Pure Gas Flow Research Articles

A new fully automated gas flowmeter at the PTBfor flow rates between 10-13 mol/s and 10-6 mol/s

For applications in vacuum metrology, gas flowmeters have to deliver pure gas flows with well-knownmolar flow rates of low (< 10-6 mol/s) and very low values. Accurate flowmeters are used to generate pressures in continuous expansion systems, to measure leak rates, and to measure pumping speeds of ultrahigh-vacuum pumps. At the Physikalisch-Technische Bundesanstalt (PTB) a new, fully automated, all-metal flowmeter was commissioned for use with a continuous expansion system in the pressure range 10-10 Pa to 3 × 10-2 Pa. It delivers gas flows with molar flow rates between 4 × 10-13 mol/s and 10-6 mol/s (throughputs 10-6 Pa l/s to 3 Pa l/s at 23 °C) withrelative standard uncertainties ranging from 1.45% at 4 × 10-13 mol/s down to 0.14% at 10-6 mol/s.

Microstructures of YBCO precursor films including BaF 2 annealed at a low pressure of oxygen atmosphere

YBCO precursor films with ≈200 nm are deposited by co-evaporation of Y, BaF 2 and Cu at room temperature. The precursor films are annealed at a low pressure with a flow of pure oxygen gas near the precursor films. No water vapor is introduced to the annealing chamber. We have found that the reaction during temperature elevation is very important to obtain the YBCO films in this process. Therefore, using a transmission electron microscope (TEM), we observe the microstructures for two kinds of specimens turned off a heater power at ≈400 °C (sample A) and 630 °C (sample B) during sample temperature elevation. Elementary analyses are also examined at some points using an energy-dispersive X-ray spectrometer (EDX). In the TEM images of the sample A, a top tin layer is Cu metal by EDX, indicating that the segregation of Cu occurs in the precursor film. In the TEM images of the sample B, the YBCO layer is already formed and the non-crystallized thin layer with ≈5 nm thick seems to exist just above the YBCO layer.

Thin films of Sr2FeMoO6 grown by pulsed laser deposition: preparation and characterization

AbstractWe report the first in situ XPS analysis of thin epitaxial films of the ferromagnetic double perovskite Sr2FeMoO6, which have been prepared by pulsed laser deposition on (100) SrTiO3 substrates under different oxygen pressures. The films consist mainly of the c‐axis‐oriented SFMO phase over a wide range of oxygen pressure (10−8–10−4 mbar) as determined by ex situ x‐ray diffraction measurements. However, different secondary phases are observed, depending on the preparation conditions. When obtained in ultrahigh vacuum conditions (10−8 mbar) the films show the presence of metallic Fe, whereas when prepared under pure oxygen gas flow (pressures above 10−6 mbar ) the Fe3O4 phase is observed. The in situ XPS analysis suggests the formation of the SrFeO3 phase in addition to SFMO, whereas the SrMoO4 phase is formed at oxygen pressures above 10−4 mbar. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Deodorizing Ability of a Diatomaceous Material as an Environmentally-Friendly Inner-Wallboard.

Deodorizing ability of a diatomaceous material mined from Wakkanai district in Hokkaido Pref. was examined in detail. This material is widely distributed in the market as a material of environmentally-friendly inner-wallboard. Alternative introductions of a model odor {NH3, CH3CHO, or (CH3)2S} mixed-N2 gas flow and a pure N2 gas flow into the diatomaceous material showed reversible adsorption and desorption of the odor components at 25°C, reconfirming regeneration of deodorizing ability for the diatomaceous-wallboard by ventilation of rooms with these wallboards. The adsorbed quantities of the odors onto the diatomaceous material during one hour readily cleared the odor level 3:2.3ppm for NH3, 0.14ppm for CH3CHO, and 0.044ppm for (CH3)2S, respectively.

