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How can some metals resist fluorine at ordinary temperatures?

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A labeled diagram of the periodic table entry for fluorine, showing its atomic number 9, symbol F, atomic weight 18.998, electron configuration, and indicating it is a halogen and a gas at room temperature. — fluorine Properties of fluorine.

Certain metals are able to resist fluorine at ordinary temperatures because they quickly become covered by a protective fluoride layer. This layer acts as a barrier that prevents the element from further attacking the metal.1

Examples of such metals include:
* Nickel
* Mild steel
* Copper
* Aluminum
* Monel (an alloy consisting of approximately 66 percent nickel and 31.5 percent copper)1

Because of this property, these materials are often used in equipment designed to handle fluorine. For instance, Monel is suitable for working with fluorine at temperatures up to 600 °C (1,100 °F), and stainless steel cylinders are used to store the element safely under pressure, provided the valves are kept free of organic matter.12