Bochum, Germany
Bochum, Germany

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Schanz T.,Ruhr University Bochum | Schanz T.,Universitatsstr | Baille W.,Ruhr University Bochum | Baille W.,Universitatsstr | And 2 more authors.
Geotechnical Testing Journal | Year: 2011

This paper analyses the effects of temperature on the quantification of soil water content by means of time domain reflectometry (TDR) method. For this purpose, the dielectric constant of soil specimens with known water content was measured at different temperatures in a range of 20-80°C. The soil types used in the present study were fine sand, sand-bentonite mixture (SBM), and sandy loam. For each soil type, the dielectric constant of at least three specimens having identical dry density but varying initial water content was measured at temperatures ranging from 20 to 80°C. The results obtained agree with previous studies showing that there are two competing phenomena during the measurement of soil water content by means of TDR: (i) The soil bulk dielectric constant increases with increasing temperature due to the release of bound water from soil solid particles and (ii) the soil bulk dielectric constant decreases with increasing temperature due to the temperature effect of free water molecules. Moreover, it has an existing equilibrium water content at which both competing phenomena compensate each other. However, for the SBM no equilibrium water content was found, but the dielectric constant increased significantly with the temperature for the whole water content range. This can be explained by the significant clay content and the high specific surface area, which leads to a dominating effect of the increase of soil bulk dielectric constant with increasing temperature. Copyright © 2011 by ASTM International.

Taffner T.,Helmut Schmidt University | Niemeyer B.,Helmut Schmidt University | Puls A.,Universitatsstr | Dreisbach F.,Universitatsstr
Open Chemical Engineering Journal | Year: 2012

Nowadays sustainable technologies gain in importance. A promising field of activity is the exhaust air treatment by adsorption, especially the removal and recovery of valuable substances like solvents. In this letter three types of adsorbents, being the critical part in technical separation processes by adsorption, are evaluated according to separation of isopropanol from humid air. Isopropanol has been chosen as it is one of the frequently used solvents which need to be separated from humid air in practice. The suitability and performance as well as information about the possible constraints are derived from state of the art measurements and multifaceted analyses of the experimental data. The evaluation is based on physical data, isotherms at different temperatures and for both components, isopropanol and water, as well as on energetic calculations and comparison with values from recent literature. © Täffner et al.

PubMed | Universitatsstr
Type: Journal Article | Journal: Pharmaceutical research | Year: 2013

The adsorption behavior of cationic aggregating substances such as antimicrobial quats or phenothiazine derivatives on silica surfaces in aqueous media has been extensively investigated. However, the chemical stability of adsorbates in such systems was unknown. Propantheline bromide (PPBr) was selected as a model to investigate the stability of hydrolyzable substances in silica-containing aqueous dispersions or in adsorbates on silica carriers used for solid drugs. The quaternary ester PPBr showed an appreciable adsorption on the silica surface, the extent of which was increased by raising the pH of the aqueous phase or by the addition of neutral salts such as NaNO3. In parallel to the adsorption process, hydrolysis of PPBr occurs in these aqueous silica dispersions to yield xanthene carbonic acid and a quaternary alcohol component. Adsorption and hydrolysis were found to be mutually influencing reactions. Because of the adsorption of PPBr, the rate of ester decomposition was enhanced in these silica dispersions when compared to aqueous solutions of PPBr at the same pH. Simultaneously, an increase in PPBr adsorption is observed, as well as adsorption of the decomposition product xanthene carbonic acid. This result can be attributed to ion-pair adsorption of the latter with PPBr. The rate constants of PPBr decomposition were found to depend directly on the silica content of the dispersion, although at higher concentrations a decreased catalytic effect was observed. These phenomena are discussed on the basis of the adsorbate structure and exchange processes.

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