Smokeless Composite Propellants

M.B. Frankel et al, Smokeless Composite Propellants Containing Carboxy- or Hydroxy-Terminated Polymers and a Nitroorganic Oxidizer , USP 3853646 (1974) CA 83, 12972 (1975) 37) A. Reichel et al, High Explo-... 

Ammonium dinitramide (ADN) is a crystalline oxidizer with the formula NH4N(N02)2, that is, it is composed ofionicaUy bonded ammonium cations, NH4, and dinitramide anions, N(N02)2- Though ADN is crystalline and has a high oxygen content, similar to AP and KP, it has no halogen or metal atoms within its structure. ADN is used as an oxidizer in smokeless composite propellants, similar to AN and HNF. It melts at about 364 K, accompanied by the latent heat of fusion. 

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. 

Similar to nitramine composite propellants and TAGN composite propellants, AN composite propellants produce halogen-free combustion products and thus represent smokeless propellants. However, their ballistic properties are inferior to those of other composite propellants the burning rate is too low and the pressure exponent is too high to permit fabrication of rocket propellant grains. In addition, the mechanical properties of AN composite propellants vary with temperature due to the phase transitions of AN particles. 

When a composite propellant composed of ammonium perchlorate (AP) and a hydrocarbon polymer burns in a rocket motor, HCl, CO2, H2O, and N2 are the major combustion products and small amounts of radicals such as OH, H, and CH are also formed. These products are smokeless in nature and the formation of carbon particles is not seen. The exhaust plume emits weak visible light, but no afterburning occurs because AP composite propellants are stoichiometrically balanced mixtures and, in general, no diffusional flames are generated. 

Thus, AP is a valuable oxidizer for formulating smokeless propellants or smokeless gas generators. However, since the combustion products of AP composite propellants contain a relatively high concentration of hydrogen chloride (HCI), white smoke is generated when they are expelled from an exhaust nozzle into a humid atmosphere. When the HCI molecules diffuse into the air and collide with H2O molecules therein, an acid mist is formed which gives rise to visible white smoke. Typical examples are AP composite propellants used in rocket motors. Based on experimental observations, white smoke is formed when the relative humidity exceeds about 40 %. Thus, AP composite propellants without any metal particles are termed reduced-smoke propellants. On the other hand, a white smoke trail is always seen from the exhaust of a rocket projectile assisted by an aluminized AP composite propellant under any atmospheric conditions. Thus, aluminized AP composite propellants are termed smoke propellants. 

Blackpowder is still used in sq ll rockets (e.g. signal or rescue rockets for carrying the rope from shore to ship or vice versa). Its limited application is due to the fact that blackpowder gives a very low specific impulse ls=from 40 to 80 sec, which is much lower than that of modern composite propellants and smokeless rocket powders which give a specific impulse of 180-200 sec. 

Accdg to compositions, cannon smokeless proplnts may be subdivided into single-base-, double-base- and triple-base-proplnts. The last two proplnts are sometimes called "compound proplnts. The so-called "composite proplnts, used in JATOS and rockets, are described under Composite Propellants... 

Primer A term for the device used to ignite smokeless powder in small arms ammunition. An impact-sensitive composition is used. When struck by a metal firing pin, a primer emits a burst of flame capable of igniting the propellant charge. Several typical primer mixtures are given in Table 6.2. 

Since some pyrotechnic compositions are relatively difficult to ignite, an "ignition train similar to that used for igniting BkPdr or smokeless propellants is used to initiate the main pyrotechn ic charge... 

For instance, for igniting propellant charges of smokeless powder, grained Black Powder is used, which in turn is ignited by means of a primary ignition composition... 

Smokeless propellants may be taken as another example of composite explosives. These may be either mixtures of nitrocellulose of differing degrees of nitration, partly in a colloidal and partly in a fibrous state with an admixture of the remaining solvent and a stabilizer or a solution of nitrocelluloses in carbamite (centralite) and nitroglycerine with an admixture of components such as aromatic nitro compounds, nitroguanidine, graphite etc. 

Propellants will be grouped on the basis of their composition, into blackpowder and similar mixtures, smokeless powders and rocket liquid propellants. 

Zinc Nitrate. See in Vol 8, N40-L and the following Addnl Refs 1) G.W. Batchelder G.A. Zimmerman, Smokeless Propellant Compositions Containing a Polyester Resin , USP 3653993 (1972) CA 79,77449 (1973) [The inventors claim that Zn nitrate acts as the burning rate catalyst in their propint formulation. Thus, the addn of 0.1% Zn nitrate to a propint contg AN (45), amm dichromate (5%), a polyester, styrene, methacrylate and lecithin increased this parameter from 0.07 to 0.11 indies/ sec] 2) Anon, Fire Protection. . . 7th Edition , NFPA, Boston (1979), 491M-445 [This source reports that Zn nitrate will expld if sprinkled on hot C. Also, that heat, shock and friction sensitive expls are formed when the nitrate is intimately mixed with the following finely divided materials Cu, metal sulfides, organic matter, P and S]... 

I960) as GerP 1031700. This DAS deals with prepn of a smokeless propellants and brisant explosives, now known as Holtex (See Ref 7 under Colloidal Explosives). All of these compositions were invented by Dr. E. von Holt (Dr. H. Freiwald, private communication, 25 Sept 1962)... 

B) W.H. Rinkenbach, Calorific Values of Smokeless Powders as Affected by Variations in Composition, Granulation, etc , PATR 673 (1935) C) C.S. Davis, Development of Improved Propellant and Primer to Reduce Flash in Caliber, 50 Ammunition (Ignition Study) , PATR 1672 (1947) D) W.H. Rinkenbach, Study of Stability of Double-Base Propellants , PATR 1674 (1948) E) J.E. Rainier W.M. Rowe, Propellant for 2ES-40,000 Jato, T29 , PATR 1692 (1948) F) N.S. Garman et al,... 

High explosives may be class d according to their physical properties as powdery, meltable, semi-meltable and plastic. Propellants may be grouped on the basis of chemical composition into gun powder and similar mixtures, nitrocellulose (single base) and nitroglycerine (double base) powders, With respect to their uses and some properties they are divided into black powder, smokeless and flashless powders, and rocket propellants. 

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