Pure Water Vapor Research Articles

Comparison between Current Methods for Measurement of High Temperature Corrosion of Boiler Steels in Steam Environments

Thirteen boiler steels were exposed in pure water vapour at 650°C for 32 weeks (5,376h). To assess their oxidation kinetics, four current discontinuous measurement methods were used. The results show that, for the T91 steel, the different investigated methods give similar results; for the other steels, the evaluation of corrosion rates depends on the method used. Thus their lifetime prediction is often over- or undervalued. This is mainly the case for steels with scales that spall off and/or steels with a non-uniform scale growth (localised oxide nodules for a rather long exposure time). This is particularly true in the steam environments which lead to oxidation processes with oxide scales different from those in dry air or oxygen. So the use of steam oxidation data and/or relations among them has to be done with caution because it can lead to a wrong prediction of performance.

A potential new method for determining the temperature of cool stars

We present high resolution (R = 90,000) mid-infrared spectra of M dwarfs. The mid infrared region of the spectra of cool low mass stars contain pure rotational water vapour transitions that may provide us with a new methodology in the determination of the effective temperatures for low mass stars. We identify and assign water transitions in these spectra and determine how sensitive each pure rotational water transition is to small (25 K) changes in effective temperature. We find that, of the 36 confirmed and assigned pure rotational water transitions, at least 10 should be sensitive enough to be used as temperature indicators.

The solubility of molybdenum dioxide and trioxide in HCl-bearing water vapour at 350 °C and pressures up to 160 bars

The solubility and speciation of the assemblage MoO 2–MoO 3 in water vapour were investigated in experiments conducted at 350 °C, P total from 59 to 160 bar and fHCl from 0 to 3.4 bar (0–2.0 mol%). Measured solubility at these conditions ranges from 22 to 2500 ppm (∑ fMo from 4.4 × 10 −4 to 6.5 × 10 −2 bar). The concentration of Mo in the vapour at fHCl below 0.1 bar is similar to that in pure water vapour, but increases by two orders of magnitude at fHCl above 0.1 bar. The fugacity of gaseous Mo species is independent of chloride concentration at fHCl below 0.1 bar, but increases with increasing fHCl above this pressure. The dominant Mo species at fHCl below 0.1 bar is interpreted to be the same as it is in pure water vapour, and to form as a result of the reaction (A1) MoO 3 ( s ) + n H 2 O ( g ) ⇔ MoO 3 · n H 2 O ( g ) where the hydration number, n, is equal to 2.3. The value of log K for reaction ( A1), which was calculated at 350 °C and 1 bar of total pressure, is −7.1. The dependence of ∑ fMo on fHCl at higher acidity points to the formation of the Mo oxychloride, MoO 2Cl 2, via the reaction (A2) MoO 3 ( g ) + 2 HCl ( g ) + ⇔ MoO 2 Cl 2 ( g ) + H 2 O ( g ) The observed change in Mo speciation from hydrated oxide to oxychloride with increasing fHCl may explain the variable association of molybdenite with either sericitic or potassic alteration in porphyry Mo ore deposits.

Water diffusion through hydrogel membranes: A novel evaporation cell free of external mass-transfer resistance

A novel evaporative cell is used to measure steady-state gradient-driven diffusion rates of water through hydrogel membranes in the absence of external mass-transfer resistance. In this cell, the bottom surface of a hydrogel membrane is exposed to pure water vapor at known activity ( a w) less than unity, while a sealed liquid-water reservoir bathes the upper membrane surface. Induced by the chemical-potential gradient between the two surfaces, the water evaporation rate is monitored by the rate of weight loss of the water reservoir. Results at ambient temperature are compared with those from measured water flux through soft-contact-lens (SCL) materials and with other published experimental results. Concentration-dependent water diffusivities are obtained by interpreting measured water fluxes for 0.11 ≤ a w ≤ 0.93 with extended Maxwell–Stefan (EMS) diffusion theory. Thermodynamic non-ideality is taken into account through Flory–Rehner polymer–solution theory. Shrinking/swelling is modeled by conservation of the total polymer mass assuming volume additivity. In spite of correction for thermodynamic non-ideality, EMS–water-diffusion coefficients increase with the water volume fraction, especially strongly for those hydrogel materials with low liquid-saturated water contents. The evaporation cell described here provides a simple robust method to establish water transport rates through soft-contact-lenses and other hydrogel membranes without the need to correct for external mass-transfer resistance.

