Dielektrisches Verhalten einiger Zeolith/Wasser-Systeme

The influence of moisture content and temperature on the dielectric permittivity (complex resistance) of the zeolite NaY was investigated for a fixed radio frequency (RF) of 13.56 MHz. Sealed glass tubes containing zeolite with defined moisture contents were simultaneously heated in a homogeneous high-frequency electromagnetic field. The dielectric loss factor, i.e. the imaginary part of the permittivity ε(r)″, was calculated from the obtained heating rates. On the basis of the resulting values for various moisture contents and temperatures and utilizing the knowledge of elementary cation hopping processes occurring at low and high frequencies (LF and HF) from the literature, a new model was introduced for the description of dielectric radio-frequency heating of moist zeolites. Since adsorption of water is correlated with an enhancement of the activation energy of the cations on SII sites, cations in the zeolite NaY are moving from SII sites to unoccupied SIII sites when the water content is increasing. Thus, four different transfer processes for the cations have to be considered in total. On the basis of these assumptions, the resulting dielectric loss factor ε(r)″ as a function of water content and temperature for a fixed frequency of 13.56 MHz was modelled. The experimental data are in good agreement with the values obtained from the model. Especially, the measured pronounced maximum of dielectric loss at temperatures below 300 °C and water contents below 4 wt.-% can be explained by the new model.

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“…The published values of Matron et al 29 are in good agreement with the obtained correlation up to a water content of about 4 wt.-%.…”

Section: Elementary Processes Of Dielectric Zeolite Heatingsupporting

confidence: 87%

Influence of moisture content and temperature on the dielectric permittivity of zeolite NaY

Kraus

Kopinke

Roland

2011

Phys. Chem. Chem. Phys.

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“…It is therefore ascribed to local movements ascribed to the hops of ions near their equilibrium positions. The charge carriers responsible for this phenomenon are usually called “bound charges”. ,, In the kilohertz region, two relaxation domains have been found by authors near room temperature on dehydrated faujasites ,, and on hydrated or partially hydrated zeolites. , However, these two relaxations are not ascribed to the same species, depending on authors. Thus, Matron et al .…”

Section: Resultsmentioning

confidence: 99%

Dielectric Properties of a Faujasite Y as a Function of the Hydration State

et al. 1997

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The evolution of conduction and polarization phenomena is studied as a function of dehydration temperature (TT varying from 100 up to 400 °C) on a faujasite Y zeolite. The measurements are carried out as a function of frequency at different temperatures. In all cases, the conductivity is ascribed to the migration of cations in large cages involving energies varying from 0.61 to 0.85 eV. Two relaxation domains are observed. It is assumed that they are due to the movement of cations of sites III‘ and II. The existence of these two domains is confirmed by the technique of the thermally stimulated currents. The spreading domain of relaxation depends on the dehydration state of the zeolite.

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“…Domain I1 has been reported to be multiple in the sense that continuous (MATRON et al;JONES, DAVIES;SCHOONHEYDT 1980a, b) or discrete (CHAPOTON et al 1972;TABOURIER et al 1983b) distributions in the relaxation times (T) have been introduced to explain the non-Debye behaviours. This is almost invariably the case for the dielectric relaxation mechanisms in both dry and hydrated zeolites.…”

Section: Relaxations and Other Polarisation Phenomena In Zeolites (A)mentioning

confidence: 99%

Molecular Mobility in Microporous Architectures: Conductivity and Dielectric Relaxation Phenomena in Natural and Synthetic Zeolites

Kalogeras

Vassilikou‐Dova

1996

Cryst. Res. Technol.

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Dielektrisches Verhalten einiger Zeolith/Wasser-Systeme

Cited by 14 publications

References 22 publications

Influence of moisture content and temperature on the dielectric permittivity of zeolite NaY

Influence of moisture content and temperature on the dielectric permittivity of zeolite NaY

Dielectric Properties of a Faujasite Y as a Function of the Hydration State

Molecular Mobility in Microporous Architectures: Conductivity and Dielectric Relaxation Phenomena in Natural and Synthetic Zeolites

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