Abstract: The active-to-passive transition in the oxidation of SiC and Si3N4 was determined in a flowing air environment as a function of temperature and total pressure. The experimentally observed transition temperatures ranged from a low of 1347 C to a high of 1543 C for partial pressures of oxygen of 2.5 and 123.2 Pa, respectively. The SiC and Si3N4 samples had approximately the same transition point for a given pressure. In general, the higher the flow rate, the higher the transition temperature for a given pressure. The transitions for SiC measured in this study agree with previous data for the transition of SiC measured in pure oxygen at reduced pressures and in oxygen inert gas mixtures.

Abstract: In this study, the oxidation of the surface of a SO/50 (at.%) NiTi alloy was studied by XPS, AES and SEM. Samples of the NiTi alloy were oxidized at 23 °C and high temperatures at an oxygen pressure of 10-' Torr and in atmosphere. At 10 - ' Torr of 0 1 and 23°e, titanium was oxidized preferentially while nickel remained in the metallic form even after 40 min of exposure. At the same oxygen partial pressure and 400°C, a mixture ofTiO" . Ti 10 3 and Ti01 was formed, and nickel remained metallic. Eventually, after 40 min of 0 1 exposure, the whole surface was covered with a layer of TiO]. In atmosphere and at 23 °e, titanium again was oxidized preferentially, but NiO was detected on the surface after the first minute of air exposure, At a higher temperature of 450 °e. areas comprising a mixture of NiO and Ti01 , and areas consisting ofTiO] only were found. Below the top surface layer, a complete layer of TiO] was detected. Underneath the TiO] layer, a nickel-rich layer was present.

Abstract: Tubular solid oxide fuel cells employ yttria-stabilized zirconia electrolyte film as an oxygen ion conductor at high temperatures. These yttria-stabilized zirconia electrolyte films are deposited by an electrochemical vapor deposition (EVD) process. The electrochemical transport of oxygen ions during the EVD process is analyzed by measuring the film growth as a function of EVD reaction time; the film growth is found to be parabolic with time. Wagner's transport theory for parabolic growth and the defect model for yttria-stabilized zirconia have been used to calculate the average electronic transport number and the partial electronic conductivity of the electrolyte film. The analysis of the data revealed that the electrolyte film growth is controlled by diffusion of electrons. It is also shown that the electrochemical transport that occurs during EVD of the electrolyte is similar to the phenomena of oxygen semipermeability wherein electrons migrate from the low-oxygen partial pressure site to the high-oxygen partial pressure side, and oxygen ions migrate in the reverse direction maintaining charge neutrality

Abstract: We have studied two types of TiO2-based oxygen sensors operating at different temperatures with different detection principles At high temperatures, TiO2 devices can be used as thermodynamically controlled bulk defect sensors to determine oxygen over a large range of partial pressures Their intrinsic behaviour can be controlled by carefully directed doping with tri- or pentavalent cations At low temperatures, we find that Pt/TiO2 Schottky diodes make extremely sensitive oxygen detection possible The latter show reversible shifts of current-voltage curves, which are determined by interface states formed by chemisorbed oxygen

Abstract: The quatenary phase relations near YBa 2 Cu 3 O 6+ x at 850°C were determined by oxygen coulometric titration and microanalysis. The phase relations change markedly as the oxygen pressure decreases, due primarily to the formation of a liquid phase and a reduced oxide, BaCu 2 O 2 . Nine invariant reactions were discovered, including decomposition of YBa 2 Cu 3 O 6+ x into Y 2 BaCuO 5 , BaCu 2 O 2 and YBa 3 Cu 2 O 6+ y . The lower limit of oxygen partial pressure at which pure YBa 2 Cu 3 O 6+ x is stable is 4.0×10 −4 atm O 2 at 850°C; the lower limit increases in the presence of BaCuO 2 and Cu 2 O impurities. These results indicate that the temperatures used for single crystal growth of YBa 2 Cu 3 O 6+ x could be lowered by using reduced oxygen pressures or, alternatively, that constant temperature crystal growth could be induced by increasing the oxygen partial pressure.

Abstract: An aircraft on-board oxygen generation system having control means 14 for cycling sieve beds of a molecular sieve-type gas separation system 10, provides product gas having a partial pressure of oxygen that more closely approaches the ideal value at any cabin altitude within the operating range of the aircraft. The control means stores a look-up table of desired product gas oxygen content at various altitude levels within the operating range and displays desired product gas oxygen content at altitudes sensed by altitude sensor means 17 for comparison with delivered product gas oxygen content sensed by oxygen content sensor means 19. The control means provides for a range of selectable cycle time and adjusts the cycle time in the sense required to null the difference between displayed and sensed oxygen content of the product gas.

