dc resistivity of ceramic Li+Na+ beta-alumina

The dc resistivity of ceramic Li⁺Na⁺ beta-alumina is reported. The sodium electrolyte was partly exchanged with lithium and the dc resistivity measured by a four-in-line electrode arrangement using Li amalgam electrodes. The mixed alkali metal electrolyte was found to be several hundred fold more resistive than the pure sodium electrolyte, the latter being measured using sodium amalgam electrodes.     

Structural studies of highly non-stoichiometric polycrystalline sodium and silver beta-aluminas

Highly non-stoichiometric (x ≈ 0.45) sodium and silver beta-aluminas have been studied by power neutron diffraction. Results on the sodium material confirm the defect mechanism previously observed in materials with a lower degree of non-stoichiometry but accurate sodium occupations in the mirror plane could not be obtained. In contrast, for the silver beta-alumina prepared by ion exchange, the silver ion distribution could be satisfactorily refined. The stable site in stoichiometric silver beta-alumina is no longer occupied.     

Characteristics of the Na/beta-alumina/Na cell as a sodium vapor pressure sensor

The EMF and voltage-current characteristics for a galvanic cell with the configuration Na vapor (P₁)/sodium beta-alumina/Na vapor (P₂) were studied. It was verified that the EMF followed the Nernst relation over a wide pressure range. For example, when P₁ = 2 × 10^-2 mm Hg and beta-alumina temperature = 340°C, the measured EMF agreed with the calculated value in P₂ range from 10^-5 to 10^-2 mm Hg. At lower pressure range, the measured EMF showed a negative deviation. Coexisting argon gas did not influence the cell EMF characteristic. In an atmosphere containing oxygen, the measured EMF was very high at first. Then it decreased and finally approached a value which agreed with the Nernst equation after several hours. At low beta-alumina temperatures, current saturation was observed in the voltage versus current relation with the anode on the P₂ side. Although the sodium pressure could be determined from saturating current measurement, the measurable pressure range was narrower than that for EMF measurement. At high beta-alumina temperature, current saturation was not clear. Values of 6 × 10^-6 (Ω cm)^-1 for the electron conductivity and 6 × 10^-10 (Ω cm)^-1 for the hole conductivity at 340° were obtained for beta-alumina from the voltage-current characteristics at low sodium pressure.     

Low frequency Raman scattering from ammonium ions is sodium beta-alumina

Based on isotopic frequency shifts and model calculations, bands observed near the region of 155 cm^-1 in Raman spectra of sodium beta-alumina containing ammonium ions have been assigned to translational modes of NH₄⁺. The spectra of a crystal containing 61% NH₄⁺ ions show a pair of bands at 165 and 145 cm^-1 (11 K). Possible origins of these bands are discussed.     

Electrical and chemical degradation of β- and β″-alumina in Na/S and Na/Na cells: An ESR study

The degradation of β- and β″-alumina in Na/Na and Na/S cells has been studied by electron spin resonance. The results have been compared with those obtained by subjecting β- and β″-alumina to sodium in the liquid or vapour state, or to high direct current voltages. Three types of ESR signals have been detected: (1) a colour centre (ESR signal I) produced only by the chemical action of sodium. (2) An ESR signal II attributed to ultra small colloidal particles of metallic sodium. These particles were produced under high direct current voltages, and also by the chemical action of sodium. In this case, they originate from the transformation of centres I. (3) An ESR signal III due to large sodium particles (or to the so-called Na dendrites), produced only under applied dc voltages.     

Sodium-rich beta-alumina

Sodium-rich beta-alumina, with a composition close to (Na₂O)_2.011Al₂O₃, has been prepared by exposure of single crystals of (Na₂O)_1.2511Al₂O₃ to oxygen-saturated sodium at 750°C. The hexagonal c axis of the sodium-rich crystals is shorter than that of the non-stoichiometric beta-alumina precursor. The ionic conductivity at 500°C is an order of magnitude lower and its activation energy higher than for (Na₂O)_1.2511Al₂O₃.     

