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Journal of Materials Science & Technology 2010年第12期26卷 1133-1138页

作者： kezhi li,dongsheng zhang,lingjun guo and hejun li state key laboratory of solidification processing,northwestern polytechnical university,xi an 710072,china [a] state key laboratory of solidification processing northwestern polytechnical university xi'an 710072 china

The hot wall reactor was used to deposit isotropic pyrocarbon. The density of the product was measured by Archimedes method. The fracture morphology and texture of the product were investigated by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Raman spectroscopy was also applied to characterizing the structure of the product. The results show that the density of the product is about 1.31 g/cm^3. The pyrocarbon consists of granular particles with the size of about 1.5 μm under SEM images. Under TEM images, the pyrocarbon is composed of irregular grains and onion-like particles are also detected. The orientation angle （180 deg.） of pyrocarbon reveals its isotropic character. The ID/IG ratio in Raman spectrum is about 1.2, indicating the isotropic feature of the product qualitatively.

关键词： Isotropic pyrocarbon Chemical vapor deposition Structure characterization Onion-like pyrocarbon

Oxidation Protective C/SiC/Si-SiC Multilayer Coating for Carbon/Carbon Composites Applying at 1873 K

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Journal of Materials Science & Technology 2010年第12期26卷 1139-1142页

作者： Yulei zhang,hejun li,xinfa Qiang and kezhi li C/C Composites Research Center,state key laboratory of solidification processing,northwestern polytechnical university,xi an 710072,china [a] C/C Composites Research Center state key laboratory of solidification processing northwestern polytechnical university xi(an 710072 china

A C/SiC/Si-SiC multilayer coating for protecting carbon/carbon （C/C） composites against oxidation was prepared by slurry and pack cementation. X-ray diffraction （XRD） and energy dispersive spectroscopy （EDS） analysis showed that the inner coating obtained from the slurry and pack cementation was a C/SiC gradient layer acting as bonding layer, and the exterior coating formed in the second pack cementation was a Si-SiC double phase coating. Oxidation tests at 1873 K in air showed that the coating exhibited excellent oxidation protective ability and thermal shock resistance. The coating could effectively protect C/C composites from oxidation at 1873 K in air for 170 h and undergo the thermal cycling between 1873 K and room temperature for 8 cycles. The weight loss of the coated C/C composites is due to the formation of cracks and holes in the coating and the volatilization of SiO2 glass at high temperature.

关键词： Carbon/carbon composites Oxidation Coating

Densification and microstructure of carbon/carbon composites prepared by chemical vapor infiltration using ethanol as precursor

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Science china(Technological Sciences) 2010年第8期53卷 2232-2238页

作者： li Wei,zhang ShouYang ,YAN xiaFeng,li hejun&li kezhi state key laboratory of solidification processing,northwestern polytechnical university,xi’an 710072,china 1. state key laboratory of solidification processing Northwestern Polytechnical University Xi’an 710072 China

Chemical vapor infiltration of carbon fiber felts with uniform initial bulk density of 0.47 g·cm-3 was investigated at the ethanol partial pressures of 5-20 kPa,as well as the temperatures of 1050,1100,1150 and 1200°***,diluted by nitrogen,was employed as the precursor of pyrolytic *** light microscopy(PLM),scanning electron microscopy and X-ray diffraction were adopted to study the texture of pyrolytic carbon deposited at various temperatures.A change from medium-to high-textured pyrolytic carbon was observed in the sample infiltrated at 1050°***,homogeneous high-textured pyrolytic carbons were deposited at the temperatures of 1100,1150 and 1200°*** angles of 19°-21° were determined for different regions in the samples densified at the temperatures ranging from 1100 to 1200°*** electron microscopy of the fracture surface after bending test indicated that the prepared carbon/carbon composite samples exhibited a pseudo-plastic fracture *** addition,fracture behavior of the carbon/carbon samples was obviously effected by their infiltration *** fracture mode of C/C composites was transformed from shearing failure to tensile breakage with increasing infiltration temperature. Results of this study show that ethanol is a promising carbon source to synthesize carbon/carbon composites with homogeneously high-textured pyrolytic carbon over a wide range of temperatures(from 1100 to 1200°C).

