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Nanocrystalline high-entropy hexaboride ceramics enable remarkable performance as thermionic emission cathodes

Fundamental Research 2023年第6期3卷 979-987页

作者： Mengdong Ma Xinyu Yang Hong Meng Zhisheng Zhao julong he Yanhui Chu School of Materials Science and Engineering South China University of TechnologyGuangzhou 510641China Center for High Pressure Science(CHiPS) State Key Laboratory of Metastable Materials Science and TechnologyYanshan UniversityQinhuangdao 066004China School of Materials Science and Engineering Hefei University of TechnologyHefei 230009China

The development of high-entropy borides with combined structural and functional performance holds untold scientific and technological potential,yet relevant studies have been rarely reported.In this work,we report nanocrystalline(La_(0.25)Ce_(0.25)Nd_(0.25)Eu_(0.25))B6 high-entropy rare-earth hexaboride(heReB6-1)ceramics fabricated through the high-pressure sintering of self-synthesized nanopowders for the first time.The as-fabricated samples exhibited a highly dense(96.3%)nanocrystalline(94 nm)microstructure with major(001)fiber textures and good grain boundaries without any impurities,resulting in a remarkable mechanical,electrical,and thermionic emission performance.The results showed that the samples possessed outstanding comprehensive mechanical properties and a high electrical resistivity from room temperature to high temperatures;these were greater than the average values of corresponding binary rare-earth hexaborides,such as a Vickers hardness of 23.4±0.6 GPa and a fracture toughness of 3.0±0.4 MPa•m^(1/2)at room temperature.More importantly,they showed high emission current densities at elevated temperatures,which were higher than the average values of the corresponding binary rare-earth hexaborides.For instance,the maximum emission current density reached 48.3 A•cm^(−2)at 1873 K.Such superior performance makes the nanocrystalline heReB6-1 ceramics highly suitable for potential applications in thermionic emission cathodes.

关键词： High-entropy ceramics hexaborides Nanocrystalline Mechanical properties Thermionic emission

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Extraordinary high-temperature mechanical properties in binder-free nanopolycrystalline WC ceramic

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Journal of Materials Science & Technology 2022年第2期97卷 169-175页

作者： Hongfeng Dong Baozhong Li BoBo Liu Yang Zhang Lei Sun Kun Luo Yingju Wu Mengdong Ma Bing Liu Wentao Hu julong he Dongli Yu Bo Xu Zhisheng Zhao Yongjun Tian Center for High Pressure Science(CHiPS) State Key Laboratory of Metastable Materials Science and TechnologyYanshan UniversityQinhuangdao 066004China School of Materials Science and Engineering Shaanxi University of TechnologyHanzhong 723001China

From the perspective of high-temperature applications,materials with excellent high-temperature mechanical properties are always desirable.The present work demonstrates that the binder-free nanopolycrystalline WC ceramic with an average grain size of 103 nm obtained by high-pressure and hightemperature sintering exhibits excellent mechanical properties at both room temperature and high temperature up to 1000℃.Specifically,the binder-free nanopolycrystalline WC ceramic still maintains a considerably high Vicker hardness H_(V)of 23.4 GPa at 1000℃,which is only 22%lower than the room temperature H_(V).This outstanding thermo-mechanical stability is superior to that of typical technical ceramics,e.g.SiC,Si_(3)N_(4),Al_(2)O_(3),etc.Nanocrystalline grains with many dislocations,numerous low-energy,highly stableΣ2 grain boundaries,and a relatively low thermal expansion coefficient,are responsible for the observed outstanding high-temperature mechanical properties.

