Currently, the electromagnetic (EM) wave absorbers usually suffer severe performance degradation when they work for a while due to the generated heat issue. Developing a high-performance EM absorber with flexibility and adjustability that can effectively absorb the EM energy and convert into thermal energy at elevated temperature is highly desired but still remains a significant challenge. Herein, we demonstrate S-doped hollow carbon nanospheres used as fillers to fabricate a flexible and controllable EM absorber toward this challenge. Owing to the insertion of S-based polar groups in the graphitization area of carbon spheres, this EM absorber exhibits outstanding electromagnetic wave absorption capability with elimination of X-band EM wave performance at a temperature range of 298−423 K. Almost 90% of the Xband EM wave can be dissipated at 373 K, while the effective absorption rate of 75% can still be achieved at 423 K.
Both the complex permittivity and permeability of nanometer SiC and nanometer SiC/CNTs composite were investigated by Hewlett-Packard 8510B Network Analyzer. The results show that the complex permittivity of nanometer SiC/CNTs composite is much higher than that of nanometer SiC. Reflection curves of nanometer SiC and nanometer SiC/CNTs composite calculated with electromagnetic wave transmission-line theory show that the addition of CNTs at 6 wt%, 12 wt% and 18 wt% in nanometer SiC absorber can improve its microwave absorption properties strongly. There is a relationship between the mass fraction of CNTs and microwave absorption ability. With increase of the mass fraction of CNTs, its microwave absorption ability firstly increased then decreased. From the simulation, it was found that nanometer SiC with 12 wt% CNTs gave the optimum microwave absorption. The corresponding frequency of maximum reflection loss value of nanometer SiC/CNTs composite gradually moves to the low frequency range with increase of thickness. The maximum reflection loss value of nanometer SiC/CNTs composite (CNTs content is 12 wt%) was -25.74dB at the corresponding frequency of 11.60 GHz with a bandwidth under -5 dB (68% absorption) is 7.16 GHz when the thickness is 2.0 mm.
The sulphur and oxygen segregation on V(100) surface is investigated in detail by AES and LEED. The relation between S and O segregation is clearly demonstrated and two new surface reconstructions, (8×1)-O and (4×l)-O,on V(100) surface are disclosed. Various superstructures on this surface under different conditions of S & O segregation are studied systematically and the relationship among these surface structures is obtained.
Samples of AISI 1045 carbon steel were surface hardened by micro plasma transferred arc (PTA) process. The hardened layer was characterized using both light optical and scanning electron microscopy and microhardness techniques. The tribological properties of the surface hardened layer and untreated substrate were investigated using a block-on-ring tribometer sliding against GCr15 steel under unlubricated condition. The worn surface morphologies and dominant wear mechanisms were identified using microscopy techniques. Results show that the surface hardened layer consists mainly of martensite and retained austensite with fine and dense structure, the microhardness of hardened layer increases from approximately HV 200 to HV 600. The wear volume loss of plasma hardened layer was 81.86×10-11m3 much better than that of untreated AISI 1045 carbon steel (743.44×10-11m3). Wear of untreated AISI 1045 carbon steel occurred by combined mechanisms of adhesion, abrasion and plastic deformation. While the worn surface of surface hardened layer is quite better with slight track and thin oxides on the worn surfaces. Plasma surface hardening has essentially changed the wear mechanism of the AISI 1045 carbon steel to slight abrasion and oxidation wear.
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