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.     

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.     

The resistivity of sodium beta-alumina samples removed from cycled sodium-sulphur cells

Conductivity studies over the temperature range 223–573 K have been carried out on sodium beta-alumina samples removed from cycled sodium-sulphur cells. Within the limits of experimental error and batch variation, it has been determined that the cell cycling has had little effect on the conductive properties of the sodium beta-alumina sinters studied. Upon removal of the electrolyte tubes from the sodium-sulphur cells, the ceramic material was observed to have undergone a colour change or “blackening”. The presence of the species causing the colour change, suggested to be atomic sodium, does not result in a highly resistive phase, nor is the electronic conductivity of the electrolyte substantially affected.     

Specific features of the luminescence of silicate glasses with silver introduced by ion exchange

The luminescence spectra of silicate glasses with silver introduced by ion exchange have been investigated. It is shown that silver introduced into glass by ion exchange exists not only in the form of ions, but also as neutral atoms and charged and neutral molecular clusters, which provide intense luminescence in the visible spectral range. Cerium ions in glass facilitate the formation of neutral molecular silver clusters, due to which the luminescence intensity increases. It is shown that Ag _n -Ce ^x+ complexes can be formed in glass containing cerium ions and neutral molecular silver clusters.     

Comparative analysis of the phonon modes in AgNbO<Subscript>3</Subscript> and NaNbO<Subscript>3</Subscript>

The lattice dynamics of silver niobate AgNbO₃ and sodium niobate NaNbO₃ is calculated from first principles. The unstable modes (i.e., tilting of oxygen octahedra and ferroelectric atomic displacements) in silver and sodium niobates are analyzed. It is shown that the existence of ferroelectric modes is associated primarily with the instability of the atomic positions of silver and sodium in the crystal lattice. The dynamic charges in the structure of silver and sodium niobates are determined. According to the first-principles calculations, both silver and sodium niobates in the ground state (T = 0) are characterized by ferroelectric atomic displacements and frozen tilting of oxygen octahedra, with the only difference being that the tilting modes of the oxygen octahedra in silver niobate correspond to the M point of the Brillouin zone, whereas those in sodium niobate are attributed to the R point of the Brillouin zone. The results of these calculations are in good agreement with experimental data.     

Potassium ion conduction in K2O·(5 − x)Ga2O3·xAl2O3

Potassium gallate in which gallium ions are partially substituted by aluminium, K₂O·(5 ? x)Ga₂O₃·xAl₂O₃, has been prepared by sintering a mixture of K₂CO₃, Ga₂O₃, Al₂O₃ at 1500°C. It was found from X-ray diffraction that the gallate had the beta-alumina type β phase and that solid solutions were formed on substituting Ga by Al. The potassium gallate thus obtained was revealed to be a relatively high potassium ion conductor by a.c. conductivity and ionic transport number measurements. The potassium ion conductivity decreases monotonically with the aluminium content. In order to analyze the decreasing behavior of the conductivity isotherm, the slot width was calculated from the lattice parameters and the apparent porosity was evaluated using the apparent and theoretical densities. The change of the potassium ion conductivity with the substituted amount of aluminium was explained well by the variation of the slot width.     

Electron distribution in silver halides

Solid fast ion conductors such as silver halides and silver chalcogenides have been recently drawing attention, because of their unusually high ionic conductivity in the high-temperature phase at about 200°C. This peculiar property is of particular importance for both research field of codensed matter physics and practical application as solid state sensors. The information of the bonding nature relevant to the electron distribution is desirable, in order to obtain insights into their characteristic property of solid fast ion conductors. An attempt will be made in this paper to review the current information of the bonding nature of silver halides in terms of the electron density distribution. Thus, this paper is primarily concerned with some physical properties of silver halides including the characteristic features of the crystal structure and the phase diagram. The data of alkali halides are also described for comparison. The experimental results of the magnetic susceptibilities of silver halides are summarized from the phenomenological point of view. The magnetic susceptibilities of silver halides were found to be sensitive to the change of temperature and crystal structure. It implies that the valence electrons of silver halides are loosely bound by the ion core. The electron density distribution in Agl and AgBr is also discussed using the results by single crystal X-ray diffractometry and the following points are suggested; in AgBr, the deformation of the charge distribution in bromine ion is much larger than that of silver ion and the radial distribution of valence electrons in bromine ion is enlarged in comparison with that of free ion state. In Agl, charge accumulation is feasible only on the c-directed bond and the difference Fourier map on the (1 1 0) plane indicates the deficiency of electrons around the silver site.     

