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91.
Quichen Zhang Ying Liang Steven B. Warner 《Journal of Polymer Science.Polymer Physics》1994,32(13):2207-2220
Heat treatment of aramid fiber was conducted in the temperature range 300–710°C nominally for 10 and 30 s in both static air and flowing nitrogen atmosphere. Crystallinity, crystal orientation, and crystallite size were determined using x-ray diffraction. Fibers with a skin–core structure were produced at intermediate temperatures, as revealed by scanning electron microscopy of fibers after partial dissolution of the fiber in 95–98% sulfuric acid. The skin, which forms in both nitrogen and air, is amorphous and brittle. It is insoluble in sulfuric acid, suggesting it is a cross-linked polymer. Formation of the skin may be facilitated by the removal of an aggressive chemical species that forms during heat treatment. The species may diffuse out of the outer layer of the fiber, allowing it to cross-link. The molecular weight of the dissolved core, analyzed using intrinsic viscosity, decreases with increasing heat treatment temperature. The tenacity, modulus, elongation-to-break, and toughness of fibers with a skin–core structure decrease with heat treatment and the fiber loses its fibrillar character. Mechanical property reductions are greater in air than nitrogen. X-ray data are also consistent with the notion that oxygen assists attack of crystals at high temperatures. Scanning electron microscopy shows that fibers have become skin–core composites with quite different mechanical properties between the two regions. A fiber failure mechanism is proposed. © 1994 John Wiley & Sons, Inc. 相似文献
92.
采用S iH4-C3H8-H2气体反应体系在S iO2/S i复合衬底上进行了S iC薄膜的APCVD生长。实验结果表明,H2表面预处理温度过高或时间过长会导致衬底表面S iO2层熔化再结晶或被腐蚀掉。通过“先硅化再碳化”的工艺方法可以较好地解决S iO2/S i复合衬底上S iC成核困难以及粘附性差的问题,同时还可以有效抑制S iO2中的O原子向S iC生长膜扩散。选择预处理温度和薄膜生长温度为1180℃、H2预处理、S iH4硅化和C3H8碳化时间均为30 s的最佳生长条件时,可以得到<111>晶向择优生长的多晶3C-S iC外延薄膜,薄膜生长速率约为2.0~2.5nm/m in. 相似文献
93.
《Chemical record (New York, N.Y.)》2018,18(1):55-64
Carbon‐based nanomaterials have been widely studied in the past decade. Three approaches have been developed for the preparation of single‐handed helical carbonaceous nanotubes. The first approach uses the carbonization of organopolymeric nanotubes, where the organic polymers are polypyrrole, 3‐aminophenol‐formaldehyde resin, and m‐diaminobenzene‐formaldehyde resin. The second approach uses the carbonization of aromatic ring‐bridged polybissilsesquioxane followed by the removal of silica. Micropores exist within the walls of the carbonaceous nanotubes. The third approach uses the carbonization of organic compounds within silica nanotubes. This hard‐templating approach drives the formation of helical carbonaceous nanotubes containing twisted carbonaceous nanoribbons. All of these helical carbonaceous nanotubes exhibit optical activity, which is believed to originate from the chiral π‐π stacking of aromatic rings. They can be used as chirality inducers, and for lithium‐ion storage. 相似文献
94.
粘胶纤维毡由化学药品LA催化预处理,然后经高温820~850℃下水蒸汽活化来制备粘胶活性炭纤维,其孔结构受热解炭化和活化过程的影响。本文研究了不同升温速率、不同温度下通入水蒸汽以及不同空速对活化结果的影响;同时考察了粘胶炭纤维与水蒸汽反应的动力学以及粘胶活性炭纤维的吸附性能。 相似文献
95.
96.
Dr. Joe Briscoe Adam Marinovic Dr. Marta Sevilla Dr. Steve Dunn Dr. Magdalena Titirici 《Angewandte Chemie (International ed. in English)》2015,54(15):4463-4468
New hybrid materials consisting of ZnO nanorods sensitized with three different biomass‐derived carbon quantum dots (CQDs) were synthesized, characterized, and used for the first time to build solid‐state nanostructured solar cells. The performance of the devices was dependent on the functional groups found on the CQDs. The highest efficiency was obtained using a layer‐by‐layer coating of two different types of CQDs. 相似文献
97.
98.
采用超临界流体精密分离(SCFE)的方法将辽河减压渣油切割成多个窄馏分,在430℃、常压条件下对各馏分进行不同时间(2~17h)的热处理,测定了反应残余物的H/C元素比并在正交偏光下对反应残余物的光学显微结构进行观察。对渣油及其超临界戊烷精密分离馏分的热反应性能及反应残余物性质与原料性质的关系进行了讨论。研究结果表明:渣油组成的变化对其在碳化过程中的中间相形成、发展有十分重要的影响,采用SCFE可以将渣油切割为具有不同族组成的窄馏分,窄馏分的碳化试验表明,对组成适宜的窄馏分,在反应中可以形成各向异性发达的中间相,SCFE是一种改善重质烃类混合物碳化性能的有效技术。 相似文献
99.
Yudong Wang Qi Liu Mengdie Xu Guiqing Shu Minjuan Jiang Gangxuan Fei 《Journal of Macromolecular Science: Physics》2017,56(9):670-681
Palladium-carbon/montmorillonite (Pd-C/MMT) heterogeneous catalysts were prepared by carbonization of chitosan in palladium-chitosan/montmorillonite (Pd-CS/MMT) composites under a N2 atmosphere. The main purpose of this study was to determine the effects of the carbonization temperature (250, 450, and 650°C) on the material microstructure and its catalytic performance. X-ray diffraction patterns revealed that the formation of an intercalation of the carbonaceous material between the clay mineral layers which was also confirmed by Fourier transform infrared spectra results. The N content of the Pd-C/MMT catalyst decreased as the carbonization temperature was increased. Thermogravimetry curves revealed that the thermal stability of the Pd-C/MMT catalyst increased obviously as the carbonization temperature was increased. Pd nanoparticles, sized at about 20 nm, were mainly dispersed on the surface of the MMT, as observed by high-resolution transmission electron microscopy (HR-TEM). The prepared Pd-C/MMT catalysts had good catalytic activity when applied in Heck coupling reactions of aromatic halides and alkenes to produce aryl olefins. The relations between the recyclability and the material composition are discussed. 相似文献
100.