Pre-ignition Reaction Research Articles

Reactivity tuning of metastable intermolecular composite Al/PFOA by polydopamine interfacial control

Controlling the high reactivity resulting from interfacial contact between nanoscale components poses a significant challenge. This study introduces an approach utilizing an aluminum (Al) surface-modified material to regulate the interaction between Al and perfluorooctanoic acid (PFOA), employing an in-situ synthesized polydopamine (PDA) interfacial layer. The optimal ratio was determined through molecular dynamics simulations. Various characterization techniques, including scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), were employed to comprehensively analyze the structure and elemental distribution of the samples. The findings indicate that the PDA coating process did not alter the surface structure of Al while maintaining the integrity of the functional groups of both PDA and PFOA. Results from simultaneous thermal analysis (TG-DSC) demonstrate that the PDA interfacial layer increased the pre-ignition reaction (PIR) peak temperature of PFOA/Al by 2 °C and enhanced the heat release of the PIR and fluorination reaction by 1.3 and 34.8 times, respectively. Thermal analysis kinetics investigation revealed a reduction of 6.66 kJ⋅mol−1 in the activation energy of the fluorination reaction and an increase of 20.28 kJ⋅mol−1 in the activation energy of the PIR. Furthermore, the combustion heat and reaction degree of PFOA/Al@PDA powder increased by 43.4 % and approximately 8 %, respectively, compared to PFOA/Al powder generated by physical mixing. This study demonstrated that the inclusion of PDA modifiers in the PFOA/Al system effectively controls the exothermic reaction between fuel and oxidant and enhances the oxidation degree of Al.

Enhanced combustion performance of Al–Zn alloys with property optimization inspired by “two-way tunneling” strategy

Fluorinated polymers (PVDF) are widely used due to their pre-ignition reaction with Al2O3 to improve the combustion of Al. In this study, a homogeneous PVDF coating layer was constructed on the surface of Al–Zn alloys by solvent evaporation, and Al-Zn@PVDF composites with “two-way tunneling” function during thermal decomposition and combustion were prepared. The constructed PVDF coating layer can react with Al2O3 to destroy the protective layer and promote the oxidation and combustion of Al–Zn from the outside to the inside. At the same time, the energy provided by the Al-Zn@PVDF during the ignition and combustion process also promotes the melting and vaporization of Zn, which achieves the rapid and full combustion of Al–Zn alloy from the inside to outside. The “ two-way tunneling” function of Al-Zn@PVDF composites significantly improves the combustion performance, resulting in a maximum combustion temperature of 1346.9 °C for Al-Zn@PVDF-40 % and a minimum combustion duration of 1.39 s for Al-Zn@PVDF-30 %, which is a significant improvement in combustion performance. The good chemical stability of PVDF also improves the hydrophobicity of Al–Zn and enhances its applicability. In conclusion, the construction of composites with “two-way tunneling” function first proposed in this study can significantly improve the thermal decomposition and combustion properties of Al–Zn, which is expected to further facilitate its application in propellants, explosives and pyrotechnics.

Energetic properties of core–shell B@PVDF/AP composite micro-units prepared by electrostatic spraying technology

In this study, to improve the ignition and combustion performance of fuel boron (B) powder. The core–shell B@ polyvinylidene fluoride (PVDF)/ ammonium perchlorate (AP) composite micro-unit with the effect of erosion activation is successfully prepared by simple and controllable electrostatic spraying technology. The results of morphology and structural composition show that PVDF and AP are tightly wrapped on the surface of B, forming a uniform shell, which effectively prevents moisture absorption and oxidation of B during storage and transportation. The results of the thermal analysis show that the hydrofluoric acid (HF) gas generated by the decomposition of PVDF at about 100 °C in advance has a pre-ignition reaction (PIR) with the boron oxide (B2O3) film on the surface of B. The PIR generates boron fluoride (BF3) gas and breaks the B2O3 film. This reduces the initial oxidation temperature of B by 12.6 % and enhances the oxidation activity of B powder. In addition, the oxygen (O2) released by AP improves the combustion performance of B and strengthens the effect of erosion activation. It is also found that all samples can be successfully ignited and burned continuously, which improves the ignition and combustion performance of B powder. It is worth noting that the ignition delay time of the composite micro-unit sample with the stoichiometric ratio of B/PVDF/AP of 2: 1: 2 can be shortened to 0.454 s at most, which is 17 % lower than that of the physical mixed sample. Moreover, its combustion intensity and flame temperature also reach the best. These results show that the core–shell B@PVDF/AP composite micro-unit provides a great strategy for application in solid propellant and pyrotechnics.

