Double SiC coating on carbon/carbon composites against oxidation by a two-step method

To improve the oxidation resistance of C/C composites, a double SiC protective coating was prepared by a two-step technique. Firstly, the inner SiC layer was prepared by a pack cementation technique, and then an outer uniform and compact SiC coating was obtained by low pressure chemical vapor deposition. The microstructures and phase compositions of the coatings were characterized by SEM, EDS and XRD analyses. Oxidation behaviour of the SiC coated C/C composites was also investigated. It was found that the double SiC coating could protect C/C composites against oxidation at 1773 K in air for 178 h with a mass loss of 1.25%. The coated samples also underwent thermal shocks between 1773 K and room temperature 16 times. The mass loss of the coated C/C composites was only 2.74%. Double SiC layer structures were uniform and dense, and can suppress the generation of thermal stresses, facilitating an excellent anti-oxidation coating.

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

In order to effectively employ the unique high temperature mechanical properties of carbon/carbon composite substrates, SiC coatings reinforced by SiC whiskers were prepared by pack cementation method. The effect of SiC whiskers on the oxidation resistance properties of the single-layer coating and double-layer coating was investigated. SiC whiskers in the single-layer SiC coating have little effect on the anti-oxidation property but obviously improve the thermal shock property. The double-layer coating with inner-layer reinforced coating exhibits more perfect anti-oxidation ability than the double-layer coating with SiC inner-layer coating.

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.

Preparation and oxidation property of ZrB_2-MoSi_2/SiC coating on carbon/carbon composites

To improve the oxidation resistance of carbon/carbon composites,ZrB2-MoSi2/SiC coating on the carbon/carbon substrate was prepared.The inner coating of SiC was prepared by pack cementation and the outer coating of ZrB2-MoSi2 was prepared by slurry painting.The phase compositions and microstructures of the coating were characterized by XRD and SEM,respectively.The preparation and the high temperature oxidation property of the coated composites were investigated.The results show that the outer coating of carbon/carbon composites is composed of ZrB2,MoSi2 and SiC phases.The mass losses of the ZrB2-MoSi2/SiC coated samples with SiC nano-whiskers after 30 h and 10 h of oxidation at 1 273 K and 1 773 K were,respectively,5.3% and 3.0%.The ZrB2-MoSi2/SiC coated samples exhibit self-sealing performance and good oxidation resistance at high temperature.

Constructing orthogonally structured graphene nanointerface on SiC nanowires reinforced carbon/carbon composites to boost mechanical strength and strength retention rate

Carbon/carbon composites with higher mechanical strength and better reliability at elevated tempera-tures are urgently needed to satisfy the practical applications requirements.SiC nanowires(SiCNWs)modified C/C(SC-CC)composites have attracted an abundance of attention for their excellent mechanical performance.To further boost the mechanical strengths of composites and maximize the reinforcing efficiency of SiCNWs,we introduce orthogonally structured graphene nanosheets(OGNs)into SC-CC composites,in which OGNs are grafted on the SiCNWs via chemical vapor deposition(CVD)method,forming SC-G-CC composites.Benefiting from the nano-interface effects,uniform stress distribution,strong SiCNWs/PyC interfacial bonding and elevated stress propagation efficiency in the PyC matrix are achieved,thus SC-G-CC composites accomplish brilliant mechanical properties before and after 1,600℃ heat treatment.As temperature rises to 2,100℃,SiCNWs lose efficacy,whereas OGNs with excellent thermal stability continue to play the nano-interface role in the PyC matrix.Therefore,SC-G-CC com-posites show better mechanical performance after 2,100℃ heat treatment,and the mechanical strength retention rate(MSR)of interlaminar shear strength,out-of-plane and in-plane compressive strength of SC-G-CC composites reach 61.0%,55.7%and 55.3%,respectively.This work proposes an alternative thought for maximizing the potentiality of nanomaterials and edifies the mechanical modification of composites.

Selective growth of SiC nanowires in interlaminar matrix for improving in-plane strengths of laminated Carbon/Carbon composites

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.

