碳碳复合材料界面热力学研究

化工材料是化工业及工业生产制造的基本元素,各种材料的性能特点决定了复合产品加工制造质量的好坏。分析碳碳复合材料界面热力学特点,主要是为了保证化工材料性能的正常发挥,使得化工生产的流程更加顺利。采用了理论研究与生产实践相结合的方式分析了碳碳复合材料的基本性质与优势,从四大热力学定律分析了材料详细的热学特点,得出了温度高低变化是影响复合材料性能的重要因素。     

碳碳复合材料的水射流钻孔技术研究

针对磨料水射流加工碳碳复合材料的冲孔过程,结合Fluent分析高压磨料水射流的射流压力、靶距对碳碳复合材料冲孔深度的影响;利用ANSYS/Ls-dyna有限元分析软件建立磨料和水的射流冲击模型,针对射流压力是冲孔分层的的主要因素进行仿真,得出材料失效时最大的应力和整个射流过程中应力的变化规律,由最大应力所在位置的层间y向位移变化确定分层情况;根据仿真结果进行相应的试验研究,并将仿真结果与实验结果进行对比分析,验证了射流仿真模型的可行性和有效性。     

超级碳碳复合材料─—德斯纳

“德斯纳”比一般的碳碳复合材料密度高、刚性好，而且不易疲劳；在3000℃高温下仍能正常工作，并可耐受各种化学物质侵蚀，还可以将钉子楔入其中。实验证明，这种新超级碳碳复合材料在1000℃高温条件下的强度要比钢高许多，而密度仅为钢的1／4，为1．8～2．0g／cm3，因此它又是一种非常好的轻质材料。这种复合材料还可以被加工成直径为0．5m的零部件坯料。另据有关资料显示，“德斯纳”还具有良好的生物亲和性，可以用来制造医用绷革、伤口缝合线等。由于具有上述这些无比优越的性能，使“德斯纳”成为材料科学中一支突起的“异军”，可望…     

碳/碳复合材料旋转指尖密封性能分析

指尖密封是近年来研究较为广泛的一种密封形式,涉及的指尖密封多与静止部件连接而呈静止状（静止指尖密封）,理论与试验研究围绕着密封泄漏和磨损性能改善而开展。提出旋转指尖密封的概念和结构,并利用碳/碳复合材料的良好自润滑性能,探索这一指尖密封新结构对泄漏性能改善的可能及机理。通过"外伸式"和"内伸式"旋转指尖密封有限元性能分析模型,分析了结构、工况以及材料参数等对两种旋转指尖密封性能的影响规律,与静止指尖密封密封性能的对比表明,外伸式旋转指尖密封具有在较高转速或跳动量下仍能维持平稳低泄漏率的特质,而内伸式旋转指尖密封的泄漏率却随着转速增大而增大,因而前者对于高速工况下的航空发动机转子密封更具应用潜质。并探索了旋转指尖密封在轴间密封工程应用的可行性,有助于航空发动机轴间密封新构型设计思路开拓、以及密封结构和性能设计的技术选择。     

沥青基碳/碳复合材料的弯曲性能

采用三点弯曲法测试了单向和三维四向碳纤维增强的两种沥青基碳/碳(C/C)复合材料(1D-C/C和3D-C/C)在室温及1 800℃高温时的弯曲性能,分析了增强体结构、温度对C/C复合材料弯曲性能的影响,并探讨了其弯曲断裂时的界面机制。结果表明:3D-C/C的弯曲模量高于1D-C/C的,但其抗弯强度却明显低于1D-C/C的;1D-C/C的弯曲断裂呈脆性断裂,而3D-C/C的弯曲断裂则表现出明显的假塑性特征;对同一种增强体结构的沥青基C/C复合材料,在1 800℃时的弯曲性能高于其在室温时的。     

密度梯度碳/碳复合材料的制备及性能

采用强制流动热梯度化学气相渗透法在1000～1 250℃制备了密度梯度碳/碳复合材料;借助三点弯曲试验和激光闪烁法测定了复合材料的弯曲性能与导热系数,用偏光显微镜及扫描电子显微镜观察了基体热解碳的组织结构及断口形貌。结果表明:该复合材料上层的最大密度为1.65g·cm~(-3),下层的最小密度为1.10g·cm~(-3),具有明显的密度梯度;复合材料的密度越大,抗弯强度越高;其导热系数也随密度的增加而增大;沉积温度是影响基体热解碳组织的主要因素,高温有利于粗糙层热解碳的生成,而低温有利于光滑层热解碳的生成。     

碳/碳复合材料机轮刹车盘机加工工艺探讨

简述了碳/碳复合材料坯体组成、增密原理、机械性能及材料使用特性.并以飞机机轮刹车盘为例,对该材料主要机加工工序（车削加工、钻削加工）进行工艺探讨.通过对坯体受力情况和破坏形式的分析,采取相应防范措施,有效地解决了该材料机加工中出现的问题.     

