Fine AP Research Articles

Study of thermal decomposition and mechanical sensitivity of ETPE propellants

Abstract In this paper, the thermal decomposition characteristics and mechanical sensitivity of ETPE propellant were characterized by differential scanning calorimeter (DSC), vacuum stability tester (VST), impact sensitivity tester and friction sensitivity tester, and the main factors affecting the safety performance of ETPE propellant were studied. The results show that ETPE propellant has good thermal stability under 185°C. The combustion activation energy of ETPE propellant is slightly lower than that of HTPB propellant. By using 100°C heating method, the net added gas of ETPE propellant is 0.81ml/g, which meets the evaluation standard of stability qualification, and the propellant did not spontaneously combust under various high temperature test conditions. By reducing the amount of fine AP and controlling the amount of RDX, it is conducive to reducing the probability of the “hot spot” generated by the propellant under the external excitation energy, reducing the mechanical sensitivity of propellant and improving the safety performance of propellant.

Catalytic Decomposition Effect and Mechanism of Energetic Complex Cu(NH3)4(AFT)2 Towards Fine AP

Catalytic Decomposition Effect and Mechanism of Energetic Complex Cu(NH3)4(AFT)2 Towards Fine AP

Preparation of Fine Ammonium Perchlorate by Employing Dual‐Sonic Premixer: Freeze‐Drying Method

AbstractAmmonium perchlorate (AP)‐based composite propellant is the most widely used solid propellant. Fine AP is required to obtain a propellant with a high burning rate. To prepare fine AP, an emulsion was prepared by emulsifying toluene and the AP solution. The emulsion was frozen rapidly with liquid nitrogen and then freeze‐dried. Fine AP was prepared by this freeze‐drying method. In this study, the emulsion was prepared with the premixer adopted dual‐sonic technology and an attempt was made to prepare finer AP. By using a dual‐sonic premixer, the emulsion was efficiently prepared, and therefore, a fine AP sample was obtained, compared with the homogenizer that is commonly used. It was found that the AP sample could be used as a propellant oxidizer according to its impact and thermal sensitivities.

Nanochromates MCr2O4 (M = Co, Ni, Cu, Zn): Preparation, Characterization, and Catalytic Activity on the Thermal Decomposition of Fine AP and CL-20.

The chromate nanoparticles such as CoCr2O4, NiCr2O4, CuCr2O4, and ZnCr2O4 were prepared by a modified sol–gel method. The structural and morphological properties of the chromate nanoparticles were characterized by X-ray diffraction (XRD) and a scanning electron microscope (SEM). The catalytic effects of chromates on the thermal decomposition of fine ammonium perchlorate (FAP) and hexanitrohexaazaisowurtzitane (CL-20) were studied by the TG-DTG measurements. Results show that the addition of CoCr2O4, NiCr2O4, CuCr2O4, and ZnCr2O4 nanoparticles makes the activation energies for the thermal decomposition of FAP decrease by 93.9, 94.0, 83.1, and 67.0 kJ·mol–1, and the thermal decomposition temperatures decrease by 45.0, 24.9, 57.7, and 38.8 K respectively. On the other hand, a similar trend exists in the case of the thermal decomposition of CL-20. Therefore, the addition of nanochromates shows high catalytic efficiency on the thermal decomposition of both FAP and CL-20 components, which would be beneficial to promote the burning rate of propellants containing FAP and CL-20 components.

Oxidation of Catocene in AP/Catocene Mixture at Low Temperature

AbstractThe mixture of Catocene and fine AP after 175 °C heat treatment was washed by acetone and water, and the washing liquids of acetone and water were characterized by SP and microwave digestion‐ICP, and the solid products were characterized by XPS, XRD, SEM‐EDS. The results show that the oxidation of Catocene is a multi‐step reaction, and the final products are nano‐sized Fe2O3 and amorphous C. DTA‐TG test shows the productions can enhance the thermal decomposition of AP. Compared with the mixture of fine AP and Catocene, the mixture of fine AP and the final solid product of Catocene decomposition is insensitive to the impact. The effective constituents of Catocene catalysis for thermal decomposition of AP are nano‐sized Fe2O3 and amorphous C. Analyzing by synthesis, the final solid product may be an effective and safe catalyst for AP based propellant.

