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.

Shell powder as a novel bio-filler for thermal insulation coatings

The feasibility of employing shell powder as a novel bio-filler to prepare fluorocarbon coating is demonstrated.According to the relevant Chinese standards, the thermal and mechanical properties of the shell powder-filled fluorocarbon coating were evaluated, and compared with those filled by commercial calcium carbonate. All the shell powder-filled coatings can meet the requirements stated in the relevant standards, and with decreasing the particle size of the shell powders, the performance of the thermal insulation coating is enhanced. The coating(SC3) filled by shell powders with an average particle size of 2.81 μm possesses a better thermal insulation performance than the coating(CC) filled by commercial calcium carbonate. The coating SC3 has comparable adhesive force and washing resistance with the coating CC, and in the washing resistance test, after 2000 cycles, the coating SC3 was still able to cover totally their substrates. This work demonstrates a high value-added disposal method for the aquacultural wastes.

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.

具有三明治结构的MXene/聚酰亚胺复合泡沫用于多尺度微波吸收

三维多孔结构可促进电磁波在材料内部的多重反射,是提升微波吸收性能的有效方法.然而,传统的三维多孔结构中,多重反射仅发生在孔内.扩大多重反射的范围应能进一步提升材料的吸收性能.因此,本文开发了一种孔壁为三明治结构的三维多孔复合泡沫,在亚毫米尺度孔和亚微米尺度孔壁中同时发生多重反射,实现多尺度微波吸收.本研究采用聚多巴胺修饰的聚酰亚胺泡沫(PDA@PIF)作为三维多孔骨架,在其孔壁表面负载Ti_(3)C_(2)T_(x).所得的Ti_(3)C_(2)T_(x)@PDA@PIF能够在整个X波段吸收超过90%的入射波.这得益于多尺度多重反射、电导损耗和界面极化.同时,该复合泡沫具有优异的柔性和低密度(~30 mg cm^(-3)).该工作为实现轻质、柔性、宽频的吸波材料提供了一种可行的方法,丰富了电磁防护的有效结构.

Influence of nano-mechanical evolution of Ti_(3)AlC_(2) ceramic on the arc erosion resistance of Ag-based composite electrical contact material

Al-containing MAX phase ceramic has demonstrated great potential in the field of high-performance low-voltage electrical contact material.Elucidating the anti-arc erosion mechanism of the MAX phase is crucial for further improving performance,but it is not well-understood.In this study,Ag/Ti_(3)AlC_(2) electrical contact material was synthesized by powder metallurgy and examined by nanoindentation techniques such as constant loading rate indentation,creep testing,and continuous stiffness measurements.Our results indicated a gradual degradation in the nano-mechanical properties of the Ti_(3)AlC_(2) reinforcing phase with increasing arc erosion times,although the rate of this degradation appeared to decelerate over arc erosion times.Specifically,continuous stiffness measurements highlighted the uneven mechanical properties within Ti_(3)AlC_(2),attributing this heterogeneity to the phase’s decomposition.During the early(1-100 times)and intermediate(100-1000 times)stages of arc erosion,the decline in the nano-mechanical properties of Ti_(3)AlC_(2) was primarily ascribed to the decomposition of Ti_(3)AlC_(2) and limited surface oxidation.During the later stage of arc erosion(1000-6200 times),the inner region of Ti_(3)AlC_(2) also sustained arc damage,but a thick oxide layer formed on its surface,enhancing the mechanical properties and overall arc erosion resistance of the Ag/Ti_(3)AlC_(2).

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.

Preparation and arc erosion properties of Ag/Ti_2SnC composites under electric arc discharging

New Ag/Ti_2 SnC(Ag/TSC) composites with uniform microstructure were prepared by powder metallurgy. The superior wettability between Ag and Ti_2 SnC was confirmed with a contact angle of 14°. Arc erosion properties of Ag/10 wt%Ti_2 SnC(Ag/10 TSC) and Ag/20 wt%Ti_2 SnC(Ag/20 TSC) contacts were investigated under 400 V/100 A/AC-3 and compared with Ag/CdO contact.The Ag/10 TSC contact exhibited comparable arc erosion property to Ag/CdO contact. The fine arc erosion resistance was attributed to the good wettability between Ti_2 SnC and Ag,the good heat-conducting property of Ag/10 TSC, and the slight decomposition of Ti_2 SnC that absorbed part of electric arc energy. The excessive Ti_2 SnC significantly decreased the thermal conducting property of the Ag/20 TSC composite, resulting in the severe heat accumulation that decomposed Ti_2 SnC and deteriorated arc erosion property. The oxidation behavior of Ti_2 SnC under high electric arc temperature was also studied and then an arc erosion mechanism was proposed to get a comprehensive understanding on the arc erosion property of Ag/TSC composites.

