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Li S.,Beihang University | Li S.,Beijing Composite Materials Co. | Zhang Y.,Beihang University
Cailiao Yanjiu Xuebao/Chinese Journal of Materials Research | Year: 2011

Amorphous Si-Al-C-N ceramics with varied aluminum contents, which were derived from polyaluminasilazanes at 1200°C, were heat-treated at 1400-1800°C. The structures of precursors and the crystallization behaviors, free-carbon and microstructure of Si-Al-C-N were characterized by Infrared spectrometry, X-ray diffraction, Raman spectra and transmission electron microscopy. The effects of aluminum contents, crystallization temperatures and times on crystallization properties of amorphous Si-Al-C-N were investigated. The results show that amorphous Si-Al-C-N ceramics are amorphous at 1400°C, but include free-carbon. Nano-scale β-Si3N4 and α-Si3N4 nuclei are precipitated at 1500°C. The α-Si3N4 nucleus transforms into β-Si3N4 after treated at 1600°C, at the same time, a minute quantity of α-SiC and 2H-SiC/AlN solid solution nuclei precipitated. At 1700°C a large number of 2H-SiC/AlN solid solution crystals and a few α/β-SiC crystals precipitated besides β-Si3N4, and the β-Si3N4 phase in the Si-Al-C-N ceramic with lowest aluminum content disappears. At 1800°C only β-SiC and 2H-SiC/AlN solid solution crystal are observed. But phase separation takes place at this temperature, leading to the formation of AlN-rich and SiC-rich solid solution region, respectively. With increasing aluminum content, crystallization ability of amorphous Si-Al-C-N ceramics and quantities of grain increase. Nano-scale crystals precipitate from the amorphous Si-Al-C-N at 1500°C, but even until 1800°C the precipitated crystals are still nano-scale crystals. The high-temperature crystallization process of amorphous Si-Al-C-N with high covalence is a process controlled by thermodynamics. © Copyright.

Li S.,Beihang University | Li S.,Beijing Composite Materials CO. | Zhang Y.,Beihang University
Chinese Journal of Inorganic Chemistry | Year: 2011

Polyaluminasilazanes with nominal Si/Al molar ratio of 3 were synthesized by reaction of poly (methylvinyl)silazane with aluminum isopropoxide at 90, 100 and 120°C, respectively. The structures of the precursors were characterized by FTIR and NMR. The results indicate that, with the synthesis temperature increasing, the intensities of Al-N FTIR vibration peak (1 450 cm-1) and AlON2 (8 ppm) and AlO2N (-1 ppm) groups of 27Al NMR increase. The higher the reaction temperature is, the more the Al-N bonds are. The dehydrocoupling process may be a three-stage reaction process and the structure of polyaluminasilazane synthesized at 120°C is the most complicated one due to the highest synthesis temperature. The pyrolysis processes of the precursors were studied by TG/DTA, FTIR and gas chromatography (GC). The synthesis temperatures have no significant effect on ceramization process and ceramic yield. Based on DTA curve, a further crosslink takes place at 475°C during pyrolysis process. Besides, the released gases during pyrolysis process are identified by GC analysis as oligosilazane, CH4, C2H4, H2 and NH3. According to the XRD and SEM results, the product pyrolyzed at 1 200°C under nitrogen atmosphere is a homogenous amorphous phase.

Li S.,Beihang University | Li S.,Beijing Composite Materials Co. | Zhang Y.,Beihang University
Journal of Non-Crystalline Solids | Year: 2012

Multinuclear solid-state NMR spectroscopy, FTIR and Raman experiments are employed to investigate the pyrolytic conversion of blended polycarbosilane and polyaluminasilazane (denoted CA) up to 800 °C, with the aim of studying structural evolutions and interactions between polycarbosilane and polyaluminasilazane during the pyrolysis process. Vinyl and SiCH 3 units can react with Si-H, SiCH 3 and Si-CH 2-Si groups below 400 °C. These crosslinking reactions can increase the ceramic yield of the blended precursors. At 500 °C aromatic carbon is formed, and N-H and Si-H groups vanish at 600 °C and 700 °C, respectively. At 600 °C, SiCH 3 and Si-H units can further react with SiCN 3, SiC 2N 2, N-H and C-H units. An amount of amorphous carbon and CSi 4 and CSi 3H groups are detectable at 800 °C. Even at this temperature there are still many aromatic protons. In addition, there are also SiC 4, SiC 3N, SiCN 3 and SiN 4 units. Silicon forms SiN 4 more readily than SiC 4. Many AlN 5 groups transform into AlN 6 groups. The D and G bands of graphite are observed in CA pyrolyzed at 1400 °C. According to the XRD patterns, the reflection of crystalline β-Si 3N 4 vanishes at 1700 °C, and the residue pyrolyzed at 1800 °C mainly contains a large number of 2H-SiC/AlN solid solution crystals and a few β-SiC crystals. © 2011 Elsevier B.V. All rights reserved.

Ding W.,University of Jinan | Chen J.,University of Jinan | Liu J.,University of Jinan | Pang Z.,Beijing Composite Materials Co. | Guan R.,University of Jinan
Asian Journal of Chemistry | Year: 2013

The influences of vinyl ester resin type sizing agent on the properties of carbon fiber and composite were studied. The yarn abrader, X-ray photoelectron spectroscopy were used to characterize wear resistance and chemical element of carbon fiber. Interlaminar shear strength of composite was tested by universal testing machine. The results indicated that wear resistance of sized carbon fiber was significantly improved. X-Ray photoelectron spectroscopy results demonstrated that the activated function groups of sized carbon fiber were more than desized one. The interfacial adhesion of sized carbon fiber/vinyl ester resin (CF/VE) composite was strengthened and interlaminar shear strength of sized carbon fiber/vinyl ester resin composite reached 45.9 MPa.

