  Electrical image potentials near a metallic or a dielectric wall of higher
dielectric constant than that of the solution are attractive, and therefore,
can concentrate salt ions near the wall. It has recently been observed that
near a metallic surface, ions in room temperature ionic liquids precipitate
(but not near a nonmetallic surface). It will be argued that a likely reason
for why precipitation of ions in salt water, as a result of electrical image
forces, has not as yet been observed is the existence of an energy barrier near
a solid surface, resulting from the decrease of ion solvation as a result of
the large decrease of the dielectric constant of water normal to a solid wall
within a short distance from the wall. We will explore the conditions under
which ions are able to get past this barrier and concentrate at a solid wall,
either as a result of a reduction of this barrier caused by screening at high
ion concentration or as a result of thermal activation over this solvation
energy potential barrier.
