低温各向同性热解炭的微观结构

采用流化床化学气相沉积工艺可制备低温各向同性热解炭,沉积工艺参数变化导致沉积的炭材料微观结构呈现多样性,不同结构炭的物理和力学性能会有很大差异.本文列举了高密度和低密度低温各向同性热解炭,分别对它们在扫描和透射电镜下的微观结构特征进行了综述.通过归纳分析,对低温各向同性热解炭的微观结构有了较为系统地认识,在此基础上对低温各向同性热解炭的研究发展方向进行了展望.     

炭/炭复合材料的摩擦磨损性能及应用

论述了炭／炭复合材料的特点，结合该材料在飞机刹车盘中的具体应用，讨论了炭／炭复合材料在不同环境气氛下的摩擦磨损行为及其影响因素，并阐明了炭／炭复合材料的研究现状和尚需解决的问题。     

CVD制备各向同性热解炭的微观结构表征及沉积机制研究

利用化学气相沉积设备及自行设计的沉积室,以高纯石墨为沉积基体,天然气为前驱体,沉积温度1200℃,在不同气体流量下(0.10,0.15,0.20m3/h)制备出了各向同性热解炭块体材料。利用XRD、Raman、SEM、TEM分析手段对材料的微观结构进行了研究。结果表明:各向同性热解炭由粒径为1.5～2.5μm的颗粒组成;热解炭微晶的Lc和La随着气体流量的增加而增大;TEM中选区电子衍射图谱中d002环为圆环,取向角为180°,定量地揭示制备的热解炭为各向同性。     

高温热处理对炭 /炭复合材料湿态摩擦性能的影响

研究了高温热处理工艺对快速定向扩散化学气相渗透炭／炭复合材料在湿态下的摩擦磨损性能的影响。实验选择了4种不同的高温热处理工艺，用于比较其对炭／炭复合材料微观结构及湿态下的摩擦磨损性能的影响。分析结果表明湿度对炭／炭复合材料的摩擦性能有显著的影响，在湿态下它的摩擦系数明显低于正常干态下的摩擦系数并且随着刹车压力和刹车惯量的增加下降得更快；高温热处理工艺对炭／炭复合材料微观结构有显著影响，通过改变炭／炭复合材料微观结构，适当的高温热处理工艺可以改善湿态下炭／炭复合材料摩擦磨损性能。结果表明，最适合的热处理温度为2000℃，在2000℃下热处理的炭／炭复合材料有足够的摩擦系数，并且湿度对其摩擦磨损性能影响较其他3种热处理工艺的炭／炭复合材料小。     

干摩擦条件下丁腈橡胶和氟橡胶摩擦磨损行为研究

采用微机控制磨粒磨损试验机研究丁腈橡胶（NBR）和氟橡胶（FKM）与45#钢配副在干摩擦条件下的摩擦磨损行为,并对NBR和FKM的磨痕表面形貌、元素含量和表面官能团变化进行分析。结果表明：当转速较低时,NBR和FKM均以磨粒磨损（微切削）为主;当转速大于200 r·min^-1时,NBR磨痕表面出现胶合现象,表现为粘着磨损,FKM的耐磨性能优于NBR。NBR和FKM的磨粒磨损机理相似,主要物理过程为宏观分层剥落;当转速较高时,橡胶/钢副接触面发生了粘着转移,在钢环表面形成了转移膜。在干摩擦过程中NBR和FKM的分子链发生断裂形成大分子自由基,大分子自由基异构化并发生氧化反应。     

不同硼含量的硼掺杂各向同性热解炭制备及微观结构研究

以CH4、H2和BCl3为原料,利用化学气相沉积方法制备了硼掺杂各向同性热解炭材料。研究了制备工艺及硼元素掺杂对热解炭微观结构和抗氧化性能的影响。结果表明,硼元素能够均匀地掺入热解炭中,其含量随着BCl3流量的增大而增加;硼掺杂并未改变热解炭的各向同性性质,但随着BCl3流量的增加,硼掺杂各向同性热解炭的结构由球形颗粒状结构逐渐向卷曲片层状结构转变,硼在热解炭中的存在形式则由单一形式(取代)逐渐过渡到混合形式(取代硼和碳化硼);硼元素的掺杂能有效抑制热解炭的氧化,大幅提高材料的起始氧化温度,显著降低氧化损失。     

热解炭微观结构对炭/炭复合材料力学性能的影响

以PAN基针刺纤维毡为基体,采用等温化学气相渗透技术,在温度1000℃、压力5.0~20.0 kPa条件下制备了2种具有不同微观结构热解炭的炭/炭复合材料,研究了其力学性能与热解炭微观结构的关系. 结果表明,压力8.0 kPa下得到的具有单一低织构热解炭的炭/炭复合材料的断裂强度较高,为86±3 MPa,热解炭与炭纤维间界面结合紧密,加载过程中二者同时断裂,呈现明显的脆性断裂行为;压力10.0~20.0 kPa下得到的具有中织构-高织构-中织构热解炭的炭/炭复合材料的断裂强度稍低,为82±4 MPa,加载过程中材料内部不同织构热解炭间多层次界面通过改变裂纹扩展路径而延缓其扩展速度,断口形貌呈现锯齿状,表现出假塑性断裂特征.     

