等离子体处理对国产高强碳纤维复合材料界面性能影响研究

在100W功率条件下,用氧等离子体对国产T800级碳纤维进行处理,通过扫描电子显微镜、原子力显微镜、X射线光电子能谱、单丝拉伸强度测试等方法对处理前后碳纤维表面物理化学特性进行表征,采用微脱粘方式研究了等离子体处理前后碳纤维环氧树脂复合材料界面的结合性能。结果表明：等离子体处理使碳纤维表面发生明显刻蚀,显著地提高了其表面化学活性;处理时间为3min时,碳纤维力学性能未发生降低,而其复合材料界面剪切强度值(IFSS)可达最高的88.61MPa,相比于未处理碳纤维复合材料而言,IFSS增幅为97.39%。     

微结构对碳/碳复合材料界面性能的影响

通过理论模型和界面顶出实验分析了微观结构对碳/碳复合材料界面性能的影响机制。使用高分辨Micro-CT系统获得C/C复合材料界面的微观结构特征,并对界面的微观结构特征进行统计分析,得到界面微观结构尺度分布的概率密度函数。对C/C复合材料的界面层建立力学分析模型,计算获得C/C复合材料界面力学性能,在计算过程中引入界面微观结构的随机性统计分布,获得C/C复合材料界面力学性能的分布规律。设计纤维束顶出实验,测试分析C/C复合材料的界面力学性能。将力学分析模型的计算结果与界面顶出实验获得的实验结果进行对比分析,表明通过模型计算获得的界面性能的均值和离散度与实验获得的结果具有较好的一致性。      

碳纤维上原位生长碳纳米管对C/C复合材料弯曲性能的影响

以碳毡为基底原位生长了碳纳米管（CNTs）,借助化学气相渗透制备了CNTs-C/C复合材料。研究了催化剂含量对碳纳米管生长的影响以及不同含量碳纳米管对C/C复合材料弯曲性能的影响。结果表明：催化剂对CNTs产量影响较大,且含量越多,生成的CNTs量越大;原位生长CNTs引入的催化剂会导致CNTs-C/C复合材料弯曲性能变差;CNTs的加入改变了热解碳的沉积行为,诱导了球状和锥状小尺寸热解碳的形成,减少了微裂纹的出现。适量CNTs能提高C/C复合材料的弯曲强度和模量,并改善材料的断裂行为。     

硅溶胶改性碳纤维对碳纤维/环氧树脂复合材料界面性能影响

以硅烷偶联剂和正硅酸乙酯(TEOS)为前躯体, 以固体酸-对甲苯磺酸为催化剂制备硅溶胶, 利用硅溶胶对碳纤维进行表面改性后, 以环氧树脂为基体, 制备碳纤维增强环氧树脂复合材料。利用SEM、 TEM、 万能试验机、 偏光显微镜等对表面改性前后的碳纤维形态、 力学性能及碳纤维/环氧树脂复合材料的界面性能进行表征, 研究了硅溶胶改性碳纤维对其复合材料界面性能影响。结果表明, 硅溶胶处理碳纤维后, 在碳纤维表面原位生成具有膜-粒结构的表面层, 改性后碳纤维的强度由2.41 GPa提高到3.00 GPa, 界面性能也得到了明显改善, 界面剪切强度(IFSS)提高了51.41%。     

碳纳米管浸润剂对碳纤维/环氧树脂界面性能的影响

制备了含碳纳米管(CNTs)的水溶液, 将该水溶液作为浸润剂浸渍碳纤维并进行烘干, 采用扫描电镜(SEM)和原子力显微镜(AFM)研究了CNTs含量及浸润工艺对碳纤维表面CNTs分布的影响, 运用单丝断裂法分析了CNTs浸润剂处理对碳纤维/环氧树脂界面粘结性能的影响和作用机制。结果表明: CNTs可在T700和T300纤维表面黏附, 浸润剂中CNTs含量越高, CNTs在纤维表面含量越高; 对于CNTs含量较低的浸润剂, 采用增加浸润次数的方法, 能有效提高碳纤维表面CNTs的含量和碳纤维表面粗糙度; 经过CNTs浸润剂处理后, 碳纤维/树脂界面处的机械啮合作用增强, 界面粘结强度明显提高, 增幅最高达35.8%。     