Characterization of the hypergolic ignition of green fuels with hydrogen peroxide by drop test and jet impingement

This work presents an experimental study on the hypergolic behavior of variants of N,N,N’,N’-tetramethylethylenediamine (TMEDA)/N,N-dimethylethanolamine (DMEA) system, named PAHyp 0, with 93 wt% hydrogen peroxide. Two different copper-based catalyst and one cobalt-based catalytic agent were dissolved in the fuels to trigger the pre-ignition reactions. When employing copper chloride dihydrate, the resultant fuel requires methanol (ternary system) as a stabilizing agent, whereas both carboxylic salts of copper and cobalt dissolved in TMEDA/DMEA deliver a stable formulation (binary system) without the need for any organic solvent. Shadowgraph high-speed imaging was used to capture the ignition process and pressure wave development of over 30 fuel samples in a modified drop test. An ignition/stability envelope was proposed to map the safe and unstable formulations. It was demonstrated that the concentration of TMEDA should be no more than 50% in the binary system, while the amount of methanol should fall within a concentration window of 33 to 50% in the ternary system. Lower loadings of catalyst, ranging from 0.5 to 1.0 wt%, are required to deliver stable fast-igniting fuels. Three promising formulations catalyzed with 1 wt% copper salts were selected to perform impinging jet fire experiments. Impinging jets yielded significantly lower ignition delay times than drop tests due to the better mixing conditions. However, it was verified that ignition may fail for low values of jet velocities, below 0.8 m/s, and for high jet velocities, exceeding 14 m/s. An attempt to explain the ignition and non-ignition events was made by using the fundamentals of explosion limits of the hydrogen/oxygen system and oxidation reactions at low temperature. Remarkably, ultra-fast ignitions of about 10 ms were measured by the impinging jet setup within near-optimal operational conditions. Therefore, TMEDA/DMEA-based fuels with reduced catalyst loadings (0.5–1.0 wt%) offer new opportunities in aerospace propulsion and should be further studied.

A new fluorocarbon adhesive: Inhibiting agglomeration during combustion of propellant via efficient F–Al2O3 preignition reaction

AbstractInhibiting the agglomeration of molten aluminum particles packed in the binder network is a promising scheme to achieve efficient combustion of solid propellants. In this investigation, the hydroxyl‐terminated structured fluorinated alcohol compound (PFD) was introduced to modify the traditional polyethylene glycol/polytetrahydrofuran block copolymerization (HTPE) binder; that is, a unique fluorinated polyether (FTPE) binder was synthesized by embedding fluorinated organic segments into the HTPE binder via crosslinking curing. The FTPE was applied in aluminum‐based propellants for the first time. Due to the complete release of fluorinated organic active segments in the range of 300°C to 400°C, the burning rate of FTPE‐based propellant increased from 4.07 (0% PFD) to 6.36 mm/s (5% PFD), increased by 56.27% under 1 MPa. The reaction heat of FTPE propellants increased from 5.95 (0% PFD) to 7.18 MJ/kg (5% PFD) under 3.0 MPa, indicating that HTPE binder modified with PFD would be conducive to inhibiting the D90 of condensed combustion products (CCPs) dropped by 81.84% from 75.46 (0% PFD) to 13.71 μm (5% PFD) under 3.0 MPa, in consistent with the significant reduction of aluminum agglomerates observed on the quenched burning surface of the propellants. Those results demonstrated that a novel FTPE binder with PFD can release fluorinated organic active segments, which motivate preignition reaction with the alumina shell in the early stage of aluminum combustion, and then enhance the melting diffusion effect of aluminum to inhibit the agglomeration.

