In August 2019, I received the first notice from an engine manufacturer that "chromium VI" had been found when removing used high-temperature insulating elements.
To be honest, it was not clear to me what this actually meant.
Chromium was known, but chromium (VI)?
A first quick search on Google and Wikipedia yielded the following result:
Source: wikipedia.de
Chromium (VI) oxide, also known as chromium trioxide (CrO3), is an oxide of chromium. It is a dark red solid that is hygroscopic and readily soluble in water. The aqueous solution reacts strongly acidic (chromic acid). The substance poses a number of hazards.
However, since the melting point was 197°C, it could not actually be the case that a substance that decomposes at 197°C would be found in systems that sometimes have 500°C and above. So dead end.
So it can't actually be chromium (VI).
Inquiries with manufacturers of insulation materials or insulation systems were also unsuccessful. If they knew what "chromium (VI)" was at all, they knew one thing for sure, namely "...that it is not contained in our products..."
The data sheets then provided by the manufacturers confirmed their statements. No chromium (VI) contained in insulation materials, dead end again!
A topic research should always be done in English
In the course of the months, in a further conversation with the engine manufacturer, the word "calcium" was mentioned for the first time and the hint that calcium probably plays a role as a reactant in the formation of "chromium (VI)".
Now I was completely confused, because "calcium" is not contained in "chromium (VI)".
"Calcium" in connection with insulations told me something very well, because I knew that "calcium" is contained in almost all insulating materials (fabrics and mats).
If you are a little older and at the beginning of your professional life at the end of the 1980s you "copied" data sheets for the insulation systems you produced yourself, and you did so on a typewriter, then you remember how often you wrote the word "calcium", namely actually in every data sheet and as "calcium oxide".
I could also remember the mass fraction, for standard products it was 10-15%, for high temperature material it was 30% and more.
So I used the search engine again and searched for "Chromium (VI)" and "Calcium".
Now came the first hits and the first one was in English, namely "calcium chromate", chemical formula CaCrO4, a so-called "chromium (VI) COMPOUND".
And then it struck me! All conversations with the engine manufacturer were in English. The English language is not always as sophisticated as the German language. In English, everything that has to do with "chromium (VI) is simply "hexavalent chromium" or in short form "chromium six"; learned something again.
Thus en.wikipedia.org writes:
"Hexavalent chromium is chromium in any chemical compound that contains the element in the +6 oxidation state (thus hexavalent)"
So that was it, the hexavalent chromium compound in combination with calcium is called "hexavalent chromium" or "chromium 6" by the English speaking person, while the German speaking person would rather say calcium chromate in this case.
The impasse broke, and I knew one thing:
If I want to get further here in this subject, it will only go on in English!