Effects of Silicon Dioxide/Graphene Oxide Hybrid Modification on Curing Kinetics of Epoxy Resin.

In this study, SiO2-grafted graphene oxide (GO-SiO2) was prepared using the oxygen-containing group on the GO surface as the active site of the reaction. The chemical structure, morphology, and particle size of GO and GO-SiO2 were carefully investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, thermogravimetry, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy, and the results proved that the grafting modification was successful. Furthermore, epoxy (EP)/GO composites were prepared, and the effects of unmodified GO and GO-SiO2 on the curing kinetics of EP were comparatively studied by differential scanning calorimetry (DSC). The results showed that, compared with neat EP and EP/GO, GO-SiO2 significantly reduces the curing temperature of the composites, indicating that GO-SiO2 has a more significant catalytic effect on the curing process of EP. The calculation results of the Kissinger method showed that the curing activation energy of EP/GO-SiO2 is obviously lower than that of EP/GO and neat EP. Results of the Ozawa method showed that the introduction of GO-SiO2 reduces the curing activation energy during the whole curing process, and in the middle and late stages of curing (α = 0.5-1) can significantly reduce the curing activation energy. The related mechanism has been proposed.

CuO/PbO Nanocomposite: Preparation and Catalysis for Ammonium Perchlorate Thermal Decomposition.

In this present article, we reported a facile and efficient milling method to prepare a series of CuO/PbO nanocomposite metal oxides (CuO/PbO NMOs), with CuO/PbO molar ratios of 1:2, 1:1, 1:0.5, and 1:0.25 as a potential catalyst to catalyze the thermal decomposition of ammonium perchlorate (AP). The obtained CuO/PbO NMOs were systematically characterized. X-ray diffraction (XRD), X-ray energy-dispersive spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS) analyses showed that the characteristic peaks of CuO/PbO NMOs were almost the superposition of nano CuO and nano PbO, while few new weak peaks were observed resulting from the lattice defects and new structural arrangements and chemical bonds between nano CuO and nano PbO during a high-energy grinding process. Scanning electron microscopy (SEM) and transition electron microscopy (TEM) observations exhibited that the particle sizes of the CuO/PbO NMOs were distributed in the range of 10-20 nm. Thermogravimetric (TG) analysis coupled with differential scanning calorimetric (DSC) techniques verified that CuO/PbO NMOs with a CuO/PbO molar ratio of 1:1 presented the best catalytic effect for AP thermal decomposition among the other CuO/PbO NMOs, as well as the single nano CuO and nano PbO. The outstanding catalytic performance is mainly reflected as follows: shifting the peak temperature of AP in high-temperature decomposition stages from 441.3 to 347.6 °C, increasing the decomposition heat of AP from 941 to 1711 J/g, and decreasing the Gibbs free energy of AP from 199.8 to 172.1 kJ/mol, supporting the existence of a synergistic catalytic effect between nano CuO and nano PbO.

High-Efficiency Dye-Sensitized Solar Cells Based on Kesterite Cu2ZnSnSe4 Inlaid on a Flexible Carbon Fabric Composite Counter Electrode.

Composite counter electrodes have been shown to be a practical and effective strategy in dye-sensitized solar cell (DSSC) application. In this work, we designed and prepared a single-crystal Cu2ZnSnSe4 (CZTSe) plate structure on flexible carbon fabric as a DSSC cathode, which combines the best of the two worlds, namely, the superior catalytic activity and hierarchical microstructure of kesterite CZTSe and the high conductivity and expanded framework of carbon fabric. The composite counter electrode presented a power conversion efficiency of 8.45% and a long-term bending reservation. The remarkable device property is due to the high catalytic activity, good adherence to conductive matrix grains, effective electron migration, and quick iodide species diffusion of the novel cathode. Our results suggest that the CZTSe@carbon fabric composite could be a high-efficiency Pt-free cathode in DSSCs.

Tuning the Reactivity of Al/NiO@C Nanoenergetic Materials through Building an Interfacial Carbon Barrier Layer.

Inspired by the crucial role of the interface layer in tuning the reactivity of nanoenergetic materials (nEMs), in this study, we report a new method to tune the energetic performances of Al/NiO@C nEMs by designing the interfacial barrier layer between the fuel and oxidizer. The carbon shell in special core-shell NiO@C nanorods derived from nickel-based metal-organic frameworks functions as a homogeneous interfacial diffusion-resistant layer between Al and NiO nanoparticles. Under the guidance of experimental time-resolved oxidation curves and theoretical simulation results, the carbon content can be easily controlled, thereby achieving the goal of tuning energetic performances. It is found that the chemical nature of the carbon barrier layer rather than its content provides the resistance against interdiffusion of Al and O atoms in the solid-state reaction, thus leading to a higher reaction onset temperature. The importance of the interfacial layer on the thermal properties of nEMs is also emphasized when compared with physically mixed ones. Combustion tests reveal that both interfacial resistance and gas generation play roles in tuning the combustion propagation, flame temperature, ignition delay time, and pressurization rate. These results indicate the promising potential of pre-engineered interfacial structure for targeted reactivity of carbon-based nEMs.

Preparation and characteristics of a novel PETN/TKX-50 co-crystal by a solvent/non-solvent method.

In order to decrease the sensitivity and broaden the application of pentaerythritol tetranitrate (PETN), a novel energetic co-crystal composed of PETN and dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50) with high energy and low sensitivity was successfully prepared through the solvent/non-solvent method. The morphology and structure of the as-prepared co-crystal were characterized by scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectrometry (XPS), fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and high performance liquid chromatography (HPLC). The thermal decomposition properties were also analyzed by simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC). The safety performance was judged by mechanical sensitivity tests. The SEM results revealed that the prepared new material was homogeneous with a mean granularity of 1 µm and the morphology was distinct from raw PETN and TKX-50. The XRD analysis indicated that a new crystalline formation appeared in the co-crystal which was quite different from the raw materials and their mixture. The XPS analysis showed peak shifts of C, N, O elements in the co-crystal. The FTIR spectra and Raman spectra suggested that hydrogen bond interactions existed between PETN and TKX-50 molecules. The molar ratio of PETN and TKX-50 was 1 : 1 determined by HPLC. There were two thermal decomposition peaks (194.1 °C and 261.3 °C) for the co-crystal at 20 °C min-1, while the raw materials and mixture had only one. Besides, the activation energy of the co-crystal increased compared to the raw materials, indicating better thermal stability of the co-crystal. The impact sensitivity and friction sensitivity of the PETN/TKX-50 co-crystal were reduced compared to raw PETN, and were even better than for 1,3,5-trimethylene trinitramine (RDX). The results showed a prospective application of the prepared PETN/TKX-50 co-crystal in the future.