Water Vapor Partial Pressure Research Articles

Hydration of lanthanum tungstate (La/W = 5.6 and 5.3) studied by TG and simultaneous TG–DSC

The hydration properties of lanthanum tungstate (La/W=5.6 and 5.3) have been studied by means of thermogravimetry in the temperature range 1100 to 300°C. The relative weight was independent of the oxygen partial pressure between oxidizing and reducing conditions over the entire temperature range showing that the oxygen stoichiometry is close to constant. The materials take up water upon decreasing temperature and increasing water vapor partial pressure, eventually reaching saturation. Moreover, there is a significant reversible change in the relative weight upon shifting from H2O to D2O containing atmospheres. The results are interpreted based on the most recent defect model for dissolution of protons in lanthanum tungstate yielding standard enthalpy and entropy changes of hydration of ΔHHydr0 ≈-90kJmol−1 and ΔSHydr0 ≈-115J (molK)−1. The hydration enthalpy was verified by direct measurements using TG–DSC, yielding -85kJmol−1. The thermodynamic parameters obtained herein are in general agreement with literature values from fitting conductivity data, and may be considered an improvement of these.

Novel aspects of the degradation process of PLA based bulky samples under conditions of high partial pressure of water vapour

This work describes differences between the degradation of poly(l-lactic acid) bulky samples in high partial pressure of a water vapour environment versus a buffered liquid medium. Analytical techniques (optical and electron microscopy, size exclusion chromatography, differential scanning calorimetry) were used to evaluate the material's morphology, molecular weight, crystallinity and thermal properties. In particular, the extent of degradation was studied separately in the core and surface of the testing specimens. The results reveal significant differences in the bulk degradation profiles and morphological changes for both environments. Degradation in the liquid medium leads to multiphase core–cortex morphology formation, while the environment with high partial pressure of water vapour provides homogeneous-like bulk degradation of the samples due to significantly different diffusion conditions on the liquid-polymer and water vapour saturated air-polymer interface.

Silicon Volatility From Alumina and Aluminosilicates Under Solid Oxide Fuel Cell Operating Conditions

Thermodynamic equilibrium modeling indicates that the introduction of H2O in oxidizing environments decreases Si stability due to formation of volatile hydroxide and oxy hydroxides. 3Al2O3·2SiO2 mullite bond offers only slight improvement over pure silica as the thermodynamic activity of silica in mullite is near unity. In reducing atmospheres Si stability is improved by the presence of H2O and Al2O3, transitioning from SiO and silane as the dominant volatile species to hydroxides, oxy hydroxides, and SiO with increasing water vapor partial pressure. Empirical studies reveal initial rapid releases of Si from stationary solid oxide fuel cell refractory materials followed by slower solid‐state diffusion limited release.

Crystal structure, hydration and ionic conductivity of the inherently oxygen-deficient La2Ce2O7

The crystal structure, hydration and ionic conductivity of the inherently oxygen deficient La2Ce2O7 system have been investigated. On the basis of Rietveld analysis of neutron diffraction data, the material is found to adopt a cation disordered oxygen-deficient fluorite structure. Impedance spectroscopy, performed in the temperature range 1000–200°C and as a function of water vapor and oxygen partial pressure, suggests that oxide ion conductivity dominates at high temperatures, while protons are the main charge carrier at temperatures below approximately 450°C. Proton conductivity was confirmed by isotope shifts under H2O and D2O. The dissolution of water was measured by means of thermogravimetry (TG). A defect chemical model is developed to derive hydration thermodynamic parameters based on TG and conductivity data. The hydration enthalpy was, moreover, determined directly by simultaneous TG and differential scanning calorimetry (TG–DSC). The TG–DSC values were in good agreement with those modeled from conductivity and TG data.

