Passivation is the process by which a material becomes ‘passive,’ meaning it is less affected by environmental factors such as corrosion. It involves the spontaneous formation of a very thin, non-reactive surface film that acts as a barrier, shielding the bulk material from further attack. This film is typically an oxide or nitride layer, a few nanometers thick.
钝化的机制是电化学的。当铬、铝或 钛 当金属暴露于氧化环境（例如空气或某些酸）时，其表面会迅速氧化。如果生成的金属氧化物稳定、致密、无孔且牢固地附着在金属表面，则会形成一层保护性钝化层。这层钝化层非常薄，通常只有1-3纳米，但它足以通过阻止金属与腐蚀环境直接接触来显著减缓腐蚀速度。
The stability of this passive film is dependent on the environment, particularly pH and the presence of certain ions like chlorides. For example, the chromium oxide ([latex]Cr_2O_3[/latex]) layer on stainless steel is highly effective in many environments but can be locally broken down by chloride ions, leading to pitting corrosion. The breakdown and reformation of this passive layer is a dynamic process. If the film is mechanically scratched or damaged, the exposed metal will often repassivate almost instantly, a property known as self-healing.
钝化可以是一个自然过程，也可以通过化学处理人工增强，例如将不锈钢浸入硝酸或柠檬酸中，以去除表面的游离铁，并促进更坚固的富铬氧化层的形成。此过程不同于使用 涂层，因为钝化层是由基底金属本身形成的。
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