Effects on Burn Rates of Pellets and Propellants with Catalyst-Embedded AP

Acoustic pressure oscillation effects on mean burning rates of plateau propellants

Abstract: Combustion instabilities constitute a well pronounced problem in all large rocket motors due to the inherent acoustic pressure oscillations established based on the port geometries. Suppression of the combustion instabilities in the solid rocket motor is required for controlling the mean burning rate variation which arises due to the interaction of acoustic pressure wave with propellant combustion. An experimental study has been carried out to investigate the effects of acoustic pressure oscillations on mean burning rates of non-aluminized and aluminized propellants which exhibit low pressure exponent index (n) in the burning rate trends. Steady and unsteady mean burning rates are determined from combustion photography method using a window bomb test facility over the pressure range of 17 MPa. A rotary valve is coupled with the window bomb setup to generate acoustic pressure oscillations inside the test chamber (cylindrical pressure vessel), which imposes the required frequencies of 140, 180 and 240 Hz respectively. The acoustic pressure amplitudes are varied from 0.04% to 1.4% of the mean chamber pressure. Both non-aluminized propellants and aluminized propellants have shown significant enhancement in the mean burning rate due to the fluctuations imposed by acoustic pressure amplitudes and frequencies on the propellant combustion. The enhancement in the mean burning rate also depends upon dynamic response of the flame to the excited frequencies and acoustic pressure amplitudes. The plateau burning behaviour of the non-aluminized propellant is completely distorted whereas it is retained in aluminized compositions. Conversely, it also shifts the mean pressure range of plateau burning rate trend. The maximum burning rate augmentation factors resulted from imposed acoustic pressure wave on non-aluminized and aluminized propellants are observed as 1.27 and 1.47 respectively.

Exploring the Roles of ZIF-67 as an Energetic Additive in the Thermal Decomposition of Ammonium Perchlorate

Abstract: Energetic additives can effectively increase the heat release of ammonium perchlorate (AP) decomposition to prevent nonenergetic additives from decreasing the energy density of composite solid prop...

Novel energetic coordination compound [Cu(AT)4]Cl2 for catalytic thermal decomposition of ammonium perchlorate

Abstract: The lower high-temperature decomposition (HTD) temperature of ammonium perchlorate (AP) and more heat release of composite solid propellants (CSPs) put forward higher requirements on thermal catalysts. Herein, a new anhydrous energetic coordination compound [Cu(AT)4]Cl2 was well-designed and synthesized by coordination reaction of copper(II) and 5-amino-1H-tetrazole (AT), in which copper(II) catalytic active center has catalytic effect on reducing the HTD temperature of AP, and energetic AT can increase heat release. The structure of [Cu(AT)4]Cl2 was well determined by single crystal X-ray diffraction. The excellent thermal stability of [Cu(AT)4]Cl2 was verified by the results of thermogravimetric analysis and non-isothermal kinetics method. The catalytic activity of [Cu(AT)4]Cl2 for AP thermal decomposition was studied by the differential thermal analytical. The results indicated that the HTD peak of AP was significantly decreased by 60 ​K–495 ​K, and the activation energy of AP decreased by 57.5 ​kJ ​mol−1 to 163.37 ​kJ ​mol−1. The results of TGA-FTIR shows that the [Cu(AT)4]Cl2 will decompose and produce HCN gas before catalyzing AP, then the thermal decomposition products participated in the thermal decomposition of AP as an effective component of catalysis. The mechanical sensitivities and energetic characteristics of [Cu(AT)4]Cl2 was also studied by mechanical sensitometer, Calvet-type differential thermal conductivity calorimeter, and Kamlet-Jacbos equations. The results indicated that [Cu(AT)4]Cl2 has lower sensitivity than Trinitrotoluene and brilliant energetic characteristics. The [Cu(AT)4]Cl2 is expected to be one candidate additive in CSPs for catalytic thermal decomposition of AP.

