Here's how we can think about "pyrophoric" in terms of a scale:
1. Degree of Pyrophoricity:
* Extremely pyrophoric: These materials ignite almost immediately upon contact with air, sometimes even at very low temperatures. Examples include:
* White phosphorus
* Triethylaluminium
* Some finely divided metals like titanium and zirconium
* Moderately pyrophoric: These materials ignite spontaneously but might require a little more exposure to air or a slight increase in temperature. Examples include:
* Diethylzinc
* Some organometallic compounds
* Finely divided iron and nickel powders
* Slightly pyrophoric: These materials are less likely to ignite spontaneously, but they can ignite with a spark or friction. Examples include:
* Some metallic powders like aluminum and magnesium
* Some hydrides
2. Factors Influencing Pyrophoricity:
* Surface Area: Finely divided materials have a much larger surface area exposed to air, increasing the likelihood of spontaneous ignition.
* Reactivity: Some materials are inherently more reactive with oxygen than others, leading to greater pyrophoricity.
* Presence of Catalysts: Certain substances can act as catalysts, promoting the reaction between the material and oxygen, thereby increasing pyrophoricity.
Instead of a specific scale, we use terms like "extremely," "moderately," and "slightly" to describe the pyrophoric properties of materials. This gives us a general idea of their ignition hazard and how much care needs to be taken when handling them.
Remember, pyrophoric materials pose a significant fire hazard. It's crucial to handle them with extreme caution and follow all safety guidelines provided by your laboratory or workplace.