In situ characterisation of Sr2FeMoO6 films prepared by pulsed laser deposition

Thin epitaxial films of the ferromagnetic double perovskite Sr 2 FeMoO 6 (SFMO) have been prepared by pulsed laser deposition on SrTiO 3 (100) substrates under different oxygen pressures. The surface electronic structure of the as-deposited films has been analysed by XPS without exposure to the atmosphere. The films consist mainly of the c-axis oriented SFMO phase over a wide range of oxygen pressure from 10 -8 to 10 -4 mbar. However, the analysis of the films by XPS and XRD revealed the presence of different secondary phases depending on the preparation conditions. The films prepared under ultra-high vacuum conditions show the presence of metallic Fe. The films prepared under pure oxygen gas flow at pressures above 10 -6 mbar did not show any trace of metallic Fe, but Fe 3 O 4 phase. In these films XPS analysis revealed the formation of the SrFeO 3 phase (SFO), or another non reported Sr-containing phase, which is not observed by XRD. At higher oxygen pressures above 10 -4 mbar there is a clear formation of SrMoO 4 phase (SMO). In conclusion, a ultra-high vacuum atmosphere favours the formation of metallic Fe, whereas the increase in oxygen pressure during deposition induces the decomposition of the SFMO phase to SFO and SMO phases. The conditions for the preparation of pure SFMO phase have not been attained so far, which would lie within a very narrow oxygen pressure window. Our best films (with no any other ferromagnetic phase than SFMO) show a saturation magnetisation of about 1 μ B /f.u. at 10 K, and T c close to 200 K. The resistivity of the films has a metallic-like behaviour and remains almost constant in the temperature range from 10 to 350 K to about 5 to 8 10 -4 Ω cm. It was measured a magnetoresistance of about -10% at 10 T and 10 K, which coincides with the values reported in the literature for SFMO films.

銅精鉱粒子の着火温度

Ignition temperature was measured for five kinds of copper concentrates in air and pure oxygen gas flows. In the air oxidation, no significant difference was observed in the ignition temperatures for the concentrates. In contrast, the ignition temperature in oxygen flow depended on the kinds of major minerals contained in respective concentrate. The ignition temperature increases when the concentrate contains higher quantity of Cu5FeS4 or FeS that have lower dissociation pressure than CuFeS2. However, the concentrates mainly composed of Cu9S5, that has a lower pressure of sulfur than CuFeS2, or FeS2 exhibited the lowest ignition temperature. This suggests that Cu9S5 in the concentrate may have a composition of high sulfur pressure, because the dissociation pressure of Cu9S5 changes significantly with minor variation of its composition.

Effect of Heat Treatment on Critical Current Density–Magnetic Field Curve for YBa2Cu3O7-δ Single Crystal and Its Microstructure

The dependences of critical current density–magnetic field (Jc–H) curves for YBa2Cu3O7-δ (Y123) single crystals on heat treatment processes were studied. The single crystals were annealed by a two-step heat treatment process, during which the crystals were annealed at 873 K for 100 h, followed by annealing at 773 K for 200 h in a pure oxygen gas flow. Furthermore, the single crystals were annealed using three different untwinning processes with uniaxial stress such as a detwinnig process and a twin-free process. The Jc–H curves and their peak effects with the H∥c-axis displayed a large dependence on the heat treatment processes. Furthermore, the microstructures in these single crystals were observed using transmission electron microscopy (TEM). The anti-phase boundaries, which depended on the heat treatment processes, were observed in the crystals. These results suggested that the anti-phase boundaries are responsible for the peak effects, which is attributed to the distribution of the pinning centers of oxygen deficient phases in the crystals.

Dusty Gas Flow in a Converging-Diverging Nozzle

The flow in a converging-diverging nozzle is studied numerically. The flowing medium is a suspension composed of gas seeded with small, spherical, solid particles. The solution covers the entire flow history, from its initiation and until a steady state flow is reached. The covered flow domain includes both the flow field inside the nozzle and part of the free jet flow outside of the nozzle exit plane. The solution is repeated for different solid particle diameters, ranging from 0.5 μm to 50 μm, and different dust loading ratios. It is shown that the presence of solid particles in the flow has a significant effect on the developed flow field, inside and outside the nozzle. In particular, by a proper choice of particles diameter lateral pressure waves and the secondary shock wave can be significantly attenuated. The solid particles size has also a marked effect on the position and size of the Mach disk appearing in the free jet flow. It is also shown that in a suspension case a steady state flow is reached faster than in a similar pure gas flow.

Effect of heat treatment on Jc– H curve for YBa 2Cu 3O 7− δ single crystal

The dependence of critical current density ( J c)– H curves for YBa 2Cu 3O 7− δ (Y123) single crystals on heat treatment processes was studied. Several two-step heat treatment processes were performed on the single crystals, which were annealed at 400°C, 500°C, or 600°C for 100 h, followed by an anneal at 500°C for 200 h in a pure oxygen gas flow. The J c– H curves with H‖ c-axis at 70 K and below showed a large dependence on the heat treatment process. These J c– H curves also showed a peak effect in a high magnetic field ( H>3 T). The peak effect was significant for the single crystal annealed at 600°C and subsequently at 500°C. Furthermore, the J c– H curves with H‖ c-axis for detwinned single crystals, which were fabricated under a uni-axial compression in 〈100〉 direction after the second heat treatment step, were compared with that for the non-detwinned crystal. These results suggested that the dependence of the peak effect on the heat treatment process was due to the difference in the oxygen configuration of the Cu–O basal planes in the single crystals.

