PVA:Nano-eggshell microcomposite as an energy storage material for supercapacitors

Journal of Materials Science: Materials in Electronics - The development and advantages of wearable flexible electronics have become attractive issues with excellent electrochemical performances in...     

Laser welding of copper‐niobium microcomposite wires for pulsed power applications

The laser welding of copper‐niobium microcomposite wires was investigated. It was determined that the joint structure does not have welding defects, while microscopic examination of the joint cross‐section showed that the microstructure of the autogenous weld consists mainly of a copper‐based solid solution strengthened by niobium‐rich precipitations. The weld obtained with use of filler material consists of two distinct zones, which are formed due to melting of filler wire and microcomposite wire. This structure of the joint provides an insignificant increase in electrical resistance and sufficient ultimate strength and plasticity of the joint. The tensile strength of the sample welded without filler material reaches 335 MPa, but such welded joints are very brittle due to very low ductility. However, an autogenous laser welding joint has about 1.6 times better ductility, and the tensile strength of the joint depends on the applied filler material and is equal to the tensile strength of this material.     

High-temperature microcomposite thin-layer coatings with the micro-, submicro-, and nanoscale structure of oxide layers

The physicochemical aspects of the formation of high-temperature heterophase microcomposite thin-layer coatings of the silicide type with micro-, submicro-, and nanoscale oxide layers on carbon-containing composite materials are studied. The coatings are designed to provide the efficiency of heat-loaded structural elements of aerospace equipment under exposure to high-enthalpy hypersonic flows of dissociated air.     

Comparison of microstructure and strength in wire-drawn and rolled Cu-9 Fe-1.2 Ag filamentary microcomposite

Comparison of microstructure and strength of Cu-9 Fe-1.2 Ag microcomposite wires and sheets obtained by cold drawing or cold rolling combined with intermediate heat treatments has been made. The primary and secondary dendrite arms are aligned along the drawing or rolling direction and elongated into filaments after cold working. The microstructural scale of wire-drawn microcomposites was found to be finer than that of rolled microcomposites at the same drawing strain. The more effective microstructural refinement induced by unidirectional metallic flow and co-deformation of filament and Cu matrix resulted in finer microstructure in microcomposite wires. The ultimate tensile strength and the conductivity of wire-drawin Cu-Fe-Ag microcomposite were higher than those of rolled Cu-Fe-Ag microcomposites. The strength of Cu-Fe-Ag microcomposites is dependent on the spacing of the Fe filaments in accord with a Hall-Petch relationship. The good mechanical and electrical properties of wires may be associated with the more uniform distribution of fine filaments. The fracture surfaces of Cu-Fe-Ag wires and sheets showed ductile-type fracture and iron filaments were occasionally observed on the fracture surfaces. The fracture surface of Cu-Fe-Ag wires showed generally finer microstructural morphology than that of Cu-Fe-Ag sheets, consistent with the finer microstructural scale in Cu-Fe-Ag wires.     

Dielectric relaxation and ionic conduction in 66%Silica/CW229-3/HW229-1 microcomposite polymer

Composites of epoxy resin with high percentage of silica fillers (66%) are designed to improve mechanical and electrical properties of transformers used in railway application. FTIR, (DRX and FE-SEM) and absorption/desorption phenomena are used to investigate the structure, the morphology and the diffusion of water in the microcomposites, respectively. Good dispersion of silica filler with size less than 10 μm was assessed by SEM, although some clustering (agglomerates) of greater than 1 μm was observed. The absorption water in the microcomposite obeys to the first Fickian law and shows saturation water of 0.6%. The calculation of the diffusion coefficient of water leads to a value of 2.9*10⁻¹² m² s⁻¹ in the studied system. Relaxation times of α-relaxation and ionic conduction relaxation processes are determined. A correlation is observed between the ionic conductivity and dielectric relaxation processes. The dc-current behavior shows a change in the conduction mechanism from electronic conduction below the T_g to ionic conduction above the T_g. Shallow traps of 0.54 eV and deep traps of 2.21 eV are determined below and above the T_g, respectively. The TSC analysis confirms the VFT behavior of the α-relaxation of the microcomposite as obtained by the dielectric spectroscopy.     

Experiments on shear deformation,debonding and local load transfer in a model graphite/glass/epoxy microcomposite

Recent statistical theories for the failure of polymer matrix composites depend heavily on details of the stress redistribution around fibre breaks. The magnitudes and length scales of fibre overloads as well as the extent of fibre/matrix debonding are key components in the development of longitudinal versus transverse crack propagation. While several theoretical studies have been conducted to investigate the roles of these mechanisms, little has been substantiated experimentally about the matrix constitutive behaviour and mechanisms of debonding at the length scale of a fibre break. In order to predict the growth of transverse and longitudinal cracks using the same micromechanical model, we microscopically observed the epoxy shear behaviour around a single fibre break in a three-fibre microcomposite tape. The planar specimens consisted of a single graphite fibre placed between two larger glass fibres in an epoxy matrix. The interfibre spacing was less than one fibre diameter (<6 m) in order to reflect the spacing between fibres found in typical composites. The epoxy constitutive behaviour was modelled using shear-lag theory where the epoxy had elastic, plastic, and debond zones. The criteria for debonding were modified from conventional shear-lag approaches to reflect the orientational hardening in the epoxy network structure. The epoxy, which is brittle in bulk, locally underwent a shear strain of about 60% prior to debonding from the fibre.     