分子量对UHMWPE干摩擦条件下的销-盘摩擦磨损行为的影响

采用销-盘试验,在转速为60 r/min,法向为载荷(392±29)N,聚合物盘与钢销摩擦副接触形式为面-面,试验时间为1.5 h,试验环境温度为20℃,相对湿度为60%的条件下,研究了200万、300万、500万和900万分子量的UHMWPE分别与钢配副干摩擦时UHMWPE分子量对其摩擦磨损性能的影响,并利用扫描电子显微镜观察其磨损表面形貌。结果表明:UHMWPE分子量其摩擦磨损性能有显著影响,UHMWPE的分子量为300万时,摩擦副的摩擦因数及UHMWPE自身的磨损为最小。     

Characteristics of pyrolytic carbon in Canadian coals

Isotropic to anisotropic pyrolytic carbon was observed in Canadian subbitumonous to bituminous coals (%R oil = 0.50−1.0) using reflected light microscopy. Morphologically, pyrolytic carbon consiste of large, well-developed spherulitic and laminated forms occuring in coal macerals and carbominerites as cell and crack filling. The spherulitic forms probably developed rapidly and laminated forms over a period of time. The presence of pyrolytic carbon in coal may indicate a thermal event and, in these coals it is of detrital nature and therefore should be grouped with inertodetrinite.     

Formation of pyrolytic carbon in a continuous reactor for coal hydrogenation

Microscopic examination of blockage material from the CSIRO laboratory-scale continuous reactor for coal hydrogenation has indicated the presence of pyrolytic carbon. Both the morphology and abundance of pyrolytic carbon were variable. In some samples pyrolytic carbon spheres (≈ 1 μm) formed large deposits with clear zonal texture. Spherical agglomerates (up to 70 μm) of these particles, and large particles were also observed. In some cases spherulitic pyrolytic carbon was embedded in vitroplast and/or mesophase. The occurrence of pyrolytic carbon in continuous reactors for coal hydrogenation is significant as it can provide, in the absence of other information, a posteriori indication of undesirable reaction conditions, i.e. large gas hold-ups and localized overheating.     

“三明治”C/C复合材料及其摩擦磨损性能

通过化学气相渗透法(CVI)制备出一种新型的"三明治"结构的C/C复合材料。其两侧是纯网胎结构的功能层,主要承担摩擦功能;中间为承担结构作用的结构层,与传统针刺毡结构一致。系统研究了材料的微观组织结构特征及其摩擦磨损性能。结果表明:"三明治"C/C复合材料各个区域的热解炭都为粗糙层结构;刹车性能较传统三维针刺结构C/C复合材料的摩擦性能稳定;在摩擦试验过程中,摩擦面能够形成一层连续均匀的薄膜,使材料在刹车过程中具有较稳定的摩擦系数并能够有效降低材料的磨损率。     

废轮胎热解再生炭黑表面活性

为克服废轮胎常压热解再生炭黑(PC)表面碳质沉积物过多、表面活性差和不适于橡胶补强应用等缺点,本文以反相气相色谱法为分析手段,分别通过硝酸酸洗和硬脂酸-硝酸酸洗等方法改性处理PC,以期改善PC结构和提高其表面性能,继而改善PC填充天然橡胶硫化胶的机械性能.系统地考察了未改性PC以及硝酸酸洗改性热解炭黑(WPC)、硬脂酸-硝酸酸洗改性热解炭黑(SWPC)表面能色散分量、极性分量、热力学函数变化以及炭黑表面不同活性点的能量分布情况,并考察了改性处理对热解炭黑填充天然橡胶硫化胶机械性能的影响.实验结果表明,硝酸酸洗改性在炭黑表面引入较多的羟基和羧基等官能团,导致其表面能过高,不利于天然橡胶补强.而在硝酸酸洗基础上,通过加入硬脂酸再改性后,可以减少炭黑颗粒之间的团聚,降低表面能,改善炭黑在硫化胶中的分散性.通过硫化胶机械性能测试实验发现,与PC和WPC相比,填充SWPC的天然橡胶具有较高的拉伸强度、扯断伸长率、300%定伸应力,能基本达到半补强炭黑的应用标准.     

