Date of Award
Doctor of Philosophy
Stainless steel system components that operate in high temperature oxidizing environments obtain protection from corrosion by means of thermally grown chromia and alumina scales. Ongoing investigations of protective scales utilize a battery of experimental and theoretical techniques. A technique which has received little attention is Raman scattering. The reason for its limited use has been long data acquisition times required to obtain suitable spectra from thin surface oxides. Because advances in detection systems, namely the multichannel CCD (charge coupled devices), have recently provided dramatic improvement in the sensitivity of Raman scattering experiments, we decided to reevaluate the technique as a probe of oxide scale evolution.
During the Raman investigation it was observed that many of the scales that formed on aluminum containing alloys fluoresced when irradiated with the laser. The origin o f some of the fluorescence was found to be due to the presence of ruby (a- Al2 0 ]:Cr) in the scale. Because ruby fluorescence has a rich history in high pressure diamond anvil cell research, it seemed likely to provide scale stress information (i.e. ruby piezospectroscopy). Thus, our research objectives were adjusted to include the evaluation of ruby piezospectroscopy as a tool for the investigation of scale stress.
The multichannel CCD was found to provide short data acquisition times (500 sec.). Both the Raman and fluorescence techniques were found to be convenient because they require little sample preparation and are non-destructive. A Raman “fingerprint” technique was found to be useful for identifying and tracking scale oxide phase behavior, during transient oxidation, steady-state oxidation, and breakaway corrosion. Raman spectroscopy and ruby piezospectroscopy have been used to provide insight into the reactive element effect. By using micro-fluorescence we have also provided insight into the thermal-mechanical behavior of scales near sample edges and of scales with convoluted (or wrinkled) interface morphologies.
Renusch, Daniel P., "Evaluation of Raman Spectroscopy and Ruby Piezospectroscopy as Tools for Investigating the Corrosion of Metallic Alloys" (1999). Dissertations. 1528.