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The flashover failure and damage of polypropylene (PP) and polyester (PET) films under nanosecond current pulses were experimentally investigated. A nanosecond pulse current test platform was established to study the flashover characteristics, performance degradation, and structural damage of dielectric films under repeated nanosecond current pulses. The accumulation and emission of surface charge influenced by field distortion and trap distribution were analyzed to clarify the mechanism by which the flashover voltage increases linearly with gas pressure at low pressure and saturates at high pressure. The significant effects of pulse energy, gas pressure, and discharge gap on film damage behavior were investigated. The damage pattern of PP and PET films includes surface deformation, reduced flash-voltage tolerance, molecular chain breakage, and group shedding. The damage of PP films is manifested as fine furrows, while PET corresponds to mountainous bumps. With the increasing number of discharges, the breakdown voltage of PP films decreased significantly, while the flash tolerance performance of PET films was more stable. Under the conditions of high pulse current amplitude, small discharge gap, and low air pressure, the damage degree of the film intensifies, which is characterized by severe destruction to the molecular structure and a significant decrease in flashover withstand voltage. Polymer films, flashover, nanosecond current pulses; performance degradation; microstructural damage. [ABSTRACT FROM AUTHOR]

Due to the lack of a standard nanosecond high-voltage pulse generator for sensor calibration, a high-stability nanosecond high-voltage pulse test system was developed in terms of circuit analysis, structural design, and performance test. By establishing the equivalent circuit model of the nanosecond pulse generator, the circuit component parameters of the five-stage Marx loop and the one-stage compression steepening unit were simulated. The influence of the action performance of the steepening gap on the characteristics of output nanosecond pulse was analyzed. The nanosecond pulse test system was established through the structural design of the nanosecond pulse-generating circuit, the development of a high-performance corona-stabilized switch, and the measurement of a fast-response resistance divider made of metal oxide thin-film resistors. The nanosecond pulse test system has the capability to output a double exponential nanosecond pulse voltages in the amplitude range of 10–60 kV with a rise time of 2.3 ± 0.5 ns and a half-peak time of 23 ± 5 ns. In addition, the output pulse voltage has a high consistency and stability in the full amplitude range. The maximum relative standard deviation of the peak value is 1.517%, and the relative standard uncertainty is less than 5‰. [ABSTRACT FROM AUTHOR]

The search for inexpensive, environmentally friendly, and highly effective catalysts to activate C-H bonds in propane dehydrogenation (PDH) reactions is still a major challenge. Co-based catalysts have gained significant attention in recent years due to their excellent ability to activate C-H bonds and their high selectivity towards olefins, despite being a non-noble and environmentally unfriendly metal. However, further improvements are necessary for practical utilization, particularly in terms of activity and anti-carbon deposition capacity. In this study, we synthesized Al2O3 nanorods with abundant pentacoordinated Al3+ (Al3+penta) sites. The supported Co on the Al2O3 nanorod (Co/Al2O3-NR) exhibited higher selectivity (>96% propylene selectivity) and stability (deactivation rate 0.15 h−1) compared to Co supported on an Al2O3 nanosheet with fewer pentacoordinated Al3+ sites. Various characterizations confirmed that Co(II) mainly exists as CoAl2O4 rather than Co3O4 in the form of Co/Al2O3-NR, which inhibits the reduction of Co(II) to Co0 and accordingly improves catalyst stability. [ABSTRACT FROM AUTHOR]

In this paper, the effect of alkali metal deposition on the activity of x‐Co3O4 (x=Na, K, Rb, Cs) catalysts for the N2O catalytic decomposition was systematically explored by DFT calculation and various experimental characterization methods. The results demonstrated that the deposition of alkali metal Na improved the activity of the Na‐Co3O4 catalyst for N2O catalytic decomposition at low temperatures. By contrast, the deposition of other alkali metals (K, Rb and Cs) suppressed the catalytic decomposition of N2O perceptibly. Analysis of the results of XRD, FT‐IR, SEM, TEM, XPS, O2‐TPD and H2‐TPR characterization of x‐Co3O4 catalysts showed that the deposition of alkali metals did not affect the morphology and structure of the catalysts. However, it affected the chemical environment around the Co ion in the x‐Co3O4 catalyst, where the deposition of alkali metal Na not only facilitated the reduction of Co3+ to Co2+, but also promoted the surface decomposition step of N2O (i. e. the oxidation of Co2+ to Co3+ by giving electrons) at low temperatures, indicating that alkali metal Na improved the electron donating capability of the catalyst active center and enhanced the performance of the Na‐Co3O4 catalyst for the DCD of N2O at low temperatures. The deposition of other alkali metals did not show the same results as that of alkali metal Na, indicating that the promotion of different alkali metals was different and would directly affect the catalytic effect. At low temperatures, the catalytic activity of catalysts deposited with the alkali metal Na was greater than that of catalysts deposited with other alkali metals. [ABSTRACT FROM AUTHOR]