Study of oxygen diffusion in NdBa 2Cu 3O 7−δ single crystal by in-situ observation of twin formation

Chemical oxygen diffusion coefficients in NdBa 2Cu 3O 7− δ (Nd123) single crystals grown by a top-seeded solution-growth (TSSG) method were estimated over a temperature range from 300° to 600°C by an accurate and easy technique of in situ observations of twinned/untwinned boundaries during annealing in a pure oxygen gas flow. The chemical oxygen diffusion coefficients of the orthorhombic phase and the tetragonal phase in the single crystals were estimated, respectively. These oxygen diffusion coefficients were almost equal. Furthermore, the oxygen diffusion coefficients in the Nd123 single crystals were compared with those in YBa 2Cu 3O 7− δ (Y123) single crystals, which were also grown by the TSSG method. The chemical oxygen diffusion coefficients in the Nd123 single crystals were also quite close to those in the Y123 single crystals. The results in the present study suggest that the oxygen diffusion in the Nd123 single crystals was affected by nonstoichiometry of the Nd123 single crystals, of which composition was Nd:Ba:Cu=1.07:0.95:3.00.

Effect of Spin State of Ni3+Ions on Electrical Properties of Nd(Cr1−xNix)O3

Orthorhombic perovskite-type Nd(Cr1−xNix)O3(0.0≤x≤0.6) was synthesized in a flow of pure oxygen gas. Magnetic measurement indicates that the 1/χ–Tcurves of Nd(Cr1−xNix)O3are linear and have deflection points (≈480 K) in the range 0.2≤x≤0.6. Measurements of the electrical resistivity (ρ) and the Seebeck coefficient (α) indicate that Nd(Cr1−xNix)O3(0.0≤x≤0.4) is a p-type semiconductor, while Nd(Cr0.4Ni0.6)O3(x=0.6) is an n-type semiconductor. logρ–1000/Tcurves are linear and have the deflection points at ≈500 K (0.2≤x≤0.6). Calculation of the activation energy (Ea) indicates thatEa(300≤T≤500 K) is slightly lower thanEa(500≤T≤900 K). From these results, it is obvious that the electrical properties are strongly affected by the spin state of the Ni3+ion.

Gas−Liquid Interfacial Area and Holdup in a Cocurrent Upflow Packed Bed Bubble Column Reactor at Elevated Pressures

Gas−liquid interfacial area have been determined by means of chemically enhanced absorption of CO2 in nitrogen as the carrier gas into DEA as well as DEA−ETG aqueous solutions in a packed bed upflow bubble column reactor with an inner diameter of 156 mm. The influence of the reactor pressure, gas and liquid superficial velocities as well as liquid phase viscosities and packing particles diameter on the interfacial areas, pressure drops, and liquid holdups has been investigated. No distinct pressure influence on the measured interfacial areas is observed, while a dependence on the gas superficial velocities has indeed been found. Results indicate that only in the bed packed with glass spheres of 10 mm diameter may two-phase flow in the interparticle voids occur. For smaller particles flow maldistributions are found and pure gas flow in part of the voids is anticipated, simultaneous to regular gas−liquid flow in the other voids.

Mechanical Separation Process and Flow Patterns of Cyclone Dust Collectors

A cyclone dust collector (called herein a cyclone) is applied in many industrial fields, for example, powder technology, combustion chambers, various chemical plants, etc. Until now, there are many types of cyclones for the purpose of separation of solid particles; however generally-speaking, the following types of the cyclone are typical: returned flow or reversed flow type, axial flow type, and rotary flow cyclone with tangential injection of the second gas flow to the cyclone body. In order to understand the performance of the cyclone and the problems of turbulent rotational flow and the separation mechanism for solid particles, this review article describes the flow pattern and distribution of the tangential velocity for pure gas flow and for dust laden gas flow, which are most important factors for estimating the pressure drop and the separation characteristics of the solid particles, and also the mechanical separation process in the centrifugal flow field. This review article includes 162 references.

