Correlation studies between outdoor exposure and accelerated laboratory corrosion tests for galvanic and non-galvanic ceramic-aluminum couples
Correlation studies between outdoor exposure and accelerated laboratory corrosion tests for galvanic and non-galvanic ceramic-aluminum couples
Date
2010-12
Authors
Srinivasan, Raghu
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[Honolulu] : [University of Hawaii at Manoa], [December 2010]
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Abstract
The objective of this research was to develop test protocols to analyze the corrosion between aluminum and ceramics in accelerated and natural-exposure corrosion tests. The focus was on correlating outdoor exposure corrosion behavior from a variety of microclimates with a series of accelerated laboratory corrosion tests for both galvanic and non-galvanic ceramic-aluminum (Al) couples. Electrolytes with varying amounts of chloride contents (0, 10, 100, 1000, 10000, and 20000 ppm chlorides) were used in the accelerated tests to improve correlation with field results. In addition, the outdoor exposure test data were used to adjust the duration of the accelerated corrosion tests so that the corrosion damage accumulated in the accelerated tests could better represent the corrosion damage accumulated in the field.
The galvanic ceramic-Al couples were those consisting of Al coupled to titanium diboride (TiB2) and boron carbide (B4C) ceramics which have resistivities of 10^-5 and 10^1 ohm-cm, respectively. The non-galvanic couples consisted of Al coupled to silicon carbide (SiC), silicon nitride (Si3N4), and aluminum nitride (AlN) ceramics which have resistivities of 10^7, 10^14, and 10^15 ohm-cm, respectively.
Ceramics and 6061-T6 Al coupons were coupled together using 6061-T6 Cclamps.
Outdoor experiments for 3, 6, and 12-month exposure periods were conducted at eight different test sites, to determine corrosion behavior for various climate and environmental conditions (i.e., rain forest, alpine, marine, volcanic, industrial, agricultural, and arid). Accelerated laboratory experiments include controlled humiditychamber experiments and cyclic corrosion test chamber (CCTC) experiments following modified GM9540P using different chloride-containing solutions. Corrosion rates were determined at the ceramic-Al interface for the outdoor and accelerated laboratory experiments using weight loss data. Polarization experiments were conducted on 6061-T6 Al to study the governing corrosion mechanisms in different chloride solutions. Zeroresistant ammeter (ZRA) studies were conducted between 6061-T6 Al and the conductive ceramics (TiB2) inside a humidity chamber by spraying different chloride solutions in intervals of 24 hours for 5 days to simulate rain and the steady-state galvanic corrosion rates (iGalv) were observed.
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Ph.D. University of Hawaii at Manoa 2010.
Includes bibliographical references.
Includes bibliographical references.
Keywords
Aluminum,
ceramic-aluminum couples,
galvanic corrosion,
crevice corrosion,
accelerated corrosion tests.
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Theses for the degree of Doctor of Philosophy (University of Hawaii at Manoa). Mechanical Engineering.
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