Brakes in cars are made of iron, and when Magnesium Chloride is used as a winter road treatment, it reacts with the metal and causes rusting. Rusting is a type of oxidation in which iron reacts with water and oxygen forming rust. “The chemical mechanism of rusting is not fully known, but is thought to involve oxidation of metallic iron to ferrous ion (Fe++) and reaction of the ferrous ion with oxygen and water to form rust” (Corrosion. Columbia Electronic Encyclopedia.) Water, acids, and metals catalyze the reaction, and this reaction is very common in brakes and catalyzed by Magnesium Chloride.