Wr. Bowen et H. Mukhtar, PROPERTIES OF MICROFILTRATION MEMBRANES - THE SURFACE ELECTROCHEMISTRY OF MIXED-OXIDE CERAMIC MEMBRANES, Colloids and surfaces. A, Physicochemical and engineering aspects, 81, 1993, pp. 93-101
The surface electrochemical properties of mixed oxide ceramic membrane
s (Rappore) have been characterised by means of computerised measureme
nts of rates of electro-osmosis as a function of pH (reported as zeta
(zeta) potentials) and computerised pH surface titration. The membrane
s have modest values of zeta potential and high titratable surface cha
rge. Remarkably for an inorganic oxide material, the membranes have a
negative zeta potential over the entire pH range 10-3. Both the zeta p
otential-pH and surface charge-pH profiles at two ionic strengths coul
d be successfully modelled by considering the surface of the membrane
to consist of a three-dimensional array (''gel'') of charged groups, b
oth protons and counterions being able to penetrate the ''gel'' layer.
Counterion penetration was found to be especially important at the lo
wer pH values, where the surface charge of the membrane was positive b
ut the zeta potential was negative. Such a model allows estimation of
the ''gel'' thickness and the relative contribution of the component o
xides to the surface chemistry. It was found that aluminium oxide grou
ps played the greatest role in determining the surface properties, eve
n though zirconium dioxide was by far the largest component of the mem
brane based on the bulk composition. The results and analysis show tha
t the surface electrochemistry of such membranes is complex, and that
in characterising such membranes it is essential to make measurements
directly on the membrane rather than on the component oxides.