含碳纳米管上浆剂的制备及对碳纤维/环氧树脂复合材料界面的影响

首先采用"Friedel-Crafts"酰化反应制备羧基化多壁碳纳米管(MWCNTs)并将其与环氧树脂、丙酮混合制成含MWCNTs的上浆剂,然后用该上浆剂浸渍碳纤维制备碳纳米管/碳纤维多尺度增强纤维。采用扫描电镜研究了上浆处理对碳纤维表面形貌的影响,采用短臂梁剪切测试方法研究了含碳纳米管的上浆剂对碳纤维/环氧树脂复合材料层间剪切强度(ILSS)的影响。结果表明,碳纳米管在上浆剂中的分散状态直接影响纤维表面碳纳米管分布的均匀性;与未浸渍的碳纤维相比,含碳纳米管上浆剂浸渍后的碳纤维/环氧树脂复合材料的ILSS提高了34.33%。通过上浆剂红外光谱表征、纤维束表面浸润性测试及ILSS试样端口形貌的观察,分析了层间增韧机理。研究表明,碳纤维束表面浸润性的提高以及碳纤维/环氧树脂界面处化学键合作用增强,是ILSS提高的主要原因。     

原位法表征碳／碳复合材料界面性能的研究

用单丝顶出和束顶出法分别测试了细编穿刺碳／碳（Ｃ／Ｃ）复合材料不同层次的界面粘结性能，研究了生产工艺对不同层次界面性能的影响，建立了顶出试验的力学模型，并用有限元方法分析了界面上应力的分布情况，对可能的界面破坏模式进行了预测，为最终优化Ｃ／Ｃ复合材料的生产工艺提供了依据。     

Technora纤维表面等离子体处理对其复合材料界面性能的影响

用扫描电子显微镜观察Technora纤维表面物理形貌并测量单丝纤维的拉伸强度以分析等离子体处理对纤维本体性能的影响,再用层间剪切强度和吸水率分别表征复合材料在室温干态和高温湿态下的界面性能,研究了等离子体处理对Technora纤维复合材料界面性能的影响。结果表明,用等离子体处理后纤维表面的物理形貌发生了显著变化,复合材料的层间剪切强度由未处理时的15.74 MPa提高到24.93 MPa,提高的幅度高达58.4%;同时,复合材料的吸水率下降而本体性能基本不受影响。上述结果表明,等离子体对Technora纤维的表面改性能有效地改善其复合材料的界面性能。     

碳纤维/碳纳米管-环氧树脂复合材料的耐老化性能

将环氧树脂基体与氨基化碳纳米管(MWNTs)复合,制备了碳纤维/氨基化碳纳米管-环氧树脂(CF/MWNTs-EP)复合材料。表征CF/MWNTs-EP三相复合材料的断面,并在标准条件下测试其冲击、拉伸等力学性能,研究了耐老化性能。结果表明:氨基化碳纳米管的加入明显提高了材料的耐盐雾性、耐热氧老化性和耐湿热性能。氨基化碳纳米管的加入改善了纤维与基体树脂间的界面性能,同时,促进了环氧树脂的固化,降低孔隙率,导致耐老化性能显著提高。当MWNTs-NH2的添加量(质量分数)为1.0%时,在72h和168h不同盐雾时间下,三相复合材料的耐盐雾老化性比CF/EP复合材料分别提高了61.8%和67.5%。在48h、96h和168h热氧老化时间下,三相复合材料的耐热氧老化性比CF/EP复合材料分别提高了43.5%、48.5%和41.7%。在72h和168h不同湿热时间下,三相复合材料的耐湿热老化性比CF/EP复合材料分别提高了52.8%和60.0%。     

碳纤维表面处理对2D碳/碳复合材料弯曲性能的影响

为改善纤维与基体的界面结合状态及提高碳/碳复合材料性能,采用1700℃惰性气体保护、2200℃惰性气体保护、400℃空气氧化三种表面处理方法对碳纤维进行了表面处理.结果表明,经过2200℃处理后的纤维表面比较粗糙,有很多沟槽,制备的碳/碳复合材料中纤维与基体结合紧密,弯曲强度比未经表面处理的纤维制备的碳/碳复合材料弯曲强度提高75%;经过400℃处理后的纤维表面凹坑、凸起较纤维未处理前增多,制备的碳/碳复合材料中纤维与基体结合强度适中,其弯曲强度比未经表面处理的纤维制备的碳/碳复合材料弯曲强度提高43%;而经过1700℃处理的纤维表面比较光滑,纤维与基体结合弱,弯曲强度比未经表面处理的纤维制备的碳/碳复合材料的弯曲强度低.     