Perfluorotetradecanoic acid-directed precipitation of P(VDF-HFP) around nano-Al for the improved ignition and combustion characteristics

In this study, the self-assembly method is used to modify Al nanoparticles (Al NPs) with perfluorotetradecanoic acid (PFTD) to obtain Al@PFTD. Based on the C–F…F–C interaction and the hydrogen bond between –CF and –CH, the adsorbed PFTD is used to direct the precipitation of P(VDF-HFP) around modified Al NPs to obtain Al@PFTD@P(VDF-HFP) composite energetic materials. Scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy are used to characterize the prepared samples, which prove a successful preparation process. The prepared Al@PFTD@P(VDF-HFP) is compared with physically mixed Al/P(VDF-HFP) counterparts by thermal analysis, electric ignition and constant-volume combustion tests. Thermal analysis results show that the reaction onset temperature of Al@PFTD@P(VDF-HFP) is 20 °C lower while its heat release is 135% higher. Electric ignition and constant-volume combustion tests show that the ignition delay, combustion time and pressurization rate are 50% shorter, 50% shorter and 40% faster, respectively. The improved energetic performance is mainly due to PFTD-directed precipitation of P(VDF-HFP) around Al NPs. Moreover, the fluorine-containing PFTD also contributes positively to energy density and reactivity through the pre-ignition reaction.

Polyphenols-inspired interface modification and reduced agglomeration of solid propellants via a functionalized fluorine-containing organic substance coating layer

Interface modification of aluminum particles plays a crucial part in reducing the agglomeration during the combustion of solid propellants. In this study, the aluminum (Al) particles are pretreated with gallic acid (GA) to get Al@GA with an adhesion-favorable surface, which facilitates the further coating procedure. One new fluorine-containing organic substance is prepared, namely p-HFBA. The p-HFBA further coats the Al@GA to produce Al@GA/p-HFBA. The interface between Al@GA and the coating layer p-HFBA forms AlF bonds and induces a pre-ignition reaction with an aluminum oxide shell. Hence, the agglomerate size of propellants containing Al@GA/p-HFBA significantly decreases from 176.30 μm to 84.72 μm. The agglomerates volume is reduced by approximately 97 %. Additionally, more gaseous products investigated by TG-MS provide the Al particles with greater impetus (aerodynamic forces, Fae), enabling them to leave the burning surface and reduce the residence time. The rise in Fae and drop in adhesion force (Fad) effectively reduce the agglomeration intensity according to the skeleton layer model. This work proves that interface modification can effectively enhance the combustion performance of aluminized solid propellants.

Construction of hollow heterogeneous microspheres containing energy storage fibers by electric spray to promote combustion of nano aluminum

To solve the problem of nano-aluminum (nAl) powder easy agglomeration and improve its thermal reaction, nAl was combined with adhesive (Viton A, F2602) and oxidizer (Ammonium perchlorate, AP) forming microspheres by electrostatic spray method. The morphology and structure were analyzed by SEM, EDS and XPS. The results showed that the microspheres (diameter≈Φ10–15 μm) were hollow structures formed by winding of fluoropolymer fibers, while AP and nano aluminum particles were embedded on the fibers. By controlling the electric spray process, the well-dispersed AP and nAl nanocrystals were assembled on the fiber. Thermal analysis indicated that the gas phase products decomposed by AP were absorbed by porous microspheres, and part of the heat was stored in polymer fibers, thus promoting the breakdown of the alumina shell and accelerating the pre-ignition reaction. The combustion and laser ignition experiments proved hollow heterogeneous microspheres have excellent thermodynamic properties. The assembled microspheres not only solved the problem of poor rheology caused by the agglomeration of nAl, but also improved the insufficient combustion of nAl and the condensation of products.

