The relationship between the electrical and mechanical properties of polymer–nanotube nanocomposites and their microstructure

A range of polymer–nanotube nanocomposites were produced using different processing routes. Both polymer-grafted and as-grown nanotubes were used and latex and polystyrene matrices investigated. The microstructures of the nanocomposites were studied, mainly by electron microscopy, in terms of the dispersion state of the nanotubes and the polymer–nanotube interface. The mechanical and electrical properties of the composites were also measured. The relationship between the microstructures observed and the resulting physical properties are discussed. It is found that composites with apparently similar microstructures can exhibit similar mechanical properties but very different electrical behaviours. Moreover, the nanocomposites produced using polymer-grafted nanotubes exhibit a clear improvement of the stress at large deformation. Thus, from our results, it appears that the mechanical and electrical properties do not necessarily depend on the same microstructural parameters. However it is still a challenge to simultaneously improve both physical properties.     

Fast and facile preparation of reduced graphene oxide supported Pt–Co electrocatalyst for methanol oxidation

In this study, we report a scalable, fast, and facile method for preparation of reduced graphene oxide (RGO) sheets supported Pt–Co electrocatalyst for methanol oxidation. Mixed reducing agents were used and the activity of the catalysts was studied. It was found that the presence of RGO leads to higher activity, which might be due to the increasing of electrochemically accessible surface areas and easier charge–transfer at the interfaces. Co can greatly enhance the electrocatalytic activity and moderate the poisoning of Pt catalyst. Under same Pt loading mass and experimental conditions, the RGO-Pt-Co catalyst shows the highest electro catalytic activity and improved resistance to carbon monoxide poisoning among the prepared catalysts.     

Plasma–chemical preparation and properties of catalysts used in synthesis of ammonia

Thorough investigations, including thermodynamic calculations, were carried out on the plasma–chemical preparation of ammonia-synthesis catalysts in a quasi-equilibrium electric-arc low-temperature plasma. Obtaining samples with maximal catalytic activity and thermal stability necessitated that the plasma–chemical process take place in a cold wall plasma–chemical reactor within the 1000–3000 K temperature interval; the activity of the plasma catalysts thus produced was higher by 15%–20% than that of their conventional industrial analogues. Various physicochemical and kinetic techniques were applied to characterize in detail the catalysts synthesized. Some considerations are given concerning the possible future development of plasma–chemical production of catalysts.     

Influence of the elastic stress relaxation on the microstructures and mechanical properties of metal–matrix composites

Role of the residual stresses on the mechanical properties of metal–matrix composites is studied. It is shown that the stress relaxation can be responsible for the morphologies and spatial distribution of precipitates. Direct measurements of the residual stress is also emphasized and the influence of dislocations in the accommodation process and during interface crossing is exemplified.     

Effects of coupling agent on the preparation and dielectric properties of novel polymer–ceramic composites for embedded passive applications

The study was carried out to investigate the effects of silane coupling agent, γ-aminopropyl triethoxy silane (KH-550), on the preparation and dielectric properties of Barium titanate (BaTiO₃)/Bisphenol-A dicyanate (2,2′-bis (4-cyanatophenyl) isopropylidene)(BADCy) composites for embedded passive implications. It was found that KH-550 accelerated the polymerization of BADCy and was beneficial to improve the compatibility between BaTiO₃ particles and BADCy matrix. The dielectric constant (ε) and dielectric loss (tanδ) both increased at first and then decreased with the increase of the KH-550 content. With the increase of the frequency, the variation ranges of the dielectric constant and dielectric loss of these composites were not obvious since the dielectric properties of cyanate ester were stable at various frequencies.     

Influence of sulphur on the microstructure and properties of Ag–Cu–Zn brazing filler metal

Abstract

The effect of sulphur on the microstructure and properties of Ag45–Cu30–Zn25 brazing filler metal was investigated. Under the given experimental conditions, the sulphuration products mainly consisted of CuS, ZnS, Ag₂S, Cu₂S and Ag₃CuS₂. These sulphides not only distributed on the surface but also diffused into the interior of the filler metal and cut apart the matrix thereby significantly damaging the tensile strength of the filler metal from 658 to 283 MPa. The corresponding fracture characterisation turned from ductile fracture to brittle fracture. The sulphides existed as solid particles, which hinder the spreading of the liquid filler metal and the spreading area dramatically decreased from 317?09 to 18?55 mm², which indicates that the filler metal rarely wets the base metal.     

