Low Water Vapor Pressure Research Articles

Initial oxidation of zirconium and Zircaloy-2 with oxygen and water vapor at room temperature

The initial oxidation of zirconium and Zircaloy-2 with oxygen and water vapor has been investigated at room temperature with Auger electron and X-ray photoelectron spectroscopies. Three suboxides of Zr 2O, ZrO and Zr 2O 3 accompanied by the oxide of ZrO 2 are formed on surfaces in both oxygen and water vapor atmospheres. Formation of ZrO 2 starts at about 0.2–0.4 L (1 L ≡ 10 −6 Torr s) oxygen exposure. The oxidation rate of zirconium with oxygen is slightly larger than that of Zircaloy-2. In the case of low pressure water vapor exposure (< 10 L), the amounts of suboxides on the zirconium are larger than on the Zircaloy-2, since dissociation of H 2O molecules proceeds more easily on the former. The ZrO 2 starts to form after a 1.0 L water vapor exposure, and its formation rate in water vapor ambience is much smaller than that in oxygen. An average composition of ZrO 1.50–1.53 and film thickness of 2.3 nm are obtained for surfaces exposed to 30 L oxygen, and a 1.3 run thick film with composition Zr 1.06 is obtained for 30 L of water vapor exposure.

Two-year follow-up study of the effect of acid fog on adult asthma patients.

Acid fog is a complex mixture of atomospheric pollutants containing multiple stimuli that may be capable of inducing bronchoconstriction. To investigate the effect of ambient acid fog on bronchoconstriction, we examined the relation between the hospital visit for asthma symptoms of 102 patients and various meteorological conditions for over the two-year period from January 1992 to December 1993. Dense fog occurs frequently every summer in Kushiro, a city located in Hokkaido, northernmost island in Japan. The acidity of the fog ranged from pH 3.32 to 6.91 (mean pH = 5.05) during this period. A significant increase (p < 0.05) of hospital visits on a foggy day was found in 9 cases, and a tendency (p < 0.10) was found in 10 cases. The odds ratio for a hospital visit on a high water vapor pressure day (> 12 h Pa) was significantly high (p < 0.01) in 5 cases among the above 19 cases. To exclude the effect of high water vapor pressure, the data was restricted to the condition of a foggy day with low water vapor pressure (< 12 hPa); 9 patients had a significant increase (p < 0.05) in hospital visits on such a day. These results indicated that hospital visits for asthma symptoms was increased on acid fog days in 8.8% of adult asthma patients. Inhalation of naturally occurring acid fog may have adverse effects on the respiratory tract of the asthmatic patient.

Power optimization of small-scale chemical oxygen-iodine laser with jet-type singlet oxygen generator

Studies of power optimization of a 5-cm gain length chemical oxygen-iodine laser (COIL) energized by a jet-type singlet oxygen generator (JSOG) are presented. For 10 mmol/s of Cl/sub 2/ flow rate, output power of 132 W with chemical efficiency of 14.5% was obtained without a water vapor trap, 163 W and 18% were achieved when coholed (173 K). He was introduced downstream of the JSOG; under these conditions, the small-signal gain was estimated to be 0.32% cm/sup -1/. 190 W and 10.5% were obtained for 20 mmol/s of CI/sub 2/ flow rate. Replacing He by N/sub 2/ as a buffer gas resulted in a 13% power decrease only. The main key for increasing the chemical efficiency of a COIL without a water vapor trap for a given iodine-oxygen mixing system is found to be high oxygen pressure and low water vapor pressure inside the reaction zone of the JSOG. The last goal was achieved by optimizing the composition and temperature of the basic hydrogen-peroxide solution (BHP). The experimental results are discussed and related to the composition and flow conditions of the gaseous reactants and of the BHP.

