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A three-dimensional (3D) honeycomb-like hematite superstructure was successfully fabricated on 100 pixel per inch (ppi) Fe foam scaffold via a straightforward hydrothermal approach. Influencing factors including the reaction temperature, time and the dosage of precipitant were systematically studied. A self-assembly growth mechanism was proposed based on the results of hydrothermal reaction. The powder catalyst in the form of zero-dimensional (0D) hematite nanoparticles acted as a reference sample was also synthesized at the same reaction conditions without Fe foam substrate. The honeycomb-like hematite structure exhibited a higher CO conversion and lower methane selectivity than the traditional powder catalyst for Fischer–Tropsch synthesis (FTS). These enhancements can be mainly attributed to its distinctive structure with high specific surface area, large Fe3O4 content, promoted reducibility and uniform particle size distribution, as well as effective diffusion of feed gas and products. [ABSTRACT FROM AUTHOR]

In steady-state operation of Hall thrusters excited by permanent magnets, the existence of temperature difference between the inner and outer permanent magnets will cause the deviation of the magnetic field configuration from the design value, thus affecting the discharge process. The simulation results show that the ion power loss on the inner wall increases by over 7.5% when the temperature difference between the inner and outer permanent magnets reaches to 140 ℃. The main reason is that the coercivity of the inner permanent magnet decreases more at higher temperature, and the magnetic field lines will incline toward the inner wall, resulting in the increment of the radial component of the electric field pointing to the inner wall. An optimized magnetic field, obtained by moving the inner permanent magnet outward in an appropriate manner, is proposed to alleviate the inner wall erosion. The optimized magnetic field has a near-symmetrical configuration, especially the nearly equal length of intersection lines of the magnetic field lines with the inner and outer walls, which is contributed to reduce the radial component of the electric field and preventing the inclination of the main ionization zone toward the inner wall, so that the peak value of ion power deposition on inner wall can be reduced by more than 50%. Based on the illustrated features and mechanism of wall erosion, an effective and easy-to-implement optimization scheme was proposed in this work to provide a useful reference for the design of long-life Hall thrusters with large height-radius ratio. [ABSTRACT FROM AUTHOR]

Micro-cathode arc thrusters have been widely used in micro-nanosatellites owing to their high specific impact, long lifetime, repeatable startup, low thrust and high control precision. Micro-cathode arc thrusters and their derivatives are currently being developed and optimized. The micro-cathode arc thruster can generate plasma stably and efficiently, and form a thrust force under a magnetic field with very low power in pulsed operation mode. This paper reviews the last 20 years of literature on micro-cathode arc thrusters, with a focus on papers published in this field in the last 5 years. In light of the development of the micro-cathode arc thruster and the latest research, the direction of future development and the application of key technologies are reviewed. Future micro-cathode arc propulsion systems are expected to exhibit higher reliability, longer lifetimes, higher specific impact, greater integration and higher thrust and to be operated in various modes. [ABSTRACT FROM AUTHOR]

The backpressure in the ground vacuum chamber significantly influences the discharge characteristics and performance of Hall effect thrusters (HETs). In this study, the propellant supplied from the anode and the propellant ingested from the background are treated as two separate components. Their ionization and acceleration processes are then studied numerically with a Particle-in-cell discharge model. It is found that the background propellant is mainly ionized near the outlet of the channel, thus affecting the local electron mobility and potential distribution inside and outside the channel. This results in an improvement in the ionization and acceleration of the anode propellant, an enhancement in the utilization of the propellant, and a reduction in the divergence of the ion beam. Consequently, the performance of the HETs is augmented. In particular, the increment in the thrust caused by the introduction of backpressure is not only due to the ionization and acceleration of the background propellant but also due to the improvement in the anode propellant discharge. [ABSTRACT FROM AUTHOR]

