Enhanced Thermal Decomposition and Safety of Spherical CL-20@MOF-199 Composites via Micro-Nanostructured Self-Assembly Regulation

The characteristics of high burning rate, high energy output, and low pressure exponent have always been the focus of development in the field of composite solid rocket propellants. In this paper, a metal-organic framework (MOF-199) compound is introduced to prepare micro-nanospherical CL-20@MOF-199 composites via the spray-drying self-assembly technique to reach the above goals. MOF-199, which acts as an attractive combustion catalyst and a safety regulator, is uniformly coated on the surface of CL-20 with close interface contact between particles, effectively accelerating the thermal decomposition of CL-20 and ensuring safety performance. The average noncovalent interaction (aNCI) analysis illustrates that there are strong C-H···O hydrogen bonds and van der Waals interaction between CL-20 and MOF-199 molecules, greatly enhancing the effect of interparticle assembly. The effects of different contents of MOF-199 on the thermal, safety, and energy properties of CL-20 were discussed. The thermal analysis demonstrates that MOF-199 has a significant thermal catalytic effect on CL-20, with an advanced peak temperature of thermal decomposition of 14.2 °C and a reduced activation energy barrier of 34.2 kJ·mol-1, mainly benefitting from more exposed catalytic active sites and close interface contact. In addition, CL-20@MOF-199 composites exhibit decreased mechanical sensitivity (IS: 21-40 cm, FS: 80-240 N) and excellent energy performance. This work clearly demonstrates that MOF-199 is both a superior combustion catalyst and a good safety buffer for CL-20, and it opens new potential for further applications of CL-20 in composite solid propellants.

Ion-Conducting Robust Cross-Linked Organic/Inorganic Polymer Composite as Effective Binder for Electrode of Electrochemical Capacitor

Poly(ionic liquid)s (PILs) are used in many electrochemical energy storage/conversion devices owing to their favorable physical properties. Therefore, PIL binders have been examined as polymeric binders for electrodes in energy storage systems (ESSs) and have shown superior performance. Several innovative technologies have been developed to improve the properties of polymers, with cross-linking being the most effective and easy strategy to achieve this. In this study, we designed a breakthrough complex cross-linking and composite technique that could successfully develop the physical properties of a polymer in a simple one-step process. Additionally, the technique could improve the thermal stability and mechanical properties of the polymer. The proposed polymeric binder showed better adhesion, higher capacitance, and good energy density with improved cyclic stability compared to that shown by conventional polyvinylidene fluoride (PVDF). This study revealed that cross-linked networks in polymeric binders are long-cycle-life features for electrochemical redox capacitors.

First-Principles Investigation of Graphene and Fe2O3 Catalytic Activity for Decomposition of Ammonium Perchlorate

The employment of catalysts is an effective way to improve ammonium perchlorate (AP) decomposition performance during the combustion of composite solid propellants. Understanding the micromechanism of catalysts at the atomic level, which is hard to be observed by experiments, can help attain more excellent decomposition properties of AP. In this study, first-principles simulations based on density functional theory were used to explore the effect of the graphene catalyst and iron oxide (Fe₂O₃) catalyst on AP decomposition. Considering the transfer of a H atom during AP decomposition, the most stable adsorption sites for aforementioned catalysts were found: the top of the C atom of the graphene surface with the adsorption energy of -0.378 eV and the top of the Fe atom of the Fe₂O₃ surface with the adsorption energy of -1.596 eV. On the basis of adsorption results, our transition state calculations indicate that, in comparison to control groups, graphene and Fe₂O₃ can reduce the activation energy barrier by ∼19 and ∼37%, respectively, to promote AP decomposition with a transfer process of a H atom on the catalyst surface. Our calculations provide a way for explaining the micromechanism of the catalytic activity of graphene and Fe₂O₃ nanocomposites in AP decomposition and guide experimental applications of graphene and Fe₂O₃ for catalytic reactions.

Highly porous Co-doped NiO nanorods: facile hydrothermal synthesis and electrocatalytic oxygen evolution properties

Highly porous 3d transition metal oxide nanostructures are opening up the exciting area of oxygen evolution reaction (OER) catalysts in alkaline medium thanks to their good thermal and chemical stability, excellent physiochemical properties, high specific surface area and abundant nanopores. In this paper, highly porous Co-doped NiO nanorods were successfully synthesized by a simple hydrothermal method. The porous rod-like nanostructures were preserved with the added cobalt dopant ranging from 1 to 5 at% but were broken into aggregated nanoparticles at higher concentrations of additional cobalt. The catalytic activity of Co-doped NiO nanostructures for OER in an alkaline medium was assayed. The 5%Co-NiO sample showed a drastically enhanced activity. This result could originate from the combination of advantageous characteristics of highly porous NiO nanorods such as large surface area and high porosity as well as the important role of Co dopant that could provide more catalytic active sites, leading to an enhanced catalytic activity of the nanocatalyst.

