A High Efficiency Aluminum-Ion Battery Using an AlCl3-Urea Ionic Liquid Analogue Electrolyte

In recent years, impressive advances in harvesting renewable energy have led to pressing demand for the complimentary energy storage technology. Here, a high coulombic efficiency (~ 99.7%) Al battery is developed using earth-abundant aluminum as the anode, graphite as the cathode, and a cheap ionic liquid analogue electrolyte made from a mixture of AlCl3 and urea in 1.3 : 1 molar ratio. The battery displays discharge voltage plateaus around 1.9 V and 1.5 V (average discharge = 1.73 V) and yielded a specific cathode capacity of ~73 mAh g-1 at a current density of 100 mA g-1 (~ 1.4 C). High coulombic efficiency over a range of charge-discharge rates and stability over ~150-200 cycles was easily demonstrated. In-situ Raman spectroscopy clearly showed chloroaluminate anion intercalation/deintercalation of graphite in the cathode side during charge/discharge and suggested the formation of a stage 2 graphite intercalation compound when fully charged. Raman spectroscopy and nuclear magnetic resonance suggested the existence of AlCl4-, Al2Cl7- anions, and [AlCl2. (urea)n]+ cations in the urea/AlCl3 electrolyte when an excess of AlCl3 was present. Aluminum deposition therefore proceeded through two pathways, one involving Al2Cl7- anions and the other involving [AlCl2.(urea)n]+ cations. This battery is a promising prospect for a future high performance, low cost energy storage device

Synthesis and characterisation of large area monolayer tungsten disulphide

Two-dimensional (2D) transition metal dichalcogenides (TMDs), equipped with direct bandgaps in the visible range of electromagnetic spectrum have extended the promise of 2D materials (graphene) to optoelectronics. Towards facilitating the future industrialization of 2D TMDs, this project focused on developing chemical vapour deposition (CVD) techniques for the growth of large area monolayer tungsten disulphide (WS2), which was followed by characterisations of their structural and semiconducting properties. It was demonstrated that controlling the introduction time and the amount of sulphur (S) vapour relative to the tungsten trioxide (WO3) precursor during the CVD growth of WS2 was critical to achieving large crystal domains on the surface of silicon wafers with a 300 nm oxide layer. This improvement for CVD techniques enabled the formation of single crystalline WS2 monolayers with edges up to 370 μm which were visible to the naked eye. Synthetic 2D materials grown by CVD are typically polycrystalline, and determining grain size within domains and continuous films is crucial for determining their structure. The thesis showed that grain boundaries (GBs) in monolayer WS2, grown by CVD, could be preferentially oxidized by controlled heating in air. Under apposite conditions, the degradation of GBs led to their clear and rapid identification using a standard optical microscope. Subsequent studies showed that how these monolayer WS2 GBs influenced the electroluminescence (EL) behaviour in lateral source-drain devices under bias. Real time imaging of the WS2 EL detected arcing between the electrodes when probing across a GB, which then localized at the GB region as it eroded under high bias conditions. Analysis of the eroded GB region showed the formation of micro- and nanoribbons across the monolayer WS2 domains. These results provide important insights into future EL devices that utilize CVD grown monolayer TMDs when GBs are present in the active device region.</p

Forming Mechanism of Weld Cross Section and Validating Thermal Analysis Results Based on the Maximal Temperature Field for Laser Welding

In this paper, the forming mechanism of weld cross sections (WCSs) was studied via thermal analysis. The melting of a WCS was first dominated by heat convection from the flowing melt until the WCS had the max cross section in the transient temperature field. Then, the melting was dominated by heat conduction from the residual heat in the weld pool, giving rise to an increase in middle width but a decrease in upper and bottom width. This indicated that the WCS obtained from the transient temperature field could not represent the section after solidification. Therefore, thermal analysis results should be validated using the WCS obtained from the maximal temperature field. This WCS was dependent upon the max temperature of each node over time. Compared with the former WCS, the latter one showed better adaptability in terms of multi-process parameters when the thermal analysis results were validated

Forming Mechanism of Weld Cross Section and Validating Thermal Analysis Results Based on the Maximal Temperature Field for Laser Welding

In this paper, the forming mechanism of weld cross sections (WCSs) was studied via thermal analysis. The melting of a WCS was first dominated by heat convection from the flowing melt until the WCS had the max cross section in the transient temperature field. Then, the melting was dominated by heat conduction from the residual heat in the weld pool, giving rise to an increase in middle width but a decrease in upper and bottom width. This indicated that the WCS obtained from the transient temperature field could not represent the section after solidification. Therefore, thermal analysis results should be validated using the WCS obtained from the maximal temperature field. This WCS was dependent upon the max temperature of each node over time. Compared with the former WCS, the latter one showed better adaptability in terms of multi-process parameters when the thermal analysis results were validated

