Ionic conductivity: also

Electrolyte — Compounds that dissociate (- dissociation) into -> ions upon dissolution in -> solvents or/and upon melting and which provide by this the - ionic conductivity. Also, compounds that possess in the solid state a rather high ionic conductivity are called - solid electrolytes. - True electrolytes are those which are build up of ions in the solid state (or pure form), whereas potential electrolytes are those which form ions only... 

Ionic conductivity also exists in redox conductors (see - solid-state electrochemistry), when ion movement accompanies (is coupled to) the electron self-exchange reaction. In those systems, the redox centers are immobilized, but there exists a relatively large population of mobile ions (counter ions) to assure the local electroneutrality. 

Most oxygen-ion transport membranes operate in the temperature range 750 to 1000 °C. This creates several problems for operation of ceramic membranes. First, the membranes must tolerate a 20 bar pressure differential at temperatures that are conducive to generating creep-induced failure. The membrane materials which have high ionic conductivity also have large numbers of lattice vacancies to facilitate mobility of the ionic species, but lattice vacancies are major contributors to elevated creep rates. 

Hydration of the perfluorinated ionic polymers (PIPs) depends on the ionie form and ion-exchange eapacity (Asaka et al. 2001). In the case of the Nation membrane, the water content decreases with the increase in the hydrophobicity of the counter cation. The ionic conductivity also depends on the ionic size, the hydration, the charge density of the ionic polymer, etc. For instance, the alkali cation-form and alkaline earth cation-form PIPs have larger conductivity than alkyl ammonium cation-form PIPs. Increasing the size of the alkyl ammonium cation decreases the conductivity. These results are closely related on the ion-cluster structure of the PIP. 

However, there have been suggestions in the literature for reference electrodes based on the aluminalaluminium couple. An electrode comprising a molten salt and aluminium was first described by Drossbach [81]. Common types of reference electrodes involve a molten aluminium pool covered by molten cryolite contained within a thin walled tube of sintered alumina or boron nitride. This housing must be electrically insulating but able to transfer ions (i.e. porous and ionically conductive). Also it must be resistive to corrosion. Electrolytes must be in contact and a tortuous path is required such that the different melts do not mix but establish a stable liquid junction. 

The most direct effect of defects on tire properties of a material usually derive from altered ionic conductivity and diffusion properties. So-called superionic conductors materials which have an ionic conductivity comparable to that of molten salts. This h conductivity is due to the presence of defects, which can be introduced thermally or the presence of impurities. Diffusion affects important processes such as corrosion z catalysis. The specific heat capacity is also affected near the melting temperature the h capacity of a defective material is higher than for the equivalent ideal crystal. This refle the fact that the creation of defects is enthalpically unfavourable but is more than comp sated for by the increase in entropy, so leading to an overall decrease in the free energy... 

Phosphazene polymers are inherently good electrical insulators unless side-group stmctures allow ionic conduction in the presence of salts. This insulating property forms the basis for appHcations as wire and cable jackets and coatings. Polyphosphazenes also exhibit excellent visible and uv radiation transparency when chromophoric substituents are absent. 

Applications. Polymers with small alkyl substituents, particularly (13), are ideal candidates for elastomer formulation because of quite low temperature flexibiUty, hydrolytic and chemical stabiUty, and high temperature stabiUty. The abiUty to readily incorporate other substituents (ia addition to methyl), particularly vinyl groups, should provide for conventional cure sites. In light of the biocompatibiUty of polysdoxanes and P—O- and P—N-substituted polyphosphazenes, poly(alkyl/arylphosphazenes) are also likely to be biocompatible polymers. Therefore, biomedical appHcations can also be envisaged for (3). A third potential appHcation is ia the area of soHd-state batteries. The first steps toward ionic conductivity have been observed with polymers (13) and (15) using lithium and silver salts (78). 

For a large number of applications involving ceramic materials, electrical conduction behavior is dorninant. In certain oxides, borides (see Boron compounds), nitrides (qv), and carbides (qv), metallic or fast ionic conduction may occur, making these materials useful in thick-film pastes, in fuel cell apphcations (see Fuel cells), or as electrodes for use over a wide temperature range. Superconductivity is also found in special ceramic oxides, and these materials are undergoing intensive research. Other classes of ceramic materials may behave as semiconductors (qv). These materials are used in many specialized apphcations including resistance heating elements and in devices such as rectifiers, photocells, varistors, and thermistors. 

In polycrystalline materials, ion transport within the grain boundary must also be considered. For oxides with close-packed oxygens, the O-ion almost always diffuses much faster in the boundary region than in the bulk. In general, second phases at grain boundaries are less close packed and provide a pathway for more rapid diffusion of ionic species. Thus the simplified picture of bulk ionic conduction is made more complex by these additional effects. 

All organic coatings show varying degrees of solubility and permeability for components of the corrosive medium, which can be described as permeation and ionic conductivity (see Sections 5.2.1 and 5.2.2). An absolute separation of protected object and medium is not possible because of these properties. Certain requirements have to be met for corrosion protection, which must also take account of electrochemical factors [1] (see Section 5.2). 

Later, Du Pont in America developed its own ionically conducting membrane, mainly for large-scale electrolysis of sodium chloride to manufacture chlorine, Nafion , (the US Navy also used it on board submarines to generate oxygen by electrolysis of water), while Dow Chemical, also in America, developed its own even more efficient version in the 1980s, while another version will be described below in connection with fuel cells. Meanwhile, Fenton et al. (1973) discovered the first of a... 

Electrolyte a substance, liquid or solid, which conducts electrical current by movement of ions (not of electrons). In corrosion science, an electrolyte is usually a liquid solution of salts dissolved in a solvent, or a molten salt. The term also applies to polymers and ceramics which are ionically conductive. 

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