The ground GNSS tomography – unconstrained approach

The GNSS signal along its more than 20,000km line of sight is bended, attenuated and delayed. These effects are results of the Earth’s atmosphere, and Sun radiation. Amongst all mentioned effects the one considered in this paper is a signal phase delay in troposphere.This paper presents investigations in the field of GNSS ground tomography, a remote sensing technique able to capture distribution of water vapour partial pressure in the troposphere. In this method, observations are Slant Wet Delays (SWD), the phase delay of GNSS signal due to the presence of water vapour in the troposphere.One of the most important limitation in GNSS tomography is so far mandatory usage of constraints to improve design matrix rank score and in consequence the ability to obtain meaningful troposphere parameters. Solution proposed here is based on combination of SWDs from several consecutive observation epochs to increase rank score. Another important goal is to perform careful selection of singular values in the process of pseudo inverse, to limit the observation noise influence. Three different methods to select singular values are investigated: functional analysis, significant testing and L-curve fitting. The obtained results are validated by means of internal uncertainties propagation, and comparison with external model. With the simulated data the unconstrained stacked GNSS produce reliable results with uncertainties on the level of 0.3hPa in terms of water vapour partial pressure and with mean discrepancies on the level of 0.1hPa. The same measures transform to the 0.03% and 0.01% of relative error on the ground level and 100% and more, above 8km. Moreover all instabilities inside profiles were resolved properly. The simulations shows that to attain such optimistic results at least 10 observations epoch have to be stacked.

Capacitive-discharge VUV lamp based on a water-vapor–argon mixture

This paper presents the results of a study of the spectral characteristics of the plasma radiation (175–200 nm) of a pulse-periodic capacitive-discharge lamp that operates with a mixture of water vapor and argon. It is shown that capacitive discharge at low argon pressure is a broad-band source of vacuum ultraviolet radiation. The intensity of the emission bands of the capacitive-discharge plasma is optimized as a function of the partial pressures of argon and water vapor. The electron kinetic coefficients are calculated for a discharge in a mixture of argon and water vapor.

Planetary boundary layer heights from GPS radio occultation refractivity and humidity profiles

The height of the planetary boundary layer (PBL) is an important parameter that relates to the various processes associated with the PBL. In this paper, we use Global Positioning System radio occultation (GPSRO) measurements to derive a global climatology of PBL heights. Utilizing the strength of GPSRO in capturing fine vertical structures, the top of the PBL is defined to be the height at which the vertical gradient of the refractivity or water vapor partial pressure is minimum, corresponding to the height where the refractivity or water vapor pressure changes most rapidly. A “sharpness parameter” is defined that quantifies the applicability of these definitions. The sharpness parameter is largest over the subtropical regions characterized by strong subsidence. When the sharpness parameter is large, the refractivity‐ and moisture‐based heights are shown to converge. We derived global PBL height climatology using three years (Dec. 2006–Nov. 2009) of COSMIC/FORMOSAT‐3 measurements and compared with values calculated from ECMWF Reanalysis Interim (ERA‐Int). We found that the mean PBL heights from GPSRO shared similar spatial and seasonal variations with ERA‐Int; however, GPSRO heights were higher by 500 m. The standard deviation was also higher from GPSRO, especially in the tropics. We present detailed comparisons between GPSRO and ERA‐Int over the Pacific Ocean and the Sahara desert and examine the PBL height distributions as well as its annual and diurnal variabilities. These results suggest that the underlying causes of the bias between GPSRO and ERA‐Int likely vary from region to region.

Gypsum board dehydration kinetics at autogenous water vapour partial pressure

In this paper, the dehydration kinetics of a commercial gypsum board, at autogenous water vapour partial pressure, are investigated. Differential scanning calorimetry measurements, under non isothermal conditions and in an inert atmosphere, were carried out at temperatures up to 300°C, with different heating rates. Samples of deionized water and commercial gypsum board, in conjunction with pin hole lid crucibles, were used in order to study the evaporation of the free moisture and the dehydration of the chemically bound water at autogenous water vapour pressure conditions. Model-free and model-fitting approaches were used for the definition of the kinetic parameters of the examined reactions.

