电化学氧化对炭纤维界面性质的影响

对粘胶基炭纤维进行电化学氧化表面处理，对表面处理前后的炭纤维进行强力测试，分析表面处理条件对炭纤维强度的影响，通过测定炭纤维与几种浸润液的接触角，分析了电化学氧化表面处理对炭纤维浸润特性的影响，在电镜下观察表面处理前后炭纤维表面形貌的变化，并测其比表面积的变化，分析处理条件对其表面粗糙度的影响，通过炭纤维的拉曼散射，分析表面处理前后炭纤维表面微晶大小的变化，最后，对处理前后炭纤维的相关性能指标进行比较，分析其性能变化的机理及其性能变化对炭纤维复合材料界面粘结性能的影响。     

不同处理方法对碳纤维表面形态及Cf/C复合材料强度的影响

采用浓硝酸和电化学两种不同的表面处理技术,对碳纤维表面处理,利用SEM对纤维表面进行了分析,并对其所制备的Cf/C复合材料抗弯性能进行了测试.结果表明:采用低电压,短时间处理,对碳纤维表面作用较温和,粗糙度和比表面积增加,对复合材料的增强效果较浓硝酸氧化处理的显著.经10V,10min处理后,纤维表面出现"松树皮"状凸起,复合材料力学性能下降.电化学处理碳纤维以提高复合材料界面性能的机理至少包括薄弱外层的去除和对纤维表面的刻蚀两种作用,在混合作用中,对纤维表面刻蚀作用占据主导地位.     

超高模量环氧树脂/碳纤维复合材料的研究进展

通过对碳纤维及环氧树脂进行改性处理,在降低树脂含量的同时提高其结合强度来改善碳纤维复合材料的力学性能。     

不同碳硅比对合成高比表面积碳化硅的影响

以淀粉和工业水玻璃为原料,经过碳热还原反应制备出碳化硅纳米线.采用XRD、SEM、氮吸附-脱附和荧光光谱仪(PL)对所制备的样品进行表征,同时考察了碳硅比(物质的量比,下同)对碳化硅形貌、比表面积和荧光性能的影响.结果表明,当碳硅比为4.5时,合成的碳化硅为直的纳米线,比表面积为45m2/g,发光强度也达到最大.     

Characteristics of plasma surface treated composite adhesive joints at high environmental temperature

When an adhesive joint is exposed to high environmental temperature, the load transmission capability of the adhesive joint decreases because the stiffness and strength of structural adhesive decrease. The load transmission capability of adhesive joint at high environmental temperature can be improved by increasing the surface free energy of adherends with surface pretreatments.

In this paper, a capacitively coupled radio frequency plasma system was designed for the surface treatment of carbon/epoxy composites. The suitable plasma surface treatment conditions were experimentally investigated with respect to gas flow rate, vacuum pressure, power intensity, and surface treatment time through measurement of surface free energy by investigating strength of single lap composite adhesive joint. The surface free energy and adhesive joint strength were investigated with respect to the surface characteristics of the carbon/epoxy composite adherend measured with atomic force microscope. Also the failure mode of the composite adhesive joint was studied with respect to surface treatment and environmental temperature.     

Surface transformations of carbon (graphene, graphite, diamond, carbide), deposited on polycrystalline nickel by hot filaments chemical vapour deposition

The deposition of carbon has been studied at high temperature on polycrystalline nickel by hot filaments activated chemical vapor deposition (HFCVD). The sequences of carbon deposition are studied by surface analyses: Auger electron spectroscopy (AES), electron loss spectroscopy (ELS), X-ray photoelectron spectroscopy (XPS) in a chamber directly connected to the growth chamber. A general scale law of the (C/Ni) intensity lines is obtained with a reduced time. Both, shape analysis of the AES C KVV line and the C1s relative intensity suggest a three-step process: first formation of graphene and a highly graphitic layer, then multiphase formation with graphitic, carbidic and diamond-like carbon and finally at a critical temperature that strongly depends on the pretreatment of the polycrystalline nickel surface, a rapid transition to diamond island formation. Whatever the substrate diamond is always the final product and some graphene layers the initial product. Moreover it is possible to stabilize a few graphene layers at the initial sequences of carbon deposition. The duration of this stabilization step is strongly depending however on the pre-treatment of the Ni surface.     

