Preparation and Analysis of Carbon Fiber-Silicon Carbide Thermally Conductive Asphalt Concrete

An experimental investigation into the thermal conductivity of CF-SiC two-phase composite asphalt concrete is presented.The main objective of this study was to verify the possibility of using SiC powder instead of mineral powder as the thermal conductive filler to prepare a new type of asphalt concrete and improve the efficiency of electrothermal snow and ice melting systems accordingly.The thermal conductivity of asphalt concrete prepared with different thermally conductive fillers was tested by a transient plane source method,and the related performances were measured.Then the temperature rise rate and surface temperature were studied through field heating tests.Finally,the actual ice melting efficiency of the thermally conductive asphalt concrete was evaluated using an effective electrothermal system.As shown by the experimental results,the composite made of SiC powder and carbon fiber has a high thermal conductivity.When SiC replaces mineral powder,the thermal conductivity of the asphalt mixture increases first and then decreases with the increase of carbon fiber content.In the present study,in particular,the thermal conductivity attained a peak when the carbon fiber content was 0.2%of the aggregate mass.

Influence of Carbon Content on Element Diffusion in Silicon Carbide-Based TRISO Composite Fuel

The coating layers of Tri-structural Isotropic Particles(TRISO)serve to protect the kernel and act as barriers to fission products.Sintering aids in the silicon carbide matrix variably react with TRISO coating layers,leading to the destruction of the coating layers.Investigating how carbon content affects element diffusion in silicon carbide-based TRISO composite fuel is of great significance for predicting reactor safety.In this study,silicon carbide-based TRISO composite fuels with different carbon contents were prepared by adding varying amounts of phenolic resin to the silicon carbide matrix.X-ray Diffraction(XRD)and Scanning Electron Microscopy(SEM)were employed to characterize the phase composition,morphology,and microstructure of the composite fuels.The elemental content in each coating layer of TRISO was quantified using Energy-Dispersive X-ray Spectroscopy(EDS).The results demonstrated that the addition of phenolic resin promoted the uniform distribution of sintering aids in the silicon carbide matrix.The atomic percentage(at.%)of aluminum(Al)in the pyrolytic carbon layer of the TRISO particles reached its lowest value of 0.55%when the phenolic resin addition was 1%.This is because the addition of phenolic resin caused the Al and silicon(Si)in the matrix to preferentially react with the carbon in the phenolic resin to form a metastable liquid phase,rather than preferentially consuming the pyrolytic carbon in the outer coating layer of the TRISO particles.The findings suggest that carbon addition through phenolic resin incorporation can effectively mitigate the deleterious reactions between the TRISO coating layers and sintering aids,thereby enhancing the durability and safety of silicon carbide-based TRISO composite fuels.

Evidence of the Role of Carbon Vacancies in Nickel-Based Ohmic Contacts to n-Type Silicon Carbide

N-wells are created by P＋ ion implantation into Si-faced p-type 4H-SiC epilayer. Ti and Ni are deposited in sequence on the surface of the active regions. Ni2Si is identified as the dominant phase by X-ray diffraction （XRD） analysis after metallization annealing. An amorphous C film at the Ni2 Si/SiC interface is confirmed by an X-ray energy-dispersive spectrometer （XEDS）. The Ni2Si and amorphous C film are etched away selectively,followed by deposition of new metal films without annealing. Measurement of the current-voltage characteristics shows that the contacts are still ohmic after the Ni2 Si and amorphous C film are replaced by new metal films. The sheet resistance Rsh of the implanted layers decreases from 975 to 438f2/D, because carbon vacancies （Vc） appeared during annealing,which act as donors for electrons in SiC.

Structural feature and electronic property of an (8, 0) carbon-silicon carbide nanotube heterojunction

A supercell of a nanotube heterojunction formed by an （8, 0） carbon nanotube （CNT） and an （8, 0） silicon carbide nanotube （SiCNT） is established, in which 96 C atoms and 32 Si atoms are included. The geometry optimization and the electronic property of the heterojunction are implemented through the first-principles calculation based on the density functional theory （DFT）. The results indicate that the structural rearrangement takes place mainly on the interface and the energy gap of the heterojunction is 0.31 eV, which is narrower than those of the isolated CNT and the isolated SiCNT. By using the average bond energy method, the valence band offset and the conduction band offset are obtained as 0.71 and -0.03 eV, respectively.