Measurement of moisture outgassing of the plastic-bonded TATB explosive LX-17

Moisture outgassing during isothermal heating of LX-17, a plastic-bonded explosive consisting of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), was monitored. A moisture outgassing measurement system was constructed to directly monitor the water vapor released from the heated material in real time using an aluminum oxide probe mounted in the stainless steel sample chamber. The total pressure in the sample chamber was also monitored. After an initial high vacuum pump down at room temperature and nitrogen backfill, solid samples were heated and monitored for 2 weeks at 65°C. Moisture outgassing occurred mainly in the first 10–20h, reaching approximately 50–70ppm (parts water per million parts LX-17). The total pressure exceeded the water vapor partial pressure, indicating that outgassing of other species occurred. Good agreement (within an order of magnitude) with previous moisture outgassing studies on TATB-based materials was demonstrated. In addition, the data appeared to validate use of a recently developed kinetic model for predicting moisture outgassing rates of solid TATB formulations.

The effect of the partial pressure of water vapor on the surface tension of the liquid water–air interface

Precise measurements of the surface tension of water in air vs. humidity at 5, 10, 15, and 20°C are shown. For constant temperature, surface tension decreases linearly for increasing humidity in air. These experimental data are in good agreement with a simple model based on Newton’s laws here proposed. It is assumed that evaporating molecules of water are ejected from liquid to gas with a mean normal component of the speed of “ejection” greater than zero. A high humidity in the air reduces the net flow of evaporating water molecules lowering the effective surface tension on the drop. Therefore, just steam in air acts as an effective surfactant for the water–air interface. It can partially substitute chemical surfactants helping to reduce their environmental impact.

An electrochemical method for high accuracy measurements of water transfer in fuel cells

A novel method for the high accuracy measurement of water transfer in differential polymer electrolyte fuel cells (PEFCs) is proposed. This method is based on the potential difference forming in a H2/H2 concentration cell in the presence of humidity differences between the electrodes. In the present work, the relation between the partial pressures of hydrogen and water vapor and the potential difference over the concentration cell are verified. Furthermore, a validation experiment allowed to confirm that the targeted accuracy of 0.25% for the differential humidity can be obtained with our method, making it suitable for the measurement of water transfer in small‐scale differential cells.

Effects of water vapour and oxygen partial pressures on low carbon steel oxidation in N2–H2–H2O mixtures

AbstractA low carbon, low silicon steel was oxidised at temperatures of 900–1000 °C in flowing N2–H2–H2O gas mixtures in which oxygen and water vapour partial pressures were varied independently. Scales of dense, single‐phase, coarse grained wüstite grew rapidly, according to parabolic kinetics. Both the scaling rate and the oxide grain growth increased with $p_{{\rm O}_{2} } $ at constant $p_{{\rm H}_{2} {\rm O}} $, and also with $p_{{\rm H}_{2} {\rm O}} $ at constant $p_{{\rm O}_{2} } $. An inert marker experiment showed that significant oxygen transport but majority metal transport supported scale growth. Gas composition effects are interpreted using point defect models involving formation of hydroxyl species on anion sites as well as cation vacancies.

Air Dehumidification with the Porous Hydrophobic Wall in Underground Tunnel

Air can be dehumidified with the porous hydrophobic wall in mostly underground tunnel in constant zone of subsurface temperature. For water vapor through the wall, it must produce a concentration difference between both sides of the wall. According to this principle, a test is done combined with repair works on an underground tunnel. The hydrophobic porous mortar is scraped on geotextile, which is pasted on the painted original tunnel wall as hydraulic conductivity layer where vapor condense and water flow away. It is recognized that temperature and mass transfer rate is relative to tunnel air velocity, air temperature and partial pressure of water vapor, the temperature in constant zone of subsurface temperature and the saturated water vapor partial pressure. Comparative test results show that the condensation dew on the wall is disappeared completely, the wall dehumidifies air effectively, and saving dehumidifier power is more than 50% in normal humidity range.