Studies on poly(vinylidene fluoride-co-hexafluoropropylene) based gel electrolyte nanocomposite for sodium-sulfur batteries

Experimental investigations on a sodium ion conducting gel polymer electrolyte nanocomposite based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), dispersed with silica nanoparticles are reported. The gel nanocomposites have been obtained in the form of dimensionally stable, transparent and free-standing thick films. Physical characterization by X-ray diffraction (XRD), Fourier transform Infra-red (FTIR) spectroscopy and Scanning electron microscopy (SEM) have been performed to study the structural changes and the ion-filler-polymer interactions due to the dispersion of SiO₂ nanoparticles in gel electrolytes. The highest ionic conductivity of the electrolyte has been observed to be 4.1 × 10⁻³ S cm^− 1 at room temperature with ~ 3 wt.% of SiO₂ particles. The temperature dependence of the ionic conductivity has been found to be consistent with Vogel-Tammen-Fulcher (VTF) relationship in the temperature range from 40 to 70 °C. The sodium ion conduction in the gel electrolyte film is confirmed from the cyclic voltammetry, impedance analysis and transport number measurements. The value of sodium ion transport number (t_Na+) of the gel electrolyte is significantly enhanced to a maximum value of 0.52 on the 15 wt.% SiO₂ dispersion. The physical and electrochemical analyses indicate the suitability of the gel electrolyte films in the sodium batteries. A prototype sodium-sulfur battery, fabricated using optimized gel electrolyte, offers the first discharge capacity of ~165 mAh g^− 1 of sulfur.     

Oxygen-ion conducting electrolyte materials for solid oxide fuel cells

Oxygen-ion conducting solid electrolyte systems have been reviewed with specific emphasis on their use in solid oxide fuel cells. The relationships between phase assemblage, electrolyte stability and ionic conductivity have been discussed. The role of parameters such as sintering temperature and atmosphere which influence the segregation of impurities, present in the starting ceramic powders, at grain boundaries and at the external surface of the electrolyte compacts has been emphasised. The stability of various electrolyte materials in contact with other fuel cell components and in fuel environments has been discussed in detail. The ageing behaviour at fuel cell operating temperatures has been described. Data on ionic conductivity, mechanical and thermal properties have been presented for a number of electrolyte materials.     

Impurities and solid electrolyte failure

A thermodynamically based model is used to assess the effects of the formation of a layer of lowered ionic conductivity and increased electronic conductivity on the applied voltage at which solid electrolyte failure is to be expected. Such a layer can result from electrolyte contamination with electrode impurities. It is found that when a significant electrolyte resistivity increase is produced, electrolyte failure can be initiated by a mechanism that deposits sodium internally in the solid electrolyte. The results stress the necessity of operating solid electrolyte cells, such as Na/S, in a manner that minimizes electrode contamination.     

电解法制备纳米银溶胶及其SERS活性研究

分别用柠檬酸三钠溶液、硝酸银和聚乙烯醇混合液作为电解液,用银棒作为电极,加上7 V直流电压,通电1 h,用电解方法得到了纳米银溶胶。为测试该纳米银溶胶是否具有表面增强拉曼散射1(SERS)活性,选用了阳离子型分子碱性品红(Fuchsine basic)、亚甲基蓝(Methylene blue),阴离子型分子苯甲酸(Benzoic acid),甲基橙(Methyl orange)、中性分子吖啶橙(Alcidine orange)、苏丹红(Sudan red)作为测试分子,进行SERS研究,结果发现用两种电解液制备的纳米银都具有很强的SERS活性,但用硝酸银和聚乙烯醇混合液作为电解液制备的纳米银溶胶具有更广泛的SERS 活性。在该方法制备的纳米银上,得到了在常规方法制备的胶态纳米银上及用柠檬酸三钠溶液作为电解液制备的纳米银上得不到的甲基橙分子的SERS谱,对可能的原因进行了讨论。     

Electrical properties of ZnO stabilized beta″-alumina

The electrical conductivity of ZnO doped (1?5 wt%) beta″-alumina ceramic samples has been measured by the complex admittance method. The smallest value of electrical resistivity was in the case of the samples doped with 3 wt% ZnO. The bulk conductivity dependence (in lnσT?1/T coordinates) is characterized by two slopes, with a bend occuring at about 250°C. The low temperature activation energy of bulk conductivity is not influenced by the doping level. The high temperature activation energy decreases with increasing ZnO content. The change in the slope of the Arrhenius plot of the beta-alumina bulk conductivity is in agreement with what should be expected from Wang's model.     