Anti-oxidation behavior of chemical vapor reaction SiC coatings on different carbon materials at high temperatures

To protect carbon materials from oxidation,SiC coatings were prepared on carbon/carbon(C/C)composites and graphite by chemical vapor reaction.SEM and XRD analyses show that the coatings obtained are composed of SiC grains and micro-crystals. The influence of different carbon substrates on oxidation behavior of coated samples was investigated,and then their oxidation mechanisms were studied.Oxidation test shows that the SiC coated graphite has a better oxidation resistance than SiC coated C/C composites at high temperatures(1 623 K and 1 823 K).In the oxidation process,the oxidation curves of SiC coated C/C composites are linear,while those of SiC coated graphite follow a quasi-parabolic manner.The oxidation mechanism of the former is controlled by chemical reaction while the latter is controlled by oxygen diffusion based on the experimental results.The variation of oxidation behavior and mechanism of SiC coatings on two kinds of carbon substrates are primarily contributed to their structure differences.

TENSILE PROPERTIES AND INTERFACIAL FEATURE OF SiC COATED C/Al COMPOSITE WIRES UNDER ISOTHERMAL HEAT TREATMENT

The effect of different regimes of heat treatment on the tensile strength of SiC coated composite of C fibers reinforced Al wires has been investigated.Their tensile strength may increase under treatment either at 500℃ for 2h or 550℃ for 1h,but decrease over 600℃.After the strength tests of extracted fibers from composite wires,the SiC coating is an excellent protection to C fibers.EPMA and EDAX showed that the C/Al interface of the composite wires is stable under treatment below 600℃,but unstable at 650℃

Influence of Preparation Technology on the Structure and Phase Composition of MoSi_2-Mo_5Si_3 /SiC Multi-coating for Carbon/Carbon Composites

Oxidation protective MoSi2-MosSi3/SiC multi-coatings for carbon/carbon composites were prepared by chemical vapor reaction and slurry-sintering method. The influence of preparation technology on the structure and phase composition of the coating was investigated by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS） and X-ray diffraction （XRD） analyses, and then their relationship was discussed. The results indicate that the Si/Mo ratio of the slurry and sintering processing were two main factors that significantly affected the structure and phase composition of the multi-coating. Appropriate sintering process and relatively high Si/Mo ratio were essential for preparing the multi-coating with dense structure and favorable phase composition. After being sintered at 1723 K for 2 h and with the Si/Mo ratio of the slurry being 4.5 （weight ratio）, a dense structure accompanied by favorable phase composition of the coating can be obtained. When heat treated at 2373 K for I h, this coating became more compact and continuous. Oxidation tests （performed at 1623 and 1823 K） demonstrated that both of these two obtained multi-coatings exhibited better anti-oxidation property than single layer SiC coating.

Simultaneously enhancing mechanical and tribological properties of carbon fiber composites by grafting SiC hexagonal nanopyramids for brake disk application

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.

Oxidation behaviors of carbon fiber reinforced multilayer SiC–Si_(3)N_(4) matrix composites

Oxidation behaviors of carbon fiber reinforced SiC matrix composites(C/SiC)are one of the most noteworthy properties.For C/SiC,the oxidation behavior was controlled by matrix microcracks caused by the mismatch of coefficients of thermal expansion(CTEs)and elastic modulus between carbon fiber and SiC matrix.In order to improve the oxidation resistance,multilayer SiC–Si_(3)N_(4) matrices were fabricated by chemical vapor infiltration(CVI)to alleviate the above two kinds of mismatch and change the local stress distribution.For the oxidation of C/SiC with multilayer matrices,matrix microcracks would be deflected at the transition layer between different layers of multilayer SiC–Si_(3)N_(4) matrix to lengthen the oxygen diffusion channels,thereby improving the oxidation resistance of C/SiC,especially at 800 and 1000℃.The strength retention ratio was increased from 61.9%(C/SiC–SiC/SiC)to 75.7%(C/SiC–Si_(3)N_(4)/SiC/SiC)and 67.8%(C/SiC–SiC/Si_(3)N_(4)/SiC)after oxidation at 800℃for 10 h.

Structural characteristics and formation mechanisms of crack-free multilayer TaC/SiC coatings on carbon-carbon composites

In order to improve high temperature(over 2 273 K)ablation resistance,TaC and TaC/SiC composite coatings were deposited on carbon-carbon composites by CVD method utilizing reactive TaCl5-C3H6-H2-Ar and TaCl5-C3H6-CH3SiCl3-H2-Ar systems respectively.The structure and morphology of these coatings were analyzed by XRD and SEM.The results show that the double carbide coatings have good chemical compatibility during preparation.Two distinctive composition gradients are developed and used to produce multilayer TaC/SiC coatings with low internal stress,free crack and good resistant to thermal shock.A transition layer consisting of either C-TaC or C-SiC formed between the coating and the C/C matrix can reduce the residual stress effectively. The processing parameters were optimized and the possible growth mechanisms for these coatings were proposed.A designing methodology to prepare high performance multilayer TaC/SiC composite coatings was developed.