关键词： Binder-free nanopolycrystalline WC High-pressure and high-temperature synthesis High-temperature mechanical properties Dislocation Σ2 Grain boundary

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Fibre Metallurgy Characteristic of Short Cast Iron Fibre and Its Applications for Diamond Wheel

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Journal of Materials Science & Technology 1994年第4期10卷 246-250页

作者： Shizhen CheN Dongli YU julong he Yongjun TIAN and Dongchun LI (Yanshan University, Qinhuangdao City, 066004, China) Yanshan Univ Qinhuangdao China

A kind of diamond grinding wheel bonded by short cast iron fibres has been developed. ln comparison with high quality bronze bonded diamond grinding wheel. the new wheel was more suitable to grind hard and brittle materials like ceramics. For Si3N4, the grinding efficiency has been raised two times and the grinding ratio five times

关键词： Cast Fibre Metallurgy Characteristic of Short Cast Iron Fibre and Its Applications for Diamond Wheel MPa

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Discovery of carbon-based strongest and hardest amorphous material

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National Science Review 2022年第1期9卷 25-35页

作者： Shuangshuang Zhang Zihe Li Kun Luo julong he Yufei Gao Alexander V.Soldatov Vicente Benavides Kaiyuan Shi Anmin Nie Bin Zhang Wentao Hu Mengdong Ma Yong Liu Bin Wen Guoying Gao Bing Liu Yang Zhang Yu Shu Dongli Yu Xiang-Feng Zhou Zhisheng Zhao Bo Xu Lei Su Guoqiang Yang Olga P.Chernogorova Yongjun Tian Center for High Pressure Science (CHiPS) State Key Laboratory of Metastable Materials Science and Technology Yanshan University Key Laboratory for Microstructural Material Physics of hebei Province School of Science Yanshan University Department of Engineering Sciences and Mathematics Lule a University of Technology Department of Physics Harvard University Center for High Pressure Science and Technology Advanced Research Department of Materials Science Saarland University Key Laboratory of Photochemistry Institute of Chemistry University of Chinese Academy of Sciences Baikov Institute of Metallurgy and Materials Science Russian Academy of Sciences

Carbon is one of the most fascinating elements due to its structurally diverse allo tropic forms stemming from its bonding varieties(sp,sp~2 and sp~3).Exploring new forms of carbon has been the eternal theme of scientific research.herein,we report on amorphous(AM) carbon materials with a high fraction of sp~3 bonding recovered from compression of fullerene C60 under high pressure and high temperature,previously unexplored.Analysis of photoluminescence and absorption spectra demonstrates that they are semiconducting with a bandgap range of 1.5-2.2 eV,comparable to that of widely used AM silicon.Comprehensive mechanical tests demonstrate that synthesized AM-Ⅲ carbon is the hardest and strongest AM material known to date,and can scratch diamond crystal and approach its strength.The produced AM carbon materials combine outstanding mechanical and electronic properties,and may potentially be used in photovoltaic applications that require ultrahigh strength and wear resistance.

关键词： amorphous carbon ultrahard ultrastrong semiconductor phase transition

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Experimental Observation of Cubic C_3N_4 Compound in Carbon Nitride Thin Films

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Journal of Materials Science & Technology 1999年第5期15卷 480-482页

作者： Furen XIAO Dongli YU Yongjun TIAN julong he Dongchun LI and Wenkui WANG(College of Materials Science and Chemical Engineering, Yanshan University, Qinhuangdao 066004, China To whom correspondence should be addressed E-mail: fhcl@*** ) College of Materials Science and Chemical Engineering Yanshan University Qinhuangdao 066004 China

Cubic C3N4 compound in the C-N thin films on Si and NaCl substrates was prepared by ion beam sputtering of a pure graphite target with discharge gas of pure N2. X-ray photoelectron spectroscopy indicated that nitrogen atoms combined with sp2- and sp3- coordinated C atoms in the film, respectively. X-ray diffraction, selected area electron diffraction and high-resolution electron microscopy were used to identify the cubic C3N4 phase. The results reconfirm the ab initio calculations on metastable structure in C-N compounds

关键词： Thin Experimental Observation of Cubic C3N4 Compound in Carbon Nitride Thin Films Rev

