Study of ammonia decomposition in a proton conducting solid electrolyte cell

The reaction of NH₃ decomposition was studied at 500–700 °C and atmospheric total pressure using a single-chamber cell-reactor. The proton conductor was a strontia-ceria-ytterbia (SCY) perovskite of the form: SrCe_0.95Yb_0.05O_3−α. Silver films served as cathodic and anodic electrodes. The effects of imposed current, temperature and inlet gas composition on the reaction rate were examined. Paper presented at the 8th EuroConference on Ionics, Carvoeire, Algarve, Portugal, Sept. 16–22, 2001.     

Polarization phenomena at the metal/proton conducting electrolyte interphase

The electrokinetics at the H₂ - Pd/SrCe_0.95Yb_0.05O_3−α interphase are presented. Current-overpotential (I-η) curves were obtained at 400–700 °C and at hydrogen partial pressures from 1 kPa to 100 kPa, using a three electrode single chamber cell. The present data were assumed to be free of mass transfer effects. The anodic and cathodic charge transfer coefficients as well as the exchange current density were calculated from the experimental results by using the Butler-Volmer equation. The high and low field approximations were used to simplify the analysis. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002.     

Hydrogenation of carbon dioxide in a proton conducting cell reactor

The CO₂-H₂ reaction was studied at 723–973 K and atmospheric total pressure using a proton conducting double-chamber cell-reactor. The proton conductor was a strontia-ceria-ytterbia (SCY) perovskite of the form: SrCe_0.95Yb_0.05O_3−α. Palladium films served as cathodic and anodic electrodes. CO₂/He mixtures were introduced over the cathodic electrode while high-purity hydrogen was passing over the anode. The effects of both the imposed current and the inlet gas composition on the reaction rates and product distribution were examined. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

Well-known perovskites (cerates, cuprates, manganates): Problems and facts; A review of nontraditional approaches

Phenomena and processes either new or not studied in-depth occurring in perovskite oxides and in systems which contain these compounds are reported and summarized. The materials under consideration are well-known for specific properties, e.g., cerates of alkaline earths are high-temperature proton conductors, manganates are electrode materials of SOFCs and show the effect of colossal magnetoresistance or YBa₂Cu₃O₇ cuprates YBa₂Cu₃O₇ are “high-temperature” superconductors. The presented nontraditional approach consists of considering physical and chemical phenomena and processes, which do not relate to the indicated main properties of the compounds. For instance, BaCeO₃ undoped and slightly doped has partially cerium in the form of Ce⁺³, which provides the effect of blue luminescence which is controlled by thermochemical treatment; H₂YBa₂Cu₃O₇ manifests mixed proton-electron conduction at 400–550 K under water vapor of 100–300 Pa; La_0.67Ca_0,33MnO_2.84 can dissolve some part of water vapor as this occurs in traditional HTPC. The electrochemical cells Pd | HTPC | hydrocuprate | HTPC | Pd and the more simple one Pd | HTPC | Pd show e.m.f. values near 1 V under certain conditions after polarization by d.c. currents at 420–520 K under different atmospheres. The system water vapor — membrane of undoped BaCeO₃-hydride is described. Defect chemistry equations are used to describe some of the phenomena which are employed for the production and storage of pure hydrogen.     

Yields of H+ and He+ at the energy for elastic scattering from H2+3He+ incident on Ag and Pd

Yields, Y, of H⁺ and He⁺ emerging specularly with the energy for single binary elastic collisions have been measured from polycrystalline Ag and Pd surfaces bombarded with mixed monoenergetic (300 < E₀ < 2600 eV) beams of H₂⁺³He⁺ impinging at an angle of 45° from the surface normal. The surfaces were exposed to H₂⁺ at a dynamic pressure of 8 × 10^?3 Pa (6 × 10^?5 Torr) during the measurements. The He⁺ yields from Pd are slightly larger than from Ag, and the H⁺ yields from Pd are 10 to 40 times as large as those from Ag. These results suggest that differences between Pd and Ag in the amount of hydrogen adsorbed and in the character of the hydrogen-metal bond may be responsible for the yield differences through shadowing by, and possibly the sputtering of, adsorbed hydrogen. The Y versus E₀ curves for all four systems have qualitatively the same singly peaked shape which implies that reactive and noble gas ions undergo similar neutralization processes during elastic surface collisions. The ratios of the yields from Ag and Pd do not exhibit the theoretically expected exponential dependence on collision time over the entire range studied, but at the lowest energies the ratios lead to estimates of the difference of neutralization constants which do agree with theory. The potential utility of the large difference in proton yields from Ag and Pd for studying the Ag-Pd alloy system is noted.     