Colorando Auro: contribution to the understanding of a medieval recipe to colour gilded silver plates

The colour of gildings can be modified by many artistic techniques. This article refers to the possibility of a specific chemical treatment to change the colour of gildings. The model samples—gilded silver plate, the mixture and the application of a medieval recipe based on ancient writings from Theophilius and Cellini have been described. We propose a strategy to identify the chemical processes involved in the change of colour of the metallic surface through the advanced study of these model samples. Synchrotron X-ray photoelectron spectroscopy and X-ray absorption spectroscopy were carried out both on the gilding with and without the application of the treatment with the aim to understand the chemical reactions occurring during the treatment.     

Improving nucleation in the fabrication of high-quality 3D macro-porous copper film through the surface-modification of a polystyrene colloid-assembled template

A new approach is developed to the fabrication of high-quality three-dimensional macro-porous copper films. A highly-ordered macroporous copper film is successfully produced on a polystyrene sphere (PS) template that has been modified by sodium dodecyl sulfate (SDS). It is shown that this procedure can change a hydrophobic surface of PS template into a hydrophilic surface. The present study is devoted to the influence of the electrolyte solution transport on the nucleation process. It is demonstrated that the permeability of the electrolyte solution in the nanochannels of the PS template plays an important role in the chemical electrodeposition of high-quality macroporous copper film. The permeability is drastically enhanced in our experiment through the surface modification of the PS templates. The method could be used to homogeneously produce a large number of nucleations on a substrate, which is a key factor for the fabrication of the high-quality macroporous copper film.     

Structural and electrical properties of pure and NaBr doped poly (vinyl alcohol) (PVA) polymer electrolyte films for solid state battery applications

A sodium ion conducting polymer electrolyte based on poly (vinyl alcohol) (PVA) complexed with sodium bromide (NaBr) was prepared using solution cast technique. Several experimental techniques such as XRD, FTIR, SEM, temperature-dependant conductivity and transference number measurements have been performed. XRD and FTIR studies confirm the complexation of salt with the polymer. Surface morphology was studied using Scanning Electron Microscopy. DC conductivity was measured in the temperature range of 303–373 K, and the conductivity was found to increase with the increase of dopant concentration as well as temperature. Transference number data suggests that the charge transport in this polymer electrolyte system is mainly due to ions. Using these polymer electrolyte films, electrochemical cells were fabricated with configuration Na/(PVA:NaBr)/V₂O₅ and Na/(PVA:NaBr)/(I2+C+electrolyte) and their discharge characteristics like open circuit voltage (OCV), short circuit current (SCC), power density, energy density were evaluated and compared. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Ionic conductivity and battery characteristic studies on PEO+NaClO3 polymer electrolyte

Solid polymer electrolyte films based on poly (ethylene oxide) PEO complexed with NaClO₃ have been prepared by a solution-cast technique. The solvation of Na⁺ ion with PEO is confirmed by XRD and IR studies. Measurements of the a.c. conductivity in the temperature range 308 – 378 K and the transference numbers have been carried out to investigate the charge transport in this polymer electrolyte system. Transport number data show that the charge transport in this polymer electrolyte system is predominantly due to ions. The highest conductivity (2.12.10⁻⁴ S/cm) has been observed for the 70:30 composition. Using the polymer electrolyte solid state electrochemical cells have been fabricated. The various cell parameters are evaluated and reported.     

