Low Water Vapor Pressure Research Articles

Low pressure water vapour discharge as a light source: II. Electrical characteristics

The electric field strength, electrode fall voltage, light emission characteristics and efficiency of a (Ar + H2O) dc discharge as functions of water vapour content, argon pressure and electric current are presented. The data show that the main processes of 306.4 nm OH band generation are (1) a collision between an excited argon atom and a water molecule with simultaneous excitation of OH into the A 2Σ+ state and (2) electron excitation of a ground state hydroxyl molecule produced by a quenching process from a water molecule. Electric field strength measurements make it possible to conclude that the light production efficiency of the plasma under study can reach 35 lm W−1. It is possible, with these data, to propose a model of the plasma in question having reasonable accordance with the experiment and show the way to further increase the efficiency.

Space and time resolved optical emission spectroscopy characterization of inductively coupled RF water vapour plasma

Inductively coupled RF water vapour plasma generated in a linear glass tube was studied by means of optical emission spectroscopy. Low pressure water vapour plasma was created by an 8 turn coil with an EM field oscillating at 13.56 MHz. Various total pressures (5–14 Pa) and discharge powers (100–300 W) were investigated. Excitation temperatures (between 0.6 and 1.0 eV) of the plasma discharge were determined from emission spectra by employing the Boltzmann plot method. E- and H-modes of plasma and transitions among them were observed. Hysteresis effects were observed by the change in water vapour pressure and discharge power through monitoring of O, H and OH spectral features.

Tautomerism of cytosine probed by gas phase IR spectroscopy

The tautomerism of the gaseous protonated cytosine is studied using infrared multiple photon dissociation (IRMPD) spectroscopy of singly hydrated complexes of protonated cytosine in the 2700–3750 cm −1 wavenumber range. The hydrated complexes are formed through argon-mediated collisions between bare electrosprayed cytosine and low-pressure water vapor. In the spectra, where X–H (X C, O, and N) stretching vibrations are probed, evidence is found for the coexistence in the gas phase of hydrated complexes of two different cytosine tautomers. As the addition of a water molecule to either tautomer of protonated cytosine is energetically highly unlikely to induce interconversion, it is deduced that both C(2) O and N(3) protonated tautomers of cytosine are formed under electrospray conditions.

Study on reaction mechanism of YBa2Cu3O7–x; film by TFA-MOD process

This paper systematically investigates the intermediate phases of YBa2Cu3O7−x (YBCO) film prepared by metalorganic deposition method using trifluoroacetates (TFA-MOD). According to x-ray diffraction and Raman analyses, the precursor film decomposed in a mixture of BaF2, Y2O3 and CuO after the pyrolysis process. Then these intermediate phases converted into tetragonal YBa2Cu3O6.5 at about 725°C. The influence of water vapour pressure on the YBa2Cu3O7−x film growth on LaAlO3 single-crystal substrates was also studied. The films prepared at low water vapour pressures (40–140 hPa) showed poor electrical performance due to the a-axis grain structure and impurity phases. However, the films prepared at 190 hPa exhibited the highest critical temperature of 90 K and the highest Jc of 3.8 MA/cm2, which was attributed to the formation of a purer YBCO phase and stronger biaxial texture.

La0.85Sr0.15Cr0.9Ni0.05Pd0.05O3 Perovskite Anode for SOFC

A Pd doped perovskite La0.85Sr0.15Cr0.9Ni0.05Pd0.05O3 (LSCNP) was investigated as a candidate for a metal-free anode material of solid oxide fuel cell. The deposition and the solid dissolution by reduction and oxidation treatment were observed by FE-SEM and the change of crystal structure was observed by XRD. The performance of anode prepared by mixing LSCNP and Sm doped ceria (SDC) was measured using H2 and dry CH4 as fuel. The anode voltage gradually decreased during the power generation, but recovered by oxidation treatment. Electrochemical impedance spectra were measured and the interfacial resistance increased during the power generation, but it decreased by oxidation treatment. The recovery of the performance due to the deposition and solid solution was confirmed. The performance of LSCNP-SDC anode using dry CH4 as fuel showed a maximum at 5ccm, and the maximum current density was 500 mA cm–2. From the impedance spectroscopy, it was revealed that when the flow rate was high, the relatively low water vapor pressure diminished the reforming reaction, whereas when the flow rate was low, the insufficient supply of fuel increased the diffusion resistance.