Fabrication and reaction mechanism study of Co(OH)F@Al nanowire arrays: A functional fluorine-containing metastable intermolecular composite

Metastable intermolecular composites (MICs) comprising solid fuels and oxidizers at nano-scale exhibit high energy densities and fast reaction speeds. As most metal and metalloid fuels are passivated by the natural oxide layer on the surface which acts as a reaction barrier, fluorine-containing oxidizers are of particular interest to promote the reactivity through interfacial fluoridation. In this work, cobalt hydroxy fluoride (Co(OH)F) was introduced as a functional fluorine-containing oxidizer, and core-shell structured Co(OH)F@Al nanoarray was fabricated onto a glass substrate. The thermal behavior and reaction mechanism of pure Co(OH)F and Co(OH)F@Al composites were thoroughly investigated, and Co(OH)F@Al was compared with CoO@Al and Co3O4@Al with identical morphology. In the Co(OH)F@Al composite, a pre-ignition reaction was observed which was attributed to the etching of Al2O3 shell by HF and the fluoridation of Al core by HF and CoF2. With the assistance of pre-ignition reaction, Co(OH)F@Al can complete main exothermal reaction before Al melting in a solid-state mechanism, and its peak temperature is around 200 ℃ lower than those of MICs employing CoO and Co3O4 as oxidizers.

Synthesis of Co(OH)F@Al nanobelt array on various substrates for pyro-MEMS

Metastable intermolecular composites (MICs) composed by solid fuel and oxidizer can undergo violent redox reaction with release of huge amount of energy. Integration of MIC with microelectromechanical-system (MEMS) is of particular interest to meet the demand of miniaturization in modern pyrotechnic devices. Meanwhile, fluorine-containing oxidizers are favored in MIC owing to their potential to fluorinate the oxide passivation layer in common elemental fuels. Herein, Co(OH)F was employed for the first time as a novel fluorine-containing oxidizer in Al-based MIC. Vertically aligned Co(OH)F@Al nanobelt arrays (NAs) with tunable morphology were successfully fabricated on a variety of substrates (Si, glass, Ni, Cu, Ti) via a facile hydrothermal synthesis followed by electron beam evaporation. The whole fabrication process is highly compatible with modern MEMS technology. The thermal behavior of pure Co(OH)F and Co(OH)F@Al composites was comprehensively investigated by TG-DSC and a series of ex-situ and in-situ characterization. It was found that, Co(OH)F@Al composites achieved main exothermal reaction before melting of Al regardless of morphology and equivalence ratio. This feature is attributed to the etching of Al2O3 shell by HF released from Co(OH)F which is termed as pre-ignition reaction. To elucidate the effect of micro-structure on the actual specific heat release, we proposed a phenomenological model which can be a reference for future micro-structure design of MIC.

Oxidation mechanism of perfluorooctanoic acid-functionalized aluminum metastable intermolecular composites regulated by Preignition reactions interface fuel-oxidizer ratio

PFOA-functionalized Al Metastable Intermolecular Composites (MICs) refer to the system using aluminum nanoparticles as fuel and PFOA as oxidant. Aluminum is the most widely used metal fuel in energetic materials. Al NPs are widely used because they are relatively cheap, easily accessible, nontoxic, excellent in thermodynamic performance. Fluorine has higher density and stronger oxidation capacity than oxygen element. PFOA has a high fluorine content (68.8%). PFOA-functionalized Al MICs mixed the high calorific value of aluminum and oxidizing fluorine in nano-sized. In this paper, PFOA-functionalized Al MICs with different PIR interface fuel-oxidizer ratios were prepared by electrostatic spray. The microstructure of the MICs was characterized by TEM. PFOA is uniformly coated on the Al NPs. The composition of MIC system was analyzed by FTIR and XRD. The combustion performance of MICs was tested by laser ignition, and the decomposition mechanism of PFOA-functionalized Al MICs was studied by DSC-TG. Results show that the exothermic process and activation energy of MICs are affected by the Preignition reactions (PIR) interface fuel-oxidizer ratios. The ignition and combustion processes of MICs and pressurization rate increase with the increase of oxidizer, and the burning rate decreases with the increase of oxidizer.

