Zeolite electrical properties

Electrical Properties of Hydrated and Partially Hydrated Zeolites X and Y... 

Differential heats of adsoiption for several gases on a sample of a polar adsorbent (natural zeolite chabazite) are shown as a function of die quantities adsorbed in Figure 5 (4). Consideration of the electrical properties of the adsorbates, included in Table 2, allows the correct prediction of the relative order of adsoiption selectivity7 ... 

Because of these attractive properties, zeolites have been intensively investigated for hydrogen adsorption capacities [45]. The presence of strong electrostatic forces inside the channels and pores should enable hydrogen retention in the free volumes of the zeolite. The electric field is produced by the additional metal ions and it increases with increasing charge and decreasing size. 

Abstract. After a brief introduction on zeolite constitution, structure and properties, the suitability of thermal analysis in characterizing the zeolite materials and in investigating their potential behavior in different application fields is analyzed. Kinetics and thermodynamics of water desorption, thermal stability, phase transformations, occluded phase decomposition and gas evolution, structure collapse and recrystallization, change in electrical properties, all in relation to thermal treatments, are the specific subjects reviewed. Use of thermal analysis in the evaluation of zeolite content in multicomponent mixtures and in the characterization of zeolite catalysts are the two additional main topics discussed. 

The effect of natural zeolite addition on the electrical properties of porcelain bodies were investigated between 50 °C < T< 600 °C [10D2]. The addition of zeolites increases the resistivity of the samples at 50 °C and decreases the resistivity at higher temperatures. The resistivity depends on sintering temperature. The activation energy of electrical resistivity of the samples was found to be in the range of 0.79... 0.87 eV. 

Revil A, Hermitte D, Spangenberg E, CochemS JJ (2002) Electrical properties of zeolitized volcaniclastic materials. J Geophys Res 107(B8) 2168... 

Extraframework cations are needed in anionic zeolites for charge balance, and for several zeolite topologies their locations are well investigated [281, 282]. Different cations have been investigated by solid state NMR in the past with different NMR properties and different project targets. We restrict this section to a tutorial example on sodium cation motion in sodalite and cancrinite structures [283-285], 23Na has a nuclear electric quadrupole moment, and quadrupolar interaction is useful to investigate jump processes, especially when they are well defined. 

Another characteristic feature of the hydrogen-reduced transition metal zeolites is their acidic properties, as demonstrated by their catalytic behavior (7). Naccache and Ben Taarit (8) gave IR evidence of the subsequent formation of protons on hydrogen-reduced Cu(II)-Y zeolite. Furthermore, transition metal ions have various oxidation states. Owing to the shielding effect caused by the zeolite network and the electric fields, the transition metal ions may be stabilized in unusual oxidation states—i.e. Ni(I) (9). 

Egerton and Stone (29), taking into account that synthetic sodalite zeolites did not adsorb CO molecules, concluded that CO does not enter the sodalite cages of the Y zeolites. However, the strong electric fields present in zeolites could also produce changes in the adsorptive properties of the solids thus the energies associated with the cationic sites in crystalline zeolites must be considered. From our IR results, we concluded that CO molecules were located in the volume of the sodalite cages. Thus, the steric effect alone cannot explain the different adsorptive properties exhibited by sodalite and faujasite. 

In recent years investigations were begun in which the variation of adsorbent properties, such as electrical conductivity (1, 2), dielectric permeability (3-5), and linear sizes (6-11), were studied. In these systems the adsorbents were usually active carbons and porous glasses. Only a few studies were carried out on zeolites these studies are interesting because of the perfect porous structures (12-14) of zeolites. All these studies showed that during adsorption the properties of adsorbents do not remain constant. 

Figure 7. Variation of properties during water adsorption on zeolite NaA. (a) Our dilatometric curve (6) differential heats adsorption (17) (c) electrical conductivity (1) (d) dielectric constant (18).

In contrast to zeolites, i. e. the traditional molecular sieve materials which are electrical insulators, it has been shown that cetineites are crystalline nanoporous materials with a photosemiconducting host lattice191. The present paper reports on the optical properties of the phases with A = Na, K and X = S, Se from an experimental and theoretical point of view. 

The properties of these continua have not been explored to date. They may be metallic, and transitions in properties might occur as a function of temperature. They may be viewed as metal allotropes filled with electrons to a level far below their Fermi level. In addition, these "metals" would be very much effected by the electric fields of the zeolite framework. The mean charge on each non-framework cation in the structure can be varied by changing the composition of the zeolite framework, and by varying the extent of sorption. 

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