Growth control of carbon nanotubes by plasma enhanced chemical vapor deposition

Plasma enhanced chemical vapor deposition (PECVD), which enables growth of vertically aligned carbon nanotubes (CNTs) directly onto a solid substrate, is considered to be a suitable method for preparing CNTs for nanoelectronics applications such as electron sources for field emission displays (FEDs). For these purposes, establishment of an efficient CNT growth process has been required. We have examined growth characteristics of CNTs using a radio frequency PECVD (RF-PECVD) method with the intention to develop a high efficiency process for CNT growth at a low enough temperature suitable for nanoelectronics applications. Here we report an effect of pretreatment of the catalyst thin film that plays an important role in CNT growth using RF-PECVD. Results of this study show that uniform formation of fine catalyst nanoparticles on the substrate is important for the efficient CNT growth.     

The formation and characterization of diamond crystallites by microwave plasma enhanced chemical vapor deposition – a comparison of gaseous and solid carbon sources as precursors

Commercial diamond powders are in irregular shapes and have been used as seeds for growing well crystallized fine diamond grits in this study. The surfaces of irregular diamond particles would serve as the seed for the subsequent growth of the diamond crystallites using microwave enhanced chemical vapor deposition (MPECVD). Both gaseous and solid carbon sources were used to transform the irregular shaped diamond seeds with sharp edges and corners along with the increase in size to the final equilibrium form of diamond crystallites. In case of gaseous carbon source, the effect of increasing methane content and applying negative dc bias voltage on the formation of diamond crystallites was significant. While in case of solid carbon source, well-faceted diamond crystallites can he extracted from the molten metal-carbon-hydrogen (M-C-H) system. Surface etch pits are numerous; especially noticeable after long exposure in hydrogen plasma. Both growth rates of diamond crystallite irrespective of the carbon sources tend to be parabolic at the later stage of growth. Electronic Publication     

Adherent amorphous hydrogenated carbon films on metals deposited by plasma enhanced chemical vapor deposition

This paper reports the findings of a study of the structural, mechanical, and tribological properties of amorphous hydrogenated carbon (a-C:H) coatings for industrial applications. These thin films have proven quite advantageous in many tribological applications, but for others, thicker films are required. In this study, in order to overcome the high residual stress and low adherence of a-C:H films on metal substrates, a thin amorphous silicon interlayer was deposited as an interface. Amorphous silicon and a-C:H films were grown by using a radio frequency plasma enhanced chemical vapor deposition system at 13.56 MHz in silane and methane atmospheres, respectively. The X-ray photoelectron spectroscopy technique was employed to analyze the chemical bonding within the interfaces. The chemical composition and atomic density of the a-C:H films were determined by ion beam analysis. The film microstructure was studied by means of Raman scattering spectroscopy. The total stress was determined through the measurement of the substrate curvature, using a profilometer, while micro-indentation experiments helped determine the films' hardness. The friction coefficient and critical load were evaluated by using a tribometer. The results showed that the use of the amorphous silicon interlayer improved the a-C:H film deposition onto metal substrates, producing good adhesion, low compressive stress, and a high degree of hardness. SiC was observed in the interface between the amorphous silicon and a-C:H films. The composition, the microstructure, the mechanical and tribological properties of the films were strongly dependent on the self-bias voltages. The tests confirmed the importance of the intensity of ion bombardment during film growth on the mechanical and tribological properties of the films.     

Structure control of carbon nanotubes using radio-frequency plasma enhanced chemical vapor deposition

Carbon nanotube structures such as tube diameter, growth site, and formation density are controlled using radio-frequency (RF, 13.56 MHz) plasma enhanced chemical vapor deposition (RF-PECVD) method. We have produced uniformly well-aligned multi-walled carbon nanotubes (MWNTs) grown over the large scale area and linearly arrayed MWNTs grown in a selected area without any highly-sophisticated patterning process. In our RF-PECVD experiment, furthermore, individually grown single-walled carbon nanotubes (SWNTs) or their thin bundles are synthesized for the first time within the scope of the PECVD methods. These results indicate that PECVD method provides the high potential for the further development of nano-technology.     

