Capacitors (electrolytics, specifically) explode if you put reverse voltage or excessive voltage to them. How does this happen? Aren't electrolytics just two metal films with a seperator and doused in some electrolyte? What is the mechanism behind this explosion?
The electrolyte in an aluminum electrolytic capacitor is conductive, but a thin layer of aluminum oxide on the anode acts as a dielectric. Applying more than about 1.6V of reverse voltage strips the dielectric of its oxygen atoms causing the capacitor to become a near short circuit. Current flowing through the capacitor generates heat which eventually boils the electrolyte. The electrolyte vapor then expands, in time rupturing the case of the capacitor.