The influence of heat treatment parameters on pyrolysed TFA-derived YBCO films deposited by inkjet printing

An anhydrous TFA-derived YBa2Cu3O7−δ precursor solution was deposited on all chemical solution deposition fully buffered metallic tape by means of electromagnetic drop-on-demand inkjet printing and pyrolysed in a flowing wet O2 atmosphere. The influence of the annealing temperature and time, the gas flow rate and water vapour partial pressure on phase formation, and the morphology and superconducting performance of the resulting film, were investigated. It was found by scanning Hall probe magnetometry that reproducible superconducting films with a critical current density of 0.18MA/cm2 can be produced after annealing for 2h at 728°C, without metal substrate oxidation, in a flowing 200ppm O2 in Ar atmosphere with 31mbar water vapour partial pressure.

Comparison of the Characteristics of Small Commercial NDIR CO2 Sensor Models and Development of a Portable CO2 Measurement Device

Many sensors have to be used simultaneously for multipoint carbon dioxide (CO2) observation. All the sensors should be calibrated in advance, but this is a time-consuming process. To seek a simplified calibration method, we used four commercial CO2 sensor models and characterized their output tendencies against ambient temperature and length of use, in addition to offset characteristics. We used four samples of standard gas with different CO2 concentrations (0, 407, 1,110, and 1,810 ppm). The outputs of K30 and AN100 models showed linear relationships with temperature and length of use. Calibration coefficients for sensor models were determined using the data from three individual sensors of the same model to minimize the relative RMS error. When the correction was applied to the sensors, the accuracy of measurements improved significantly in the case of the K30 and AN100 units. In particular, in the case of K30 the relative RMS error decreased from 24% to 4%. Hence, we have chosen K30 for developing a portable CO2 measurement device (10 × 10 × 15 cm, 900 g). Data of CO2 concentration, measurement time and location, temperature, humidity, and atmospheric pressure can be recorded onto a Secure Digital (SD) memory card. The CO2 concentration in a high-school lecture room was monitored with this device. The CO2 data, when corrected for simultaneously measured temperature, water vapor partial pressure, and atmospheric pressure, showed a good agreement with the data measured by a highly accurate CO2 analyzer, LI-6262. This indicates that acceptable accuracy can be realized using the calibration method developed in this study.

Investigation on Proton Conductivity of La2Ce2O7 in Wet Atmosphere: Dependence on Water Vapor Partial Pressure

AbstractThe AC conductivity of fluorite‐structured La2Ce2O7 ceramic was measured under air and argon with different humidity between 250 and 550 °C. It was observed that the total conductivity in wet air and argon was higher than that under dry atmospheres. The effect of water vapor partial pressure ($ {P_{\rm {H_2{\rm O}}}} $) on the conductivity of La2Ce2O7 in air was investigated in detail. The total conductivity increased remarkably with the water vapor partial pressure, and this phenomenon became more notable at lower temperatures. The enhancement of the conductivity was attributed to the proton conduction behavior of La2Ce2O7 in wet atmospheres, and the proton conductivity reached 6.68 × 10–5 S cm–1 in wet air (3% H2O) at 550 °C. The relationship between the proton conductivity (σH) and $ {P_{\rm {H_2{\rm O}}}} $ in wet air could be fitted to $ \sigma_{\rm H} \propto {P_{\rm {H_2{\rm O}}}^{1/2}} $. The estimated proton transport number increased with increasing water vapor partial pressure and decreasing temperature, and varied between 0.05 and 0.89 in this study.

