Kurt R. Hebert
Professor
2037 Sweeney Hall
Iowa State University
Ames, IA 50011-2230
Phone (515)294-6763
Fax (515)294-2689
krhebert
iastate.edu
Education
B.S., ChE, Princeton University, 1978
M.S., ChE, University of Illinois, 1981
Ph.D., ChE, University of Illinois, 1985
Honors and Awards
Young Engineering Faculty Research Award, 1994
Host laboratory for French Government CSN program (Chercheur du Service National -
Chercheurs Scientifiques), October 1997-December 1998
Plenary Invited Lecture, Electrochemical Society Symposium, Spring Meeting, Seattle, May 1999
Advanced Materials SBIR-STTR Phase II Proposal Review Panel, National Science Foundation,
Arlington, VA, March 2000
Teaching/Office Hours Schedule
Research Interests
Many metals used in structures and devices are intrinsically reactive with their environments and depend on thin surface films, formed by oxidation, for protection against corrosion. When corrosion initiates on oxide-covered metals, it does so on microscopic areas where the oxide film has been locally removed. Because the corrosion rate is very large, these areas can rapidly grow from microscopic dimensions to sizes where structural failure is a concern. The goal of our research is to develop a fundamental understanding of critical chemical and physical processes involved in localized corrosion which will lead to engineering strategies for improved corrosion control. We are investigating both the nature of sites where corrosion is likely to initiate, and the progress of corrosion on these sites once it has begun. This information is also important in etching applications where patterns of microscopic cavities are desired.
Other Information
Member of the Electrochemical Society
Research Projects
Study of Corrosion-Related Solid State DefectsStudies to reveal the nature of microscopic corrosion sites on aluminum have been carried out using positron annihilation spectroscopy (PAS) and atomic force microscopy (AFM). PAS is a technique which has found extensive use in materials science for the detection of atomic-scale defects produced by various operations in electronic device processing. In our work, these measurements have been carried out in collaboration with researchers at Washington State University. The PAS and AFM results reveal 20-200 nm large voids at the aluminum-aluminum oxide film interface. We have shown that corrosion initiates at a void when the overlying oxide dissolves, thereby exposing its highly reactive metal surface. Interfacial voids are present on all aluminum surfaces we have examined so far, and therefore appear to be a very common type of corrosion site. Currently, we are exploring surface treatments which can produce regular patterns of interfacial voids on the aluminum surface. This would enable us to fabricate "nanostructures" by simple etching processes and without using lithographic masks.
Modeling of Structure and Transport Behavior of Surface Oxide Films on Metals
These modeling studies are focused on obtaining a clearer understanding of defects in surface oxide films. This knowledge is likely to be important to the mechanism of chemical breakdown of these films, at the onset of localized corrosion, as well as in the electrochemical production of thin dielectric films. A mathematical model has been developed to predict mass transport rates of metal and oxygen ions in amorphous oxide films on metals. The model is based on a new mechanism for ionic transport in the film by oxygen vacancy-like defects (i.e., defects consisting of a missing oxygen ion). In the mechanism, local relaxation of ions around the defect allows nearby metal ions to move downfield. A certain number of these metal ions are transported along with the oxygen vacancy. We can for the first time successfully predict the relative mass transport rates of metal vs. oxygen ions as a function of the applied electric field.
Experimental and Modeling Studies of the Development of the Shapes of Etching Cavities
An aluminum etch tunnel is a type of microscopic corrosion cavity with a unique linear shape, produced by electrochemical etching in HCl. A high density of micron-wide tunnels is produced intentionally in the manufacture of electrodes for high voltage electrolytic capacitors. Research has focussed on developing a mathematical simulation of tunnel growth, which can be used to help optimize the etching process. The simulation is based entirely on independently verifiable models for heterogeneous reaction kinetics and solution thermodynamics and transport processes. For a variety of etching conditions, the simulation successfully predicts the spontaneous initiation of tunnels from cubic etch pits, as well as the detailed shape evolution of tunnel structures during their growth. It is likely that the quantitative understanding of corrosion processes developed in this work will find application in modeling the progress of corrosion and etching processes in other metal-electrolyte systems.
Selected Publications
K. R. Hebert, H. Wu, T. Gessmann, and K. G. Lynn, " Positron Annihilation Spectroscopy Study of Interfacial Defects Formed by Dissolution of Aluminum in Aqueous Sodium Hydroxide," J. Electrochem. Soc., 148, B92 (2001).
T. Martin and K. R. Hebert, "Atomic Force Microscopy Study of Anodic Etching of Aluminum: Etching Morphology Development and Caustic Pretreatment," J. Electrochem. Soc., 148, B101 (2001).
K. R. Hebert, "A Mathematical Model for the Growth of Aluminum Etch Tunnels," J. Electrochem. Soc., 148, B236 (2001).
K. R. Hebert, "Analysis of Current-Potential Hysteresis During Electrodeposition of Copper With Additives, J. Electrochem. Soc., 148, C726 (2001).
