Hydrohausmannite nanoparticles (approximately 10 nm) were prepared by the hydrothermal method at 100 degrees C for 72 h. Subsequent annealing was done in air at 400 degrees C and 800 degrees C for 10 h, Mn(3)O(4) nanoparticles (approximately 25 nm) and 3D Mn(2)O(3) porous networks were obtained, respectively. The products were characterized by XRD, TEM, SAED and FESEM. Time-dependent experiments were carried out to exhibit the formation process of the Mn(2)O(3) networks. Their microwave absorption properties were investigated by mixing the product and paraffin wax with 50 vol%. The Mn(3)O(4) nanoparticles possess excellent microwave absorbing properties with the minimum reflection loss of -27.1 dB at 3.1 GHz. In contrast, the Mn(2)O(3) networks show the weakest absorption of all samples. The absorption becomes weaker with the annealing time increasing at 800 degrees C. The attenuation of microwave can be attributed to dielectric loss and their absorption mechanism was discussed in detail.
ZnO nanocombs and nanorods with different morphologies have been successfully synthesized through a simple metal vapour deposition route at 600–750 °C using pure zinc powder or zinc and graphite powders as source materials. The structures and morphologies of the products were characterized in detail by using x-ray diffraction, scanning electron microscopy, transmission electron microscopy and laser Raman spectrometer. The morphologies of the products can be easily controlled by tuning the following four factors: reaction temperature, the distance between the source and the substrates, the kinds of substrates and the kinds of precursors. Possible growth mechanisms for the formation of ZnO nanostructures with different morphologies are discussed. Photoluminescence studies show that there are sharp UV and broad defect-related green emissions for all products. Relative intensity of the UV to defect-related green emissions decreases from ZnO nanorods to nanocombs. Microwave absorption properties of these nanocombs are also investigated. The value of the minimum reflection loss is −12 dB at 11 GHz for the ZnO nanocomb composite with a thickness of 2.5 mm.
Cocrystallization techniques have become extremely important methods for obtaining novel high-energy insensitive energetic materials, and it has attracted great attention for the development of high-energy explosives and propellants, etc. in recent years. Several scale-up cocrystallization techniques including solvent-nonsolvent, semibatch reaction, bead milling, and spray drying methods et al. have been applied for obtaining the energetic cocrystals, and the preparation processes of these methods were also shown. The types and quality of raw materials and solvents, the synthetic times, morphology, and size of these cocrystals were described and compared by using different synthetic techniques in the review. Moreover, the principle, advantages and disadvantages of scale-up preparation methods were shown. More importantly, the preparation efficiency, the ratio between the quality of raw materials and the volume of solvent, and yield of different methods were also exhibited and discussed, which can provide key information and experiences for the future application of the materials. Finally, future research trends are suggested from different perspectives involving the formation mechanisms in the preparation process by using intermolecular interaction simulation, experimental study, and thermodynamic calculations, the optimization of traditional scale-up techniques, and the exploitation of novel methods for the energetic cocrystals.
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