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heat-treated glassy carbon under pressure exhibiting superior hardness,strength and elasticity

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Journal of Materiomics 2021年第1期7卷 177-184页

作者： Meng Hu Shuangshuang Zhang Bing Liu Yingju Wu Kun Luo Zihe Li Mengdong Ma Dongli Yu Lingyu Liu Yufei Gao Zhisheng Zhao Yoshio Kono Ligang Bai Guoyin Shen Wentao Hu Yang Zhang Ralf Riedel Bo Xu julong he Yongjun Tian Center for High Pressure Science(CHiPS) State Key Laboratory of Metastable Materials Science and TechnologyYanshan UniversityQinhuangdao066004China Fachbereich Material-und Geowissenschaften Technische Universitat DarmstadtOtto-Berndt-Str.3Darmstadt64287Germany Key Laboratory for Microstructural Material Physics of hebei Province School of ScienceYanshan UniversityQinhuangdao066004China High Pressure Collaborative Access Team(HPCAT) Advanced Photon SourceArgonne National LaboratoryIL60639USA Institute of High Energy Physics Chinese Academy of ScienceBeijing100049China

Glassy carbon(GC)is a type of non-graphitizing disordered carbon material at ambient pressure and high temperatures,which has been widely used due to its excellent mechanical properties.here we report the changes in the microstructure and mechanical properties of GC treated at high pressures(up to 5 GPa)and high temperatures.The formation of intermediate sp2-sp3 phases is identified at moderate treatment temperatures before the complete graphitization of GC,by analyzing synchrotron X-ray diffraction,Raman spectra,and transmission electron microscopy images.The intermediate metastable carbon materials exhibit superior mechanical properties with hardness reaching up to 10 GPa and compressive strength reaching as high as 2.5 GPa,nearly doubling those of raw GC,and improving elasticity and thermal stability.The synthesis pressure used in this study can be achieved in the industry on a commercial scale,enabling the scalable synthesis of this type of strong,hard,and elastic carbon materials.

关键词： Glassy carbon Industrially achievable pressure sp2-sp3 intermediate carbon Hardness Strength Elasticity

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Synthesis and oxidation behavior of boron-substituted carbon powders by hot filament chemical vapor deposition

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Science China(Technological Sciences) 2008年第9期51卷 1464-1469页

作者： HU QianKu WU QingHua SUN Guang LUO XiaoGuang XU Bo YU DongLi he julong State Key Laboratory of Metastable Materials Science and Technology Yanshan UniversityQinhuangdao 066004China School of Materials Science and Engineering Henan Polytechnic UniversityJiaozuo 454010China

Boron-substituted carbon powder, BxC1-x with x up to 0.17, has been successfully synthesized by hot filament chemical vapor deposition. The boron concentration in prepared BxC1-x samples can be controlled by varying the relative proportions of methane and diborane. X-ray diffraction, transmission electron microscopy, and electron energy loss spectrum confirm the successful synthesis of an amorphous BC5 compound, which consists of 10―20 nm particles with disk-like morphology. Thermogravimetry measurement shows that BC5 compound starts to oxidize ap-proximately at 620℃ and has a higher oxidation resistance than carbon.

关键词： carbon boron hot filament chemical vapor deposition substitution oxidation behavior

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Degradation of Azo dye direct black BN based on adsorption and microwave-induced catalytic reaction

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Frontiers of Environmental Science & Engineering 2018年第1期12卷 71-83页

作者： Shanshan Ding Wen Huang Shaogui Yang Danjun Mao julong Yuan Yuxuan Dai Jijie Kong Cheng Sun Huan he Shiyin Li Limin Zhang . State Key Laboratory of Pollution Control and Resource Reuse School of the Environment Nanjing University Nanjing 210023 China.. School of Environment Nanjing Normal University Nanjing 210023 China

