Abstract

R.G. Buchheit
Fontana Corrosion Center
Chair, Department of Materials Science and Engineering
The Ohio State University, Columbus, Ohio

Monday, May 12, 2008
Wilsdorf Hall, RM 101
4:00 - 5:00 pm

Please join us beforehand for refreshments at 3:30

" Vanadium (V) Compounds and Corrosion Protection: Exploiting Complex Speciation, Inorganic Polymerization and Ion Exchange to Extend Inhibitor Functionality "

ABSTRACT:

Vanadate compounds are potent corrosion inhibitors for Al alloys, but are not used widely at the present time. This is due in part to a lack of means for introducing the compounds into corrosion protection schemes, and an incomplete understanding of vanadate inhibition. In this presentation, results from work in our laboratories related to these issues will be presented.

Electrochemical and solution phase nuclear magnetic resonance (NMR) measurements show that vanadates suppress corrosion mainly by inhibiting the oxygen reduction reaction (ORR). They also show that ORR inhibition is strongly dependent on speciation. Tetrahedrally coordinated metavanadates ([VO3-]x) are powerful ORR inhibitors, but octahedrally coordinated decavanadates; namely V100286-, V10027(OH)5- and V10026(OH)24- are not. In fact, decavanadates may stimulate corrosion slightly because they are reducible. Because of the relationship between ORR inhibition and vanadate coordination, the dependence of ORR inhibition on concentration is inverted in the pH range of 4 to 6. Inhibition is observed in 0.1 to 1.0 millimolar solutions at pH 4, but a 100 mM vanadate concentration is needed to accomplish inhibition at pH 6. This characteristic has practical consequences for use of vanadates as corrosion inhibitors.

Using different approaches, octahedrally coordinated forms of vanadate can be made useful for corrosion protection. At pH 2 near the pHpzc, VO(OH)3 can change coordination from tetrahedral to octahedral enabling inorganic polymerization and gel formation. Gel formation is promoted using a NaF activator and K3Fe(CN)6 additions to aqueous process solutions to form a vanadate-based conversion coating that releases a vanadate inhibitor with a self-healing protective response. Vanadate inhibitors can also be imparted to protective organic coatings using synthetic ion exchange compound pigments.

Vanadate corrosion inhibitors have been delivered using Zn-Al hydrotalcite pigments intercalated with exchangeable V10O286- ion. It is necessary to use decavanadate to achieve pigment synthesis, but for corrosion protection speciation to metavanadate is required once the decavanadate is exchanged into solution. Solution phase NMR measurements show that the formation of metavanadates by decomposition of released decavanadate does in fact occur over time scales relevant for corrosion protection. How vanadate corrosion inhibition translates to corrosion protection during accelerated exposure testing of organic coatings containing this compound will also be described.

BIOGRAPHY:

Rudolph G. Buchheit is Professor and Chair of Materials Science and Engineering. His research is in the area of corrosion science and engineering with emphasis on localized corrosion, corrosion protection and corrosion prediction; mainly of light metals. He has also worked extensively in the area of corrosion inhibition, surface modification and corrosion resistant coatings. He has published 180 technical articles (95 peer reviewed) on these subjects with students and colleagues, and holds 8 patents related to surface treatments and coatings. He has contributed 7 chapters to books, edited 3 technical proceedings and co-authored one book. He earned a BS in Engineering Science at Loyola College in Maryland in 1985, and MS and PhD in Materials Science from the University of Virginia in 1987 and 1991. He was a Senior Member of the Technical Staff in the Materials and Process Sciences Directorate at Sandia National Laboratories New Mexico from 1990 until joining the faculty in the Fontana Corrosion Center in Materials Science and Engineering at Ohio State in 1997. He is a Fellow of NACE International, and past Chair of the Research Committee. He is also an active member of the Electrochemical Society and serves on the Executive Committee for the Corrosion Division. He serves on the Editorial Boards for Corrosion Journal, Corrosion Engineering, Science and Technology and is a former Principal Editor for the Journal of Materials Science. He is the recipient of the H. H. Uhlig Educator's Award from NACE, and the Morris Cohen Award from the Corrosion Division of the Electrochemical Society. He is also the recipient of the Stanley E. Harrison Faculty Award from the College of Engineering at Ohio State, and the Charles E. MacQuigg Award for outstanding teaching.

 

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