Analysis of Hydrostatic Bearings Based on a Unstructured Meshing Scheme and Turbulence Model

Guideway hydrostatic bearings with the function of supporting and moving loads are a key component of ultra-precision heavy-duty machine tools. Because the dimension difference between the oil gap and the overall structure is great, it is difficult to generate the three-dimensional mesh, which has limited the improvement of bearing performance through structural innovation. To solve these problems, we propose an approach using the global fluid domain for performance analysis. The grid skewness of the film region and other regions are less than 0.4 and 0.8, respectively, which can satisfy the demands of static and dynamic high-accuracy simulation. Then, we used supporting load capacity, stiffness and damping to analyze the performance of hydrostatic bearings. The average error between the simulation result and the actual value was 10.76%, which is better than the result calculated by the traditional empirical formulae. The stiffness and damping of the bearings are easy to obtain by application of dynamic mesh technology. Furthermore, many obvious vortices were shown by visualization analysis in the bearing internal flow pattern in the bearing moving state of 400 mm/s. Finally, a specially designed double-slit septum successfully suppressed the formation of visible vortices. This structural improvement, combining the advantages of deep and shallow recesses, is expected to make hydrostatic bearings at high-speed conditions more stable for ultra-precision machine tools

Editorial for the Special Issue on Advanced Materials, Structures and Processing Technologies Based on Pulsed Laser

Pulsed lasers are lasers with a single laser pulse width of less than 0 [...

Evolution Mechanism of Transient Strain and Residual Stress Distribution in Al 6061 Laser Welding

Considering the harm that residual stress causes to the mechanical properties of a weld joint, the evolution mechanisms of transient strain and residual stress distribution are investigated in laser welding of Al 6061, considering that these originate from non-uniform temperature distribution and are intensified further by the unbalanced procedure of melting and solidification. Thermal-elastic-plastic finite element method is developed and analyzed, while the actual weld profile is novel fitted by a B-spline curve. Transient strain is extracted by strain gauges. Longitudinal strain starts from a fluctuating compressive state and progresses to an ultimate residual tension state at the starting and ending welding positions, respectively. The maximum fitting deviation of the weld profile is 0.13 mm. Experimental and simulation results of residual strain are 842.0 μ and 826.8 μ, with a relative error of 1.805% at the starting position and −17.986% at the ending position. Near the weld center, mechanical behavior is complexly influenced by thermal expansion and contraction in the weld zone and the reaction binding force of the solid metal. Within a distance between −10 mm and 10 mm, and longitudinal stress is in a tension state, transverse stress fluctuates with a high gradient (~100 MPa)

PI Film Laser Micro-Cutting for Quantitative Manufacturing of Contact Spacer in Flexible Tactile Sensor

The contact spacer is the core component of flexible tactile sensors, and the performance of this sensor can be adjusted by adjusting contact spacer micro-hole size. At present, the contact spacer was mainly prepared by non-quantifiable processing technology (electrospinning, etc.), which directly leads to unstable performance of tactile sensors. In this paper, ultrathin polyimide (PI) contact spacer was fabricated using nanosecond ultraviolet (UV) laser. The quality evaluation system of laser micro-cutting was established based on roundness, diameter and heat affected zone (HAZ) of the micro-hole. Taking a three factors, five levels orthogonal experiment, the optimum laser cutting process was obtained (pulse repetition frequency 190 kHz, cutting speed 40 mm/s, and RNC 3). With the optimal process parameters, the minimum diameter was 24.3 ± 2.3 μm, and the minimum HAZ was 1.8 ± 1.1 μm. By analyzing the interaction process between nanosecond UV laser and PI film, the heating-carbonization mechanism was determined, and the influence of process parameters on the quality of micro-hole was discussed in detail in combination with this mechanism. It provides a new approach for the quantitative industrial fabrication of contact spacers in tactile sensors

Research on Arc Length Tracking Control Technology of Tube-Sheet Welding Based on Pulsed TIG

During tungsten inert gas welding process, arc length will change due to thermal deformation, uneven surface of workpiece and tungsten electrode loss. Considering the large fluctuation of arc length in all-position annular seam welding under the action of multi-variable coupling, a mathematical model of arc length and arc voltage was established in this paper, and an isolated and high frequency arc voltage acquisition circuit was designed. An improved sliding filtering algorithm was proposed, and after filtering the real-time arc voltage data, fuzzy control algorithm was used to realize the online tracking control of arc length in annular seam welding, in order to improve the reliability and stability of welding quality of tube-sheet. The experimental results show that the dynamic response time of the proposed arc length tracking compensation method is not more than 40 ms, and the arc length tracking deviation is less than 0.2 mm, which can fully meet the requerements of welding seam tracking of tube-sheet welding