The novel microwave catalyst MgFe204-SiC was synthesized via sol-gel method, to remove azo dye Direct Black BN （DB BN） through adsorption and microwave-induced catalytic reaction. Microwave- induced catalytic degradation of DB BN, including adsorption behavior and its influencing Factors of DB BN on MgFc204-SiC were investigated. According to the obtained results, il indicated thai the pseudo-second-order kinetics model was suitable fbr the adsorption of DB BN onto MgFc204-SiC. Besides, the consequence of adsorption isotherm depicted that the adsorption of DB BN was in accordance with the Langmuir isotherm, which verified that the singer layer adsorption of MgF%O4- SiC was dominant than the multi-layer one. The excellent adsorption capacities of MgFe204-SiC were kept in the range of initial pH from 3 to 7. In addition, it could be concluded that the degradation rate of DB BN decreased over ten percent after the adsorption equilibrium had been attained, and thc results from the result of comparative experiments manitbsted that the adsorption process was not conducive to the process of microwave-induced catalytic degradation. The degradation intermediates and products of DB BN were identified and determined by GC-MS and LC-MS. Furthermore, combined with the catalytic mechanism of MgFe204-SiC, the proposed degradation pathways of DB BN were the involution of microwave-induced OH and holes in this catalytic system the breakage of azo bond, hydroxyl substitution, hydroxyl addition, nitration reaction, dcamination reaction, dcsorbate reaction, dehydroxy group and ring-opening reaction.

关键词： AdsorptionMicrowave-induced catalytic degradationDirect black BNDegradation pathway

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Multithreaded Conductive Carbon:1D Conduction in 3D Carbon

Multithreaded Conductive Carbon:1D Conduction in 3D Carbon

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中国晶体学会第六届学术年会暨会员代表大会（极端条件晶体...

作者： Yilong Pan Meng Hu Mengdong Ma Zihe Li Yufei Gao Mei Xiong Guoying Gao Zhisheng Zhao Yongjun Tian julong he State Key Laboratory of Metastable Materials Science and Technology Yanshan University

Carbon possesses various allotropes with diverse electronic properties from insulation to conduction due to the sp,sp,and spbonding types.here,a new sp-spcarbon allotrope,called C,is proposed.Cpresents a lilac-like st...

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低频声波作用下液滴群氢氧同位素效应实验与理论分析

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应用基础与工程科学学报 2022年第6期30卷 1357-1365页

作者：柏文文魏加华杨海娇贺巨龙时洋李琼青海大学水利电力学院黄河上游生态保护与高质量发展实验室三江源生态与高原农牧业国家重点实验室水利部江河源区水生态治理与保护重点实验室青海西宁810016 清华大学水沙科学与水利水电工程国家重点实验室清华大学水利水电工程系北京100084

声波能引起流体介质中微滴群携带运动、碰撞团聚并促进重力沉降.本文旨在研究声波干预下河水和雨水源液滴群同位素响应特征.通过室内实验和理论分析,研究了环境和液滴物理参数对沉降滴群D-^(18)O同位素值的影响.研究发现:(1)声波干预后... 详细信息

声波能引起流体介质中微滴群携带运动、碰撞团聚并促进重力沉降.本文旨在研究声波干预下河水和雨水源液滴群同位素响应特征.通过室内实验和理论分析,研究了环境和液滴物理参数对沉降滴群D-^(18)O同位素值的影响.研究发现:(1)声波干预后液滴群特征粒径增大,液滴沉降过程中会与环境水汽发生同位素交换,其同位素值受滴群参数(粒径分布和浓度)和声波参数(频率、声强及作用时间)的综合影响;(2)液滴群同位素理论计算值能较好拟合δ^(18)O和δD的线性关系并反映与沉降环境的交叉接近现象,相对误差在5.53%以内.本文所研究的大气同位素特征,对野外降水同位素变化特征的认识具有一定的借鉴意义.

关键词：低频声波液滴声波团聚氢氧同位素环境水汽

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