Suppression of Osmotic Distillation in Gas Membrane Processes

Suppression of osmotic distillation of water is important for the commercial scale application of gas membranes. We have equalized the water vapor pressure on either side of the membrane by increasing the temperature of the stream with the lower water vapor pressure. The experimentally determined temperature gradient is many times larger than predicted from water vapor pressure–temperature data. The larger temperature gradient may be explained by considering the heat flux across the membrane. The economic viability of adjusting the temperature of the feed and strip streams to suppresses water vapor transport depends on the additional energy costs involved.

Electrical conductivity and thermal stability of (1 − x)CsH2PO4/xSiP y O z (x = 0.2–0.7) composites

The physicochemical properties of (1 − x)CsH2PO4/xSiP y O z (x = 0.2–0.7) composites containing fine-particle silicon phosphates as heterogeneous additives have been studied at different humidities. The introduction of silicon phosphates suppresses the superionic phase transition of CsH2PO4 and increases the low-temperature conductivity of the materials, which depends significantly on humidity. The CsH2PO4-SiP y O z materials offer high conductivity (∼3 × 10−3 to 10−2 S/cm at ∼110–230°C) at low water vapor pressures (3 mol % H2O). Amorphization of the CsH2PO4 in the composites markedly changes its thermodynamic properties. The effect of long-term isothermal holding (210°C, 3 mol % H2O) on the conductivity of the composites has been studied.

The heptahydrate of sodium sulfate: Does it have a role in terrestrial and planetary geochemistry?

Sodium sulfate readily forms a metastable heptahydrate from concentrated aqueous solutions on cooling to around 10 °C. It crystallises much more easily than the well recognised and less soluble decahydrate (mirabilite), although the existence of the heptahydrate is almost entirely ignored in the geochemical literature on sodium sulfate. There is strong evidence that the heptahydrate is stable below a triple point temperature of −9.5 °C at low water vapour pressures, conditions which are found in cold dry environments such as the surface of Mars and the icy moons of Jupiter.

Low pressure water vapour discharge as a light source: I. Spectroscopic characteristics and efficiency

Spectral and electrical characteristics of a low pressure dc discharge formed from a mixture of one of the rare gases Ne, Ar or Kr plus water vapour are studied. Water vapour is only a minor additive to the rare gas. It has been shown that enhanced emission of the OH 306.4 nm band is registered from the discharge of Ar mixed with water vapour. Plasmas from the other investigated rare gases yielded considerably less OH 306.4 nm emission. Data about consumed electric power, spectra and relative efficiencies are presented.

The emission characteristics of low-pressure water vapor discharge UV emitters

We have studied the characteristics of UV emission sources operating on low-pressure normal (H2O) and heavy (D2O) water vapor excited by periodic-pulsed and glow discharges. The emission in a 300–330 nm wavelength interval has been studied in detail for water vapor pressures ranging from 50 to 2500 Pa. A comparison of the characteristics of emission from discharge plasma at low (50–150 Pa) and elevated (2.0–2.5 kPa) water vapor pressures reveals significant differences in the character of emission spectra, which can be related to the different types of emitting species (hydroxy radicals versus small clusters of such radicals and water molecules). Discharge current and emission intensity pulses in the periodic-pulsed discharge regime have been measured.

Experimental study of the sublimation of ice through an unconsolidated clay layer: Implications for the stability of ice on Mars and the possible diurnal variations in atmospheric water