Low-uncertainty H 2O line intensities for the 930-nm region

We measured room-temperature H 2O spectra of the 3 ν polyad within the wave number range 10 603 cm −1 to 10 852 cm −1 using frequency-stabilized cavity ring-down spectroscopy. More than 70 transitions, divisible into two groups based on their relative intensities (strong and weak) were investigated. For the 23 lines comprising the set of strong transitions, the water vapor sample was prepared as a dilute mixture in a steady flow of N 2 carrier gas, and the measurement of the water vapor sample number density was linked to primary methods of humidity generation. For these strong transitions, the measured line intensities were within 1% of previous measurements. The line intensity measurements of the weaker H 2O transitions, were made on samples of static pure water vapor, and these results were systematically greater than previous measurements by approximately 20%.

A comparative study of zirconia and alumina supported Pt and Pt–Sn catalysts used for dehydrocyclization of n-octane

Abstract Alumina and zirconia supported Pt and Pt–Sn catalysts have been tested in the dehydrocyclization (DHC) of n-octane at 823 K to alkylaromatics as desired products using pure hydrogen (H2) and water vapour containing hydrogen (WVH2) atmospheres. The materials were characterized by nitrogen adsorption, NH3-TPD, TPR, XRD, XPS, TEM and EDX. The characterization results reveal the formation of PtSn alloys on alumina support after a catalyst precursor reduction in H2 at 873 K. This observation enables an interpretation of the higher on-stream stability of Pt–Sn/Al2O3 catalyst in H2 as well as in WVH2 compared to the monometallic sample, using the well-known concept of the ensemble effect of Sn by alloying to Pt. The alumina supported Pt and Pt–Sn catalysts act bifunctionally in H2 atmosphere, producing a mixture of benzene, mono- and dialkylaromatics, near the chemical equilibrium. In WVH2 atmosphere, however, o-xylene and ethylbenzene are predominant among the aromatic products, indicating a monofunctional action mode of the catalyst. Independent of the reaction atmosphere, the zirconia supported Pt and Pt–Sn catalysts act monofunctionally with o-xylene and ethylbenzene as predominating products among the aromatics produced. The zirconia supported samples are more stable in WVH2 than in H2 atmosphere. The addition of Sn significantly increases the activity of that catalyst but does not retard its deactivation in H2. The formation of PtSn alloys is not evidenced in the Pt–Sn/ZrO2 catalyst after hydrogen treatment. The behaviour of the zirconia supported catalysts can be interpreted considering the weak-acidic character of the support and its interactions with Pt as well as with SnO2.

Photoelectrochemical Study of Oxides Thermally Grown on Titanium in Oxygen or Water Vapor Atmospheres

Titanium oxide thin scales isothermally grown at on titanium metal in pure oxygen, pure water vapor, or water vapor/oxygen mixtures were submitted to room temperature photoelectrochemical characterization (PEC) to assess the nature of oxides in function of the composition of the oxidizing atmosphere. The results indicated that minor lower valency oxides were present in addition to rutile, of which the bandgap energy was experimentally determined to be . As bandgap energies of and have not been reported in the literature, an empirical model relating bandgap energy and reticular enthalpy was revisited and adapted to the case of oxides. From photoelectrochemical measurements on thermal oxides, new bandgap values of for and for were obtained, correctly matching the empirical model. High sensitivity of the technique was demonstrated as these phases could be identified by PEC on samples grown in oxygen, where classical techniques of characterization like X-ray diffraction could not detect them. They were observed in larger amounts on samples grown in the presence of water vapor, showing closer metal-oxide equilibrium during thermal oxidation.

Water line parameters from refitted spectra constrained by empirical upper state levels: Study of the 9500– [formula omitted] region

A fitting technique is proposed which gives more reliable spectral line parameters for blended and very weak lines. The technique uses common upper state energies to fix frequencies in cases where these are poorly determined. Room temperature Fourier Transform absorption spectra of pure water vapour due to Schermaul et al. [The water vapour spectrum in the region 8600– 15 , 000 cm - 1 : experimental and theoretical studies for a new spectral line database I: laboratory measurements. J Mol Spectrosc 2001;208:32–42; The water vapour spectrum in the region 8600– 15 , 000 cm - 1 : experimental and theoretical studies for a new spectral line database I: laboratory measurements. J Mol Spectrosc 2002;211:169–78] recorded at several pathlengths are refitted. Parameters are obtained for over 10,700 transitions of H 2 O 16 covering the frequency region 9500– 14 , 500 cm - 1 . Only 73 of the lines remain unassigned. Comparisons with previous studies on water vapour absorption in this region suggest that the new parameters give a more consistent representation of the underlying spectrum.

