Metal fuels, solid rocket propellant

Combustion of powdered aluminum with steam is a potentially attractive propulsion system for torpedoes, because of the very high-energy density (energy per unit volume) that can be achieved. Since the oxidizer can be taken from the environment, on-board storage is required only for the aluminum propellant. A study of potential torpedo propellant/oxidizer combinations including Al, Zr, Mg, and Li metals, hydrocarbon fuels, and typical solid rocket propellants, and... 

Metallic Fuels. In rocket applications where exhaust smoke is not a major concern, the use of metallic fuels adds considerable impulse to the composition. By far, the most common metal in use as a solid propellant fuel is finely divided aluminum, because of a combination of several desirable properties ... 

Misch metal, an alloy of cerium with other lanthanides is a pyrophoric substance and is used to make gas lighters and ignition devices. Some other applications of the metal or its alloys are in solid state devices rocket propellant compositions as getter in vacuum tubes and as a diluent for plutonium in nuclear fuel. 

The "newest" oxidizer to appear in pyrotechnics, ammonium perchlorate has found considerable use in modern solid-fuel rocket propellants and in the fireworks industry. The space shuttle alone uses approximately two million pounds of solid fuel per launch the mixture is 70% ammonium perchlorate, 16% aluminum metal, and 14% organic polymer. 

In recent years, the great majority of solid rockets have utilized composite propellants. Most composite propellants are based on a solid oxidizer and a curable liquid polymeric binder. The binder also serves as fuel. Optionally, metallic fuels such as aluminum or boron may also be used.45 The propellant components are mixed together, and then the binder is cured to give the tough, flexible, elastomeric (rubbery thermoset) solid propellant required for modem missile use. An excellent source of information on the formulation of solid propellants is a report by Oberth.46... 

The newest oxidizer to appear in significant use in pyrotechnics, anunonium perchlorate (AP), has found considerable use in modem solid-fuel rocket propellants and in the firewoiks industry. The Space Shuttle alone uses approximately 2 million pounds of solid fuel per launch the mixture is 70% ammonium perchlorate, 16% almninum metal, and 14% organic polymer/epoxy, with a trace of iron oxide catalyst that can be varied to modify the bum rate. The aluminum powder is a surprising ingredient to find in a propellant, since it generates solid rather than gaseous reaction products, but its substantial heat output as a fuel and its excellent thermal conductivity both contribute to an enhancement of the bum rate of this propellant formulation. 

In the first part of the twentieth century, beryhium was used as coating inside fluorescent electric hght tubes, but proved carcinogenic (causes cancer) when broken tubes produced beryllium dust that was inhaled. Because of this potential to cause cancer, since 1949 berylhum has no longer been used as the inside coating of fluorescent tubes. Beryllium is also used for computer parts, electrical instrument components, and solid propellant rocket fuels. Because it is one of the few metals that is transparent to X-rays, it is used to make special glass for X-ray equipment. 

Thixotropic gels are also useful as propellants for rocket applications. These are commonly called thixotropes or gels. Normal fuels and oxidizers are converted into thioxotropes by the addition of a small quantity of a gelling agent in order to ensure uniform suspension of solid additives (usually metal additives) during storage. It is reported that if very finely pulverized particles of beryllium or aluminum are suspended in the liquid fuel, it is possible to increase the specific impulse substantially. 

Another non-equilibrium effect arises when the product composition contains a condensible substance. Solid propellant formulations based upon potassium perchlorate form solid potassium chloride and the acetylenic monopropellants upon decomposition form large quantities of carbon particles, as do very fuel-rich mixture ratios of hydrocarbon propellant systems. More recently metal and metal compounds have been used as fuels and form product oxides which are very high boiling point compounds that condense to varying degrees in the rocket chamber and nozzle. For example, estimates indicate that the normal boiling points of Li20, BeO,... 

Solid propellants are also used as rocket fuels. The mixture used in the booster rockets of the space shuttles (Figure 6.17) is a fuel containing aluminum metal powder. An oxidizer of ammonium perchlorate, NH4CIO4, is mixed with the fuel. 

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