aluminum, powdered

Powdered aluminum is the commonest fuel for solid-propellant rocket motors. It consists of round particles, 5–60 micrometers in diameter, and is used in a variety of composite propellants. During combustion the aluminum particles are oxidized into aluminum oxide, which tends to stick together to form larger particles. The aluminum increases the propellant density and combustion temperature, and thereby the specific impulse (a measure of the efficiency of a rocket engine).