On fatigue crack propagation enhancement by a gaseous atmosphere: Experimental and theoretical aspects

This paper is concerned with environmentally-assisted stage II fatigue crack propagation and specifically the interaction between the fatigue damage mechanisms and the exposure of the material to an active environment like ambient air. A brief state-of-the-art in the understanding of these well-knit connected processes is first presented. On the basis of original experimental results obtained on a high-strength low-alloy steel exposed to an atmosphere of very low water vapour pressure, a new light is shed on the physical description and on the modelling of environmentally-assisted fatigue damage. The salient feature is that physical adsorption of water vapour on freshly cracked surfaces can by itself enhance the damage process at the crack tip and therefore promote the stage II crack propagation in a wide range of alloys.

Evolution of structural and physical parameters of clays during experimental compaction

To provide a better understanding of sedimentary basin geological history, it is important to describe correctly the evolution of the various physical, mechanical and hydraulic properties of clayey rocks as a function of burial depth. As a contribution to this field, a programme of experimental studies on reworked clay samples compacted under various load pressures in oedometric conditions has been set up. The evolution of samples under compaction was followed with microscopic and macroscopic measurements. In a specially designed oedometric cell, samples are compacted under different total stresses from 0.1 to 50 MPa. In this cell, cylindrical cores are submitted to progressive loading from both ends under controlled pore pressure conditions. The symmetrical loading allows more even deformation about the midplane of the sample. This device allows the evolution of hydraulic pressure, radial stress, displacement and expelled pore fluid to be followed as a function of time. In a first step, kaolinite was chosen because it retains a high permeability (compared with other clays such as illite or smectite), which allows compaction tests to be performed within a few days. A complete set of measurements was performed after the tests. These measurements are: (1) micro-structures investigated by means of transmission electron microscopy (TEM), mercury porosimetry, water removal under low water vapour pressure, granulometry and specific area measured by ethylene glycol adsorption; and (2) various physical parameters measured including hydraulic conductivity and thermal conductivity. TEM gives an understanding of the arrangement of particles. It was found that each particle is composed of several crystal units, each unit formed by ≈25 individual kaolinite layers. During compaction, these particles remain undeformed, but are rotated. The angular distribution of grain orientation is a function of the applied effective stress. This reorientation is in agreement with the observed decrease in porosity and pore size. It also explains the occurrence of a strong anisotropy in the thermal conductivity and hydraulic permeability. The combination of these experimental results allows a qualitative and quantitative understanding of the behaviour of kaolinite with respect to parameters such as permeability, porosity, mechanical and thermal properties, the knowledge of which are necessary for basin modelling.

Parameterization of the downward long-wave radiation at the Earth’s surface in polar regions

Various parameterization schemes for the downward long-wave radiation at the Earth's surface which have been frequently applied in sea ice and snow cover models are tested with the aid of one year's measurements at the German stations Koldewey and Neumayer in the Arctic and Antarctic, respectively. All of these concepts are based on the Stefan-Boltzmann radiation was with an empirically derived effective atmospheric emissivity e A . Our data confirm the distinct dependency of the latter on cloudiness. But no other influences e.g. due to falling ice crystals (diamond dust) could be detected as significant. And the low level atmospheric water vapour pressure needs not be considered explicitly in the formulae. Thus, we propose a rather simple scheme for e A which is competable to the more sophisticated ones at least for polar regions. Our parameterization reproduces the observations with root mean square (RMS) deviations of less than 16 W/m 2

Photocatalytic Degradation of Gaseous Pyridine over Zeolite-Supported Titanium Dioxide

The photocatalyzed degradation of pyridine in the gas phase was investigated using titanium dioxide semiconductor supported on mordenite. The complete mineralization was found to occur over a catalyst containing 75 wt% TiO2 and 25 wt% mordenite in about 180 min in the presence of saturated water vapor at 0°C (4.6 Torr). Low water vapor pressure of 0.096 Torr was found to be sufficient to achieve a reasonably high percentage and rate of degradation. Diffusion of pyridine within the catalyst adversely affects the activity when the thickness of the catalyst coating exceeds the penetration depth of illumination. The activity of the zeolite-supported catalysts was higher than that of TiO2. The photonic efficiency for the complete mineralization of pyridine to CO2 was determined to be 0.48.

