有机/无机纳米复合相变储能材料的制备

利用十六烷基三甲基溴化铵（CTAB）嵌入到具有层状结构的膨润土层间,使膨润土层间得到改必,通过交换反应,使三羟甲基丙烷和新戊二醇嵌入膨润土层间而制得有机／无机纳米复合相变储能材料,利用X射线衍射（XRD）和差示扫描量热法（DSC）对制得有机／无机纳米复合相变储能材料进行了表征。     

Effect of interlayer addition on microstructure and mechanical properties of NiTi/stainless steel joint by electron beam welding

NiTi/Stainless Steel(SS) sheets have been welded via a vacuum electron beam welding process, with three methods(offsetting electron beam to SS side without interlayer, adding Ni interlayer and adding Fe Ni interlayer), to promote mechanical properties of the Ni Ti/SS joints. The joints with different interlayers are all fractured in the weld zone near the Ni Ti side, which is attributed to the enrichment of intermetallic compounds including Fe2 Ti and Ni3 Ti. The fracture mechanisms of different joints are strongly dependent on the types of interlayers, and the joints without interlayer, adding Ni interlayer and adding Fe Ni interlayer exhibit cleavage fracture, intergranular fracture and mixed fracture composed of cleavage and tearing ridge, respectively. Compared with the brittle laves phase Fe2 Ti, Ni3 Ti phase can exhibit certain plasticity, block the crack propagation and change the direction of crack propagation. The composite structure of Ni3 Ti and Fe2 Ti will be formed when the Fe Ni alloy is taken as the interlayer, which provides the joint excellent mechanical properties, with rupture strength of 343 MPa.     

Effects of cobalt doping on the electrical characteristics of Al-doped ZnO varistors

The effects of cobalt additive on the electrical characteristics of the Al-doped ZnO varistors are studied in this paper. The current-voltage characteristics of the varistor samples have been investigated in a range from small to large current. With the amount of the doped cobalt increased, the leakage currents of the Al-doped ZnO varistors are inhibited, and their nonlinear coefficients increase remarkably as well. In addition, their breakdown electric fields increase in a small extent and their residual voltage ratios change slightly. Furthermore, the donor densities and the barrier heights of samples decrease with the cobalt content increased. The XRD patterns show that the Bi-rich phase and the willemite phase vary obviously in the varistor samples with various content of cobalt additive.     

Correlation of interlayer diffusion with the stoichiometric composition of RF sputtered Pt/Co/Pt sandwiched structures

Sandwiched structures comprising Pt/Co/Pt layers with varying cobalt deposition time was studied and its importance on the alloy composition, by correlating the effective interlayer diffusion with the atomic stoichiometry, has been presented. A structural phase transition from ordered L1₂ CoPt₃ –? L1₀ CoPt –? L1₂ Co₃Pt was observed with increasing Co deposition time after annealing at 700 °C. The cross-sectional SEM image of the as-deposited film clearly shows a cobalt layer sandwiched between platinum layers. Rutherford back scattering (RBS) analysis shows a multipeak signature for the as-deposited films. A detailed RBS investigation on the extent of interatomic diffusion reveals an equiatomic composition for 20 and 30 min deposition time after annealing. The equiatomic CoPt phase shows a magnetically hard behaviour with a maximum coercivity of 15000 Oe. The reported dependence of (BH)_max on coercivity concludes that by tailoring an additional parameter of deposition time, diverse combinations of structural and magnetic properties can be achieved for appropriate practical applications.     

Face centred cubic cobalt ultrathin-layers in Au/Co(111) multilayers: a study by electron diffraction and by HREM

The structure of various Co/Au(111) multilayers has been investigated, using electron diffraction and high resolution electron microscopy (HREM). The multilayers were grown by electron beam evaporation on a float glass substrate. The cobalt layers exhibit a face centred cubic (f.c.c.) structure with the cobalt [111] axis parallel to the gold [111] axis. For cobalt layers, this f.c.c. structure hadn't been observed in Co/Au multilayers before. Measurements were done on digitized electron diffraction patterns and high resolution images. An important volume expansion of the cobalt lattice and good epitaxial relations between cobalt and gold were observed.     