Effect of processing routes on mechanical and thermal properties of copper–graphene composites

In this paper, copper–graphene composites were fabricated by using two different processing routes (ball milling (BM) and ultrasonication) followed by spark plasma sintering. Vickers hardness and anisotropic thermal conductivity of the composites were measured and observed that ultrasonicated fabricated composites gave better result compared with BM composite and even from pure copper. The hardness values obtained for ultrasonicated copper–graphene composite were 69?HV (57% higher) and thermal conductivity 387?W/m?K (13% higher) by using only 0.5?wt-% of graphene, while for pure copper the values were 44?HV and 341?W/m?K. The value of anisotropic thermal conductivity ultrasonicated composites was also 1.97 which is much higher than pure copper 0.94.     

In situ prepared polypyrrole–Ag nanocomposites: optical properties and morphology

Polypyrrole–silver (PPy–Ag) nanocomposites with various silver contents have been synthesized via a kinetically favorable one-step chemical oxidative polymerization process. The oxidant, ammonium persulfate, was used to oxidize pyrrole monomer for growing chains of PPy. And AgNO₃ was used as a precursor for metallic silver nanoparticles. The detailed characterization techniques, UV–Vis–NIR, fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy, field-emission scanning electron microscopy, and transmission electron microscopy (TEM), have been used to reveal electronic environment, structure, and morphology of composites as well as as-synthesized PPy. The synthesis environment prior to polymerization has also been investigated by absorption spectroscopy. The TEM images of PPy–Ag nanocomposites reveal that silver nanoparticles are deeply embedded into the polymer matrix in addition to surface adsorption. It is observed that the size distribution of inorganic nanoparticles (ca. 4–10 nm, depending on the metal ion concentrations) as well as structural morphology is altered by the initial concentrations of silver ions.     

Preparation of novel fibre–silica–Ag composites: the influence of fibre structure on sorption capacity and antimicrobial activity

Novel fibre–silica–Ag composites with biocidal activity were successfully produced by chemical modifying cotton (CO), wool (WO), silk (SE), polyamide (PA) and polyester (PES) fabrics and CO/PES and WO/PES fabric blends. A silica–Ag coating was prepared using a two-step procedure that included the creation of a silica matrix on the fibre surface via the application of an inorganic–organic hybrid sol–gel precursor [reactive binder (RB)] using a pad-dry-cure method, followed by the in situ synthesis of AgCl particles within the RB-treated fibres from solutions of 0.10 mM and 0.50 mM AgNO₃ and NaCl. The presence of the coating on the fibres was verified by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The bulk concentration of Ag in the coated fibres was determined using inductively coupled plasma mass spectroscopy. The antimicrobial activity was determined for the bacteria Escherichia coli and Staphylococcus aureus and the fungus Aspergillus niger. The results show that the chemical and morphological structures of the fibres directly influenced their absorptivity and affinity for the Ag compound particles. As the amorphous molecular structure of the fibres and the amount of functional groups available as binding sites for Ag⁺ were increased, both the silver solution uptake and the concentration of the absorbed Ag compound particles increased. The chemical binding of Ag to the fibres significantly reduced the effectiveness of the antimicrobial activity of the Ag compound particles. Accordingly, an increase in the concentration of absorbed Ag was required to achieve a biocidal effect.     

Preparation and plasmonic properties of polymer-based composites containing Ag–Au alloy nanoparticles produced by vapor phase co-deposition

Nanocomposite (NC) thin films with noble metal nanoparticles (NPs) embedded in a dielectric material show very attractive plasmonic properties due to dielectric and quantum confinement effects. For single component NPs, the plasmon resonance frequency can only be tuned in a narrow range. Much interest aroused in bimetallic NPs, however, many wet chemical approaches often lead to core shell particles, which exhibit multiple plasmon resonances or do not allow large variation of the NPs alloy composition and filling factor. Here, we report a vapor phase co-deposition method to produce polymer–metal NCs with embedded homogeneous Ag–Au alloy particles showing a single plasmon resonance. The method allows production of NPs with controlled alloy composition (x), metal filling (f), and nanostructure in a protecting Teflon AF matrix. The nanostructure size and shape were characterized by transmission electron microscope. Energy dispersive X-ray spectroscopy was used to determine x and f. The optical properties and the position of surface plasmon resonance were studied by UV–Vis spectroscopy. The plasmon resonance can be tuned over a large range of the visible spectrum associated with the change in x, f, and nanostructure. Changes upon annealing at 200 °C are also reported.     

