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Influence of oligomeric silsesquioxane coating treatment on interfacial properties of CF/PAA composites
ZHANG Xuezhong, HUANG Yudong, WANG Tianyu, HU Lijiang
Front. Mater. Sci.. 2007, 1 (1): 40-48.
https://doi.org/10.1007/s11706-007-0008-y
Carbon fibres (CF) were modified with different oligomeric silsesquioxane (SSO) coatings to improve the interfacial property of carbon fibres/polyarylacetylene (CF/PAA). The interlaminar shear strength (ILSS) of CF/PAA was tested to determine the effect of the treatment. Atomic force microscopy (AFM) in force modulation mode was adopted to study the cross-section surface of unidirectional CF/PAA composites and the relative stiffness of various phases, including CF, interphase and resin. The probability histogram and line distribution of CF/PAA cross-section surface relative stiffness, obtained from the statistical analysis of relative stiffness image, were used to compare and study the interface characterizations of composites. The results show that the ILSS increases effectively and the effects on interfacial characterizations are distinguished from each other in accordance with the CF surface modified with different SSO coatings owing to the various structures. Cage oligomeric silsesquioxane, including large organic groups (methacryl isobutyl-POSS), has better treatment result. AFM observations lead to the conclusion that an interfacial transition layer with different morphology and stiffness appears in CF/PAA composites after being treated by the SSO coatings of different structures. It can be inferred that the appearance of the transition layer may contribute to the improvement of fibre/matrix adhesion.
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Effect of lead on formation and dielectric tunability of (Pbx,Sr1–x)0.85Bi0.1TiO3 thin films
ZHAO Yonglin, DU Piyi, WENG Wenjian, HAN Gaorong
Front. Mater. Sci.. 2007, 1 (1): 59-64.
https://doi.org/10.1007/s11706-007-0011-3
(Pbx,Sr1 x)0.85Bi0.1TiO3 thin films with the perovskite phase structure were prepared on an ITO glass substrate by sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and an impedance analyzer were respectively used in order to characterize the phase status, morphology and dielectric properties of the thin films. The results show that during the formation process of (Pbx, Sr1 x)0.85KBi0.1TiO3 thin films, the nucleus of the perovskite phase are initially formed and then congregated. These aggregated nucleus are then transformed as the perovskite-phase crystalline in the thin film. Finally, the crystalline phase grows and separates gradually to form the perfect crystalline-phase structure. The content of the perovskite phase formed in the thin film under rapid thermal process (RTP) is more than that formed under traditional heat treatment with kinetic equilibrium. This is due to the high active decomposed ions that form the perovskite phase directly when heat-treated by RTP. The formation of the perovskite phase therefore overcomes a much lower barrier under RTP than that under traditional calcinations. The structure of the perovskite phase has a close relation to the ratio of Pb/Sr in the system because of the radius difference between Pb2+ and Sr2+. The transformation temperature between the cubic and the tetragonal structures of the perovskite phase increases with increasing Pb2+ content because the radius of Pb2+ is larger than that of Sr2+. It appears at room temperature when the content of Pb2+/Sr2+ is about 40/60 in the thin film. Meanwhile, the tetragonality of the perovskite phase is increased when Pb2+ ions increase due to its high polarization. The higher tunability of the (Pbx,Sr1 x)0.85Bi0.1TiO3 thin film is exhibited when the film composition is close to the transformation point between the paraelectric and ferroelectric phases. Pb2+ions show a dominant factor to affect the Curie point of the system and then changing tunability.
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TTT diagram and phase structure control of 2/4 functional epoxy blends used in advanced composites
ZHANG Ming, AN Xuefeng, TANG Bangming, YI Xiaosu
Front. Mater. Sci.. 2007, 1 (1): 81-87.
https://doi.org/10.1007/s11706-007-0015-z
A 2/4 functional epoxy blend system (DGEBA/TGMDA) cured with 4,4´-diamino diphenyl sulphone (DDS) was used as the raw material in this research. Round disk compression mode DMA (dynamic mechanical analyzer) was employed to study the gelation at the different temperatures, and the relationship between gel-time (tgel) and temperature was obtained. The cure kinetics was studied by dynamic DSC (differential scanning calorimetry) analysis, and the parameters of the cure reaction were obtained to establish a phenomenological model. The relationship between glass transition temperature (Tg) and cure degree (α) was analyzed by an isothermal plus dynamic DSC method based on the DiBenedetto equation, which gave a mathematical description of Tg as a function of both time and temperature. Characteristic temperatures such as Tg0, gelTg and Tg" were also determined. The cure degree at gelation turned out to be 0.4539, while the temperature at which vitrification line and gel line transected was found to be 70.2?C. The time-temperature-transition (TTT) diagram was plotted based on the work above, which served as a tool for process optimization in the manufacture of advanced composites. A new cure procedure of this practical thermosetting system was extracted from the TTT diagram by prolonging the pre-gel time to restrict the diffusion ability and the flow ability of the solution. The final phase structure was proved by SEM to be ex-situ phase morphology compared with the traditional in-situ phase structure by exerting different cure procedures.
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Preparation and properties of ZnO thin films deposited by sol-gel technique
LAN Wei, PENG Xingping, LIU Xueqin, HE Zhiwei, WANG Yinyue
Front. Mater. Sci.. 2007, 1 (1): 88-91.
https://doi.org/10.1007/s11706-007-0016-y
Zinc oxide (ZnO) thin films were deposited on (100) Si substrates by sol-gel technique. Zinc acetate was used as the precursor material. The effect of different annealing atmospheres and annealing temperatures on composition, structural and optical properties of ZnO thin films was investigated by using Fourier transform infrared spectroscopy, X-ray diffraction, atomic force microscopy and photoluminescence (PL), respectively. At an annealing temperature of 400vH in N2 for 2 h, dried gel films were propitious to undergo structural relaxation and grow ZnO grains. ZnO thin film annealed at 400vH in N2 for 2 h exhibited the optimal structure and PL property, and the grain size and the lattice constants of the film were calculated (41.6 nm, α = 3.253 Åand c = 5.210 Å). Moreover, a green emission around 495 nm was observed in the PL spectra owing to the oxygen vacancies located at the surface of ZnO grains. With increasing annealing temperature, both the amount of the grown ZnO and the specific surface area of the grains decrease, which jointly weaken the green emission.
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Portevin-Le Chatelier effect of LA41 magnesium alloys
WANG Cong, WANG Cong, HAN Enhou, HAN Enhou, XU Yongbo, XU Yongbo
Front. Mater. Sci.. 2007, 1 (1): 105-108.
https://doi.org/10.1007/s11706-007-0019-8
Uni-axial tensile deformation of LA41 magnesium alloy has been carried out and the Portevin-Le Chatelier (PLC) effect, also known as serrated flow or plastic instability, is observed. This kind of alloy exhibits negative strain rate sensitivity (SRS) at room temperature, that is, SRS is negative at the strain rate range from 3.33?10-4 to 6.66?10-3 s-1 at ambient temperature. Both ultimate stress (?b) and 0.2% proof stress (?0.2) decrease when strain rate (ε°) increases, whilst critical strain (εc) of serrated flow is found to rise with enhancing ε°. A new explanation for this unusual phenomenon is presented. The model of dynamic strain aging (DSA) is established through diffusion of solute atoms to mobile dislocations, which are temporarily arrested at obstacles. Such interaction renders the movement of mobile dislocations more difficult so as to necessitate the required force to overcome the obstacles.
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21 articles
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