The reaction mechanism of Al NPs/PVDF high energy fuel: A ReaxFF MD and DFT study meshing together laser-ignition experimental verification

Aluminum nanoparticles (Al NPs) with the high energy can be used in rocket propulsion, but the propellant performance will be limited by the easy agglomeration property. The surface modification of Al NPs by polyvinylidene fluoride (PVDF) can inhibit their agglomeration and improve their combustion efficiency. However, there is a lack of essential understanding of the microscopic reaction mechanism of PVDF to promote the combustion of Al NPs. Hence, the oxidation and combustion processes of Al NPs/PVDF were investigated by using reactive molecular dynamics (RMD) simulations and density functional theory (DFT) calculations. Moreover, the combustion performance of Al NPs/PVDF was examined by laser ignition experiments. In the oxidation of Al NPs/PVDF, the PVDF is decomposed by the catalytic action of Al NPs. The dissociated F atoms react with the oxide shell to form AlxOyFz species, which elucidates the mechanism of the pre-ignition reaction of Al NPs with PVDF at the microscopic level. In the combustion of Al NPs/PVDF, the increase in PVDF content and temperature is favorable to the consumption of Al NPs. The experimental results also verify that the addition of PVDF can significantly enhance the combustion performance of Al NPs. These results reveal the promotion effects of PVDF on Al NPs in the ignition and combustion process at the atomic level and the macroscopic perspective, and lay the theoretical foundation for the early application of Al NPs/PVDF in propellants.

Nanoenergetic Composites with Fluoropolymers: Transition from Powders to Structures.

Over the years, nanoenergetic materials have attracted enormous research interest due to their overall better combustion characteristics compared to their micron-sized counterparts. Aluminum, boron, and their respective alloys are the most extensively studied nanoenergetic materials. The majority of the research work related to this topic is confined to the respective powders. However, for practical applications, the powders need to be consolidated into reactive structures. Processing the nanoenergetic materials with polymeric binders to prepare structured composites is a possible route for the conversion of powders to structures. Most of the binders, including the energetic ones, when mixed with nanoenergetic materials even in small quantities, adversely affects the ignitability and combustion performance of the corresponding composites. The passivating effect induced by the polymeric binder is considered unfavorable for ignitability. Fluoropolymers, with their ability to induce pre-ignition reactions with the nascent oxide shell around aluminum and boron, are recognized to sustain the ignitability of the composites. Initial research efforts have been focused on surface functionalizing approaches using fluoropolymers to activate them further for energy release, and to improve the safety and storage properties. With the combined advent of more advanced chemistry and manufacturing techniques, fluoropolymers are recently being investigated as binders to process nanoenergetic materials to reactive structures. This review focuses on the major research developments in this area that have significantly assisted in the transitioning of nanoenergetic powders to structures using fluoropolymers as binders.

Preparation and characterization of energetic composite films with mutual reactions based on B/PVDF mosaic structure

In this study, to solve the boron oxide (B2O3) formed on the boron (B) surface, which reduces the reactivity and energy release. The energetic composite films with mutual reactions of B as fuel and polyvinylidene fluoride (PVDF) as oxidant are designed, based on the mosaic structure. Then, samples with different contents of B are successfully prepared by the novel synergistic emulsification and transient freezing methods. The morphology and composition results show that B is embedded in PVDF films, which makes the energetic composite films have excellent hydrophobicity and oxidation resistance. Interesting, the thermal analysis results show that in the low-temperature stage, the addition of B advances the initial decomposition temperature of PVDF; in the high-temperature stage, the gas product hydrogen fluoride (HF) of PVDF decomposition has a pre-ignition reaction (PIR) with B2O3, which destroys the shell of B2O3 and accelerates the oxidation of internal active B. And the heat release of 50 % B content is the highest (3845.4 J/g). Furthermore, the ignition and combustion results show that all samples can be ignited smoothly and easily. But the combustion performance is greatly affected by the content of B. Finally, the reaction mechanism of samples is preliminarily obtained by molecular model through the characterization of combustion products. These results show that composite films with mutual reactions based on B/PVDF mosaic structure have an excellent prospect for application in thermite with fluoropolymer.

