This painless condition occurs when the little bumps on your tongue grow long and trap bacteria that live in your mouth -- making the tongue look black and hairy. Causes can include antibiotic use, poor oral hygiene, smoking, drinking a lot of tea or coffee, and not producing enough saliva.
Hello, Jie. The word passivate is a bit troublesome because aluminum cannot be passivated in the same sense as stainless steel; but it can be passivated in the same sense as zinc plating, i.e., with a chromate conversion coating.
The action is by oxygen and water on a clean surface. It is our policy to passivate the SUS 316L and SUS 316LN austenitic SS tanks with 14% by volume cold Nitric acid. It is also our policy not to include hydrofluoric acid in a passivation solution. Hydro-flouric acid is a pickler which removes chromium and nickel along with heat hardened scale, it NOT a passivator. The concentrated acid you get on board in 200 litre drums is usually 68%. Contact time for Nitric acid is 2 hours.