Effect of Soaking in Hot Saline Solution and Humid Atmosphere on the Passive Film Behavior of a Ni-Cr-Mo Alloy
Alloy 22, a Ni-Cr-Mo alloy, is the candidate material for fabrication of canisters for disposal of high-level and spent nuclear fuel waste in the proposed Yucca Mountain repository in Nevada. This paper investigated the passive film behavior and corrosion properties on Alloy 22 as a function of soaking in hot, saline environments and in hot, humid atmospheres. Environmental parameters include potential, temperature, pH in chloride and multi-species solutions. Hot, humid exposures are planned for temperatures up to 300 C. Soaking times are planned to extend for up to 1000 hours. This work is part of a multi-investigator study to determine the durability of passive films and localized corrosion processes in metal exposed to moist particulate and deposits. Of particular interest are the long-term stability of the passive film and the effects of soaking in aqueous solutions or hot, humid atmospheres. A combination of electrochemical methods measure changes in passive film properties, and a combination of surface analysis techniques are used to characterize the film composition and structure. Electrochemical methods include Potentiodynamic Polarization tests for the general corrosion behavior; along with Electrochemical Impedance Spectroscopy (EIS) and Mott-Schottky (M-S) analysis for electronic properties of the passive films. Alterations in the chemical composition and structure of the passive film are characterized using X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) and Transmission Electron Microscopy (TEM). Results for freshly formed films are shown in figure 1. The EIS results show that the interfacial impedance increased with increasing potential to maximum within the passive range and then decreased as the potential was increased further. interfacial impedance was found to decrease with increasing temperature. Mott-Schottky analysis indicated that the oxide film which is n-type in the passive region changes to p-type in the transpassive region. Figure 2 shows the representative chemical soaking results at 90 C for up to 240 hours; the interfacial impedance increased with soaking time. Results from this work are combined with those from collaborative studies to correlate the passive film properties with the resistance to localized corrosion using multi-crevice assemblies and micro-corrosion cells. The passive film growth and dissolution are interpreted with reference to processes based on the point defect model.
- Research Organization:
- Yucca Mountain Project, Las Vegas, NV (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- NA
- OSTI ID:
- 893811
- Report Number(s):
- NA; MOL.20060712.0167, DC# 47970; TRN: US0606178
- Country of Publication:
- United States
- Language:
- English
Similar Records
Evaluation of an Oxide Layer on NI-CR-MO-W Alloy Using Electrochemical Impedance Spectroscopy and Surface Analysis
IN SITU INVESTIGATION OF THE PASSIVATION OF ALLOY C22 AND OF THE PASSIVE FILMS FORMED ON ALLOY C22 IN ACIDIC ELECTROLYTES AT ROOM TEMPERATURE AND AT 90 DEGREES C
Related Subjects
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
ALLOYS
AQUEOUS SOLUTIONS
AUGER ELECTRON SPECTROSCOPY
CHEMICAL COMPOSITION
CHLORIDES
CONTAINERS
CORROSION
FABRICATION
IMPEDANCE
NUCLEAR FUELS
OXIDES
PARTICULATES
POINT DEFECTS
POLARIZATION
SPECTROSCOPY
TRANSMISSION ELECTRON MICROSCOPY
WASTES
X-RAY PHOTOELECTRON SPECTROSCOPY
YUCCA MOUNTAIN
SPENT FUELS