AN pyrolants

In general, pyrolants composed of a polymeric material and AN particles are smokeless in character, their burning rates are very low, and their pressure exponents of burning rate are high. However, black smoke is formed as i decreased and carbonaceous layers are formed on the burning surface. These carbonaceous layers are formed from the undecomposed polymeric materials used as the matrix of the pyrolant. When crystalline AN particles are mixed with GAP, GAP-AN pyrolants are formed. Since GAP burns by itself, the GAP used as a matrix for AN particles decomposes completely and bums with the oxidizer gases generated by the AN particles. 

The combustion products of aluminized GAP-AN pyrolants at 10 MPa are HjO, Hj, Nj, GO, GOj, and AI2O3. The mass fraction of AljOj increases linearly while that of HjO decreases linearly with increasing Iai- This is caused by the overall reaction of 2A1 -I- 3H2O AI2O3 -t 3H2. 

The AN particles incorporated into GAP-AN pyrolants form a molten layer on the burning surface and decompose to form oxidizer fragments. The fuel-rich gas produced by the decomposition of GAP interdiffuses with these oxidizer fragments on and above the burning surface and produces a premixed flame. A luminous flameis formed above the burning surface. 

When AP particles are added to GAP-AN pyrolants, a number of luminous flame-lets are formed above the burning surface. These flamelets are produced as a result of diffusional mixing between the oxidizer-rich gaseous decomposition products of the AP particles and the fuel-rich gaseous decomposition products of the GAP-AN pyrolants. Thus, the temperature profile in the gas phase increases irregularly due to the formation of non-homogeneous diffusional flamelets. 

When A1 particles are added to GAP-AN pyrolants, agglomerated A1 fragments are formed on the burning surface. However, when A1 particles are mixed with pyrolants composed of GAP, AN, and AP, numerous flame streams are formed in the gas phase. The A1 particles are oxidized by the gaseous decomposition products evolved by the AP particles. The combustion efficiency of the A1 particles is improved significantly by the addition of the AP particles. 

When AN powder is mixed with a polymeric material, the oxygen gas produced by the decomposition of the AN powder reacts with the hydrocarbon fragments of the thermally decomposed polymeric material. The major combustion products are GO2 and H2O. Nitropolymers are not used as fuel components of AN pyrolants because of the reaction between the NO2 formed by their decomposition and the AN powder. This reaction occurs very slowly and damages the physical structure of the AN pyrolant. Instead, polymeric materials containing relatively high mass fractions... 

The burning rates of AN pyrolants are of the order of 1-3 mm s" at 10 MPa, which is very slow compared with AP pyrolants. Decomposition catalysts for AN powder, such as chromium trioxide (Cr203) and ammonium dichro-mate((NH4)2Cr207), need to be incorporated into AN pyrolants to aid their successive burning. Very unstable burning occurs without these catalysts. 

Table 12.6 Physicochemical properties of an AN pyrolant (mass fraction).

Since the combustion temperature of AN pyrolants is very low compared with other composite pyrolants, their specific impulse when used as rocket propellants is also low. However, they are used as gas generators for the control of various types of mechanics owing to the low temperature and low burning rate characteristics. 

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