SPECIATION MODELING OF THE ELECTROPRECIPITATION OF RARE-EARTH CUPRATEAND NICKELATE MATERIALS - SPECIATION OF AQUEOUS-SOLUTIONS NOT AT EQUILIBRIUM

Films of insoluble metal hydroxide have been obtained by cathodic elec troprecipitation from aqueous solutions containing the nitrate salts o f a lanthanide (La3+ or Nd3+) and a transition-metal cation (Ni2+ or C u2+). Manipulation of deposition parameters, such as deposition voltag e, V-a and solution composition, allows for extensive variation in mol e fractions, x, of each metal in the final bimetallic hydroxide produc t. The variations in x are attributed to changes in the chemical envir onment within the Nernst layer at the electrode/solution interface, oc curring in tandem with differences in the solution-and solid-phase spe ciation characteristics of the two metals and their hydroxides. The ex perimentally obtained compositions of the deposited solid oxyhydroxide have been correlated with thermodynamically derived overall formation constants, beta, and calculations of concentration obtained using a f ull speciation analysis. This model can be used to correctly predict c ompositions, which is taken to verify the model of electroprecipitatio n used.