Two-dimensional carbon/carbon(2D C/C)composites are a special class of carbon/carbon composites,generally obtained by combining resin-impregnated carbon fiber clothes,which are then cured and carbonized.This study dea...Two-dimensional carbon/carbon(2D C/C)composites are a special class of carbon/carbon composites,generally obtained by combining resin-impregnated carbon fiber clothes,which are then cured and carbonized.This study deals with the preparation of a protective coating for these materials.This coating,based on graphite,was prepared by the slurry method.The effect of graphite and phenolic resin powders with different weight ratios was examined.The results have shown that the coating slurry can fill the pores and cracks of the composite surface,thereby densifying the surface layer of the material.With the increase of the graphite powder/phenolic resin weight ratio,the coating density is enhanced while the coating surface flatness decreases;moreover,the protective ability of coating against erosion first increases(from 1:3 to 2:2)and then decreases(from 2:2 to 3:1).When the weight ratio is about 1:1,the coating for 2D C/C composites exhibits the best erosion resistance,which greatly aids these materials during gas quenching.In this case,the erosion rate is decreased by approximately 41.5%at the impact angle of 30°and 52.3%at normal impact,respectively.This can be attributed to the ability of the coating slurry to infiltrate into the substrate,thereby bonding the fibers together and increasing the compactness of the 2D C/C composites.展开更多
A coating of composition Si-40Mo (wt pct) was prepared by fused slurry coating method on the two-dimensional carbon/carbon (2D-C/C) composite to improve oxidation resistance. In the procedure of the fabrication, pure ...A coating of composition Si-40Mo (wt pct) was prepared by fused slurry coating method on the two-dimensional carbon/carbon (2D-C/C) composite to improve oxidation resistance. In the procedure of the fabrication, pure St slurry inner layer in the pre-coating was necessary to apply because of infiltration of liquid Si into the substrate during the sintering. The coating consists of Si continuous phase and MoSi2 particles. In addition, the infiltration of Si into the substrate and the SiC reaction layer between the coating and the C/C composite were observed. Oxidation behavior of coated and uncoated C/C composites was studied in cyclic mode. The oxidation resistance and the thermal shock resistance of the Si-Mo fused slurry coating were quite excellent at 1370℃.展开更多
Polysiloxane(PSO)was adopted as the matrix of the repair agents,and SiCeZrB_(2)powder was used as the filler,to repair the prefabricated defects on the SiCeZrB_(2)/SiC(SZS)coating of carbon/carbon(C/C)composites.The r...Polysiloxane(PSO)was adopted as the matrix of the repair agents,and SiCeZrB_(2)powder was used as the filler,to repair the prefabricated defects on the SiCeZrB_(2)/SiC(SZS)coating of carbon/carbon(C/C)composites.The repair agents were brushed on the defect areas and then underwent preoxidation(PR)or heat-treatment(HR)in a vacuum.The effects of different treatment processes on the chemical composition,microstructure of the repair agents,and the oxidation resistance behavior of the repaired coating were investigated.The repaired agents after both processes were pyrolyzed and generated SiOC ceramics,and they were well combined with the original coating.The thermal stability of PSO after preoxidation is poorer than that after heat-treatment,resulting in a weight loss rate of 5.88%after oxidation at 1500℃for 270 min,while that of the HR coating is only-0.87%,yet both have been great improvement compared with the unrepaired coating.This work provides an effective and simple approach to repairing damaged coatings for high-temperature applications.展开更多
Carbon fiber reinforced carbon composites(C/Cs),are the most promising high-temperature materials and could be widely applied in aerospace and nucleation fields,owing to their superior performances.However,C/Cs are ve...Carbon fiber reinforced carbon composites(C/Cs),are the most promising high-temperature materials and could be widely applied in aerospace and nucleation fields,owing to their superior performances.However,C/Cs are very susceptible to destructive oxidation and thus fail at elevated temperatures.Though matrix modification and coating technologies with Si-based and ultra-high temperature ceramics(UHTCs)are valid to enhance the oxidation/ablation resistance of C/Cs,it’s not sufficient to satisfy the increasing practical applications,due to the inherent brittleness of ceramics,mismatch issues between coatings and C/C substrates,and the fact that carbonaceous matrices are easily prone to high-temperature oxidation.To effectively solve the aforementioned problems,micro/nano multiscale reinforcing strategies have been developed for C/Cs and/or the coatings over the past two decades,to fabricate C/Cs with high strength and excellent high-temperature stability.This review is to systematically summarize the most recent major and important advancements in some micro/nano multiscale strategies,including nanoparticles,nanowires,carbon nanotubes/fibers,whiskers,graphene,ceramic fibers and hybrid micro/nano structures,for C/Cs and/or the coatings,to achieve high-temperature oxidation/ablation-resistant C/Cs.Finally,this review is concluded with an outlook of major unsolved problems,challenges to be met and future research advice for C/Cs with excellent comprehensive mechanical-thermal performance.It’s hoped that a better understanding of this review will be of high scientific and industrial interest,since it provides unusual and feasible new ideas to develop potential and practical C/Cs with improved high-temperature mechanical and oxidation/ablation-resistant properties.展开更多
