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NiCoLDH nanosheets grown on MOF-derived Co_(3)O_(4) triangle nanosheet arrays for high-performance supercapacitor

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Journal of Materials science & Technology 2021年第3期62卷 60-69页

作者： Xuemin Yin Hejun Li Ruimei Yuan Jinhua Lu State Key Laboratory of Solidification Processing Carbon/Carbon Composites Research CenterNorthwestern Polytechnical UniversityXi’an 710072China

Hierarchical Co_(3)O_(4)@NiCoLDH nanosheets(NSs)were prepared on carbon cloth through a multistep method,containing Metal-organic frameworks(MOF)-templated thermal annealing and *** triangle-shaped Co_(3)O_(4 NSs)were firstly obtained by thermal treatment of MOF templates in ***,ultrathin NiCoLDH_(NSs)were in-situ electrodeposited on the surface of Co_(3)O_(4NSs),constructing a core-shell *** the unique hierarchical structure,high conductivity of Co_(3)O_(4 NSs)core and large surface area of NiCoLDHNSs shell,the Co_(3)O_(4)@NiCoLDH_(NSs)array served as supercapacitor electrode exhibits excellent electrochemical properties,such as high specific capacitance of 1708 F g^(-1)(850 C g^(-1))at a current density of 1 A g^(-1),good rate capability,and excellent cycling ***,the asymmetric supercapacitor assembled by Co_(3)O_(4)@NiCoLDH_(NSs)and activated carbon,also displays superior electrochemical perfo rmance with high energy density and power ***,the strategy of constructing core-shell structure based on MOF templates could be extended to other electrochemical fields.

关键词： NiCoLDH Co_(3)O_(4) Core-shell Supercapacitor MOF

The Infiltration Process and Texture Transition of 2D C/C Composites

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Journal of Materials science & Technology 2009年第1期25卷 109-114页

作者： Hejun Li Guozhong Xu Kezhi Li Chuang Wang Wei Li Miaoling Li carbon/carbon Composites research center Key Laboratory of Ultrahigh Temperature Composites Northwestern Polytechnical University Xi＇an 710072 China

2D needle-punched fiber felt was infiltrated by a kind of rapid isothermal chemical vapor infiltration technique. The infiltration process and texture transition of the infiltrated C/C composites were investigated. The porosity and the variations of the cumulative pore volume were determined by mercury porosimetry. The texture of matrix carbon was studied under a polarized light microscope. The results show that the relative mass gain of the sample increases directly as the infiltration time at the initial stage until 20 h, and subsequently the increasing rate of the relative mass gain decreases gradually with the prolonging of infiltration time. Three layers of pyrocarbon were formed around fibers. Low-textured pyrocarbon was obtained at the initial stage. With the densification going on, high-textured pyrocarbon was formed on the surface of low-textured pyrocarbon. Then, low-textured pyrocarbon was produced again during the final stage of densification. The texture transition is ascribed to the variation of the ratio of cumulative inner surface area to volume of pores and the gas partial pressure in pores.

关键词： C/C composites Isothermal chemical vapor infiltration (ICVI) Pyrocarbon Mercury porosimetry Polarized light microscope

Ablation Mechanism of carbon/carbon Composites Modified by HfC–SiC in Two Conditions Under Oxyacetylene Torch

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Journal of Materials science & Technology 2017年第1期33卷 71-78页

作者： Ke-Zhi Li Tao Duan Jia-Ping Zhang Ning-Kun Liu Mao-Yan Zhang State Key Laboratory of Solidification Processing Carbon/Carbon Composites Research Center Northwestern Polytechnical University Xi'an 710072 China

C/C-HfC-SiC composites prepared by precursor infiltration and pyrolysis process were ablated by oxyacetylene torch under two different flame conditions. The ablation performance of the composites was investigated in the heat flux of 2.38 MW/m2 （HF-L） and 4.18 MW/m2 （HF-H） for 60 s. The mechanical denudation in 4.18 MW/m2 （HF-H） was higher than that in 2.38 MW/m2 （HF-L）, while the results indicated that the composites had a similar and good ablation property under two different flame conditions. C/C- HfC-SiC composites can adapt the heat flux from 2.38 MW/m2 to 4.18 MW/m2. The Hf02 was not melted completely in the heat flux of 2.38 MW/m2 （HF-L）. So, both Hf02 and Si02 layers acted as an effective barrier to the transfer of heat and oxidative gases into the underlying carbon substrate. SiO2 was severely consumed in 4.18 MW/m2 （HF-H）, where the HfO2 molten layer played a more important role in protecting the inner composite.