关键词： C/C composites ethanol ICVI high-textured pyrolytic carbon

Fabrication of Isotropic Pyrocarbon at 1400 ℃ by Thermal Gradient Chemical Vapor Deposition Apparatus

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Journal of Wuhan university of Technology(Materials Science) 2009年第5期24卷 728-731页

作者：郭领军 state key laboratory of Thermostructure Composites Materials Northwestern Polytechnical University

An experiment was designed to prepare isotropic pyrocarbon by thermal gradient chemical vapor deposition apparatus. The deposition was performed under ambient atmosphere at 1400 ℃, with natural gas volume flow of 3.5 m^3/h for 80 h. The results show that the thickness and the bulk density of the deposit are about 1.95 g/cm^3 and 10 mm, respectively. The microstructure of the deposit was examined by polarized light microscopy and scanning electron microscopy, which shows that the deposit is constituted of sphere isotropic pyrocarbon, pebble pyrocarbon and laminar pyrocarbon.

关键词： isotropic pyrocarbon chemical vapor deposition laminar pyrocarbon pebble pyrocarbon

X-ray Diffraction and Raman Spectroscopy Characterization of Isotropic Pyrocarbon Obtained by Hot Wall Chemical Vapor Deposition

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Journal of Wuhan university of Technology(Materials Science) 2013年第2期28卷 358-361页

作者：张东生 li kezhi JIA Yan guo lingjun li hejun LU Jinhua state key laboratory of solidification processing Northwestern Polytechnical University

Varying the flow rate of natural gas from 50 to 80 to 120 l/h, isotropic pyrocarbon produced by hot wall chemical vapor deposition at 1000 ℃ were examined by X-ray diffraction and Raman spectroscopy. The X-ray data were evaluated by Scherrer equation, and the intensity ratio of D to G band derived from Raman data was used to evaluate the lateral extension of isotropic pyrocarbon. The experimental results show that the d002-spacing of isotropic pyroearbon decreases from 0.3499 nm to 0.3451 nm, while the stack height increases from 6.5 to 8.4 nm with the increase of flow rate of natural gas. The intensity ratio of D to G band and lateral extension of isotropie pyrocarbon increases with natural gas flow rate increasing. After heat treatment, all the crystallite parameters （stack height, lateral extension, and d002-spacing） decrease, indicating the improvement of the arrangement of the basic structural units of isotropic pyrocarbon.

关键词： isotropic pyrocarbon X-ray diffraction raman spectroscopy chemical vapor deposition characterization

MG63 Osteoblast-like Cells Growth Behaviour on Carbon/Carbon Composites with Different Carbon Matrixes

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Chinese Journal of Mechanical Engineering 2011年第2期24卷 303-308页

作者： zhang Leilei li hejun li kezhi ZHAO Xueni WU Heng CAO Sheng state key laboratory of solidification processing Northwestern Polytechnical University Xi ＇an 710072 China

