Protective Graphite Coating for Two-Dimensional Carbon/Carbon Composites

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.

SiC-Si-ZrSiO_4 Multiphase Oxidation Protective Coating for Carbon/Carbon Composites

In order to improve the anti-oxidation property of carbon/carbon （C/C） composites, a novel SiC-Si-ZrSiO4 multiphase oxidation protective coating was produced on the surface of C/SiC coated carbon/carbon compo ites by a pack cementation technique. The phase composition and microstructure of the as-prepared coatings were characterized by XRD （X-ray diffraction）, SEM （scanning electron microscopy） and EDS （energy dispersive spectroscopy）. Oxidation behavior of the multiphase coated C/C composites was also investigated. It showed that the as-prepared coating characterized by excellent oxidation resistance and thermal shock re- sistance could effectively protect C/C composites from oxidation at 1773 K for 57 h in air and endure the thermal cycle between 1773 K and room temperature for 12 times, whereas the corresponding weight loss is only 1.47%. The excellent oxidation protective ability of the SiC-Si-ZrSiO4 coating could be attributed to the C/SiC gradient inner layer and the multiphase microstructure of the coating.

Fabrication method and microstructural characteristics of coal-tar-pitchbased 2D carbon/carbon composites

The lignin-cellulosic texture of wood was used to produce two-dimensional （2D） carbon/carbon （C/C） composites using coal tar pitch. Ash content tests were conducted to select two samples among the different kinds of woods present in lran, including walnut, white poplar, cherry, willow, buttonwood, apricots, berry, and blue wood. Walnut and white poplar with ash contents of 1.994wt% and 0.35 lwt%, respectively, were selected. The behavior of these woods during pyrolysis was investigated by differential thermal analysis （DTA） and thermo gravimetric （TG） analysis. The bulk density and open porosity were measured after carbonization and densification. The mierostruc- tural characteristics of samples were investigated by scanning electron microscopy （SEM）, X-ray diffraction （XRD）, and Fourier-transform infrared （FT-IR） spectroscopy. The results indicate that the density of both the walnut and white poplar is increased, and the open porosity is decreased with the increasing number of carbonization cycles. The XRD patterns of the wood charcoal change gradually with increasing py- rolysis temperature, possibly as a result of the ultra-structural changes in the charcoal or the presence of carbonized coal tar pitch in the composite＇s body.

Preparation and Microstructure of a Si-Mo Fused Slurry Coating on Carbon/Carbon Composites for Oxidation Protection

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℃.

Si-Al-Ir Oxidation Resistant Coating for Carbon/Carbon Composites by Slurry Dipping

A Si-Al-lr oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping. The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-lr coating were studied by XRD （X-ray diffraction）, SEM （scanning electron microscopy）, and isothermal oxidation test at 1773 K in air, respectively. The surface of the as-prepared Si-Al-lr coating was dense and the thickness was approximately 100 um. Its anti-oxidation property was superior to that of the inner SiC coating. The weight loss of SiC/Si- Al-lr coated carbon/carbon composites was less than 5 wt. pct after oxidation at 1773 K in air for 79 h. The local oxidation defects in the coating may result in the failure of the SiC/Si-Al-Ir coating.

Influence of Thermal Shock on the Mechanical Behavior of Si-SiC Coated Carbon/Carbon Composites

Si-SiC coating was prepared on the surface of carbon/carbon （C/C） composites by a two-step technique of pack cementation, and the influences of thermal shock between 1773 K and room temperature in air on the mechanical property and fracture behavior of the coated C/C were studied. The results show that, after thermal shock between !773 K and room temperature for 5, 10 and 15 times, the flexural strength of coated composites increases by 4.29%, 15.00% and 24.20%, respectively. The toughness of the coated C/C enhances gradually during the thermal shock test. The improvement of the mechanical property after the thermal shock test is primarily caused by the weakening of the fiber-matrix interface and the reduction of residual thermal stresses by thermal shock.

Behavior of pure and modified carbon/carbon composites in atomic oxygen environment

Atomic oxygen （AO） is considered the most erosive particle to spacecraft materials in low earth orbit （LEO）. Carbon fiber, car-bon/carbon （C/C）, and some modified C/C composites were exposed to a simulated AO environment to investigate their behaviors in LEO. Scanning electron microscopy （SEM）, AO erosion rate calculation, and mechanical property testing were used to characterize the material properties. Results show that the carbon fiber and C/C specimens undergo significant degradation under the AO bombing. According to the effects of AO on C/C-SiC and CVD-SiC-coated C/C, a condensed CVD-SiC coat is a feasible approach to protect C/C composites from AO degradation.

