Electrolytic Zr02 Coatings

ZrO2 coatings were deposited on graphite and titanium from an aqueous olution based on a water-soluble precursor. A two-step mechanism is suggested for the ZrQ formation: generation of hydroxyl ions (OH) at the cathodic substrate by reduction of NO ~ 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 (ZrQ). 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. Ceramic coatings are currently of much interest for ap-plications in high-temperature and severely corrosive en-vironments. A variety of methods are available for their production, including plasma spraying (1, 2), chemical vapor deposition (CVD) and sputtering (1), and sol-gel pro-cesses (3-5). Formation of ceramic coatings by electrochemica