Preparation and properties of continuous Al-containing silicon carbide fibers

Continuous SiC(OAl) fibers, named KD-A fibers, were prepared by the melt-spinning of ceramic precursor polyaluminocarbosilane, air-curing, and pyrolizing at 1 300 ℃. These fibers contained small amount of aluminum and 7%- 9% oxygen. The KD-A fibers were converted into sintered SiC(Al) fibers, named KD-SA, by sintering at 1 800 ℃. The fibers were characterized by chemical analysis, tensile strength test, SEM and XRD. The tensile strength, elastic modulus and diameter of the KD-A fibers are 2.6 GPa, 210 GPa, 12 - 14 μm, respectively. The KD-A fibers have higher thermal stability, more excellent oxidation resistance than the Nicalon fibers. The properties of the KD-A fibers have reached the level of Hi-Nicalon fibers. The tensile strength, elastic modulus and diameter of the KD-A fibers are 2.1 GPa, 405 GPa, 10 - 12 μm, respectively. The KD-SA fibers with nearly stoichiometric component have stable performance at high temperature, and better creep resistance than the Tyranno SA fibers.

Electrochemical behavior of insulin on pretreated carbon black electrode enhanced with silicon carbide nanostructure

We previously reported the direct electrochemical detection of insulin at bare carbon electrodes. Here a novel modified acetylene carbon black paste electrode(SiC/CB-CPE), based on the outstanding characteristics of silicon carbide nanostructure,was developed for the electrooxidation of insulin in alkaline solution and it was characterized by cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS) in 5 mmol/L Fe(CN)63-/4- solution. It is found that silicon carbide nanostructure doped into the CB-CPE greatly facilitates the redox electrochemistry of Fe(CN)63-/4- probe and the electrochemical oxidation of insulin. The electrooxidation of insulin is a one-electron and one-proton reaction and an irreversible adsorption-controlled electrode process. The anodic oxidation current increases linearly with the concentration of insulin from 1×10-7mol/L to1.2×10-6mol/L in 0.1 mol/L Na2CO3-NaHCO3 buffer solution(pH 10.0) and the detection limit was 50 nmol/L. In addition, the SiC/CB-CPE shows good sensitivity, reproducibility, renewability and capacity of resisting disturbance.

Density functional theory calculation of the properties of carbon vacancy defects in silicon carbide

As a promisingmaterial for quantumtechnology,silicon carbide(SiC)has attracted great interest inmaterials science.Carbon vacancy is a dominant defect in 4H-SiC.Thus,understanding the properties of this defect is critical to its application,and the atomic and electronic structures of the defects needs to be identified.In this study,density functional theorywas used to characterize the carbon vacancy defects in hexagonal(h)and cubic(k)lattice sites.The zero-phonon line energies,hyperfine tensors,and formation energies of carbon vacancies with different charge states(2−,−,0,+and 2+)in different supercells(72,128,400 and 576 atoms)were calculated using standard Perdew-Burke-Ernzerhof and Heyd-Scuseria-Ernzerhof methods.Results show that the zero-phonon line energies of carbon vacancy defects are much lower than those of divacancy defects,indicating that the former is more likely to reach the excited state than the latter.The hyperfine tensors of VC+(h)and VC+(k)were calculated.Comparison of the calculated hyperfine tensor with the experimental results indicates the existence of carbon vacancies in SiC lattice.The calculation of formation energy shows that the most stable carbon vacancy defects in the material are VC 2+(k),VC+(k),VC(k),VC−(k)and VC 2−(k)as the electronic chemical potential increases.

Preparation and Characterization of Axial Gradient Silicon Carbide Fibers with Sinusoidal Electrical Resistivity

Two types of silicon carbide fibers with sinusoidal electrical resistivity were prepared by using different pyrolysis technology. The relationship between the microstructure and the electrical resistivity of these fibers was investigated and compared. The results indicated that carbon layer was the main conductive phase in the SiC fibers obtained by means of one step pyrolysis, whereas a free carbon phase governed the conductivity of the SiC fibers prepared through two step pyrolysis mode.

Influence of pyrolysis temperature on structure and dielectric properties of polycarbosilane derived silicon carbide ceramic

β-SiC ceramic powders were obtained by pyrolyzing polycarbosilane in vacuum at 800-1200 °C. The β-SiC ceramic powders were characterized by TGA/DSC, XRD and Raman spectroscopy. The dielectric properties of β-SiC ceramic powders were investigated by measuring their complex permittivity by rectangle wave guide method in the frequency range of 8.2-18 GHz. The results show that both real part ε′ and imaginary part ε″ of complex permittivity increase with increasing pyrolysis temperature. The mechanism was proposed that order carbon formed at high temperature resulted in electron relaxation polarization and conductance loss, which contributes to the increase in complex permittivity.