During the process that implant materials are used for bone replacement,the cell responses to implant materials determine the long-term stability of bone *** microstructure of implant materials is considered as a critical factor that influences the cell ***/Carbon composites（C/C composites） are novel implant materials,but there are few reports on the effect of their microstructure,especially the carbon matrixes and holes,on cell *** this paper,C/C composites with different carbon matrixes are prepared by chemical vapor infiltration and pressure impregnation carbonization technique,*** structure of holes is *** cell responses to C/C composites with different carbon matrixes are evaluated with MG63 osteoblast-like *** morphologies of MG63 osteoblast-like cells on the surface of C/C composites,especially in the holes are assessed by scanning electron microscope,and cell proliferation behavior is evaluated by 3-[4,5-dimethylthiozol-2-yl]-2,5-diphenyltetrazolium bromide（MTT） assay. The results show that MG63 osteoblast-like cells have a lamellar morphology with similar sizes and spreading areas as well as the same proliferation behaviors for C/C composites with different carbon *** matrix shows unapparent influence on the cell growth ***,MG63 osteoblast-like cells have various interactions with the holes of C/C *** cells stride over the holes with 6～8μm in size,and connect with each other or grow along the curvature wall of the holes with a size of 30-40μm;the cells present three-dimensional morphologies inside the holes and display circular shapes along the ridge of the *** cell-material interactions are found according to the size and position of the holes,which provides theoretical foundation for the microstructure design of clinical C/C composites.

关键词： Carbon/Carbon composite matrix osteoblast growth behavior microstructure

Hierarchical,seamless,edge-rich nanocarbon hybrid foams for highly efficient electromagnetic-interference shielding

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Journal of Materials Science & Technology 2021年第13期72卷 154-161页

作者： liyuan Han Qiang Song kezhi li Xuemin Yin Jiajia Sun hejun li Fengpei zhang xinran Ren xi Wang state key laboratory of solidification processing Shannxi Province Key Laboratory of Fiber Reinforced Light Composite MaterialsCarbon/Carbon Composites Research CenterNorthwestern Polytechnical UniversityXi’an710072China

lightweight,flexible,ultrahigh-performance electromagnetic-interfe rence(EMI)shielding materials are urgently required in the areas of aircraft/aerospace,portable and wearable ***,1 D carbon nanotubes(CNT)and carbon nanofibers(CNF)with 2 D edge-rich graphene(ERG)are used to form a lightweight,flexible CNT-ERG-CNF hybrid *** foam was fabricated through a self-sacrificial templating chemical vapor deposition process,where nanocarbons bond through covalent bonding,forming a hierarchical 3 D hybridized carbon *** conductive networks and heterogeneous interfaces were constructed using edge-rich nanocarbons to increase the induced currents and interfacial polarization which makes great contributions to achieve high absorption electromagnetic shielding effectiveness(SEA).The CNT-ERG-CNF hybrid foam exhibits EMI shielding effectiveness(SE)exceeding55.4 dB in the X-band while the specific SE(SSE,SE divided by mass density)achieves 9200 dB cm^(3)g^(-1),which surpasses that of nearly all other carbon-based composite ***,the structural stability and durability of the flexible CNT-ERG-CNF hybrid foams is examined by measuring EMI SE after 10000 times cyclic ***,this work not only provides a new idea for preparing hierarchical carbon materials for a wide range of applications,but presents some fundamental insights for achieving higher absorption losses in EMI shielding materials.

关键词： Electromagnetic interference shielding Edge-rich nanocarbons 3D hierarchical hybrid foams lightweight Flexible

Effects of Carbon Nanotubes by Electrophoretic Deposition on Interlaminar Properties of Two Dimensional Carbon/carbon Composites

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Journal of Wuhan university of Technology(Materials Science) 2017年第5期32卷 994-1000页

作者：黎云玉 guo lingjun li hejun MA Haili 宋强 state key laboratory of So'lidification processing Northwestern Polytechnical University Xi 'an 710072 China Center for Nano Energy Materials Northwestern Polytechnical University Xi'an 710072 China

