Critical Factors for the Transition from Chromate to Chromate-Free Corrosion Protection

Abstract

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503 AGENCY USE ONLY (Leave blank)2. REPORT DATE December 1, 1999 REPORT TYPE AND DATES COVERED Annual Technical Report TITLE AND SUBTITLE Critical Factors for the Transition from Chromate to Chromate-Free Corrosion Protection AUTHOR(S)Rudolph G. Buchheit, et. al. FUNDING NUMBERS N/A PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)The Ohio State University Army Research Laboratory Air Force Research Laboratory PERFORMING ORGANIZATION REPORT NUMBERN/A SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) SERDP901 North Stuart St. Suite 303 Arlington, VA 22203 SPONSORING / MONITORING AGENCY REPORT NUMBERN/A SUPPLEMENTARY NOTESNo copyright is asserted in the United States under Title 17, U.S. code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Government purposes. All other rights are reserved by the copyright owner. 12a. DISTRIBUTION / AVAILABILITY STATEMENTApproved for public release: distribution is unlimited. 12b. DISTRIBUTION CODEA ABSTRACT (Maximum 200 Words)The overall objective of this research program is to acquire a fundamental understanding of the chemical and physical processes and mechanisms of corrosion protection by chromate-based coatings applied to metal surfaces with a specific focus on corrosion protection of aluminum alloys. The key functional attributes of chromate coating formation and breakdown must be identified and understood so that ultimately, they might be duplicated using environmentally friendly corrosion protection methods. Environmentally friendly corrosion protection methods must be found to replace chromate corrosion protection methods because environmental regulations are forcing elimination of products and processes (like chromates) whose formulations use or produce toxic substances. SUBJECT TERMSSERDP Project BackgroundThe Department of Defense (DOD) and Department of Energy (DOE) have committed to replace chromate-based metal finishing in present and next generation systems. At issue is whether this change will occur in a timely manner without performance or cost penalties that could compromise operational readiness. Additionally, undue delay in determining and implementing new corrosion protection practices poses enormous risk for existing assets. Faced with the request from the user community for chromate-free corrosion protection, ...

Cerium-based conversion coatings on aluminium alloys: a process review

“…1 It works extremely well as a soluble inhibitor in cooling water systems, 2 as an inhibiting pigment in paints 2-5 and as a component in deoxidisers 2,4,6 and anodised coatings. 2,4,7 Most importantly, in the context of this review, chromate is a near ideal conversion coating, 1,2,6 as it provides outstanding corrosion resistance 4,[8][9][10][11][12][13][14] and paint adhesion, 10,[14][15][16][17] ease of application, 8,9,[11][12][13][18][19][20][21] self-healing 6,8,9,11,14,18,19,21 and electrical conductivity. 18,19,[21][22][23] It works rapidly 14 at room temperature 14 on a wide variety of metals and alloys 24 while requiring a minimum of maintenance.…”

“…1,5,[12][13][14][30][31][32] An enormous amount of work has been carried out on chromate, and there are a number of excellent reviews that cover chromate chemistry and practice. 6,14,[33][34][35] An enormous amount of data on potential chromate replacements for aluminium has also been published. 1 This is not only because of the importance of the topic but also because of the breadth of the replacement chemistries available for aluminium.…”

“…1 This is not only because of the importance of the topic but also because of the breadth of the replacement chemistries available for aluminium. These include molybdate, 1,11,26,30,36,37 permanganate, 6,11,26,[36][37][38] refractory metal oxyfluorides (mainly Ti/Zr, but also Hf, Nb and Ta), 6,11,26,[36][37][38][39][40] phosphates, 1,26 silanes, 6,26,36,37,39,41,42 sol-gels, 1,6,11 self-assembling monolayers, 6,26,[39][40][41][42] conducting polymers, 1,6,11,30 cobalt based coatings, 6,24,26,38,43 hydrotalcites 6,…”

“…In addition, a number of excellent reviews on chromate replacements have subsequently appeared in which rare earth coatings appear as part of the discussion, 1,5,6,11,26,30 but as they only represent one option among many, the coverage is necessarily limited. The review by Bethencourt et al 50 is probably the most comprehensive, but is quite dated now.…”

“…Some of the best information on rare earth conversion coatings is found not in reviews but in the primary literature. For instance, an excellent summary of the development of the cerium coating process is found in the introduction of the paper by Campestrini et al, 51 and probably the most useful background material on the process is found in the introduction of the paper of Palomino et al 52 and in the discussion in the paper by Buchheit et al 53 From the view of process conditions, the best coverage is found in papers by Chemetall 41,42 and in the review by Buchheit and Hughes, 6 although these are still limited in their coverage of the published literature.…”