When Copper Oxide meets graphene oxide: A core-shell structure via an intermittent spray coating route for a highly efficient ammonium perchlorate thermal decomposition

Abstract: Ammonium perchlorate (AP) is the primary oxygen source for solid propellants; its thermal decomposition behavior is determinant for the overall performance of the ensuing propellant. In this perspective, a novel Intermittent, Spray Coating, Draying, and Mixing (ISCDM) method is introduced herein to prepare AP@CuO, PA@GO, and AP@CuO@GO core-shell composites. The as-synthesized materials morphological information, crystalline structure, and elemental composition are probed by powder X-ray diffraction, Raman spectroscopy, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. The as-prepared CuO nanospheres were effectively embedded into the AP microparticles surface. AP@CuO microparticles were continuously coated with graphene oxide (GO) nanosheets. Particle size analyzer was used to probe the particle size distribution of core-shell composites. Results show that the application of ISCDM method results in a typical narrow gaussian size distribution with an average diameter of hundred microns ranking from 158.56 μm to 166.22 μm. The thermal decomposition and the catalytic performances were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). AP@CuO@GO core-shell composite exhibits an excellent thermal decomposition behavior: a low thermal decomposition temperature (LTD) of 337 ˚C, reduced values of the High thermal decomposition temperature HTD to be overlapped with the LTD step, and a significant energy release of 1543 J.g−1 are registered.

Zeolite Imidazolate Frameworks-67 Precursor to Fabricate a Highly Active Cobalt-Embedded N-Doped Porous Graphitized Carbon Catalyst for the Thermal Decomposition of Ammonium Perchlorate.

Abstract: The more apparent specific heat release at a lower high-temperature decomposition (HTD) temperature of ammonium perchlorate (AP) poses a challenge for the development of highly active catalysts. In this work, a well-designed cobalt-embedded N-doped porous graphitized carbon (Co@NC) catalyst is obtained by high-temperature calcination of a zeolite imidazolate frameworks-67 precursor, in which the cobalt catalytic active center realizes effective nanoscale dispersion; meanwhile, the cobalt and N-doped porous graphitized carbon can release considerable heat after oxidation, and the cobalt oxides have an excellent catalytic effect on reducing the HTD temperature of AP. The catalytic activity of Co@NC was tested by a differential thermal analytical method. The results indicated that the HTD peak of AP was significantly decreased by 100.5 °C, the apparent activation energy of the HTD reaction of AP was reduced by 82.0 kJ mol-1, and the heat release compared with pure AP increased 2.9 times. On teh basis of these findings, Co@NC is expected to be one of the best candidate materials for AP thermal decomposition.

Effect of nano-aluminium in plateau-burning and catalyzed composite solid propellant combustion

Abstract: Nano-aluminium particles of ∼50 nm size, produced at this laboratory, are added to composite solid propellants based on ammonium perchlorate and hydroxyl-terminated poly-butadiene binder that exhibit plateau burning rate trends and those including burning rate catalysts. The nano-aluminized propellant burning rates are compared with corresponding micro-aluminized and non-aluminized ones in the 1–12 MPa pressure range. The mid-pressure extinction of the matrixes containing the fine-sized ammonium perchlorate particles in the propellant along with the binder is investigated in all the cases to understand the mechanism of plateau-burning. Further, the variations in aluminium content, the aluminium size (within nano- and micro-ranges), bimodal combination of nano- and micro-aluminium are considered. Ferric oxide and titanium dioxide are the burning rate catalysts considered. Large scale accumulation of aluminium is observed not only in micro-aluminized matrixes, but also in nano-aluminized ones as clusters of 1–5 μm size. Since aluminium is added at the expense of the coarse ammonium perchlorate particles to preserve the total-solids loading in the present formulations, addition of micro-aluminium decreases the burning rate; whereas, nano-aluminized propellants exhibit ∼80–100% increase in the burning rate under most conditions. The near-complete combustion of nano-aluminium close to the burning surface of the propellant provides heat feedback that controls the burning rate. Mid-pressure extinctions of matrixes and plateau burning rates of propellants are washed out when nano-aluminium is progressively added beyond 50% in bimodal aluminium blends, but low pressure-exponents are observed in the nano-aluminized propellant burning rates at elevated pressures. Adjusting the plasticizer content in the binder alters the pressure range of plateau burning rates in non-aluminized propellants. Catalysts increase the burning rate by ∼50–100% in non-aluminized and micro-aluminized propellants, but in nano-aluminized propellants, the μm-sized catalyst does not affect the burning rate significantly; whereas, the nanometre size catalysts increases the burning rate merely by ∼5–15%.