Exchange of first row transition metal ions with n-butylamine intercalate of tin(IV) hydrogenphosphate

The exchange of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) on n-butylamine tin phosphate intercalate was achieved at 25°C by using metal ion acetate solutions. The uptake behaviour of Mn(II), Co(II) and Ni(II) is similar and there is a progressive decrease of the interlayer distance; while for Cu(II) and Zn(II), there is a gradual disappearance of the reflection which corresponds to the interlayer distance of the n-butylamine tin phosphate intercalate, and a new reflection appears, which correspond to the interlayer distance of the fully exchanged phase. All compounds were examined by diffuse reflectance spectroscopy, X-ray diffraction, magnetic susceptibility measurements ans DTA-TG. Manganese, cobalt and nickel compounds present an actahedral stereochemistry, while, the copper compound is octahedral with a tetragonal distortion. The probable stereochemistry of the anhydrous phases obtained by heating at 480°C is also given.     

Pulsed laser deposition of hydroxyapatite on titanium substrate with titania interlayer

Pulsed laser deposition (PLD) has been used to deposit hydroxyapatite (HA) ceramic over titanium substrate with an interlayer of titania. PLD has been identified as a potential candidate for bioceramic coatings over metallic substrates to be used as orthopedic and dental implants because of better process control and preservation of phase identity of the coating component. However, direct deposition of hydroxyapatite on titanium at elevated temperature results in the formation of natural oxide layer along with some perovskites like calcium titanate at the interface. This leads to easy debonding of ceramic layer from the metal and thereby affecting the adhesion strength. In the present study, adherent and stable HA coating over Ti6Al4V was achieved with the help of an interlayer of titania. The interlayer was made to a submicron level and HA was deposited consecutively to a thickness of around one micron by exposing to laser ablation at a substrate temperature of 400°C. The deposited phase was identified to be phase pure HA by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, and inductively coupled plasma spectrometry. The mechanical behavior of coating evaluated by scratch test indicates that the adhesion strength of HA coating was improved with the presence of titania interlayer.     

Overview of transient liquid phase and partial transient liquid phase bonding

Transient liquid phase (TLP) bonding is a relatively new bonding process that joins materials using an interlayer. On heating, the interlayer melts and the interlayer element (or a constituent of an alloy interlayer) diffuses into the substrate materials, causing isothermal solidification. The result of this process is a bond that has a higher melting point than the bonding temperature. This bonding process has found many applications, most notably the joining and repair of Ni-based superalloy components. This article reviews important aspects of TLP bonding, such as kinetics of the process, experimental details (bonding time, interlayer thickness and format, and optimal bonding temperature), and advantages and disadvantages of the process. A wide range of materials that TLP bonding has been applied to is also presented. Partial transient liquid phase (PTLP) bonding is a variant of TLP bonding that is typically used to join ceramics. PTLP bonding requires an interlayer composed of multiple layers; the most common bond setup consists of a thick refractory core sandwiched by thin, lower-melting layers on each side. This article explains how the experimental details and bonding kinetics of PTLP bonding differ from TLP bonding. Also, a range of materials that have been joined by PTLP bonding is presented.     

Reduction of interlayer Co2+ ions in fluorine mica using diethylene glycol

Reduction of interlayer Co²⁺ ions in expandable fluorine mica has been attempted. The polyol process using diethylene glycol as a reducing agent was employed. The co²⁺ -exchanged mica was refluxed at about 225–235 °C in liquid diethylene glycol for 10–120 minutes. Consequently, zero-valence Co metal (Co⁰) intercalated mica having a metallic grey colour was obtained by in situ reduction of interlayer Co²⁺ ions, showing different properties from Co²⁺ -exchanged mica as a precursor. The layer charge of Co-metal-intercalated mica is compensated by protons which are produced through the course of reduction of interlayer Co²⁺ ions. The reduced sample heated at 350 °C, which had no organic molecules, exhibited a basal spacing of 1.28 nm, indicating the presence of 0.34 nm cobalt metal clusters after subtracting the thickness of the host silicate layer. During the process of reduction in diethylene glycol, cobalt metal particles were expelled from the interlayers which grew to about 0.5 m onto the external surfaces of host mica crystals with increasing refluxing time.     

