Papers by Keyword: Graphitization

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Authors: Zhi Yu Gao, Wei Hua Xue, Xin Ren, Yue Jun Sun, Shao Bin Yang
Abstract: Statistical values (S′) of phase structure formation factor (S) of alloying elements in cast iron are calculated by the calculation method on statistical value of alloy phases electronic structure parameters based on the empirical electron theory of solids and molecules (EET), and the solidification process of cast iron is discussed by S′. According to the effects of phase structure formation factor (that is S′) on the formation process of graphite, cementite and austenite, electronic structure parameters criterion of graphitization behavior of alloying elements is advanced and the results agree well with the practical cases.
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Authors: Anatoly M. Strel'chuk, Eugene B. Yakimov, Alexander A. Lavrent’ev, Evgenia V. Kalinina, Alexander A. Lebedev
Abstract: 4H-SiC p+nn+ structures fabricated by implantation of Al into a commercial n-type 4H-SiC epitaxial layer doped to (3-5)Ÿ1015cm-3 have been studied. Structures with unstable excess forward current were characterized by electron beam induced current (EBIC) and secondary electron (SE) methods and by Auger-electron spectroscopy (AES). Numerous defects were found with a depth which exceed the thickness of the p+-layer. Also, it was demonstrated that the concentration of carbon on the SiC surface always exceeds that of silicon, which may be the reason for the initially unstable conductivity via the defects.
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Authors: Xiu Juan Guo, Shu Rong Wang
Abstract: In this study, the pyrolytic char from fast pyrolysis of bamboo powder was activated with KOH solvent at 500, 600 and 700°C. And the characterization of chars before and after activation was carried out by means of N2 physisorption, XRD, FTIR and SEM. A better porous structure of activated chars was found. Compared with pyrolytic char, activated chars had higher fixed carbon content and BET surface areas, and fewer active functional groups on the surface to increase the degree of graphitization. With the temperature increasing, the activated char became much more suitable as the substitute of commercial activated carbon. Therefore, the char activated at 700°C was most stable and had the best properties as catalyst support and absorbent material
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Authors: Graham R. Lobley, Waleed L. Al-Otaibi
Abstract: Unexpected tube failure is the major factor causing unreliability in utility boilers. The first step in analyzing tube failures is to identify the active damage mechanisms. Three tube damage mechanisms related to overheating are presented and possible root causes are discussed to resolve these tube failures. Damage mechanisms can be recognized by metallurgical evaluation, comprising a combination of both visual and microexamination, complemented by chemical analyses of tube or fireside deposits, as appropriate. Characterizing the degree of microstructural degradation can also help to confirm and separate various potential high temperature tube damage modes, such as long or short term overheating, as well fuel ash attack. Carbon steel is the standard tube material for high pressure boilers (typically up to 625 psig steam) and has a normal design temperature limit of about 440 °C. However, microstructural changes occurring as a result of higher temperature exposures in service can include carbide spheroidization, graphitization and other transformations. Metallography is powerful tool for evaluating overheated failures and also for fire damage assessment. Evaluating overheated steel microstructures utilizes the principles of steel heat treatment and application of the iron-iron carbide equilibrium diagram.
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Authors: Hao Xiao, Yong Gen Lu, Xian Ying Qin, Ya Wen
Abstract: An investigation was conducted to determine the influence of high temperature treatment from 1600°C to 2800°C under stretching stress of 10MPa on PAN-based carbon fiber structure and physical properties. The tensile strength of fibers decreased from 4.5GPa to 2.97GPa with increasing treatment temperature up to 2800°C,while the modulus of fibers increased from 230GPa to 375GPa The texture in the longitudinal surface of fibers through heat treatment was characterized using a scanning electron microscopy. The contours of fiber surface became accidented with gaps becoming deeper as temperature increased. It has been observed that both the crystallite sizes (La, Lc) and the degree of preferred orientation increasd, while the crystallite interlayer spacing (d002) decreased by X-ray diffraction analysis with increasing heat-treatment temperature. The total porosity of fibers decreased from 21.01% to 15.09% and while the density of fibers increased from 1.720g/cm-3 to1.886 g/cm-3 with increasing heat-treatment. In addition, the relationship between mechanical properties and structure of variants was also explored in detail.