关键词： carbon/carbon composites Corrosion Ablation performance

Spatiotemporal characteristics and influencing factors of vegetation water use efficiency on the Tibetan Plateau in 2001–2020

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Journal of Geographical sciences 2025年第1期35卷 39-64页

作者： HE Chenyang WANG Yanjiao YAN Feng LU Qi School of Ecological and Environmental science East China Normal University Institute of Ecological Conservation and Restoration Chinese Academy of Forestry National Climate center China Meteorological Administration

Water use efficiency （WUE）,as a pivotal indicator of the coupling degree within the carbon–water cycle of ecosystems,holds considerable importance in assessment of the carbon–water balance within terrestrial ***,in the context of global warming,WUE evolution and its primary drivers on the Tibetan Plateau remain *** study employed the ensemble empirical mode decomposition method and the random forest algorithm to decipher the nonlinear trends and drivers of WUE on the Tibetan Plateau in 2001–*** indicated an annual mean WUE of 0.8088 gC/mm·m2across the plateau,with a spatial gradient reflecting decrease from the southeast toward the *** manifesting monotonous trends of increase or decrease in WUE accounted for 23.64%and 9.69%of the total,***,66.67%of the region exhibited trend reversals,i.e.,39.94%of the area of the Tibetan Plateau showed transition from a trend of increase to a trend of decrease,and 26.73%of the area demonstrated a shift from a trend of decrease to a trend of *** factors accounted for 70.79%of the variability in *** leaf area index and temperature served as the major driving forces of WUE variation.

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Cu/Co mixed hierarchical tubular heterostructures for alkaline supercapacitors

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Journal of Materiomics 2021年第3期7卷 640-647页

作者： Ruimei Yuan Hejun Li Xuemin Yin Peipei Wang Jinhua Lu Leilei Zhang carbon/carbon Composites research center Northwestern Polytechnical UniversityXi’an710072China

The hierarchical hollow structures of electrode materials s of supercapacitors is effective for the large specific surface area and fast ions and charge *** nanowires as self-engaged templates provide sites and paths for the nucleation and growth of the ***,Cu atoms can disperse into metal organic frameworks(MOFs)to form Cu-Co mixed oxides and construct *** this case,Cu nanowires are used as a template and an activated part to improve the internal electronic *** electrochemical performance can be improved due to these ***,Cu nanowires and MOFs are combined via a mild and efficient approach to fabricate Cu-Co-O/CuO electrode *** electrode exhibits excellent electrochemical performance with a specific capacitance of 834.1 F g^(-1) at 1 A g^(-1).The assembled asymmetric supercapacitor(ASC)shows an ultra-high energy density of 40.7 W h kg^(-1) at a power density of 915 W kg^(-1) and a good capacitance retention after 8000 cycles in a 2 M KOH aqueous *** results otained in this work indicate a strategy of the combination of reactive metals with metal organic frameworks used as electrode materials for electrochemical supercapacitors.

关键词： Oxidizable nanowires MOF-Derived Hierarchical Hollow Energy storage

Sublayer design and ablation resistance of CVD-TaC alternate coatings with different crystallite morphologies for C/C composites

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Journal of Materials science & Technology 2023年第10期141卷 1-10页

作者： Jing’an Kong Yulei Zhang Hanhui Wang Guohui Chen Wenhan Gai Pengfei Zhang Hejun Li State Key Laboratory of Solidification Processing Carbon/Carbon Composites Research CenterNorthwestern Polytechnical UniversityXi’anShanxi 710072China

Tantalum carbon(TaC)alternate coatings with sublayers comprised of different crystallite morphologies were prepared on carbon/carbon composites by chemical vapor *** ablative behaviors and defending mechanisms were both *** specimen with the sublayer composed of columnar crystals exhibited a better ablation resistance due to the toughness enhancement induced by the lami-nated ***,the mechanical denudation of the sample only containing acicular crystals and the coating spallation caused by superfluous gaseous products of the sample with the sublayer composed of nanocrystals both indicate their inferior anti-ablation *** is believed that the results will be helpful for the structural design and practical application of chemical vapor deposition(CVD)alternate coatings.

