What is a substance that ignites spontaneously upon contact with others called?

The term that describes a substance that ignites spontaneously upon contact with others is known as hypergolic. Hypergolic materials are characterized by their ability to combust immediately upon mixing with an oxidizer without the need for an external ignition source. This property makes hypergolic fuels particularly valuable in certain aerospace applications, such as rocket propulsion, where reliable ignition is critical.

Flammable substances can catch fire easily but require an ignition source like a spark or flame to do so, so they do not qualify as hypergolic. Combustible materials are those that can ignite and burn, but again, they typically need an external ignition source. Explosive materials undergo rapid combustion that produces large volumes of gas and pressure but do not necessarily ignite spontaneously upon contact like hypergolic substances.

Understanding the specific characteristics of hypergolic materials is important in fields such as aerospace engineering and fire safety, as they present unique challenges and require specialized handling and storage procedures.