Facet effect of Co3O4 nanocatalysts on the catalytic decomposition of ammonium perchlorate

Crystal facets can affect the catalytic decomposition of ammonium perchlorate, but the underlying mechanisms have long remained unclear. Here, we use the nanorods, nanosheets and nanocubes of Co₃O₄ catalysts exposing {110}, {111} and {100} facets as model systems to investigate facet effects on catalytic AP decomposition. The peak temperature of high temperature decomposition (HTD) process (T_HTD) of AP by nanorods, nanosheets and nanocubes Co₃O₄ decrease from 437.0 °C to 289.4 °C, 299.9 °C and 326.3 °C, respectively, showing obvious facet effects. We design experiments about AP decomposition under different atmospheres to investigate its mechanism and verify that the accumulation of ammonia (NH₃) on AP surface can inhibit its decomposition and that the facet effects are related to the adsorption and oxidation of NH₃. The binding energies of NH₃ on the {110}, {111} and {100} planes calculated via density functional theory (DFT) are -1.774 eV, -1.638 eV, and -1.354 eV, respectively, indicating that the {110} planes are more favorable for the adsorption of NH₃. Moreover, the {110} planes are readily to form CoNO structure, which benefits the further oxidation of the NH₃.

Exploring the Coordination Effect of GO@MOF-5 as Catalyst on Thermal Decomposition of Ammonium Perchlorate

Prepared composite materials based on [Zn₄O(benzene-1,4-dicarboxylate)₃] (MOF-5) and graphene oxide (GO) via a simple green solvothermal method, at which GO was used as platform to load MOF-5, and applied to the thermal decomposition of AP. The obtained composites were characterized by various techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption, Fourier transform infrared (FT-IR), differential scanning calorimetry and thermalgravimetric (DSC-TG). The analyses confirmed that the composite material (GO@) MOF-5 can not only improve the decomposition peak temperature of AP from the initial 409.7 ^°C to 321.9 ^°C, but also can improve the enthalpy (△H) from 576 J g^-1 to 1011 J g^-1 and reduce the activation energy (E_a), thereby accelerating the decomposition reaction. The high-specific surface area of the MOF material can provide a large number of active sites, so that the transition metal ions supported thereon can participate more effectively in the electron transfer process, and GO plays its role as a bridge by its efficient thermal and electrical conductivity. Together, accelerate the thermal decomposition process of AP.

Controllable synthesis of multi-shelled NiCo2O4 hollow spheres catalytically for the thermal decomposition of ammonium perchlorate

The compatible catalytic structure of NiCo₂O₄ was modified into multi-shelled hollow spheres by one-pot synthesis, followed by heat treatment. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer–Emmet–Teller (BET) and N₂ adsorption–desorption approaches were used for the characterizations of nanoparticles and multi-shelled hollow porous structures and the morphologies and crystal structures of these hollow spheres, respectively. Differential scanning calorimetry (DSC) was adopted for comparing the thermal decomposition performances of ammonium perchlorate (AP) catalyzed by adding different contents of multi-shelled NiCo₂O₄ hollow spheres. Impressively, the experimental results showed that the NiCo₂O₄ hollow spheres exhibited more excellent catalytic activity than NiCo₂O₄ nanoparticles as a result of their large specific surface areas, good adsorption capacity and many active reduction sites. The decomposition temperature of AP with multi-shelled NiCo₂O₄ hollow spheres could be reduced up to 322.3 °C from 416.3 °C. Furthermore, a catalytic mechanism was proposed for the thermal decomposition of AP over multi-shelled NiCo₂O₄ hollow spheres based on electron transfer processes.

Double-shelled NiCo₂O₄ hollow spheres synthesized by a facile hydro-thermal method showed excellent catalytic properties for the thermal decomposition of AP.

Solvent-Tuned Synthesis of Mesoporous Nickel Cobaltite Nanostructures and Their Catalytic Properties

In this paper, we prepared mesoporous nickel cobaltite (NiCo2O4) nanostructures with multi-morphologies by simple solvothermal and subsequent heat treatment. By adjusting the solvent type, mesoporous NiCo2O4 nanoparticles, nanorods, nanowires, and microspheres were easily prepared. The as-prepared products were systematically characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) method. Furthermore, the catalytic activities towards the thermal decomposition of ammonium perchlorate (AP) of as-prepared NiCo2O4 nanostructures were investigated.

