碳化硅纳米线增强多孔碳化硅陶瓷基复合材料的制备

构建多孔碳化硅纳米线(SiCNWs)网络并控制化学气相渗透(CVI)过程,可设计并获得轻质、高强度和低导热率SiC复合材料。首先将SiCNWs和聚乙烯醇(PVA)混合,制备具有最佳体积分数(15.6%)和均匀孔隙结构的SiCNWs网络;通过控制CVI参数获得具有小而均匀孔隙结构的SiCNWs增强多孔SiC(SiCNWs/SiC)陶瓷基复合材料。SiC基体形貌受沉积参数(如温度和反应气体浓度)的影响,从球状颗粒向六棱锥颗粒形状转变。SiCNWs/SiC陶瓷基复合材料的孔隙率为38.9%时,强度达到(194.3±21.3) MPa,导热系数为(1.9 ± 0.1) W/(m∙K),显示出增韧效果,并具有低导热系数。     

温度脉冲方法制备碳/碳化硅复合材料界面的微观结构与性能研究

采用温度脉冲化学气相渗透沉积的方法制备了碳/碳化硅复合材料界面. 以六甲基二硅胺烷(Hexamethyldisilazane , HMDS) 为前驱体, 以3k, 三维四向的石墨化碳纤维编织体为预制体, 通过强制流动热力学梯度化学气相渗透沉积的方法(FCVI)制备出密度为1.98g·cm^-3的C _f/SiC复合材料. 运用透射电子显微镜(TEM)对复合材料的界面微观结构进行了分析. 复合材料的平均弯曲强度为458MPa, 平均断裂韧性为19.8MPa·m^1/2. 应用扫描电子显微镜(SEM)对复合材料的断裂形貌进行了分析研究.     

纤维增强碳化硅陶瓷基复合材料高导热性能研究进展

作为一种先进的高温结构及功能材料,高效传热和高温耐热相结合对纤维增强碳化硅陶瓷基复合材料(silicon carbide matrix composites, SiC CMC)在热管理领域(thermal management, TM)中的应用至关重要。常见的纤维增强碳化硅陶瓷基复合材料,如碳纤维增强碳化硅陶瓷基复合材料(C_f/SiC或C_f/C-SiC)、碳化硅纤维增强碳化硅陶瓷基复合材料(SiC_f/SiC)等,增强纤维的石墨化程度较低,难以形成有效的热输运网络。本文综述了纤维增强碳化硅陶瓷基复合材料制备及高导热性能等方面的最新研究进展。可通过引入高导热相、优化界面结构、粗粒化碳化硅晶体、设计预制体结构等方式提高纤维增强碳化硅陶瓷基复合材料的热输运能力。此外,展望了纤维增强碳化硅陶瓷基复合材料发展趋势,即综合考虑影响高导热碳化硅陶瓷基复合材料性能要素,灵活运用复合材料结构与性能的构效关系,以期制备尺寸稳定、性能优异的纤维增强碳化硅陶瓷基复合材料。     

孔隙率对三维针刺C/C复合材料电磁屏蔽性能的影响

通过多次重复先驱体浸渍裂解(PIP)工艺过程,改变材料的孔隙率和体密度,制备不同孔隙率的三维针刺碳/碳(C/C)复合材料,并研究了在8.2~12.4GHz频率范围内(X波段)不同孔隙率C/C复合材料的电磁屏蔽效能。结果表明:适当降低孔隙率有利于提高C/C复合材料的总电磁屏蔽效能和电磁吸收屏蔽效能,当开气孔率为33.4%时,C/C复合材料具有最大的电磁屏蔽效能(40dB),且电磁吸收屏蔽效能(30dB)远大于电磁反射屏蔽效能(12dB),是极具潜力的高吸收低反射电磁屏蔽材料。     

碳化硅衍生碳/中间相沥青炭复合材料的制备及表征

通过聚碳硅烷和中间相沥青在320℃共混及不同温度热解、炭化、石墨化处理得到碳化硅/中间相沥青炭前驱体,然后采用Cl_2在1 000℃对前驱体进行刻蚀,成功制备碳化硅衍生碳/中间相沥青炭复合材料。采用偏光显微镜、X射线衍射、扫描电子显微镜、透射电子显微镜和拉曼光谱对产物的微观形貌和结构进行了表征,利用物理吸附仪分析其比表面积和孔结构特征。结果表明,随着热处理温度的升高,聚碳硅烷热解形成的SiC的晶体尺寸变大,同时沥青炭的石墨化程度也变高;刻蚀后碳化硅衍生碳的结构以无定形碳为主,有明显的石墨化碳层分散其中,样品的比表面积随热处理温度升高而减小,微孔孔径增大。     

