Determination of Cr(VI) contained in Corrosion Resistant Coatings for Automotive Parts

Current status VDA AK Cr(VI) analytics

According to Directive 2000/53/EC of the European Parliament and of the Council of September 2000, hexavalent chromium is prohibited in anti-corrosion coatings of vehicles as of 01.07.2007 [1].

The different biological and toxic impacts of the trivalent and hexavalent compounds require the valence-selective determination of chromium. Chromate is toxic and classified as mutagenic and carcinogenic [2].

On account of the end-of-life vehicle regulation of the EU the VDA (Verband der Automobilindustrie e.V.) and the ZVO (Zentralverband Oberflächentechnik e.V.) have set up work teams to prepare simple and user-friendly methods for the determination of Cr(VI) in zinc and zinc-alloy coatings of Cr(VI)-free processes.
On the basis of existing analysis regulations, a number of these regulations have been validated in round robin tests, the results of which are now submitted to the respective sub-committees of the standards committees.
This means that only qualitative evidence of Cr(VI) is required for the quality control of these parts. Such evidence should however be reliable and applicable in all types of coatings also under sealant.

The difficulty in developing a method for quantitative evidence was to find an elution system that releases the Cr(VI) from the wash primer quantitatively without new Cr(VI) being generated or Cr(VI) being reduced to Cr(III).
The subsequent determination of Cr(VI) from the solution can be effected by means of spectrophotometry after the derivative with diphenyl carbazide in compliance with DIN38405 D24 [3].

Round robin tests were conducted for the validation, which formed the basis for defining a limit for Cr(VI) to be set at 0.1µg/cm2 for all methods. As shown on the public pages of the IMDS (International Material Data System), coatings falling below this concentration are defined as Cr(VI)-free. Reproducability is higher than 10%.

To enable the access of as many users in Europe as possible to these analysing methods, it is planned to develop these methods further for integration in a German and European standard.

Literature:

[1] "Directive 2000/53/EG, Annex II of the European Parliament and of the Coucil of 18 September 2000 on end-of life vehicles", Brüssel (2000)

[2] I. Franchini, A. Mutti: "Metabolism and toxicity of Chromium Compounds", in Environmental Inorganic Chemistry, K.J. Irgolic, A.E. Martell (eds.), Verlag Chemie, Weinheim (1985), Seiten 473-786

[3] DIN38405, Deutsche Einheitsverfahren zur Wasser-, Abwasser- und Schlammuntersuchung, Anionen (Gruppe D): "Photometrische Bestimmung von Cr(VI) mittels 1,5-Diphenylcarvazid (D24)", Normausschuss Wasserwesen (NAW) im Deutschen Institut für Normung e.V. (DIN) (1985)