Structural Characteristics of Metal Nanoparticles in Glass Upon Irradiation-Assisted Processing

Irradiation-assisted processing, i.e. ion, electron and laser irradiation, have been applied to fabricate metal/glass nanocomposites. The particle configurations are studied by transmission electron microscopy to get some insight into the rather complex formation mechanisms. Special attention is given to spheroidally shaped particles surrounded by smaller secondary particles observed upon ion beam mixing of silica/silver/silica layer compounds as well as irradiating femtosecond laser pulses on sodium silicate glass containing spherical silver particles. Another unique type of structure are cavities observed in silver particles formed by high fluence ion implantation into silica as well as upon laser pulse irradiation of silver particles in glass. The experimental findings are discussed in terms of irradiation-induced defect formation and radiation-enhanced diffusion.     

Sensing and fluorescence behaviors of complex formation between new lariat crown ethers bearing fluorescence sidearm and metal ions in methanol solution

Fluorescence spectroscopic properties of the complex formation between six new C-pivot16-crown-5 ethers bearing fluorescence side arms and metal ions are studied. Six new C-pivot 16-crown-5 ethers that carry fluorescence side arms were synthesized. The research also included the examination of different fluorescent behavior of the new lariat ethers in the presence of silver and sodium ions (Ag⁺ and Na⁺) in methanol. Because of the good fit of the cavity size of these 16-crown-5 ethers with the Ag⁺ and Na⁺ ions, remarkable change in fluorescent spectra were observed. The results showed that the new lariat crown ethers exhibited enhanced selectivity towards sodium ion, but silver ion show quenching abilities towards the ligands. Cooperative participations of the C-pivot side arm oxygen with the ring oxygen molecules in complexation was also confirmed by the single crystal X-ray crystallography of the complex, (C₂₇H₃₀O₇)·NaClO₄. The freezing of crown ring conformation and the diminishment of the chance of sidearm oscillation that occurred upon complexation with sodium ion are the main causes of fluorescent enhancement. The quenching caused by the addition of silver ion was found to explainable by the photo-induced electron transfer that results in the reduction of silver ions.     

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.     

Multimode strip waveguide formed by ion-electro-diffusion from solid state silver: Side diffusion reduction

Multimode strip waveguides are formed in glass plates by field-assisted silver-sodium ion exchange using evaporated silver as ion supplier. Two kinds of anodes are considered, metal layer and sodium nitrate melt. Study of the side broadening (side diffusion) is carried out for both cases. It is shown that a reduction of the side broadening can be achieved using melted sodium nitrate as anode, which makes it possible to control a two-dimensional index profile.     

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.     

Glass‐embedded silver nanoparticle patterns by masked ion‐exchange process for surface‐enhanced Raman scattering

Glass‐embedded silver nanoparticle patterns were fabricated by masked silver–sodium ion‐exchange process followed by etching to reveal the particles for surface‐enhanced Raman scattering (SERS). The intensity of the enhanced Raman signal is comparable to that of the fluorescence, and the detection limit of 1 nM for Rhodamine 6G has been achieved. Raman images at different etching depths and corresponding morphological images are compared to find optimal SERS signal. Our results demonstrate that silver nanoparticle patterns embedded in glass can be used as SERS‐active substrates. Nanoparticles can be formed in a glass of high optical quality and have potential to be integrated with optical waveguides for a sensor chip. Copyright © 2010 John Wiley & Sons, Ltd.     

