Investigating lightweight electromagnetic microwave absorption materials is still urgent because of the issue related to the electromagnetic pollution or military defense. Our findings indicate that core−shell MnO@carbon nanowires (MnO@C NWs) achieve substantially enhanced microwave absorption, suggesting the suitable impedance matching induced by the synergetic effect between MnO and carbon. Furthermore, the peapod-like MnO@C NWs with internal void space can be facially synthesized by partial etching of core−shell MnO@C NWs. The peapod-like MnO@C NWs with internal voids/cavities exhibit dramatically enhanced electromagnetic microwave absorption property when the carbon content is about 64 wt %, a minimum reflection loss (RL) of −55 dB at 10 wt % loading was observed at 13.6 GHz, and the bandwidth of RL less than −10 dB (90% absorption) covers 6.2 GHz at the thickness of 2 mm. The excellent electromagnetic microwave absorption performance is superior to the most of MnO x /C composites in the literatures, which probably benefits from the dielectric polarization among conductive network structure between MnO and carbon, as well as the multiple reflection and absorption induced by internal void space. Our work is expected to pave an effective way to extend the electromagnetic microwave absorption performance of MnO/C composites through partial etching to create a void space.

Pitting corrosion is one of the most destructive forms of corrosion that can lead to catastrophic failure of structures. This study presents a thermodynamically consistent phase field model for the quantitative prediction of the pitting corrosion kinetics in metallic materials. An order parameter is introduced to represent the local physical state of the metal within a metal-electrolyte system. The free energy of the system is described in terms of its metal ion concentration and the order parameter. Both the ion transport in the electrolyte and the electrochemical reactions at the electrolyte/metal interface are explicitly taken into consideration. The temporal evolution of ion concentration profile and the order parameter field is driven by the reduction in the total free energy of the system and is obtained by numerically solving the governing equations. A calibration study is performed to couple the kinetic interface parameter with the corrosion current density to obtain a direct relationship between overpotential and the kinetic interface parameter. The phase field model is validated against the experimental results, and several examples are presented for applications of the phase-field model to understand the corrosion behavior of closely located pits, stressed material, ceramic particles-reinforced steel, and their crystallographic orientation dependence. INTRODUCTIONCorrosion is the gradual destruction of materials (usually metallic materials) via chemical and/or electrochemical reaction with their environment. It costs about 3.1% of the gross domestic product (GDP) in the United States, which is much more than the cost of all natural disasters combined. Localized corrosion, such as pitting corrosion, is one of the most destructive forms of corrosion; it leads to the catastrophic failure of structures and raises both human safety and financial concerns. 1-3 Pitting corrosion of stainless steel usually occurs in two different stages: (1) pit initiation from passive film breakage 4-6 and (2) pit growth. 2,3,[7][8][9][10][11][12] In this study, we focused on the development of a phase-field modeling capability to study pit growth by considering both anodic and cathodic reactions.In the past few decades, great efforts have been made to develop numerical models for pitting corrosion. The moving interface and the electrical double layer at the metal/electrolyte interface are the two challenging problems faced by most of these numerical models. These numerical models can be divided according to the method in which a moving interface is incorporated in their models. Several steady state 9,10,13-18 and transient state 19-28 models have been developed over the years that did not allow for changes in the shape and dimensions of the pits/crevices as corrosion proceeds.Recent advances in numerical techniques, such as the finite element method, the finite volume method, the arbitrary Lagrangian-Eulerian method, the mesh-free method, and the level set method have encouraged researchers to model the evolving morphology...

A diaphragm-based interferometric fiber optical microelectromechanical system sensor with high sensitivity is designed and tested for on-line detection of the acoustic waves generated by partial discharges (PD) inside high-voltage power transformers. In principle, the sensor is made according to Fabry Perot interference, which is placed on a micro-machined rectangular silicon membrane as a pressure-sensitive element. A fiber-optic readout scheme has been used to monitor sensor membrane deflection. Sensor design, fabrication, characterization, and application in PD acoustic detection are described. Test results indicate that the fiber optical sensor is capable of detecting PD acoustic signals propagating inside transformer oil with high sensitivity.

Graphdiyne (GDY) has been considered as an appealing anode candidate for K-ion storage since its triangular pore channel, alkyne-rich structure, and large interlayer spacing would endow it with abundant active sites and ideal diffusion paths for K-ions. Nevertheless, the low surface area and disordered structure of bulk GDY typically lead to unsatisfied K storage performance. Herein, we have designed a GDY/graphene/GDY (GDY/Gr/GDY) sandwiched architecture affording a high surface area and fine quality throughout a van der Waals epitaxy strategy. As tested in a half-cell configuration, the GDY/Gr/GDY electrode exhibits better capacity output, rate capability, and cyclic stability as compared to the bare GDY counterpart. In situ electrochemical impedance spectroscopy/Raman spectroscopy/transmission electron microscopy are further applied to probe the K-ion storage feature and disclose the favorable reversibility of GDY/Gr/GDY electrode during repeated potassiation/depotassiation. A full-cell device comprising a GDY/Gr/GDY anode and a potassium Prussian blue cathode enables a high cycling stability, demonstrative of the promising potential of the GDY/Gr/GDY anode for K-ion batteries.

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Three-dimensional individual S-doped porous red-blood-cell-like graphene (SRBCG) microspheres with double concave-surface morphology duplicated from a template-directed chemical vapor deposition process in a fluidized bed reactor not only exhibit high porosity, good structural stability, and strong anticompression properties but also present superior capacitive energy-storage abilities with respect to a symmetric supercapacitor (great compatibility at different rates) and a Li ion capacitor (no capacitance loss after 3500 cycles at 2 A g −1 ). The well-kept integrity of the electrode configuration after cycling benefits from the intrinsic robust scaffold which acts as a structural buffer for volume expansion to inhibit structure collapse. The unique individual microarchitecture with well-developed pore channels of SRBCG can effectively prevent the obtained graphene from aggregation or restacking, expanding the contact area between electrolyte ions and the electrode. The excellent capacitive behaviors of SRBCG are guaranteed by the unique robust microarchitecture accompanied by the good structural stability. Additionally, the fluidized bed technology is conducive to the realization of the homogeneous growth and scalable production of SRBCG.