39138
Accession Number
26162
Author
Buchwald, Vagn F.; Clarke, Roy S., Jr.
Author Affiliation
The Technical University. Department of Metallurgy;Smithsonian Institution. National Museum of Natural History. Division of Meteorites
Title Of Article Chaper
Corrosion of Fe-Ni alloys by Cl-containing akaganéite (beta-FeOOH): The Antarctic meteorite case
Title Of Journal Book
American mineralogist
Volume
74
Pages
656-667
Collation
12 p. : ill.
Reference Bibliography
Includes bibliographical references
Language Of Text
English
Language Of Summary
English
Literature Type
Serial
Literature Level
Analytic
Abstract
A suite of 12 iron and 8 stony meteorites from various environments and locations in Antarctica was studied, representing a range of compositions, metallographic structures, and degrees of weathering. Polished sections of meteoritic metal with adhering corrosion products were examined microscopically, with the electron microprobe and SEM, and were used as samples for X-ray diffraction examination. The major corrosion products are Cl-containing akaganéite (up to 5wtper thousand Cl) and goethite, with minor amounts of lepidocrocite and maghemite. Cl is not native to the meteorites but, owing to the electrochemical nature of the corrosion of Fe-Ni alloys, is attracted from the snow and ice, or rocky soil, environment that contains low amounts of Cl. Akaganéite precipitates near the reaction front, incorporating Cl<sup>-</sup>ions into ion-exchange sites, where they may be retained, made available for further depassivating, corrosive action, or become flushed from the system. With time and distance from the reaction surface, akaganéite ages and transforms to mainly goethite and maghemite. It is again argued that lawrencite (FeCl 2) is not a mineral in meteorites. In the stormy Antarctic, wind-blown terrestrial particles may become attached to the weathering products on the meteorite and in time themselves decompose, delivering terrestrial ions to the meteorite corrosion system. The ions may move a significant distance from the surface, and in particular Cl may be found along almost invisible cracks in the deep interior. Trace-element work and age determinations (<sup>36</sup>Cl) should take this problem into account.
Keywords
corrosion;alloy;akaganéite;meteorite
pub_id
39138