碳碳复合材料快速沉积炉石墨加热系统设计

本文以开发的碳碳复合材料快速沉积炉为依托,详细介绍碳碳复合材料快速沉积炉(CVI:Chemical Vapor Infiltration)石墨加热器的设计过程,根据设备和工艺使用要求,重点介绍加热保温系统中的加热器设计、加热器表面负荷校核、加热器应力校核。实验结果表明:所设计的石墨加热器满足生产工艺要求;项目在实际生产过程中取得了1mm/h的碳沉积速度;产品在硅单晶炉热场使用中达到了预期使用寿命,成本价与同规格石墨价格接近,满足使用要求。     

固体滲碳剂气化滲碳試驗

一引言固体渗碳的最大缺点之一,是起因于另件和渗碳剂在渗碳箱中直接接触所引起的倾向于形成过饱和的渗碳表层。这种渗碳层在冷却时会变成脆性的网状碳化物,而大大地降低渗碳另件的强度。苏联学者柯兹洛夫斯基及奥尔叶莱毫夫斯基在研究渗碳钢的强度时,曾得出这样的结论:当渗碳层表面区的含碳量在1.05％以下(即在0.8％至1.05％时),钢的疲劳强度最为合适,若含碳量继续增高,则疲劳强度就会急剧下降。因此如何降低渗碳另件表面的含碳量,也就成为机械制造和热处理工作者所关心的问题了。     

纳米碳对酚醛树脂碳微结构的影响

采用透射电子显微镜研究碳／酚醛烧蚀碳层中含纳米碳微粒的酚醛树脂碳微结构，结果表明：在碳分布均匀状态的树脂碳中，纳米碳微粒约50nm，为圆球形，碳粒周围的树脂碳结构均匀，属于具有一定石墨化程度的网络结构；碳微粒呈聚集态，或微粒尺寸较大时，树脂碳的微结构比较复杂。     

Tribological properties of carbon nanotube-doped carbon/carbon composites

Carbon nanotube (CNT)-doped carbon/carbon (C/C) composites were fabricated by the chemical vapor infiltration (CVI) method to investigate the effect of CNTs on tribological properties of C/C composites. CNTs, which had been synthesized by catalytic pyrolysis of hydrocarbons, were added to carbon fiber formed preforms before CVI process. Ring-on-block-type wear tests were performed to evaluate the frictional properties of CNT-doped C/C composites. Results show that CNTs can not only increase wear resistance of C/C composites but also maintain stable friction coefficients under different loads. Polarized light microscopy, X-ray diffraction, scanning electron microscopy and Raman spectroscopy analyses demonstrate that favorable effects of CNTs on tribological properties of C/C composites have been achieved indirectly by altering microstructure of pyrocarbons and directly by serving as high-strength lubricative frictional media at the same time. Electron dispersive spectroscopy (EDS) analyses verify the existence of adhesive wear mechanism in both pure C/C composites and CNT-doped C/C composites albeit the two-body abrasive mechanism dominates in pure C/C composites.     

Effect of carbon nanotube addition on the tribological behavior of carbon/carbon composites

Carbon nanotube composite coatings were applied onto carbon/carbon composites to improve wear properties. Carbon nanotubes have been prepared by catalytic pyrolysis of hydrocarbons. The nanotube slurry was prepared by addition of phenolic resin and solvent to infiltrate into C/C composites. The nanotube added composites were then carbonized in a nitrogen atmosphere. Ball-on-disc type wear tests were performed to evaluate the tribological properties of the carbon nanotube added carbon composites. The result showed that addition of nanotube has the potential to increase the wear resistance of carbon composites. Changes in Raman spectra, morphology and surface damage were studied to explain observed wear behavior.     

Influence of matrix carbon texture on the temperature field of carbon/carbon composites during braking

The friction, wear and thermal properties and temperature fields of three C/C composites with different matrix carbon textures were investigated in simulations of normal landing condition for aircraft brake disks. Temperature fields were also simulated using a finite element method. The matrix carbon textures had important influence on temperature fields. The sample with rough laminar pyrolytic carbon is the best choice for airplane brake disk due to its excellent friction, wear and thermal properties and lower temperature at the friction interface and thermal gradient by contrast with the samples with resin-derived carbon and smooth laminar pyrolytic carbon.     