Effect of nanoclays on physico-mechanical properties and adhesion of polyester-based polyurethane nanocomposites: structure–property correlations

Polyester–polyurethane nanocomposites based on unmodified and modified montmorillonite clays were compared in terms of their morphology, mechanical, thermal, and adhesive properties. Excellent dispersion of the modified nanoclay in polymer with 3 wt% loading was confirmed from X-ray diffraction, and low-, and high-magnification transmission electron micrographs. The properties of the clay-reinforced polyurethane nanocomposites were a function of nature and the content of clay in the matrix. The nanocomposite containing 3 wt% modified clay exhibits excellent improvement in tensile strength (by ~100%), thermal stability (20 °C higher), storage modulus at 25 °C (by ~135%), and adhesive properties (by ~300%) over the pristine polyurethane.     

Production and properties of steel–TiC composites for Wear applications

Abstract

Fe–(WTi)C composite granules containing up to 80 wt-% carbide have been produced by a selfpropagating high temperature synthesis reaction. These can be readily distributed in conventional steel melts. Additions up to 17 wt-% carbide have been made to a 0·4 wt-%C steel which was subsequently cast and hot rolled to plate. The microstructures of cast, rolled, and heat treated. samples display a homogeneous distribution of carbides which do not significantly affect the rolling performance of the steels. The carbides and grain refinement in heat treated samples result in a marked improvement in mechanical properties. The most significant improvement as a fraction of carbide additions is seen in abrasive wear performance.

MST/3196     

Ultra-high-modulus polyethylene fibre composites: I—The preparation and properties of conventional epoxy resin composites

It has been shown that conventional techniques can be used to prepare epoxy resin composites incorporating ultra-high-modulus polyethylene (UHMPE) fibres as the reinforcing phase, either as continuous filament yarn or woven fabric. These composites showed very satisfactory values of stiffness and strenght, and very good energy absorption in Charpy impact tests. The interlaminar shear strength of the composites could be significantly increased by plasma etching of the fibres in oxygen gas. This treatment reduced resin cracking in flexural and impact tests, but did not reduce the impact energy absorption very greatly because the latter is primarily associated with plastic deformation of the fibres. The composites were also subjected to preliminary environmental tests, with very encouraging results.     

Development and mechanical properties of metal–particulate glass matrix composites from recycled glasses

The great number of glasses available from recycling activity and vitrification treatment of industrial wastes leads to the need for new applications, with the development of new materials, such as low-cost composite materials from a powder technology route. In the present work a variety of recycled glasses is investigated, in order to obtain aluminium reinforced glass matrix composites via cold-pressing and viscous flow sintering. A good compatibility between lead silicate glasses from cathode ray tubes dismantling and aluminium reinforcement is found to be effective. Composites exhibiting good mechanical properties were developed from these materials. A particular attention was due to fracture toughness (K_IC) determination. The absolute K_IC of glass matrix composites value remains low, but a notable increment in relation to unreinforced matrix is observed.     

Damage accumulation and mechanical properties of particle-reinforced metal–matrix composites during hydrostatic extrusion

The effects of hydrostatic extrusion on particle cracking and on the subsequent tensile properties of some prototypical particle-reinforced metal–matrix composites are investigated. In most cases, tensile failure occurs through a plastic instability in accordance with the Considere criterion for necking. The corresponding failure strain is therefore dictated by the global flow and hardening characteristics of the composites, as influenced by the intrinsic flow properties of the matrix as well as the extent and rate of particle cracking. Such cracking leads to significant reductions in the hardening rate and thus causes a reduction in the failure strain relative to that of the neat matrix alloy. Extrusion prior to tensile testing has the effect of saturating the flow stress of the matrix and limiting the tensile ductility to low values, largely because of the very low hardening rate of the matrix. Particle cracking during extrusion causes a further reduction in ductility. The dominant role of the matrix hardening is demonstrated through re-tempering treatments of extruded billets prior to tensile testing. A micromechanical model of particle cracking is developed, taking into account the effects of both the hydrostatic and the deviatoric stress components in axisymmetric loadings. The model is used to rationalize the observed trends in damage accumulation with particle content, particle type, and loading configuration (tension vs. extrusion).     