Uni-directional carbon/carbon composites with high thermal conductivity are suitable to supply continuous thermal protection for future reentry vehicles since they could reduce surface temperature and ablation rates s...Uni-directional carbon/carbon composites with high thermal conductivity are suitable to supply continuous thermal protection for future reentry vehicles since they could reduce surface temperature and ablation rates simultaneously in harsh environments.In this work,the high thermal conductivity carbon/carbon composites were prepared by chemical vapor infiltration.After heat-treatment,both their open porosity and internal friction increase due to the fiber/matrix thermal expansion mismatch;while their thermal conductive performance become better due to more complete carbon structure.With raising heat-treatment temperature from 1800℃to 2450℃,the mass and linear ablation rates of C/C composites with fibers vertical to the oxyacetylene torch for 60 s decrease from 0.66 mg/s and 2.95μm/s to 0.51 mg/s and 2.05μm/s respectively.The improved ablation resistance is resulted from the increased thermal conductivity from 282 to 508 W/(m·K)and more carbon fibers exposed to the flame during ablation,which have better oxidation resistance than those of carbon matrix.While such ablation rates become larger for composites with fibers parallel to the flame,from 1.02 mg/s and 3.73μm/s to 1.28 mg/s and 5.0μm/s respectively since the ablation occurred more easily through gaps at the fiber/matrix interfaces,which become larger and are always exposed to the flame for this case.展开更多
β-SiC nanowires(SiCNWs) were selectively grown in the interlaminar matrix with a volume fraction of0.65% by applying a pyrocarbon coating on carbon fibers, which realizes the proper reinforcement of C/C composites. T...β-SiC nanowires(SiCNWs) were selectively grown in the interlaminar matrix with a volume fraction of0.65% by applying a pyrocarbon coating on carbon fibers, which realizes the proper reinforcement of C/C composites. The thickness of the pyrocarbon is optimized to 0.5 μm based on the analysis of in-situ fiber strengths with the fracture mirror method. The pyrocarbon coating increased the in-situ fiber strength by^7% and prevent brittle fracture of the composites. Compared with C/C, the interlaminar shear and flexural strength of SiCNW-C/C(10.06 MPa and 162.44 MPa) increase by 158% and 57%. Incorporating SiCNWs changes the crystallite orientations and refines the crystallite size of pyrocarbon matrix. The functions of SiCNWs vary with their loading density. When SiCNWs are sufficient in the matrix, they help reinforcing and improving the critical failure stress of the matrix. When their density decreases to a certain degree, SiCNWs help changing the crystallite orientations of pyrocarbon and toughening the matrix.展开更多
The effect of pyrocarbon(PyC) concentration on the thermal physical and mechanical properties of quasi 3dimensional carbon fiber fabrics reinforced pitch-based carbon matrix composites was investigated.As the PyC conc...The effect of pyrocarbon(PyC) concentration on the thermal physical and mechanical properties of quasi 3dimensional carbon fiber fabrics reinforced pitch-based carbon matrix composites was investigated.As the PyC concen-tration increased from 0 to 22.9vol.%,the tensile strength of pitch-based C/C(Carbon/Carbon) composites initially in-creased and then decreased,so was the tensile modulus.The coefficients of thermal expansion(CTE) were in the sequence of 10.2vol.%<0<22.9vol.%in Z direction.Under the same temperature conditions,PyC layer had a positive-going influence on the TC of the C/C composite,the composite with 22.9vol.%PyC concentrations possessed the highest TC value.The thermal shock resistance of the material with 10.2vol.%PyC concentrations showed the highest value.It is logical to conclude that by adding the a suitable PyC concentration into the carbon fabrics,thermo- mechanical properties,the major concerns for the safety design of load-bearing structural parts,can be tailored,which increase the reliability of pitch-based C/C composites as a structure unit.展开更多
Graphite as a promising anode candidate of K-ion batteries(KIBs)has been increasingly studied currently,but corresponding rate performance and cycling stability are usually inferior to amorphous carbon materials.To pr...Graphite as a promising anode candidate of K-ion batteries(KIBs)has been increasingly studied currently,but corresponding rate performance and cycling stability are usually inferior to amorphous carbon materials.To protect the layer structure and further boost performance,tempura-like carbon/carbon nanocomposite of graphite@pitch-derived S-doped carbon(G@PSC)is designed and prepared by a facile and low-temperature modified molten salt method.This robust encapsulation structure makes their respective advantages complementary to each other,showing mutual promotion of electrochemical performances caused by synergy effect.As a result,the G@PSC electrode is applied in KIBs,delivering impressive rate capabilities(465,408,370,332,290,and 227 m A h g^(-1)at 0.05,0.2,0.5,1,2,and 5 A g^(-1))and ultralong cyclic stability(163 m A g^(-1)remaining even after 8000 cycles at 2 A g^(-1)).On basis of ex-situ studies,the sectionalized K-storage mechanism with adsorption(pseudocapacitance caused by S doping)-intercalation(pitch-derived carbon and graphite)pattern is revealed.Moreover,the exact insights into remarkable rate performances are taken by electrochemical kinetics tests and density functional theory calculation.In a word,this study adopts a facile method to synthesize high-performance carbon/carbon nanocomposite and is of practical significance for development of carbonaceous anode in KIBs.展开更多