Evaluation of solid electrolyte cells with a versatile electrochemical technique

Voltage losses in fuel cells and other solid electrolyte systems are due to several mass transport and kinetics processes at the electrode/electrolyte interface as well as to ohmic contributions from the electrolyte, electrodes, current collectors and contact resistances. Electrochemical impedance spectroscopy (EIS) has been in use for several decades in fuel cell research and is quite effective in determining the contribution of individual electrode and electrolyte processes. However, data acquisition and analysis can be time-consuming and the technique has many limitations whilst cell performance and operating conditions are varying rapidly with time especially when the cells are under current load. The galvanostatic current interruption (GCI) technique is fast and can be used under a wide range of operating as well as for rapidly varying loads and cell performance conditions. In this paper a totally new and very simple way of adapting commercially available equipment has been described to perform high quality, reliable and fast GCI measurements over a range of different currents in one sequence without having to use an electronic switch or a solid state relay or a separate fast data logging system. Its versatility has been demonstrated with a number of standard RC circuits simulating slow electrode and fast electrolyte processes and by evaluating a number of solid oxide fuel cell materials. The GCI technique has been shown to be able to determine the composition of all standard test circuits within ±1 % of those determined from the EIS technique and actual values of circuit components. The technique has been applied to investigating solid electrolyte cells and produced excellent results.     

Applying colour science in colour design

Although colour science has been widely used in a variety of industries over the years, it has not been fully explored in the field of product design. This paper will initially introduce the three main application fields of colour science: colour specification, colour-difference evaluation and colour appearance modelling. By integrating these advanced colour technologies together with modern colour imaging devices such as display, camera, scanner and printer, some computer systems have been recently developed to assist designers for designing colour palettes through colour selection by means of a number of widely used colour order systems, for creating harmonised colour schemes via a categorical colour system, for generating emotion colours using various colour emotional scales and for facilitating colour naming via a colour-name library. All systems are also capable of providing accurate colour representation on displays and output to different imaging devices such as printers.     

Is colour cognitive?

In recent years, colour-vision abilities have been rather generously ascribed to various invertebrates and even bacteria. This uncertainty of when to diagnose colour vision stems in part from confusing what colour vision can do with what it is. What colour vision can do is discriminate wavelength independent of intensity. However, if we take this as a definition of what colour vision is, then we might be obliged to conclude that some plants and bacteria have colour vision. Moreover, there is a similar confusion of what are necessary and what are sufficient mechanisms and behavioural abilities for colour vision. To humans, seeing in colour means seeing an image in which objects/lights have chromatic attributes—in contrast to the sensation that we have when viewing monochrome movies, or our experience in dim light when only rod vision is possible. The necessary basic equipment for this is to have at least two types of photoreceptors that differ in spectral sensitivity, and at least one type of spectrally opponent cell to compare the signals from the photoreceptors. Clearly, however, a necessary additional prerequisite for colour vision is to have vision, which entails the identification of shapes, sizes and locations of objects in the world. Thus, if an animal has colour vision, it should see an image in which distinct objects/lights have colour attributes. This distinguishes colour vision from wavelength discrimination, but also from what has historically been called wavelength-specific behaviour: a type of behaviour triggered by fixed configurations of spectral receptor signals; however, we discuss difficulties in diagnosing wavelength-specific behaviour as an indicator of the absence of colour vision. Finally, we discuss whether colour vision, by definition, contains a cognitive dimension for ordering and classifying perceptual experience.     

室温钠离子电池材料及器件研究进展

在众多电化学储能技术中,室温钠离子电池除具有能量密度高、循环寿命长的特点外,还具有其他电池体系所不具有的资源丰富和成本低廉的优势,是一种较理想的规模储能电池体系.中国科学院物理研究所自2011年以来致力于低成本、安全环保的钠离子电池技术的研发,在正、负极材料和电解质材料开发中取得了多项原创性的研究成果,并研制出Ah级钠离子软包电池.例如,首次发现Cu~(2+)/Cu~(3+)氧化还原电对高度可逆并设计了Na-Cu-Fe-Mn-O基低成本层状氧化物正极材料;首次通过简单的一步碳化法制备出性价比高的无烟煤基负极材料;首次将一种新型的钠盐NaFSI应用于碳酸酯非水电解质以大幅度提升电极材料的性能等.本文综述了物理所在钠离子电池材料及器件研究中所取得的重要进展和突破,期待经过进一步不懈地努力为实现钠离子电池的产业化做出重要贡献.     

Colour naming

An experimental study exploring colour ranges corresponding to different colour names has been conducted. Available colour terms in Turkish language have been identified and the most frequently known or used colour terms have been attained. Using the Munsell Color System, colour ranges reflecting the colour naming and colour perception of Turkish people, have been constructed for each colour term. The discussion of the findings and observations during the research are also included.