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Tuesday, March 16, 2010: 2:00 PM
214 D (Henry B. Gonzales Convention Center)
The surface films formed on Ni-10Cr-8Fe, Ni-5Cr-8Fe, Alloy 600, Alloy 690 as well as unalloyed nickel and chromium in 300°C water containing 1200 ppm borate and 2 ppm Li were investigated by in situ surface enhanced Raman spectroscopy (SERS). Trends in the SER spectra of the films formed on Ni-10Cr-8Fe and Ni-5Cr-8Fe and on Alloy 600 and Alloy 690 assisted in the assignment of peaks in the SER spectra. Three main components were detected: Cr2O3, NiCr2O4, and NiO. The relative amounts of the three components differed for the four alloys. The surface film of Alloy 690 consisted mostly, if not entirely, of Cr2O3. All three components were detected in the films of the other three alloys: the amounts of Cr2O3 and NiCr2O4 increased with the alloys chromium concentration and the amount of NiO decreased with the alloy’s chromium concentration.
The SERS results for the films of the four different alloys could be explained/understood by Diffusion Path analyses. The key assumption underlying Diffusion Path analyses is that ion transport through the film is the rate-determining step of film growth. The diffusion paths of the films for the four alloys are sketched in the hypothetical Ni-Cr-Water ternary phase diagram presented in Figure 1. The results indicate that (1) the film of Alloy 690 is highly resistive to cation transport; (2) the films of Alloy 600 and Ni10Cr8Fe and Ni5Cr8Fe are similar and relative to the Alloy 690’s film do not provide much of a barrier to cation transport.
One possible major shortcoming of our analysis is that we have not included iron in the surface films. Iron is undoubtedly present in a number of the phases present in the film. The omission of iron from our analysis is equivalent to assuming that iron does not have a significant role in determining the phases that are contained in the surface films.
Acknowledgements
We are pleased to recognize the financial support provided by the Electric Power Research Institute of Palo Alto, Ca, and several helpful discussions with Dr. Peter Chou. Dr. Chris Kumai of University of Caifornia, Berkeley, and Dr. Peter Andresesn of General Electric’s Corporate Research and Development Center provided critical advice in the design and construction of our high temperature, high pressure apparatus. Dr. Kumai also assisted in the configuration of our SERS spectrometer.
The SERS results for the films of the four different alloys could be explained/understood by Diffusion Path analyses. The key assumption underlying Diffusion Path analyses is that ion transport through the film is the rate-determining step of film growth. The diffusion paths of the films for the four alloys are sketched in the hypothetical Ni-Cr-Water ternary phase diagram presented in Figure 1. The results indicate that (1) the film of Alloy 690 is highly resistive to cation transport; (2) the films of Alloy 600 and Ni10Cr8Fe and Ni5Cr8Fe are similar and relative to the Alloy 690’s film do not provide much of a barrier to cation transport.
One possible major shortcoming of our analysis is that we have not included iron in the surface films. Iron is undoubtedly present in a number of the phases present in the film. The omission of iron from our analysis is equivalent to assuming that iron does not have a significant role in determining the phases that are contained in the surface films.
Acknowledgements
We are pleased to recognize the financial support provided by the Electric Power Research Institute of Palo Alto, Ca, and several helpful discussions with Dr. Peter Chou. Dr. Chris Kumai of University of Caifornia, Berkeley, and Dr. Peter Andresesn of General Electric’s Corporate Research and Development Center provided critical advice in the design and construction of our high temperature, high pressure apparatus. Dr. Kumai also assisted in the configuration of our SERS spectrometer.