The Variational Principle for a Class of Asymptotically Abelian C*-Algebras

Let (A,α) be a C^*-dynamical system. We introduce the notion of pressure P _α(H) of the automorphism α at a self-adjoint operator H∈A. Then we consider the class of AF-systems satisfying the following condition: there exists a dense α-invariant *-subalgebra ? of A such that for all pairs a,b∈? the C^*-algebra they generate is finite dimensional, and there is p=p(a,b)∈ℕ such that [α ^j (a),b]= 0 for |j|≥p. For systems in this class we prove the variational principle, i.e. show that P _α(H) is the supremum of the quantities h _φ(α) −φ(H), where h _φ(α) is the Connes–Narnhofer–Thirring dynamical entropy of α with respect to the α-invariant state φ. If H∈A, and P _α(H) is finite, we show that any state on which the supremum is attained is a KMS-state with respect to a one-parameter automorphism group naturally associated with H. In particular, Voiculescu's topological entropy is equal to the supremum of h _φ(α), and any state of finite maximal entropy is a trace. Received: 19 April 2000 / Accepted: 14 June 2000     

NH3 decomposition in a single-chamber proton conducting cell

The catalytic and electrocatalytic decomposition of NH₃ was studied at 350–650 °C and atmospheric total pressure, using a single-chamber H⁺ conducting cell-reactor. The H⁺ conductor was a strontia–ceria–ytterbia (SCY) perovskite of the form: SrCe_0.95Yb_0.05O_3−a. A Ru film was used as catalyst-electrode. The effects of imposed currents, temperature and inlet gas composition on the reaction rate were examined.     

Catalytic and electrocatalytic activation of methane over manganese oxides deposited on YSZ

The catalytic and the electrocatalytic behavior of MnO_x oxides deposited on Yttria Stabilized Zirconia (YSZ) in the form of thin porous films, was studied during the reaction of methane activation at high methane to oxygen ratios. Experiments were carried out in a continuous flow well-mixed reactor (CSTR), at atmospheric total pressure and in a temperature range between 500–850 °C. It was found that the electrochemical pumping of oxygen anions (O²⁻) through the solid electrolyte (YSZ) affect drastically the rates of CO₂, C₂H₄ and C₂H₆ formation and consequently the C₂ selectivity. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Study of the state of Ag and Pd in silver-palladium catalysts on a titanium dioxide substrate by IR spectroscopy of adsorbed CO

We have used IR spectroscopy of adsorbed CO to study the effect of the method for preparation of silver-palladium catalysts on a TiO₂ substrate and exposure to an oxidizing or reducing gaseous atmosphere on the state of Ag and Pd centers. We have shown that as a result of the metal-support interaction, the reducibility of the Ag and Pd particles is increased, which leads to a change in their adsorption and catalytic properties. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 16–20, January–February, 2007.     

Synthesis of vanadium-doped palladium nanoparticles for hydrogen storage materials

Palladium–vanadium (Pd/V) alloy nanoparticles stabilized with n-pentyl isocyanide were prepared as new hydrogen storage materials by a facile polyol-based synthetic route with tetraethylene glycol and NaOH at 250 °C. The size distribution of the nanoparticles thus obtained featured two peaks at 4.0 ± 1.1 and 1.4 ± 0.3 nm in diameter, which were the mixture of Pd/V alloy and Pd nanoparticles. The ratio between the number of Pd/V and that of Pd nanoparticles was 51:49, and the Pd:V ratio of the overall product was 9:1 in wt%, indicating that the 4.0 nm Pd/V nanoparticles were composed of 81% Pd and 19% V. The inclusion of vanadium caused the increase in the d-spacing and thus expansion of lattice constant. A rapid increase in hydrogen content at low H₂ pressures was observed for the Pd/V nanoparticles, and a 0.47 wt% H₂ adsorption capacity was achieved under a H₂ pressure of 10 MPa at 303 K. Hydrogen storage performances of Pd/V alloy nanoparticles was superior compared with Pd nanoparticles.     

Synthesis and structural investigation of Pd/Ag bimetallic nanoparticles prepared by the solvothermal method

Pd/Ag bimetallic nanoparticles have been synthesized successfully by reducing PdCl₂ and AgNO₃ mixture in ethylene glycol solution using the solvothermal method. The prepared samples have been characterized by UV–vis, XRD, TEM, HRTEM, EDS, and XPS, respectively. Moreover, the bimetallic particles possess alloy and core-shell structure from the HRTEM images. Here, the lattice fringe spacing of Pd/Ag bimetallic nanoparticles corresponds to its (111) plane, which is between that of the Pd and Ag nanoparticles prepared under the same conditions. Furthermore, the possible formation mechanism and factors influencing the formation of Pd/Ag bimetallic nanoparticles, such as reaction temperature and time, have also been investigated.     