用于电泳显示的纳米炭黑粒子的表面改性

采用氧化还原自由基聚合的方法,将丙烯酸甲酯单体接枝到氧化炭黑的表面,并进行粒径分布、扫描电子显微镜,及zeta电位对其在IsoparL中分散性表征,结果显示,聚丙烯酸甲酯接枝的炭黑在IsoparL中的分散性有明显的提高。将表面修饰后的纳米炭黑粒子用作电泳显示器件的黑色显色粒子,在0．3V／μm的驱动电场下,具有良好的显示性能,对比度达到5．25,响应时间934ms。     

活性炭硝酸表面改性对催化剂分散度的影响

无论是活性炭作为催化剂载体还是在活性炭本身的催化制备过程中,催化剂在活性炭或活性炭前体上的高度分散都是至关重要的。通过X射线能谱(EDX)和扫描电子显微镜(SEM)技术直接观察、研究了活性炭表面经硝酸氧化改性对硝酸铜在煤基活性炭中分散度的影响。此外,将经硝酸表面改性的商品活性炭采用浸渍法负载上硝酸铜催化剂,再经水蒸气二次活化制备了一种新的活性炭。结果表明,硝酸处理造成活性炭吸附性能的下降,并且硝酸处理的强度越高,活性炭吸附性能的下降程度越大。然而,对硝酸处理的活性炭经简单的水洗可恢复其吸附性能。研究结果还表明,活性炭经硝酸氧化提高了炭表面含氧官能团的数量,使催化剂在活性炭的内外表面均能均匀分布,提高了催化剂的分散度和抗烧结能力。活性炭经硝酸改性后再负载硝酸铜进行二次活化制备高性能活性炭,可使硝酸铜的催化性能得到进一步的提升。     

纳米碳管/活性炭复合电极苦咸水淡化的研究

通过对活性炭的N2吸附发现:活性炭具有高的比表面积和大的孔容,适合用于脱盐,但是其存在能耗大并且强度低等缺点.而纳米碳管是一种低电阻率,高强度的新型材料,采用活性炭复合纳米碳管,可以结合两者的优点,开发出一种低能耗、高脱盐率的复合电极.对各种复合比例的复合电极脱盐和能耗的测试发现:当纳米碳管的质量比占电极的10%时,脱盐量、能耗和强度达到最佳工艺,并且将该复合电极片数增大的测试发现:该电极脱盐效果好,在循环周期的大部分时间内以脱盐为主,脱盐率超过95 %.     

The effect of milling conditions on microstructures and mechanical properties of Al/MWCNT composites

Strengthening efficiency of multi-walled carbon nanotubes (MWCNTs), depending on their morphology and interface structure, is investigated for aluminum-based composites. The composites were fabricated by hot-rolling the powders which were ball-milled under various conditions. Milling variables affect the dispersion, dimension and interface structure of MWCNTs. With an insufficient milling intensity, MWCNTs are mostly located on the surface of powder, exposed to severe impact, and readily damaged. As the milling intensity increases, MWCNTs are embedded inside the powder and then dispersed through plastic deformation of the powder. Furthermore, aluminum infiltrates the core of MWCNTs during milling, increasing the diameter of MWCNTs. The outer surface of the Al-infiltrated MWCNTs sticks to the matrix, providing a strong interface by mechanical interlocking. The Al-infiltrated MWCNTs exhibit superior strengthening efficiency. On the other hand, the composite with unfilled MWCNTs, fabricated with a higher milling intensity, exhibits better ductility and pull-outs of the tubes in tensile fracture.     

Growth of graphene sheets under an oxyacetylene flame without a catalyst北大核心CSCD

High quality graphene sheets that had a low I-D/I-G and a high 2D intensity in Raman spectra were prepared by a catalyst-free acetylene flame method. The sheets were grown vertically on the surface of carbon particles to form a petal-like morphology. A high temperature, high pressure and short residence time of the flame intensified the decomposition and cyclization reaction's of acetylene, leading to the formation of graphene sheets in the gas phase. The turbulent flame and the gases released during the formation of the graphene sheets from carbon nuclei could be responsible for their petal-like morphology instead of an onion-like structure.     

Sidewall Functionalization of Single-Walled Carbon Nanotubes by Organometallic Chromium-Centered Free Radicals

The interaction of organometallic chromium-centered free radicals generated by the homolytic dissociation of (pentamethylcyclopentadienyl)chromiumtricarbonyl dimer in toluene with single-walled carbon nanotubes (SWNT) was investigated using ESR spectroscopy. Low values of g-factors of the radical species formed from chromium-centered free radicals and SWNT as well as invariability of disorder mode (D band) intensity in Raman spectra of pristine and functionalized SWNT after this reaction indicated that chromium-centered free radicals added to the surface of nanotubes through rather oxygen atoms than to sidewall carbon atoms. This is the first chromium-derivatization of carbon nanotubes.     

Crack closure and surface microcrack thresholds — Some experimental observations

Threshold stress intensity data at several positive stress ratios are reported for surface microcracks in an EN8 designation 0.40% carbon steel. It is proposed that observed anomalies in short crack behaviour can be explained by using a crack closure argument, and an indirect method of measuring crack closure changes in the short crack regime (where the value of the threshold stress intensity is not constant) is used to rationalize threshold behaviour for all crack lengths.     