The effect of decorated graphene addition on the burning rate of ammonium perchlorate composite propellants

Catalysts are often added to solid propellant formulations to tailor burning rates. Nanocatalysts can increase propellant burning rates over standard catalyst sizes due to the increase in surface area per unit weight. However, the increased surface area that the binder must wet can be prohibitive if large amounts of nanocatalysts are used. Additionally, agglomeration of the nanocatalyst can result in micron-scale particles, reducing catalyst effectiveness. In this study a nanoscale iron oxide catalyst has been used to decorate graphene. By decorating graphene with the catalyst, nanoscale features are kept but the catalyst is stabilized to reduce agglomeration. Changes in burning rate between the catalyzed and uncatalyzed propellants are investigated. The effect on burning rate of encapsulating the catalyst inside the fine AP crystals compared to propellants where it is added to the binder is also investigated. We also compare propellants with decorated graphene and propellants with undecorated graphene catalysts. The three comparisons are made for two different graphene preparation methods. It is found that the highest burning rates occur in propellants where the graphene is decorated with catalyst and encapsulated in the fine AP. The next highest burning rates occur in propellants with decorated graphene that is physically mixed into the propellant. The lowest burning rates are found in propellants where the graphene is undecorated, where there is little difference between encapsulated or physically mixed graphene blanks, or compared to a baseline propellant. Burning rates are found to be similar between graphene preparation methods considered.

Burning Rate – Pressure Relationship of NG‐PE‐PCP‐based High Energy Propellants

AbstractNitramines are known to produce lower burning rates and higher pressure exponent (η) values. Studies on the burning rate and combustion behavior of advanced high‐energy NG/PE‐PCP/HMX/AP/Al based solid propellant processed by slurry cast route were carried out using varying percentages of HMX and AP. It was observed that propellant compositions containing only AP and Al loaded (total solids 75 %) in NG plasticized PE‐PCP binder produce comparatively lower pressure exponent (η) values similar to AP‐Al filled HTPB based composite propellants. However, energetic propellants containing high level of nitramine (40–60 %) produce high pressure exponent (0.8–0.9) values in the same pressure range. Incorporation of fine particle size AP (ca. 6 μm) and change in its concentration in the propellant composition reduces η value marginally and influences the burning rate. However, such compositions have higher friction sensitivity.

Burning Characteristics and Thermochemical Behavior of AP/HTPB Composite Propellant Using Coarse and Fine AP Particles

AbstractThe burning rate of AP/HTPB composite propellant increases with increasing AP content and with decreasing AP size. In addition, the burning rate can be enhanced with the addition of Fe2O3. The burning characteristics and thermal decomposition behavior of AP/HTPB composite propellant using coarse and fine AP particles with and without Fe2O3 at various AP contents were investigated to obtain an exhaustive set of data. As the AP content decreased, the burning rate decreased and the propellants containing less than a certain AP content self‐quenched or did not ignite. The self‐quenched combustion began at both lower and higher pressures. The lower limit of AP content to burn the propellant with coarse AP was lower than that with fine AP. The lower limit of AP content to burn was decreased by the addition of Fe2O3. The thermal decomposition behavior of propellants prepared with 20–80 % AP was investigated. The decrease in the peak temperature of the exothermic decomposition suggested an increased burning rate. However, a quantitative relationship between the thermochemical behavior and the burning characteristics, such as the burning rate and the lower limit of AP content to burn, could not be determined.

Coupling of leading edge flames in the combustion zone of composite solid propellants

The burning rate trends of both pure binder sandwiches and those containing a mixture of binder with fine ammonium perchlorate particles are investigated over appreciable ranges of pressure and thickness of the middle lamina in the sandwich. The crucial aspect of this study is the wide variation of the fine ammonium perchlorate/binder ratio in the middle lamina of the sandwiches. The sandwiches with fine ammonium perchlorate particles have been quenched by rapid depressurization and their surface profiles have been carefully mapped for different conditions. The gas phase flame structure is estimated through numerical simulation, with the observed surface profiles and burning rates taken as inputs. It is found that, as the fine ammonium perchlorate particles are added to the binder in small quantities, they tend to dilute the fuel and increase the lamina thickness for maximum interaction between the leading edge flames, but the trend in the variation of the optimum thickness for maximum burning rate with increase in pressure is reversed when compared to the case of pure binder sandwiches reported earlier. The burning rates of these sandwiches decrease slightly relative to those of the pure binder sandwiches. With higher fine AP content, there is greater interaction between the leading edge flames due to the inward shift of the stoichiometric surface and the extension of the fuel-rich sides of the leading edge flames over the middle lamina, ultimately resulting in the establishment of the canopy premixed flame between them. This restores the optimum thickness trends with pressure as in the case of pure binder sandwiches.

EXAMPLES OF UNSTEADY COMBUSTION IN NON-METALLIZED PROPELLANTS

For over thirty years the T-Burner has been the de facto standard for determining the unstable response of solid propellants. This paper reviews some of the different approaches that have been used, and briefly summarizes advantages and disadvantages of the different techniques. Data from a variety of sources have been reviewed and summarized showing the effect of various test conditions and propellant formulation variations. Much of the data taken in the 60's and early 70's were with so-called research propellants, with relatively low solids loading and usually monomodal AP as the oxidizer. Later data were obtained with propellants containing solids loading more typical and practical propellants. Several distinct differences were observed in the data for the different types of propellants. Data varying AP particle size distributions indicate that either additional fine AP or finer AP usually increases the propellant response. A significant reduction in the response can be achieved by reducing the amount of fine AP, while holding burning rate constant either by adding a catalyst or by varying the overall AP size distribution. A significant amount of data has been obtained for reduced smoke propellants containing stability additives. The data indicate that the additives provide significant particle damping, and most often, also reduce the propellant response. Data from double base propellants indicate a much broader response over a wide frequency range. This implies that double base propellants should be more unstable in tangential modes than composite propellants. This trend seems to be consistent with observed motor data. Measuring the response of metallized propellants has been a challenge due to the large damping due to metal oxide particles in the gas. Data from metallized propellants are not presented here, but will be summarized in a future paper.