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Authors: Yun Jiang, Hong Wen Ma, Yu Qin Liu
Abstract: The structure and composition of carbon materials affect obviously the result of carbothermic reduction of magnesia. Coke, charcoal and graphite were used in reduction experiments under the same conditions. The reactivity ratio of magnesia and XRD pattern of residues were analyzed and compared. The reactivity ratio of magnesia by coke was similar to the one by charcoal. The amorphous carbon in coke graphitized partly in reduction experiments of 1673K. The results show that the effective composition in coke is the amorphous carbon. It also suggests that the temperature of reaction should be control less than 1700K to avoid the amorphous carbon’s graphitization.
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Authors: Jörg Pezoldt
Abstract: Carbon is able to crystallise in different allotrope modifications. They mainly differ in the dominating bindings formed in dependence on the hybridization sp, sp2 and sp3 of the carbon atoms. The present work demonstrates the formation of two different forms of car¬bon allotropes by heating both polar surfaces of on axis 6H-SiC(0001) and 6H-SiC(000 ) crystals to temperatures above 1600°C. In consequence of the structural evolution graphite-like (sp2-hybridised) and carbine-like (sp-hybridised) allotropic carbon modifications were obtained.
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Authors: Gemma Rius, Narcis Mestres, Yayoi Tanaka, Hidetoshi Miyazaki, Osamu Eryu, Philippe Godignon
Abstract: SiC crystal is a wide band gap material of high hardness and chemical inertness. Graphene is nowadays a ubiquitous 2D material that would revolutionize many applications. Combining the characteristics of SiC and graphene higher performance and efficiency are expected, e.g. for high frequency electronic devices. The obtaining of graphene directly on SiC substrates by a single step thermal decomposition process is promising, but optimal standardized conditions are not established. We present the use of chemical-mechanical polishing (CMP) as a pre-graphene growth SiC conditioning to enable deep comprehension of the mechanisms of SiC decomposition and control towards selective formation of graphene.
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Authors: H.M. Mobarak, E. Niza Mohamad, H.H. Masjuki, M.A. Kalam, K.A.H. Al Mahmud
Abstract: Large amount of unsaturated and polar component of oils enhance the lubrication of ferrous materials. DLC coatings can effectively lower the coefficient of friction (CoF) and wear rate of engine components, consequently improving the fuel efficiency and durability of these components. Therefore, the interaction between nonferrous coatings (e.g., DLC) and vegetal oil must be investigated. A ball-on-plate tribotester was used to run the experiments using stainless steel plates coated with amorphous hydrogenated (a-C:H) DLC and hydrogen-free tetrahedral (ta-C) DLC sliding against 440C stainless steel ball. Raman analysis was performed to investigate the structural change of the coatings. At high temperatures, the CoF decreases in both coatings but the wear rate increases in the a-C:H and decreases in the ta-C DLC-coated plates. CoF and wear rate (coated layer and counter surface) are mostly influenced by coating graphitization. The degree of graphitization increases with increasing temperature. Graphitization occurs in the tribological contact because of friction-induced heating under contact and high contact stress conditions.
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Authors: Hai Sheng Shi, Guang Min Luo, Jun Fei Fan, Yi Jian Lin, Jing Guo Zhang
Abstract: The effect of hot rolling parameters on graphitization of a spray formed ultra high carbon steels(UHCSs) was described. The number of graphite stringers and graphite area fractions increased with the increase of rolling reduction. Graphite stringers nucleated at small pores and grew by carbon diffusion from adjacent austenite during hot rolling. Alloy contents, pores and hot deformation atγ+Fe3C phase range are the key factors for graphitization.The graphite stringers of UHCSs have little effect on tensile strength, but reduce the ductility at room temperature.
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