Passivation and oxidation of an ammonia iron catalyst

A process of ammonia iron catalyst passivation and oxidation with oxygen and water vapour was investigated by thermogravimetry, Mössbauer spectroscopy and X-ray diffraction. The optimal passivation conditions (T ≤ 100 °C, pO2≤0.0013bar) have been proposed. The thickness (0.9–1.1 nm) and the structure (paramagnetic Fe2O3) of a protective, passive layer have been determined. It was found that oxidation of a reduced catalyst with pure oxygen (pO2=1bar) and water vapour (pH2O=0.023bar) did not lead to its passivation. The oxidation with pure oxygen, at temperatures above 250 °C, led to a creation of magnetite layer with built-in aluminum oxide. The thickness of the magnetite layer decreased and the amount of the built-in aluminum oxide grew along with the increase of oxidation temperature. An adsorption model has also been introduced for the interpretation of oxidation with water vapour: the whole iron nanocrystallites were oxidized successively from the smallest to the largest ones, and the oxidation process was limited by dissociative adsorption of water vapour on the iron surface.

High-resolution cavity ring-down spectroscopy measurements of blended H2O transitions

We probed four closely spaced rovibrational water vapor absorption transitions near $\tilde{\nu}$ =7100 cm-1 using frequency-stabilized cavity ring-down spectroscopy. Room-temperature spectra were acquired for pure water vapor in the Doppler limit and for mixtures containing ≈6.6 μmol mol-1 of water vapor in N2 at total gas pressures ranging from 6.5 kPa to 53 kPa. By measuring Lamb dips for each transition, we demonstrated a resolution of 50 kHz and determined relative transition frequencies with an uncertainty <0.4 MHz over a 10 GHz range. Pressure-induced broadening, collisional narrowing coefficients of the component transitions and line areas were retrieved by fits of model line shapes to the measured spectra. Standard and advanced models were considered including those which incorporated the combined effects of collisional narrowing and speed-dependent line broadening and line shifting. By measuring water vapor concentration with a transfer standard hygrometer, we determined line intensities in terms of measured line areas with a combined relative uncertainty of 0.6%.

Monte Carlo simulations of equilibrium solubilities and structure of water in n-alkanes and polyethylene

Gibbs ensemble Monte Carlo methods based on a force field that combines the simple point charge [Berendsen et al., in Intermolecular Forces, edited by Pullman (Reidel, Dordrecht, 1981), p. 331] and transferable potentials for phase equilibria [Martin and Siepmann, J. Phys. Chem. B 102, 2659 (1998)] models were used to study the equilibrium properties of binary systems consisting of water and n-alkanes with chain lengths from hexane to hexadecane. In addition, systems where extended linear alkane chains (up to 300 carbon units long) were used to represent amorphous polyethylene were simulated in the presence of water using a connectivity altering osmotic Gibbs ensemble. In these simulations the equilibrium between a liquid water phase and a polymer phase into which water was inserted was studied. The predicted solubilities, which were determined between 350 and 550 K, are in good agreement with experiment, where experimental results are available, and the density of water molecules in the hydrocarbons is approximately 63% as high as in saturated water vapor under the same conditions. At the lower temperatures most of the water exists as monomers; increasing the temperature leads to an increase in the density of water in the alkane phase and hence in the fraction of molecules that participate in clusters. Dimers are the most prevalent clusters in all hydrocarbons and at all temperatures studied, and the fraction of clusters of given size decrease with increasing cluster size. A large fraction of trimers, tetramers, and pentamers, which are the cluster sizes for which topologies have been studied, are cyclic at low temperatures, but at higher temperatures linear structures predominate. The same properties are observed for pure water vapor clusters in equilibrium with the liquid phase, showing that the cluster topologies are not significantly affected by the surrounding hydrocarbon.

Pure water vapor continuum measurements between 3100 and 4400 cm−1: Evidence for water dimer absorption in near atmospheric conditions

Despite the potentially important role that water dimers may play in the Earth's energy balance, there is still a lack of firm evidence for absorption of radiation by dimers in near‐atmospheric conditions. We present results of the first high‐resolution laboratory measurements of the water vapor continuum absorption within the 3100–4400 cm−1 spectral region at a range of near‐room temperatures. The analysis indicates a large contribution of dimer absorption to the water vapor continuum, significantly in excess of that predicted by other modern representations of the continuum. The temperature dependence agrees well with that expected for dimers.