We have studied the sublimation of ice and water vapor transport through various thicknesses of clay (<63 μm grain size). We experimentally demonstrate that both adsorption and diffusion strongly affect the transport of water, and that the processes of diffusion and adsorption can be separately quantified once the system comes to a steady state. At shallow depths of clay, water vapor transport is determined by diffusion through both the atmosphere and the clay layer, whereas at greater depth the rate of sublimation of the ice is governed only by diffusion through the clay. Using two different models, we determine the diffusion coefficient for water vapor through unconsolidated clay layer to be 1.08 ± 0.04 × 10 −4 and 1.29 ± 0.06 × 10 −4 m 2 s −1 . We also determined the adsorption isotherms for the clay layer, which follow the Langmuir theory at low water vapor pressure (<100 Pa, where a monolayer of water molecules forms on the surface of the clay) and the BET theory at higher pressure (where multiple water layers form). From our analysis of both types of isotherms we determined the adsorption constants to be α = 4.9 ± 1.0 × 10 −2 Pa −1 and c = 30 ± 10 , respectively, and specific surface areas of 1.10 ± 0.2 × 10 5 and 9.0 ± 0.7 × 10 4 m 2 kg −1 , respectively. Finally, we report a theoretical kinetic model for the simultaneous diffusion and adsorption from which we determine adsorption kinetic constants according to the Langmuir theory of k a = 2.5 ± 0.5 × 10 −4 s −1 and k d = 8.7 ± 3.6 × 10 −5 s −1 . If the martian regolith possesses diffusive properties similar to those of the unconsolidated montmorillonite soil we investigated here, it would not represent a significant barrier to the sublimation of subsurface ice. However, at the low subsurface temperatures of high latitude (180 K on average), ice could survive from the last glaciation period (about 300 to 400,000 years ago). Higher subsurface temperatures in the equatorial regions would prevent long-timescale survival of ice in the shallow subsurface. In agreement with previous work, we show that adsorption of water by a clay regolith could provide a significant reservoir of subsurface water and it might account for the purported diurnal cycle in the water content of the atmosphere.

Monochromatic-Tunable Terahertz-Wave Sources Based on Nonlinear Frequency Conversion Using Lithium Niobate Crystal

We review widely tunable terahertz (THz)-wave generation by optical parametric processes using lithium niobate crystal. Applying the parametric oscillation of or a MgO-doped crystal pumped by a nanosecond Q-switched Nd:YAG laser, we realized coherent THz-wave sources with a simple configuration widely tunable in the range of 0.7-3 THz. For efficient coupling of the THz wave, we used a monolithic grating coupler or a Si-prism array coupler. In addition, Fourier transform limited THz-wave spectrum narrowing was achieved by introducing the injection seeding method. A line width of about 110 MHz (0.003 cm-1) was assured by measuring the absorption spectrum of low-pressure water vapor. Using the difference frequency generating method with a periodically poled crystal, we achieved higher conversion efficiency and realized continuous THz-wave generation. This room temperature operated, tabletop system promises to be a widely tunable THz-wave source suited to a variety of applications.

Thermal change of amorphous indium tin oxide films sputter-deposited in water vapor atmosphere

Amorphous ITO thin films were deposited on silicon wafers at room temperature by RF + DC magnetron sputtering at water vapor partial pressures between 0 and 6 × 10 − 5 Torr. The O/(In + Sn) ratio was determined by Rutherford backscattering spectroscopy. The effect of water vapor on the thermal crystallization process was monitored by high-temperature X-ray diffraction (XRD) analysis. We found a simple dependence between the crystallization temperature and the water vapor partial pressure. After the high-temperature XRD, the films deposited at low water vapor pressures (2 × 10 − 5 Torr or lower) exhibited <100> preferred orientation, whereas those deposited at high water vapor pressures (3 × 10 − 5 Torr or higher) exhibited <111> preferred orientation. Introduction of water vapor during the deposition decreased carrier concentration and increased mobility. The carrier concentration after thermal crystallization was dependent on the water vapor partial pressure.

Mass transfer process of hydrogen via ceramic proton conductor membrane of electrochemical hydrogen pump

Abstract The blanket tritium recovery system using the electrochemical hydrogen pump with proton conductor membrane has been proposed. The feature of the electrochemical hydrogen pump is that the driving force of hydrogen transportation is a potential difference. Therefore, it might be effective to apply the hydrogen pump to the blanket sweep gas (the low hydrogen and water vapor pressure). Perovskite-type ceramic such as SrCe 0.95 Yb 0.05 O 3− α , is one of the candidate proton conductor for hydrogen pump and its ionic hydrogen transportation properties have been investigated. In this work, the basic mass transfer equation for hydrogen, in which the apparent proton conductivity is used as the over-all mass transfer coefficient, is proposed. And then, the apparent proton conductivities were estimated from experimental data using these equations, and mass transfer of hydrogen via proton conductor membrane was discussed by using the apparent conductivity.