Abstract: YBa2Cu3O7–x thin films deposited by laser evaporation were studied by transmission electron microscopy. The crystal structure and microstructure of the films depend sensitively on the oxygen partial pressure during deposition. Cooling conditions affect primarily the oxygen sublattice and thus determine electrical properties in the superconducting state. Deposition of technologically relevant thin films requires an oxygen partial pressure of 0.3 mbar during deposition and slow cooling in an oxygen atmosphere. Such films have a Tc of 90 K and a transition width of 0.6 K. Electron diffraction patterns yielded a relative lattice parameter difference (b – a)/b of 1.6%, from which the oxygen content can be determined with considerable accuracy. Extended crystal defects and second phases were analyzed by analytical and high-resolution electron microscopy. Films deposited at lower oxygen partial pressures (≈10–2 mbar) exhibit a strongly strained crystal structure with lattice planes heavily bent on an atomic scale. In these films evidence for a decomposition reaction of YBa2Cu3O7–x was found by the simultaneous presence of BaCu2O2 grains and Y2O3 precipitates. The films deposited at low oxygen partial pressure become superconducting when cooled slowly in an oxygen atmosphere. The onset of the broad transitions lies at 50 K.

Abstract: The oxygen nonstoichiometry of Bi 2.00 Sr 1.88 Ca 1.00 Cu 2.14 O y was determined as a function of temperature and oxygen partial pressure. It was found that the shape of y −log P 0 2 curves above 800°C is quite different from that below 800°C. Above 800°C, the y −log P 0 2 relation resembled those of other kinds of high T c superconducting oxides such as Ba 2 YCu 3 O 7−δ and (La 1− x Sr x ) 2 CuO 4−δ . However, below 800°C y slightly depended on the temperature but did not depend on the oxygen partial pressure. It was found by chemical analysis on quenched samples that the copper valence was 2.07 irrespective of the annealing condition, and the bismuth valence was nearly constant when the annealing temprature was above 800°C but increased with the decrease of the annealing temperature below 800°C. The tailing of resistivity-temperature curves in the vacinity of the critical temperature seemed to be due to the existence of Bi 5+ and neutral oxygen species.

Abstract: The oxidation of chemically vapor-deposited SiC in wet O2 (water vapor partial pressure = 0.01 MPa, total pressure = 0.1 MPa) was examined using a thermogravimetric technique in the temperature range of 1823 to 1923 K. The oxidation kinetics follow a linear-parabolic relationship over the entire temperature range. The activation energies of linear and parabolic rate constants were 428 and 397 kJ · mol−1, respectively. The results suggested that the rate-controlling step is a chemical reaction at an SiC/SiO2 interface in the linear oxidation regime, and the rate-controlling step is an oxygen diffusion process through the oxide film (cristobalite) in the parabolic oxidation regime.

Abstract: Among the most critical parameters in the fabrication of rf‐sputtered SrTiO3 films is the argon/oxygen ratio in the sputter gas and the substrate temperature, both during sputtering and during postannealing. After sputtering at 500 °C, SrTiO3 layers on Al2O3 substrates are partially crystalline. In this case the SrTiO3 lattice is enlarged compared to the bulk material. With increasing temperatures of postannealing, the crystallites grow and the lattice shrinks. In particular, films that are sputtered with a sputter gas containing oxygen show an additional phase of TiO2 when they are annealed at temperatures of more than 1000 °C. This paper shows for the first time results of the investigation of sputtered SrTiO3 films on Al2 O3 substrates as a function of oxygen partial pressure P(O2 ). The measurements performed on the sputtered films indicate semiconducting properties in agreement with the bulk material: At temperatures between 700 and 1100 °C the electrical conductivity of sputtered layers changes from...

Abstract: The oxidation of single‐crystal in dry oxygen (10−3‐1 atm and 1200°–1500°C) followed parabolic kinetics. The oxygen partial pressure dependence of the oxidation rate of the (0001) carbon face decreased with increasing temperature (from 0.6 at 1200°C to 0.3 at 1500°C). A kinetic model based on parallel transport of oxidants through the oxide via molecular and ionic oxygen diffusion mechanisms fits the observed oxidation behavior. Both diffusivity and activation energy values for oxidants permeating through the oxide derived from the model using the experimental data are similar to those for molecular oxygen permeating through vitreous . Ionic oxygen diffusion inward via the lattice presumably via a vacancy mechanism becomes more important when oxidation takes place at higher temperatures and at low oxygen partial pressures. Both diffusivity and activation energy values for the ionic oxidant diffusion derived from the model using the experimental data are similar to those values for the diffusion of oxygen through silica reported in the literature.

