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The kinetics of thin oxide film formation on iron using proton-impact-excited x-ray analysis.

Needham PB Jr.; Leavenworth HW Jr.; Driscoll TJ
J Electrochem Soc 1973 Jun; 120(6):778-783
Studies of the oxidation of high-purity iron samples at 224 deg., 285 Deg., and 350 deg. C have been conducted in an oxygen partial pressure of 4 x 10-6 torr for exposure times ranging from 25 to 2,000 sec. The oxide films were measured and quantitatively analyzed for trace carbon impurities using proton-impact-excited characteristic x-rays. Analytical surface sensitivities to the equivalent of 10-3 monatomic layers have allowed direct studies of ultrathin (<50 a) oxide film kinetics. A two-stage logarithmic oxidation rate law was observed at all temperatures with the transition from the first to second stage occurring at oxide thicknesses of 25, 36, and 52 a at 224 deg., 285 Deg., and 350 deg. C, respectively. This observation is discussed in term of uhlig's theory for logarithmic oxidation. Quantitative measurements of carbon impurities on the iron surfaces show that an increase in the preoxidation surface coverage from 0.1 to 1.0 Monolayer results in a significant suppression of the oxidation process. In a discussion in a later issue of the journal, J. Electrochem. Soc. 1973 120(1)2:1791 <a href=""target="_blank"></a> the authors respond to b. Chattopadhyay's use of their results to support his theory of metallic oxidation. The authors point out two errors in Chattopadhyay's theory that appear to invalidate his conclusions concerning the relative effects of surface state charge and space charge on the electrical potentials across growing iron oxide layers.
Mining-industry; Mineral-processing; Metals; Author Keywords: iron; oxidation; thin films; reaction kinetics; chemical analysis; high-temperature effects; impurities; double-logarithmic oxidation; proton-impact-excited x-rays; carbon surface impurities
Publication Date
Document Type
OP; Journal Article
Fiscal Year
Identifying No.
OP 90-74
Issue of Publication
NIOSH Division
Source Name
Journal of the Electrochemical Society
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