Thermodynamic properties of the LiCl–H 2O system at vapor–liquid equilibrium from 273 K to 400 K

A formulation of the thermodynamic properties of the LiCl–H 2O system at vapor–liquid equilibrium is presented in the form of separate Gibbs energy equations for the vapor and solution phases. Explicit thermodynamically consistent equations for density, isobaric heat capacity, enthalpy, entropy, enthalpy of dilution and osmotic coefficient are given. The pressure at vapor–liquid equilibrium is calculated from the condition of phase equilibrium. The description of the properties is valid from 273 K or from the crystallization line up to 400 K in temperatures and for solution composition from 0 to 50 wt% of LiCl in the solution, which is the region covewred by available experimental data. The thermodynamic properties of the gas phase are approximated by the properties of pure water vapor computed from the IAPWS formulation 1995. The Gibbs energy equation for solution is based upon a body of experimental data that have been critically assessed. Within the present study, 136 experimental works have been collected containing a total of 2921 data points on various thermodynamic properties of the LiCl–H 2O solutions. Gaps in the database are shown to give experimenters orientation for future research. The uncertainties associated with correlation are estimated to be ±0.4% for density, ±2.0% for pressure and ±2.4% for isobaric heat capacity. The uncertainty in values of enthalpy is estimated to be less than ±10 kJ kg −1 and less than ±0.03 kJ kg −1 K −1 for entropy. Values of the particular properties generated by the representative equations are provided to assist with the confirmation of computer implementation of the calculation procedure.

Ajuste de isotermas de sorção de sementes de cultivares de feijoeiro

É possível estabelecer uma relação entre o teor de água livre na semente e sua conservação, expresso pela atividade de água, através da relação entre a pressão de vapor de água em equilíbrio na semente e a pressão de vapor de água pura, à mesma temperatura. Uma isoterma é uma curva que descreve a relação de equilíbrio de uma quantidade de água sorvida por componentes da semente e a pressão de vapor ou umidade relativa, a uma temperatura específica. O objetivo deste trabalho foi estudar as isotermas de sorção para sementes de feijoeiro dos cultivares Tibatã e Una. Os graus de umidade das sementes foram ajustados, antes do armazenamento, em dessecadores com sílica gel ou através de reidratação sobre água. Para o controle da quantidade de água removida ou absorvida, as subamostras foram pesadas periodicamente, sendo o processo encerrado ao ser atingido o peso correspondente ao grau de umidade final desejado para cada tratamento. Foram realizadas determinações de umidade e de atividade de água e utilizados diferentes modelos de equações empíricas que correlacionam dados experimentais das isotermas de sorção em materiais biológicos. O melhor ajuste das isotermas de sorção foi alcançado pelos modelos de Oswin e Peleg para sementes de feijoeiro, cultivares Tibatã e Una, respectivamente.

In-situ fatigue in an environmental scanning electron microscope – Potential and current limitations

The present study provides a survey on in situ fatigue devices suitable for loading specimens in a scanning electron microscope (SEM). Particular emphasis is placed on the experimental methods employed to operate a small-scale load frame in an environmental SEM (ESEM). Specimen design and surface preparation, various modes of conducting the fatigue tests, specimen heating and imaging at elevated temperatures are considered. In addition, recent data from in situ fatigue studies conducted in an ESEM between room temperature and 600 °C are summarized. Fatigue tests conducted on AM60B cast magnesium demonstrate a substantial environmental effect on cyclic deformation and fatigue damage evolution even at room temperature. Fatigue behaviour of high-temperature titanium alloy IMI 834 at 400 °C illustrates a completely different effect of environment on slip band formation and crack nucleation as compared to AM60B. Investigations performed on IMI 834 at 600 °C reveal current limitations of the in situ fatigue technique applied. An approach to overcome these limitations is discussed. Ambient conditions can be simulated in an ESEM using pure water vapour atmosphere at a pressure similar to the partial pressure of the ambient environment. This is demonstrated for AM60B at room temperature and IMI 834 at 400 °C. However, this approach cannot necessarily be applied to all other material/environment combinations as is exemplarily shown for in situ fatigue loading of IMI 834 at 600 °C. Data obtained from in situ fatigue testing are compared to those from post-mortem SEM studies of failed specimens, which portray a wrong impression in certain cases. Experimental issues specific to environmental in situ testing at elevated temperatures are addressed as are the ramifications of such tests with respect to modelling of fatigue life.

