Characterization of the Surface Film Growth During the Electrochemical Process : Part II

In order to understand the resistance of passive films formed during corrosion processes, an analytical technique using x-ray diffraction was developed to examine the structure of metal in closest proximity to the metal / liquid interface. The in-situ structure at the metal liquid interface was examined for 90 % copper and 10 % nickel (90-10 Cu-Ni) in KOH solution at room temperature and at four different potentistatically controlled potentials (-0.5 V, 0.1 V, + 0.5 V and +0.10 V versus Ni/NiO). The chemical changes at the metal interface were studied over a period of 48 hours. It was found that the integrity of the 90-10 Cu-Ni foil in KOH was lost after a continued application of the potential over 48 hours. The x-ray diffraction results indicated that the structure of both the inner and the outer passive layers, at -0.5V and 0.1 V (versus Ni/NiO), is comprised of Ni(OH)2, Cu(OH)2, NiOOH and Cu20 NiO. Similarly the structure of the interfaces at + 0.5 V and + 0.10 V (versus Ni/NiO) contains NiO, Ni203, Cu20 NiO and Ni2Cu03. XPS analysis of the surface structure (primarily of the outer passive layer) suggests that at 0.50 V (versus Ni/NiO) the structure consists of Ni(OH)2, Cu(OH)2 and CuO. The structure at +0.50 V (versus Ni/NiO) consists of NiO, Ni203, Ni(OH)2, Cu(OH)2 and CuO. It is therefore possible that the structure of inner passive layer may be NiOOH at 0.5 V and 0.10 V and Ni(OH)2 at + 0.50 V and + 0.1 V. ADMTNSTRATIVE INFORMATION This project was funded by the Electric Power Research Institute (EPRI), Palo Alto, CA and administered by the Materials Corrosion Program manager, Dr. Larry J. Nelson, under the Strategic Research Initiative Program. The work was performed at the Carderock Division of the Naval Surface Warfare Center (CDNSWC) under the Contract Number: W08041-10 and Work Unit Number 1-6120-600. This work was supervised Within the Metals Department (Code 61) by Dr. L. F. Aprigliano (Code 612).