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101.
High dielectric constant (high-k) polymer composites are of great interest for embedded capacitor applications. Previously,
we demonstrated that epoxy—aluminum composites are promising for embedded capacitor applications, because they have a high
dielectric constant and a low dielectric loss due to the core—shell structure of the self-passivated aluminum particles. In
this work, to further understand the dielectric behavior of aluminum composites, lower-loss polymers such as silicone, polyimide,
polynorbornene, and benzocyclobutene were explored as matrices for the aluminum composites. It is found that the polymer matrices
can significantly change the dielectric properties of the aluminum composites. A polymer matrix with a lower dielectric constant
generally results in a lower dielectric constant of its aluminum composites. In this regard, polymer—aluminum composites have
a similar dielectric characteristic as polymer—ceramic composites. Thermomechanical properties of aluminum composites were
characterized by a thermomechanical analyzer. 相似文献
102.
Thermochemical analyses of interfacial reactions in titanium, zirconium, and hafnium diboride reinforced oxidematrix composites have been carried out to evaluate the chemical compatibility. The chemical reactivity of these diborides with oxygen and the high volatility of B2 O3 ( l ) at reduced oxygen pressures are concerns during processing and operating conditions. The thermochemical stability and the vaporization behavior of B2 O3 ( l ) are discussed in terms of partial pressures of dominant gaseous species of the boron-oxygen system at 1700 and 2300 K. The TiB2 /ZrO2 and TiB2 /HfO2 systems are thermodynamically stable in a limited oxygen pressure range. The TiB2 /Al2 O3 system is stable, but the reactions in this system may apparently be accompanied by formation of gaseous products (B2 O3 , AlO, Al2 O, and lower boron oxides) in the presence of elemental oxygen. These thermochemical considerations are very useful in evaluating the effectiveness of oxides as diffusion barrier coatings on diboride reinforcements. 相似文献
103.
T. Chatterjee K. Yurekli V.G. Hadjiev R. Krishnamoorti 《Advanced functional materials》2005,15(11):1832-1838
Dispersions of single‐walled carbon nanotubes (SWNTs) in poly(ethylene oxide) (PEO) assisted by a lithium‐based anionic surfactant demonstrate an electrical percolation of 0.03 wt.‐% and a geometrical percolation, inferred from melt rheometry, of 0.09 wt.‐%. Both the melting temperature and the extent of crystallinity of the PEO crystals decrease with increasing SWNT loading. Raman spectroscopy of the nanocomposites indicates a down‐shift of the SWNT G‐modes and suggests that the nanotubes are subjected to tensile stress transfer from the polymer at room temperature. 相似文献
104.
Asbestos fibres, of the chrysotile variety, and chopped carbon fibres were pretreated by an in-situ polycondensation technique eventually resulting in a polyamide coating on the fibre surface. Ionomer based composites containing either carbon or asbestos fibres in random in plane fibre orientation were prepared, and the influence of this coating process on the tensile properties was investigated. It was found that for the asbestos-filled composites the presence of the nylon 6,6 interlayer improves the tensile performance, especially at moderate polyamide depositions. This is not the case with the pretreated carbon-filled composites for which carbon fibres with higher polyamide contents are preferred. Combinations of the treated asbestos fibres with carbon and/or aramid fibres may be used to reduce the asbestos content in asbestos-only based engineering plastics. 相似文献
105.
The effect of heat treatment on microstructure of a plain-weave carbon fabric reinforced carbon-carbon composite with phenolformaldehyde-derived carbon matrix was investigated by X-ray diffraction. The diffraction patterns were analysed by the least-square fitting program Carbonxs. After heat treatment from 1000 to 2800 °C the interplanar distance of (002) planes decreased from 3.488 to 3.420 Å and the lattice parameter in basal plane increased from 2.440 to 2.464 Å, respectively. Simultaneously, the coherent block size in the basal plane directions increased from 18 to 54 Å, which was accompanied by an increase of the fraction of organised carbon atoms from 0.50 to 0.85. The 002 diffraction profile of the composite was much narrower than the sum of peaks of the matrix and fabric alone. This can probably be caused by a better crystallographic ordering (or by a partial graphitisation) of the matrix in the composite. On the other hand, the composite Young’s modulus slightly decreased with the treatment temperature increasing from 2200 to 2800 °C in spite of the established strong improvement of fibre crystallinity and, therefore, fibre modulus. The mechanisms diminishing the modulus of composite (e.g. partial matrix graphitisation at the fibre/matrix interface and decreasing fibre/matrix contact area) probably prevailed over the increasing contribution of the fibre modulus. 相似文献
106.