Thermal conductivity and bending strength of SiC composites reinforced by pitch-based carbon fibers

In this work,pitch-based carbon fibers were utilized to reinforce silicon carbide(SiC)composites via reaction melting infiltration(RMI)method by controlling the reaction temperature and resin carbon content.Thermal conductivities and bending strengths of composites obtained under different preparation conditions were characterized by various analytical methods.Results showed the formation of SiC whiskers(SiC_(w))during RMI process according to vapor–solid(VS)mechanism.SiC_(w) played an important role in toughening the C_(pf)/SiC composites due to crack bridging,crack deflection,and SiC_(w) pull-out.Increase in reaction temperature during RMI process led to an initial increase in thermal conductivity along in-plane and thickness directions of composites,followed by a decline.At reaction temperature of 1600℃,thermal conductivities along the in-plane and thickness directions were estimated to be 203.00 and 39.59 W/(m×K),respectively.Under these conditions,bending strength was recorded as 186.15±3.95 MPa.Increase in resin carbon content before RMI process led to the generation of more SiC matrix.Thermal conductivities along in-plane and thickness directions remained stable with desirable values of 175.79 and 38.86 W/(m×K),respectively.By comparison,optimal bending strength improved to 244.62±3.07 MPa.In sum,these findings look promising for future application of pitch-based carbon fibers for reinforcement of SiC ceramic composites.

沉积温度和碳纳米管对CVD SiC涂层微观形貌的影响

以三氯甲基硅烷（CH3SiCl3）为前驱体,采用化学气相沉积法（Chemical vapor deposition,CVD）,在原位生长有碳纳米管（Carbon nanotubes,CNTs）的C/C复合材料表面制备SiC涂层。用扫描电镜（SEM）和X射线能谱仪（EDS）观察和分析涂层微观形貌及成份。研究沉积温度（1 000~1 150℃）对SiC涂层的表面、截面以及SiC颗粒的微观形貌的影响。结果表明：在1 000℃下反应时,得到晶须状SiC;沉积温度为1 050℃时涂层平整、致密;沉积温度提高到1 100℃时,涂层粗糙,致密度下降;1 150℃下形成类似岛状组织,SiC颗粒团聚长大,涂层粗糙,并有很多裂纹和孔洞,致密度低。对涂层成份和断口形貌研究表明,基体和涂层之间有1个过渡区,SiC涂层和基体之间结合良好。

炭/炭复合材料 SiC /Mo( Six、Al1-x)2抗氧化涂层( 英文)

为了提高炭/炭(C/C)复合材料的高温抗氧化性能,应用多相反应技术在C/C复合材料表面制备SiC/Mo(Six、Al1-x)2复合涂层。利用扫描电镜、电子能谱、X射线衍射仪等测试手段对涂层材料的微观结构和物相组成进行分析,同时研究涂层C/C复合材料在超音速气流中的抗氧化性能。结果表明,C/C复合材料表面形成的抗氧化涂层显示出明显的双层结构,从外向内分别为Mo(Six、Al1-x)2与SiC的复合层和纯SiC层,同时有少量的Mo4.8Si3C0.6存在于涂层中。在温度为1800K、气体速率1500m/s的超音速气流中氧化冲刷96 s,以及在2550 K和室温下热循环24次的测试条件下,制备的SiC/Mo(Six、Al1-x)2涂层材料均未发生破坏现象。涂层材料优良的抗氧化性能和抗热震性能主要归因于基体C/C复合材料的高强度以及在氧化过程中材料表面形成的连续稳定的SiO2和Al2O3玻璃相。

Transparent and Biocompatible Electrodes Based on Carbon Nanotubes/Albumin Composite

We describe a new method for transparent and conductive films based on carbon nanotubes and bovine serum albumin composite development. Films are deposited from an aqueous solution of carbon nanotubes/bovine serum albumin by drop-coating and rod-coating methods. Sheet resistances of as-prepared films vary from 200 Ohm/sq with 50% transmittance to 30 KOhm/sq with 90% transmittance. The maximum sdc/sop ration found in this work is 2.27, which gives a DC conductivity of 4.55 × 104 S·m-1. Atomic force microscopy and Raman spectroscopy studies of the films show that the process of film formation produces neither structural nor chemical changes in the nanotubes. Possibility of using these films for cell culturing is tested on human embryonic fibroblast cell line. Therefore, it is first time ever in literature, when proposed a method, allowing fabricating at the same time transparent, high-conductive and biocompatible CNT films.