Weibull strength statistics for graphite fibres measured from the break progression in a model graphite/glass/epoxy microcomposite

Recent statistical theories for the failure of fibrous composities focus on the initiation and growth of clusters of broken fibres within the composite. These theoreis require the probability distribution for fibre strength at the length scale of micromechanical load transfer around a cluster of broken fibres. Such lengths are of the order of 10 to 150 fibre diameters, and thus the associated strengths have previously been unmeasurable by direct means. Using Weilbull/weakest-link rules, researchers have resorted to extrapolation of tension test results from gauge lengths two orders of magnitude longer. In this paper, a technique is developed to study the break progression of a single graphite fibre in an epoxy microcomposite tape, where the graphite fibre is flanked by two, proof-tested, glass fibres. These results are interpreted using a Weibull/Poisson model of the break progression, the number of breaks in the graphite fibre as a function of applied strain, which accounts for stress decay at the fibre ends. It is shown that such extrapolations of tension test data are too optimistic. In addition, different fibres from the same yarn cross-section, apparently have different flaw populations, unlike that which occurs at longer gauge lengths.     

Crystallization of amorphous antimony films on silver films

The crystallization process in amorphous antimony films 70–330 Å thick evaporated onto silver films 10–150 Å thick which have previously been evaporated onto glass is directly observed through an optical microscope. The conditions under which the crystallization process in the amorphous antimony films is observed are found to be severely limited by the preparation conditions of the silver films. The crystallization can only be observed on silver films thinner than 30–40 Å which have previously been exposed to oxygen or nitrogen gas. The crystallization thickness of amorphous antimony films on these substrates is estimated to be 123-75 Å as the substrate temperature varies from 20 to 80 °C and the activation energy for crystallization to be 0.23-0.30 eV as the film thickness varies from infinity to 200 Å.     

Electrodeposited films

This investigation covers: a) control of characteristics of electrodeposited vs. vacuum deposited Permalloy films; b) the preparation of substrates for electrodeposition; c) aging kinetics of electrodeposited NiFeSxfilms from 60° to 90°C; and d) comparison of aging of NiFeSxfilms with electrodeposited films containing other impurities, e.g., NiFeP, and with films made by other techniques, e.g., vacuum deposition. The concluding discussion is principally concerned with aging effects.     

炭膜

炭膜是由炭构成的膜状物质,也可以说,具有不同杂化轨道形成的碳所组成的膜体.按其制法、结构、性能和用途分类,它又可细分为热解炭膜、四配位非晶炭膜、纳米管炭膜、玻璃状炭膜、无定形炭膜、高结晶度石墨炭膜;机械用炭膜、分离用炭膜、工具领域用金刚石炭膜、为消除静电堆积用晶须炭膜等.     

Magnetic properties of Ni-Fe films coupled with stripe-domain films

A study was made of the change in anisotropy field, coercivity, angular dispersion, and creep threshold of an ordinary Ni-Fe film when coupled with a stripe-domain film. It was found that the values of these properties all increased as a result of the coupling.     

Transparent conducting films

We present here a new technique, called vapour phase spray pyrolysis, for deposition ofto andito films. Undopedto film showed semiconducting nature, a sheet resistance of 1088 Ω/□, a donor ionization energy level of 40 meV, average visible transmittance of 75·4% andn-type conductivity. The indium doped (ito) film 10 wt % showed metallic nature, a sheet resistance of 15 Ω/□, average visible transmittance of 80·4 % andp-type conductivity. Thus theto andito films showed fairly good electro-optical qualities, comparable to those obtained by sophisticated and costly techniques.     

Magnetic oxide films

Polycrystalline and epitaxial magnetic oxide films have been fabricated by several investigators. This paper deals predominantly with epitaxial films grown by chemical vapor deposition. The majority of the discussion is concerned with substrates, the deposition process, and film characterization. Where possible, comparisons are made with bulk crystals and with films produced by other fabrication techniques.     

Polymer-metal composite films

Simultaneous deposition of polymer and metal evaporated from separate sources results in a three-dimensional dispersion of metal islands within a polymer matrix. Of the polymers and metals investigated, the mixture of polyethylene with copper is of most interest, exhibiting sheet resistivity changes from 10¹³ to 10⁷ ohms;/? when heated through 200°K. The electrical conduction mechanisms have been examined for both d.c. and a.c. conditions.