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.
Passivation only removes free iron contamination from the stainless steel surface. Pickling, on the other hand, removes surface iron contamination, heat tint and weld scale. After Pickling, it will produce a dull matt uniform grey finish on the metal that is the effect of chemical micro-etching.