Activation of organoclays and preparation of polyethylene nanocomposites

AbstractA dimethyl dihydrogenated tallow ammonium bentonite, edge modified with 1-hydroxydodecane-1,1-diphosphonic acid, was activated by intercalation of polyethylene-block-poly(ethylene glycol). A high-density polyethylene (HDPE) nanocomposite was produced by the gradual dilution of the intercalated organoclay with HDPE, via melt mixing, until a final clay concentration of 0.3 wt% was reached. While polymer crystallinity was unaffected by the addition of the clay, polymer transparency increased dramatically. Microscopic examination of compression molded films verified that polymer nucleation increased to such an extent that the normal spherulitic structure was completely absent. A significant reduction in gas transmission accompanied the increased film clarity. Compared to the pure polymer, oxygen and water vapor permeabilities were reduced by approximately 55 and 70%, respectively. With proper dispersion, significant improvements in both physical and barrier properties are achievable by the incorporation of nanoclays into polyolefins. Additionally, it is significant that these benefits can be realized at clay concentrations consistent with those of common polymer additives, like stabilizers, clarifiers, and colorants.

Fundamental studies of the cluster ion bombardment of water ice

The fundamental sputtering properties of water ice are of interest for molecular depth profiling of biological samples in their native environment. We report on a method of studying amorphous water ice films of precise thicknesses in which pure water vapor is condensed onto a pre-cooled, silver-coated quartz crystal microbalance (QCM). This scheme allows for the determination of water ice sputter yields for any primary projectile as well as providing a means for studying escape depths of atoms and molecules beneath the deposited water ice layer. Specifically, we find a removal of approximately 2500 water molecule equivalents/20 keV C 60 + projectile with an underlying silver ion escape depth of 7.0 Å.

Determination of an effective heat transfer coefficients for can headspace during thermal sterilization process

Heat transfer through can headspace was investigated using an inverse heat conduction problem (IHCP) approach. Solution for heat flux at the can headspace side was accomplished by using one dimensional heat conduction equation with one known boundary condition and internal temperature measurements. The estimation for the unknown heat flux at the headspace side was accomplished sequentially in time using the function specification algorithm. The accuracy of the estimated heat flux was investigated using the direct solution of the heat conduction equation employing the estimated heat flux to calculate the temperature distribution in the axial direction. From the knowledge of the calculated temperature at the sensor position and the experimental value the root mean square error (RMS) was calculated yielding a maximum value of 0.24 °C, this indicates the accuracy of the calculated heat flux. From the calculated heat flux and the surface temperature an effective heat transfer coefficients history was estimated for each of the three levels of headspace investigated (10%, 14% and 20% (v/v)). The calculated average effective heat transfer coefficients are 54.2, 53.2 and 50.8 W/(m 2 °C) for headspaces 10%, 14% and 20% (v/v), respectively. These values seem to be close due to presence of pure water vapor in the headspace with similar thermo-physical properties as dictated by phase equilibrium consideration resulting apparently in the same natural convection effects in the headspace. The technique used here could be useful for the estimation of an effective heat transfer coefficient for cases of water vapor gases mixture.

Modelling of water/organic vapor dehydration by glassy polymer membranes

Hydrophilic glassy polymers are suitable membranes for the dehydration of water/organic vapor mixtures. Vapor permeation is the predominant process for the dehydration of organic vapors employing glassy polymers. The permeation of vapor mixtures through this type of membrane is usually analyzed in terms of a dual-mode transport model which fails to predict well the separation behavior of a vapor mixture. The dehydration of organic vapor mixtures by glassy polymers was modeled using the Maxwell–Stefan formulation approach considering multicomponent thermodynamic and kinetic coupling effects. The model developed is a general one, applicable to all permeation processes for the separation of gaseous and vapor mixtures using a glassy polymer. The equilibrium sorption behavior of the vapor mixture was described by the dual-mode sorption model and the concentrationdependent diffusivities were recovered from sorption and permeation data. The experimental data available in the literature for sorption and permeation of pure ethanol and water vapor and their mixture through glassy polyvinylcholoride were used to examine the validity of the developed model. The results indicated that the model developed showed good predictability for mixed vapor permeation using the data from only pure component and also gave good information about the transport mechanism within the membrane.

FTIR in situ transmission studies on the kinetics of paper degradation via hydrolytic and oxidative reaction paths

This study deals with the quantitative and qualitative interpretation of transmission FTIR spectra of aged model paper samples to prepare the basis for a kinetic model of cellulose degradation involving mixed hydrolytic and oxidative mechanism. The ageing experiments were performed in situ under various conditions (pure water vapour, dried air, 100, 150 °C) to discriminate between hydrolytic and oxidative paths. Our focus was on the spectra between 1500–1900 cm-1, where the products of paper ageing appear in the form of various carbonyl groups. A procedure of spectra standardization was used to interpret the bands area in terms of the conversion of carbon atoms in cellulose. From the time evolution of the bands the overall kinetic curves were generated. The positions of the carbonyl bands were verified by independent experiments and theoretical calculations (DFT method). A simple model involving a hydrolytic reaction route and first order kinetics was positively tested on the available experimental basis.