Multifunctional MXene/C Aerogels for Enhanced Microwave Absorption and Thermal Insulation

Two-dimensional transition metal carbides and nitrides(MXene)have emerged as promising candidates for microwave absorption(MA)materials.However,they also have some drawbacks,such as poor impedance matching,high self-stacking tendency,and high density.To tackle these challenges,MXene nanosheets were incorporated into polyacrylonitrile(PAN)nanofibers and subsequently assembled into a three-dimensional(3D)network structure through PAN carbonization,yielding MXene/C aerogels.The 3D network effectively extends the path of microcurrent transmission,leading to enhanced conductive loss of electromagnetic(EM)waves.Moreover,the aerogel’s rich pore structure significantly improves the impedance matching while effectively reducing the density of the MXenebased absorbers.EM parameter analysis shows that the MXene/C aerogels exhibit a minimum reflection loss(RL_(min))value of−53.02 dB(f=4.44 GHz,t=3.8 mm),and an effective absorption bandwidth(EAB)of 5.3 GHz(t=2.4 mm,7.44–12.72 GHz).Radar cross-sectional(RCS)simulations were employed to assess the radar stealth effect of the aerogels,revealing that the maximum RCS reduction value of the perfect electric conductor covered by the MXene/C aerogel reaches 12.02 dB m^(2).In addition to the MA performance,the MXene/C aerogel also demonstrates good thermal insulation performance,and a 5-mm-thick aerogel can generate a temperature gradient of over 30℃ at 82℃.This study provides a feasible design approach for creating lightweight,efficient,and multifunctional MXene-based MA materials.

MXenes with applications in supercapacitors and secondary batteries:A comprehensive review

Two-dimensional(2D)materials have received tremendous attention because they possess a set of merits not available in bulk materials,such as large specific surface area,low energy barrier for electron transportation and short ion diffusion path.These advantages are desirable especially for the electrodes in electrochemical energy storage devices.MXenes,first synthesized in 2011 by etching their MAX phase precursors,have plural reasons to represent a new family of 2D materials.Their rich diversity in structure and composition together with the uncommon combination of good electrical conductivity and hydrophilicity makes themselves outstand in the whole 2D materials world.Based on these advantages,MXenes hold great promise for various technologically important applications,particularly in developing new energy storage techniques for advanced smart systems,such as portable and flexible electronics.There have been remarkable research achievements in the synthesis and application of MXene-based materials.While new synthesis routes being continuously reported,MXenes with new composition and novel structure have also been routinely discovered,which will undoubtedly help understand the fundamental properties and expand the application scope of MXenes.As for their energy storage-related applications,to cope with the intrinsic weakness of MXenes,many endeavors have been made by doping,structure-tuning and compositing with hybrid ingredients.In this review,the current status of MXenes synthesis and up-to-date progress of their applications in supercapacitors,metal-ion batteries and lithium sulfur batteries are summarized and discussed,and the typical work on the application of MXenes for the aforementioned three categories is respectively tabulated for reference and comparison.

One-dimensional core-sheath Sn/SnO_(x)derived from MAX phase for microwave absorption

One-dimensional(1D)metals are highly conductive and tend to form networks that facilitate electron hopping and migration.Hence,they have tremendous potential as microwave-absorbing(MA)materials.Traditionally,1D metals are mainly precious metals such as gold,silver,nickel,and their preparation methods often have low yield and are not environmentally friendly,which has limited the exploration in this area.Herein,the unique nanolaminate structure and chemical bond characteristics of Ti_(2)SnC MAX phase is successfully taken advantages for large-scale preparation of Sn whiskers,and then,core-sheath Sn/SnO_(x)heterojunctions are obtained by simply annealing at different temperatures.The heterojunction annealed at 500℃possesses favorable MA performance with an effective absorption bandwidth of 5.3 GHz(only 1.7 mm)and a minimum reflection loss value of51.97 dB;its maximum radar cross section(RCS)reduction value is 29.59 dB·m^(2),confirming its excellent electromagnetic wave attenuation ability.Off-axis electron holography is used to visually characterize the distribution of charge density at the cylindrical heterogenous interface,confirming the enhanced interfacial polarization effect.Given the diversity of MAX phases and the advantages of the fabrication method(e.g.,green,inexpensive,and easily scalable),this work provides significant guidance for the design of 1D metal-based absorbers.