Spectral characteristics and force constants of irradiated α-SiO<Subscript>2</Subscript> single crystals

The IR-radiation reflectance spectra of α-SiO₂ single crystals exposed, in a reactor, to fast neutrons with fluences changing in a wide range have been investigated. The regularities of the change in spectral characteristics of the antisymmetric and degenerate vibrations of the bridge bonds of the crystals studied and in the dynamic parameters of these crystals in the process of their irradiation have been determined. The critical dynamics of the crystal lattice in the region of antisymmetric stretching and degenerate modes and the extremum radiation kinetics of the ion-polarizability parameters and the force constants of the indicated crystals were detected. The changes in some characteristics of these crystals, arising on their irradiation as a result of the damage of the substance, the rupture and extension of some silicon—oxygen bonds, and the transformation of the structure of α-SiO₂ single crystals by two mechanisms, have been considered. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 773–777, November–December, 2005.     

Atmospheric pressure chemical vapour synthesis of silicon–carbon nanoceramics from hexamethyldisilane in high temperature aerosol reactor

Silicon–carbon nanoceramics have been synthesised from hexamethyldisilane (HMDS) by the atmospheric pressure chemical vapour synthesis (APCVS). Direct aerosol phase synthesis enables continuous production of high purity materials in one-stage process. The particle formation is based on the decomposition of the precursor in a high temperature reactor. Reaction of the gas phase species leads to homogeneous nucleation and formation of the nanoparticles with a narrow size distribution (geometric mean diameter range of particle number size distribution 160–200 nm with 1.5–1.6 geometric standard deviation at reaction temperatures 800–1200 °C). A systematic investigation of the influence of the process temperature on the powder characteristics, including the particle size, crystallinity, chemical structure, surface and bulk composition and surface morphology, was carried out. At the reactor temperature of 800 °C, the synthesised nanoparticles were amorphous preceramics containing mostly SiC₄, Si–CH₂–Si and Si–H units. The composition of the powder turned towards nanocrystalline 3C–SiC (crystal size under 2 nm) when the reaction temperature was increased to 1200 °C. The reaction temperature appeared to be a key parameter controlling the structure and properties of the synthesised powders.     

Generalized Ginzburg-Landau equation and the properties of superconductors with Ginzburg-Landau parameter κ close to 1

An expression is derived for the free energy of a superconductor near the critical temperature, taking account of the terms of next highest order in the parameter 1−T/T _c. These terms become important for Ginzburg-Landau parameter values |κ−1|≪1, and in this case, in an external magnetic field H ₀ close to H _c2, the structure of the order parameter is determined by the relative values of the three small parameters |κ−1|, 1−T/T _c, and (H _c2−H ₀)/H _c2. Three types of lattices are investigated: triangular with one and two flux quanta per cell and square with one flux quantum per cell. Zh. éksp. Teor. Fiz. 115, 726–739 (February 1999)     

Temperature dependence of a nanoporous Pd film hydrogen sensor based on an AAO template on Si

In this study, hydrogen sensing properties of nanoporous Pd films based on Anodic Aluminium Oxide (AAO) templates grown on a silicon substrate have been investigated at various temperatures (25–100°C) and hydrogen concentrations (100–1000 ppm) to determine the temperature-sensitivity relationship. For this purpose, a hexagonally shaped AAO template of approximately 50 nm in diameter and 700 nm in length with 80 nm interpore distances was fabricated using two-step anodization of an Al film deposited on an n-type (100) oriented oxidized Si substrate. Then, the nanoporous surface of the AAO template was used as a substrate for supporting a nanoporous Pd film of an approximately thickness of 60 nm. The morphologies of the AAO template and Pd film coated on the AAO template were studied mainly by Scanning Electron Microscopy (SEM). Hydrogen sensing properties of the nanoporous Pd film were measured using a resistance transient method. It was found that the sensor response of the nanoporous Pd films on the AAO template was better than the traditional Pd thin film sensors, the sensitivity of the sensor was approximately 1.8% for 1000 ppm H₂, and the detection limit was lower than 100 ppm at room temperature. The highest sensitivity was measured at room temperature.     

