THE ELECTROCHEMICAL POLARIZATION OF ZIRCONIUM IN NACL SOLUTIONS
TEXAS UNIV AT AUSTIN CORROSION RESEARCHLAB
Pagination or Media Count:
Cathodic and anodic polarization curves of Zr in neutral NaCl solution were determined at constant current densities in the range of 3.5 x 10 to the power of -8 to 3.5 x 10 to the power of -3 ampsq cm. All potentials were steady state. In aerated 0.5 M NaCl, the cathode reaction occurring below the O limiting diffusion current of 2 x 10 to the power of -4 ampsq cm was the reduction of O to OH. At current densities above the diffusion wave, H was evolved. A change in salt concentration resulted in a slight shift of the diffusion current due to different O solubilities in the different salt concentrations. In deaerated 0.5 M chloride solution, the O diffusion current decreased with a decrease in O concentration. The value for the slope of the Tafel line was 0.12, and the H overvoltage was 0.83 v at 1 masq cm. Another wave occurred at 2 x 10 to the power of -6 ampsq cm and can best be explained as the reduction of a surface oxide layer on the metal. Anodically, Zr dissolved in 0.5 M NaCl. The dissolution potential, 0.15 v, was constant with a change in current density. Commerical Zr and pure Hf also dissolved under similar conditions. In neutral sulfate solutions, Zr was passive under anodic treatment. At the higher current densities, above 1 x 10 to the power of -3 ampsq cm, the potential apparently reached a constant value in about 10 min, followed by a sudden increase in potential to 28.5 v. This high potential was a result of an IR drop across a surface of oxide present on the Zr coupon.
- Inorganic Chemistry