Dielectric breakdown driven by flexoelectric and piezoelectric charge generation as hotspot ignition mechanism in aluminized fluoropolymer films

Using multiphysics simulations and experiments, we demonstrate that dielectric breakdown due to electric charge accumulation can lead to sufficient hotspot development leading to the initiation of chemical reactions in P(VDF-TrFE)/nAl films comprising a poly(vinylidene fluoride-co-trifluoroethylene) binder and nano-aluminum particles. The electric field (E-field) development in the material is driven by the flexoelectric and piezoelectric responses of the polymer binder to mechanical loading. A two-step sequential multi-timescale and multi-physics framework for explicit microscale computational simulations of experiments is developed and used. First, the mechanically driven E-field development is analyzed using a fully coupled mechanical–electrostatic model over the microsecond timescale. Subsequently, the transient dielectric breakdown process is analyzed using a thermal–electrodynamic model over the nanosecond timescale. The temperature field resulting from the breakdown is analyzed to establish the hotspot conditions for the onset of self-sustained chemical reactions. The results demonstrate that temperatures well above the ignition temperatures can be generated. Both experiments and analyses show that flexoelectricity plays a primary role and piezoelectricity plays a secondary role. In particular, the time to ignition and the time to pre-ignition reactions of poled films (possessing both piezoelectricity and flexoelectricity) are ∼10% shorter than those of unpoled films (possessing only flexoelectricity).

One-dimensional modeling approaches for the piloted ignition of poly (methyl methacrylate)

An unsteady one-dimensional solid-gas model is presented for the spontaneous and the piloted ignition of poly (methyl methacrylate) exposed to thermal irradiance. The mathematical description of the igniter (electrical spark) is given special attention. The simplest approach, namely the heating spark model, describes heat transfer from a pulsating high-temperature plane source (direct heating), together with the heat released by the pre-ignition reactions (indirect heating). A high overestimation of the thermal effects of the spark is observed owing to the one-dimensional approximation. An iterative solution method, indicated as the non-heating spark model, is also implemented to eliminate direct and indirect spark heating which, however, also cuts off possible flashing phenomena. The third approach, indicated as the chemical spark model, disregards the direct spark heating but still describes pre-ignition combustion. This approach is the simplest and the most effective for providing predictions in agreement with literature measurements for both the process dynamics and the ignition delay times.

Preparation and characterization of multifunctional piezoenergetic polyvinylidene fluoride/aluminum nanocomposite films

We prepared poly(vinylidene fluoride) (PVDF) and aluminum composite dense films using a tape caster and investigated the microstructural, thermal, and electrical properties and the combustion behavior of the films as a function of nano-aluminum (nAl) solids loading (5–30 wt. %). We found that the addition of nAl facilitates the formation of piezoelectric β and γ phases of PVDF as determined by x-ray diffraction and Fourier transform infrared spectroscopy. At higher nAl solid loadings, the lower onset temperature of the pre-ignition and decomposition reactions have been observed. Moreover, the intentionally incorporated porosity into the films slightly affected the thermal decomposition behavior. While the dielectric constant of the films increases with higher nAl content, the dielectric breakdown strength of the films decreases significantly. The critical active nAl content for the films to exhibit self-propagated reaction was determined to be between 10 and 15 wt. %. Thermochemical calculations using the NASA CEA code showed the maximum flame temperature of 1750 °C near the stoichiometric ratio (∼20 wt. %). The burning rate of the films is enhanced drastically at ambient conditions with further addition of nAl. However, the films with active nAl content over 20 wt. % showed lower flame temperatures, which is due to the reduction of hydrofluoric acid gas generation and the incomplete combustion of Al to form aluminum monofluoride (AlF), instead of aluminum fluoride (AlF3) gas. The fabrication of energetic thin films with tunable properties could enable their use in multifunctional energetic material systems.