Surface modification of poly(hydroxybutyrate) films to control cell–matrix adhesion

Tailoring surface properties of degradable polymer scaffolds is key to progress in various tissue engineering strategies. Poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) thin films were modified by low pressure ammonia plasma, low pressure water vapour plasma, or immersion in a sodium hydroxide solution to elaborate means to control the cell-matrix adhesion of human umbilical cord vein endothelial cells grown on these materials. Fibronectin (FN) heteroexchange and cell adhesion were correlated to the physicochemical characteristics of the modified polymer surfaces which were investigated by X-ray photoelectron spectroscopy (XPS), scanning force microscopy (SFM), electrokinetic measurements, and contact angle measurements. All treatments increased the hydrophilicity of the polymer samples, which could be accounted to newly created amine or carboxyl functionalities for ammonia plasma or water vapour plasma treatments, respectively, and ester hydrolysis for treatments with alkaline aqueous solutions. Main features of cell adhesion and FN reorganisation-evaluated after 1h and after 5 days-could be attributed to the anchorage strength of pre-coated FN layers at the polymer surface, which was, in turn found to be triggered by the type of modification applied. In line with earlier studies referring to different materials cell adhesion and matrix reorganisation were shown to be sensitively controlled through the physicochemical profile of poly(hydroxybutyrate) surfaces.

Investigation of the water sorption properties of Mars-relevant micro- and mesoporous minerals

Encouraged by recent results of the Mars Odyssey spacecraft mission and the OMEGA team (Mars Express) concerning water in equatorial latitudes between ±45° on Mars and the possible existence of hydrated minerals, we have investigated the water sorption properties of natural zeolites and clay minerals close to martian atmospheric surface conditions as well as the properties of Mg-sulfates and gypsum. To quantify the stability of hydrous minerals on the martian surface and their interaction with the martian atmosphere, the water adsorption and desorption properties of nontronite, montmorillonite, chabazite and clinoptilolite have been investigated using adsorption isotherms at low equilibrium water vapor pressures and temperatures, modeling of the adsorption equilibrium data, thermogravimetry (TG), differential scanning calorimetry (DSC), and proton magic angle spinning nuclear magnetic resonance measurements ( 1H MAS NMR). Mg-sulfate hydrates were also analyzed using TG/DSC methods to compare with clay mineral and zeolites. Our data show that these microporous minerals can remain hydrated under present martian atmospheric conditions and hold up to 2.5–25 wt% of water in their void volumes at a partial water vapor pressure of 0.001 mbar in a temperature range of 333–193 K. Results of the 1H MAS NMR measurements suggest that parts of the adsorbed water are liquid-like water and that the mobility of the adsorbed water might be of importance for adsorption-water-triggered chemistry and hypothetical exobiological activity on Mars.

What is the usual internal carbon dioxide concentration in C&lt;sub&gt;4&lt;/sub&gt; species under midday field conditions?

The carbon dioxide concentrating system in C4 photosynthesis allows high net photosynthetic rates (PN) at low internal carbon dioxide concentrations (Ci), permitting higher PN relative to stomatal conductance (gs) than in C3 plants. This relation would be reflected in the ratio of Ci to external ambient (Ca) carbon dioxide concentration, which is often given as 0.3 or 0.4 for C4 plants. For a Ca of 360 µmol mol-1 that would mean a Ci about 110-140 µmol mol-1. Our field observations made near midday on three weedy C4 species, Amaranthus retroflexus, Echinochloa crus-galli, and Setaria faberi, and the C4 crop Sorghum bicolor indicated mean values of Ci of 183-212 µ mol mol-1 at Ca = 360 µmol mol-1. Measurements in two other C4 crop species grown with three levels of N fertilizer indicated that while midday values of Ci at high photon flux were higher at limiting N, even at high nitrogen Ci averaged 212 and 196 µmol mol-1 for Amaranthus hypochondriacus and Zea mays, respectively. In these two crops midday Ci decreased with increasing leaf to air water vapor pressure difference. Averaged over all measurement days, the mean Ci across all C4 species was 198 µmol mol-1, for a Ci/Ca ratio of 0.55. Prior measurements on four herbaceous C3 species using the same instrument indicated an average Ci/Ca ratio of 0.69. Hence midday Ci values in C4 species under field conditions may often be considerably higher and more similar to those of C3 species than expected from measurements made on plants in controlled environments. Reducing gs in C4 crops at low water vapor pressure differences could potentially improve their water use efficiency without decreasing PN.