In situ sputter cleaning of vias using a getter electrode

An aluminum electrode is rf powered before sputter cleaning of wafers to reduce the partial pressure water vapor in an evaporator. Prolonged sputter cleaning times are thereby avoided because regrowth of the aluminum oxide during sputter cleaning is practically nil. Wafers with temperature sensitive resists, for example, with a polyimide or photoresist lift off mask for fabrication of the conductor lines can be sputter cleaned and low via resistance obtained without mask damage. Histograms of the via resistance as a function of the sputter cleaning time in the range from 15 to 60 s are presented for the as-deposited and sintered metallization. The tooling and the process to obtain low via resistance are described. The author believes, that the principle method and electrode design may be useful for similar applications where a low partial pressure water vapor in a vacuum apparatus is required.

Compressed condensation of water vapor on chilled brine

Inexpensive removal of low-pressure water vapor is an essential requirement for economically attractive direct freeze concentration. The currently used method is condensation on a chilled metal surface rinsed by a recirculating saline solution. Although simple condensation is inexpensive on a large scale, the requirement of a large condensing surface and low capital cost lead to poor heat transfer, especially for facilities less than about 20 kg/h. An alternative approach is to combine condensation with mechanical compression, but little information is publicly available that can be used to determine the feasibility of this approach. Our measurements of condensation rate in a chilled liquid ring (LR) vacuum pump show that correlations for smooth films do not describe condensation in these pumps. The measured condensation rates indicate that LR pump compression does not substantially increase condensation.

Contact angle relaxation on low energy surfaces

The spontaneous relaxation of the water—vapour interface, in contact with the “low energy” solids poly(ethylene terephthalate) (PET) and poly(methyl methacrylate) (PMMA), has been investigated after forced advancing and receding movement. A tensiometric apparatus has been used to probe the three-phase contact zone during relaxation for periods of up to 24 h. The measured force—time trace differs from that which might be anticipated, due to extraneous phenomena such as bulk evaporation/condensation/absorption. It is clear that even for a pure low viscosity liquid such as water, an imbalance in interfacial energies in the neighbourhood of the three-phase contact line (TPCL) exists for extended periods. Measurements have been made at both high and low water vapour pressures. In the advancing case, the TPCL is pinned and equilibration occurs via an essentially evaporative mechanism. In the receding case, the TPCL is mobile and the approach to equilibrium, which also occurs by an evaporative mechanism, is much slower. Indeed our results lead us to question whether equilibrium in the receding case is experimentally accessible. Contact angle hysteresis was found to be significantly smaller in magnitude than that typically measured within seconds or a few minutes of the cessation of forced TPCL movement.

Thermal Behavior of Cadmium-Containing Apatites

The behaviour of cadmium hydroxy- and fluorapatites at 500-1000°C and under low or high water vapor pressure were examined by X-ray diffraction and IR spectrometry. Heat treatment induces decomposition of both hydroxyapatites and fluorapatites. The decomposition temperature and the nature of the crystalline phases (cadmium oxide, tetracadmium phosphate, trimetallic phosphate) are strongly dependent on water vapor pressure and the nature and cadmium content of the initial compounds. Fluorapatites appear to be more stable than hydroxyapatites; a cadmium rate increase destabilizes the apatitic structure and high water vapor pressure stabilizes the hydroxyapatites.