Based on the experiments, the standard enthalpy△H■of the possible pyrolysis reactions of the carbon matrix precursor toluene was investigated by means of DFT method UB3LYP/ 3-21G *(based on semi-empirical method UAM...Based on the experiments, the standard enthalpy△H■of the possible pyrolysis reactions of the carbon matrix precursor toluene was investigated by means of DFT method UB3LYP/ 3-21G *(based on semi-empirical method UAM1 and ab initio method UHF/3-21G*). The com- putation results with UB3LYP/3-21G* coincide with the experimental values well. Then, the mechanism for all types of the pyrolysis reactions of toluene was studied by UB3LYP/3-21G * The geometries of the reactant and the product radicals were optimized, meanwhile, the standard thermodynamic parameters of the pyrolysis reaction at different temperatures (298, 773, 843, 963 and 1 073 K) were calculated. The thermodynamic computation result shows that when the pyrolysis temperature of toluene is lower than 963 K, the reaction path supported by thermody- namics is that the C-H bond of the methyl on the benzene ring breaks and bitoluene form, while the temperature increases (about 1 073 K), the thermodynamic calculation result turns to support the reaction path producing phenyl radicals and methyl radicals. This mechanism is in accord with the experiments.展开更多
Targeted regulation of heat transfer in carbon/carbon composite structure is built for cooling electronic device.A three-dimensional data-driven design model coupling genetic algorithm(GA) with self-adaption deep lear...Targeted regulation of heat transfer in carbon/carbon composite structure is built for cooling electronic device.A three-dimensional data-driven design model coupling genetic algorithm(GA) with self-adaption deep learning for targeted regulation of heat transfer in built structure is proposed.The self-adaption deep learning model predicts the temperature of built structure closer to optimal value in GA model.The distributions of pore and carbon fiber bundles in built structure are optimized by the proposed model.The surface temperature of electronic device in the optimized structures is 19.1%-27.5% lower than that in the initial configurations when the porosity of built structure varies from 3% to 11%.The surface temperature of electronic device increases with an increase in porosity.The built structure with carbon fiber bundles near the surface of electronic device and pore distribution in the middle of structure has a higher heat dissipation capacity compared with that in the initial configuration.Besides,the computation time of the proposed model is less than one tenth compared with that of the traditional genetic algorithm.展开更多
Extensive attention has been drawn to the development of carbon fiber composites for their application in brake disks due to the increasing demand for brake disks with high mechanical strength and better tribological ...Extensive attention has been drawn to the development of carbon fiber composites for their application in brake disks due to the increasing demand for brake disks with high mechanical strength and better tribological properties.Herein,we design SiC hexagonal nanopyramids modified carbon/carbon(SiCNPsC/C)composites,in which SiCNPs are radially grafted on the carbon fibers by the combined sol-gel and carbothermal reduction method,and pyrolytic carbon(Py C)matrix is deposited on nucleation sites including carbon fibers and SiCNPs by isothermal chemical vapor infiltration(ICVI).Benefiting from the special structure,SiCNPs-C/C composites exhibit superior mechanical and frictional performance.Compared with C/C composites,SiCNPs-C/C composites have 147%,90.3%,70.6%,and 117.9%improvement in the hardness,interlaminar shear strength,and out-of-plane and in-plane compressive strength,respectively,which is attributed to the optimized fiber/matrix(F/M)interfaces bonding and the enhanced cohesion strength of Py C matrix.In addition,the friction coefficient of SiCNPs-C/C composites increases by 25.5%,and the wear rate decreases by 38.0%.This work provides an optional design thought for the nanomaterials and enlightens the mechanical and frictional modification of composites in the field of the brakes.展开更多
Tantalum carbon(TaC)alternate coatings with sublayers comprised of different crystallite morphologies were prepared on carbon/carbon composites by chemical vapor deposition.Their ablative behaviors and defending mecha...Tantalum carbon(TaC)alternate coatings with sublayers comprised of different crystallite morphologies were prepared on carbon/carbon composites by chemical vapor deposition.Their ablative behaviors and defending mechanisms were both investigated.The specimen with the sublayer composed of columnar crystals exhibited a better ablation resistance due to the toughness enhancement induced by the lami-nated structure.However,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 properties.It is believed that the results will be helpful for the structural design and practical application of chemical vapor deposition(CVD)alternate coatings.展开更多