This paper reports on the dynamic characteristics of the distribution of ion energy during Hall thruster discharge in the low-frequency oscillation time scale through experimental studies, and a statistical analysis of the time-varying peak and width of ion energy and the ratio of high-energy ions during the low-frequency oscillation. The results show that the ion energy distribution exhibits a periodic change during the low-frequency oscillation. Moreover, the variation in the ion energy peak is opposite to that of the discharge current, and the variations in width of the ion energy distribution and the ratio of high-energy ions are consistent with that of the discharge current. The variation characteristics of the ion density and discharge potential were simulated by one-dimensional hybrid-direct kinetic simulations; the simulation results and analysis indicate that the periodic change in the distribution of ion energy during the low-frequency oscillation depends on the relationship between the ionization source term and discharge potential distribution during ionization in the discharge channel. [ABSTRACT FROM AUTHOR]

A 200 W No-Wall-Losses Hall Thruster (NWLHT-200 W) is designed and processed to verify the technology of pushing down magnetic field with two permanent magnetic rings. To create a magnetic field, NWLHT-200 W uses two permanent magnetic rings (inner and outer) in the absence of magnetic screen or magnetic component. The anode is at the internal magnetic separatrix position, and the thruster shell is hollow to enhance the heat dissipation of ceramics. The magnetic field strength at the channel outlet is 90% of the maximum magnetic field. In this study, the experimental results concerning the thrust, discharge current, specific impulse, and efficiency are presented and examined. Our experiments show that 'no erosive discharge' of wall is achieved within the range of 120-460 W; the maximum efficiency of the anode may reach 49%. The thruster designed can work stably for a long time, without any auxiliary heat dissipation equipment (heat pipe or radiator), which significantly prolongs the life of Hall thrusters. [ABSTRACT FROM AUTHOR]

This study adopts double permanent magnetic rings and four permanent magnetic rings to form two symmetrical magnetic peaks and two asymmetrical magnetic peaks in the channel of a Hall thruster, and uses a 2D-3V PIC-MCC model to analyze the influence of magnetic strength on the discharge characteristic and performance of Hall thrusters with an intermediate electrode and double-peaked magnetic field. As opposed to the two symmetrical magnetic peaks formed by double permanent magnetic rings, increasing the magnetic peak value deep within the channel can cause propellant ionization to occur; with the increase in the magnetic peak deep in the channel, the propellant utilization, thrust, and anode efficiency of the thruster are significantly improved. Double-peaked magnetic field can realize separate control of ionization and acceleration in a Hall thruster, and provide technical means for further improving thruster performance. Graphical abstract: [ABSTRACT FROM AUTHOR]

Two simply and highly selective aluminium ion fluorescent probes based on 4-aminoantipyrine derivate have been successfully synthesized and systemically characterized, The investigation of absorption and emission spectra revealed that the compounds exhibited highly selective fluorescence behaviours toward Al in aqueous media and showed differential fluorescent emission peaks corresponding to blue and green. which resulted from different fluorophores, and the fluorescence process is attributed to the Photoinduced Electron Transfer (PET) mechanism, In addition, the association constants between sensors L1 and L2 with aluminum ion are 1.58 × 10 M and 8.72 × 10 M, respectively, which were obtained by fluorescent titration experiments. Moreover, the binding site of sensors with Al were determined by HNMR titration experiments. [ABSTRACT FROM AUTHOR]

The effect of the magnetic-field intensity near an intermediate electrode in the discharge channel of a Hall thruster with a double-peaked configuration, on the thruster discharge and performance is investigated by applying the particle-in-cell Monte Carlo collision model. The result shows that by increasing the magnetic-field intensity near the intermediate electrode while keeping the magnetic-field peak intensity and position unchanged, the current received by the intermediate electrode is gradually reduced, whereas the propellant utilization and thrust are increased. Thus, the specific impulse and efficiency are improved. The efficiency can be increased by more than 10%. Increasing the magnetic-field strength near the intermediate electrode is conducive to improving the performance of the thruster, which provides a reference for the design of a Hall thruster with a double-peaked magnetic field. [ABSTRACT FROM AUTHOR]