Effect of mechanical stretching on electrical conductivity and positive temperature coefficient characteristics of poly(vinylidene fluoride)/carbon nanofiber composites prepared by non-solvent precipitation

Poly(vinylidene fluoride) (PVDF)/carbon nanofiber (CNF) composites with filler content ranging from 0.047 to 4.7 vol.% were prepared with non-solvent precipitation followed by melt compression. The morphology and electrical conductivity of the composites before and after mechanical stretching were examined. The results showed that CNFs were dispersed homogeneously in the PVDF matrix and a low electrical percolation threshold of 0.90 vol.% CNFs was obtained. Mechanical stretching led to a sharp decrease in the electrical conductivity of a composite containing 0.94 vol.% CNF. This was caused by the destruction of a conducting network structure when the fillers aligned along the stretching direction. This did not happen when the filler content was increased to 1.88 vol.%. The percolating composites displayed a positive temperature coefficient (PTC) effect with the effect being larger in stretched composites. This can be attributed to the presence of PVDF β-phase in stretched composites as revealed by X-ray diffraction and Fourier transform infrared spectroscopy.     

可见光和近红外熔池图像融合方法

为了获取质量信息更佳的熔池图像，设计用分束镜将采集的同一路光源平均传输给两个相机，利用同步触发装置，建立了可见光和近红外熔池图像同路光源同步采集系统. 由于两个相机的图像之间具有不同的形变，提出了基于仿射变换的熔池图像配准方法，配准了可见光和近红外熔池图像. 在此基础上，提出了基于主成分分析的图像融合方法对可见光和近红外熔池图像进行图像融合. 结果表明，与加权平均融合，亮度色度饱和度融合和小波融合等传统图像融合方法相比，主成分分析图像融合方法最有效，得到的熔池图像质量最好.     

High Temperature Deformation of a β''''(NiAl) Precipitation Strengthened Ferritic Alloy

A β'(NiAl) precipitation strengthened ferritic Fe-19Cr-2Al-4Ni alloy was tested under low cycle fatigue and creep at elevated temperatures. The dislocation microstructures developed were examined by transmission electron microscopy (TEM). The deformation behavior of the alloy was interpreted in terms of dislocationprecipitate configurations and interactions.fatigue deformation.     

The Effect of Compatibilization of Maleated Polypropylene on a Blend of Polyamide-6 and Liquid Crystalline Copolyester

Blends of polyamide-6 (PA6) and thermotropic liquid crystalline polymer (LCP) compatibilized with various maleic-anhydride-grafted polypropylene (MAP) contents were injection-moulded. The effect of compatibilization on the mechanical properties of the blends was investigated by means of tensile testing, drop weight Charpy impact measurement and dynamic mechanical analysis. The static tensile measurement showed that the strain-at-break depends strongly on the MAP content. The impact test also indicated that the critical strain energy release rate (G_IC) is dependent on the MAP concentration. These results revealed that the 80%PA6/MAP(86/14)–20%LCP blend exhibits the highest strain-at-break and G_IC values. Moreover, the tensile ductility and impact toughness tended to decrease dramatically with increasing MAP content. This was attributed to the chemical and thermal decomposition of PA6 during blending for the LCP/PA6 blends containing higher MAP concentration. © of SCI.     

Mechanical performance of ternary in situ polycarbonate/poly(acrylonitrile‐butadiene‐styrene)/liquid crystalline polymer composites

Ternary in situ polycarbonate (PC)/poly(acrylonitrile‐butadiene‐styrene) (ABS)/liquid crystalline polymer(LCP) composites were prepared by injection molding. The LCP used was a versatile Vectra A950, and the matrix of composite specimens was PC/ABS 60/40 by weight. Maleic anhydride (MA) copolymer and solid epoxy resin (bisphenol type‐A) were used as compatibilizers for these composites. The tensile, dynamic mechanical, impact, morphology, and thermal properties of the composites were studied. Tensile tests showed that the tensile strength of the PC/ABS/LCP composite in the longitudinal direction increased markedly with increasing LCP content. However, it decreased slowly with increasing LCP content in the transverse direction. The modulus of this composite in the longitudinal direction appeared to increase considerably with increasing LCP content, whereas the incorporation of LCP into PC/ABS blends had little effect on the modulus in the transverse direction. The impact tests revealed that the Izod impact strength of the composites in both longitudinal and transverse direction decreased with increasing LCP content up to 15 wt %; thereafter it increased slowly with increasing LCP. Dynamic mechanical analyses (DMA) and thermogravimetric measurements showed that the heat resistance and heat stability of the composites tended to increase with increasing LCP content. Scanning electron microscopy observation and DMA measurement indicated that the additions of epoxy and MA copolymer to PC/ABS matrix appeared to enhance the compatibility between the PC and ABS, and between the matrix and LCP. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2274–2282, 1999     

Laser surface alloying of ferritic Fe-40Cr alloy with ruthenium

An investigation is made of the laser surface alloying of an experimental ferritic Fe-40Cr alloy with a rutherium powder coating using a continuous wave CO₂ laser. Themicrostructure and corrosion behaviour of the laser surface alloying layer and the Fe-40Cr bulk allyo were examined by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, microhardness, potentiodynamic and corrosion potential measurements. The results of the microstructural examination showed that fine cellular dendrites with a ruthenium content as high as 51.84wt.% were produced by laser surface alloying. The extended solubility of ruthenium in the cellular dendrites resulted in a dramatic increase of the hardness in the laser alloying layer. Potentiodynamic and open circuit corrosion potential measurements indicated that the ruthenium-containing surface layer spontaneously passivated in hydrochloric and sulphuric acid solutions, whereas the bulk Fe—40Cr alloy remained in the active state when exposed in these reducing acid solutions.     

Spark Plasma Sintered Hydroxyapatite/Graphite Nanosheet and Hydroxyapatite/Multiwalled Carbon Nanotube Composites: Mechanical and in Vitro Cellular Properties

Hyroxyapatite (HA) and its nanocomposites reinforced with 0.5, 1, 1.5, and 2 wt% graphite nanosheets (GNs) and multi‐walled carbon nanotubes (MWNTs) are fabricated by means of spark plasma sintering (SPS) process. The effects of MWNT and GN additions on the morphology, mechanical behavior, cell adhesion, and biocompatibility of HA were studied. Three‐point‐bending test shows that the bending strength of MWNT/HA nanocomposites increases with increasing MWNT content. However, the bending strength of GN/HA nanocomposites initially increases by adding 0.5 wt% GN, and then decreases markedly as the filler content increases. Cell culture and viability test results demonstrate that the GNs with diameters of several micrometers retard osteoblast cell adhesion and proliferation on the GN/HA nanocomposite. In contrast, the addition of 2 wt% MWNT to HA is beneficial to promote osteoblast adhesion and proliferation, thereby enhancing the biocompatibility of MWNT/HA nanocomposite.