Explosives and energetic materials store and rapidly release large amounts of energy for demolition, munitions, missile propulsion, and explosive-forming applications. Examples include gunpowder, flash powder, flashless powder, thermite, rocket propellants, and explosive aerogels. Gunpowder is an explosive mixture of sulfur, charcoal, and potassium nitrate that burns rapidly. Flash powder is a pyrotechnic material that contains an oxidizer and a metallic fuel. Flashless powder can be made from artillery feedstock propellants and used in small arms ammunition. Thermite is a pyrotechnic material made of a metal oxide (usually iron) and aluminum powder. Rocket propellants come in both liquid and solid form. Explosive aerogels are newer explosives and energetic materials with structures that can be manipulated on the nanoscale. Selecting explosives and energetic materials requires an understanding of product types. For example, according to the National Firearms Association (NFA), there are two types of gunpowder: black powder and smokeless powder. There are many different types of flash powder. The constituent materials determine properties such as color, speed, and stability. For example, strontium nitrate is used to produce a red flame. Magnesium metal powder causes the pyrotechnic material to burn more rapidly. Different categories of thermite materials are also available. The two most common types of these explosives and energetic materials are made with either hematite or magnetite. Both are iron oxides that are mixed with a finely-powdered aluminum metal. When the thermite reacts, liquid iron and aluminum oxide is produced. This thermite reaction or Goldschmidt reaction releases a substantial amount of energy. Explosives and energetic materials include propellants, fuel/oxidizer mixtures that move objects via chemical reactions. There are two basic types of products: liquid propellants and solid propellants. Rockets that use liquid propellants store the fuel and the oxidizer in separate tanks and then feed the components through a system of pipes to a combustion chamber. There are three basic types of liquid propellants: petroleum, cryogenic, and hypergolic. Petroleum propellants include a type of highly-refined kerosene called RP-1. Cryogenic propellants are liquefied gases stored at very low temperatures. Typically, they use liquid hydrogen as the fuel and liquid oxygen as the oxidizer. Hypergolic products are liquid propellants that ignite on contact without an ignition source. Explosives and energetic materials also include two types of solid rocket propellants: homogenous and composite. Hybrid rocket propellants are also available.