosion rate of aluminum in Na2S4 at 350-degrees-C was less-than-or-equal-to 150-mu-m/a and the activation enthalpy around 300 kJ/mol. At sufficiently high cathodic currents the corrosion rates were observed to increase linearly with the square of the total current. Upon anodic polarisation the thickness of the passivating film was increased, but there was not much influence on the mean corrosion rate. However, there were indications of local differences of the corrosion rate. The steel X10CrAl24 corroded by growth of a film according to the parabolic rate law until a steady state corrosion rate was attained being 90-mu-m/a at 350-degrees-C. The steel X10CrNiMoTi 18 10 not containing aluminium corroded at the rate of 1.5 mm/a. The corrosion rate of chromium was even higher. On the other hand, Stellite 6 and glassy carbon corroded at rates < 2-mu-m/a.