Monitoring unidirectional carbon/carbon composite processing by light microscopy

Unidirectional carbon/carbon composites were prepared using polyacrylonitrile-based carbon fibres and a commercial coal-tar pitch. The preparation includes a three-sequential-step process: (i) prepreging, (ii) moulding/pressing, and (iii) carbonization to 1000 °C. The effect of the process parameters including pressure, mould characteristics, and temperature and duration of pressure application on the microstructure of composites was monitored by light microscopy. Results show that the application of a pressure of 1 MPa close to the temperature of pitch solidification produces lower porosity composites. This porosity is significantly reduced when the solidification of the pitch is tempered by the introduction of a soak time of 10 h at the temperature at which pressure is applied.     

Mechanics of single-walled carbon nanotubes inside open single-walled carbon nanocones

This study investigates the mechanical characteristics of single-walled carbon nanotubes (CNTs) inside open single-walled carbon nanocones (CNCs). New semi-analytical expressions are presented to evaluate van der Waals (vdW) interactions between CNTs and open CNCs. Continuum approximation, along with the the Lennard-Jones (LJ) potential function, is used in this study. The effects of geometrical parameters on alterations in vdW potential energy and the interaction force are extensively examined for the concentric CNT-open CNC configuration. The CNT is assumed to enter the nanocone either through the small end or the wide end of the cone. The preferred position of the CNT with respect to the nanocone axis is fully investigated for various geometrical parameters. The optimum nanotube radius minimizing the total potential energy of the concentric configuration is determined for different radii of the small end of the cone. The examined configuration generates asymmetric oscillation; thus, the system constitutes a nano-oscillator.     

High-intensity carbon ion injector

An injector of intense beams of carbon ions is described. The device uses an array of carbon plasma guns to inject ions directly into a magnetically insulated acceleration gap. Ion currents exceed 3 kA with beam energies between 100 and 300 keV (for C+) and 200 and 600 keV (for C+ +) over a 700-ns pulselength.     

Effect of densification cycles on continuous friction behavior of carbon–carbon composites

This paper studies the continuous friction behavior of carbon–carbon composites (C/C) fabricated by the coal tar pitch densification process. In the densification process, different numbers of densification cycle are adopted to investigate the influence on physical properties, mechanical properties, microstructure and friction behavior. Experimental results indicate that open porosity decreases with the number of densification cycle. Both bulk density and flexural strength increase with the number of densification cycle. Apparent reduction in wear rate and average friction coefficient can be detected even if the lower densification cycle is adopted. As the number of densification cycle increases, C/C specimens exhibit the lower wear rate and smoother friction coefficient curves. Morphological observations show that the number of open pores for these materials decreases and they exhibit a denser morphology as the number of densification cycle increases. Furthermore, as the number of densification cycle increases, a smooth, adherent lubricating film is formed on the sliding surface. Therefore, the variation in average friction coefficient of specimens becomes smoother; in the meantime, the wear rate becomes lower.     

影响TOC有机碳分析仪测定土壤碳含量的因素

土壤碳含量是评价土壤质量的重要指标。本文以日本岛津TOC-SSM-5000A作为测量仪器,研究了土壤粒度粗细、进样量和磷酸浓度对总碳和无机碳测定的影响,为准确测定土壤碳含量提供了理论依据和技术支撑。结果表明,土壤粒径不是越细越好,0．20mm粒径比较合适;进样量越大,测定时间越长,40mg的进样量较为理想;测定土壤无机碳时,采用100％浓磷酸的测定值最高。     

A study on ultrasonic evaluation of material defects in carbon/carbon composites

It is desirable to perform nondestructive evaluation to assess material properties and part homogeneity because manufacturing of carbon/carbon (C/C) composites requires complicated and costly processes. In this work several ultrasonic techniques were applied to carbon/carbon composites for the evaluation of spatial variations in material properties that are attributable to the manufacturing process. In a large carbon/carbon composite manufactured by chemical vapor infiltration (CVI) method, the spatial variation of ultrasonic velocity was measured and found to be consistent with the densification behavior in CVI process in order to increase the density of C/C composites. Ultrasonic velocity and attenuation depend on a density variation of materials. Low frequency through-transmission scans based on both amplitude and time-of-flight of the ultrasonic pulse were used for mapping out the material property inhomogeneity. These results were compared with that obtained by dry-coupling ultrasonics. Pulse-echo C-scans was used to image near-surface material property anomalies such as the placement of spacers between disks during CVI. Also, optical micrograph had been examined on the surface of C/C composites using a destructive way.