Journal
APPLIED SURFACE SCIENCE
Volume 273, Issue -, Pages 758-768Publisher
ELSEVIER
DOI: 10.1016/j.apsusc.2013.02.131
Keywords
Tetraethylorthosilicate; Organophosphonic acid; Sol-gel synthesis; Aluminum alloy; Electrochemical impedance spectroscopy
Categories
Funding
- MICINN
- FEDER funds [MAT2009-09138, MAT2012-34498]
- DIUE of the Generalitat de Catalunya [2009SGR925]
- Generalitat de Catalunya
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This work describes a new mechanism for the incorporation of organophosphonic acid into silane self-assembly monolayers, which has been used to protect AA1100 aluminum alloy. The protection improvement has been attributed to the fact that phosphonic structures promote the formation of strongly bonded and densely packed monolayer films, which show higher surface coverage and better adhesion than conventional silane systems. In order to evaluate the linking chemistry offered by phosphonic groups, two functionalized organophosphonic groups have been employed, 1,2-diaminoethanetetrakis methylenephosphonic acid (EDTPO) and aminotrimethylenephosphonic acid (ATMP), and combined with tetraethylorthosilicate (TEOS) films prepared by sol-gel synthesis. Results suggest that phosphonic acids may interact with the surface through a monodentate and bidentate coordination mode and, in addition, form one or more strong and stable linkages with silicon through non-hydrolysable bonds. Therefore, the incorporation of a very low concentration of phosphonic acids on TEOS solutions favors the complete coverage of the aluminum substrate during the silanization process, which is not possible using TEOS alone. The linking capacity of phosphonic acid has been investigated by FTIR-RA spectroscopy, SEM and EDX analysis, X-ray photoelectron spectroscopy (XPS), and quantum mechanical calculations. Finally, electrochemical impedance spectroscopy has been used to study the corrosion protection revealing that EDTPO-containing films afforded more protection to the AA1100 substrate than ATMP-containing films. (c) 2013 Elsevier B.V. All rights reserved.
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