先驱体转化法制备碳纤维增强碳化硅复合材料的研究

本文采用有机硅先驱体聚碳硅烷转化成碳化硅制备连续碳纤维增强的碳化硅基复合材料。对其制备工艺,如碳纤维体积分数的控制、液相浸渍聚碳硅烷热解转化成碳化硅基体的致密化等进行了研究。结果表明,该工艺对制备连续纤维增强的陶瓷基复合材料是一种有效的方法,易于实现纤维和基体的成型、复合。致密化过程不损伤纤维。对其C/SiC复合材料的性能进行了表征,C纤维具有明显增韧碳化硅的效果,其断裂机制表现为韧性特征。     

纤维增强碳化硅陶瓷基复合材料高导热性能研究进展EI北大核心

作为一种先进的高温结构及功能材料,高效传热和高温耐热相结合对纤维增强碳化硅陶瓷基复合材料(silicon carbide matrix composites,SiC CMC)在热管理领域(thermal management,TM)中的应用至关重要。常见的纤维增强碳化硅陶瓷基复合材料,如碳纤维增强碳化硅陶瓷基复合材料(C_(f)/SiC或C_(f)/C-SiC)、碳化硅纤维增强碳化硅陶瓷基复合材料(SiC_(f)/SiC)等,增强纤维的石墨化程度较低,难以形成有效的热输运网络。本文综述了纤维增强碳化硅陶瓷基复合材料制备及高导热性能等方面的最新研究进展。可通过引入高导热相、优化界面结构、粗粒化碳化硅晶体、设计预制体结构等方式提高纤维增强碳化硅陶瓷基复合材料的热输运能力。此外,展望了纤维增强碳化硅陶瓷基复合材料发展趋势,即综合考虑影响高导热碳化硅陶瓷基复合材料性能要素,灵活运用复合材料结构与性能的构效关系,以期制备尺寸稳定、性能优异的纤维增强碳化硅陶瓷基复合材料。     

乙醇热解制备炭/炭复合材料工艺探索及组织特征

以密度0.47g/cm³的碳毡为预制体,乙醇为前驱体,氮气为载气,在1125℃,压力为20kPa的条件下,用等温压力梯度化学气相渗透法,经114h致密化,制备出密度为1.67g/cm³的炭/炭复合材料.经测试,材料的弯曲强度为137MPa.偏光显微分析显示：该材料各区域沉积的基体热解碳组织结构均为高织构,其消光角为19.5°～20.5°,石墨化处理后测得热解碳的d₀₀₂为0.3362nm.断口扫描电子显微分析结果也进一步证实获得的热解碳组织为高织构.表明乙醇是一种极具潜力的制备炭/炭复合材料的前驱体.     

碳/碳化硅陶瓷基复合材料的研究及应用进展

碳/碳化硅(C/SiC)陶瓷基复合材料是重要的热结构材料体系之一.综述了近年来发展的有关制备C/SiC陶瓷基复合材料的各种技术及其在航空航天、光学系统、空间技术、交通工具(刹车片、阀)、能源技术等领域的应用,展望了可应用于玻璃工业中的纳米碳颗粒与亚微米碳化硅复合的陶瓷基复合材料制备工艺,可拓宽该陶瓷基复合材料的应用领域.     

热管理用高导热碳化硅陶瓷基复合材料研究进展

碳化硅陶瓷基复合材料以其高比强度、高比模量、高导热、良好的耐烧蚀性能、高温抗氧化性、抗热震性能等特性,广泛应用于航空航天、摩擦制动、核聚变等领域,成为先进的高温结构及功能材料。本文综述了高导热碳化硅陶瓷基复合材料制备及性能等方面的最新研究进展。引入高导热相,如金刚石粉、中间相沥青基碳纤维等用以增强热输运能力;优化热解炭炭与碳化硅基体界面用以降低界面热阻;热处理用以获得结晶度更高、导热性能更好的碳化硅基体;设计预制体结构用以建立连续导热通路等方法,提高碳化硅陶瓷基复合材料的热导率。此外,本文展望了高导热碳化硅陶瓷基复合材料后续研究方向,即综合考虑影响碳化硅陶瓷基复合材料性能要素,优化探索高效、低成本的制备工艺;深入分析高导热碳化硅陶瓷基复合材料导热机理,灵活运用复合材料结构与性能的构效关系,以期制备尺寸稳定、具有优异热物理性能的各向同性高导热碳化硅陶瓷基复合材料。     