To prevent the C/C composites from ablation, HfC-HfO_2 protective coating was prepared by supersonic atmospheric plasma spraying. The morphology and microstructure of HfC-HfO_2 coating were characterized by X-ray diff...To prevent the C/C composites from ablation, HfC-HfO_2 protective coating was prepared by supersonic atmospheric plasma spraying. The morphology and microstructure of HfC-HfO_2 coating were characterized by X-ray diffraction and scanning electron microscopy. The ablation resistance test was carried out by an oxyacetylene torch. The results show that the as-prepared coating is dense with little pinholes and crack free. The elements Hf, C and O were uniformly distributed in the cross-section. After ablation for different time, the mass ablation rate fluctuated along with the change of ablation time. The ablation process of the surface coating could be divided into rapid oxidation and solid state sintering stages. During ablation, an Hf CxOy-HfO_2 transitional layer was generated in the coating, which resulted from the active oxidation of Hf C. After cooling, some microcracks were observed on the surface of coating, and the structure of cross-section was broken, which were due to the phase transition of HfO_2.展开更多
To explore the influence of sublayer numbers on the structure evolution and thermal stress level,an alternate coating consisting of ZrC-10 vol.%SiC and ZrC-70 vol.%SiC sublayers was designed in this work.With a basica...To explore the influence of sublayer numbers on the structure evolution and thermal stress level,an alternate coating consisting of ZrC-10 vol.%SiC and ZrC-70 vol.%SiC sublayers was designed in this work.With a basically consistent general thickness,three coatings constituted by 2,4 and 6 sublayers were prepared by plasma spraying,which then were assessed using an oxyacetylene torch under cyclic and long-term exposure.The coating with 6 sublayers was supposed to be the one with the best ablation property,finite element analysis also evidenced its least thermal stress among all these samples.After being ablated for 240 s,the linear and mass ablation rates of the coating with 6 sublayers decreased by 51.27%and 14.41%as compared to that with 4 sublayers.Post-test analysis proved the existence of Si-based products,which help the outmost surface to develop a dense profile.Additionally,the yielded alternate dense/porous scale had a preferable toughness,allowing it to maintain a good integrity.展开更多
Core-shell structured SiC@SiO_(2)nanowires and Si@SiO_(2)nanowires were prepared on the surface of carbon/carbon(C/C)composites by a thermal evaporation method using SiO powders as the silicon source and Ni(NO3)2 as t...Core-shell structured SiC@SiO_(2)nanowires and Si@SiO_(2)nanowires were prepared on the surface of carbon/carbon(C/C)composites by a thermal evaporation method using SiO powders as the silicon source and Ni(NO3)2 as the catalyst.The average diameters of SiC@SiO_(2)nanowires and Si@SiO_(2)nanowires are about 145 nm,and the core-shell diameter ratios are about 0.41 and 0.53,respectively.The SiO_(2)shells of such two nanowires resulted from the reaction between SiO and CO and the reaction of SiO itself,respectively,based on the model analysis.The growth of these two nanowires conformed to the vapor-liquid-solid(VLS)mode.In this mode,CO played an important role in the growth of nanowires.There existed a critical partial pressure of CO(pC)determining the microstructure evolution of nanowires into whether SiC@SiO_(2)or Si@SiO_(2).The value of pC was calculated to be 4.01×10^(-15) Pa from the thermodynamic computation.Once the CO partial pressure in the system was greater than the pC,SiO tended to react with CO,causing the formation of SiC@SiO_(2)nanowires.However,the decomposition of SiO played a predominant role and the products mainly consisted of Si@SiO_(2)nanowires.This work may be helpful for the regulation of the growth process and the understanding of the growth mechanism of silicon-based nanowires.展开更多
基金This paper has obtained the support of the National Natural Science Foundation of China(No.51902039)High-Level Talents Innovation Support Plan of Dalian(No.2020RQ127)Scientific Research Project of Liaoning Provincial Department Education(No.LJKZ0722)。
文摘Two-dimensional carbon/carbon(2D C/C)composites are a special class of carbon/carbon composites,generally obtained by combining resin-impregnated carbon fiber clothes,which are then cured and carbonized.This study deals with the preparation of a protective coating for these materials.This coating,based on graphite,was prepared by the slurry method.The effect of graphite and phenolic resin powders with different weight ratios was examined.The results have shown that the coating slurry can fill the pores and cracks of the composite surface,thereby densifying the surface layer of the material.With the increase of the graphite powder/phenolic resin weight ratio,the coating density is enhanced while the coating surface flatness decreases;moreover,the protective ability of coating against erosion first increases(from 1:3 to 2:2)and then decreases(from 2:2 to 3:1).When the weight ratio is about 1:1,the coating for 2D C/C composites exhibits the best erosion resistance,which greatly aids these materials during gas quenching.In this case,the erosion rate is decreased by approximately 41.5%at the impact angle of 30°and 52.3%at normal impact,respectively.This can be attributed to the ability of the coating slurry to infiltrate into the substrate,thereby bonding the fibers together and increasing the compactness of the 2D C/C composites.