The effects of plasma pre-treatment and post-treatment on diamond-like carbon films synthesized by RF plasma enhanced chemical vapor deposition

Diamond-like carbon (DLC) films were synthesized by RF plasma enhanced chemical vapor deposition and the effects of plasma pre-treatment and post-treatment on the DLC films were investigated. Experimental results show that the surface roughness of the substrate, ranging from 0.2 to 1.2 nm, created by the plasma pre-treatment, will affect the surface roughness of the DLC films deposited using methane as the carbon source. However, the film surface roughness (0.1-0.4 nm) is much smaller than that of the substrate. Raman analysis and hardness measurement by nanoindentation indicate that the structure and the hardness of the DLC films are relatively unchanged for the film surface roughness investigated. For the argon or hydrogen plasma post-treatment of the DLC films deposited using acetylene as the carbon source, it is found that surface roughness decreases with the post-treatment time. Although the hardness decreases after post-treatment, it remains relatively constant with increasing post-treatment time.     

等离子体化学气相沉积参量对Ar等离子体电子特性的影响

采用加热的调谐单探针技术。研究了射频辉光放电Ar等离子体空间电子能量分布函数,电子平均能量和电子密度,并系统分析了等离子体增强化学气相沉积工艺参量对等离子体空间电子特性的影响。     

Investigation of the properties of diamond-like carbon thin films deposited by single and dual-mode plasma enhanced chemical vapor deposition

In this study diamond-like carbon (DLC) films were deposited by a dual-mode (radio frequency/microwave) reactor. A mixture of hydrogen and methane was used for deposition of DLC films. The film structure, thickness, roughness, refractive index of the films and plasma elements were investigated as a function of the radio frequency (RF) and microwave (MW) power, gas ratio and substrate substance. It was shown that by increasing the H₂ content, the refractive index grows to 2.63, the growth rate decreases to 10 (nm/min) and the surface roughness drops to 0.824 nm. Taking into consideration the RF power it was found that, as the power increases, the growth rate increases to 11.6 (nm/min), the variations of the refractive index and the roughness were continuously increasing, up to a certain limit of RF power. The Raman G-band peak position was less dependent on RF power for the glass substrate than that of the Si substrate and a converse tendency exists with increasing the hydrogen content. Adding MW plasma to the RF discharge (dual-mode) leads to an increase of the thickness and roughness of the films, which is attributed to the density enhancement of ions and radicals. Also, optical emission spectroscopy is used to study the plasma elements.     

CF-CNTs多尺度增强体的制备及CF-CNTs/环氧树脂复合材料力学性能

利用化学气相沉积(CVD)法在碳纤维(CF)表面生长碳纳米管(CNTs),制备了CF-CNTs多尺度增强体,增强体与环氧树脂(EP)结合得到CF-CNTs/EP复合材料。采用场发射扫描电镜(FESEM)、高分辨透射电镜(HRTEM)等方法研究了不同CVD工艺参数对CF-CNTs多尺度增强体的影响,并研究了不同CVD时间对CFCNTs/EP复合材料力学性能的影响。结果表明:沉积温度为500℃、沉积时间为10min、反应压力为0.02 MPa时,制备得到的多尺度增强体性能最好。CF-CNTs多尺度增强体较未生长CNTs的碳纤维与环氧树脂的浸润性明显提高。在CVD时间为10min时,所得CF-CNTs/EP复合材料的界面剪切强度(IFSS)最大可提高90.6%,层间剪切强度(ILSS)最大可提高24.4%。同时,在制备环氧树脂复合材料过程中碳纤维的不加捻与加捻相比,其ILSS提高了11.3%。     

Growth of well-aligned carbon nanotubes by RF-DC plasma chemical vapor deposition

Highly aligned carbon nanotubes (CNTs) were grown under high sheath electric field and gas pressure conditions by the radio frequency (RF) plasma-enhanced direct current (DC) plasma chemical vapor deposition (CVD) method due to a stabilized DC discharge. The uniform growth of highly aligned multi-walled CNTs was achieved over the entire surface area of a 50 × 50 mm² iron foil. The growth of multi-walled CNTs on a 75 × 75 mm² iron foil was also confirmed.     

Laterally organized carbon nanotube arrays based on hot-filament chemical vapor deposition

Lateral porous anodic alumina (PAA) templates were used to organize carbon nanotubes (CNTs) grown by a hot-filament assisted chemical vapor deposition (HFCVD) process. For the CNT growth, we used a modified “home-made” HFCVD system with two independently powered filaments which are fitted respectively on the methane (CH₄) gas line, which serves as a carbon precursor and on the hydrogen (H₂) gas line, which acts as an etching agent for the parasitic amorphous carbon. Various activation powers of the hot filaments were used to directly or indirectly decompose the gas mixtures at relatively low substrate temperatures. A parametric study of the HFCVD process has been carried out for optimizing the confined CNTs growth inside the lateral PAA templates.