Synthesis,Characterization and A.C. Susceptibility of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">x</Emphasis></Subscript> / Polyethylene Composites

A series of flexible composites are fabricated by mixing a high-T _c YBa₂Cu₃O_7−x superconductor with Low Density Polyethylene (LDPE). The synthesized polymer composites are characterized by X-ray diffraction technique. Superconducting nature of the composites is confirmed by the Meissner effect. The surface morphology of the composites is studied by scanning electron microscopy. The crystallization temperature of the polymer and its composites is determined by using differential scanning calorimetry (DSC). The composites showed a large diamagnetic susceptibility that increases with increasing volume fraction of superconductor filler. Susceptibility measurements showed that the intrinsic diamagnetic properties of the superconducting materials are preserved in the composites and there is no change in the transition temperature of the superconductor. Potential applications in the areas of shielding and levitation are discussed.     

SMA粒子和短纤维填充的复合材料的力学特性

形状记忆合金（SMAs）由于其可塑的记忆效果,短期弹性、高阻抗容量和其他特性,因而具有感知和激励的功能。利用SMAs独一无二的特性,结合其他材料可用来制造出智能化或灵敏的合成材料。研究利用镍钛合金短纤维和颗粒制造的环氧合成材料的力学性能。由于加入了SMA,SMA／环氧合成材料具有更强的抗弯抗剪能力。特别在高温下,存储系数随着SMA显著增加。试验结果表明,SMA每增加3．5％,存储系数将有显著的增加,影响量级为环氧的6倍。当SMA相变接近120°时,存储系数增大到了最大值。SMA／ER3合成材料的损失因素随着SMA的增加而增加。基于Halpin-Tsai理论,具有SMA的薄层可以代表整个材料动力性能。相对于其他试验材料,在现有模型上得到的结论可以合理地预测这些动力响应。     

Spectroelectrochemistry of two-layered composites of polyaniline and poly(o-aminophenol)

Electropolymerization of aniline on poly(o-aminophenol)(POAP)-coated gold and indium-doped tin oxide (ITO)-coated glass electrodes yields polyaniline(PANI)/POAP two-layer composite films, exhibiting reversible redox functions in aqueous acidic solution. The PANI deposition on the POAP-coated electrodes was monitored by cyclic voltammetry (CV) and in situ UV-vis spectroelectrochemistry. CV results show that PANI/POAP composite films exhibit better stability as compared to PANI films during potential cycling in aqueous acidic solutions. Characteristic UV-vis and Raman features of the composite films have been identified and their dependencies on the electrode potential are discussed. They were significantly different from the corresponding spectral characteristics of PANI and POAP films alone.     

Facile synthesis and electrochemical capacitance of composites of polypyrrole/multi-walled carbon nanotubes

Composites of polypyrrole (PPy) and multi-walled carbon nanotubes (MWCNTs) were synthesized by a facile method involving one-step electrochemical deposition from a thin-layer of ionic liquid solution attached on a glassy carbon electrode. The morphology of the composites was characterized by field emission scanning electron microscopy, and the capacitance properties were investigated by cyclic voltammetry (CV). The charge-discharge behavior of the composites prepared in this work was examined by chronopotentiometry at a constant current density for multi-cycle scans. The results show that the PPy/MWCNT composites have a porous 3D nanostructure, with high specific capacitance (SC) of 890 F/g (for the mass of the PPy in the composites) calculated from CV at 2 mV/s in 1.0 M KCl. The stability of the composites in 1.0 M KCl electrolyte was also examined by multi-cycle CV and only 9% decrease of SC value was observed for the 1000 cycles.     

Microstructure and electrochemical properties of the Co-BN composites

The Co-BN composites are synthesized by ball-milling metallic Co and boron nitride (BN) powder with a different Co/BN weight ratio. The microstructure, morphology and chemical state of the obtained Co-BN composites are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). After ball milling, Co nanoparticles of 10-30 nm in size are distributed on the amorphous BN matrix. The electrochemical measurements, including galvanostatic method and cyclic voltammetry (CV), show that the Co-BN composite with the Co/BN weight ratio of 5/1 has a good cycle performance and a high reversible electrochemical capacity in 6 M KOH solution. Moreover, the Co-BN composite can be discharged directly without the first charging process. The higher initial discharge capacity, observed in the first cycle of the pre-charged sample, can be explained by an initial reduction of the oxidized species on the surface of the Co-BN composite and subsequent oxidation. The partial dissolution of Co(OH)₂ in alkaline solution would further increase the active surface area of the material for the considerable decrease in overpotential after the first cycle. Based on a structure analysis and electrochemical measurement, the reversible faradic reaction of the highly dispersed active Co nanoparticles in the Co-BN composite is dominant.     

