The performance of energetic materials is mainly reflected in two aspects, thermal performance and combustion performance. To figure out the differences in reaction performance, in this paper, ...thermal and combustion properties of Al/CuO, Al/Fe2O3 and Al/MnO2 nanothermites were studied respectively by thermal analysis and fast heating wire experiments. According to the thermal analysis, the exothermic peak temperature points of Al/MnO2, Al/CuO, Al/Fe2O3 nanothermites were 552.1 °C, 563.1 °C and 565.3 °C, respectively, while the sequence of activation energy calculated from low to high was Al/Fe2O3, Al/CuO, Al/MnO2 nanothermites. By the way, the values of Al/CuO and Al/Fe2O3 nanothermites showed little difference in temperature and activation energy. The ignition energy characterized by direct current had little difference among them, and the sequence from low to high was Al/MnO2, Al/Fe2O3, Al/CuO nanothermites, corresponding to 1.169 A, 1.214 A and 1.221 A, respectively. As for burning rate, Al/CuO burnt the fastest clearly while the Al/Fe2O3 burnt the longest. In terms of combustion performance, Al/CuO and Al/MnO2 were basically the same, with little splash of sparks, and the concentrations of combustion energy were better. The combustion phenomenon of Al/Fe2O3 nanothermite was quite unique with a large number of scattered sparks and poor energy concentration. Finally, the intrinsic reasons for above different phenomena of these three nanothermites were analyzed and discussed.
•Sequence of exothermic peaks was Al/MnO2, Al/CuO, Al/Fe2O3 nanothermites.•Sequence of activation energy from was Al/Fe2O3, Al/CuO, Al/MnO2 nanothermites.•Fastest burning was Al/CuO nanothermite, while the longest was Al/Fe2O3.•Combustion phenomenon of Al/CuO was similar to that of Al/MnO2.•Al/Fe2O3 produced lots of scattered sparks with poor energy concentration.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A series of new candidates as nonlinear optical materials, tetra-nuclear heterobimetallic clusters MOS
3M
3′Y(PPh
3)
3 (M
=
Mo, M′
=
Ag, Y
=
Br
1; M
=
W, M′
=
Ag, Y
=
I
2; M
=
Mo, M′
=
Cu, Y
=
I
3; M
...=
W, M′
=
Cu, Y
=
I
4), have been synthesized by newly developed ligand-redistribution reaction for third-order nonlinear optical (NLO) studies. Single-crystal X-ray diffraction shows that clusters MoX(μ
3-S)
3(μ
3-Br)(AgPPh
3)
3
1 and WX(μ
3-S)
3(μ
3-I)(CuPPh
3)
3
4 (X
=
O
0.5S
0.5
1, O
4) adopt an isomorphous neutral cubane-like skeleton. Their optical nonlinearities were measured by
Z-scan technique with an 8
ns pulsed laser at 532
nm. These clusters were found to exhibit effective nonlinear absorption, self-focusing effects and large optical limiting capabilities. The effective NLO susceptibilities
χ
(3) and the corresponding second-order hyperpolarizabilities
γ of these clusters are also reported. The influence of cluster composition on NLO properties has been discussed accordingly.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Nano-rod Mn-doped carbon coating LiFePO4 composites have been synthesized by a sample solvothermal process coupled with calcination, which shows an excellent performance at high rate condition. The ...morphology and microstructure of the composites were evidenced by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical properties were evaluated by constant current charge/discharge test. Mn-doping magnified the interplanar spacing, providing a smoother aisle for ionic transport, it is beneficial to improve electrochemical properties at high rate. The stability was enhanced as well combined with carbon coating. In electrochemical measurement of the specific charge capacity, rate capacity and cycling stability, the obtained composite rod-like materials offer remarkably promising results for application, the initial discharge capacity is 160 mAh·g-1 at 0.2 C and 120 mAh·g-1 at 10 C, the capacity retention ratio is 94% at 0.2 C and 93% at 10 C after 50 charge-discharge cycles.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this article, the original Li1.2Mn0.54Ni0.13Co0.13O2 lithium-rich manganese-based cathode material with a uniform distribution of polygonal prisms was synthesized by a simple and reproducible ...sol-gel method, followed by a simple chemical deposition method. The structure and electrochemical performance of the original and modified cathode materials were characterized by XRD, XPS, EDS, SEM, TEM, and constant current charge/discharge tests. The results showed that LaF3 was uniformly coated on the surface of the original material and the thickness of the 2 wt% coating layer was about 2-3 nm. With this coating amount, the cathode material could obtain the best cycling and rate performance. The first coulomb efficiency of the modified material was 73%, which was 7% higher than that of the original material. Secondly, the cycling performance was improved. When the coated material was cycled at 0.2 C for 50 cycles, the discharge capacity was 325mAh∙g-1, and the capacity retention rate was 99.21%, while the original material was only 78.73%. Finally, the performance was also improved at high current density. The coated material could still reach 170mAh∙g-1 at 5C, which was 70% higher than the original material. The significant improvement in electrochemical performance was attributed to the fact that the LaF3 coating layer made the material avoid direct contact with the electrolyte which could reduce the occurrence of side reactions and increase the stability of the material. Besides, expanded layer space resulted from lattice expansion after coating could broaden the transmission channel of lithium ions and facilitate the insertion-extraction of lithium ions during charge and discharge.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this article, the original LiFePO4/(C+RGO) cathode material with a uniform distribution of cuboid morphology was synthesized by hydrothermal method, and then 3 wt% nano silver was coated on the ...surface of the original material by a simple chemical deposition method. The surface structure and electrochemical performance of the original and modified cathode materials were characterized by XRD, SEM, TEM, and constant current charge/discharge tests. The results showed that the one-dimensional silver nano-chains with spiral structure and the two-dimensional graphene plane structure formed an uniform three-dimensional network coating layer, and the structure of the original material has not been changed. The cathode electrode material after coating had the best cycle and rate performance. The modified material had an initial charge-discharge capacity of 150.7 mAh·g-1 at 0.2C, which is 25.4% higher than the original material (LiFePO4/C). Secondly, the cycle performance is improved. After the coated material was cycled at 0.2C for 100 cycles, the discharge capacity is 157mAh/g, and the capacity retention rate was 104.2%, while the original material (LiFePO4/C) is only 79.6%. The rate performance was also greatly improved. The coated material could still reach 107.1 mAh·g-1 at 5C, which is 39.3% higher than the original material (LiFePO4/C). The significant improvement in electrochemical performance was attributed to the three-dimensional conductive network formed by the composite coating layer, which increased the conductivity of the material and the migration rate of lithium ions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To explore the effect of the addition of poly(vinylidene fluorine) (PVDF) to a nanothermite system, an Al/MnO
