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Aluminum particles have the problems of difficult ignition, easy agglomeration, incomplete combustion, etc. Therefore, it is of great scientific significance and engineering value to find ways to improve the ignition and combustion performance of aluminum particles in order to promote the full release of energy of aluminum particles. In this paper, spherical nano-sized ferric oxide (nFe2O3) and ammonium perchlorate (AP), a commonly used oxidizer in propellants, were used to synergistically improve the ignition and combustion performance of aluminum particles. AP modified the aluminum particles by both mixing and coating methods, respectively. On the basis of coating AP, nFe2O3 was added in order to further enhance the ignition and combustion performance of the aluminum particles. Scanning electron microscope, laser particle size analyzer, thermal analysis system and laser ignition experiment system were used to test the physicochemical properties and ignition combustion performance of different samples. The results showed that AP and nFe2O3 could be coated relatively uniformly on the surface of aluminum particles using the recrystallization method. The thermal reaction behavior of the samples showed that coating was beneficial to the decomposition of AP compared with mixing, and the addition of nFe2O3 could further improve the decomposition efficiency of AP. Ignition and combustion experiments showed that coating AP was more conducive to improving the ignition and combustion performance of aluminum particles than mixing AP, and the addition of nFe2O3 could further significantly enhance the combustion intensity and flame propagation speed of the sample. However, the addition of nFe2O3 increased the ignition delay time of the sample, which may be related to the cold agglomeration phenomenon caused by the nanoparticles. The microscopic combustion flame morphology of different samples showed that coating AP and the introduction of nFe2O3 could significantly reduce the agglomeration phenomenon of aluminum particles. Overall, coating AP reduces the distance between the aluminum particles and the oxidizer, thus significantly improving the ignition and combustion performance of the aluminum particles. The addition of nFe2O3 can further improve the combustion performance of aluminum particles, but at the same time, it also increases the ignition delay time. Hence, the cold agglomeration problem caused by nanoparticles should be fully considered when nFe2O3 is used to improve the ignition and combustion performance of aluminum particles. [ABSTRACT FROM AUTHOR]

The potential of the Al-F reaction in suppressing agglomeration during propellant combustion and enhancing combustion performance is investigated by introducing fluorinated graphene as a fluorinated oxidizer. Comparative analyses of ignition combustion and agglomeration behaviors are conducted on novel composite powders and propellant samples modified with varying contents of fluorinated graphene using laser and hot wire ignition visualization systems. Characterizing parameters such as characteristic spectra, flame grayscale, ignition delay time, combustion duration, and burning rate are measured during combustion at different pressures. Additionally, agglomerated particles are collected via quenching techniques under 7 MPa pressure to explore the influence mechanism of fluorinated graphene on agglomeration near the burning surface, and a comprehensive influence mechanism is proposed. Results indicate that fluorinated graphene promotes ammonium perchlorate decomposition, accelerates oxidizing gas release, and enhances thermal conduction at the burning surface. The reaction between Al and F decreases the formation of intermediates (AlO and Al 2 O), while the interaction of F with Al and Al 2 O 3 effectively inhibits the clustering of Al particles, replacing conventional oxidation reactions and resulting in a unique micro-explosion jetting phenomenon. The introduction of 15 % fluorinated graphene concentrates most product particles around 10 μm, enhancing energy release during combustion. Overall, this composite powder containing fluorinated graphene effectively improves the combustion performance of aluminum-containing composite propellants, inhibiting Al particle agglomeration and potentially reducing specific impulse loss in solid rocket motors. • Fluorinated graphene promotes advanced decomposition and combustion. • Composite particles increase the combustion intensity of Al-based propellants. • F-O competition reaction suppresses the formation of agglomerations. • Multi-factor induced micro-explosions in agglomerations. [ABSTRACT FROM AUTHOR]

Overcoming the difficulty of ignition and combustion of aluminium in water vapour is the key to being applied in underwater propellant applications. The effect of coating or blending 20 mass% ammonium perchlorate (namely, AP@Al or AP–Al samples) on the ignition and combustion of Al particles in a 1.0 MPa water vapour–Ar environment was investigated using a constant temperature pressurized combustion chamber and a CO 2 laser. The results show that the combustion of Al particles in a water vapour–Ar environment is a non-homogeneous reaction and that agglomeration processes of Al droplets are observed. The ignition and combustion properties of the AP@Al and AP–Al samples under water vapour were greatly improved due to the decomposition of AP for heat/oxygen (particularly, O 2 provided a new pathway for AlO(g) generation) supply and the effect of dispersed particles. The maximum pressure change and combustion temperature (T max) were increased significantly for the AP@Al and AP–Al samples combustion, while their ignition delay time (t i) and combustion time (t c) decreased remarkably. In addition, the coating form is more effective in the combustion-promoting effect of AP than the blending form. Interestingly, the increase in water vapour concentration is not conducive to the ignition and combustion of samples in this work. It is probably because the reaction system is lean-fuel where the excess water vapour absorbs some of the heat and prevents effective collisions among the radicals. In addition, the chemical equilibrium largely influences the combustion temperature, resulting in a conspicuous effect of changes in water vapour concentration on the T max values. The reaction interface largely influences the combustion reaction rate of Al, so changes in particle size have a significant effect on the t i and t c values. [ABSTRACT FROM AUTHOR]

Coating boron particles with materials having multiple mechanisms of action is a promising way to promote the ignition and combustion properties of boron. The differences in thermal oxidation properties and ignition combustion characteristics of micron-sized boron composite particles (namely, AP@B, FR@B, and GAP@B) coated with 20 wt% ammonium perchlorate (AP), fluoropolymer (FR), or glycidyl azide polymer (GAP) were comparatively investigated using TG–DSC and CO 2 laser ignition test systems. The results showed that the starting reaction temperature and activation energy of the composite particles were significantly reduced by the lower pyrolysis temperatures of the three modified materials. However, their oxidation phase lagged behind that of the original boron particles, most likely because the coating agglomerated 27% of the fine boron particles (<0.1 μm) into micron-sized particles. In addition, the slow heating approach did not allow the particles to reach the ignition temperature immediately and may indirectly aggravate the oxide layer thickness. Nevertheless, the coating modifier effectively promoted energy release (the heat release was increased by 93.76%, 28.65%, and 24.20% for FR@B, GAP@B, and AP@B, respectively). Generally, the ignition delay time (t i) decreases, whereas the combustion time (t c), self-sustaining combustion time (t f), maximum combustion temperature (T max) and burnout rate (α) increase after the coating of modified materials. First, AP decomposition produced O 2 and other gases to provide an oxidant for boron combustion and disperse the particles into space, which promotes extremely rapid energy release. Thus, the T max and α of AP@B were significantly enhanced. Second, FR pyrolysis gas production can vaporize B 2 O 3 and then promote the exposure of internal boron to react with oxygen. Thus, the t f and α of FR@B were significantly enhanced. However, the T max value was not the highest since the highest calorific value (up to 15,094 J•g−1) of FR@B is released at a slow rate. Finally, GAP can significantly shorten t i due to its lower activation energy, and this modification effect can be significantly improved by increasing the O 2 content. Since boron is characterized by high oxygen consumption, increasing the oxygen partial pressure can significantly promote ignition and combustion. The T max values of four samples in a mixed O 2 –N 2 environment under 1.0 MPa even exceeded the boiling point of B 2 O 3 , which is favorable for the reaction of internal boron with oxygen due to the gasification of the oxide layer at this time. [ABSTRACT FROM AUTHOR]