Synthesis and characterization of chemically and electrochemically prepared conducting polymer/iron oxalate composites

Poly(3-octyl-thiophene) (POT) and polypyrrole (PPy) iron oxalate composites were synthesized through a post-polymerization oxidative treatment. The composite of the latter has been prepared also by electrochemical polymerization. The samples have been characterized by X-ray diffraction (XRD), impedance spectroscopy, scanning electron microscope (SEM) combined with energy dispersive X-ray (EDX) spectroscopy, Mössbauer spectroscopy, cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). In case of PPy, two peaks in the XRD spectra show the presence of iron containing composite, while with POT only the layered structure originating from the octyl side-chain interactions was modified by the composite formation. The assumption of the weakening of short- and long-range interactions was proven by the decrease in conductivity of the composite. The successful electrochemical synthesis resulted a composite of ∼5% iron content, determined by EDX. Mössbauer spectroscopy measurements evidenced a composite containing mixed valence iron oxalate doping ions, which supports the indirect EQCM data.     

New polyaniline(PAni)-polyelectrolyte (PDDMAC) composites: Synthesis and applications

Conducting and electroactive polymer blends of polyaniline (PAni) with polyelectrolyte, poly(diallydimethylammoniumchloride) (PDDMAC) have been synthesized by an in situ polymerization method and the resulting composites have been characterized by FT-IR, UV–Vis, XRD, AFM and electrochemical techniques. The blends are conducting and electroactive with even lower loadings of PAni and can be cast as films. The conductivity of the cast films containing 0.04–1.5 wt% PAni ranged from 4.5 × 10⁻⁶ to 42 × 10⁻⁶ S/cm. Some of the composites are tested for their corrosion inhibition property for pure iron in 1 M HCl solutions and were found to be active inhibitors.     

Experimental study of the influence of adhesive reinforcement in lap joints for composite structures subjected to mechanical loads

The paper deals with experimental investigations on reinforcing the adhesive in single lap joints subjected to mechanical loads such as tensile, bending, impact and fatigue. The adhesive used for bonding was an epoxy reinforced with unidirectional and chopped glass fibres as well as micro-glass powder. The adherends were glass reinforced composite laminates. The bonding surfaces were prepared before joining. In the case of unidirectional fibres in the adhesive region, the fibre orientations considered were 0°, 45° and 90°. The volume fraction of fibres in the adhesive layer in all the cases was 30%. The volume fractions of micro-glass powder were 20%, 30% and 40%. The tensile, bending, impact and fatigue tests on the prepared specimens were conducted according to ASTM standards. The results show that except the 90° unidirectional orientation, reinforcing the adhesive with glass fibres or powder increases the joint strength. The use of volume fraction of 30% of micro-glass powder gave the best performance in the above loading conditions. The fatigue life increased by 125%, the ultimate joint strength in tension increased by 72%, the bending ultimate joint strength increased by 112% and the impact joint strength increased by 63%. The microstructure of the debonded area was examined and three modes of failure could be observed namely cohesive failure, light fibre-tear failure and thin layer cohesive failure.     

Functionally graded laminated composites fabricated from MAX-phase filled preceramic papers: Microstructure,mechanical properties and oxidation resistance

This paper describes the fabrication and characterization of novel preceramic paper-derived functionally graded materials (FGMs) based on Ti₃(Si,Al)C₂ MAX phase. The FGMs with different architecture were fabricated via spark plasma sintering of stacked preceramic papers at 1250 °C for 5 min. Microstructure, phase composition and elemental distribution were analyzed by scanning electron microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy, respectively. Oxidation tests were performed in air at 1300 °C for 5 h. FGMs containing Al- and Si-enriched MAX-phase layers were formed. The fabricated materials exhibit high flexural strength (over 600 MPa), which are dependent on microstructure and composition of individual layers as well as the architecture of composites. It was found that texturing of MAX phase grains during SPS results in anisotropic hardness of the composite. The difference in the composition of the individual layers also provides a hardness gradient in the composite. It was shown that the formation of the outer layer from the Al-enriched Ti₃Al(Si)C₂ MAX phase increases the corrosion resistance of Ti₃SiC₂-based composites. The high corrosion resistance of FGMs is due to the growth of a continuous and dense Al₂O₃ oxide layer.     

Characterization of carbon fiber-reinforced ultra-high temperature ceramic matrix composites fabricated via Zr-Ti alloy melt infiltration

Carbon fiber-reinforced ultra-high temperature ceramic matrix composites (C/UHTCMCs) were fabricated via Zr-Ti alloy melt infiltration (Zr-Ti MI) using carbon-carbon composite (C/C) preforms and alloys with three different compositions. Alloys were successfully infiltrated into C/C to form solid solutions of TiC and ZrC, with melting temperatures > 2900 °C. Notably, residual alloys were not observed after MI occurred at 1750 °C. Bending strength and fracture toughness of the C/UHTCMCs at room temperature and 1500 °C in air/Ar revealed that mechanical properties of the composites were similar to those of the C/C preform. During arc wind tunnel tests at 2000 °C, a recession of C/UHTCMCs fabricated using Ti-rich alloys was observed; however, this behavior was not observed for the composites prepared using Zr-rich alloys owing to the formation of a ZrO₂ solid solution. Accordingly, Zr-Ti MI is a viable method for preparing C/UHTCMCs without degrading the mechanical properties of the C/C preform, while increasing the ablation resistance.