关键词： Alternate coating Chemical vapor deposition Crystallite morphology carbon/carbon composite Ablation behavior

(Hf_(0.5)Ta_(0.5))C ultra-high temperature ceramic solid solution nanowires

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Journal of Materials science & Technology 2023年第16期147卷 91-101页

作者： Hui Chen Yulei Zhang Yanqin Fu Jiachen Meng Qing Miao Jianhua Zhang Hejun Li State Key Laboratory of Solidification Processing Carbon/Carbon Composites Research CenterNorthwestern Polytechnical UniversityXi’an 710072China carbon Matrix Composites research Institute Henan Academy of SciencesZhengzhou 450046China

Ultra-high temperature ceramic(UHTC)nanowires are potential reinforcement materials due to it combines the perfect properties of bulk materials and unique geometric properties of one-dimensional(1D)***,developing 1D nanomaterials that have excellent morphology and structure retention in ultra-high temperature environments is of prime importance to bring their outstanding performance into full ***,we report the novel solid solution((Hf_(0.5)Ta_(0.5))C)ceramic nanowires,which could not only maintain morphological and structural stability at 1900°C but also exhibit 1D nanostructures under oxyacetylene scouring and ablation at 2300°*** morphology evolution of nanowires obeys the Rayleigh instability mechanism,and the internal structure and element distribution of nanowires remain unchanged even if the surface atoms are *** fascinating nanowires are demonstrated to have great potential as ideal reinforcement materials of composite materials and toughening phases of ceramics that are applied in ultra-high temperature environments,as well as excellent performance enhancement phases of functional *** work may provide new insights into the development of ceramic nanowires and widen their applications.

关键词： (Hf_(0.5)Ta_(0.5))C solid solution nanowires Vapor-liquid-solid mechanism Catalyst/nanowire interface High-temperature stability Ablation resistance

Modification of Maxwell model for conductivity prediction of carbon nanotubes-filled polymer composites with tunneling effect

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Applied Mathematics and Mechanics(English Edition) 2025年第1期46卷 25-36页

作者： Jue ZHU Longyuan LI Ningtao ZHU Zhejiang Provincial Engineering research center for the Safety of Pressure Vessel and Pipeline Key Laboratory of Impact and Safety Engineering (Ningbo University) Ministry of Education School of Engineering Computing and Mathematics University of Plymouth Xi'an Zhanshi Testing & Engineering Co.Ltd.

carbon nanotubes(CNTs) have garnered great attention in recent years due to their outstanding electrical, thermal, and mechanical properties. The incorporation of small amounts of CNTs in polymers can substantially improve the sensitivity of the polymer's electrical conductivity. This paper presents a modified Maxwell model to evaluate the electrical conductivity of CNTs-filled polymer composites by introducing a transition zone to account for the tunneling effect. In this modified Maxwell model, the CNTs-filled polymer composite is modeled as a three-phase composite, consisting of a matrix(polymer), inclusions(CNTs), and a transition zone(tunneling zone). The effective electrical conductivity(EEC) of the composite is calculated based on the volume fractions and electrical conductivities of the matrix, inclusions, and transition zone. The model's validity is confirmed through the use of available test data, which demonstrates its capability to accurately capture the nonlinear conductivity behavior observed in CNTs-polymer composites. This study offers valuable insights into the design of high-performance conductive polymer nanocomposites, and enhances the understanding of electrical conduction mechanisms in CNT-dispersed polymer composites.

关键词： Nanoclay

Laser ablation mechanism of ZrC-SiC-MoSi_(2) ternary ceramic modified C/C

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Journal of Materials science & Technology 2023年第18期149卷 214-224页

作者： Li Geng Su Cheng Guanghai Liu Qiangang Fu Hejun Li Shaanxi carbon/carbon Composites Engineering Technology research center Northwestern Polytechnical UniversityXi’an 710072China National Engineering research center of Ceramic Matrix Composite Manufacture Technology Xi’an 710000China

C/C composites were prepared by chemical vapor infiltration(CVI),and then were subjected to Si,Zr,and MoSi_(2) reactive melt infiltration(RMI)to obtain C/C-SiC,C/C-SiC-ZrC,and C/C-SiC-ZrC-MoSi_(2) *** ablation behavior of these three composites was evaluated by high-energy CO 2 laser *** surface temperature distribution of composite materials was simulated by finite element *** results show that the ablation resistance mechanisms of the three materials are entirely *** C/C-SiC-ZrC-MoSi_(2) com posite showed the best ablation performance among *** is at-tributed to the lower oxygen permeability and richer heat dissipation mechanism of the C/C-SiC-ZrC-MoSi_(2) composite within the total temperature threshold.

关键词： C/C composite Laser ablation UHTCs modification Thermodynamic analysis Finite element simulation