Enhancement of electrical conductivity and emission stability of oxide cathodes using Ni addition

An investigation has been carried out into the use of conductive phase additions to enhance the conductivity and emission behavior of the oxide cathode coating as used in CRTs. Electrical and emission characteristics have been studied for various additions of filamentary nickel (Ni) added to the sprayed strontium-barium carbonate precursors prior to spray deposition, followed by conventional thermal conversion and activation processes in vacuum. The conductivity and the electronic activation energy have been studied as a function of temperature in the range 300 to 1250 K, during conversion and activation processes allowing the conduction behavior to be compared to conventional materials. The conduction behavior has been found to change as a function of heat-treatment temperature as the conduction paths develop and subsequently evolve in the microstructure of the resultant composite coating during conversion, activation and subsequent aging/service life conditions, with metallic-dominated conduction at temperatures below 850 K and pore conduction mechanisms dominating at higher temperatures. The emission characteristics immediately after conversion are impaired by the Ni addition, however, the long-term emission characteristics show improvement with the conductive phase.     

Thermal decomposition of ferrous oxalate dihydrate studied by direct current electrical conductivity measurements

The feasibility of the use of direct current electrical conductivity,, measurements in the study of solid-state reactions involved in the synthesis of-Fe₂O₃ from ferrous oxalate dihydrate has been reported. The study has been carried out in static air, dynamic air, dry nitrogen and dynamic air + water vapour environments. The conductivity data determined in static air are quite complex; nevertheless, the formation of Fe₃O₄ and-Fe₂O₃ with the probable intermediate formation of-Fe₂O₃ has been indicated. In dry nitrogen the step corresponding to dehydration is well resolved in the temperature region 145–220° C; the formation of FeO and Fe₃O₄ is also well characterized. In dry dynamic air the reaction further proceeds to the formation of-Fe₂O₃. In dynamic air containing water vapour there are definite indications of the formation of-Fe₂O₃ prior to the formation of-Fe₂O₃. Definite experimental conditions have been determined for the formation of-Fe₂O₃ in dynamic air containing water vapour. The conductivity measurements have been supplemented with infra-red spectroscopy and X-ray diffraction pattern measurements. The electrical conductivity measurements were found to give additional information on the solid-state reaction to that obtained from conventional thermal analytical techniques (such as differential thermal, thermogravimetric and differential thermogravimetric analyses).Fe₂O₃, obtained from the decomposition of FeC₂O₄ · 2H₂O in dynamic air + water was found to have a coercive force of 3.142 A m^–1, a saturation magnetization value of 7.1 T kg^–1 and a ratio of remanence to saturation magnetization of 0.64.     

Thermal conductivity of inhomogeneous materials

The effective thermal conductivity is calculated from the rate of entropy production per unit volume. Thermal conductivity and the temperature field are expressed in terms of Fourier components and these are related. The rate of entropy production is then obtained in terms of the volume-averaged thermal conductivity and the Fourier components of thermal conductivity. A simple expression for the effective thermal conductivity is found. In the case of striations it leads to well-known results. The formalism is applied to solids with inhomogeneously distributed solutes. It is shown that the thermal conductivity is less than the volume-averaged thermal conductivity and that homogenization by diffusion increases the thermal conductivity. Similar results would apply to the electrical conductivity of inhomogeneous alloys.     

Thermal conductivity of crystalline particulate materials

In order to explore the relationship between effective thermal conductivity of an evacuated powder and the bulk thermal conductivity of the same material, the effective thermal diffusivities of particulate NaCl and Dianin's inclusion compound with ethanol guests (abbrev. ED) with effective porosities 0.5 were measured and used to determine their effective thermal conductivities below 300 K. Calculations showed that contact heat conduction is the predominant mechanism, i.e., heat transfer by radiation and by conduction through the gas phase are negligible in the measurement conditions. The effective thermal conductivity of particulate as-synthesised ED powder was found to be proportional to the bulk thermal conductivity for three different samples. On the other hand, the effective thermal conductivity of NaCl powder was found to have a softer temperature dependence than the bulk thermal conductivities reported for measurements of NaCl single crystals. This was related to increased concentration of structural defects formed during mechanical grinding of the NaCl sample.     

Thermal conductivity of moist porous materials

We propose both a model and a method of calculating the effective thermal conductivity of moist porous materials made of a three-component structure with interpenetrating components.Translated from Inzhenerno-Fizi-cheskii Zhurnal, Vol. 56, No. 2, pp. 281–291, February, 1989.     