Combination of supported bimetallic rhodium–molybdenum catalyst and cerium oxide for hydrogenation of amide

Hydrogenation of cyclohexanecarboxamide to aminomethylcyclohexane was conducted with silica-supported bimetallic catalysts composed of noble metal and group 6–7 elements. The combination of rhodium and molybdenum with molar ratio of 1:1 showed the highest activity. The effect of addition of various metal oxides was investigated on the catalysis of Rh–MoO_x/SiO₂, and the addition of CeO₂ much increased the activity and selectivity. Higher hydrogen pressure and higher reaction temperature in the tested range of 2–8 MPa and 393–433 K, respectively, were favorable in view of both activity and selectivity. The highest yield of aminomethylcyclohexane obtained over Rh–MoO_x/SiO₂ + CeO₂ was 63%. The effect of CeO₂ addition was highest when CeO₂ was not calcined, and CeO₂ calcined at >773 K showed a smaller effect. The use of CeO₂ as a support rather decreased the activity in comparison with Rh–MoO_x/SiO₂. The weakly-basic nature of CeO₂ additive can affect the surface structure of Rh–MoO_x/SiO₂, i.e. reducing the ratio of Mo–OH/Mo–O⁻ sites.     

A fractographic study exploring the relationship between the low cycle fatigue and metallurgical properties of laser metal wire deposited Ti–6Al–4V

Additive manufacturing (AM) has achieved large attention within the aerospace industry mainly because of the possibility to lower the material and the manufacturing cost. For titanium alloys several AM techniques are available today. In the present paper, the focus has been on laser metal wire-deposition of Ti–6Al–4V. Walls were built and low cycle fatigue specimens were cut out in two orientations with respect to the deposition direction. An extensive fractographic evaluation was carried out after testing and the results indicated anisotropic behaviour at low strain ranges. Defects such as pores and lack of fusion (LoF) were observed and related to the fatigue life and specimen orientation. The LoF defects are regarded to have the most detrimental influence on the fatigue life, whilst the effect of pores was not as straightforward. Noteworthy in present study is that one large LoF defect did not influence the fatigue life, which is explained by the prevalence of the LoF defect in relation to the loading direction.     

One-step synthesis of Co–Ni ferrite/graphene nanocomposites with controllable magnetic and electrical properties

Co_1−xNi_xFe₂O₄/graphene nanocomposites were synthesized through a one-step solvothermal method. The as-synthesized products were characterized by X-ray powder diffraction, field emission scanning microscopy, transmission electron microscope, and high-resolution transmission electron microscope. The results show that the Co_1−xNi_xFe₂O₄ nanoparticles are uniformly dispersed on graphene sheets. The dependence of structure, magnetic and electrical properties of Co_1−xNi_xFe₂O₄/graphene nanocomposites on the Ni²⁺ concentration and the graphene content were also studied. The saturation magnetization and electrical conductivity of the as-prepared products reached 51.82 emu/g and 1.00 × 10² S/m, respectively.     

A review of noble metal (Pd,Ag, Pt,Au)–zinc oxide nanocomposites: synthesis,structures and applications

As a promising candidate for future catalytic applications, the noble metal–ZnO nanocomposites are gaining increasing interest due its high catalytic property, and super stability. In this review, the noble metal–ZnO nanocomposites with various composites and structures for catalytic applications will be discussed. We introduce the multi-catalytic properties and design concept of the noble metal–ZnO nanocomposites, and then particular highlight key finding of synthesis method for various noble metal–ZnO nanocomposites. The catalytic activity of noble metal–ZnO nanostructures has been found to rely on not only the species of noble metal but also the architecture of the catalyst material. Moreover, the typical works of modification on noble metal–ZnO nanostructures have been introduced. Critically, the challenges for future research development and our future perspectives are presented.