The high temperature oxidation of metals forming cation-diffusing scales
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The High Temperature Oxidation of Metals Forming Cation-Diffusing Scales
ROBERT A. RAPP
In the past two decades, researchers have repeatedly shown that Wagner's classical parabolic scaling theory has a limited temperature regime of applicability. In particular, at intermediate temperatures--generally the highest permitted for long-lived engineering systems--parabolic oxidation rates are higher and activation energies are lower than those values extrapolated from higher temperatures where lattice-diffusion-limited growth occurs. Short-circuit cation diffusion via scale grain boundaries and dislocations supports oxidation in the intermediate temperature regime, and scale growth at the scale/gas interface takes place at ledges provided by screw dislocations intersecting the surface. These dislocations in the scale are formed by growth stresses or are inherited from the metal. In situ observations of scale growth in a hot-stage environmental scanning electron microscope have provided insight into scale growth mechanisms and the formation of nonplanar oxidation products: whiskers, pyramids, and pits. Specific reference is made to the evolution of oxidation product morphologies for copper, nickel, iron, and chromium.
The Edward DeMille Campbell Memorial Lecture was established in 1926 as an annual lecture in memory of and in recognition of the outstanding scientific contributions to the metallurgical profession by a distinguished educator who was blind for all but two years of his professional life. It recognizes demonstrated ability in metallurgical science and engineering.
Dr. ROBERT A. RAPP is Professor of Metallurgical Engineering at The Ohio State University, Columbus, Ohio. He received his B.S. in Metallurgical Engineering from Purdue University in 1956, M.S. and Ph.D. in Metallurgical Engineering from Carnegie-Mellon University in 1959 and 1960. He was a Postdoctoral Fulbright Scholar at the Max Planck Institut f~r Physikalische Chemie, Grttingen, Germany from 1959-60.
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A research metallurgist at Wright-Patterson Air Force Base, Dayton, Ohio from 1960-63, Dr. Rapp joined The Ohio State University in 1963 as Assistant Professor. He became Associate Professor in 1966 and Full Professor in 1969. His many awards include: John Bray Award, Purdue University, 1956; Fulbright Scholarship, MPI Phys. Chem., 1959; ASM Bradley Stoughton Young Teacher Award, 1967; Guggenheim Fellowship, Ecole Nationale Superieure d'Electrochimie, Grenoble, France, 1972; ASM Henry Marion Howe Medal, 1973; MacQuigg Teaching Award, College of Engineering, The Ohio State University, 1977; Distinguished Research Award of The Ohio State University, 1982; Outstanding Research Award of O.S.U. College of Engineering, 1984. Dr. Rapp was selected as a Fellow of ASM in 1980, of TMS-AIME in 1982, and is a member of Tau Beta Pi and Sigma Xi. He is a registered Professional Engineer in the State of Ohio and is a member of the Electrochemical Society and the National Association of Corrosion Engineers. He holds four patents, h
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