Abstract: The phase diagram of the Y-Ba-Cu-O system is given as a function of temperature and partial pressure of oxygen over the range between 500°C and 1000°C and 10-6

Abstract: Linearity and stability of the pressure response of five different commercial quadrupole partial pressure analyzers and the influence of ion source parameters (emission current, electron energy, and ion energy) on the response has been investigated over the range 10−7–10−1 Pa for He, N2, and Ar. In the 10−3–10−1 Pa range, each instrument developed a maximum (as large as a factor of 100 in one instrument) in the sensitivity versus pressure relation when operated with ‘‘low’’ ion energy (about 2–3 eV). All but one of the instruments also showed significant low‐pressure nonlinearity, down to pressures as low as 10−7 Pa in one instrument, when operated at ‘‘high’’ ion energies (greater than about 7 eV). These results bring into question the often‐assumed linearity of such instruments at low pressures. The dependence of the signal developed from a constant pressure (10−6 Pa) trace gas as a function of the pressure of another gas (the matrix) was studied using He and Ar as the trace and matrix, and vice versa. ...

Abstract: Commonly used electronic conductivity sensors show significant cross-sensitivities for different gases and usually irreproducible results above or below certain temperatures and partial pressures of critical components in the gas phase. The present paper characterizes conditions for reversible sensor response with respect to partial pressures of CO, CH 4 and H 2 O and temperature. Sensitivities and selectivities of the SnO 2 -based sensors are modified chemically in a systematic way. The results are discussed by using analytical expressions describing conductivity changes upon partial pressure changes. After introducing briefly the general concept of multicomponent analysis to identify the concentration of n components with m sensors in analytical chemistry, we present a simple application to identify CO and CH 4 partial pressures in gas mixtures by using chemically modified sensors at different temperatures.

Abstract: It is now well established that the microstructure of physically vapour deposited films dictates many of their mechanical properties which in turn determine the tribological performance of the film. In particular phase composition and texture need to be taken into consideration if the properties of a film are to be fully understood. By controlling the partial pressure of nitrogen during reactive sputtering it has been possible to produce films of compositions ranging from pure chromium to CrN. At low nitrogen partial pressures the films contained a mixture of Cr2N and CrN phases, but with increasing nitrogen partial pressure the CrN phase became dominant and exhibited a change in texture from {200} to {111}. The hardness, adhesion and tribological behaviour of these films (under both abrasive and adhesive wear conditions) have been determined and related to microstructure and phase composition. Under similar deposition conditions of pressure, coating time and substrate bias voltage, the hardest films consist of {200}-textured CrN, an effect attributed to the lower density of the films containing a mixture of Cr2N-CrN. Best abrasive wear properties are obtained for the hardest films, but the results of sphere-on-disc wear tests show that optimum sliding wear behaviour occurs for the smoothest of the {200}-textured CrN films.

Abstract: This invention is a method of preparing and utilizing oxygenated liquids for medical and therapeutic purposes. Non-blood liquid solutions are oxygenated using a gas liquid contact apparatus. Conditions of increased ambient pressure and decreased temperature are created to maximally dissolve gaseous oxygen into liquids. In addition, an electromagnetic stirring is used to homogeneously mix the gaseous oxygen and liquid. Following the oxygenation of the liquid is anaerobically procured from the gas liquid contact apparatus in order to maintain high dissolved oxygen partial pressures in the liquid. The oxygenated liquid may be intravenously injected to titrate blood oxygen levels, or the oxygenated liquid may be systemically administered for absorption into tissues and the bloodstream.

Abstract: Electrical conductivity of thermally grown Cr2O3 has been measured as a function of temperature and over a range of oxygen partial pressures from that of air to that of the Cr/Cr2O3 equilibrium. The conductivity showed p-type behavior over the range of the present investigation. At temperatures above 1000°C, the conductivity values were independent of oxygen partial pressure and indicated intrinsic semiconductor behavior. The mobility of holes, determined by measuring conductivity at fixed compositions (i.e., fixed δ in Cr2-δO3), increased with temperature. This behavior can be attributed to hopping-type conduction. For δ ∼ 10−5, the activation energy for hole hopping was 0.248 eV, and the calculated hole mobilities were 5.4x10−2 and 2.4x10−1 V/cm2 · s at 500 and 1000°C, respectively. The oxidation kinetics of Cr were determined by measuring the electrical conductivity and electromotive force across the oxide layer at 875°C. The result agreed well with the oxidation data obtained in thermogravimetric tests.