The roles of temperature and water vapor at different stages of the polar mesospheric cloud season

Temperature, or alternatively, saturation vapor pressure (PSAT), dominantly controls the polar mesospheric cloud (PMC) seasonal onset and termination, characterized by a strong anticorrelated relationship between the Solar Occultation for Ice Experiment (SOFIE)‐observed PMC frequency and PSAT on intraseasonal time scales. SOFIE is highly sensitive to weak clouds and can obtain a nearly full spectrum of PMCs. Both the SOFIE PMC frequency and PSAT indicate a rapid onset and termination of the season. Compared to PSAT, the water vapor partial pressure (PH2O) exhibits only a slight increase from before to after the start of the season. We are able to use the PSAT daily minimum and two averaged PH2O levels taken before and after the solstice, respectively, to estimate the start and end days of the PMC season within 1–2 days uncertainty. SOFIE ice mass density and its relationship to PH2O and PSAT are examined on intraseasonal scales and for two extreme conditions, i.e., strong and weak cloud cases. In the strong cloud case, such as those bright clouds that occur during the core of the season, PH2O far exceeds PSAT and dominantly controls the ice mass density variation, while in the weak cloud case, such as those clouds that occur at the start and end of the season, PH2O and PSAThave comparable magnitudes, vary in concert, and have similar effects on the ice mass density variation. These results suggest that the long‐term brightness trends reported by DeLand et al. (2007) are primarily driven by changes in water vapor (H2O), not temperature.

50 mol% indium substituted BaTiO3: Characterization of structure and conductivity

BaTi0.5In0.5O3−δ was prepared by solid state reaction at 1400 °C. Rietveld analysis of high resolution X-ray powder diffraction data indicated phase pure as-prepared material that adopts a cubic perovskite structure with a = 4.1536(1) Å. Thermogravimetric analysis revealed the presence of significant levels of protons in the as-prepared material and 57% of the theoretically achievable protonation was attained on exposure to a humid environment at 185 °C. After hydration the cell parameter increased to 4.1623(1) Å. Electrical conductivity was measured both with fixed and variable frequency ac impedance methods as a function of temperature, oxygen-, water vapour- and heavy water vapour partial pressures. In the temperature range 400–800 °C a slight increase in the total conductivity with increasing oxygen partial pressure is encountered, characteristic of a contribution from p-type charge carriers. The effect of the water vapour pressure on conductivity below 600 °C is much more prominent indicative of dominant proton conduction. At 300 °C the total conductivity in wet O2 was estimated to be 9.30 × 10−5 S/cm. At T > 800 °C the material is a pure oxide ion conductor.

The precision of humidity in GNSS tomography

The GNSS signal passing through the layers of the atmosphere, including troposphere is subjected to many effects. One of the effect is a change of signal phase propagation speed due to the change of density. The large fluctuation of density is due to water vapor content - the most important greenhouse gas. The ground GNSS tomography is a tool to obtain the wet refractivity of the discrete model above the network of receivers. The wet refractivity could be converted into water vapor partial pressure, using the additional temperature information. This paper presents rigorous approach to obtain uncertainties of the final product - water vapor partial pressure in the voxel. All factors influencing the final uncertainty has been taken into account, mainly uncertainty of: Zenith Troposphere Delay, pressure, antenna phase center height, satellite elevation angle, mapping function, tomography solution and temperature. The analyzed error budget shows, great influence of cofactor matrix topology on tomography solution uncertainty. It is also shown that ground GNSS tomography is feasible to obtain water vapor partial pressure in the troposphere up to 0.5hPa so in average 6km above the ground.

VUV lamp based on mixtures of inert gases with water molecules pumped by a pulsed-periodic capacitive discharge

The spectral characteristics of the emission in the 140-315 nm range from pulsed-periodic capacitive discharges in mixtures of water vapor and helium and argon are described. In the VUV the most intense bands have maxima at λ = 156.0, 180.3, and 186.0 nm, and in the region of 300–315 nm, at λ = 312.1 and 313.4 nm. The brightness of the emission from the capacitive discharge plasma is optimized with respect to the partial pressures of helium, argon, and water vapor. The electron kinetic coefficients of discharges in argon and water vapor mixtures are calculated for E/N = 1–1000 Td.