Thermal Decomposition of AMMO/AP Composite Propellants

Thermal decomposition of AMMO/AP composite propellants was studied by DTA, TGA and DSC in helium atmosphere. The effects of accelerated aging at 347 K for 370 days on decomposition kinetics were also measured. AMMO/AP propellant showed two different decomposition steps, which were mainly the AMMO binder decomposed region and the reaction of AP dominated region. These regions were separated at around 20 % weight loss point at the condition used in this study. AMMO binder decomposition and AP decomposition were strongly related each other. The heat generated by the AMMO binder decomposition initiated and accelerated the thermal decomposition of AP. Although both Fe₂O₃ and CFe activated the thermal decomposition of AMMO/AP propellants, CFe mainly accelerated the decomposition of AMMO binder and Fe₂O₃ catalyzed the AP reactions which consisted of the AP decomposition and the reaction between decomposed AP and decomposed AMMO binder. AMMO/AP composite propellants were thermally stable even after aging at 347 K for 370 days.     

Effect of Binders on the Burning Rate of AP Composite Propellants

The burning rate characteristics of ammonium perchlorate (AP) based composite propellants is studied as a function of the chemical nature of the polymers used as binders. The following five types of polymers are used:(1) hydroxy‐terminated polybutadiene (HTPB)(2) polypropyleneglycol (PPG)(3) polysulfide (PS)(4) polyesterpolyol (PO)(5) azidomethylmethyloxetane (AMMO) Experiments are conducted using differential thermal analysis (DTA), thermogravimetric analysis (TG), and burning rate analysis. The AP/PS propellant shows the highest burning rate and the AP/PO propellant shows the lowest burning rate within the propellants tested. Though the burning rate appears to be very dependent on the type of binder used, the characteristics of burning rate versus pressure cannot be correlated with the thermochemical data obtained by DTA and TG. The results of the photographic observation of the burning surface indicate that the formation of a melting layer of the binder reduces the burning rate due to the reduced reaction rate between the binder and the AP particles.     

Friction sensitivity mechanism of Ammonium Perchlorate Composite Propellants

Friction sensitivity of ammonium perchlorate (AP) composite propellants has been studied experimentally by means of thermal analysis and micro-thermocouple techniques. Several types of catalysts were mixed with AP in order to examine the effect of the reactivity on the sensitivity. The results of friction sensitivity test show that the samples are sensitized when the concentration of catalysis which are used for high burning rate propellants is increased. Metal contents within the catalysts tend to give some effects on the friction sensitivity. Based on the results of the temperature profile measurements in combustion waves, it is found that the friction sensitivity is correlated with the burning surface temperature of the propellants. The catalysts which accclerate the AP decomposition are responsible for the friction sensitivity but not for the fallhammer sensitivity.     

Synthesis and Sensitivity of Hexanitrohexaaza-isowurtzitane(HNIW)

Hexanitrohexaaza-isowurtzitane(AC-HNIW) was synthesized by using a precursor invented by Asahi. The purity, which was measured by high performance liquid chromatography(HPLC), was determined to be 99.2%. From the results, it is expected that the propellants or explosives composed of AC-HNIW indicated higher performance in specific impulse, ballistics and detonation velocity. The structure of AC-HNIW was identified by IR and NMR. The results indicated that AC-HNIW had the same structure as CL-20 which was produced by Thiokol corporation. The sensitivity and thermal decomposition properties of AC-HNIW were also measured in order to elucidate HNIW performance. The results were compared with CL-20. The sensitivity of AC-HNIW was determined to be the same as CL-20.     

Energetics of AMMO

The thermal decomposition process and combustion wave structure of azide polymer were studied to determine the parameters which control the burning rate. The azide polymer studied was 3-azidomethyl-3-methyl oxetane (AMMO) which contains energetic –N₃ groups. From the experiments, it was found that the thermal decomposition process of AMMO consists of a two-stage weight loss process: the first-stage corresponds to an exothermic reaction which is caused by the scission of N-N₂ bond, and the second-stage corresponds to the decomposition of the remaining fragments. The burning rate of AMMO is approximately 50% of the burning rate of GAP propellant and is as high as that of conventional double base propellant. The heat feedback from gas phase to the burning surface increase with increasing pressure. The burning surface temperature and the heat of reaction at the surface decrease with increasing pressure.     

Plateau Burning Characteristics of AP Based Azide Composite Propellants

The site and mechanism by which iron oxide catalyst acted to enhance burning rate and produced plateau burning behavior at high pressure was studied. The condensed phase chemistry study was conducted by isothermal thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), and rapid-scan FTIR spectroscopic technique. Uncatalyzed ammonium perchlorate (AP) based azide composite propellant showed unstable combustion at relatively lower pressure region. The heat balance at the buring surface would be unstable at these pressures. However, iron oxide altered the burning property of the propellant and enhanced the burning rate with the plateau-mesa burning characteristics. Such pressure insensitiveness of the burning rate indicated that the condensed phase chemistry played important role in the catalytic mechanism of action. According to the microrocket motor tests, physical effect, melted fuel binder covered the AP particles and prevented the further decomposition of AP, had not affected the plateau burning. Fe₂O₃ was more effective on the burning rate augmentation than Fe₃O₄. However, the pressure exponent of the burning rate point of view Fe₃O₄ was favored catalyst to the propellant used here.