Fuzzy white stuff on Aluminium Clamps

[serendepidy]

We have some aluminium clamps on some water cooled cables which carry electrical energy from a 200 MW generator to a transformer for distribution.

There is a white crystalline substance that has formed on the clamps, it appears to be a fine threaded substance resembling spider web rolled into a ball. The substance is most prevailent in the crevices but also is present on the clamps in regions where there are no crevices. In some instances the substance also appears to be mucous like, resembling spit, but when touched cleaves like a brittle crystalline substance.

The corrosion in not excessive, but I am just curious as to whether anyone can tell me why this substance is forming.

My current paradigm is that the substance is aluminium hydroxide precipitate from a crevice type corrosion mechanism. The mechanism is exacerbated perhaps by the condensation of liquid on the water cooled cables.

I have been suggested to see whether the deposit dissolves in acid and not base, which will indicate the presence of aluminium hydroxide.

 

[kenvlach]

Probably Al(OH)₃. Some 5000 series Al alloys will form Mg(OH)₂, but not in large amounts.
Of course, Al(OH)₃ forms because it is thermodynamically more stable than Al + water.

However, Al(OH)₃ dissolves in strong alkalies (e.g., NaOH solutions) as well as acids -- aluminum is amphoteric.