Abstract: The electrochemical vapor deposition (EVD) method is a very promising technique for making gas-tight dense solidelectrolyte films on porous substrates. In this paper, theoretical and experimental studies on the kinetics of the depositionof dense yttria-stabilized zirconia films on porous ceramic substrates by the EVD method are presented. The more systematictheoretical analysis is based on a model which takes into account pore diffusion, bulk electrochemical transport, andsurface charge-transfer reactions in the film growing process. The experimental work is focused on examining the effectsof the oxygen partial pressure and substrate pore dimension on the EVD film growth rates. In accordance with thetheoretical prediction, the pressure of oxygen source reactant (e.g., water vapor), the partial pressure of oxygen and substratepore dimension are very important in affecting the rate-limiting step and film growth rate of the EVD process. In thepresent experimental conditions (e.g., low pressure of oxygen source reactant and small substrate pore-size/thicknessratio), the diffusion of the oxygen source reactant in the substrate pore is found to be the rate-limiting step for the EVDprocess.

Abstract: The vaporization of liquid and solid alloys of the Al — Ni system in the range xNi = 0.7 to 1 has been extensively investigated by the use of Knudsen effusion mass spectrometry in the temperature range between 1389 and 1734 K. 15 alloy samples of different compositions of the complete concentration range were studied in the course of 25 runs and their Al and Ni partial pressures determined. The vapour pressure measurements in the course of the individual runs were carried out over temperature ranges of up to about 300 K covering the solid and the liquid state for many of the alloys investigated. Chemical activities and chemical potentials for Al and Ni as well as Gibbs energies were evaluated at 1600 K for the solid and at 1728 K for the liquid state. Two independent methods were used for the determination of Ni activities of the solid alloys yielding consistent results. The large temperature range of the partial pressure measurement for the solid AlNi3 phase with xNi = 0.750 rendered possible the determination of a complete set of partial and integral thermodynamic functions (ΔG, ΔH, ΔS) for the formation of this phase. The values obtained are discussed. The partial and integral enthalpies of formation are compared with the enthalpies of dissociation of the gaseous species Ni2(g), Al2(g), and AlNi(g). The integral enthalpy of formation, obtained for the first time by vapour pressure measurements, agrees well with the results of a recent calorimetric study.

Abstract: The characterization of Y‐Ba‐Cu‐O thin films prepared by 193‐nm‐ArF laser deposition at partial oxygen pressures ranging wide from 0.01 mTorr to 5 Torr has been investigated. These films have been grown on (100) SrTiO3 substrates held at 700 °C. Surface morphology, superconducting transition temperature and crystalline orientation strongly depend on a partial oxygen pressure during deposition. The smooth and highly crystal‐oriented films with the superconducting transition temperature above 80 K and transport critical current densities of 1.0×105 A/cm2 (without magnetic field at 77 K) have been obtained at 10 to 50 mTorr of oxygen.

Abstract: A systematic study of the solubility of PbO in the ( Bi 1− x Pb x ) 2 Sr 2 CaCu 2 O 8+ y compound at various oxygen partial pressures has been carried out. The solubility was found to increase as the oxygen partial pressure decreased. The change in lattice parameter with PbO concentration supported the solubility data. By annealing the 2212 phase with a large amount of PbO under a high oxygen partial pressure, a secondary phase having an XRD pattern similar to that of Ca 2 PbO 4 was precipitated. Simultaneously, the 2212 phase transformed from a monoclinic (nearly orthorhombic) to a tetragonal structure in the 2212 phase with a small amount of PbO. The annealing effect in the (Bi, Pb)-based superconductor can be explained by the variation of the solubility of PbO due to the oxidation of the Pb 2+ ions, when the secondary phase is assumed to be isostructural with Ca 2 PbO 4 .

Abstract: A process for removing water vapor from water vapor-containing gases is carried out by contacting a feed gas mixture containing water vapor with one side (22) of a semi-permeable membrane (20) selective to the passage of water vapor. A water vapor partial pressure differential is maintained across membrane (20) under conditions such that water vapor selectively permeates through membrane (20) from high pressure side (22) to a lower pressure side (24) of membrane (20). The opposite and lower pressure side (24) is contacted with a dry condensable sweep gas supplied through line (14), which is collected and condensed, thereby causing separation of the sweep gas containing permeated water into an organic liquid phase and an aqueous liquid phase.

Abstract: The partial vapor pressures over liquid or supercooled solutions of water and nitric acid and of water and sulfuric acid are calculated for temperatures below 0°C. From these results the partial vapor pressures over the ternary system water-nitric acid-sulfuric acid (liquid or supercooled) have been estimated and compared with the available experimental data of Vandoni at 0°C. Some possible implications for the formation of stratospheric aerosols are also discussed.