Electrical conductivity and stability of concentrated aqueous alumina suspensions

This work describes the effect of solids load and ionic strength on the
electrical conductivity (K-S) of concentrated aqueous suspensions of
commercial alpha-alumina (1-35 vol% solids). The results obtained show
that the dependency of the electrical conductivity of the suspending
liquid (K-L) on the volume fraction of solids is well described by
Maxwell's model. The change in the conductivity of the suspensions
relative to that of the suspending liquid (K-S/K-L) was found to be
inversely proportional to the solids content, as predicted by Maxwell's
model. The relative conductivity rate, Delta K, could be interpreted in
terms of the DLVO theory and the particles double layer parameter,
kappa alpha, and used as a stability criterion. As kappa alpha changes,
in response to the changes in ionic strength, so does the conducting to
insulating character of the particles and, as such, their contribution
to the overall suspension conductivity (expressed by Delta K). When the
particles become insulating, the suspension conductivity decreases when
the solids load increases. The turning point in this particle behaviour
corresponds to a critical concentration of ions in the solution that
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destabilises the suspension and is associated with the critical
coagulation concentration (ccc). It is the electrical double layer that
ultimately determines the conducting or insulating character of the
particles, and that character can be made to change, as required for
suspension stability, and accessed by the relative conductivity rate.