Water Adsorption Experiments Research Articles

Study on water uptake of proton exchange membrane by using tritiated water sorption method

It is recognized that the behavior of water in the proton exchange membrane (PEM) is to be understood to optimize the performance of the proton exchange membrane fuel cell (PEMFC). It is considered by the present authors that a certain amount of structural water exists besides adsorbed water in the film of PEM. The structural water represents any chemically adsorbed water, crystal water and some chemical groups containing hydrogen which are strongly connected with the structure. Accordingly, the amount of structural water cannot be measured by the water adsorption method because the amount of structural water does not depend on the vapor pressure. The amount of adsorption together with the amount of structural water is measured in this study by using the tritiated water sorption method where the isotope exchange reaction between tritium in water vapor and hydrogen in structural water makes it possible to quantify the structural water. The observed values for the total amount of uptake water, which includes the structural water, is 0.45–0.57 (g H 2 O/cm 3 PEM) at the room temperature. This value is about 1.5 times larger than the amount reported so far from the water adsorption experiments. The permeation behavior of hydrogen, oxygen and helium through the film of PEM is also measured in this study and change of partial pressure of hydrogen or oxygen in PEMFC at stop of the fuel flows is estimated.

Effects of ultrasound on zeolite A synthesis

Synthesis of zeolite A from a clear-to-the-eye sodium aluminosilicate solution was carried out in the presence of ultrasound at different temperatures and times and the results were compared to those obtained by performing conventional static syntheses under similar conditions. It was possible to obtain highly crystalline zeolite A in the presence of ultrasound, which influenced the types and stability areas of the phases that formed during metastable phase transformations. Nucleation and crystallization rates, as well as the yield of zeolite A increased as a result of the application of ultrasound. Thermogravimetric analyses and water adsorption experiments revealed that the development of micropore adsorption capacity, which started very early in the X-ray amorphous samples obtained from this so-called “clear” solution, was also speeded up with the application of ultrasound.

Adsorption Characteristics of Lead-, Barium- and Hydrogen-Rich Clinoptilolite Mineral

The carbon dioxide and water vapour adsorption properties of local clinoptilolite-rich material, both as the original and as lead-, barium- and hydrogen-rich forms, were examined. The lead- and barium-rich forms were prepared by treatment of the original clinoptilolite with Pb(NO3)2 and BaCl2 respectively, while the hydrogen-rich form was prepared by NH4Cl and heat treatment. Water and CO2 adsorption experiments were conducted in a volumetric system under static conditions, with low-pressure adsorption data being used for the characterization of the natural, Pb-rich, Ba-rich and H-rich clinoptilolite samples. Although the existence of barium-exchange was not noted, an appreciable decrease in CO2 adsorption was observed with the Pb-rich and H-rich forms due to a decrease in the electrostatic interaction between the surface and the adsorbate. Application of the Dubinin–Astakhov equation to the water adsorption data established the existence of micropores of different sizes that exhibited different adsorption mechanisms.

Preparation and characterization of hydrophobic calcium hydroxyapatite particles grafting oleylphosphate groups

Grafting of oleylphosphate (OP) molecules to the surface of calcium hydroxyapatite particles (HAP) was carried out by a coprecipitation method with a Ca(OH) 2–H 3PO 4 system in the presence of disodium oleylphosphate (DSOP). All the particles exhibited a single-crystal nature with rod-like shape and were elongated along c-axis from 36 to 122 nm in particle length with an increase in the concentration of DSOP. It was suggested that 0∼84% of the phosphate ions exposed on the ac or bc faces of the HAP particles are exchanged with phosphate ions of DSOP molecules directing oleyl groups outward. The hydrophobicity of OP-grafted HAP particles was enhanced with an increase in the DSOP concentration. This high surface hydrophobicity was further confirmed by water adsorption experiments. The materials with the surface oleyl groups adsorbed much less water than the HAP particles produced without DSOP.

