Thermal decomposition of energetic materials 71: Structure-decomposition and kinetic relationships in flash pyrolysis of Glycidyl Azide Polymer (GAP)

• Published in: Combustion and flame Vol. 112; no. 4; pp. 533 - 544
• Main Authors: Arisawa, H., Brill, T.B.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01-03-1998; Elsevier Science
• Subjects: Applied sciences; Combustion. Flame; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Miscellaneous; Theoretical studies. Data and constants. Metering; Liquid propellants; Flash pyrolysis; Kinetics; Experimental study; Organic azide; Thermal decomposition
• ISSN: 0010-2180; 1556-2921
• DOI: 10.1016/S0010-2180(97)00162-4

Well-characterized, purified samples of glycidyl azide polymer
(
MW
―
≃
700
)
having one, two, or three terminal -OH groups were flash pyrolyzed (d
T/d
t = 800 K/s) to 540–600 K under 2 atm Ar by T-jump/FTIR spectroscopy. This technique emphasizes condensed-phase pyrolysis chemistry as opposed to gas-phase flame chemistry. The volatile products identified from the condensed phase were CH
4, HCN, CO, C
2H
4, NH
3, CH
2O, CH
2CO, H
2O, and GAP oligomers. IR-inactive N
2 is, of course, also present. The low MW products result from homolysis of the heavy atom bonds and H-atom migration, as opposed to heavy atom recombination reactions. After N
2 release, the relations between the mole fractions of the products and the parent GAP structure were determined. The NH
3 content increases with the -OH content, which suggests that NH
3 is mostly formed by the end-chain azide groups. The hydrocarbon mole fractions correlate with the structure of the parent sample of GAP. CO appears to form from both the parent polymer and secondary sources, such as CH
2O and CH
2CO, at higher temperature. The HCN/NH
3 ratio increases with increasing temperature. By using the product mole fractions and heat of formation of GAP, the calculated heat of decomposition (⋍−1.4 kcal/g) is found to be three times larger than that measured by DSC (⋍−0.43 kcal/g). The large Δ
H
d
helps explain the reported high surface temperature. The relatively low reported flame temperature during combustion reflects the limited number of secondary exothermic reactions that are possible among the products. If it occurs during combustion, the apparent release of some GAP oligomers observed during flash pyrolysis would raise the flame temperature by allowing the decomposition of some of the GAP in the gas phase. The kinetics of formation of NH
3 [
E
a = 49 kcal/mol, In(A/s) = 42] were determined below the autothermal stage. Above the autothermal stage, the products form at too rapid a rate to be measured by the methods used.