Investigations of the interactions of CO2, O3 and UV light with silver surfaces by in situ IRRAS/QCM and ex situ TOF-SIMS

The characterization of the reactions occurring during the atmospheric corrosion of silver surfaces at the metal-atmosphere interface is of great importance as only the exact knowledge of the degradation mechanisms enables the development of suitable corrosion inhibiting steps. For in situ surface analysis three complementary experimental techniques have been combined in order to study the surface chemistry of silver samples exposed to humidified air, CO₂, ozone (O₃) and ultraviolet (UV) light. In situ infrared reflection absorption spectroscopy (IRRAS) combined with a quartz crystal microbalance (QCM) as well as ex situ time of flight secondary ion mass spectrometry (TOF-SIMS) provide an overall picture of the processes occurring at the metal-atmosphere interface. Investigations were carried out by exposing polycrystalline silver samples to synthetic air containing 50-90% relative humidity (RH) and 250 ppm CO₂. Additionally, the samples were exposed to UV light or O₃ for certain time periods. The formation of the main corrosion products on the sample surfaces, depending on the relative humidity, O₃ content and UV light exposure could be observed in a time resolved way. These investigations reveal the different reaction mechanisms and reaction rates occurring on a silver surface.     

One-pot green fabrication and antibacterial activity of thermally stable corn-like CNC/Ag nanocomposites

Corn-like cellulose nanocrystals/silver (CNC/Ag) nanocomposites were prepared by formic acid/hydrochloric acid hydrolysis of commercial microcrystalline cellulose (MCC), and redox reaction with silver ammonia aqueous solution (Ag(NH₃)₂(OH)) in one-pot green synthesis, in which the preparation and modification of CNCs were performed simultaneously and the resultant modified CNCs could be as reducing, stabilizing and supporting agents for silver nanoparticles. The influences of the Ag⁺ ion concentrations on the morphology, microstructure, and properties of the CNC/Ag nanocomposites were investigated. It is found that corn-like CNC/Ag nanocomposites containing Ag nanoparticles with diameter of about 20–40 nm were obtained. Compared to the MCCs, high crystallinity of 88.5 % and the maximum degradation temperature (T _max) of 364.5 °C can be achieved. Moreover, the CNC/Ag nanocomposites showed strong antibacterial activity against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Furthermore, such nanocomposites can act as bifunctional nanofillers to improve thermal stability, mechanical property, and antibacterial activity of commercial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(lactic acid).     

Synthesis of biomacromolecule-stabilized silver nanoparticles and their surface-enhanced Raman scattering properties

In this work, water soluble silver nanoparticles stabilized by biomacromolecule, were produced through using an aqueous solution of silver nitrate with Bovine Serum Albumin (BSA) under different reducing agents (such as sodium borohydride, hydrazine, N,N-dimethyl formamide) at the room temperature, where BSA provided the main function to form monodispersed silver nanoparticles. UV–vis spectroscopy, Fluorescence spectra, TEM and HR-TEM are used to characterize the BSA-capped silver nanoparticles under different condition. The results show that the formed silver nanoparticles have different size and morphology under the three different reducing agents. Moreover, the fluorescence intensity of BSA was drastically quenched in presence of Ag nanoparticles from the results of fluorescence spectra. Furthermore, the surface-enhanced Raman scattering effects of the formed silver nanoparticles were also displayed and we made a comparison under three different reducing agents.     

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.     