CVD of silica on a palladium-loaded zeolite: a method of cancelling activity retardation by water vapor in the reduction of NO

The activity of NO reduction with methane in the presence of oxygen on Pd/HZSM-5 is suppressed by the addition of water vapor: however, it is recovered by the deposition of silica on the zeolite by the chemical vapor depositon of Si(OCH 3) 4. It was found from a transient experiment that water vapor retarded the activity both reversibly and irreversibly. The irreversible deactivation for NO reduction was similar to that in the oxidation of methane. The irreversible retardation of methane oxidation was caused by the deactivation of palladium due to water vapor in the presence of oxygen. A water adsorption experiment showed that the equilibrium amount of adsorbed water was reduced by the deposition of silica on the external surface. Based on these experimental findings, a scheme of the deactivation of Pd by the presence of water and a recovery of activity by the deposited silica is proposed.

Adsorption and Desorption Behavior of Tritiated Water on the Piping Materials

The behavior of tritium on the surface of various piping materials must be investigated for establishment of the safety confinement technology of tritium or for development of the effective fuel handling technology in a D-T fusion reactor, because tritiated water or gaseous tritium is captured on the piping surface through adsorption or isotope exchange reaction. The present authors carried out the water adsorption and desorption experiments on 304 stainless steel, copper, and aluminum in the temperature range from 5 to 100°C and in the partial pressure range of water vapor between 11.8 and 198Pa using a breakthrough method and quantified the amount of water adsorbed and the overall mass transfer coefficients in adsorption and desorption of water. It was observed in this study that aluminum adsorbed more water than stainless steel or copper. It was also observed that the adsorption and desorption rates of water for three materials showed almost the same values. The breakthrough behavior of tritiated water in a 100 m pipe of stainless steel was also evaluated applying the results of this work. It is concluded that water adsorption and desorption reactions influence the behavior of tritiated water in the piping system under the condition where the partial pressure of tritiated water vapor is lower than several pascals.

Adsorption and Desorption Behavior of Tritiated Water on the Piping Materials.

The behavior of tritium on the surface of various piping materials must be investigated for establishment of the safety confinement technology of tritium or for development of the effective fuel handling technology in a D-T fusion reactor, because tritiated water or gaseous tritium is captured on the piping surface through adsorption or isotope exchange reaction. The present authors carried out the water adsorption and desorption experiments on 304 stainless steel, copper, and aluminum in the temperature range from 5 to 100°C and in the partial pressure range of water vapor between 11.8 and 198Pa using a breakthrough method and quantified the amount of water adsorbed and the overall mass transfer coefficients in adsorption and desorption of water. It was observed in this study that aluminum adsorbed more water than stainless steel or copper. It was also observed that the adsorption and desorption rates of water for three materials showed almost the same values. The breakthrough behavior of tritiated water in a 100 m pipe of stainless steel was also evaluated applying the results of this work. It is concluded that water adsorption and desorption reactions influence the behavior of tritiated water in the piping system under the condition where the partial pressure of tritiated water vapor is lower than several pascals.

Absolute Moisture Content Determination of Aspen Wood Below the Fiber Saturation Point using Pulsed NMR

Abstracting & Indexing

The preparation and properties of some activated carbons modified by treatment with phosgene or chlorine

Treatment of coal or coconut shell activated carbons with either phosgene or chlorine at 180°C followed by washing with methanol or water results in chlorinated carbons with very similar pore structures to their precursors. Water adsorption experiments show that the modified materials are relatively Hydrophobic, presumably as a result of replacement of oxygen-containing surface groups by chlorine. Adsorption of the model hydrophobic vapour chloropicrin from humid air is usually better for the modified carbons which, unlike the controls, do not appear to be subject to degradation in performance on ageing in a humid atmosphere. The stability of the modified carbons is probably a consequence of the chlorination of those sites on the control carbons that are prone to ready oxidation or hydroxylation.