Ablation Property of Ceramics/Carbon Fibers/Resin Novel Super-hybrid Composite

A novel super-hybrid composite (NSHC) is prepared with three-dimension reticulated SiC ceramic (3DRC), high performance carbon fibers and modified phenolic resin (BPR) in this paper. Ablation performance of super-hybrid composite is studied. The results show that the NSHC has less linear ablation rate compared with pure BPR and CF/BPR composite, for example, its linear ablation rate is 50% of CF/BPR at the same fiber content. Mass ablation rate of the NSHC is slightly lower than that of pure BPR and CF/BPR composite because of their difference in the density. Scanning electron microscopic analysis indicates that 3DRC can increase anti-erosion capacity of materials because its special reticulated structure can control the deformation of materials and strengthen the stability of integral structure.

Bulk Composite Nanomaterial with Multiwall Carbon Nanotubes

The properties of the composite nanomaterials (CNM) based on bovine serum albumin (BSA) and multi-walled carbon nanotubes (MWCNT), both functionalized and non-functionalized, were investigated. In order to obtain the solid-state bulk CNM from the ultradispersed aqueous solutions of 25 wt.% BSA and (0.0015 - 0.04) wt.% MWCNT, the methods of nanotechnology and laser technology were used. It is revealed that the CNM density is 10% - 20% higher than that of water and the hardness is higher than that of BSA by a factor of 3 - 6 times. An increase in hardness Hv (by Vickers) of CNM correlated with an increase in the concentration of MWCNT, and Hyreached ~300 MPa for the case of the non-functionalized MWCNT, while for the case of the functionalized MWCNT, i.e. MWCNTf, Hy was 25% lower.

喷涂-烧结法制备SiC涂层及抗冲蚀性能的研究

为了提高低密度C/C复合材料的抗冲蚀性能,使用喷涂-烧结法在其表面制备了均匀完整的SiC涂层,研究了反应原材料中蔗糖、葡萄糖、活性炭、磷粉四种碳源对SiC涂层的物相组成、微观形貌以及抗冲蚀性能的影响。结果表明:碳源种类对涂层中的物相组成产生影响,蔗糖和葡萄糖作为碳源时涂层均以单一的SiC物相存在,在10次冲蚀性能测试后涂层仍完整覆盖基体表面,冲蚀损失率分别为1.288%和1.144%,可能是由于残碳现象的改善以及大体积SiC颗粒的生成使冲蚀粒子发生了回弹作用,导致抗冲蚀性能提升。

SiC纳米线改性C/C复合材料的制备及其电磁波吸收性能研究

C/C复合材料因低密度、耐高温等特性在航空航天材料方面具有很广泛的应用,通过改性的方法提高该类材料的电磁波吸收性能有望拓宽其应用领域。本文以酚醛树脂、Si和SiO_(2)粉体,以及催化剂二茂铁为原料,采用先驱体浸渍裂解法制备C/C复合材料,然后通过化学气相反应法在C/C复合材料中生成SiC纳米线(SiC_(nw)),制备出SiC_(nw)改性C/C复合材料(SiC_(nw)/C/C)。研究了C/C和SiC_(nw)/C/C复合材料的结构与性能,探讨了SiC_(nw)含量对C/C复合材料电磁波吸收性能的影响。结果表明,通过本方法可在C/C复合材料中成功引入具有核壳结构的SiC_(nw),并且随着SiC_(nw)含量增加,C/C复合材料的电磁波吸收性能显著提升。当SiC_(nw)含量为15.4%(质量分数)时,SiC_(nw)/C/C复合材料在厚度为2.07 mm处的最小反射损耗值为-38.02 dB,明显低于同类其他材料,表现出优异的电磁波吸收性能。本文研究制备的SiC_(nw)/C/C复合材料可为高性能碳/陶复合材料的制备提供技术和理论支撑。