From structural ceramics to 2D materials with multi-applications:A review on the development from MAX phases to MXenes

MAX phases(Ti_(3)SiC_(2),Ti_(3)AIC_(2),V_(2)AlC,TiqAlN_(3),etc.)are layered ternary carbides/nitrides,which are generally processed and researched as structure ceramics.Selectively removing A layer from MAX phases,MXenes(Ti_(3)C_(2),V_(2)C,Mo_(2)C,etc.)with two-dimensional(2D)structure can be prepared.The MXenes are electrically conductive and hydrophilic,which are promising as functional materials in many areas.This article reviews the milestones and the latest progress in the research of MAX phases and MXenes,from the perspective of ceramic science.Especially,this article focuses on the conversion from MAX phases to MXenes.First,we summarize the microstructure,preparation,properties,and applications of MAX phases.Among the various properties,the crack healing properties of MAX phase are highlighted.Thereafter,the critical issues on MXene research,including the preparation process,microstructure,MXene composites,and application of MXenes,are reviewed.Among the various applications,this review focuses on two selected applications:energy storage and electromagnetic interference shielding.Moreover,new research directions and future trends on MAX phases and MXenes are also discussed.

Slip casting and pressureless sintering of Ti3AlC2

Slip casting and subsequent pressureless sintering(PLS)allow the preparation of complex-shaped and large-sized Ti3AlC2 components for many potential applications.The behaviors of the suspensions,green compacts,and sintered samples of Ti3AlC2 were studied in this paper.The optimized condition of 1 wt%of arabic gum as dispersant at pH=10 results in a Ti3AlC2 suspension for slip casting Ti3AlC2 green compacts without macro defects or cracks.The sintering temperature and Al4C3 embedding powder are found to dominate the properties of the sintered Ti3AlC2 samples.The Ti3AlC2 sample sintered at 1450℃for 1.5 h with Al4C3 embedding powder reaches the best properties,namely 95.3%relative density,hardness of 4.18 GPa,thermal conductivity of 29.11W·m-1·K-1,and electrical resistivity of 0.39μΩ·m.The findings in this work may pave the way for the application of MAX phases with large size and complex shape.

Confining effect of oxide film on tin whisker growth

Spontaneous tin whisker growth has been mysterious and catastrophic for more than half century. The difficulty in the research on this topic consists of the randomness of the whisker growth, the slow growth rate and many other tricky factors. Herein, with Ti2SnC-Sn as a new platform, fast tin whisker growth is realized to facilitate the research. The whisker morphology is found to be modulated by oxide film. A striated whisker morphology forms as growing in air, whereas a faceted morphology forms in vacuum.Furthermore, the evolution to the faceted morphology is attributed to the reconstruction of the whisker surface driven by surface energy reduction. The findings might open a new avenue to uncover the myths of this long-standing issue, and thus develop a long-awaited lead-free tin whisker mitigation strategy.

Role of MXene surface terminations in electrochemical energy storage:A review

MXenes are a group of recently discovered 2D materials and have attracted extensive attention since their first report in 2011;they have shown excellent prospects for energy storage applications owing to their unique layered microstructure and tunable electrical properties.One major feature of MXenes is their tailorable surface terminations(e.g.,-F,-O,-OH).Numerous studies have indicated that the composition of the surface terminations can significantly impact the electrochemical properties of MXenes.Nonetheless,the underlying mechanisms are still poorly understood,mainly because of the difficulties in quantitative analysis and characterization.This review summarizes the latest research progress on MXene terminations.First,a systematic introduction to the approaches for preparing MXenes is presented,which generally dominates the surface terminations.Then,theoretical and experimental efforts regarding the surface terminations are discussed,and the influence of surface terminations on the electronic and electrochemical properties of MXenes are generalized.Finally,we present the significance and research prospects of MXene terminations.We expect this review to encourage research on MXenes and provide guidance for usingthese materials for batteries and supercapacitors.