Graphitization of polyacrylonitrile carbon fibers and graphite irradiated by γ rays

To investigate the effect of γ-ray radiation on the microstructure of carbon fibers (CF) and graphite, the carbon fibers and graphite were irradiated by ⁶⁰Co source at room temperature. X-ray diffraction results indicate that the interlayer spacing d₀₀₂ of CF and graphite decreased after irradiation. The intensity of (002) peak in CF decreased while the peak of the (002) plane in graphite becomes sharper after irradiation. Scanning electron microscopy combined with energy dispersive X-ray spectroscopy determines that γ-ray irradiation slightly improves the carbon content of CF surface layer. Compton scattering effect and heating caused by γ-ray are proposed to be responsible for the graphitization of CF and graphite.     

Effect of acoustic cavitation on ease of infiltration of molten aluminum alloys into carbon fiber bundles using ultrasonic infiltration method

Continuous M40J carbon fiber reinforced aluminum–magnesium alloy composite wires have been fabricated using ultrasonic infiltration. The infiltration phenomenon is examined from the viewpoint of acoustic cavitation. The ease of infiltration of the molten alloys was found to be proportional to the maximum intensity of the acoustic cavitation. The ease of infiltration and the intensity were enhanced by the addition of surfactant elements into the molten aluminum. Thus, a decrease in surface tension caused an increase in the generation of acoustic cavitation thereby resulting in infiltration. Therefore, the generation of the acoustic cavitation is an infiltration controlling factor during the use of ultrasonic vibration.     

Heating of three-layer solid aerosol particles by laser radiation

The heating of lidar-irradiated multilayer particles is analyzed theoretically and numerically by solution of the heat conduction equation. The internal intensity and temperature distributions are presented for particles composed of air, quartz, and carbon. It is shown that the heating times of such particles substantially depend on particle radii, layer position, and shell thickness. In particular, the decrease in thickness of the surface carbon layer can result in a reduction of the heating time of multilayer particles.     

Impact of Internal Pipe Grooves on Flow-Accelerated Corrosion of Small-Bore A-106 Carbon Steel Pipes

Segments of welded small-bore A-106 carbon steel from a piping system that experienced severe flow-accelerated corrosion were characterized for surface damage due to flow-accelerated corrosion (FAC). A computational fluid dynamics (CFD) analysis was done to compare findings of CFD model versus observed surface FAC damage inside the pipes. CFD results expressed in terms of turbulence intensity showed good agreement with actual surface damage due to FAC. It was concluded that the presence of internal grooves would cause turbulent flow regime, and therefore, it would cause pipe material damage.     

金属磁记忆技术检测低碳钢静载拉伸破坏的实验研究

为探索磁记忆现象的物理机制,在地磁场环境中,静载拉伸低碳钢板状试件.对应试件加载前、静载拉伸过程中不同的载荷水平以及断裂后等不同阶段,分别采用EMS-2003磁记忆诊断仪检测试样表面磁场强度垂直分量信号的变化.结果发现,加载前各试件初始磁状态对试件断裂后信号有影响.试件拉伸过程中塑性变形阶段内磁信号无较大数值变化,断裂后信号突变.拉伸过程中过零点漂移,最后集中在断口处.过零点对判定损伤破坏的铁磁构件危险区域具有一定意义.     

电热载荷对碳纤维复丝拉伸性能的影响

由于复合材料具有组成多元、各向异性等特点,电热载荷作用下碳纤维复合材料内部的响应行为十分复杂。为了研究碳纤维复合材料的电热响应,首先采用自制电热损伤试验平台,测试了不同电流强度下碳纤维复丝试样的表面温度分布,获得了碳纤维复丝电阻随温度的变化规律,初步揭示了碳纤维复丝具有温敏效应。然后,考察了不同电流处理条件下碳纤维复丝拉伸强度、断裂伸长率和拉伸模量的变化规律,并运用SEM和FTIR对电流处理前后材料的形貌和微观结构变化进行了分析。研究结果表明:纤维在通电过程中的产热效应促进了基体的进一步固化,同时提高了复丝界面的粘结性能;然而,当电流强度过大时,复丝的拉伸强度会因纤维本体的损伤或基体及界面层的烧蚀破坏而降低,从而降低了碳纤维复合材料的性能。      

The effects of stress ratio and grain size on near-threshold fatigue crack propagation in low-carbon steel

The effects of the stress ratio and the grain size on the fatigue crack growth near the threshold in a low carbon steel were analysed based on the crack-closure measurement and the microscopic observations of cracktip slip deformation and the fracture surface. The low-rate region A was divided into regions A1 and A2 in the relation of the rate against the effective stress intensity range. In regions A2 and B, the rate was expressed in a unique power function of the effective range without respect to the stress ratio and the grain size. In region A1 very close to the threshold, the rate was slower for larger grain sized material, and the effective threshold stress intensity factor increased linearly with the square root of the grain size. The slip-band zone in this region was rather independent of the stress intensity and was sized by the grain dimension. A model of the crack-tip slip bands blocked by the grain boundary was confirmed to be useful for analysing very slow growth as well as the threshold condition. The shear-mode fracture surface observed on the surface in region A1suggests the repeated nucleation mechanism for crack growth. The effects of the stress ratio and the grain size on the crack closure behavior near the threshold was quantified.