Fabrication of solid-phase-sintered Si C-based composites with short carbon fibers

Solid-phase-sintered Si C-based composites with short carbon fibers（Csf/SSi C） in concentrations ranging from 0 to 10wt% were prepared by pressureless sintering at 2100°C. The phase composition, microstructure, density, and flexural strength of the composites with different Csf contents were investigated. SEM micrographs showed that the Csf distributed in the SSi C matrix homogeneously with some gaps at the fiber/matrix interfaces. The densities of the composites decreased with increasing Csf content. However, the bending strength first increased and then decreased with increasing Csf content, reaching a maximum value of 390 MPa at a Csf content of 5wt%, which was 60 MPa higher than that of SSi C because of the pull-out strengthening mechanism. Notably, Csf was graphitized and damaged during the sintering process because of the high temperature and reaction with boron derived from the sintering additive B4C; this graphitization degraded the fiber strengthening effect.

Prefabrication of SiC whiskers through induction of carbon fiber

A new way to prepare SiC whiskers through the induction of carbon fiber was suggested. With the processing steps of opening furnace firstly and then shutting it, rice hall, as the only raw material, was carbonified to get excess quantity of Si in rice hull. After a certain catalyzer was added, SiC whiskers were prepared by means of the induction of carbon fiber. The component and morphology of the whisker were analyzed by XRD, SEM and TEM. The results reveal that the diameters of the whiskers range in 0.5-2μm and their lengths in 100-500μm. The whiskers are straightβ-SiC crystals with smooth surface. The whisker is homogeneous and its productivity is 100%. Two kinds of formation mechanisms, both VLS mechanism and vapor formation mechanism, are involved during the growth of the whiskers. But the vapor formation mechanism relatively plays a key role.

氧化硼对Al_(2)O_(3)-SiC-C质浇注料力学性能的影响

为了利用氧化硼“间接烧结”特性,进一步提升Al_(2)O_(3)-SiC-C质浇注料的力学性能,以氧化硼(≤0.075 mm)为助烧剂,制备了以FM60莫来石颗粒、致密刚玉、碳化硅、α-Al_(2)O_(3)微粉等为主要原料的浇注料,探究了氧化硼细粉加入量(加入质量分数分别为0、0.2%、0.4%和0.6%)对Al_(2)O_(3)-SiC-C质浇注料结构与性能的影响。结果表明,添加氧化硼细粉会显著提升浇注料的加水量,但其有利于晶须状莫来石的生成,从而加强骨料和基质间的结合强度,试样的力学性能得到明显提升。但当氧化硼细粉加入量提高至0.6%(w)时,试样中莫来石晶须长径比减小,试样的强度降低。综合以上结果,氧化硼最佳加入量为0.4%(w)。

Mesoporous silicon carbide nanofibers with in situ embedded carbon for co-catalyst free photocatalytic hydrogen production

Silicon carbide （SIC） has been considered a promising metal-free photocatalyst due to its unique photoelectrical properties and thermal/chemical stability. However, its performance suffers from the fast recombination of charge carriers. Herein, we report mesoporous SiC nanofibers with in situ embedded graphitic carbon （SiC NFs-Cx） synthesized via a one-step carbothermal reduction between electrospun carbon nanofibers and Si powders. In the absence of a noble metal co-catalyst, the hydrogen evolution efficiency of SiC NFs-Cx is significantly improved under both simulated solar light （180.2 μmol.g-1.h-1） and visible light irradiation （31.0 ~amol-g-l-h-~） in high-pH solution. The efficient simultaneous separation of charge carriers plays a critical role in the high photocatalytic activity. The embedded carbon can swiftly transfer the photogenerated electrons and improve light absorption, whereas the additional hydroxyl anions （OH-） in high- pH solution can accelerate the trapping of holes. Our results demonstrate that the production of SiC NFs-Cx, which contains exclusively earth-abundant elements, scaled up, and is environmentally friendly, has great potential for practical applications. This work may provide a new pathway for designing stable, low- cost, high efficiency, and co-catalyst-free photocatalysts.

碳化硅纳米材料及其衍生碳在超级电容器领域的应用

超级电容器由于充放电速度快、循环寿命长、成本低、环境友好等特性在众多储能器件中脱颖而出。在各类电极材料中,碳化硅(SiC)纳米材料及其衍生碳因其高稳定性、优异的导电性等优势被认为是极具应用前景的超级电容器电极材料。本文首先系统地阐述了SiC纳米材料及其衍生碳的常用制备方法;然后,详细综述了SiC纳米材料及其衍生碳在超级电容器应用中的研究进展,总结“高导电碳材料复合”、“杂原子掺杂”、“赝电容材料复合”、“多级孔结构的设计”、“化学活化”等电化学性能的提升策略;最后,对SiC纳米材料及其衍生碳在超级电容器储能领域中应用存在的挑战和机遇进行展望。