Environmental fatigue of an Al-Li-Cu alloy: Part II. Microscopic hydrogen cracking processes

Microscopic fatigue crack propagation (FCP) paths in peak-aged unrecrystallized alloy 2090 are identified as functions of intrinsicda/dN- δK kinetics and environment. The FCP rates in longitudinal-transverse (LT)-oriented 2090 are accelerated by hydrogen-producing environments (pure water vapor, moist air, and aqueous NaCl), as defined in Part I. Subgrain boundary cracking (SGC) dominates for δK values where the cyclic plastic zone is sufficient to envelop subgrains. At low δK, when this crack tip process zone is smaller than the subgrain size, environmental FCP progresses on or near 100 or 110 planes, based on etch-pit shape. For inert environments (vacuum and He) and pure O2 with crack surface oxidation, FCP produces large facets along 111 oriented slip bands. This mode does not change with δK, and T1 decorated subgrain boundaries do not affect an expectedda/dN- δK transition for the inert environments. Rather, the complex dependence ofda/dN on δK is controlled by the environmental contribution to process zone microstructure-plastic strain interactions. A hydrogen embrittlement mechanism for FCP in 2090 is supported by similar brittle crack paths for low pressure water vapor and the electrolyte, the SGC and 100/110 crystallographic cracking modes, the influence of cyclic plastic zone volume (δK), and the benignancy of O2. The SGC may be due to hydrogen production and trapping at T1 bearing sub-boundaries after process zone dislocation transport, while crystallographic cracking may be due to lattice decohesion or hydride cracking.

Optimization of the surface morphology of GaAs epitaxial layers grown by close-spaced vapor transport

GaAs epitaxial layers were grown on (100) GaAs and vicinal substrates (2° off (100) toward (110)) by close-spaced vapor transport (CSVT) using water vapor as transport agent. We demonstrate that the temperature at which water vapor is injected into the reactor, Tinj, is a criticial parameter for the layer morphology. Furthermore, the optimum Tinj, is a function of water partial pressure, [Formula: see text]. For each [Formula: see text], there is a Tinj range for which specular layers are obtained. This range is defined for [Formula: see text] Torr (1 Torr = 133.3 Pa). The only defects appearing on the specular layers grown on (100) GaAs substrates are oval hillocks (structureless oval defects, and occasionally oval plateaus and oval defects with a faceted central core head). All oval hillocks have their long axis, L1, parallel to &lt; 110 &gt;. By measuring L1 and L2 (the short axis of the defect, perpendicular to L1), lateral growth rates of GaAs are obtained. They vary with [Formula: see text]. At high [Formula: see text], [Formula: see text] is 1 at low water vapor pressure. All oval hillocks result from the contamination of the substrate surface. By using vicinal GaAs substrates, the oval hillock density was decreased to about 500 cm−2, a result similar to that obtained with molecular beam epitaxy.

The effect of water vapour pressure on the kinetics of the thermal dehydration of erbium formate dihydrate

The kinetics of the thermal dehydration of erbium formate dihydrate has been studied by means of isothermal gravimetry under various water vapour pressures from 5 × 10 −4 to 8 Torr. The kinetics of the dehydration, on the whole, can be described by the contracting volume model, R 3. The rate of dehydration k exhibited an unusual dependence upon the water vapour pressure: with increasing water vapour pressure, the rates increased at first, passed through a maximum, and then decreased gradually to a constant value. These phenomena were analogous to the Smith-Topley effect, and seemed to be correlated to the crystallinity of the dehydrated products. At low water vapour pressure (≈ 10 −4 Torr), the amorphous dehydrated products cover the surface of the reaction particles and interfere with the escape of the dissociated water molecules. Therefore, the rate of dehydration is slow. The presence of a few water molecules seems to promote recrystallization of the dehydrated products. The recrystallization results in the formation of wide channels between the dehydrated particles, and the dissociated water molecules can easily escape through these channels. Therefore, the dehydration rate seems to increase. At higher vapour pressure, the rate decreased gradually because of the reverse reaction caused by atmospheric water molecules.

