What is Passivation?
When the amount of chromium (in an iron matrix) exceeds 10 %, a complex chrome oxide forms instantaneously that prevents the further diffusion of oxygen into the surface and results in the “passive” nature of stainless steel and its resistance to oxidation (or corrosion). A chemical “dip” into 10% nitric acid plus 2% hydrofluoric acid bath will enhance the development of this “passive” oxide.
Passivation is the treatment of stainless steel in an acid solution (typically dilute nitric or citric acids) to remove iron contamination on the surface. The contamination might come from fabrication steps such as stamping, drilling, machining, welding, cutting, forming, or wire brushing. Passivation does not change the appearance of the stainless. Passivation is not necessary to form the protective oxide coating; re-forms immediately upon exposure of the stainless steel to air, water, etc. However, specific passivation treatments can thicken and change the composition of the protective oxide layer, increasing the corrosion resistance of the passivated material.
