The electrodeposition of Al-Nb alloys from chloroaluminate electrolytes

Abstract

The electrochemical behavior of niobium in a 52:48 mole ratio AlCl 3:NaCl molten salt electrolyte was examined by linear sweep voltammetry, chronoamperometry and chronopotentiometry at 190 °C. Niobium oxidation begins at about 1.10 V versus Al but appears to be limited to a charge of about 3.7 mC/cm 2 before the electrode becomes inhibited. This inhibition is likely due to the limited solubility of the niobium oxidation product. The inhibition region extends from about 1.20 V to 1.40 V. At higher oxidation potentials, the current can be continuously increased up to the anodic limit of the chloroaluminate electrolyte. Aluminum-niobium alloys can be electrodeposited from the above electrolyte following Nb dissolution. Alloys containing a Nb atomic fraction of up to 13.4 % have been electrodeposited. X-ray diffraction and transmission electron microscopy examination of these electrodeposits indicate that the low Nb deposits are face centered cubic aluminum. As the Nb content increases, an amorphous phase is introduced into the structure. The exact composition of the amorphous phase as well as the phase distribution in the 3 % to 13.4 % Nb alloys have yet to be determined.