Ren M.,Dalian University of Technology | Li T.,Queensland University of Technology | Huang Q.,Beijing Composite Materials Co. | Wang B.,Dalian University of Technology
Journal of Reinforced Plastics and Composites | Year: 2014

Advanced grid stiffened composite cylindrical shell is widely adopted in advanced structures due to its exceptional mechanical properties. Buckling is a main failure mode of advanced grid stiffened structures in engineering, which calls for increasing attention. In this paper, the buckling response of advanced grid stiffened structure is investigated by three different means including equivalent stiffness model, finite element model and a hybrid model (H-model) that combines equivalent stiffness model with finite element model. Buckling experiment is carried out on an advanced grid stiffened structure to validate the efficiency of different modeling methods. Based on the comparison, the characteristics of different methods are independently evaluated. It is arguable that, by considering the defects of material, finite element model is a suitable numerical tool for the buckling analysis of advanced grid stiffened structures. © The Author(s) 2014.

Ren M.,Dalian University of Technology | Huang Q.,Beijing Composite Materials Co. | Liu C.,Dalian University of Technology | Li T.,Queensland University of Technology
Journal of Reinforced Plastics and Composites | Year: 2015

The co-curing process for advanced grid-stiffened (AGS) composite structure is a promising manufacturing process, which could reduce the manufacturing cost, augment the advantages and improve the performance of AGS composite structure. An improved method named soft-mold aided co-curing process which replaces the expansion molds by a whole rubber mold is adopted in this paper. This co-curing process is capable to co-cure a typical AGS composite structure with the manufacturers recommended cure cycle (MRCC). Numerical models are developed to evaluate the variation of temperature and the degree of cure in AGS composite structure during the soft-mold aided co-curing process. The simulation results were validated by experimental results obtained from embedded temperature sensors. Based on the validated modeling framework, the cycle of cure can be optimized by reducing more than half the time of MRCC while obtaining a reliable degree of cure. The shape and size effects of AGS composite structure on the distribution of temperature and degree of cure are also investigated to provide insights for the optimization of soft-mold aided co-curing process. © The Author(s) 2015.

Huang Q.Z.,Beijing Composite Materials Co. | Hu Z.H.,Beijing Composite Materials Co.
Advanced Materials Research | Year: 2013

Water absorption behavior and mechanical properties variation of the carbon fiber reinforced epoxy matrix composites (CFRP) immersed into artificial seawater were investigated by experiments. The rate of water absorption of the composite specimens is gradually reducing as the duality of immersion increasing. Due to the reversible and irreversible changes in the resin matrix and the failure of the fiber/matrix interface, the tensile strength, the flexural strength, and the ILSS of the composite specimens after 70 days' immersion decreased 9.3%, 13%, and 17% respectively. And the tensile modulus and the flexural modulus the specimens after desorption were 83% and 70% of the original state, respectively. © (2013) Trans Tech Publications, Switzerland.

Fu Y.,Beijing Institute of Technology | Song J.,Beijing Composite Materials Co. | Song J.,Beijing University of Chemical Technology | Zhu Y.,Beijing Institute of Technology | Cao C.,Beijing Institute of Technology
Journal of Power Sources | Year: 2014

Amorphous mesoporous Ni(OH)2 nanoboxes are synthesized by template-engaged routes. The nanoboxes are characterized by SEM, TEM, XRD, XPS and BET methods. The nanoboxes have uniform morphology of 450-500 nm, high surface area of 214.6 m2 g-1 and mesoporous structure of 4-20 nm. Electrochemical characterization are tested using cyclic voltammetry, chronopotentiometry and impedance spectroscopy, respectively. These amorphous mesoporous Ni(OH)2 hollow nanoboxes shows high specific capacitance of 2495, 2378, 2197, 1993 F g-1 at discharge current of 1, 2, 5 and 10 A g-1 respectively. The property tests demonstrate the high specific capacitance and excellent cycling of the amorphous Ni(OH)2 nanoboxes material for high-performance electrochemical pseudocapacitors. © 2014 Elsevier Ltd. All rights reserved.

Zou C.,National University of Defense Technology | Zhang C.,National University of Defense Technology | Xiao Y.,Beijing Composite Materials Co. | Li B.,National University of Defense Technology | And 2 more authors.
Journal of Non-Crystalline Solids | Year: 2012

SiNO f/BN composites with silicon oxynitride fibers in a boron nitride matrix were prepared by precursor infiltration and heating (PIH) using borazine as precursor. The densification, microstructure and mechanical properties of the composites were studied. The density of SiNO f/BN composites increased rapidly with PIH cycles. The composites prepared by two and three PIH cycles are highly tolerant of damage due to the high retained fiber strength, dense matrix and moderate bonded fiber/matrix interface. Desirable high temperature mechanical properties of SiNO f/BN composites were also obtained. The residual flexural strength and elastic modulus of composites at 1300 °C were 131.0 MPa and 26.6 GPa, respectively. © 2012 Elsevier B.V.

Liu K.,National University of Defense Technology | Zhang C.,National University of Defense Technology | Xiao Y.,Beijing Composite Materials Co. | Cao F.,National University of Defense Technology | And 2 more authors.
Materials Science and Engineering A | Year: 2013

Si3N4-BN composites were fabricated via die pressing and PIP route using borazine as the precursor. The composites are composed of h-BN, α-Si3N4 and β-Si3N4 with 3.46wt% α to β phase transition. Desirable mechanical properties of the composites were achieved and special interfacial microstructures can be observed. © 2013 Elsevier B.V.

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