Chloride melts, aggressiveness

One interesting feature of comparative experiments with a series of salts having a common anion is that the aggressiveness of the salts towards metals is dependent on the nature of the cation. The aggressiveness of chloride melts in contact with air is in the order... 

Electrochemical corrosion of metals Since the aggressiveness of salt melts is governed by redox equilibria, and is often controlled by composition of the external atmosphere, effects analogous to electrochemical or oxygen-concentration corrosion in aqueous systems can occur in salt melts. Tomashov and Tugarinov determined cathodic polarisation curves in fused chlorides and concluded that the cathodic reactions of impurities could be represented as ... 

In the case of CaCl2 and NaCl, the order corresponds with the corrosion behaviour expected from cathodic polarisation curves . The order of aggressiveness of chlorides can also be explained on the basis of redox potentials of the melts, calculated on thermodynamic grounds from the free energies of formation of the appropriate oxides and chlorides . The order of aggressiveness of nitrates is complicated by passivity effects , while that of alkalis in contact with air is... 

The active phase of the Deacon catalyst is usually assumed to be a complex melt of copper or chromium and alkaline metal chlorides under reaction conditions, which is distributed within the pore network of an inert carrier [42]. Such supported liquid-phase catalysts (SLPC) are eminently suitable for adsorbing large amounts of the reacting components as sorption takes place in a bulk phase and is not restricted to only a limited number of suitable surface sites. The periodic expansion and contraction of the melt as a result of (de) sorption imposes considerable strains on the carrier structure hence, special mechanically robust support materials are needed to withstand such strains and prevent the catalyst crumbling away and disintegrating after a few cycles. In addition, even when it is immobilized on the carrier, the melt is extremely aggressive and resistant materials must be used for reactor construction. 

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