Molten salts primitive

The popular and well-studied primitive model is a degenerate case of the SPM with = 0, shown schematically in Figure (c). The restricted primitive model (RPM) refers to the case when the ions are of equal diameter. This model can realistically represent the packing of a molten salt in which no solvent is present. For an aqueous electrolyte, the primitive model does not treat the solvent molecules exphcitly and the number density of the electrolyte is umealistically low. For modeling nano-surface interactions, short-range interactions are important and the primitive model is expected not to give adequate account of confinement effects. For its simphcity, however, many theories [18-22] and simulation studies [23-25] have been made based on the primitive model for the bulk electrolyte. Ap-phcations to electrolyte interfaces have also been widely reported [26-30]. 

For molten salts one sets so = 1. For electrolyte solutions solvent-averaged potential [37]. Then, in real fluids, eo in Eq. (11) depends on the ion density [167]. Usually, one sets so = s, where e is the dielectric constant of the solvent. A further assumption inherent in all primitive models is in = , where is the dielectric constant inside the ionic spheres. This deficit can be compensated by a cavity term that, for electrolyte solutions with e > in, is repulsive. At zero ion density this cavity term decays as r-4 [17, 168]. At... 

Models of molten salts have evolved with time and so have the inter-ionic potentials relevant to them. The restricted primitive model (RPM) considers the ions to be charged hard spheres of uniform size (radius rj) interacting through their coulomb potentials. The potential function is then ... 

The numerical coefficient has been changed from that in [145] to account for the average deviation of the calculated from the experimental values for the alkali metal halides. Cavity formation in molten salts is compatible with their restricted primitive model (RPM), Eq. (3.8) [146]. For a molten salt having N ions of mean diameter d = (r+ + r ) in a volume V, the size distribution of cavities with radii r < 0.5r/ is ... 

The corresponding states theory was developed by Reiss, Mayer and Katz [138] to deal with molten salts. It employs the primitive model with a single distance parameter d (=2ri in Eq. 3.8) to which all the inter-ionic distances in the entire volume of the molten salt V are proportional = 4ijd for all ions I and J, whether 1 = J or 1 / J. Reduced thermodynamic quantities are then defined as ... 

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