Thermal Behavior and Decomposition Mechanism of Ammonium Perchlorate and Ammonium Nitrate in the Presence of Nanometer Triaminoguanidine Nitrate

Nanometer triaminoguanidine nitrate (TAGN) with mean size of 218.7 nm was fabricated, and its structures were characterized by scanning electron microscopy, X-ray diffraction, IR, and X-ray photoelectron spectroscopy analyses. As an energetic accelerator for thermal decomposition of ammonium perchlorate (AP) and ammonium nitrate (AN), 10% nano TAGN blended with AP and AN, and samples "[90% AP + 10% (nano TAGN)]" and "[90% AN + 10% (nano TAGN)]" were obtained, respectively. Differential scanning calorimetry (DSC) analyses were employed to investigate the decomposition kinetics and thermodynamics of the samples. The results indicated that [90% AP + 10% (nano TAGN)] presented a higher activation energy (152.34 kJ mol^-1) than pure AP (117.21 kJ mol^-1) and [90% AN + 10% (nano TAGN)] possessed a lower activation energy (147.51 kJ mol^-1) than pure AN (161.40 kJ mol^-1). All activation free energies (ΔG ^≠) were positive values. This means that activation of the molecules was not a spontaneous process. The decomposition peak temperature of AP decreased from 478.5 °C (for pure AP) to 287.2 °C (for [90% AP + 10% (nano TAGN)]). The decomposition peak of AN also advanced via doping with nano TAGN. Using DSC-IR analysis, the decomposition products of nano TAGN, pure AP, [90% AP + 10% (nano TAGN)], pure AN, and [90% AN + 10% (nano TAGN)] were investigated, and their decomposition mechanisms were proposed. The key factors, i.e., the formation of hydrazine in the decomposition of nano TAGN, were speculated, which substantially promoted the consumption of HNO₃, HClO₄, and their decomposition products in kinetics. Additionally, the energy performances of AP- and AN-based propellants doping with TAGN were evaluated. It is disclosed that the introduction of TAGN would not result in improvement in the energy performance of propellants, but due to its energetic property and high hydrogen content, proper introduction of TAGN will not reduce the energy performance of propellants in a large degree compared with the introduction of inert catalysts.

Effect of rGO–Fe2O3 nanocomposites fabricated in different solvents on the thermal decomposition properties of ammonium perchlorate

rGO–Fe₂O₃ composites were fabricated using different solvents via a solvothermal method, and used for thermal decomposition of ammonium perchlorate (AP).

Enhanced Thermal Decomposition Properties of CL-20 through Space-Confining in Three-Dimensional Hierarchically Ordered Porous Carbon

High energy and low signature properties are the future trend of solid propellant development. As a new and promising oxidizer, hexanitrohexaazaisowurtzitane (CL-20) is expected to replace the conventional oxidizer ammonium perchlorate to reach above goals. However, the high pressure exponent of CL-20 hinders its application in solid propellants so that the development of effective catalysts to improve the thermal decomposition properties of CL-20 still remains challenging. Here, 3D hierarchically ordered porous carbon (3D HOPC) is presented as a catalyst for the thermal decomposition of CL-20 via synthesizing a series of nanostructured CL-20/HOPC composites. In these nanocomposites, CL-20 is homogeneously space-confined into the 3D HOPC scaffold as nanocrystals 9.2-26.5 nm in diameter. The effect of the pore textural parameters and surface modification of 3D HOPC as well as CL-20 loading amount on the thermal decomposition of CL-20 is discussed. A significant improvement of the thermal decomposition properties of CL-20 is achieved with remarkable decrease in decomposition peak temperature (from 247.0 to 174.8 °C) and activation energy (from 165.5 to 115.3 kJ/mol). The exceptional performance of 3D HOPC could be attributed to its well-connected 3D hierarchically ordered porous structure, high surface area, and the confined CL-20 nanocrystals. This work clearly demonstrates that 3D HOPC is a superior catalyst for CL-20 thermal decomposition and opens new potential for further applications of CL-20 in solid propellants.

The effect of the phase structure on physicochemical properties of TMO materials: a case of spinel to bunsenite

It is worthwhile to comprehensively investigate the relationship between different phase structures and physicochemical properties of TMO materials.

Freestanding CuS nanowalls: ionic liquid-assisted synthesis and prominent catalytic performance for the decomposition of ammonium perchlorate

Freestanding CuS nanowalls, with excellent catalytic activity for AP thermal decomposition, were grown and assembled at the [C₁₀mim]Br-modulated liquid–liquid interface.