A general theory of ignition and combustion of nano- and micron-sized aluminum particles

Sundaram, Dilip Srinivas; Puri, Puneesh; Yang, Vigor

doi:10.1016/j.combustflame.2016.04.005

Cited by 268 publications

(102 citation statements)

References 58 publications

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“…Up to now, the controlling mechanism in low‐temperature oxidation is not understood in deep. It has been suggested that at the temperature below the melting point, a slow oxidation process is controlled by the diffusion of oxygen through the oxide shell . Based on the core–shell model as shown in Figure , herein, we use Fick's first law of diffusion to evaluate the diffusive flux of O 2

\frac{d N_{{normalO}_{2}}}{d t} = - 4 π r^{2} D (T) \frac{\partial {normalc}_{{normalO}_{2}}}{\partial r}

where r is the radius of ANPs, D(T) is the effective diffusion coefficient of O 2 in Al 2 O 3 or FAS‐17, and

{normalc}_{{normalO}_{2}}

is the molar concentration of O 2 .…”

Section: Discussionmentioning

confidence: 99%

“…One other query related to this study is that why the pure ANPs cannot be ignited by the hot wire while the AFNPs can proceed with self‐sustaining combustion even aged in water for several days. A well‐accepted theory about the ignition mechanism of ANPs lies in the out‐diffusion of molten Al through the cracking of the Al 2 O 3 layer as shown in Figure a . After melting, the decreased density of Al core will exert tensile stresses to fracture the oxide layer.…”

Section: Discussionmentioning

confidence: 99%

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Superhydrophobic Fluorine‐Containing Protective Coating to Endow Al Nanoparticles with Long‐Term Storage Stability and Self‐Activation Reaction Capability

Guo²,

Gou³

et al. 2019

Adv Materials Inter

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The stability of aluminum (Al) nanoparticles (ANPs) is a key issue that can determine the energetic properties of Al‐based energetic materials. In this study, a surface functionalization approach is employed, using the chemical adsorption and auto polymerization effects of the 1H, 1H, 2H, 2H‐perfluorodecyltriethoxysilane (FAS‐17), to set up a highly stable barrier coating to water and further endow ANPs with long‐term storage stability and self‐activation reaction capability. The FAS‐17‐modified ANPs (AFNPs) with a superhydrophobic surface show their excellent stability in air and unique strengths in corrosion resistance to water by enhancing diffusion resistance of O2 and preventing the hydration reaction. In terms of energetic performances, compared to the two‐step slow oxidation of ANPs, the heat‐release rate of AFNPs is significantly enhanced, resulting in a drastic oxidation process profiting from the surface reaction between the FAS‐17 and alumina (Al2O3) layer. More importantly, the ignition and combustion properties of AFNPs are also greatly improved, which can undergo self‐propagation combustion with a fairly high energy output even after stored in water. At last, the possible mechanisms of oxidation resistance and self‐activation reaction capacities are also proposed.

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\frac{d N_{{normalO}_{2}}}{d t} = - 4 π r^{2} D (T) \frac{\partial {normalc}_{{normalO}_{2}}}{\partial r}

where r is the radius of ANPs, D(T) is the effective diffusion coefficient of O 2 in Al 2 O 3 or FAS‐17, and

{normalc}_{{normalO}_{2}}

is the molar concentration of O 2 .…”

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Superhydrophobic Fluorine‐Containing Protective Coating to Endow Al Nanoparticles with Long‐Term Storage Stability and Self‐Activation Reaction Capability

Guo²,

Gou³

et al. 2019

Adv Materials Inter

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show abstract

“…Noor et al [29] and Vorozhtsov et al [30] presented the staged oxidation process at low heating rates below 30 K/min. Sundaram et al [31] summarized the oxidation process of Al nanoparticles during combustion, including three stages: particle heating to core melting point, phase transformations and ignition, and surface combustion. However, the division on ignition is different from the phenomena in this study, neglecting the evaporation stage of aluminum before ignition.…”

Section: Ignition Stage Of Al Nanoparticlesmentioning

confidence: 99%

Effect of Heating Rate on Ignition Characteristics of Newly Prepared and Aged Aluminum Nanoparticles