Influence of interface modification and phase separation on damping properties of epoxy concrete

A preliminary study has been conducted to investigate the influences of interface modification and rubber phase separation on damping behaviour of epoxy concrete (EPC). The main parameters studied here are loss factor (η), i.e. damping, and dynamical modulus of elasticity (E_d). It is found that the tenacity of EPC can be improved by controlling rubber phase separation, and that the mechanical vibration can be absorbed while keeping a high enough E_d value by forming an elastic interlayer using a coupling agent and acrylonitrilebutadiene rubber with end carboxyl group. The values of η and E_d obtained in this paper are in the range of 0.0436–0.0534 and 20.97–26.72 GPa, respectively. The interface microstructure of EPC has been characterized by means of XPS and FTIR here. The results suggest that a weak Lewis acid-base reaction has taken place and chemically bonded joints have formed in the interlayer of EPC, and the rubber phase separation has been characterized by the technique of microimage analysis.     

Diameter-selective encapsulation of metallocenes in single-walled carbon nanotubes

Encapsulation of organic molecules in carbon nanotubes has opened a new route for the fabrication of hybrid nanostructures. Here we show that diameter-selective encapsulation of two metallocene compounds bis(cyclopentadienyl) cobalt and bis(ethylcyclopentadienyl) cobalt has been observed in single-walled carbon nanotubes. In particular, bis(cyclopentadienyl) cobalt is observed to fill only nanotubes of one specific diameter. Electron transfer from the cobalt ions to the nanotubes has been directly observed through a change in the charge state of the encapsulated molecules. The filling of the tubes is found to induce a red-shift of the photoluminescence emission, which is attributed to the formation of localized impurity states below the conduction band of the nanotubes.     

Effects of silicon nitride interlayer on phase transformation and adhesion of TiNi films

TiNi films with different Ti/Ni ratios were deposited on Si substrates with and without silicon nitride interlayer. Near-equiatomic TiNi films were found to have the lowest residual stress and the highest recovery stress regardless of the existence of silicon nitride interlayer. The addition of silicon nitride interlayer between film and Si substrate did not cause much change in phase transformation behavior as well as adhesion properties. X-ray photoelectron spectroscopy (XPS) analysis revealed that there is significant interdiffusion of elements and formation of Ti-N and Si-Si bonds at TiNi film/silicon nitride interface. Scratch test results showed that adhesion between the TiNi film and substrate was slightly improved with the increase of Ti content in TiNi films.     

Structure and magnetic properties of hierarchical cobalt dendrites

Hierarchical cobalt dendrites with ferromagnetic properties have been synthesized by using the in situ produced cobalt carbonate together with cobalt oxalate as precursor and hypophosphite (H₂PO₂⁻) as the reducing agent in mixed solutions at 160 °C. XRD and SAED patterns reveal that the as-prepared cobalt dendrites have a single-crystalline structure with a [001] growth orientation. The shape evolution of the hierarchical cobalt dendrites was investigated.     

Sulphidation of cobalt at high temperatures

The kinetics and mechanism of cobalt sulphidation have been studied as a function of temperature (773–1023 K) and sulphur partial pressure (1–104 Pa) by means of thermogravimetric, SEM and X-ray techniques, and also using inert-marker and ratio-tracer methods. It has been shown that the sulphidation process is diffusion controlled, the rate-determining step being the outward volume diffusion of cations. According to the phase diagram of the Co–S system, the sulphide scale on cobalt is heterogeneous. At sulphur pressures higher than the dissociation pressure of the CoS2 phase, the sulphidation rate is pressure independent, and at lower pressures it increases with rising pressure, in agreement with theoretical predictions. The apparent activation energy of sulphidation is considerably higher for multilayer than for double-layer scale formation, because the main part of multilayer scale is growing at the dissociation pressure of the CoS2 phase, which increases with increasing temperature. Over the whole temperature and pressure range studied, the rate of cobalt sulphidation is more than three orders of magnitude higher than the oxidation rate of this metal. Rapid degradation of cobalt in a sulphur atmosphere results mainly from a very high defect concentration in Co1-yS and Co9S8 sulphides, participating in comparable amounts in the scale formation on this metal at T>900 K. The only sulphide of cobalt in which the defect concentration may be very low is CoS2, the growth rate of this sulphide layer being more than two orders of magnitude lower than that of other cobalt sulphides. © 1998 Chapman & Hall     

