Study of the processes occurring when sputtering YBa2Cu3O7-x in pure oxygen

The sputter deposition of YBa2Cu3O7-x in a de-diode was performed in pure oxygen medium and an optical spectroscopic study of the resultant discharge revealed strong emissions from both metal atoms and oxygen ions. Emission intensities were studied in pressure range from 0.5 to 3 mbar, with substrate temperatures from 150 to 850 degrees C. Raising the substrate temperature to 850 degrees C increased the number of positive ions and excited neutral atoms. Raising the pressure decreased the emission intensities of excited neutral and ionic species. The results have been compared with those obtained from Langmuir probe measurements. The rise in emission intensities of excited neutrals and ions with temperature suggested the possibility of chemically enhanced physical sputtering of YBa2Cu3O7-x. The effect of process conditions on film composition and quality is also discussed.

High Oxygen Storage Capacity and High Rates of CO Oxidation and NO Reduction Catalytic Properties of Ce1-xSnxO2 and Ce0.78Sn0.2Pd0.02O2-delta

Ce1-xSnxO2 (x = 0.1-0.5) solid solution and its Pd substituted analogue have been prepared by a single step solution combustion method using tin oxalate precursor. The compounds were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and H-2/temperature programmed redution (TPR) studies. The cubic fluorite structure remained intact up to 50% of Sri substitution in CeO2, and the compounds were stable up to 700 C. Oxygen storage capacity of Ce1-xSnxO2 was found to be much higher than that of Ce1-xZrxO2 due to accessible Ce4+/Ce3+ and Sn4+/Sn2+ redox couples at temperatures between 200 and 400 C. Pd 21 ions in Ce0.78Sn0.2Pd0.02O2-delta are highly ionic, and the lattice oxygen of this catalyst is highly labile, leading to low temperature CO to CO2 conversion. The rate of CO oxidation was 2 mu mol g(-1) s(-1) at 50 degrees C. NO reduction by CO with 70% N-2 selectivity was observed at similar to 200 degrees C and 100% N-2 selectivity below 260 degrees C with 1000-5000 ppm NO. Thus, Pd2+ ion substituted Ce1-xSnxO2 is a superior catalyst compared to Pd2+ ions in CeO2, Ce1-xZrxO2, and Ce1-xTixO2 for low temperature exhaust applications due to the involvement of the Sn2+/Sn4+ redox couple along with Pd2+/Pd-0 and Ce4+/Ce3+ couples.

Oxygen transfer and energy dissipation rate in surface aerator

The dissipation rate of turbulent kinetic energy (epsilon) is a key parameter for mixing in surface aerators. In particular, determination epsilon across the impeller stream, where the most intensive mixing takes place, is essential to ascertain that an appropriate degree of mixing is achieved. Present work by using commercial software VisiMix (R) calculates the energy dissipation rate in geometrically similar unbaffled surface aeration systems in order to scale-up the oxygen transfer process. It is found that in geometrically similar system, oxygen transfer rate is uniquely correlated with dissipation rate of energy. Simulation or scale-up equation governing oxygen transfer rate and dissipation rate of energy has been developed in the present work.

Oxygen transfer and energy dissipation rate in surface aerator

The dissipation rate of turbulent kinetic energy(e)is a key parameter for mixing in surface aerators. In particular, determination e across the impeller stream, where the most intensive mixing takes place, is essential to ascertain that an appropriate degree of mixing is achieved. Present work by using commercial software VisiMix calculates the energy dissipation rate in geometrically similar unbaffled surface aeration systems in order to scale-up the oxygen transfer process. It is found that in geometrically similar system,oxygen transfer rate is uniquely correlated with dissipation rate of energy. Simulation or scale-up equation governing oxygen transfer rate and dissipation rate of energy has been developed in the present work.

Effect of chlorine on the adsorption of oxygen on Cu and Ag surfaces

Based on XPS and UVPS studies, it is shown that oxygen is preferentially adsorbed molecularly in the singlet state on Cu and Ag surfaces containing presorbed chlorine. Adsorption of chlorine on Cu and Ag surfaces containing presorbed atomic oxygen causes a disappearance of the oxygen. Extended Hückel calculations predict the observed behaviour.

Oxygen-reducing electrodes for acid fuel cells

Electrochemical data are reported for oxygen reduction on platinized coconut-shell charcoal electrodes in 2.5M H*SO,, and 7M HsF’04. In both these media the electrodes exhibit good activity and can sustain currents up to 600 mA cm-* at a polarization of about 400 mV from their rest potentials. The overall performance is comparable with the best type of carbonsupported platinum electrodes reported in the literature.

