Zeolites ionic conductivity

Aluminosilicate zeolites because of their structure, composition, and properties offer a superior ionic strength environment [172,173], Even though these materials are electronic insulators, when hydrated, they are solid solutions of high ionic mobility, and when dehydrated exhibit fair ionic conductivity (see Section 8.2.7) [38,112,119,172], The properties of aluminosilicate zeolites that are responsible for affecting the charge-transfer reactions in electrochemical systems are [172,174] ... 

When zeolites are hydrated shows a notable ionic conductivity [112], Consequently, since all electrode processes depend on the transport of charged species zeolites provide an excellent solid matrix for ionic conduction [172], In 1965 [175], Freeman established the possibility of using zeolites in the development of a functional solid-state electrochemical system, that is, a battery where a zeolite, X, was used as the ionic host for the catholyte, specifically, Cu2, Ag+, or Hg2+, and as the ionic separator in its sodium-exchanged form, that is, Na-X. Pressed pellets of Cu-X and Na-X were sandwiched between a gold current collector and a zinc anode. Then, the half-cell reactions are the oxidation of Zn —> Zn2+ + 2e and the reduction of Cu2+ + 2e —> Cu, with type X providing a solid-state ionic path for cationic transport [175], The electrochemical system obtained can be represented as follows (Au I Cu11 -XI Na-X I Zn). 

Beattie (6, 7) investigated the electrical conductivity of dehydrated analcites and chabazite. Freeman and Stamires (19) confirmed the conclusions of Barrer and Rees (4) and Beattie (6, 7) by electrical conductivity measurements at 200 Hz on various ion-exchanged forms of dehydrated synthetic zeolites of type A, X, and Y. They found a purely ionic conduction with a strong dependence of the activation energies on the nature of the zeolite and the kind of cation. The decrease of the activation energy in X and Y zeolites with increasing monovalent cationic... 

The LT Mechanism. The dielectric behavior of the zeolites in the low-temperature region is more complicated than at high temperatures. A frequency-dependent process is superposed on the ionic conductivity, and the relative intensity of the 2 phenomena varies from sample to sample. The understanding of the LT mechanism requires the interpretation of the dissipation factor tg 8, which is obtained experimentally as the ratio between the imaginary and the real part of the complex dielectric constant e"/e. For a purely ionic conduction mechanism, the plot of tg 8 as a function of the temperature at a fixed frequency would show a... 

Most of the zeolites for which the ionic conductivity has been reported have been subject to ion exchange. In principle, the EFC-ions of any zeolite can be exchanged by up to 100% with another cation. Such exchange has often been claimed. In practice, however, 100% exchange is extremely difficult and time consuming. For this reason, most zeolites contain more than one kind of EFC-ion. 

Unfortunately HU As is the only proton-conducting hydrate for which available oxygen diffusion coefficient data allow direct verification of the vehicle mechanism. For other compounds there is just an indication that this may be the mechanism. These are e.g. diffusion bottleneck considerations for ionic conduction in zeolites or the exceptionally high temperature factors for the water oxygen in and some heteropoly-... 

The ionic conductivities of the Sn-ferrierites and Sn-silicalites, prepared by treatment of H-zeolite with tin chloride dihydrate, were mentioned in literatrrre [93K1]. The ac birlk corrductivity of Sn-ferrierite is higher than that of H-ferrierite and depends on the water content - Fig. 57. The bulk conductivities are almost indeperrdeirt on temperature in the range between 298 and 388 K. 

The separation layer may be dense (non-porous), such as Pd or Pd-alloy membranes for hydrogen separation and mixed (electronic, ionic) conducting oxide membranes for oxygen separation, or porous, such as metal oxides, silicalite, or zeolite membranes. Inorganic membranes are generally named for this separation layer, since it determines the properties and application of the membrane. The flux and selectivity of inorganic membranes are mainly determined by the quality of the separation layer, which is required to be defect-free and as thin as possible. 

Faujasites are of particular importance for industrial catalysis. As do all zeolites, they exhibit ionic conductivity, by motion of the cations in the internal channel structure. The cationic mobility is considerable, as shown by Table IX. The conductivity of zeolites is greater than that of most other crystals. At a temperature of 25°C the diffusion coefficient of the sodium ion in hydrated zeolite is only three orders of magnitude smaller than that of simple ions in aqueous solution. The conductivity increases with temperature at 335°C the conductivity of the anhydrous zeolite is greater than that of the... 

Ionic phosphonates, which contain loosely bound alkali metal ions, are of interest from the point of view of modeling zeolites containing dissolved metal ions displaying conductive hyperlattices. Reactions of fBuP(0)(OH)2 with alkali metal salts of tetraalkylgallates provide a convenient route to ionic phosphates (Chart ll).31 A... 

Dubbe, A., Hagen, G. and Moos, R. (2006) Impedance spectroscopy of Na+ conducting zeolite ZSM-5. Solid State Ionics 177,2321-3. 

Eguizabal A, Lemus J, Urbiztondo M, Moschovi A.M, Ntais S, Nikolakis V, Soler J, Pina MP. Ammonium based ionic liquids immobilized in large pore zeolites Encapsulation procedures and proton conduction performance. J Power Sources 2011 196(9) 4314-4323. 

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