Protonic conductivity in hydrates

The protonic conductivity of three acid hydrates, HUO 2PO 4·4H 2O, Ce(HPO 4) 2· nH 2O,V 2O 5· nH 2O has been studied as a function of the partial pressure of water. The evolution of their conductivity is related to experimental water adsorption isotherms and to the theoretical Brunauer adsorption isotherms. Conclusions can then be drawn about the origin of the conductivity (bulk-type or surface conductivity) and about the type of water molecules involved in the protonic diffusion process. These three compounds are each representative of a different class of protonic conductors, the lattice hydrates, the particle hydrates, and the swelling hydrates respectively.

The sedimentary cycle of the boron isotopes

Abstract Marine sediments contain two isotopically distinct components: a non-desorbable fraction with δ11B between −4.3 and +2.8 per mil (n = 10) and a desorbable component with δ11B between 13.9 and 15.8 per mil (n = 6). The adsorption coefficient, K, for the uptake of B from seawater by fluvial suspended material (Mississippi) has an experimentally determined value of 1.54 ± 0.05. The associated isotope fractionation factor, α, is 0.974 ± 0.003. Empirical values for K, determined from the analysis of marine sediments (n = 6), were between 3 and 4. The amount of B adsorbed onto fluvial suspended material during estuarine mixing is about 9 × 109 moles/yr. Based on pore water data, adsorption experiments and comparative size fraction analyses (suspended sediments from the Mississippi River vs. bottom deposits from the Delta) there is no evidence for the incorporation of B into detrital sediments at low temperature. However, the high B content of Bauer Deep metalliferous sediments must be due to incorporation of seawater B during formation of authigenic silicates. The δ11B of these minerals is 2 ± 3 per mil. Hydrothermally altered sediments from DSDP Hole 477, Guaymas Basin, Gulf of California have variable B contents, from 33 ppm, similar to the unaltered detritus, to 1.2 ppm in the recrystallized material. The latter has δ11B as low as −9.0 per mil, substantially lower than the unaltered material. Hydrothermal solutions collected from vents adjacent to the hole have boron contents elevated by about a factor of 4 relative to seawater and δ11B between 16.5 and 23.2 per mil. The B mobilized from the sediments is isotopically fractionated with the fluids being preferentially enriched in the heavy isotope. Analysis of an oxisol profile developed over granite in the Guyana Shield showed that boron is partially mobilized during weathering with an isotopic offset of 2.5 per mil between bedrock and soil. The observed enrichment of B in shales relative to igneous rocks does not occur during weathering or during exposure to seawater at low temperature. Incorporation occurs only during burial diagenesis at temperatures greater than about 60°C. However, the enrichments cannot be attained during a single cycle of primary weathering and burial but must be cumulative over many cycles.

The hydration of phospholipids and phospholipid-cholesterol complexes

The hydration characteristics of phosphatidylcholines and the effect of cholesterol on these were studied with differential thermal analysis and water vapour adsorption experiments. Also the water adsorption of egg phosphatidylethanolamine and the effect of cholesterol on this was studied and compared with corresponding qualities of phosphatidylcholine. The differential thermal analysis study showed that the monohydrates of egg, dipalmitoyl, and dioleoyl phosphatidylcholine tightly bind ∼9 molecules of water per phosphatidylcholine molecule. Cholesterol is proved to somewhat increase the water binding of the phospholipids. Cholesterol is also shown to decrease the heat change of the chain melting transition of dioleoyl phosphatidylcholine, but not to abolish it completely. The water adsorption experiments indicate that the hydration of phosphatidylcholines takes place in two steps; a strong initial water binding and a second phase of weak binding. The adsorption isotherm of egg phosphatidylethanolamine is strikingly different from that of egg phosphatidylcholine. Cholesterol is shown, also by this method, to increase the hydration of phospholipids especially that of dipalmitoylphosphatidylcholine. The results in this study are in good agreement with those presented by many other authors. Starting with the accumulated information of the hydration characteristics of phosphatidylcholines the organization of the bound water around the polar group is discussed and the most probable model is evaluated.