文摘A coating of composition Si-40Mo (wt pct) was prepared by fused slurry coating method on the two-dimensional carbon/carbon (2D-C/C) composite to improve oxidation resistance. In the procedure of the fabrication, pure St slurry inner layer in the pre-coating was necessary to apply because of infiltration of liquid Si into the substrate during the sintering. The coating consists of Si continuous phase and MoSi2 particles. In addition, the infiltration of Si into the substrate and the SiC reaction layer between the coating and the C/C composite were observed. Oxidation behavior of coated and uncoated C/C composites was studied in cyclic mode. The oxidation resistance and the thermal shock resistance of the Si-Mo fused slurry coating were quite excellent at 1370℃.
基金supported by the National Key R&D Program of China(2021YFA0715800,2021YFA0715803)Science Center for Gas Turbine Project(P2021-A-IV-003-001)National Natural Science Foundation of China(52125203,52130205,52002321).
文摘Polysiloxane(PSO)was adopted as the matrix of the repair agents,and SiCeZrB_(2)powder was used as the filler,to repair the prefabricated defects on the SiCeZrB_(2)/SiC(SZS)coating of carbon/carbon(C/C)composites.The repair agents were brushed on the defect areas and then underwent preoxidation(PR)or heat-treatment(HR)in a vacuum.The effects of different treatment processes on the chemical composition,microstructure of the repair agents,and the oxidation resistance behavior of the repaired coating were investigated.The repaired agents after both processes were pyrolyzed and generated SiOC ceramics,and they were well combined with the original coating.The thermal stability of PSO after preoxidation is poorer than that after heat-treatment,resulting in a weight loss rate of 5.88%after oxidation at 1500℃for 270 min,while that of the HR coating is only-0.87%,yet both have been great improvement compared with the unrepaired coating.This work provides an effective and simple approach to repairing damaged coatings for high-temperature applications.
基金supported by the National Natural Science Foundation of China(Nos.91860203,51821091,51872239,52002321 and 52061135102)the China Postdoctoral Science Foundation(No.2019M660265)+3 种基金the Fundamental Research Funds for the Central Universities(China,Nos.G2019KY05116,G2020KY05125)the Innovation Talent Promotion Plan of Shaanxi Province for Science and Technology Innovation Team(No.2020TD003)the Creative Research Foundation of Science and Technology on Thermostructural Composite Materials Laboratory(Nos.614291102010517,5050200015 and 5150200033)the Shaanxi Provincial Education Department of China(No.2020JQ-170)。
文摘Carbon fiber reinforced carbon composites(C/Cs),are the most promising high-temperature materials and could be widely applied in aerospace and nucleation fields,owing to their superior performances.However,C/Cs are very susceptible to destructive oxidation and thus fail at elevated temperatures.Though matrix modification and coating technologies with Si-based and ultra-high temperature ceramics(UHTCs)are valid to enhance the oxidation/ablation resistance of C/Cs,it’s not sufficient to satisfy the increasing practical applications,due to the inherent brittleness of ceramics,mismatch issues between coatings and C/C substrates,and the fact that carbonaceous matrices are easily prone to high-temperature oxidation.To effectively solve the aforementioned problems,micro/nano multiscale reinforcing strategies have been developed for C/Cs and/or the coatings over the past two decades,to fabricate C/Cs with high strength and excellent high-temperature stability.This review is to systematically summarize the most recent major and important advancements in some micro/nano multiscale strategies,including nanoparticles,nanowires,carbon nanotubes/fibers,whiskers,graphene,ceramic fibers and hybrid micro/nano structures,for C/Cs and/or the coatings,to achieve high-temperature oxidation/ablation-resistant C/Cs.Finally,this review is concluded with an outlook of major unsolved problems,challenges to be met and future research advice for C/Cs with excellent comprehensive mechanical-thermal performance.It’s hoped that a better understanding of this review will be of high scientific and industrial interest,since it provides unusual and feasible new ideas to develop potential and practical C/Cs with improved high-temperature mechanical and oxidation/ablation-resistant properties.
