Das dielektrische Verhalten an γ-Aluminiumoxyd sortierter Wassermolekeln

Ebert, G.; Langhammer, G.

doi:10.1007/bf01520369

Cited by 26 publications

(4 citation statements)

References 40 publications

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“…Dielectric analogues of both Langmuir and BET adsorption curves can be obtained on real rocks (Adamson 1982). It should be noted, however, that unlike adsorption curves, dielectric isotherms are sensitive not only to the water content, but also to the frequency of excitation (Ebert & Langhammer 1961).…”

Section: Experimental Data and Discussionmentioning

confidence: 99%

Electrical spectroscopy of porous rocks: a review-II. Experimental results and interpretation

1999

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In the frequency range from millihertz to hundreds of megahertz, many different physical and physico‐chemical processes contribute to the electrical polarization of porous water‐bearing rocks. This makes the interpretation of their electrical spectra a complicated problem and requires both elaborate theories and model experiments. At high frequencies, the Maxwell–Wagner–Bruggeman–Hanai (MWBH) theory of effective media, which takes into account only bulk properties, shape and partial volume of components, is very appropriate. At low frequencies, surface films, polarization of the electrical double layer (EDL) and clustering of conductive components can produce very strong polarization; corresponding theoretical models are considered in a companion paper (Chelidze & Gueguen 1999, hereafter referred to as Paper I). This paper is devoted to the review of experimental data and their comparison with theoretical models. Experiments on saturated mineral powders and rocks with various surface areas and surface chemistries confirm the existence of significant surface contributions to the electrical spectra of conductivity and polarization of water‐bearing rocks and the dominance of this contribution over MWBH values at low frequencies. The effective dielectric constant of porous saturated rocks increases with the surface‐to‐volume ratio of the system and strongly depends on the surface charge (ζ potential). At ζ potential, equal to zero, the low‐frequency dielectric permittivity (DP) is minimal. The experimental data on relaxation times and the magnitude of the surface polarization of water‐bearing porous systems can be satisfactorily explained by theories of film polarization, diffusional polarization generated by deformation of an ‘open’ electrical double layer (EDL) and percolation.

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Section: Experimental Data and Discussionmentioning

confidence: 99%

Electrical spectroscopy of porous rocks: a review-II. Experimental results and interpretation

1999

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“…The presence of amorphous ice or water with unusual structure in the surface layers is suggested by the dielectric measurements of Dransfield, Frisch, and Wood (22) and Ebert and Langhammer (13).…”

Section: Length Anomalies Below -50" Cmentioning

confidence: 97%

Phase Transitions of Water and Xenon Adsorbed in Porous Vycor Glass

Litvan¹,

McIntosh²

1963

Can. J. Chem.

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ABSTRACT1Ieasurements of the expansion of porous Vqcor glass containing fixed quantities of adsorbed water indicate that in every instance a phase transition starts belo\\ -50" C, with the main change occurring below -160" C. Two other anomalies of the length variation mere observed near -22" C and -7" C when the amount of adsorbed water exceeded the value equivalent to two monolayers. The length of the adsorbent after co~npletion of a temperature cycle was different from the initial length. This is thought to be due to damage suffered by the glass aiid t o the fact that the length of the adsorbent is different for adsorption and desorption although the quantity adsorbed may be the same.The phase transition of adsorbed xenon takes place below the normal triple point and is a function of surface concentration as shown by length variations and equilibrium pressures for fixed quantities adsorbed. All transitions are gradual aiid hysteresis is exhibited by the isosteres. The adsorption isotherms for xenon -I'ycor glass show a decreasing adsorptive capacity and a contraction of the hysteresis loop with lower temperature. The inadequacy of the capillary coildensation theory of adsorption in relation t o these results is discussed.The capillary condensation theory assumes that the free energy of the adsorbate is less than that of bulk material a t the same temperature because it is held under concave menisci in the pores of the adsorbent. The vapor pressure of the condensed substance is calculated by the relationship due to Kelvin. The theory implies that the adsorbent is inert, and only the shape and size of the pores play any role in determining the adsorptive characteristics. I t follo\vs also that the adsorbate has bulk properties except the lowered free energy arising from the presence of the concave meniscus.There is, however, ample experimental evidence to the contrary. The observed dimensional changes of the adsorbents (0.37, in the case of 17ycor glass -water system (1)) during the adsorption process indicate that the solid is perturbed by the presence of the adsorbate. Similarly, the infrared spectra of the adsorbate contain lines caused by forbidden transitions normally observable only in the Raman spectra (2,3) showing that the adsorbed liquid is in a state different from the bulk state. The crystal structure of the frozen adsorbate, too, has been found by X-ray diffraction methods to differ from the one of the bulk crystal (4). Accordingly, solidified adsorbates failed to nucleate undercooled bulk liquid of the same composition (5). These findings are to be expected in view of the fact that adsorption is the result of molecular interaction between adsorbate and adsorbent, and this interaction perturbs both.On applying the equation due to Kelvin the question arises: is it permissible to use the relationship even as an approximation when most of the quantities involved are not only unknown quantitatively but are meaningless on a molecular scale? Surface tension (or even the tern1 surface itself) of a liquid ...

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“…Subsequent to the important studies by Palmer and coworkers [see Palmer (102) and Cownie and Palmer (23)], Ebert and Langhammer (39) have pursued the problem of the dielectric properties of water adsorbed on various solids and, in particular, dealt with water adsorbed on aluminum oxide. While it is not possible here to summarize all the significant findings of Ebert and coworkers, we call particular attention to one feature.…”

Section: E Water Adsorbed On Aluminamentioning

confidence: 99%