Unidirectional (UD) and multidirectional (MD) flax/polypropylene composites were studied. Flax with varying retting degree and boiled flax was used as reinforcement for the UD composites and unmodified and maleic acid anhydride modified polypropylene (MAA-PP) was used as matrix. Multidirectional flax/polypropylene composites were manufactured on laboratory scale and on pilot scale. They were made from needle-punched hybrid flax/PP non-wovens. Normally retted flax as well as boiled flax was used. For the specimens made on pilot scale, a third kind of flax, namely bleached flax was also studied. The influence of different process times and temperatures on the mechanical properties of the composites was analysed. Generally, the composites have adequate good mechanical properties. The unidirectional composites of boiled flax combined with MAA-PP show the best mechanical properties. Contrary to the UD composites, flax treatment did not lead to the expected property improvements for MD composites. 相似文献
107.
Donghua Zhang 《应用聚合物科学杂志》2006,101(6):4372-4377
Polyaniline (PANI) was synthesized by chemical oxidative polymerization of aniline (ANI) in the presence of alumina (Al2O3) particles. The polymerization of ANI occurred preferentially on the surfaces of the particles, resulting core–shell structured alumina–polyaniline (Al2O3‐PANI) particles. Morphology examination showed that with decreasing of the weight ratio of Al2O3/ANI in the reactants, the thickness of the PANI layer increased and changed from an even surface morphology to a particulate morphology. UV–vis and Fourier transformed infrared (FTIR) spectra indicated that there is no chemical interaction between the PANI layer and the Al2O3 surfaces. The PANI layer adhered well to the particles and can be used as anticorrosive fillers for polymer coatings. Enhanced corrosion protection performance was achieved for the emeraldine base (EB) form of PANI deposited Al2O3 particles (Al2O3‐EB) filled epoxy coating on carbon steel in 3.0 wt % aqueous NaCl solution. The particles demonstrate both excellent corrosion protection performance and lower cost, which will be of great importance in practical applications. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4372–4377, 2006 相似文献
108.
Antonios E. Giannakopoulos Kristin Breder 《Journal of the American Ceramic Society》1991,74(1):194-202
The improved fracture resistance of whisker-reinforced ceramic-matrix composites involves more than one energy-absorbing mechanism. The possible mechanisms are reviewed and a micromechanical model evaluating the relative contributions to the overall toughness is presented. The mechanisms involve microcracking, load transfer, bridging, and crack deflection. The synergism of these mechanisms is examined using an energy release rate balance equation. The basic assumption of the proposed model is that the load transfer between the matrix and the whiskers is due to Coulomb friction. The model has been applied to an Al2 O3 /SiC whisker composite and shows reasonable agreement with reported experimental results. The role of the thermal residual stresses is also examined in light of the frictional load transfer assumption. 相似文献
109.
Two kinds of SiC whiskers were annealed at temperatures similar to those for the processing of ceramic matrix composites. The morphology and structure of the as-received and postannealed whiskers were investigated by SEM, TEM, and XRD, and the influence of processing temperature on the mechanical properties of ceramic matrix composites was discussed. 相似文献
110.
Jun Rong Li Jun Wang Jia Rui Xu Ming Qiu Zhang Min Zhi Rong Qiang Zheng 《Composites Science and Technology》2006,66(16):3126-3131
The authors of this paper synthesized a series of amphiphilic triblock copolymers of polystyrene-b-poly(ethylene glycol)-b-polystyrene (PS-PEG-PS) having different PEG/PS ratios with nearly identical molecular weights of the entire copolymers. The interfacial interactions in the composites consisting of carbon black and the copolymers can thus be tailored. When these conducting composites are exposed to certain solvent vapors, their electrical resistances greatly increase, showing the gas sensitivity. The present work indicated that this switching behavior is controlled by the structural relaxation of the composites because matrix swelling acts as the main mechanism. The response time has been correlated with absolute temperature by Arrhenius equation, and the estimated activation energy reflects mobility of the fillers involved in the solvent induced expansion of the surrounding polymer. Therefore, by using the gas sensibility of the conductive composites, the structure evolution of the composite materials in solid state and the effect of filler/matrix interfacial interaction on the relaxation property of the matrix polymer has been inspected. It was found that lower activation energy represents stronger interfacial interaction in case good solvent of the matrix was used for the test. 相似文献