M.S Donley

Nanostructured sol–gel derived conversion coatings based on epoxy- and amino-silanes

Abstract Inorganic/organic hybrid conversion surface coatings for long-term protection of aluminum alloys against atmospheric corrosion have been developed based on a unique self-assembled nanophase particle (SNAP) coating process. Nano-particles with peripheral epoxy functional groups are pre-formed in an aqueous sol–gel process and then assembled and crosslinked upon application on the substrate surface. Mono-, di-, and tri-functional amino-silanes have been used as crosslinking agents. Corrosion resistance properties of these hybrid nanocomposite coatings studied by a variety of electrochemical testing methods including electrochemical impedance spectroscopy, scanning vibrating electrode technique, and potentiodynamic scan method, indicate excellent barrier protection performance of the coatings. For comparison, coatings crosslinked with amino-silanes offer significant improvement in coating performance over the previously described SNAP formulations with a conventional amine crosslinker—diethylenetriamine.

Testing and evaluation of nonchromated coating systems for aerospace applications

Abstract The advanced corrosion resistant aircraft coatings program (ACRAC) is part of the Air Force strategy to improve performance and reduce environmental impact of coatings used on Air Force weapon systems. The program addresses the Air Force near and mid-term strategies to eliminate chromate corrosion inhibitors and reduce steps in the outer mold line coating process. Evaluation of the coating process (surface preparation, conversion coating, primer, topcoat) as a system is a key feature of the ACRAC program. Results to date indicate that the current-state-of-the-art nonchromated coating systems are significantly less effective than those with chromate. A chromate conversion coating is required for the nonchromate primer system to meet minimum requirements. Sol–gel-process based conversion coatings can replace chromate conversion coatings provided a chromated primer is used. Several approaches to incorporating inhibitors into sol–gel coatings are discussed. Electrochemical methods for testing coating performance are discussed and a new procedure based on impedance spectroscopy for evaluating active damage repair is presented.

Nanostructured silicon sol-gel surface treatments for Al 2024-T3 protection

Current coatings for aircraft corrosion protection are based on chromate surface treatments, primers, and topcoats. One approach to developing a chromate-free surface treatment is through the use of sol-gel materials that interact strongly with both the substrate and the subsequent polymer layers. Results are reported here on a new sol-gel technique using a pre-formed, self-assembled, nano-phase particle (SNAP) sol-gel system. SNAP films have been investigated by infrared spectroscopy, atomic force microscopy, and electrochemical methods. Potentiodynamic polarization and electrochemical impedance spectroscopy demonstrated that the SNAP system generates high quality, defect-free, durable films. Formulation parameters, including crosslink density and coupling agent application, were optimized based on experimental results.

Modeling of nano-sized macromolecules in silane-based self-assembled nano-phase particle coatings

Abstract Molecular simulation approaches have been used to enhance the understanding of complex chemical interactions in coatings related processes. The Self-assembled NAno-phase Particle (SNAP) coating process relies on aqueous solution processes, similar to those used in conventional sol–gel synthesis, to form siloxane nano-sized structures, which are subsequently cross-linked upon film application. This process has been shown to produce a dense, protective thin film on metal substrates. The SNAP process involves design and selection of the coating constituents, based on the desired functionalities for network formation and cross-linking chemistry. In order to facilitate the design of coating components at the molecular level, it is imperative to gain a fundamental understanding of these complex phenomena. Molecular simulations on several oligomers with different side chains have been performed to study components of the of Si–O networks during the SNAP particle formation process. Several ring structures of tetramethyl orthosilicate (TMOS) and 3-glycidoxypropyltrimethoxysilane (GPTMS) have been considered. Geometry optimization of the cyclic Si–O structure formation has been performed, and ring strain parameters have been calculated.

Investigation of nanostructured Al-based quasicrystal thin films for corrosion protection

Abstract Quasicrystals belong to a particular type of solids, which consist of highly symmetric atom clusters. The structure is neither periodically ordered, as in crystalline materials, nor amorphous, as in a glass. Recent work has shown that thin film quasicrystal coatings can have unique properties such as very high electrical and thermal resistivities and very low surface energy, which may result in interesting corrosion properties. For example, aluminum alloy based quasicrystals are insulator alloys containing about 70% of aluminum. Other interesting properties involving, for instance, adhesion, corrosion, friction, and hardness suggest that quasicrystal coatings are promising materials for a variety of industrial applications. The corrosion related properties of aluminum alloy based quasicrystal thin film coatings have been studied on coated AA2024 substrates. The thin film deposition parameters are briefly discussed. Results of the microstructural, surface chemistry, and surface energy analysis of the quasicrystal films are presented. The corrosion protection properties of the films have been studied by potentiodynamic scan and electrochemical impedance spectroscopy. Analysis of the electrochemical data indicates that nanostructured quasicrystal films significantly resist corrosion of AA2024-T3 substrates in a constant immersion environment.

Erratum to "Real time mapping of corrosion activity under coatings" (Prog. Org. Coat. 41 (2001) 266-272)

Corresponding author. Present address: University of Dayton Research Institute, Research Institute, 300 College Park, Dayton, OH 45469 0168, USA. Tel.:+1-937-255-9050; fax:+1-937-258-8075.E-mail address:mohammad.khobaib@afrl.af.mil (M. Khobaib).0300-9440/02/

Hybrid organo-ceramic corrosion protection coatings with encapsulated organic corrosion inhibitors

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