Which element is crucial for the ignition of pyrophoric materials?

The ignition of pyrophoric materials is primarily caused by their contact with air. Pyrophoric materials are those that can ignite spontaneously when exposed to oxygen in the air due to their highly reactive nature. This reactivity is a result of the surface oxidation that occurs when these materials come into contact with atmospheric oxygen, often resulting in self-ignition at room temperature.

In contrast, high temperature is generally a requirement for the ignition of many materials but is not necessary for pyrophoric substances, which can ignite without an external heat source. Direct sunlight and moisture are less relevant to the ignition of pyrophoric materials. Sunlight does not provide the necessary conditions for ignition, while moisture typically helps to stabilize certain reactive materials and may inhibit their ability to ignite by preventing oxidation. Thus, the contact with air is the key element that makes pyrophoric materials prone to ignition.