Thermal and electrical conductivity of binary magnesium alloys

Thermal conductivity is a key parameter for thermal design and management of the electronic components in their passive cooling processes. In this work, thermal and electrical conductivities of six groups of binary Mg alloys (Mg–Al, Mg–Zn, Mg–Sn, Mg–Zr, Mg–Mn, and Mg–Ca) in as-cast, as-solution, and annealed states were measured and the corresponding microstructures were observed. In both as-cast and as-solution states, thermal/electrical conductivities of the six groups of Mg alloys decreased with composition. Effects of solution treatment and annealing on thermal/electrical conductivities of the as-cast samples were also investigated and discussed. Moreover, the specific thermal/electrical resistivity (thermal/electrical resistivity increment of the alloy derived from one atom addition) of the solute elements for Mg alloys was drawn as follows, Zn < Al < Ca < Sn < Mn < Zr. Atomic volume difference of the solute elements with Mg atom (ΔV/V _Mg), valency, and configuration of extra-nuclear electron of the solute were believed as the main reasons for the differences.     

Dielectric permittivity and electrical conductivity of polycrystalline materials

This paper examines the influence of composition, structure, and size factor on the dielectric permittivity and electrical conductivity of polycrystalline materials. We demonstrate that, if the 3D structure of a substance remains unchanged, reducing the grain size increases its permittivity, up to 10⁵–10⁶ for nanocrystalline powders.     

Thermal conductivity analysis and applications of nanocellulose materials

Abstract

In this review, we summarize the recent progress in thermal conductivity analysis of nanocellulose materials called cellulose nanopapers, and compare them with polymeric materials, including neat polymers, composites, and traditional paper. It is important to individually measure the in-plane and through-plane heat-conducting properties of two-dimensional planar materials, so steady-state and non-equilibrium methods, in particular the laser spot periodic heating radiation thermometry method, are reviewed. The structural dependency of cellulose nanopaper on thermal conduction is described in terms of the crystallite size effect, fibre orientation, and interfacial thermal resistance between fibres and small pores. The novel applications of cellulose as thermally conductive transparent materials and thermal-guiding materials are also discussed.     

Thermal conductivity and quasihomogeneity criterion of disperse materials

We suggest a method of numerical calculation of the effective thermal conductivity and the time for establishing quasihomogeneity of disperse materials. The method is based on the principle of generalized conductivity realizable within the framework of a nonstationary thermal problem. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 3, pp. 441–446, May–June, 1998.     

氮化硼和氧化锌晶须共掺杂环氧树脂复合材料的导热与绝缘性能

双酚A环氧树脂（EP）因其具有优异电绝缘性能而被广泛应用于电子器件中,但EP的热导率较低,通过填充高导热无机填料而构建导热通路是当前提高聚合物复合材料热导率的有效策略。本文综合利用溶液共混与热压工艺制备得到了六方氮化硼（h-BN）-四针状氧化锌晶须（T-ZnOw）/EP复合材料,并对复合材料的微观形貌与物相结构、导热性能及绝缘性能进行了系统表征与分析。结果表明,复合填充h-BN-T-ZnOw/EP复合材料兼具良好的导热性和绝缘性,当h-BN-T-ZnOw的填充含量为30wt%/5wt%时,25℃下热导率为0.55 W/（m·K）,相比于纯EP提升了2.9倍,同时复合材料体积电阻率大于10¹⁵Ω·m,表现出良好的绝缘性。     

Thermal conductivity of multiphase particulate composite materials

Hollow particle filled composites, called syntactic foams, are used in weight sensitive structural applications in this paper. In this paper, homogenization techniques are used to derive estimates for thermal conductivity of hollow particle filled composites. The microstructure is modeled as a three-phase system consisting of an air void, a shell surrounding the air void, and a matrix material. The model is applicable to composites containing coated solid particles in a matrix material and can be further expanded to include additional coating layers. The model is successful in predicting thermal conductivity of composites containing up to 52% particles by volume. Theoretical results for thermal conductivity are validated with the results obtained from finite element analysis and are found to be in close agreement with them. A simplified approximation of the theoretical model applicable to thin shells is also validated and found to be in good agreement with the corresponding finite element results. The model is applicable to a wide variety of particulate composite materials and will help in tailoring the properties of particulate composites as per the requirements of the application.     

The electrical conductivity of doped and undoped uranium oxide

The conductivity of undoped and doped uranium dioxide was investigated over the temperature range of approximately 300–1600 K. Activation energies calculated for the undoped samples and those doped with Cr₂O₃ and Gd₂O₃ are in agreement with previously published values. The values calculated for TiO₂- and La₂O₃-doped samples were nearly twice that for the undoped UO₂. The addition of Nb₂O₅ resulted in the extension of the intrinsic region of conductivity to lower temperatures than had been previously reported. The dependence of the extrinsic conductivity of Gd₂O₃- and Cr₂O₃-doped samples on the dopant level supports an impurity compensation model of conduction.     

