The Electrodeposition of Aluminum-Niobium Alloys from Chloroaluminate Electrolytes

Abstract

The electrochemical behavior of niobium in a 52:48 mole ratio AlCl3:NaCl molten salt electrolyte was examined by linear sweep voltammetry, chronoamperometry and chronopotentiometry at 190 °C. Niobium oxidation begins at about 1.10 V vs. Al but appears to be limited to a charge of about 4 mC/cm2 before the electrode becomes inhibited. This inhibition is likely due to 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. Gravimetric analysis during oxidation indicates that the dissolution of Nb at 1.50 V is a two-electron process. Aluminum-niobium alloys can be electrodeposited from the above electrolyte following Nb dissolution. Alloys containing a Nb atomic fraction of up to 13.5 % have been electrodeposited. X-ray diffraction and transmission electron microscopy examinations of these electrodeposits indicate that the low Nb concentration deposits (< 5% Nb) are face centered cubic (fcc) aluminum. As the Nb content increases, an amorphous phase is introduced into the structure.