基金supported by the National Natural Science Foundation of China [grant numbers 51572223,51727804]
文摘Uni-directional carbon/carbon composites with high thermal conductivity are suitable to supply continuous thermal protection for future reentry vehicles since they could reduce surface temperature and ablation rates simultaneously in harsh environments.In this work,the high thermal conductivity carbon/carbon composites were prepared by chemical vapor infiltration.After heat-treatment,both their open porosity and internal friction increase due to the fiber/matrix thermal expansion mismatch;while their thermal conductive performance become better due to more complete carbon structure.With raising heat-treatment temperature from 1800℃to 2450℃,the mass and linear ablation rates of C/C composites with fibers vertical to the oxyacetylene torch for 60 s decrease from 0.66 mg/s and 2.95μm/s to 0.51 mg/s and 2.05μm/s respectively.The improved ablation resistance is resulted from the increased thermal conductivity from 282 to 508 W/(m·K)and more carbon fibers exposed to the flame during ablation,which have better oxidation resistance than those of carbon matrix.While such ablation rates become larger for composites with fibers parallel to the flame,from 1.02 mg/s and 3.73μm/s to 1.28 mg/s and 5.0μm/s respectively since the ablation occurred more easily through gaps at the fiber/matrix interfaces,which become larger and are always exposed to the flame for this case.
基金supported by the National Natural Science Foundation of China under Grant Nos. 51502242, 51432008, U1435202the Fundamental Research Funds for the Central Universities (3102016ZY009)
文摘β-SiC nanowires(SiCNWs) were selectively grown in the interlaminar matrix with a volume fraction of0.65% by applying a pyrocarbon coating on carbon fibers, which realizes the proper reinforcement of C/C composites. The thickness of the pyrocarbon is optimized to 0.5 μm based on the analysis of in-situ fiber strengths with the fracture mirror method. The pyrocarbon coating increased the in-situ fiber strength by^7% and prevent brittle fracture of the composites. Compared with C/C, the interlaminar shear and flexural strength of SiCNW-C/C(10.06 MPa and 162.44 MPa) increase by 158% and 57%. Incorporating SiCNWs changes the crystallite orientations and refines the crystallite size of pyrocarbon matrix. The functions of SiCNWs vary with their loading density. When SiCNWs are sufficient in the matrix, they help reinforcing and improving the critical failure stress of the matrix. When their density decreases to a certain degree, SiCNWs help changing the crystallite orientations of pyrocarbon and toughening the matrix.
文摘The effect of pyrocarbon(PyC) concentration on the thermal physical and mechanical properties of quasi 3dimensional carbon fiber fabrics reinforced pitch-based carbon matrix composites was investigated.As the PyC concen-tration increased from 0 to 22.9vol.%,the tensile strength of pitch-based C/C(Carbon/Carbon) composites initially in-creased and then decreased,so was the tensile modulus.The coefficients of thermal expansion(CTE) were in the sequence of 10.2vol.%<0<22.9vol.%in Z direction.Under the same temperature conditions,PyC layer had a positive-going influence on the TC of the C/C composite,the composite with 22.9vol.%PyC concentrations possessed the highest TC value.The thermal shock resistance of the material with 10.2vol.%PyC concentrations showed the highest value.It is logical to conclude that by adding the a suitable PyC concentration into the carbon fabrics,thermo- mechanical properties,the major concerns for the safety design of load-bearing structural parts,can be tailored,which increase the reliability of pitch-based C/C composites as a structure unit.