Periodic fluctuation of Ba/Nd ratio in single crystals of high-Jc NdBa2Cu3O7−δ superconductor

A single crystal of NdBa2Cu3O7−δ was synthesized by the Top Seeded Solution Growth method (TSSG method). Then, the crystal was heat-treated 500 °C for 400 h and then 340 °C for 200 h in a pure oxygen gas flow. This sample showed critical current density (Jc) as high as 15,000 A/cm2 under a magnetic field, of 5 T, applied along the c-axis of the crystal. Electron microscopic studies with energy dispersive x-ray spectroscopy (EDS) have revealed that the Ba/Nd ratio fluctuates between 2.0 and 0.7 with a wavelength of a few tens of nanometer. This implies that superconducting phase of Nd1.0Ba2.0Cu3O7−δ and nonsuperconducting phase of Nd1.8Ba1.2Cu3O7−δ mingle with each other, which is the ideal structure for high-Jc superconducting material.

Study of twin formation in NdBa2Cu3O7−δ single crystal by using high temperature polarized optical microscopy

In order to determine an accurate tetragonal–orthorhombic structural transition temperature for NdBa 2 Cu 3 O 7− δ (Nd123) single crystal easily, in-situ observation of twin formation during annealing of the Nd123 single crystal was performed by using high temperature polarized optical microscopy. The Nd123 single crystal was grown under 21% oxygen partial pressure atmosphere by a top-seeded solution-growth (TSSG) method. The cut sample was heated to 700°C in a pure argon gas flow, followed by a step-wise cooling treatment every 10°C from 700°C, in a 100 and a 21% oxygen partial pressure gas flow until the twin was formed. The twin formation, which takes place with a tetragonal–orthorhombic structural phase transition, was observed at 660 and 620°C in a 100 and a 21% oxygen partial pressure gas flow, respectively. Furthermore, the oxygen contents (7− δ ) in the Nd123 single crystal, which are changed by oxygen absorption and desorption in the crystal, were examined with a thermogravimetry (TG) on powder samples and an iodometric titration technique. The relations between the annealing temperatures and the oxygen contents (7− δ ) were determined under 100 and 21% oxygen partial pressure atmospheres. These relations suggested that the critical oxygen content with which the tetragonal–orthorhombic structural phase transition took place was around 6.80 for the Nd123 single crystal.

APPLICATION OF THE CONSTANT MOLAR FLOW METHOD IN THE STUDY OF MASS TRANSFER OF GASES AND VAPORS IN BIDISPERSE STRUCTURED SOLIDS

In this paper, we provide exact analytical solutions for a new method of constant molar flow of pure gas into a reservoir containing solid adsorbents having a bidispersed structure, such as zeolite, activated carbon and alumina. Depending on the diffusion mechanism, two models are proposed under the isothermal conditions and linear isotherm. One is applicable to zeolite, and the other for alumina and activated carbon. The solutions of these two models are in the form of an infinite series, and its eigenvalues are determined from a transcendental equation. This transcendental equation is such that the eigenvalues are lumped into infinite but countable groups, and in each group there are infinite but countable eigenvalues. The dominant eigenvalues are generally the first ten to thirty eigenvalues (depending on the value of time at which the series is evaluated) in each group. The pressure response of the reservoir is a function of time as the result of the introduction of adsorbate into the reservoir, and a...

Crystal Structure and Magnetic Properties of (Mg6−xLix)MnO8

Murdochite-type (Mg6−xLix)MnO8(0.0 ≤x≤ 0.3) was synthesized at 973 K in a flow of pure oxygen gas using a solid state reaction. The cell constants, the (Mg, Li)–O(1) distance, and the Mn–O(1) distance monotonously decrease with increasingx. The variation of the effective magnetic moment (μeff) calculated from the magnetic measurement indicates that both the Mn4+and the Mn5+ions coexist in (Mg6−xLix)MnO8(0.0 ≤x≤ 0.2). The binding energies of the Mg 2s1/2, Li 1s1/2, Mn 2p3/2, and O 1s1/2levels of (Mg6−xLix)MnO8were determined by X-ray photoelectron spectroscopy (XPS), and they are independent of the composition.