/PVDF energetic nanocomposite was prepared using an electrospray method, Al/MnO
...nanothermite was prepared as a control group. Then, the energetic nanocomposite and nanothermite were tested and analyzed by XRD, FE-SEM and TG-DSC, and the reaction products were collected. The results show that energetic nanocomposite would have three obvious exothermic peaks in the range of room temperature to 800 °C with a total more than 1700 J g
heat release while the control experiment, Al/MnO
nanothermite, could be found one exothermic peak with a 1100 J g
heat release. The residues are mainly MnAl
O
, MnF
and AlF
which indicates that Al/MnO
/PVDF energetic nanocomposite could make full use of manganese oxide. Finally, thermal analysis experiments were carried out under different heating rates to calculate the activation energy. The calculation results show that the addition of PVDF could significantly reduce the activation energy, which would help spark the thermite at comparatively low energy and temperature.
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IJS, KILJ, NUK, UL, UM, UPUK
To explore the effect of potassium perchlorate (KClO
) on Al nanoparticles/MnO
-nanorods nanothermite systems, in this paper, Al/MnO
nanothermites with different mass fraction of KClO
were prepared ...by electrospray. The samples were characterized by XRD, SEM, TG-DSC analysis. According to the results of TG-DSC, the addition of KClO
seemed to cause no direct improvement on their exothermic reactions. But the results of activation energy calculations showed that KClO
could remarkably reduce the activation energy of nanothermite systems by up to 48.8%. The XRD results indicated that residues consisted mainly of Mn
O
. The reasons why KClO
has little effect on thermal properties but makes a great difference on kinetics were analyzed and discussed. Finally, onset combustion tests were carried out. The results and findings provide a useful approach to decrease the activation energy and combustion rate of nanothermites, which may facilitate practical and combustible applications.
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IJS, KILJ, NUK, UL, UM, UPUK
A mechanistic study on the nucleation of polyaniline nanotubes (PANI-NT) through template-free method is explored by in situ solution-state 1H NMR experiments via a careful analysis of the spectral ...evolution of the major species in the course of the reaction. Before polymerization, aniline and salicylic acid have assembled into loosely packed micelles due to electrostatic interactions and the proton exchange reaction between aniline and anilinium. A three-stage polymerization with a formation, accumulation of aniline dimers, as well as a generation of phenazine-like oligomers is observed, which can be attributed to the monomer transformation from neutral aniline molecules to anilinium cations and the significantly lowered pH in the reaction. Strong π–π stacking interactions from the phenazine-like oligomers facilitate the intermolecular aggregation which initiates the formation of PANI-NT. At first, such aggregates, locating at the outermost layer of anilinium composed micelles, shield in situ formed protons from releasing into the aqueous bulk but into the micelle instead. Due to the continuously increased charge in the micelle, a sphere-to-rod structural transition occurs which leads the oligomer aggregates to be sheathed at the exterior of the rod. Further consumption of anilinium in the micelle leaves the internal cavity while the fusion between the micelles elongates the length of the tubes. Our work demonstrates that (i) loosely packed anilinium composed micelles, highly mobile monomers within the micelle, and efficient blockage of the proton-releasing to the aqueous bulk are three key factors for the generation of tubular structures; and (ii) dynamic NMR line shape analysis provides a new perspective for resolving the formation profile of nanostructured polymers.
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IJS, KILJ, NUK, PNG, UL, UM
Aqueous solutions of graphene oxide (GO) and citrate‐stabilised gold nanoparticles (AuNPs) are two classic, negatively charged colloids. Using the surface plasmon resonance spectra of AuNPs as a ...probe, we illustrate how the two like‐charged colloids interact with each other and in so doing, reveal the unique solution behaviour of GO. We demonstrate that the electrical double layer of the GO sheets in water plays a key role in controlling the interaction between GO and AuNPs, which displays a one‐way gate effect. It is shown that GO can capture and disperse AuNPs in water in a controllable fashion, without the need for additional chemical linkers. This discovery allows the successful synthesis of uncapped, yet solution‐dispersible metal‐nanoparticle assemblies. Such metal nanostructures have long been pursued for nano‐plasmonics and sensing applications, but have remained difficult to prepare using conventional polymer dispersants. This work also makes clear that the combination of the two‐dimensional conformation of GO along with its large molecular size and self‐contained functional groups allows it to act as a unique soluble nanocarrier/substrate (the thinnest, functionalised flat substrate possible in nature) for the synthesis of new, soluble functional materials.
Between the sheets: Colloidal graphene oxide sheets can serve as a unique molecular substrate to capture gold nanoparticle clusters in a controllable fashion (see image). This discovery provides a simple and facile method for synthesis of uncapped, yet solution‐dispersible nanoparticle assemblies.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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