MoSi_2-SiC-Si-B Anti-oxidation Coating on Carbon/Carbon Composites by Fused Slurry

A simple and low cost method was used to fabricate a MoSi2-SiC-Si-B anti-oxidation coating on Carbon/Carbon composites.The microstructures and crystalline structures of the as-obtained coating were characterized by optical microscopy,X-ray diffractometry and scanning electron microscopy with energy dispersive spectroscopy.The results indicate that the coating with 200-250 μm in thickness has two-layer structures,which composed of SiC bonding-layer and MoSi2-Si main-layer containing boron and SiC particles.The MoSi2-SiC-Si-B coating has excellent oxidation resistance at temperature range of 1200-1400 ℃ and the maximum cumulative weight loss per unit area is only 0.01 g/cm2 for 20-hours of isothermal cyclic oxidation.

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

During the process that implant materials are used for bone replacement,the cell responses to implant materials determine the long-term stability of bone replacement.The microstructure of implant materials is considered as a critical factor that influences the cell responses.Carbon/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 behavior.In this paper,C/C composites with different carbon matrixes are prepared by chemical vapor infiltration and pressure impregnation carbonization technique,respectively.The structure of holes is analyzed.The cell responses to C/C composites with different carbon matrixes are evaluated with MG63 osteoblast-like cells.The 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 matrixes.Carbon matrix shows unapparent influence on the cell growth behavior.Besides,MG63 osteoblast-like cells have various interactions with the holes of C/C composites.The 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 holes.Diverse 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.

Effect of SiC whiskers on the oxidation protective properties of SiC coatings for carbon/carbon composites

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Improved oxidation resistance of chemical vapor reaction SiC coating modified with silica for carbon/carbon composites

To protect carbon/carbon (C/C) composites from oxidation, a SiC coating modified with SiO2 was prepared by a complex technology. The inner SiC coating with thickness varying from 150 to 300 μm was initially coated by chemical vapor reaction (CVR): a simple and cheap technique to prepare the SiC coating via siliconizing the substrate that was exposed to the mixed vapor (Si and SiO2) at high temperatures (1 923?2 273 K). Then the as-prepared coating was processed by a dipping and drying procedure with tetraethoxysilane as source materials to form SiO2 to fill the cracks and holes. Oxidation tests show that, after oxidation in air at 1 623 K for 10 h and thermal cycling between 1 623 K and room temperature 5 times, the mass loss of the CVR coated sample is up to 18.21%, while the sample coated with modified coating is only 5.96%, exhibiting an obvious improvement of oxidation and thermal shock resistance of the coating. The mass loss of the modified sample is mainly contributed to the reaction of C/C substrate with oxygen diffusing through the penetrating cracks formed in thermal shock tests.

Effect of Thermal Shock and Oxidation on Mechanical Property of Carbon/Carbon Composites with a Silicide Coating

A SiC whisker-toughened MoSi2-SiC-Si coating was prepared on carbon/carbon (C/C) composites surface by a two-step technique of slurry and pack cementation, and the effects of thermal shock and oxidation on the mechanical property of the coated C/C were studied. The flexural strength of C/C composites was improved by 6.8% after coated by SiC whisker-toughened MoSi2-SiC-Si. After thermal cycle between 1773 K and room temperature in air for 10 times, the mass loss of the coated sample was 5.08% and the percentage of remaining strength was 81.97%. After oxidation at 1773K in air for 60 min, the mass loss of the coated sample was 2.57% and the percentage of remaining strength was 89.63%. The decrease of the flexural strength during the thermal cycle and oxidation tests was primarily due to the oxidation of C/C substrate resulting from the cracking of coating.

Microstructure and thermal conductivity of carbon/carbon composites made with different kinds of carbon fibers

The microstructure and surface state of three kinds of polyacrylonitrile-based carbon fibers (T700,T300 and M40) before and after high temperature treatment were investigated. Also,the pyrocarbon and thermal conductivity of carbon/carbon composites with different carbon fibers as preform were studied. The results show that M40 carbon fiber has the largest crystallite size and the least d002,T300 follows,and T700 the third. With the increase of heat treatment temperature,the surface state and crystal size of carbon fibers change correspondingly. M40 carbon fiber exhibits the best graphitization property,followed by T300 and then T700. The different microstructure and surface state of different carbon fibers lead to the different microstructures of pyrocarbon and then result in the different thermal conductivities of carbon/carbon composites. The carbon/carbon composite with M40 as preform has the best microstructure in pyrocarbon and the highest thermal conductivity.