The effects of bimodal aluminum with ultrafine aluminum on the burning rates of solid propellants

Abstract: Burning rates were measured for aluminized composite propellants with different aluminum (Al) sizes(monomodal distribution) and with bimodal Al distributions containing various amounts of ultrafine Al (UFAl). Enhanced rates were found for fine Al, with the enhancement increases for reduced Al size. The fine Al also burned in an intense region very close to the propellant surface, suggesting improved heat feedback in the form of radiation and conduction. Major modification of the burning rate could be achieved with moderate amounts of UFAl. Results obtained with various fine oxidizer particle sizes and mass fractions suggest that the degree of burning-rate modification depends on the ability to ignite the UFAl, for example, with leading-edge flames, as well as the availability of oxidizer near the Al-containing regions of the propellant.

Deflagration rate, surface structure, and subsurface profile of self-deflagrating single crystals of ammonium perchlorate

Abstract: Pure ammonium perchlorate single crystal self deflagration, determining energy transfer mechanisms from pressure effects, combustion characteristics and subsurface profile

Combustion of ammonium perchlorate

Abstract: Deflagration of ammonium perchlorate studied using cleaved sections of large single crystals grown from water solution, discussing burning rate and combustion zone

Studies on the role of iron oxide and copper chromite in solid propellant combustion

Abstract: Iron oxide and copper chromite are the known burn rate enhancers used in a composite solid propellant. Lot of research has been carried out to understand the mechanism or location of action of the burn rate modifiers so as to better tailor the burning rate of a composite propellant. The literature is still very confusing in affirming the mechanism. Here, a systematic study has been carried out, by undertaking experiments at varying levels of combinations of the individual components (ammonium perchlorate, which is oxidizer and hydroxyl terminated poly butadiene, which is both fuel and binder) of composite solid propellant. Firstly, thermal gravimetric analysis, differential scanning calorimetry and burning rate measurements on the individual components are carried out to study the effect of iron oxide and copper chromite on the components themselves. It has been noticed that though both iron oxide and copper chromite are effective on ammonium perchlorate, iron oxide is slightly more effective than copper chromite. Also, copper chromite enhanced the binder melt flow, while iron oxide reduced it. These are followed-up by experiments on sandwich propellants, which give greater insight and enables better understanding of the behavior of iron oxide and copper chromite in composite propellants, as these are simple two-dimensional analogue of the composite solid propellants. Finally, experiments are carried out on the composite solid propellants to obtain a holistic understanding of the behavior/location of action of iron oxide and copper chromite in them. These studies are used to explain certain unexplained but observed phenomena, at the same time elucidating the location of action of these burn rate modifiers in composite solid propellant combustion. Based on these observations, it has been proposed that both iron oxide and copper chromite are primarily acting on the condensed phase. These studies are further complimented with experiments to analyze the thermal conductivity measurements of various propellant samples. This is pursued to understand the reason for the differences in burn rate pressure index for the composite propellants with iron oxide and with copper chromite. It has been understood from these studies that the thermal conductivity of a composite propellant is a key parameter, which affects the burn rate pressure index. Literature has never addressed it from this perspective.