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.
Stainless steel is passivated through a cleaning cycle to remove oils, grease, compounds, lubricants, and residue followed by a nitric or a citric acid bath or a by an oxidant that removes free iron and contaminates. Passivation is performed on clean stainless steel, providing the surface has been thoroughly cleaned or descaled.