Spectroscopic study of unique line broadening and inversion in low-pressure microwave generated water plasmas

It was demonstrated that low pressure (~0.2 Torr) water vapor plasmas generated in a 10 mm inner diameter quartz tube with an Evenson microwave cavity show at least two features which are not explained by conventional plasma models. First, significant (> 0.25 nm) hydrogen Balmer_ line broadening, of constant width, up to 5 cm from the microwave coupler was recorded. Only hydrogen, and not oxygen, showed significant line broadening. This feature, observed previously in hydrogen-containing mixed gas plasmas generated with high voltage dc and rf discharges was explained by some researchers to result from acceleration of hydrogen ions near the cathode. This explanation cannot apply to the line broadening observed in the (electrodeless) microwave plasmas generated in this work, particularly at distances as great as 5 cm from the microwave coupler. Second, inversion of the line intensities of both the Lyman and Balmer series, again, at distances up to 5 cm from the coupler, were observed. The line inversion suggests the existence of a hitherto unknown source of pumping of the optical power in plasmas. Finally, it is notable that other aspects of the plasma including the OH* rotational temperature and low electron concentrations are quite typical of plasmas of this type.

Epitaxial ZrC thin films grown by pulsed laser deposition

ZrC thin films were grown on (0 0 1)Si, (1 1 1)Si and (0 0 0 1)sapphire substrates by the pulsed laser deposition (PLD) technique. X-ray diffraction, X-ray reflectivity and Auger electron spectroscopy investigations were used to characterize the structure and composition of the deposited films. It has been found that films grown at temperatures higher than 700 °C under very low water vapor pressures were highly textured. Films deposited on (0 0 1)Si grew with the (0 0 1) axis perpendicular to the substrate, while those deposited on (1 1 1)Si and (0 0 0 1)sapphire grew with the (1 1 1) axis perpendicular to the substrate. Pole figures investigations showed that films were epitaxial, with in-plane axis aligned to those of the substrate.

Hydroxylation-induced modifications of the Al 2O 3/NiAl(0 0 1) surface at low water vapour pressure

STM, STS, LEED and XPS data for crystalline θ-Al 2O 3 and non-crystalline Al 2O 3 ultra-thin films grown on NiAl(0 0 1) at 1025 K and exposed to water vapour at low pressure (1 × 10 −7–1 × 10 −5 mbar) and room temperature are reported. Water dissociation is observed at low pressure. This reactivity is assigned to the presence of a high density of coordinatively unsaturated cationic sites at the surface of the oxide film. The hydroxyl/hydroxide groups cannot be directly identify by their XPS binding energy, which is interpreted as resulting from the high BE positions of the oxide anions (O 1s signal at 532.5–532.8 eV). However the XPS intensities give evidence of an uptake of oxygen accompanied by an increase of the surface coverage by Al 3+ cations, and a decrease of the concentration in metallic Al at the alloy interface. A value of ∼2 for the oxygen to aluminium ions surface concentration ratio indicates the formation of an oxy-hydroxide (AlO x OH y with x + y ∼ 2) hydroxylation product. STM and LEED show the amorphisation and roughening of the oxide film. At P(H 2O) = 1 × 10 −7 mbar, only the surface of the oxide film is modified, with formation of nodules of ∼2 nm lateral size covering homogeneously the surface. STS shows that essentially the valence band is modified with an increase of the density of states at the band edge. With increasing pressure, hydroxylation is amplified, leading to an increased coverage of the alloy by oxy-hydroxide products and to the formation of larger nodules (∼7 nm) of amorphous oxy-hydroxide. Roughening and loss of the nanostructure indicate a propagation of the reaction that modifies the bulk structure of the oxide film. Amorphisation can be reverted to crystallization by annealing under UHV at 1025 K when the surface of the oxide film has been modified, but not when the bulk structure has been modified.