Fabrication of NdBa 2Cu 3O 7−δ single crystals by the top-seeded solution-growth method in 1%, 21%, and 100% oxygen partial pressure atmosphere

Single crystals of NdBa 2Cu 3O 7−δ (Nd123) have been successfully grown by the top-seeded solution-growth (TSSG) method in 1%, 21% and 100% oxygen partial pressure atmosphere (( P(O 2) = 0.01 atm, P(O) 2) = 0.21 atm and P(O 2) = 1.00 atm). BaCuO solvent with a Ba to Cu ratio of 3:5 was used in a Nd 2O 3 crucible. Nd is supplied by the reaction between the molten solvent and the Nd 2O 3 crucible. Compositions of Nd123 single crystals grown in different oxygen partial pressure atmospheres were analyzed by inductivity coupled plasma atomic emission spectrometry (ICP-AES) and confirmed to be Nd:Ba:Cu = 1.01:1.97:3.00 for P(O 2) = 0.01 atm, Nd:Ba:Cu = 1.07:1.95:3.00 for P(O 2) = 0.21 atm and Nd:Ba:Cu = 1.10:1.90:3.00 for P(O 2) = 1.00 atm, respectively. The Nd123 single crystals grown in different oxygen partial pressure atmospheres were annealed in a pure oxygen gas flow, and the temperature dependence of the DC magnetization for these crystals was measured using a superconducting quantum interference device (SQUID) magnetometer. The Nd123 single crystal grown in P(O 2) = 0.01 atm, and annealed at 340°C for 200 h showed a steep superconductive transition at 96 K. On the other hand, the Nd123 crystal grown in P(O 2) = 0.21, 1.00 atm and, annealed at 340°C for 200 h exhibited a broad transition at 92 K for P(O 2) = 0.21 atm and at 88 K for P(O 2) = 1.00 atm, respectively. Therefore for Nd123 single crystal production with high quality superconductive characteristics, a low oxygen partial pressure atmosphere during crystal growth is found to be effective for minimizing the substitution of Nd ions into Ba sites.

Heat treatment and anomalous peak effect in Jc- H curve at 77 K for NdBa 2Cu 3O 7−δ single-crystal superconductor

To investigate whether for NdBa 2Cu 3O 7−δ (Nd123) an anomalous peak effect in the magnetization hysteresis ( M- H) loops at 77 K is an intrinsic property or not, different series of heat treatments were performed in a pure oxygen gas flow using Nd123 single crystal, and critical current density ( J c- H curves at 77 K were determined from the M- H loops. The J c- H curves with either H∥ α-axis or H∥ c-axis for a constant heat treatment at 340°C for 200 h showed no anomalous peak effect. On the other hand, when two step heat treatments, where the first step heat treatments was set to be at 500°C for 100 h and the second one was set to be at 340°C for 200 h, were carried out, the J c- H curve at 77 K with only H∥ c-axis exhibited an anomalous peak effect. These results indicated that for Nd123 the anomalous peak effect in the J c- H curve at 77 K (in other words, the M- H loop) with H∥ c-axis was considered to be not due to an intrinsic property. Further it was thought that the solid reaction occurred at 500°C and this solid reaction resulted in the formation of an anisotropic structure, causing an anomalous peak effect in the J c- H curve at 77 K with only H∥ c-axis. Further the anomalous peak effect could be eliminated by the heat treatment. Therefore this solid reaction was found to be a reversible reaction. Accordingly the existence of the anomalous peak in the J c- H curve at 77 K could be considered to be controlled by the heat treatment. We propose that the phase separation which is derived from the spinodal decomposition of an unstable solid solution takes place and the nano-scale microstructure resulting from phase separation leads to the anomalous peak effect and anisotropic property in the J c- H curve at 77 K.

Shock-wave reflection over a semicircular cylinder in a dusty gas

The unsteady shock-wave reflection and diffraction generated by a shock wave propagating over a semicircular cylinder in a dusty gas are studied numerically. The mathematical model is a multiphase system based on a multifluid Eulerian approach. A second-order Godunov scheme is used to solve the gas-phase Euler equations and an upwind scheme is used to solve the particle-phase conservation equations on an unstructured adaptive mesh. For the validation of the model, the numerically predicted one-dimensional shock-wave attenuation is compared with experimental results. Shock-wave reflection and diffraction over a semicircular cylinder in a pure gas flow is simulated first to show the excellent agreement between the present computation and the experimental results. For a shock-wave reflection and diffraction in a dusty gas, the effects of particle size and particle loading on the flowfield are investigated. Gas and particle-density contour plots are presented. It has been shown that the shock-wave configuration differs remarkably from pure gas flow depending on the particle parameters. The difference is explained as the result of momentum and heat exchange between the two phases.