In providing propellants and

The Role of Chemical Engineering in Providing Propellants and Explosives for the U.K. Armed Forces... 

Ayerst, R. P. et al. The Role of Chemical Engineering in Providing Propellants and Explosives for the UK Armed Eorces , in William E. Eurter (ed.). History of Chemical Engineering (Washington, DC American Chemical Society, 1980), 331—392. 

The 12 kW pilot-scale tests conducted during the Demo II tests specifically tested for the DRE of components in M28 propellant and tetrytol. These tests provided evidence that high DREs (99.9999 percent) could be achieved for components of M28 propellant (nitrocellulose and nitroglycerine). However, lower DREs ( 99.7 percent) were achieved with the components of tetrytol. 

Exothermic oxidation—reduction reactions provide the energy released in both propellant burning and explosive detonation. The reactions are either internal oxidation—reductions, as in the decomposition of nitroglycerin and pentaerythritol tetranitrate, or reactions between discrete oxidizers and fuels in heterogeneous mixtures. 

Rocket Propellants. SoHd rocket propellants are mostly based on chemically cross-linked polymeric elastomers to provide the mechanical properties required in launchings and the environmental conditions experienced in storage, shipment, and handling (see Elastomers, synthetic). Double-and triple-based nitrocellulose propellants are also employed as rocket propellants. 

Polymer-based rocket propellants are generally referred to as composite propellants, and often identified by the elastomer used, eg, urethane propellants or carboxy- (CTPB) or hydroxy- (HTPB) terrninated polybutadiene propellants. The cross-linked polymers act as a viscoelastic matrix to provide mechanical strength, and as a fuel to react with the oxidizers present. Ammonium perchlorate and ammonium nitrate are the most common oxidizers used nitramines such as HMX or RDX may be added to react with the fuels and increase the impulse produced. Many other substances may be added including metallic fuels, plasticizers, stabilizers, catalysts, ballistic modifiers, and bonding agents. Typical components are Hsted in Table 1. 

Oxidizers. The characteristics of the oxidizer affect the baUistic and mechanical properties of a composite propellant as well as the processibihty. Oxidizers are selected to provide the best combination of available oxygen, high density, low heat of formation, and maximum gas volume in reaction with binders. Increases in oxidizer content increase the density, the adiabatic flame temperature, and the specific impulse of a propellant up to a maximum. The most commonly used inorganic oxidizer in both composite and nitroceUulose-based rocket propellant is ammonium perchlorate. The primary combustion products of an ammonium perchlorate propellant and a polymeric binder containing C, H, and O are CO2, H2, O2, and HCl. Ammonium nitrate has been used in slow burning propellants, and where a smokeless exhaust is requited. Nitramines such as RDX and HMX have also been used where maximum energy is essential. 

Pyrotechnic mixtures may also contain additional components that are added to modify the bum rate, enhance the pyrotechnic effect, or serve as a binder to maintain the homogeneity of the blended mixture and provide mechanical strength when the composition is pressed or consoHdated into a tube or other container. These additional components may also function as oxidizers or fuels in the composition, and it can be anticipated that the heat output, bum rate, and ignition sensitivity may all be affected by the addition of another component to a pyrotechnic composition. An example of an additional component is the use of a catalyst, such as iron oxide, to enhance the decomposition rate of ammonium perchlorate. Diatomaceous earth or coarse sawdust may be used to slow up the bum rate of a composition, or magnesium carbonate (an acid neutralizer) may be added to help stabilize mixtures that contain an acid-sensitive component such as potassium chlorate. Binders include such materials as dextrin (partially hydrolyzed starch), various gums, and assorted polymers such as poly(vinyl alcohol), epoxies, and polyesters. Polybutadiene mbber binders are widely used as fuels and binders in the soHd propellant industry. The production of colored flames is enhanced by the presence of chlorine atoms in the pyrotechnic flame, so chlorine donors such as poly(vinyl chloride) or chlorinated mbber are often added to color-producing compositions, where they also serve as fuels. 

Many methods have been proposed and are used to study the thermal stability of propellants and to ensure the absence of possible autocatalysed decompositions during storage. None are sufficiently reliable to merit individual description. In practice, stabilisers are added, the usual being diphenylamine for nitrocellulose powders and symmetrical diethyl diphenyl urea (carbamate or centralite) for double base propellants. Provided a reasonable proportion of stabiliser remains, the propellant can be assumed to be free from the possibility of autocatalytic decomposition. The best test of stability is therefore a chemical determination of the stabiliser present. 

The Composition B-4 was provided to LANL in the form of large flakes and was used as received. The tetrytol was in large to medium-size chunks. The Ml propellant and the M28 propellant were provided and used as small grains. The M8 propellant was provided in stacks of three sheets weighing 30-35 g each and sewn together with cotton thread. The sheets were not separated before being manually fed into the reactor. 

There was no accumulation of metals in either the anolyte or catholyte circuits when a spike of metals was fed with the M28 propellant to simulate particles from antiresonance rods. AEA attributes this success to the use of the catholyte-to-anolyte recycle and the anolyte purge operation. Lead, present in M28 propellant as lead stearate (approximately 0.5 weight percent), was oxidized to lead oxide (Pb02) and did not accumulate in solution. Lead oxide was found on the electrode surfaces and as a deposit in the bottom of the cell cavities (AEA, 2001d). A demonstration test successfully removed the lead oxide using an offline formic acid wash of the cell electrode cavities. This is the planned approach for removing accumulating lead oxide. No lead material balance was provided. 

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