Selective growth of tin whiskers from its alloys on Ti_(2)SnC

The spontaneous growth of metal whiskers has been investigated for more than 70 years.However,there is still no agreement on its growth mechanism,and moreover,new characteristics of this whiskering phenomenon continue to emerge.In this study,Ti_(2)SnC is found to be capable of extracting Sn out of its alloys(Sn Bi,Sn Ag)by selectively growing Sn whiskers,and the Sn whiskers share the features of the traditional whiskers on platings and solders.Replacing the Ti_(2)SnC substrate with Ti C or Si C,under the same conditions,however,the selective growth of Sn whisker does not happen,which means Ti_(2)SnC plays a critical role in it.Based on the unique crystal structure of Ti_(2)SnC,active Sn atoms diffusing through the basal planes of Ti_(2)SnC is proposed to explain the selectivity.The driving force is suggested to be the high interfacial energy between Ti_(2)SnC and tin.This study is of importance to further understand the growth mechanism of metallic whiskers,and it may be also possible to be harnessed to develop paradigm-shifting technologies of metal purification and metallic whisker/nanowire preparation.

Spontaneous Growth of Metal Whiskers on Surfaces of Solids:A Review

Spontaneous metal whisker growth phenomenon has been studied for -70 years, but still resists in- terpretations, which has haunted the electronics-rich systems from the birth of the industry since whiskers may lead to short circuits and hence other disasters. In addition to reliability problems, threat of Pb whiskers to human health is also significant due to the toxicity of the element and its geometry as well as its nanometer size. This issue becomes more attention drawing and urgent due to the restrictions on Pb use in ELI, Japan etc., which phases out the Pb-addition practice to mitigate Sn whiskers. This paper reviews the origin of the whiskering phenomenon and whisker-induced problems, ranging from early in the World War II to the present; details the development of this issue in the electronics-rich systems including the phenomenon, problems and remedies; pictures the long history of the developments of the growth mechanisms and models which are full of hardship and contradictions. New aspects on the spontaneous whisker growth in some different substrates, such as in brasses and MAX phase materials are reviewed in more details. The latter was found to be a promising system to understand the whisker growth phenomenon, with new growth models proposed that may shed new light to the intricate battle field of the metal whisker research in general.

Directly integrated mixed-dimensional van der Waals graphene/perovskite heterojunction for fast photodetection

Mixed-dimensional(2D/3D)van der Waals(vdW)heterostructures made with complementary materials hold a lot of promise in the field of optoelectronic devices.Beyond simple mechanical stacking,directly growing the single-crystal perovskite on 2D materials to construct a high-quality vdW heterojunction can better promote carrier transport.In this work,a monolithic integrated graphene/perovskite heterojunction device is fabricated by directly growing a single-crystal hybrid perovskite on monolayer graphene.Due to the strong inter-face coupling,the hybrid device achieves self-powering behavior and exhibits prominent photoresponse properties with a fast response speed of up to 2.05μs.Moreover,the responsivity and detectivity can be boosted to up to 10.41 A W1 and 4.65×10^(12)Jones under the actuation of3 V bias.This technique not only improves the device performance,but also provides an effective guideline for the development of next-generation directly integrated vdW optoelectronic devices.

Tin whiskers prefer to grow from the [001] grains in a tin coating on aluminum substrate

This work aims at understanding the features of the Sn grains from which whiskers prefe rentially grow.The growth behavior of Sn whiskers on a 50 μm thick hypereutectic Sn-Al alloy coating was observed in situ by mapping the grain orientations before and after aging using the electron backscatter diffraction(EBSD) technique.Sn whiskers were found to grow preferentially from the(001) or near-(001) grains surrounded by the grains having perpendicular orientations,such as(100),(110) and(210).The compre s sive stress in the coating was heterogeneous,and the(001) grains exhibited the higher compressive stress close to the grain boundaries.The orientation relationship between α-Al phase and β-Sn phase was confirmed as(200)_(α-A)||(200)_(β-Sn,[011]_(α-A)||[001]_(β-Sn).The plane matching resulted in approximately0.7 % misfit strain in β-Sn,which had little impact on the growth of whiskers.Dislocations pile-ups were found in the(001) grains and repulsed by the Sn oxide layer,giving the probability of cracking the oxide.Grain boundaries were found between the whisker and underneath grain.The dominant diffusion mode for early whisker growth was grain boundary diffusion aided by pipe diffusion.

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.