Metallized propellant systems

Mechanism for Deriving Energy. The mechanism by which propulsive energy is derived from propellant systems containing metals and their compounds is somewhat different from that of conventional liquid propellant systems. For hydrazine and nitrogen tetroxide, for example, their combustion leads to the formation of N2, H20, and H2 through a relatively simple series of intermediate species ... 

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,... 

These boiling point temperatures of the metal oxides increase with pressure and thus can be seen to be appreciably greater than the corresponding equilibrium combustion chamber temperature of propellant systems. 

Figure IV. A. 1. immediately predicts that of elements with atomic numbers greater than 10 only Mg. Al. and Si and their hydrides would be worth considering from a specific impulse point of view. Mg, Al, and Si being metals, can be adopted in a liquid system, only as slurries. Some of their alkylates may be liquids however, no matter in what form they are introduced in liquid propellant systems their performance will not be higher than hydrogen. The reason is that these metals do not have a heat release appreciably greater than hydrogen and also form solid oxide products. Such products cannot be expanded through the nozzle and thus a specific impulse penalty is paid.

High specific impulse always has been the primary reason for developing new propellant systems. The discussion in the previous sections has shown that one of the best means of augmenting the performance of a propellant system is by adding greater quantities of the light metallic elements. It has been this desire to add additional metal to the system which has brought the recent innovations in rocket developments to the forefront. 

Figure IV. B. 1. concentrates on the storable propellant systems. The morphology obviously can be extended to include the cryogenics. Again, the method by which the metal particles are introduced determines the approach. Both the hybrid and the gelling procedure would be considered. The only perturbation would be in the case of the hybrid in which both fuel and oxidizer are injected as liquids and the binder is used simply as a vehicle to carry the metal particles.

Apart from the alkali metals, the reactions of which have been reviewed in Section 2, very few metals are sufficiently volatile to enable gas-phase diffusion flame studies to be undertaken. The high temperatures required for vaporization would destroy organic materials, so only reaction with inorganic gases can be considered. The combustion of some metals has been studied, as they are of importance as possible rocket propellant systems. The kinetics, however, are complex. Metals burn predominantly, and in some cases exclusively, by heterogeneous reactions [305], since both the fuel and the products are usually in the condensed state. In metal combustion, transport processes exert at least a partially controlling influence, and so information on reaction kinetics is difficult to obtain. The reaction may occur at the surface of the metal, or on the surface of... 

Boranes, boron clusters, and in particular, carboranes are of special interest due to their unique properties that cannot be found in organic counterparts. These uniqne properties are based either on the element boron, due to its electron deficiency, or on the structnral featnre of the cluster compound. Borane clusters as a class of materials have a wide range of potential applications. This is not only due to their unique electronic and nuclear features the fields of application, to name but a few, range from materials science through medical applications to catalysis, which will be described in more detail below [13]. Carboranes can be applied as liquid crystals in electro-optical displays [14], non-linear optics [15], and ion-selective electrodes [16] in the materials science arena. If carboranes are vaporized and fired at high temperatures they create boron films that are applied in Tokamak reactors for nuclear fusion [17]. Boranes have furthermore found application in airbag propellant systems in cars [18], as the stationary phase in gas chromatography [19] and in metal ion extraction systems, for example, for nuclear waste [20]. In medical applications, boron neutron capture therapy (BNCT), a special field of anti-cancer therapy, is noteworthy. 

Helping to propel capacities upward has been the advent of greatly improved preheaters, which partially calcine the stone and significantly improve thermal efficiency. Modem preheaters improve capacity by 15—20% and decrease fuel consumption a similar percentage. Other kiln appurtenances and accessories that enhance efficiency and lime quahty are the contact coolers, and such kiln internals as metal refractory trefoil systems that act as heat exchangers, dams, and lifters. 

Cavitation erosion With increasing ship speeds, the development of high-speed hydraulic equipment, and the variety of modem fluid-flow applications to which metal materials are being subjected, the problem of cavitation erosion becomes ever more important. Erosion may occur in either internal-flow systems, such as piping, pumps, and turbines, or in external ones like ships propellers (36). 

Whenever corrosion resistance results from the formation of layers of insoluble corrosion products on the metallic surface, the effect of high velocity may be to prevent their normal formation, to remove them after they have been formed, and/or to preclude their reformation. All metals that are protected by a film are sensitive to what is referred to as its critical velocity i.e., the velocity at which those conditions occur is referred to as the critical velocity of that chemistry/temperature/veloc-ity environmental corrosion mechanism. When the critical velocity of that specific system is exceeded, that effect allows corrosion to proceed unhindered. This occurs frequently in small-diameter tubes or pipes through which corrosive liquids may be circulated at high velocities (e.g., condenser and evaporator tubes), in the vicinity of bends in pipelines, and on propellers, agitators, and centrifugal pumps. Similar effects are associated with cavitation and mechanical erosion. 

Existing knowledge on perchloric acid and its salts was reviewed extensively in 1960 in a monograph including the chapters Perchloric Acid Alkali Metal, Ammonium and Alkaline Earth Perchlorates Miscellaneous Perchlorates Manufacture of Perchloric Acid and Perchlorates Analytical Chemistry of Perchlorates Perchlorates in Explosives and Propellants Miscellaneous Uses of Perchlorates Safety Considerations in Handling Perchlorates [1], There is a shorter earlier review, with a detailed treatment of the potentially catastrophic acetic anhydride-acetic acid-perchloric acid system. The violently explosive properties of methyl, ethyl and lower alkyl perchlorate esters, and the likelihood of their formation in alcohol-perchloric acid systems, are stressed. The instability of diazonium perchlorates, some when damp, is discussed [2],... 

The COINS process uses an overhead conveyor system that collects metal parts containing explosive energetics components (fuzes and bursters) into baskets that are moved through a tank containing a caustic bath that hydrolyzes the energetic materials in the metal parts. No propellant is sent to the COINS. 

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... 

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