ELECTROCHEMICAL PROPERTIES OF SOLUTIONS OF CRCL2 AND CRCL3 IN MOLTEN ALKALI CHLORIDES

Pulse techniques were used to study the electrochemical properties of chromium chlorides dissolved in the fused LiCl + KCl eutectic mixture. The reaction Cr(III) + e- half arrow right over half arrow left Cr(II) was shown to be reversible. At 450-degrees-C the standard potential is -0.847 V vs. the chlorine electrode. In the temperature range 380-550-degrees-C the diffusion coefficients of both species obey the Arrhenius equation: D = D-degrees exp(- DELTAH/RT) with D(Cr(III))-degrees = 1.87 x 10(-2) cm2 s-1, DELTA H(Cr(III)) = 44.8 kJ mol-1 and D(Cr(II))-degrees = 9.55 x 10(-3) cm2 s-1, DELTAH(Cr(II)) = 40.8 kJ mol-1 (T in K). Deposition under galvanostatic or potentiostatic conditions leads to dendritic deposits. However, study of the reaction kinetics indicated the existence of an adsorption step. This property leads to a better chromium coating procedure using a pulsed current with short duration of a few milliseconds.