Official Answer
Answer
Passivation is a chemical treatment (usually in nitric or citric acid) that removes 'free iron' from the surface of the stainless steel ring and enhances the protective chromium-oxide layer. For medical applications, this is critical to prevent 'rust' spots and ensure biocompatibility. The process follows ASTM A967 standards. In a spiral ring, which has multiple layers in close contact, passivation must be performed carefully to ensure the acid reaches the surfaces between the turns. If free iron remains trapped between turns, it can lead to localized galvanic corrosion. Post-passivation, the rings are rinsed in deionized water to ensure no chemical residue remains, which could cause adverse reactions in a clinical setting.