基金the financial support from the National Natural Science Foundation of China(No.91963118)the 111 Project(No.B13013)supported by the Open Project Program of Key Laboratory of Preparation and Application of Environmental Friendly Materials(Jilin Normal University),Ministry of Education,China(No.2020004)。
文摘Graphite as a promising anode candidate of K-ion batteries(KIBs)has been increasingly studied currently,but corresponding rate performance and cycling stability are usually inferior to amorphous carbon materials.To protect the layer structure and further boost performance,tempura-like carbon/carbon nanocomposite of graphite@pitch-derived S-doped carbon(G@PSC)is designed and prepared by a facile and low-temperature modified molten salt method.This robust encapsulation structure makes their respective advantages complementary to each other,showing mutual promotion of electrochemical performances caused by synergy effect.As a result,the G@PSC electrode is applied in KIBs,delivering impressive rate capabilities(465,408,370,332,290,and 227 m A h g^(-1)at 0.05,0.2,0.5,1,2,and 5 A g^(-1))and ultralong cyclic stability(163 m A g^(-1)remaining even after 8000 cycles at 2 A g^(-1)).On basis of ex-situ studies,the sectionalized K-storage mechanism with adsorption(pseudocapacitance caused by S doping)-intercalation(pitch-derived carbon and graphite)pattern is revealed.Moreover,the exact insights into remarkable rate performances are taken by electrochemical kinetics tests and density functional theory calculation.In a word,this study adopts a facile method to synthesize high-performance carbon/carbon nanocomposite and is of practical significance for development of carbonaceous anode in KIBs.
基金the Foundation of board of education of Shanxi province(99K1100).
文摘Based on the experiments, the standard enthalpy△H■of the possible pyrolysis reactions of the carbon matrix precursor toluene was investigated by means of DFT method UB3LYP/ 3-21G *(based on semi-empirical method UAM1 and ab initio method UHF/3-21G*). The com- putation results with UB3LYP/3-21G* coincide with the experimental values well. Then, the mechanism for all types of the pyrolysis reactions of toluene was studied by UB3LYP/3-21G * The geometries of the reactant and the product radicals were optimized, meanwhile, the standard thermodynamic parameters of the pyrolysis reaction at different temperatures (298, 773, 843, 963 and 1 073 K) were calculated. The thermodynamic computation result shows that when the pyrolysis temperature of toluene is lower than 963 K, the reaction path supported by thermody- namics is that the C-H bond of the methyl on the benzene ring breaks and bitoluene form, while the temperature increases (about 1 073 K), the thermodynamic calculation result turns to support the reaction path producing phenyl radicals and methyl radicals. This mechanism is in accord with the experiments.
基金supported by Guangdong Basic and Applied Basic Research Foundation (2023A1515012297)。
文摘Targeted regulation of heat transfer in carbon/carbon composite structure is built for cooling electronic device.A three-dimensional data-driven design model coupling genetic algorithm(GA) with self-adaption deep learning for targeted regulation of heat transfer in built structure is proposed.The self-adaption deep learning model predicts the temperature of built structure closer to optimal value in GA model.The distributions of pore and carbon fiber bundles in built structure are optimized by the proposed model.The surface temperature of electronic device in the optimized structures is 19.1%-27.5% lower than that in the initial configurations when the porosity of built structure varies from 3% to 11%.The surface temperature of electronic device increases with an increase in porosity.The built structure with carbon fiber bundles near the surface of electronic device and pore distribution in the middle of structure has a higher heat dissipation capacity compared with that in the initial configuration.Besides,the computation time of the proposed model is less than one tenth compared with that of the traditional genetic algorithm.
基金the National Natural Science Foundation of China(Nos.51872232,51972271,and 51872234)Natural Science Basic Research Plan in Shaanxi(No.2022JC-25)。
文摘Extensive attention has been drawn to the development of carbon fiber composites for their application in brake disks due to the increasing demand for brake disks with high mechanical strength and better tribological properties.Herein,we design SiC hexagonal nanopyramids modified carbon/carbon(SiCNPsC/C)composites,in which SiCNPs are radially grafted on the carbon fibers by the combined sol-gel and carbothermal reduction method,and pyrolytic carbon(Py C)matrix is deposited on nucleation sites including carbon fibers and SiCNPs by isothermal chemical vapor infiltration(ICVI).Benefiting from the special structure,SiCNPs-C/C composites exhibit superior mechanical and frictional performance.Compared with C/C composites,SiCNPs-C/C composites have 147%,90.3%,70.6%,and 117.9%improvement in the hardness,interlaminar shear strength,and out-of-plane and in-plane compressive strength,respectively,which is attributed to the optimized fiber/matrix(F/M)interfaces bonding and the enhanced cohesion strength of Py C matrix.In addition,the friction coefficient of SiCNPs-C/C composites increases by 25.5%,and the wear rate decreases by 38.0%.This work provides an optional design thought for the nanomaterials and enlightens the mechanical and frictional modification of composites in the field of the brakes.
基金supported by the National Natu-ral Science Foundations of China(Nos.51727804,52130205,and 91860203)the National Key R&D Program of China(No.2021YFA0715803)The authors also thank the Analytical&Testing Center of Northwestern Polytechnical University for the characteri-zation of our samples.