Distribution of phosphorus and oxygen between liquid steel and basic oxygen steelmaking slag

The efficiency of dephosphorisation is governed by the thermodynamic behaviour of phosphorus and oxygen in molten metal, and P2O5 and FeO in slag. The equilibrium distribution of phosphorus and oxygen, for a wide range of chemical compositions simulating the evolution of slag composition during a typical BOF blow, has been experimentally determined. A mathematical model for estimation of the activity coefficients, as a function of the chemical composition, was also attempted.

Formative time lags in nitrogen, oxygen and dry air In crossed electric and magnetic fields

Formative time lags in nitrogen, oxygen, and dry air are measured with and without a magnetic field over a range of gas pressures (0.05 ' p ' 20.2 torr 5 kPa to 2 MPa, electric field strengths (1.8xO14 EEs 60xlO V m l) and magnetic field strengths (85xl0-4 < B ' 16x10-2 Tesla). For experiments below the Paschen minimum, the electrodes are designed to ensure that breakdown occurs over longer gaps and for experiments above the Paschen minimum, a coaxial cylindrical system is employed. The experimental technique consists of applying pulse voltages to the gap at various constant values of E/p and B/p and measuring the time lags from which the formative time lags are separated. In the gases studed, formative time lags decrease on application of a magnetic field at a given pressure for conditions below the Paschen minimum. The voltages at which the formative time lags remain the same without and with magnetic fields are determined, and electron molecule collision frequencies (v/p) are determined using the Effective Reduced Electric Field [EREF] concept. With increasing ratio of E/p in crossed fields, v/p decreases in all the three gases. Measurements above the Paschen minimum yield formative time lags which increase on application of a magnetic field. Formative time lags in nitrogen in ExB fields are calculated assuming an average collision frequency of 8.5x109 sec-1 torr 1. It is concluded that the EREF concept can be applied to explain formative time lags in ExB fields.

X-ray and ultraviolet photoelectron spectroscopy studies of the interaction of carbon monoxide with oxygen adsorbed on silver covered with potassium, caesium or barium

X-ray and He(II) ultraviolet photoelectron spectroscopy studies of the interaction of CO with oxygen on potassium-, caesium- and barium-covered Ag surfaces have shown the formation of carbonate at 300 K. While on a caesium-covered surface only carbonate formation takes place, on the potassium- and barium-covered surfaces molecularly chemisorbed CO is also formed. The variation of the surface concentrations of carbon and oxygen with temperature has been examined and a reaction sequence for the interaction of CO with adsorbed oxygen on potassium-, caesium- and barium-covered Ag surfaces is suggested.

05-ions in a low pressure glow discharge of oxygen

0:- ions have been detected and measured in a positive column of glow discharge in oxygen between 0.04 and 0.17 Torr. A suitable ion-molecule reaction has been proposed, which appears to be supported by the mass spectrometer measurements.

Absorption of electromagnetic radiation by superconducting YBa2Cu3O7: an oxygen-induced phenomenon

In the superconducting state, YBa2Cu3O7 absorbs electromagnetic radiation over a wide range of frequencies (8 MHz-9 GHz). The absorption is extremely sensitive to temperature, particle size and the magnetic field and depends crucially on the presence of oxygen. A possible explanation for the phenomenon based on the formation of Josephson junctions is suggested.

Photoemission study of YBa2Cu3O7 through the superconducting transition: Evidence for oxygen dimerization

Photoemission spectra of YBa2Cu3O7-δ in the normal and superconducting states provide direct evidence for dimerization of oxygen below Tc. Cu2+ is found to reduce to Cu1+ concomitantly. These changes may be of vital importance to the mechanism of high-temperature superconductivity.

Mechanism of high-temperature superconductivity in YBa2Cu3O7−δ: Crucial role of oxygen

Oxygen atoms in the middle Cu---O layer of YBa2Cu3O7 consisting of strings of corner-connected (CuO4)∞ units are shown to be crucial for superconductivity. Importance of hole-hole pairing giving rise to O---O bonds is also indicated.

O2- and O1- types of oxygen species on Ni and barium-dosed Ni and Cu surfaces

He II UPS and XPS study of oxygen adsorption on Ni and barium-dosed Ni and Cu surfaces at 300 K show two types of oxygen species which are assigned to O2- and O1- (ad).

Mechanism of oxidation of α,β-unsaturated thiones by singlet oxygen

Photo-oxidation of α,β-unsaturated thiones yields the corresponding ketones as the only product. Studies carried out on three systems, namely thioketones, α,β-unsaturated thiones and thioketenes, have revealed that there exists a similarity in their mechanism of oxidation. It has been suggested that the thiocarbonyl chromophore is the site of attack by singlet oxygen in α,β-unsaturated thiones and that the adjacent C-C double bond is inert under these conditions. Absence of sulphine during the oxidation of α,β-unsaturated thiones is attributed to the electronic factors operating on the zwitterionic/diradical intermediate. While α,β-unsaturated ketones are poorly reactive, α,β-unsaturated thiones are highly reactive toward singlet oxygen.