This project employs a novel in-situ transmission electron microscopy (TEM) method to study corrosion reactions at liquid-solid interfaces in real-time. Using a micro-fluidic chamber sealed between electron transparent membranes, nanoscale corrosion processes that occur at interfaces between water and pure aluminum or aluminum alloys are studied. The program focuses on the fundamental issue of pit initiation in passivating films. This in-situ method addresses a long standing problem of examining passive films in electron microscopes where vacuum is known to affect the structure and properties of the films by maintaining hydrated surfaces throughout the characterization of the passivation and corrosion processes. This in-situ technique allows the observation of the formation of passive films and also allows the introduction of pit inducing chloride solutions in real time. By synthesizing passivating films of varying crystallinity and thickness prior to initiating corrosion, differentiation between nucleation events dominated by the intrinsic surface structure and chemistry of the films, and those controlled by the structure and chemistry of the metal can be accomplished. Alloy films of Al-Li and Al-Cu, will also be studied to understand the interaction of the alloying elements with the growth and stability of the passivating films and the subsequent pitting reactions. While it is known at the micrometer scale that alloying elements affect pitting behavior, it is not known if that is due to electrochemical interactions at the nanometer level or if the elements are also incorporated into the passive films, thus affecting the intrinsic resistance of the films to localized breakdown. The in-situ TEM methods are supplemented by x-ray photoelectron spectroscopy and Auger electron spectroscopy, utilizing deposition and reaction chambers directly attached to the instruments.
NON-TECHNICAL SUMMARY: The impact of corrosion upon the national infrastructure and upon manufactured goods is enormous (estimated at 5-10% of GNP), creating a substantial drain on the national economy and having major impacts upon infrastructure and transportation safety. A recent study published by the National Academies of Science and Engineering identified a number of important research areas that should be pursued to alleviate the drain of corrosion on the nation's resources. Among those areas identified is the problem of localized corrosion such as pitting, since its occurrence is often unpredictable. This project employs a novel in-situ transmission electron microscopy (TEM) method to study corrosion reactions at liquid-solid interfaces at the nano-scale in real-time. The fundamental knowledge derived under this research program may help to understand, and subsequently to mitigate, localized corrosion reactions. While this program primarily addresses passive film formation and local breakdown on aluminum and aluminum alloy films, the information obtained from the program will be applicable to the technological problem of localized corrosion in other metal and alloy systems. The advantage of an in-situ, real time examination method is that it allows the observation of nanometer-scale phenomena under environmental conditions typical of actual corrosion events. In addition to advancing scientific knowledge of an important corrosion phenomenon, this project contributes to the nation's intellectual base by educating graduate students at the Ph.D. level. In the aforementioned NAS/NAE study of the nation's needs in corrosion research, the absence of an adequate cadre of trained corrosion scientists was clearly identified. Another major aspect of the program is that it uses undergraduate laboratory researchers, exposing them to advanced research methods and the opportunity to be involved in the understanding and possible mitigation of an important technical problem.