Jin

Yang

et al. 2020

Propellants Explo Pyrotec

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Aluminum (Al) nanoparticles have been widely applied in propellants, but the ageing of Al nanoparticles will result in the degradation of propellant ignition performance. This paper experimentally investigates the ignition characteristics of newly prepared and aged Al nanoparticles, and improves the ignition performance of aged Al nanoparticles through elevating the heating rate. It was observed that, despite newly prepared or aged Al nanoparticles, their ignition included three stages: stage I – heating, stage II – melting, and stage III – evaporation. The temperature rise and time in stage I, melting temperature, and time in stage II and ignition temperature in stage III were separately discussed. It is found that the duration of each stage during the ignition of aged Al nanoparticles was much longer than that of newly prepared Al nanoparticles, testifying that ignition temperature of Al nanoparticles increased and ignition delay time elongated due to ageing. At elevated power density, the heating rate of Al nanoparticles increased, the heating, melting, and evaporating time shortened. The difference of ignition delay time between newly prepared and aged Al nanoparticles was significantly reduced. It means that the ignition performance can be improved through increasing the heating rate. Simultaneously, the energy conversation equation of each stage was built and discussed. It will be beneficial to deeply understand the ignition process and reveal the ignition mechanism of aged Al nanoparticles.

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“…The µAl is typically air-passivated, thus showing a core-shell particle structure with the metal core surrounded by an amorphous Al 2 O 3 layer [26][27][28]. The micrometric size, together with the particle morphology and the specific surface area (SSA) <1 m 2 /g, yields µAl high metal content (typically >95 wt.%), relatively low reactivity, and inherent safety (i.e., high ignition temperature, reduced dispersion in air, and limited aging influence) [28][29][30][31]. The reactivity of µAl can be enhanced by reducing the particle size down to the nanoscale [32][33][34][35] and by activation processes [23,24,[36][37][38][39].…”

Section: Introductionmentioning

confidence: 99%

Nano-Sized and Mechanically Activated Composites: Perspectives for Enhanced Mass Burning Rate in Aluminized Solid Fuels for Hybrid Rocket Propulsion

Paravan

2019

Aerospace

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This work provides a lab-scale investigation of the ballistics of solid fuel formulations based on hydroxyl-terminated polybutadiene and loaded with Al-based energetic additives. Tested metal-based fillers span from micron- to nano-sized powders and include oxidizer-containing fuel-rich composites. The latter are obtained by chemical and mechanical processes providing reduced diffusion distance between Al and the oxidizing species source. A thorough pre-burning characterization of the additives is performed. The combustion behaviors of the tested formulations are analyzed considering the solid fuel regression rate and the mass burning rate as the main parameters of interest. A non-metallized formulation is taken as baseline for the relative grading of the tested fuels. Instantaneous and time-average regression rate data are determined by an optical time-resolved technique. The ballistic responses of the fuels are analyzed together with high-speed visualizations of the regressing surface. The fuel formulation loaded with 10 wt.% nano-sized aluminum (ALEX-100) shows a mass burning rate enhancement over the baseline of 55% ± 11% for an oxygen mass flux of 325 ± 20 kg/(m2∙s), but this performance increase nearly disappears as combustion proceeds. Captured high-speed images of the regressing surface show the critical issue of aggregation affecting the ALEX-100-loaded formulation and hindering the metal combustion. The oxidizer-containing composite additives promote metal ignition and (partial) burning in the oxidizer-lean region of the reacting boundary layer. Fuels loaded with 10 wt.% fluoropolymer-coated nano-Al show mass burning rate enhancement over the baseline >40% for oxygen mass flux in the range 325 to 155 kg/(m2∙s). The regression rate data of the fuel composition loaded with nano-sized Al-ammonium perchlorate composite show similar results. In these formulations, the oxidizer content in the fuel grain is <2 wt.%, but it plays a key role in performance enhancement thanks to the reduced metal–oxidizer diffusion distance. Formulations loaded with mechanically activated ALEX-100–polytetrafluoroethylene composites show mass burning rate increases up to 140% ± 20% with metal mass fractions of 30%. This performance is achieved with the fluoropolymer mass fraction in the additive of 45%.

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A general theory of ignition and combustion of nano- and micron-sized aluminum particles

Cited by 268 publications

References 58 publications

Superhydrophobic Fluorine‐Containing Protective Coating to Endow Al Nanoparticles with Long‐Term Storage Stability and Self‐Activation Reaction Capability

Superhydrophobic Fluorine‐Containing Protective Coating to Endow Al Nanoparticles with Long‐Term Storage Stability and Self‐Activation Reaction Capability

Effect of Heating Rate on Ignition Characteristics of Newly Prepared and Aged Aluminum Nanoparticles

Nano-Sized and Mechanically Activated Composites: Perspectives for Enhanced Mass Burning Rate in Aluminized Solid Fuels for Hybrid Rocket Propulsion

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