Stainless Steel Passivation
An interesting phenomenon of stainless steel is its natural ability to develop an extremely thin and inert protective layer when exposed to air. This layer, combined with the composition of the base metal, is what makes stainless steel so resistant to corrosion.
However, that doesn’t mean that stainless steels are completely impervious to rusting. One common mode of corrosion in stainless steels is through contamination with foreign particles that become embedded during manufacturing and handling, before that protective layer has a chance to properly form.
Passivation is a chemical process that is employed to ensure that the protective layer forms on virgin material, free of contaminants.
The parts are dipped in an acidic passivation solution (typically nitric acid or citric acid), which removes those impurities without harming the base metal. Once the part is removed and exposed to atmosphere again, chromium oxide forms and the protective layer is in place, with no impurities underneath.
And we’re talking thin! On average, the layer is only about 2 Angstoms thick. That’s only 0.0000002 mm or 0.000000008”!
Stainless steel components that are not passivated can corrode over time, which manifests itself in a few different ways. The parts may exhibit a reddish brown tinge or brown spots that become more pronounced over time.
Karve Shaving Co. has its own in-house passivation line and all stainless steel parts are passivated as a final manufacturing step.