An investigation on wear behavior of UHMWPE/carbide composites at elevated temperatures

Ultra-high molecular weight polyethylene (UHMWPE) is extensively used in frictional applications due to its advanced wear resistance. This advanced polymer is reinforced with hard particulate fillers for further developments against wear conditions. Since elevated temperatures prevail in the service conditions, wear behavior of UHMWPE composites is an important issue for the engineering applications. In the present work, UHMWPE-based composites including silicon carbide (SiC) fillers were fabricated in a compression molding chamber. In the specimen preparation stage, molding pressure, filler amount, and filler particle size were varied to investigate the influence of these variables. Upon deciding the optimum parameters from the wear tests conducted at room temperature, the wear experiments were repeated for the optimum specimen at elevated temperatures, such as 40 and 60°C. According to the results, the wear behavior of the SiC/UHMWPE composites is heavily changed by the effect of elevated temperature. Adhesive effect is pronounced at elevated temperatures while the wear characteristics possess the abrasive effect in the sliding path. In addition, the composites exhibit an accelerated material loss as temperature increases during the frictional system.     

Influence of solid lubricant reinforcement on wear behavior of Kevlar fabric composites

The friction and wear behavior of Kevlar fabric composites reinforced by PTFE or graphite powders was investigated using a Xuanwu‐III friction and wear tester at dry sliding condition, with the unfilled Kevlar fabric composite as a reference. The worn surfaces were analyzed by means of scanning electron microscope, and X‐ray photoelectron spectroscopy. It was found that PTFE or graphite as fillers could significantly improve the tribological behavior of the Kevlar fabric composites, and the Kevlar fabric composites filled with 20% PTFE exhibited the best antiwear and antifriction ability among all evaluated cases. The transfer films established with two lubricants in sliding wear of composites against metallic counterparts made contributions to reducing friction coefficient and wear rate of Kevlar fabric composites. In particular, FeF₂ generated in the sliding of Kevlar fabric composites filled with PTFE against counterpart pin improved the bonding strength between the transfer film and counterpart surface, which accounted for the lowest friction coefficient and wear rate of the Kevlar fabric composites filled with PTFE measured in the testing. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.     

废轮胎热解炭黑与工业炭黑的粒径及化学组成

用激光粒度分析仪测定了废轮胎热解炭黑的粒径分布,用扫描电子显微镜、X-射线衍射法及X-射线光电子能谱法分析了热解炭黑和工业炭黑的形态、表面化学组成以及表面碳元素的结合状况。结果表明,热解炭黑的粒径分布是添加在轮胎中各种型号工业炭黑粒径分布的叠加。热解炭黑表面形态和组成接近于工业炭黑N660;热解炭黑的表面附着更多的有机物以及ZnO、ZnS等无机物,且随着热解温度的升高,附着的有机物含量减小,无机物中ZnO含量减小,ZnS含量增多。     

Mechanical reinforcement and wear resistance of aligned carbon nanotube/epoxy nanocomposites from nanoscale investigation

The anisotropic mechanical reinforcement compression and scratch resistance of epoxy nanocomposites filled with well-aligned carbon nanotubes (ACNTs) sliding in different orientations were investigated by nanoindentation techniques. It was found the addition of ACNTs to epoxy very effectively improved the microscopic hardness, elastic modulus, and nanoscratch resistance of pure epoxy, and the nanocomposites in antiparallel orientation of ACNTs showed the highest enhancement. However, macroscopic compression test showed the normal orientation of ACNTs enhanced the compression strength the most. Based on nanoscale observations, new ACNTs related reinforcing and scratch resistance mechanisms were further proposed and discussed. This study will enhance the understanding of the anisotropic reinforcement effect of ACNTs with new characteristics, and will be helpful for the design and application of ACNT nanocomposite materials into precision instruments and related anisotropic nanomaterials.     

Influence of graphitization temperature on microstructure and mechanical property of C/C-SiC composites with highly textured pyrolytic carbon

C/C-SiC composites with highly textured pyrolytic carbon (HT PyC) were prepared by a combining chemical vapor infiltration and liquid silicon infiltration. The effect of HT PyC graphitization before and after 2327 and 2723 K on C/C-SiC composites was investigated. The mechanical properties decreased with increasing graphitization temperature, but graphitization treatment changed the fracture behavior from brittle like to pseudo-ductile. The decrease in bending strength from 306.21 to 243.69 MPa resulted from the weak interfacial bonding between HT PyC and fiber, and the good orientation of graphite layers. The crack at border of fiber bundle and longitudinal crack in HT PyC shortened the path of crack propagation, resulting in fracture toughness decrease from 21.11 to 14.72 MPa·m^1/2. A more pseudo-ductile behavior was due to the longer pull-out of fibers, the better orientation of graphite layers, the sliding of sublayers, and the deflection and propagation caused by the transverse cracks.