Behaviour of graphite in friction under various environments: Connection with the surface reactivity

We have shown that the relative slip under load at an interface of copper/polycrystalline graphite in the presence of a low water vapour pressure, leads to the gradual growth of a superficial boundary of strongly oriented graphite with basal planes parallel to the friction surface. X-ray analysis has shown an analogy with the structure of high oriented pyrolitic graphite (HOPG) and the mechanical properties of this thin boundary are excellent. It is load resistive and the friction coefficient is very low and near 0.1.

Diffusivity of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in Organic Solvents

ABSTRACT The extremely low water solubility and vapor pressure of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) cause it to be a very persistent soil contaminant. TCDD transport may occur when an orga...

Diffusion of OH− during hydration of YBa2Cu3O7-y by exposing to water vapor

The hydration of YBa2Cu3O7-y in water vapor was investigated at various values of y and at two different PH2O by measuring the weight of the specimen. The reaction was relatively insensitive to the values of y and was extensive in the water vapor pressure of 2.7 kPa at room temperature and 140 °C. This was due to the decomposition of YBa2Cu3O7-y by reacting with H2O. The weight gain was also detected in the water vapor pressure of 270 Pa. The weight gain under lower water vapor pressure was supposed to be controlled by diffusion of OH− in YBa2Cu3O7-y. The diffusion coefficient calculated from the measurement was compared favorably with the oxygen diffusion coefficient.

Effects of steaming on the shape selectivity and on the acidity of HZSM 5

The effect of steaming on HZSM 5 has been characterized by using two model reactions: n-heptane cracking and m-xylene isomerization. For both reactions, the activity of HZSM 5 was increased by steaming at low water vapor pressure, but at a high pressure it became lower than that of the non-steamed sample. Modifications in the acidity and a slight blockage of the pores by extralattice aluminium can explain this behavior.

Photosynthesis in an open field for exotic versus native vines of the southeastern United States

The potential importance of leaf gas exchange to the prolific growth characteristics of the exotic vines Pueraria lobata and Lonicera japonica versus the native vines Rhus radicans, Parthenocissus quinquefolia, Vitis vulpina, and Clematis virginiana was evaluated. Under high irradiance and low leaf-air water vapor pressure difference, photosynthesis was similar (23 – 27 μmol∙m−2∙s−1) among species with the exception of R. radicans (16 μmol∙m−2∙s−1). Conductance and transpiration were greater in Pueraria lobata than in the other species. When the leaf-air vapor pressure difference was high (4.0 kPa) photosynthesis in the exotic vines decreased more than in several of the native species. Photosynthesis in L. japonica and Parthenocissus quinquefolia, and to a lesser extent in Pueraria lobata, was reduced by high vapor pressure differences even though internal CO2 partial pressures remained relatively high, suggesting a nonstomatal reduction of photosynthetic capacity. Thus, the highly prolific growth typical of the exotic vines may not be attributable to greater steady-state photosynthesis.

ChemInform Abstract: Migration of Molybdenum into Intracrystalline Cavities in Molybdate-Impregnated NaY Zeolite.

Abstract Molybdenum-containing Y-type zeolites have been prepared by thermal decomposition of molybdate-impregnated samples according to a nonconventional procedure which uses a constantrate decomposition at very low water vapor pressure (10 N m−2). The combined results of X-ray diffraction, mid-infrared, surface area, and sorption (water and n-hexane) capacity measurements show that zeolite structure was largely retained when the impregnated material was activated at temperatures below 623 K. However, a progressive loss of crystallinity and a parallel decrease of the surface Mo Si ratio, as obtained from the X-ray photoelectron spectra, was observed at higher temperatures. Furthermore, on heating at higher temperatures (793 K), the electron spin resonance spectra indicated that a fraction of the Mo(V) ions are essentially isolated in the sodalite cages or hexagonal prisms of the zeolite. A mechanism which involves “vaporization” of MoO3 from the external surface of the zeolite by water vapor is proposed to describe the redistribution of molybdenum in the impregnated precursor.