BALLISTIC AND COMBUSTION PROPERTIES OF HIGH-PRESSURE EXPONENT HYDROCARBON-BASED FUEL-RICH PROPELLANTS

The ballistic properties of hydrocarbon-based fuel-rich propellants can be manipulated by various methods. Incorporating fine AP and large surface area ferric oxide particles can substantially increase the burning rate. Alternative oxidizers like KP and RDX can lower the burning rate. Studies showed that the burning rate measurements are highly dependent on three measuring techniques: optical bomb, strand burner and BEM test motors. Pictures of burning fuel-rich propellant showed the formation of a thick porous zone during combustion. The flame temperature of fuel-rich propellants measured with visible spectroscopy differs from values calculated with thermodynamic calculations.

Development of high burn rate azide polymer propellant

The combustion characteristics of high burn rate azide polymer composite propellant were examined by using ø 70 mm BMI composite rocket motor of L/D = 16. Azide polymer propellants have much higher specific impulse than HTPB propellant at below the AP content of 85%. AP/B/N propellants showed a plateau-mesa burning at a pressure range between 7 MPa and 15 MPa with a burn rate of approximately 28 mm/s. Very fine AP, however, diminished this favorable combustion characteristics. The AP/B/N also had excellent mechanical properties at an operational temperature range to enable the case bonded. The BMI motors burned stably and showed an excellent performance. The thickness of the insulation at the aft closure, 5.5 mm including a stress relief boot, was good enough.

BURN RATE STUDEES OF GAS GENERATOR PROPELLANTS CONTAINING AP/RDX

This paper reports burn rate results of AP/RDX-based compositions with Epoxy / Epoxy-GAP binder Bimodal AP composition with 40% Epoxy binder gave burn rates of 2.1−2.4 mm/s in the pressure range of 1−8.8 MPa and appeared to be suitable for the primary combustor in ramjet applications. Incorporation of 10−30% GAP at the cost of epoxy binder resulted in a 30−250% increase in bum rates, and replacement of coarse AP by fine AP (4 and 10u) led to a 1.5−5 -fold increase in bum rates. Addition of 2 parts of copper chromite / ferric oxide as a catalyst resulted in a moderate increase in burn rates, while incorporation of butyl ferrocene led to a 1.3−3 -fold increase in bum rates. Ballistically modified AP/Epoxy/GAP compositions with bum rates ranging from 5−15 mm/s at 1 MPa to 15−30 mm/s at 8.8 MPa and moderate flame temperatures have potential for gas generator application. The effect of replacement of AP by RDX on bum rates was also studied during this work.

Aluminum agglomeration in ammonium perchlorate/cyclotrimethylene trinitramine/aluminum/hydroxy-terminated polybutadiene propellant combustion

Aluminum combustion efficiency and agglomeration in 13 equal-composition AP/RDX/A1/HTPB propellants were experimentally investigated using a quenched particle collection bomb (QPCB) under pressures up to 6895 kN/m. Formulation parameters studied included RDX size, Al size, fine AP size, and AP coarse/fine weight ratio. The results indicate that formulation variables can affect the combustion efficiency through either propellant microstructure changes, or extended condensed phase reactions associated with significant fine AP fraction. Effects of formulation variables on combustion efficiency are in qualitative agreement with the trends predicted by Cohen's pocket model. The addition of RDX has an adverse effect on agglomerate size, possibly through formation of a molten layer that facilitates the retention and coalescence of AI particles on the burning surface. Agglomerate sizes are adequately characterized by two microstructure parameters from a simplified pocket model. A correlation for estimation of agglomerate size of AP/Nitramine/Al/HTPB propellent is tentatively proposed based on the data from various sources. Moreover, the combustion efficiency was found to be inversely proportional to the agglomerate size.

Aluminum Agglomeration in Solid-Propellant Combustion

-... Results of a series of tests on AP/aluminum/PBAN propellants, with particular attention to bimodal AP particle size distribution, show the effect of particle size of fine AP and the concentration of fine AP on aluminum agglomeration and ignition. Results are interpreted in terms of the distribution of aluminum in propellant microstructure and the proximity of AP-binder flamelets to precipitate ignition of the accumulating aluminum.