Carbon nanotubes（CNTs） were deposited uniformly on carbon cloth by electrophoretic deposition（EPD）. Thereafter, CNT-doped clothes were stacked and densified by pyrocarbon via chemical vapor infiltration to fabricate two-dimensional（2 D） carbon/carbon（C/C） composites. Effects of EPD CNTs on interlaminar shear performance and mode Ⅱ interlaminar fracture toughness（GⅡc） of 2 D C/C composites were investigated. Results showed that EPD CNTs were uniformly covered on carbon fibers, acting as a porous coating. Such a CNT coating can obviously enhance the interlaminar shear strength and GⅡc of 2 D C/C composites. With increaing EPD CNTs, the interlaminar shear strength and GⅡc of 2 D C/C composites increase greatly and then decrease, both of which run up to their maximum values, i e, 13.6 MPa and 436.0 J·m-2, when the content of EPD CNTs is 0.54 wt%, 2.27 and 1.45 times of the baseline. Such improvements in interlaminar performance of 2 D C/C composites are mainly beneficial from their increased cohesion of interlaminar matrix, which is caused not only by the direct reinforcing effect of EPD CNT network but also by the capacity of EPD CNTs to refine pyrocarbon matrix and induce multilayered microstructures that greatly increase the crack propagation resistance through ＂crack-blocking and-deflecting mechanisms＂.

关键词： electrophoretic deposition carbon nanotube C/C composite interlaminar performance reinforcing mechanism

Effect of pH on Crystallization of Nanocrystalline Zirconia in a Microwave-hydrothermal Process

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Journal of Wuhan university of Technology(Materials Science) 2016年第1期31卷 68-73页

作者：欧阳海波李翠艳 li kezhi li hejun zhang Yulei College of Materials Science & Technology Shaanxi University of Science & Engineering Xi'an 710021 China state key laboratory of solidification processing Northwestern Polytechnical University Xi'an 710072 China

Nanocrystalline zirconia（ZrO） was synthesized using a microwave-hydrothermal *** effect of pH on the crystallization of the ZrO2 powders was *** phase and microstructure of ZrO2 powders were examined using X-ray diffraction（XRD）,Raman spectroscopy,and transmission electron microscopy（TEM）.Results show that pure m-ZrO2 can be obtained at low pH（pH＆lt;2）.Pure t-ZrO2 is formed at pH = 7 and *** size of the ZrO2 crystals is in the range of 8-26 nm and decreases with increasing *** formation of m-ZrO2 results from the precipitation of ZrO2 from *** t-ZrO2 is formed through the in-situ structural rearrangement of amorphous Zr（OH）*** stabilization of t-ZrO2 is attributed to the small crystal size and the adsorption of hydroxy ions on the surfaces of the crystals.

关键词： microwave-hydrothermal nanocrystalline zirconia crystallization mechanism pH

Low-cost, green synthesis of highly porous carbons derived from lotus root shell as superior performance electrode materials in supercapacitor

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Journal of Energy Chemistry 2016年第1期25卷 26-34页

作者： xin Wang Mengjiao Wang Xuemei zhang hejun li xiaohui guo key Lab of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education and the College of Chemistry and Materials ScienceNorthwest UniversityXi'an 710069ShaanxiChina School of Materials Science and Engineering the State Key Laboratory of Solidification ProcessingNorthwestern Polytechnical UniversityXi'an 710069ShaanxiChina

Facile production of high quality activated carbons from biomass materials has greatly triggered much attention presently. In this paper, a series of interconnected porous carbon materials from lotus root shells biomass are prepared via simple pyrolysis and followed by a KOH activation process. The prepared carbons exhibit high specific surface areas of up to 2961 m^2/g and large pore volume～1.47 cm3/g. In addition, the resultant porous carbons served as electrode materials in supercapacitor exhibit high specific capacitance and outstanding recycling stability and high energy density. In particular, their specific capacitance retention was almost 100% after 10500 cycles at a current density of 2 A/g. Remarkabely, the impact of the tailored specific surface areas of various carbon samples on their capacitive performances is systematically ***, it was believed that the highly-developed porosity features（including surface areas and pore volume and pore size-distributions）, together with the good conductivity of activated carbon species, play a key role in effectively improving the storage energy performances of the porous carbon electrode materials in supercapacitor.

关键词： Carbon Porous Biomass Surface area Capacity