Number

319-EN

Section

General Section

Use

Abstract

Chromium VI is used in manufacturing of anti-corrosion coatings for various applications. Using cerium oxides as a possible substitute of chromates in applications for military aircraft gave promising results.

Substituted substances

Alternative Substances

Reliability of information

Internet information: data are from an internet document and only a basic and partial evaluation could be performed

Reason substitution

CMR
other toxic effects
ecotoxicity
physical hazards

Hazard Assessment

Substances to be substituted: Hexavalent chromium conversion coatings are obtained from chromic acid which is actually an acid mixture containing chromium trioxide, is a Substance of very high concern and is included on the REACH authorisation list, according to Article 62 of Regulation (EG) No. 1907/2006. (REACH Regulation). Strontium chromate is a Substance of very high concern and is included on the REACH authorisation list, according to Article 62 of Regulation (EG) No. 1907/2006. (REACH Regulation). Alternative substances: Cerium oxide, cerium(III) chloride heptahydrate and cerium dioxide are not included in the current EU harmonised classification and are not listed in the Database for substances of concern according to SUBSPORTplus criteria.

Description of Substitution

Coating systems used for military aircraft generally consist of a hexavalent chromium conversion coating in direct contact with the metallic substrate, followed by a strontium chromate primer, and a final resin topcoat over the primer. A project was run to test the possibility of replacing the traditional three layer system with a two-layer system: a non-chromate conversion coating and a self-priming coating that incorporates nontoxic corrosion inhibitors. Cerium oxide was found to be a potentially viable corrosion inhibitor and replacement for chromate conversion coatings on aluminium alloys. The cerium oxide coating is deposited on the aluminium alloy surface by an electrochemically driven precipitation process from aqueous solutions of cerium chloride, using a technology similar to the one used for chromium deposition. The project also studied the possibility to integrate the cerium anticorrosive protection with UV-curable coatings (aliphatic urethane acrylates). Such coatings will have the advantage of allowing the elimination of isocyanate crosslinking agents or solvents. Results indicate that UV-curable, self-priming topcoats are comparable to the performance of the chromium based protection. Optimisation of the process for different type of aluminium alloys as well as the possibility to extend it to other alloys were set as further objectives of the research team.

Case/substitution evaluation

The substitution will allow the elimination of hexavalent chromium compounds (chromic acid, chromium trioxide) that are classified as carcinogenic, reprotoxicant and mutagenic. Hexavalent chromium is regulated under REACH Annex XIV (authorisation) and XVII (restriction). Therefore, it is a necessary and successful substitution. The technology is similar to the one using chromium, which is an advantage in its implementation, even if work still needed to be done for optimizing the process.

State of implementation

Pilot study

Availability of Alternative

The alternative substances are available on the market.

Type of information supplier

Research

Further information

Cerium dioxidehttp://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=DE&language=EN-generic&productNumber=202975&brand=ALDRICH&PageToGoToURL=http%3A%2F%2Fwww.sigmaaldrich.com%2Fcatalog%2Fsearch%3Finterface%3DProduct%2520Name%26term%3DCerium%2528IV%2529%2Boxide%26lang%3Dde%26region%3DDE%26focus%3Dproduct%26N%3D220003048%2B219853101%2B219853286%26mode%3Dmode%2520matchpartialmax" target="_blank" rel="noopener"> MSDS from Sigma Aldrich Cerium chloride MSDS">http://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=DE&language=EN-generic&productNumber=202983&brand=ALDRICH&PageToGoToURL=http%3A%2F%2Fwww.sigmaaldrich.com%2Fcatalog%2Fproduct%2Faldrich%2F202983%3Flang%3Dde">MSDS from Sigma Aldrich

Type of publication and availability

Internet article, freely available

Publication source: author, company, institute, year

The presentation is based on the article ‘Chromate-Free Corrosion Protection’ by Matt O'Keefe professor in the Department of Materials Science and Engineering and in the Graduate Center for Materials Research at the University of Missouri-Rolla. The article was published on September 12, 2006, by the Paint&Coatings Industry Magazine http://www.pcimag.com/

Publication source

Type of publication and availability

http://www.pcimag.com/articles/chromate-free-corrosion-protection

Date, reviewed

November 26, 2021