ELECTROLYTIC ZRO2 COATINGS .1. ELECTROCHEMICAL ASPECTS

ZrO2 coatings were deposited on graphite and titanium from an aqueous solution based on a water-soluble precursor. A two-step mechanism is suggested for the ZrO2 formation: generation of hydroxyl ions (OH-) at the cathodic substrate by reduction of NO3- and dissolved O2, and then reaction of the hydroxyl ions with zirconyl ions present in the solution to form the hydroxide Zr(OH)4, which in turn decomposes on drying to yield zirconia (ZrO2). Faradaic efficiencies of 20-50% were found, attributable to reduction reactions that do not produce hydroxyl ions, as well as to formation of the hydroxide at sites removed from the cathodic substrate due to diffusion of the hydroxyl ions. The effects of current density, time, and hydrodynamic conditions on coating weight, cell voltage, temperature, and pH of the solution were studied.