Temperature,roughness and depth resolution in ion sputter profiles

The depth resolutions of evaporated silver layers on polished polycrystalline copper substrates are studied at various temperatures during argon ion sputtemg with AES. A detailed analysis of the profile shape at the interface reveals the nature of contributions to the terms governing interface resolution. The profiles are all accurately described by an error function leading edge followed by an exponential trailing edge. The characteristic of the trailing edge is governed by the development of roughness which depends on the depth, z, sputtered as z^0.875. The roughness is reduced at elevated temperatures by the action of surface diffusion such that the maximum reduction occurs at the highest temperature and the lowest sputtering rate. The characteristic of the leading edge is composed of three terms added in quadrature, (i) defect-enhanced diffusion of copper into the silver film, (ii) roughness as above, and (iii) a constant term due to film nucleation. In the present samples the increased interdiffusion at elevated temperatures and low sputtering rates largely offsets the improvements in topography so that, overall, the depth resolution appears to be a very weak function of temperature. However, in other systems where interdiffusion is small, the resolution could be greatly enhanced.     

On the mechanism of diffusion in sodium beta alumina

A microscopic interstitialcy-type diffusion mechanism for sodium beta-alumina involving three crystallographically different types of cation sites but only two equilibrium configurations of interstitialcy pairs is proposed. The resulting cation-site occupation probabilities are shown to agree with the experimental neutron-diffraction data of Roth et al. For various sizes of the associated regions around the charge-compensating oxygen interstitials (in which Na⁺ ions are not freely mobile), the ratio of the radiotracer diffusivity with respect to the charge diffusivity (the so-called Haven ratio, H_R)is determined. In agreement with the measurements of Kim et al.,H_R is found to increase with increasing temperature as a result of the decrease in the average size of the associated regions. It is concluded that, while at lower temperatures all excess Na⁺ ions are found in the associated regions around the oxygen interstitials, with increasing temperature more and more of them are freely mobile in the unassociated regions of the conduction plane. The formation enthalpy associated with the thermally activated creation of mobile “interstitials” is determined to be about 0.05 eV. The slope of the slightly curved Arrhenius plot associated with the proposed mechanism therefore consists of the sum of the energy of formation of freely mobile interstitials and the energies of migration of two types of interstitialcy pairs. The Raman and IR-conductivity results are found to be compatible with this emerging picture for the microscopic diffusion process in sodium β-alumina. Spectroscopic diffusion techniques (NMR, internal friction, dielectric loss) show more than one apparent activation energy E^A while, in the same temperature region, the d.c. ionic conductivity yields a unique value of E^A; reasons for this discrepancy are discussed.     

Fabrication and characterization of silver/titanium dioxide composite nanoparticles in ethylene glycol with alkaline solution through sonochemical process

This paper aims to study fabrication and characterization of silver/titanium oxide composite nanoparticle through sonochemical process in the presence of ethylene glycol with alkaline solution. By using ultrasonic irradiation of a mixture of silver nitrate, the dispersed TiO₂ nanoparticle in ethylene glycol associated with aqueous solution of sodium oxide yields Ag/TiO₂ composite nanoparticle with shell/core-type geometry. The powder X-ray diffraction (XRD) of the Ag/TiO₂ composites showed additional diffraction peaks corresponding to the face-centered cubic (fcc) structure of silver crystallization phase, apart from the signals from the cores of TiO₂. Transmission electron microscopy (TEM) images of Ag/TiO₂ composites, which average particle size is roughly 80 nm, reveal that the titanium oxide coated by Ag nanoparticle with a grain size of about 2–5 nm. Additionally, the formation of silver nanoparticles on TiO₂ was monitored by ultraviolet visible light spectrophotometer (UV–Vis). As measured the optical absorption spectra of as-synthesized Ag nanoparticle varying with time, the mechanism of surface formatting silver shell on the cores of TiO₂ could be explored by autocatalytic reaction; the conversion of Ag particle from silver ion is 98% for the reaction time of 1000 s; and the activity energy of synthesizing Ag nanoparticles on TiO₂ is 40 kJ/mol at temperature ranging from 5 to 25 °C. Hopefully, this preliminary investigation could be used for mass production of composite nanoparticles assisted by ultrasonic chemistry in the future.