REACH and SVHC(s) Incorporated in Articles above 0.1% (w/w)
At this time, as far as we are aware, and have been notified by ECHA, our chemical suppliers, etc., the only substances of very high concern that we knowingly utilise in the application of coatings to our customers’ free issue components, are Sodium Dichromate, Potassium Dichromate, Chromium Trioxide, Chromic Acid, Strontium Chromate and some general solvents. To date, these chemicals have been included on the candidate list, and in some cases are in the process of being included in Annexe XIV, which will require authorisation to permit continued use.
Sodium/Potassium Dichromate is incorporated in low concentrations, as required by numerous aerospace specifications, in the following solutions :
1. Stainless steel passivate.
2. Brush alocrom.
3. Sulphuric acid and chromic acid dichromate seal.
As such, we are not allowed to use alternatives to sodium or potassium dichromate in these solutions when doing work to those specifications and it is not economically or environmentally sound to maintain additional solutions for the processing of work to other specifications that do permit the use of alternatives. Thus, any work requiring one of these five processes, will involve the use of sodium or potassium dichromate, as at any of our competitors.
The good news is that in the case of brush alocrom and any of the passivates they merely result in the chromate conversion of the surface and thus there is no sodium/potassium dichromate left on the article. Also, in the case of the dichromate seal used in some instances after sulphuric acid anodising and chromic anodising, the sodium dichromate results in the deposition of aluminium oxychromate and aluminium oxydichromate. Thus, in every instance, negligible (i.e. less than 0.1% w/w) sodium/potassium dichromate should be present on the coated components.
Potassium dichromate is incorporated in deoxidiser solutions used on our chromic acid anodising and alocrom lines. This is used as a pre-treatment step in these processes to strip the naturally occurring oxide film from aluminium parts and thus, in every instance, the subsequent processing should remove any residual potassium dichromate, resulting in less than 0.1% w/w on the finished coated parts.
Potassium Dichromate is also incorporated in low concentrations in the chromic acid anodising seal prescribed by G.E. and Messier-Dowty. However, again as above, it’s use results in the deposition of aluminium oxychromate and aluminium oxydichromate. Thus, negligible (i.e. less than 0.1% w/w) potassium dichromate should be present on any parts chromic acid anodised to the G.E. and Messier-Dowty specifications.
Chromic acid is obviously employed in the chromic acid anodising baths and is present in a Def Stan (03-12) type one, two and three brass passivate and our anodising control stripper. However, it is also employed in very small amounts in a very dilute chromic seal (0.02%) sometimes used for thin film sulphuric acid anodising and a very dilute (0.05%) hot chrome rinse used when phosphating components.
In the case of chromic acid anodising what is actually deposited on to the surface of the article/component is an oxide film approximately 2 – 6 microns thick and, as such, providing they are processed correctly, negligible (i.e. less than 0.1% w/w) chromic acid should be present on the anodised components.
In the case of passivate solution, chromic seal and hot chrome rinse, (like in the case of the dichromates mentioned earlier) it is merely there to provide a chromate conversion of the surface of the article and thus provide some level of corrosion resistance. Thus, in every instance, negligible (i.e. less than 0.1% w/w) chromic acid should be present on the finished coated components.
Chrome is found in many forms in the paints we commonly use, including strontium chromate, which is found in most aerospace primers in concentrations up to 25 – 30%. As it is not converted during the application process it will be present in quite high levels in the cured primer coating and, depending on the structure of the article coated (surface area to volume ratio), may exceed the 0.1% w/w permitted on finished components.
The two solvents, Methoxyethanol and Ethoxyethanol, are possibly present in some of the paints we apply. However, due to the volatile nature, upon curing of the paints, most, if not all of them, if present, should evaporate and thus, in all instances, the resultant amount on the finished article should be less than the 0.1% w/w.
Dr. K.G. Tucker