Magnesium (Mg) is a highly reactive element which burns at a staggering 3,100 degrees Celsius (5,612 degrees Fahrenheit), giving off an intense white light.
In addition to visible light, magnesium emits infrared (IR) when burned, making it perfect for use in military countermeasures such as decoy flares. Like all things, magnesium needs to be in the presence of an oxidiser when it burns – a material which takes electrons from the fuel allowing the reaction to occur.
Flares are made of Teflon ([C2F4]n) and magnesium, and it’s the fluorine in Teflon that oxidises magnesium. Fluorine is a stronger oxidiser than oxygen, as it wants to accept electrons more than oxygen, allowing for a higher temperature of combustion.
Heat-seeking missiles lock on to infrared light given off by engines in aircraft, but magnesium decoy flares throw out far more IR light than aeroplane engines, effectively confusing the missiles’ heat-seeking guidance systems and hopefully deterring the weapon from its target.
A magnesium fire cannot be extinguished with water, since the magnesium reacts with water to produce hydrogen gas – which if anything will only intensify the fire.
Instead, dry sand is generally used to stop the reaction. Other uses of magnesium have been as an illumination source in flash photography and in fireworks.