The Electrical Conductivities of Molten Dichlorides

It is well known that the molten alkali metal halides like NaCl are good electric conductors, and this is commonly taken as proof that the melt consists of ions rather than neutral molecules. As early as in 1926, Biltz and Klemm published a survey of the specific electrical conductivities of 45 metal halides at temperatures just above their melting points [22]. The resulting conductivities were found to vary over six orders of magnitude. 

No information is available about the conductivities of the Group 2 and 12 metal difluorides, presumably because of their high melting points and corrosive properties. The conductivities of the dichlorides are listed in Table 1. Like the conductivities of the alkali metal chlorides, the conductivities of the Mg, Ca, Sr, Ba, and Cd dichlorides lie in the range from 1.0 to 10 S cm . These compounds are good conductors and the melts presumably contain high concentrations of ions. 

The specific conductivity of HgCl2 at its melting point is five orders of magnitude lower, o = 3.4 X 10 S cm . It increases slowly with increasing temperature conductivity measurements under high pressures show that o reaches a maximum value of 9.3 x 10 S cm at 500°C. The concentration of ionic species in the melt is obviously very low at any temperature. Since the crystals contain covalently bonded HgCl2 molecules, it is not surprising that these should be retained in the liquid phase. 

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