An approach to the induced reaction mechanism of the combustion of the nano-Al/PVDF composite particles

Highly reactive aluminum-fluorine composites with novel structures have attracted much attention in the past decades. However, there is not a specific mechanism to explain the combustion-supporting or inducing effect of F-polymer on aluminum powders. Herein, we present a systematic study of the induced reaction mechanism and propose a new elaboration. Two types of Nano-aluminum/Poly(vinylidene fluoride) (n-Al/PVDF) composites are fabricated via electrospray and mechanical mixing method, respectively. The electrospray sample excites a Pre-Ignition Reaction (PIR) between fluorine and the Al2O3 shell at a low temperature, and simultaneously the specific surface area, surface element state and alumina shell structure of aluminum powders change to some extent. However, the surface structure of the physical mixture does not change significantly in the same temperature range. On this basis, we studied the relationship between the change of surface structure and the enhanced combustion performance of aluminum in electrospray sample. The results show that the combustion-supporting effect of PVDF on aluminum powder should be attributed to the corrosion of the alumina shell and the loose structure of the PIR product.

High energy release boron-based material with oxygen vacancies promoting combustion

Boron has a high calorific value and good application prospects in energetic materials. However, further applications of boron are hindered by its incomplete combustion. MoO3 has good catalytic properties, and its layered structure can provide good ion flow channels and embedding positions. In this study, mechanical mixtures of B/MoO3 and B/Mo were prepared. The promotion of B combustion by MoO3 and Mo was confirmed via combustion heat and burning rate tests. The mechanism by which Mo/MoO3 promote B combustion was studied by thermal analysis, high-temperature in situ X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. The maximum heat release and burning rate of B/MoO3 and B/Mo were 2.49 and 2.62 and 2.67 and 2.55 times, respectively, those of raw boron. A pre-ignition reaction occurred when boron first came into contact with the surface of MoO3. The oxygen vacancies on the MoO3 surface served as reaction sites for boron. MoO3 promoted the combustion of B by opening up oxygen channels and improving the oxygen transport capability. Mo also effectively promoted boron combustion. B/Mo and B/MoO3 have promising future applications as high energy release materials.

Nanothermite composites with a novel cast curable fluoropolymer

Structural nanoenergetic (SNE) composites consisting of nanothermites dispersed in a polymer binder are attractive for combustion applications due to their substantially higher volumetric energy, density, and tailorable energy release characteristics. Cast curing is an extensively utilized, safe, and economical method for processing energetic materials into structural composites possessing macroscale geometries. The use of cast curing as a route for processing SNE composites is limited by the lack of suitable binder systems. The widely used cast curable binder such as hydroxyl terminated polybutadiene (HTPB) if used for this purpose will render the SNE composites thermally non-ignitable. Fluoropolymers have emerged as energetic binders for aluminum containing nanothermites due to their capability to induce pre-ignition reaction and sustain the ignitability of composites. Herein, we report the synthesis of a novel cast curable fluoropolymer (FP) with 58 wt% fluorine content produced through the cationic ring opening polymerization of 3-Perfluorohexyl-1, 2-epoxypropane. We demonstrate the utility of the synthesized FP as a cast curable binder for aluminum/copper oxide (Al/CuO) nanothermite to prepare SNE composites. The SNE composites were cast cured as cylindrically shaped specimens with the FP content ranging from 30 to 50% by weight. All the SNE composites were observed to be thermally ignitable even under an inert environment, suggestive of the unique role of FP on promoting the ignitability of SNE composites. SNE composite containing 40 wt% FP recorded the highest energetic performance in terms of heat of reaction (880 cal/g) and pressure generation characteristics (pressurization rate = 3.81kPsi/s; time to maximum pressure = 340 ms). Additionally, the 40 wt% FP SNE composite generates time averaged combustion temperature of 2530 K as estimated by spectroscopic technique.