文摘Tantalum carbon(TaC)alternate coatings with sublayers comprised of different crystallite morphologies were prepared on carbon/carbon composites by chemical vapor deposition.Their ablative behaviors and defending mechanisms were both investigated.The specimen with the sublayer composed of columnar crystals exhibited a better ablation resistance due to the toughness enhancement induced by the lami-nated structure.However,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 properties.It is believed that the results will be helpful for the structural design and practical application of chemical vapor deposition(CVD)alternate coatings.
基金supported by the National Natural Science Foundation of China under Grant Nos. U1435202 and 51521061the “111” Project under Grant No. 08040the Research Fund of the State Key Laboratory of Solidification Processing (Northwestern Polytechnical University), China (Grant No. 142-TZ-2016)
文摘To prevent the C/C composites from ablation, HfC-HfO_2 protective coating was prepared by supersonic atmospheric plasma spraying. The morphology and microstructure of HfC-HfO_2 coating were characterized by X-ray diffraction and scanning electron microscopy. The ablation resistance test was carried out by an oxyacetylene torch. The results show that the as-prepared coating is dense with little pinholes and crack free. The elements Hf, C and O were uniformly distributed in the cross-section. After ablation for different time, the mass ablation rate fluctuated along with the change of ablation time. The ablation process of the surface coating could be divided into rapid oxidation and solid state sintering stages. During ablation, an Hf CxOy-HfO_2 transitional layer was generated in the coating, which resulted from the active oxidation of Hf C. After cooling, some microcracks were observed on the surface of coating, and the structure of cross-section was broken, which were due to the phase transition of HfO_2.
基金supported by the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical Univer-sity(No.CX2021006)the National Natural Science Foundation of China(Nos.91860203,51727804 and 52130205)+1 种基金the Fundamental Research Funds for the Central Universities(No.3102019TS0409)the Creative Research Foundation of Science and Technology on Thermo-structural Composite Materials Laboratory。
文摘To explore the influence of sublayer numbers on the structure evolution and thermal stress level,an alternate coating consisting of ZrC-10 vol.%SiC and ZrC-70 vol.%SiC sublayers was designed in this work.With a basically consistent general thickness,three coatings constituted by 2,4 and 6 sublayers were prepared by plasma spraying,which then were assessed using an oxyacetylene torch under cyclic and long-term exposure.The coating with 6 sublayers was supposed to be the one with the best ablation property,finite element analysis also evidenced its least thermal stress among all these samples.After being ablated for 240 s,the linear and mass ablation rates of the coating with 6 sublayers decreased by 51.27%and 14.41%as compared to that with 4 sublayers.Post-test analysis proved the existence of Si-based products,which help the outmost surface to develop a dense profile.Additionally,the yielded alternate dense/porous scale had a preferable toughness,allowing it to maintain a good integrity.
基金This work was supported by the National Natural Science Foundation of China(Nos.52061135102,52101098)Innovation Talent Promotion Plan of Shaanxi Province for Science and Technology Innovation Team(No.2020TD-003)+2 种基金Young Talents for Science and Technology Association supported by Shaanxi Province(No.20200406)the Fund of Key Laboratory of National Defense Science and Technology in Northwestern Polytechnical University(No.JCKYS2020607003)Innovation and Entrepreneurship Training Program for College Students(No.202110699088).
文摘Core-shell structured SiC@SiO_(2)nanowires and Si@SiO_(2)nanowires were prepared on the surface of carbon/carbon(C/C)composites by a thermal evaporation method using SiO powders as the silicon source and Ni(NO3)2 as the catalyst.The average diameters of SiC@SiO_(2)nanowires and Si@SiO_(2)nanowires are about 145 nm,and the core-shell diameter ratios are about 0.41 and 0.53,respectively.The SiO_(2)shells of such two nanowires resulted from the reaction between SiO and CO and the reaction of SiO itself,respectively,based on the model analysis.The growth of these two nanowires conformed to the vapor-liquid-solid(VLS)mode.In this mode,CO played an important role in the growth of nanowires.There existed a critical partial pressure of CO(pC)determining the microstructure evolution of nanowires into whether SiC@SiO_(2)or Si@SiO_(2).The value of pC was calculated to be 4.01×10^(-15) Pa from the thermodynamic computation.Once the CO partial pressure in the system was greater than the pC,SiO tended to react with CO,causing the formation of SiC@SiO_(2)nanowires.However,the decomposition of SiO played a predominant role and the products mainly consisted of Si@SiO_(2)nanowires.This work may be helpful for the regulation of the growth process and the understanding of the growth mechanism of silicon-based nanowires.