Influence of superconducting magnet winding structure on conductor cryostability

The influence of the volume of the superconducting winding interlayer space and the structure of the insulation coating upon the conductor recovery current value I_r has been investigated experimentally. An analysis of the optimum conductor insulation coating was performed, considering different forms of an organic fibre net. The optimum thickness and cell dimension of the net were chosen based on the I_r measurements. It has been shown that the optimal volume of interlayer cooling channels increases the conductor cryostability, and creation of additional gaps of 200 μm in the winding spacers is able to intensify the heat transfer.     

The F.C.C.-H.C.P. phase transition in electrolytically deposited epitaxial cobalt films

The electrolytic growth of cobalt on both copper and nickel single crystals has been examined by reflection electron diffraction for both types of substrates and by electron microscopy in the case of nickel substrates. The f.c.c. →h.c.p. phase transition in cobalt has been studied and its dependence upon film thickness and solution pH is discussed. The relief of misfit in cobalt grown on {110} substrates is also considered.     

Ionic conductivity and crystal structure of magnesium- and cobalt-doped sodium-beta-alumina

The effect of cobalt as a dopant for sodium-beta-alumina has been studied in polycrystalline materials prepared from a mixed oxide precursor. Two materials have been examined; one containing a small amount of cobalt as well as magnesium as a dopant and the other magnesium alone to produce the same molar quality of divalent dopant. The sintering behaviour, microstructure and phase composition are shown to be related to the measured ionic conductivity.     

Determination of copper(II) by displacement substoichiometric extraction with radiolabeled cobalt(II)

A substoichiometric radiochemical displacement technique has been employed for the quantification of trace amounts of copper from complex matrices. The procedure is based on higher stability of copper bipyridine complex compared to its cobalt analog, which leads to the displacement of spiked (⁶⁰Co) cobalt from its bipyridine complex in n-butanol by Cu(II). The amount of labeled cobalt stripped back into the aqueous phase is proportional to the amount of copper incorporated into the organic phase and is monitored for the quantitative estimation of copper. The interferences from various allied ions were critically examined. The proposed method has been successfully employed for the estimation of copper from various certified alloys.     

Electrical control of the ferromagnetic phase transition in cobalt at room temperature

Electrical control of magnetic properties is crucial for device applications in the field of spintronics. Although the magnetic coercivity or anisotropy has been successfully controlled electrically in metals as well as in semiconductors, the electrical control of Curie temperature has been realized only in semiconductors at low temperature. Here, we demonstrate the room-temperature electrical control of the ferromagnetic phase transition in cobalt, one of the most representative transition-metal ferromagnets. Solid-state field effect devices consisting of a ultrathin cobalt film covered by a dielectric layer and a gate electrode were fabricated. We prove that the Curie temperature of cobalt can be changed by up to 12 K by applying a gate electric field of about ±2 MV cm(-1). The two-dimensionality of the cobalt film may be relevant to our observations. The demonstrated electric field effect in the ferromagnetic metal at room temperature is a significant step towards realizing future low-power magnetic applications.     

The contribution of ion plasma sprayed coatings to performance of diamond dressing tools

The paper addresses the effect of ion plasma sprayed coatings on performance of diamond dressing tools under diamond abrasive machining conditions. The use of thick wear-resistant titanium nitride and carbide coatings with a compensating interlayer of a plastic metal (cobalt) is demonstrated to be a promising method for improving efficiency of dressing tools manufactured by electroplating and electroforming.