A new type of electrochemical cell based on the configuration NaI |PEG| I2

Different operating conditions of a new electrochemical cell based on sodium iodide and polyethylene glycol (PEG) polymer as separator as well as conducting electrolyte is reported. Five types of cells were fabricated using pure NaI, PC+NaI, water+NaI dil. HCl+NaI and dil. H₂SO₄+NaI in the cell configuration NaI |PEG| I₂ and NaI |PEG|s I₂+C. Their discharge characteristics were studied at room temperature (33 °C). From the cell parameters, it is found that the open circuit voltage ranges from 648 mV to 1023 mV and the short circuit current ranges from 29 μA to 4.8 mA.     

Electrochemical promotion of CH4 oxidation on Pd

The effect of Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA effect) or Electrochemical Promotion (EP) was used to promote the methane oxidation reaction to CO₂ and H₂O over Pd polycrystalline films interfaced with yttria-stabilized zirconia in galvanic cells of the type: CH₄, O₂, CO₂, Pd/YSZ/Au, CH₄, O₂, CO₂ It was found that by applying positive potentials or currents and thus, supplying O²⁻ onto the catalyst surface, up to 90-fold increases in CH₄ oxidation catalytic rate can be obtained. The induced changes in catalytic rate were two orders of magnitude higher than the corresponding rate of ion transfer to the catalyst-electrode surface, i.e. faradaic efficiency Λ values above 100 can be attained. The reaction exhibits electrophobic behavior under the experimental conditions of the investigation. The results can be rationalized on the basis of the theoretical considerations invoked to explain NEMCA behavior, i.e. the effect of changing work function on chemisorptive bond strengths of catalytically active electron donor or acceptor adsorbates. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Study of solar features causing GMSs with 250γ<<Emphasis Type="Italic">H</Emphasis><400γ

The effect of solar features on geospheric conditions leading to geomagnetic storms (GMSs) with planetary index,A ^P ≥ 20 and the range of horizontal component of the Earth’s magnetic fieldH such that 250γ <H < 400γ has been investigated using interplanetary magnetic field (IMF), solar wind plasma (SWP) and solar geophysical data (SGD) during the period 1978–99. Statistically, it is observed that maximum number of GMSs have occurred during the maximum solar activity years of 21st and 22nd solar cycles. A peculiar result has been observed during the years 1982, 1994 when sunspot numbers (SSNs) decrease very rapidly while numbers of GMSs increase. No distinct association between yearly occurrence of disturbed days and SSNs is observed. Maximum number of disturbed days have occurred during spring and rainy seasons showing a seasonal variation of disturbed days. No significant correlation between magnitude (intensity) of GMSs and importance ofH _α , X-ray solar flares has been observed. Maximum number of GMSs is associated with solar flares of lower importance, i.e., SF during the period 1978-93.H _α , X-ray solar flares occurred within lower helio-latitudes, i.e., (0–30)°N to (0–30)°S are associated with GMSs. NoH _α , X-ray solar flares have occurred beyond 40°N or 40°S in association with GMSs. In helio-latitude range (10–40)°N to (10–40)°S, the 89.5% concentration of active prominences and disappearing filaments (APDFs) are associated with GMSs. Maximum number of GMSs are associated with solar flares. Coronal mass ejections (CMEs) are related with eruptive prominences, solar flares, type IV radio burst and they occur at low helio-latitude. It is observed that CMEs related GMS events are not always associated with high speed solar wind streams (HSSWSs). In many individual events, the travel time between the explosion on the Sun and maximum activity lies between 58 and 118 h causing GMSs at the Earth.     

Manganese energy level in <Emphasis Type="Italic">p</Emphasis>-InAs〈Mn〉 under pressure

Resistivity ρ and the Hall coefficient R _H at atmospheric pressure in the temperature range of 77–400 K and the dependences of these parameters (ρ(P) and R _H(P)) and magnetic susceptibility (χ(P)) on hydrostatic pressures of up to P ≤ 7 GPa at 300 K in p-InAs〈Mn〉 single crystals was investigated. The baric coefficients of the ionization energy of Mn impurity centers and the pressure dependence of the dielectric constant ɛ(P) were determined.     

Perfect Transfer of Entangled States on Spin Chain

Current researches have shown that perfect states transfer over arbitrary distances is possible for a simple unmodulated spin chain by some schemes. The transfer of a single qubit state has been investigated in detail by Christandl et al. [Phys. Rev. Lett. 92, 187902(2004)] through a modified Heisenberg XX model Hamiltonian H _G . The previous study of Christandl is restricted to the first-excitation states of H _G (i.e., which correspond to the second subspace of the Hilbert space of H _G ). In this work, we extend their study to the case of the high-excitation states, and find that the entangled states in such a form, | ψ 〉 = α | 00⋯ 0〉 + β | 11⋯ 1〉, can be perfectly transfered on the spin chain. PACS numbers 03.67.Hk, 03.67.Pp, 05.50.+q.