Electrical conductivity and shielding effectiveness of poly(trimethylene terephthalate)/multiwalled carbon nanotube composites

Poly(trimethylene terephthalate) (PTT)/multiwalled carbon nanotube (MWCNT) composites have been fabricated to evaluate the potential of PTT composites as electromagnetic interference (EMI) shielding material. The room temperature electrical conductivity, complex permittivity, and shielding effectiveness (SE) of PTT/MWCNT composites were studied in the frequency range of 8.2–12.4 GHz (X-band). The dc conductivity (σ) of composites increased with increasing MWCNT loading and a typical percolation behavior was observed at 0.48 vol% MWCNT loading. The highest EMI SE of PTT/MWCNT composites was ~23 decibel (dB) at 4.76 vol% MWCNT loading which suggest that these composites can be used as light weight EMI shielding materials. The correlation among the SE, complex permittivity, and electrical conductivity was also studied. The EMI shielding mechanism of PTT/MWCNT composites was studied by resolving the total EMI SE into absorption and reflection loss.     

Electromagnetic interference shielding effectiveness of SiCf/SiC composites with PIP–SiC interphase after thermal oxidation in air

SiC_f/SiC composites with PIP–SiC interphase were prepared as electromagnetic interference (EMI) shielding materials by chemical vapor infiltration method. Effects of thermal oxidation on electrical and EMI shielding properties of the composites in X band were investigated. The as-received composites show high electrical conductivity of 0.12 S/cm and SE_T value of 29 dB, which is ascribed to the free carbon in the composites. The electrical conductivities and weight retentions of the composites decrease with oxidation temperatures or time increase. Likewise, the shielding properties deteriorate to some degree but the SE_T value exhibits more than 17 dB after oxidation at 1000 °C for 2 h and 15 dB at 900 °C for 6 h, respectively. The deterioration of electrical and EMI shielding properties during oxidation process is ascribed to the consumption of free carbon. The high SE_A value and low SE_R value imply that absorption is the dominant EMI shielding mechanism. The SiC interphase can protect the fibers and keep EMI shielding properties of the composites at a high level.     

Comparison of oxidation behaviors of 3D C/PyC/SiC and SiC/PyC/SiC composites in an O2-Ar atmosphere

Oxidation behaviors of three-dimensional woven C/PyC/SiC and SiC/PyC/SiC prepared by CVI processing were investigated in an O₂-Ar atmosphere at 600 °C, 900 °C and 1200 °C, respectively, by using thermogravimetric analysis. After machining, both composites should be protected by CVD SiC coating, which was demonstrated effectively in improving the oxidation resistance of both composites. The oxidation behavior of SiC/PyC/SiC was different from that of C/PyC/SiC. The oxidation kinetics of C/PyC/SiC was controlled by the rate of the reaction between carbon and oxygen at 600 °C and by the oxygen diffusion through the coating microcracks at 900 °C. The oxidation kinetics of SiC/PyC/SiC at both 600 °C and 900 °C were assumed to be controlled by the oxygen diffusion through channels of coating and matrix defects and looped pipelines instead of PyC interphase. At 1200 °C, the oxidation was controlled by oxygen diffusion through the SiO₂ scale, which took place mainly on the surfaces of both composites.     

Broadband electromagnetic shielding and dielectric properties of polyaniline-stannous oxide composites

Conducting polyaniline-stannous oxide (PAni-SnO) composites were synthesized by the in situ polymerization of aniline in the presence of SnO. The composites formed were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As there is a greater need for materials with electromagnetic interference (EMI) shielding properties over a large operating frequency band, the present study highlights the dielectric and EMI shielding response of PAni-SnO composites in the microwave frequency range from 8 to 18 GHz (X and Ku bands). All the computations were based on microwave scattering parameters measured by transmission line waveguide technique. The EMI shielding effectiveness (EMI SE), return loss, microwave absorption and dielectric properties of the PAni-SnO composites were evaluated for various wt% of SnO (10, 20, 30, 40 and 50 wt%) in PAni. In X-band, the composites exhibits EMI SE in the range ?18 to ?23 dB, with microwave absorbance of 70–83 % and in the Ku-band, the composites exhibits EMI SE values of ?17.5 to ?22.5 dB with 67–85 % absorbance. Our investigations reveal that the PAni-SnO composites are potential candidates for EMI shielding applications for both the X and Ku bands.     