碳纤维/氮化硅复合陶瓷的制备及其电磁屏蔽性能研究

优异的电磁屏蔽材料是保护人体健康和仪器设备正常工作必不可少的选择。通过放电等离子烧结制备含碳纤维的氮化硅基陶瓷,具备着良好电磁屏蔽性能的同时,也保持着一定的机械强度。首先,碳纤维的引入导致复合陶瓷的介电常数增加,样品表面阻抗失配增强,大部分电磁波被反射。其次,高含量碳纤维的加入,在氮化硅基体中形成完整的三维导电网络骨架,复合陶瓷的电导率最高达到2.15 S·m^(-1)。入射至样品内部的电磁波被导电骨架形成的介电损耗所吸收。最后,加入7 wt.%碳纤维后,复合陶瓷的维氏硬度、断裂韧性和电磁屏蔽效能分别达到11.90 GPa、6.05 MPa·m^(1/2)和46 dB。

C/SiC复合材料表面SiC过渡层的包埋法制备与性能

[目的]碳/碳化硅(C/SiC)复合材料是航空航天领域最有发展前景的高温热防护结构材料之一,但其表面由于制备过程中化学气相渗透而造成粗糙度低、与涂层间结合强度差的问题有待解决。[方法]以Si粉、C粉和少量Al_(2)O_(3)粉为原料,通过包埋法在C/SiC基体表面制备了SiC涂层。[结果]该涂层与基体之间具有较好的化学亲和性,热膨胀系数匹配度高,表面状态改善情况好。SiC涂层的表面粗糙度(Ra)相较于C/SiC基体实现了从1.732μm到5.531μm超2倍的提升,且涂层与基体结合良好,平均抗拉结合强度达到了4.946 MPa。[结论]该方法处理后的C/SiC复合材料满足了后续制备功能化涂层的要求。

用后铁沟料加入量对Al_(2)O_(3)-SiC-C质浇注料性能的影响

为提高用后耐火材料的再利用率,以棕刚玉、用后铁沟料、白刚玉、碳化硅、α-Al_(2)O_(3)微粉、SiO_(2)微粉等为主要原料,制备了Al_(2)O_(3)-SiC-C质浇注料。探究了用后铁沟料加入量(加入质量分数分别为0、14%、28%、42%和56%)对浇注料性能的影响。结果表明,随用后铁沟料加入量的增加,浇注料的加水量显著增加,试样经1450℃保温3 h热处理后由膨胀转变为收缩,试样经110℃保温24 h及1450℃保温3 h热处理后的体积密度、常温抗折强度、抗侵蚀性能均呈现下降趋势,但当用后铁沟料加入量不超过28%(w)时,性能下降幅度较小。将用后铁沟料加入量为28%(w)的浇注料用于1080和1350 m3高炉铁沟支沟与渣沟,取得了良好服役效果,主体结构服役周期大于70 d。

Effect of composition and structure on specific resistivity of SiC fibers

Four kinds of SiC fibers with different specific resistivities were prepared by the pyrolysis of cured polycarbosilane fiber. The results show that SiC fibers with different specific resistivities can be obtained by changing the curing and pyrolysis conditions. And the free carbon content and the ability to crystallize no longer affect the specific resistivities notably with the time when the fiber is covered with an excess carbon layer, and the fiber has a low specific resistivity. The excess carbon layer in the circular outer part is originated from the re-pyrolysis and deposition of hydrocarbon volatiles. The removal of the carbon by oxidative treatment may affect the surface property and also promote the magnitude of specific resistivity. The influence of the surface property on the specific resistivity can be considerable and should not be neglected.

纤维增强塑料在体育运动器材中的应用

体育运动器材设计制备融合了材料学、机械设计学、力学原理等多门学科知识,其中材料是体育运动器材的主要影响元素。纤维材料拥有绝缘性好、耐高温、质轻、高强度、高弹等优点。本文介绍了玻璃纤维、碳纤维、硼纤维、高强高模合成纤维、碳化硅纤维五种不同类型纤维增强塑料,并对这五种纤维在体育运动器材中的应用研究进行了综述。

有机硅及钛酸酯改性碳纤维树脂基复合材料力学性能研究

为了增韧纯环氧树脂基碳纤维复合材料,改善其力学性能,采用VARTM成型工艺制备有机硅改性碳纤维树脂基复合材料,使用傅里叶红外光谱仪、电子万能试验机、落锤式冲击试验机和SEM研究了改性后的环氧树脂官能团和化学键以及复合材料的拉伸、弯曲、冲击性能,并对其断口进行分析。结果表明:当有机硅质量分数为2%,钛酸酯偶联剂添加质量分数为0.4%时,复合材料的各项力学性能达到最佳,拉伸强度为751.55 MPa,提高了111.4%;弯曲强度为1023.64 MPa,相比未改性的复合材料提高了69.6%;冲击韧性为88.51 kJ·m^(-2),比纯环氧树脂碳纤维复合材料提高了61.3%。