Vegard’s law deviating Ti_(2)(Sn_(x)Al_(1−x))C solid solution with enhanced properties

The achievement of chemical diversity and performance regulation of MAX phases primarily relies on solid solution approaches.However,the reported A-site solid solution is undervalued due to their expected chemical disorder and compliance with Vegard’s law,as well as discontinuous composition and poor purity.Herein,we synthesized high-purity Ti_(2)(Sn_(x)Al_(1−x))C(x=0–1)solid solution by the feasible pressureless sintering,enabling us to investigate their property evolution upon the A-site composition.The formation mechanism of Ti_(2)(Sn_(x)Al_(1−x))C was revealed by thermal analysis,and crystal parameters were determined by Rietveld refinement of X-ray diffraction(XRD).The lattice constant(a)adheres to Vegard’s law,while the lattice constant(c)and internal free parameter(zM)have noticeable deviations from the law,which is caused by the significant nonlinear distortion of Ti_(6)C octahedron as Al atoms are substituted by Sn atoms.Also,the deviation also results in nonlinear changes in their physicochemical properties,which means that the solid solution often exhibits better performance than end members,such as hardness,electrical conductivity,and corrosion resistance.This work offers insights into the deviation from Vegard’s law observed in the A-site solid solution and indicates that the solid solution with enhanced performance may be obtained by tuning the A-site composition.

Tin whisker growth from titanium-tin intermetallic and the mechanism

Spontaneous growth of metal whiskers, represented by tin whiskers, has haunted tin-based platings and solder joints for decades and caused huge losses to the electronics industry. Despite numerous efforts, the underlying growth mechanism has been resisting interpretation, and the whiskering phenomenon even continues to expand its territory. Here, we report the growth of tin whiskers from a Ti6Sn5intermetallic.These tin whiskers share similar characteristics with those found on the platings or solder joints, but grow more and faster, with finer diameters. After tin whisker growth, Ti6Sn5retains its crystal structure,implying a dealloying process. Combining experimental and first-principles calculation results, we analyzed the growth mechanism of tin whiskers in detail, and proposed a diffusion-based growth model.The strain energy stored in Ti6Sn5during deformation provides a driving force for whisker growth, and the short-circuit diffusion paths generated by such deformation accelerate whisker growth. These findings identify the critical role of intermetallic substrate in the whiskering phenomenon, shedding new light for comprehensively understanding the whisker growth mechanisms. Furthermore, the plenty and rapid growth of tin whiskers also means a new method for the preparation of one-dimensional metallic materials.

LEO Baby支架在颅内远端小血管破裂动脉瘤中的应用

目的探讨LEO Baby支架辅助弹簧圈栓塞治疗颅内远端小血管破裂动脉瘤的安全性及有效性。方法回顾性分析2019年1月至2021年6月在晋城市人民医院神经外科使用LEO Baby支架辅助栓塞治疗的27例颅内远端小血管破裂动脉瘤的临床资料。27例动脉瘤均为宽颈破裂动脉瘤,所有患者均采用单支架辅助栓塞及支架半释放技术,围术期使用替罗非班行抗血小板治疗。采用Raymond分级评价患者术后即刻栓塞效果和术后半年动脉瘤的愈合情况;采用改良的Rankin量表(mRS)评分评价患者术后半年的神经功能恢复情况,其中mRS评分≤2分者为预后良好,mRS评分>2分者为预后不良。结果27例患者支架均成功释放,技术成功率为100%。术后即刻数字减影血管造影(DSA)示:RaymondⅠ级21例(77.8%),RaymondⅡ级4例(14.8%),RaymondⅢ级2例(7.4%)。围术期缺血事件3例(11.1%),无出血事件发生。术后半年复查,DSA示:RaymondⅠ级23例(85.2%),RaymondⅡ级2例(7.4%),RaymondⅢ级1例(3.7%),复发1例。所有患者均未见血管狭窄和支架内血栓形成等事件的发生。术后半年神经功能恢复情况评分示,预后良好25例(92.6%)。结论LEO Baby支架用于颅内远端小血管破裂动脉瘤的治疗安全、有效,且具有一定的血流导向作用。