SiCf/SiC复合材料界面相研究进展

分析了连续纤维增强陶瓷基复合材料(CFRCMCs)中界面相类型以及各界面相在CFRCMCs中的作用,综述了热解碳(PyC)、氮化硼(BN)、难熔氧化物以及复合界面相在SiCf/SiC复合材料中的应用现状,最后展望了SiCf/SiC复合材料界面相的发展方向。     

CNT纸/SiC对称梯度层状复合材料的高温电磁屏蔽性能和介电性能

将单层碳纳米管(CNT)纸浸渍酚醛树脂致密化,通过树脂碳层层焊接得到厚度约为2.6 mm的CNT纸/SiC层状梯度复合材料,由13个CNT纸/SiC复合材料结构层和12个膨胀石墨增韧树脂C界面层组成,SiC含量沿厚度方向由中心向两端呈递增的对称梯度分布。CNT纸/SiC层状梯度复合材料的体积密度为1.65 g/cm3,开气孔率为7.25%,在宏观尺度范围获得在SiC基体中均匀弥散分布的高含量的CNT。在X频段范围,CNT纸/SiC层状梯度复合材料600℃时的平均总屏蔽效率(37.19 dB)高于室温(35.00 dB)。较之室温时的屏蔽性能,CNT纸/SiC层状梯度复合材料600℃时的反射系数略有减小,但吸收系数明显增加,透射系数由0.0003减小至0.0002,展示了良好的在电磁屏蔽领域尤其是高温屏蔽领域的应用前景。在X频段范围,随温度由室温升高至600℃,CNT纸/SiC层状梯度复合材料的虚介电常数平均值由114.6增大至149.1;平均损耗正切值由1.62增大至1.79。      

考虑氧化损伤的陶瓷基复合材料弹性模量多尺度预测模型

分析了化学气相渗透(CVI)工艺制备的陶瓷基复合材料的氧化损伤演化规律,基于基体的微裂纹分布规律及界面、纤维、基体等组分氧化历程,建立了考虑温度、氧化时间影响的纤维和单胞两个尺度的弹性模量预测模型。预测结果表明,碳纤维(C_f)/SiC和SiC纤维(SiC_f)/SiC复合材料的拉伸弹性模量随氧化温度升高和氧化时间的增长,下降趋势越明显。通过复合材料高温氧化后的力学性能试验,验证了弹性性能预测模型的正确性:BN界面的SiC_f/SiC材料在1000℃不同时间氧化后预测结果与试验结果误差不超过2%;PyC界面的C_f/SiC在700℃不同时间氧化后预测结果与试验结果误差不超过7%。      

陶瓷基复合材料多层界面相应力传递的有限元模拟

针对陶瓷基复合材料（CMCs）多层界面相的应力传递进行了有限元模拟。采用圆柱单胞模型描述CMCs的细观结构,按相应界面相亚层的实际厚度建立明确的界面相,并假设界面相亚层之间及界面相与纤维、基体之间初始完好结合,然后赋予各界面相亚层不同的材料参数,并采用轴对称有限元法进行求解,最终建立了多层界面应力传递的模拟方法。分别对比了不同厚度热解碳（PyC）界面相、PyC和SiC两种不同成分界面相及（PyC/SiC）和（SiC/PyC）两种结构界面相的应力传递模拟结果。从剪应力沿纤维方向分布及径向分布特点可以看出,通过合理配置CMCs内部多层界面相的结构、成分和厚度,可以实现界面相应力传递及失效模式的控制和优化。     

Lightweight multi-walled carbon nanotube buckypaper/glass fiber–epoxy composites for strong electromagnetic interference shielding and efficient microwave absorption

Multi-walled carbon nanotube buckypaper (BP) reinforced glass fiber–epoxy (GF/EP) composites were selected to fabricate electromagnetic interference (EMI) shielding and microwave absorbing materials. Six different composite configurations with 3.0 mm thick have been conceived and tested over the X-band (8.2–12.4 GHz). Flexible and low-density (0.29 g/cm³) BP provided a high specific EMI SE of 76 dB with controlled electrical conductivity. GF/EP/BP₁₁₁ and GF/EP/BP₁₀₁ composites possess EMI SE as high as of 50–60 dB, which can be attributed to the number of BP inserted and variation in the wave-transmitting layer of the laminates. Furthermore, the shielding mechanism was discussed and suggested that the absorption was the dominant contribution to EMI SE. GF/EP/BP₁₁₀ laminate demonstrated suitable EMI performance (~?20 dB), whereas GF/EP/BP₀₁₁ composite revealed excellent microwave performance, achieving an effective ? 10 dB bandwidth of 3.04 GHz and minimum reflection loss (RL) value of ? 21.16 dB at 10.37 GHz. On the basis of these results, GF/EP/BP composites prepared in this work have potential applications as both EMI shielding and microwave absorber materials given their facile preparation and lightweight use.