Prediction on Carbon/Carbon Composites Ablative Performance by Artificial Neutral Net

A preliminary estimation of ablation property for carbon-carbon composites by artificial neutral net （ANN） method was presented. It was found that the carbon-carbon composites＇ density, degree of graphitization and the sort of matrix are the key controlling factors for its ablative performance. Then, a brief fuzzy mathematical relationship was established between these factors and ablative performance. Through experiments, the performance of the ANN was evaluated, which was used in the ablative performance prediction of C/C composites. When the training set, the structure and the training parameter of the net change, the best match ratio of these parameters was achieved. Based on the match ratio, this paper forecasts and evaluates the carbon-carbon ablation performance. Through experiences, the ablative performance prediction of carbon-carbon using ANN can achieve the line ablation rate, which satisfies the need of precision of practical engineering fields.

Effect of nanofibers at surface of carbon fibers on microstructure of carbon/carbon composites during chemical vapor infiltration

Before densification by chemical vapor infiltration,carbon or SiC nanofibers were grown on the surface of carbon fibers by catalytic chemical vapor deposition using electroplated Ni as catalyst.The modification and mechanism of nanofibers on the pyrocarbon deposition during chemical vapor infiltration were investigated.The results show that the nanofibers improve the surface activity of the carbon fibers and become active nucleation centers during chemical vapor infiltration.They can induce the ordered deposition of pyrocarbon and adjust the interface bonding between pyrocarbon and carbon fibers during the infiltration.

Thermal Fatigue Behavior of SiC/MBAS Glass Coated Carbon/Carbon Composites

The thermal fatigue behavior of C/C composites coated with the SiC/MBAS glass (MoSi2 particle-containing boron aluminosilicate glass) coating, prepared by the two-step process of the pack cementation and procoating-sintering, was investigated in present paper. The experimental results indicated that the SiC/MBAS glass coating had an excellent thermal shock resistance in air at temperature up to 1873 K. During quick thermal cycle between 1873K and room temperature in air, the decrease of mass and mechanical property of the coated C/C composites was all slight. After thermal cycle for 50 times, the mass loss of the SiC/MBAS glass coated sample was only 0.22%; additionally, the remaining ratio of strength and modulus was no less than 95.2% and 99.4%, respectively. The decrease of the mechanical property during the thermal cycle was primarily due to the damnification of the fiber/matrix interfaces and the oxidation of the coated samples with oxygen.

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

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＂.

Microstructural study of the ablation behaviors of 3D fine weave pierced Carbon/Carbon composites using plasma torch at ultra-high temperature

A simple and effective method of testing ablation behaviors of carbon/carbon composites at high temperature was provided, which used plasma torch as the heater. The ablation resistance of 3D fine weave pierced carbon/carbon composites at high temperature was also studied. The results show that temperature of the plasma flame is very high which is much closer to the real work environment of carbon/carbon composites. The factors that affect the ablation characters of carbon/carbon composites depend on both the properties of their components and the environmental conditions in which the material is placed. The ablation behaviors of C/C composites change from the center flame region predominantly influenced by sublimation of graphite to the region close to the outer flame influenced mainly by oxidization of graphite. The sublimation ability of carbon matrix is equal to that of carbon fibers but the oxidization ability of carbon fibers is significantly enhanced compared to that of carbon matrix.

Ti_(3)C_(2)T_(x) MXene/carbon composites for advanced supercapacitors:Synthesis,progress,and perspectives

MXenes are a family of two-dimensional(2D)layered transition metal carbides/nitrides that show promising potential for energy storage applications due to their high-specific surface areas,excellent electron conductivity,good hydrophilicity,and tunable terminations.Among various types of MXenes,Ti_(3)C_(2)T_(x) is the most widely studied for use in capacitive energy storage applications,especially in supercapacitors(SCs).However,the stacking and oxidation of MXene sheets inevitably lead to a significant loss of electrochemically active sites.To overcome such challenges,carbon materials are frequently incorporated into MXenes to enhance their electrochemical properties.This review introduces the common strategies used for synthesizing Ti_(3)C_(2)T_(x),followed by a comprehensive overview of recent developments in Ti_(3)C_(2)T_(x)/carbon composites as electrode materials for SCs.Ti_(3)C_(2)T_(x)/carbon composites are categorized based on the dimensions of carbons,including 0D carbon dots,1D carbon nanotubes and fibers,2D graphene,and 3D carbon materials(activated carbon,polymer-derived carbon,etc.).Finally,this review also provides a perspective on developing novel MXenes/carbon composites as electrodes for application in SCs.