The current work used this protocol on coatings provided by engineers from Naval Air Systems Command that had been doped with varying amounts of CeO. Initial voltage applications showed coating breakdown with increasing current at ever more positive potentials. However, a maximum was seen and at potentials above 2V, the coatings appear to have improved.
In an effort to elucidate what caused this effect, Electrochemical Impedance Spectroscopy (EIS), laser profiling, and x-ray fluorescence studies were performed to look for changes in the coating. Preliminary EIS results (Figure 1) indicate the resistance due to pores increased after higher potential application hinting the pores may be becoming smaller.[ii]The value of the real component of the complex impedance, where the left side of the semicircle begins, is the sum of the uncompensated resistance and pore resistance. Spectra were taken after the Al substrate was exposed to the indicated DC potential. While not large, it can be seen the resistance increased as the applied potential increased. X-ray results as well as laser profiling (not shown) indicate the coating at and near the surface is changing. The X-ray data show other components of the coating (Ti, Fe, etc) are migrating to/from the surface. The laser generated topographical data also shows morphological changes on the surface all of which may be the cause of the pore size reduction.
All data were taken at the U.S. Naval Academy, an undergraduate only institution, by one student. Projects such as this where the midshipmen conduct two semesters of research under the supervision of a professor, became part of USNA’s chemistry major over a decade ago. While not compulsory, some 70% of the majors elect this option and most result in at least a published conference proceeding. This is even more remarkable in that the students do not have the flexibility to conduct experiments outside the normal school day.