Thermal conductivity of pl asma-sprayed aluminum oxide

Results are shown of a study concerning the thermal conductivity of plasma-sprayed aluminum oxide, depending on the spray technology and the heat treatment.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 24, No. 1, pp. 106–111, January, 1973.     

Direct current electrical conductivity of gamma ferric oxide

The study of the direct current electrical conductivity, , of freshly prepared -Fe₂O₃ and that of a sample stored for seven days in static air suggests that -Fe₂O₃ adsorbs oxygen and water from the atmosphere. From infra-red spectra it is deduced that the absorbed water in -Fe₂O₃ is present as the physically adsorbed water and as lattice water. The adsorbed oxygen and physically adsorbed water are removed by heating to 100 C, while the lattice water remains in -Fe₂O₃ even up to 280 C. The removal of lattice water is associated with a decomposition during which some of the hydrogen formed occupies the vacancy sites. This suggested formation of the hydrogen ferrite phase is based on the kink in the log against T ^–1 curve observed at 177 C. This kink is very well resolved for a sample equilibrated at 100 C in normal atmosphere, and the measurements of above 100 C of this sample are done in an N₂ atmosphere. The suggestion that the hydrogen ferrite phase is formed has been substantiated by comparison of the X-ray diffraction patterns of -Fe₂O₃ heated under the different atmospheres. From the log against T ^–1 plot for a sample heated under a nitrogen atmosphere the activation energy is small (< 0.05 eV) up to 215 C, and it is comparatively large (0.95 eV) above 215 C. These results suggest a hopping mechanism for the direct current electrical conductivity of -Fe₂O₃. This suggestion has been substantiated by data of the temperature variation of Seebeck voltage.     

Preparation, structure, and electrical conductivity of calcium-antimonate-based materials

Metastable antimony(V) oxide compounds are prepared via mechanochemical reactions in mixtures of CaO and Sb₂O₃, followed by mild oxidizing heat treatment and calcium leaching in a hydrochloric acid solution, and are characterized by x-ray diffraction and thermal analysis. The synthesized compounds have the pyrochlore structure or a monoclinic pyrochlore-like structure (Ca₁₆Sb ₃₊ ⁸ Sb ₅₊ ⁸ O₄₈). Doping with fluorine slows down subsequent oxidation, while doping with lanthanum impedes calcium leaching. The composition and morphology of the powders (nanopores and core-shell microstructure of the grains) determine their properties: water release in a broad temperature range, proton conductivity, and low absorption capacity for Na⁺ ions. In hydrogen atmosphere, the reduction of antimony decreases their conductivity.     

Thermal stress-induced charge and structure heterogeneity in emerging cathode materials

Nickel-rich layered oxide cathode materials are attractive near-term candidates for boosting the energy density of next generation lithium-ion batteries. The practical implementation of these materials is, however, hindered by unsatisfactory capacity retention, poor thermal stability, and oxygen release as a consequence of structural decomposition, which may have serious safety consequences. The undesired side reactions are often exothermic, causing complicated electro-chemo-mechanical interplay at elevated temperatures. In this work, we explore the effects of thermal exposure on chemically delithiated LiNi_0.8Mn_0.1Co_0.1O₂ (NMC-811) at a practical state-of-charge (50% Li content) and an over-charged state (25% Li content). A systematic study using a suite of advanced synchrotron radiation characterization tools reveals the dynamics of thermal behavior of the charged NMC-811, which involves sophisticated structural and chemical evolution; e.g. lattice phase transformation, transition metal (TM) cation migration and valence change, and lithium redistribution. These intertwined processes exhibit a complex 3D spatial heterogeneity and, collectively, form a valence state gradient throughout the particles. Our study sheds light on the response of NMC-811 to elevated temperature and highlights the importance of the cathode’s thermal robustness for battery performance and safety.     

高容量层状锰基氧化物正极材料研究进展

层状锰基氧化物Li[Lix(MnM)1-x]O2(M=Ni,Co,Cr…)正极材料具有比容量高的优点,引起了研究者的广泛关注。结合课题组的研究工作,综述了这一领域的最新研究进展。重点对层状锰基氧化物正极材料的结构、电化学性能,特别是对其独特充放电机制和电化学性能的改善进行了总结和探讨。最后总结了高容量层状锰基氧化物正极材料目前存在的主要问题以及未来的研究重点。