M. Rasmusson et S. Wall, ELECTROSTATIC CHARACTERIZATION OF AL-MODIFIED, NANOSIZED SILICA PARTICLES, Colloids and surfaces. A, Physicochemical and engineering aspects, 122(1-3), 1997, pp. 169-181
Al-modified, nanosized silica particles have been studied with an elec
troacoustic technique. Also slightly aggregated silica particles have
been investigated with this method. zeta-potentials calculated from th
e measured dynamic mobilities were found to be in good agreement with
previous reported zeta-potentials obtained from streaming potential me
asurements. This indicates that the magnitude of the dynamic mobility
is very similar to the electrophoretic mobility for moderately charged
nanosized particles. The degree of Al-substitution was varied so that
between 0 and 16% of the surface silicon atoms were replaced by alumi
nium. It was found that the magnitude of the titratable surface charge
density increased with increasing degree of Al-substitution. This was
especially pronounced in the neutral pH region. The behaviour of the
zeta-potential as a function of Al-substitution was more complex than
the behaviour of the surface charge density: increasing the degree of
Al-substitution stepwise up to 7%, raised the magnitude of the zeta-po
tential both in 2 and 10 mM NaCl. A further increase of the degree of
Al-substitution lead to a reduction of the magnitude of the zeta-poten
tial. However, in 50 mM NaCl, it was favourable to include as much as
16% aluminium in the surface structure of the particle. The behaviour
of the zeta-potential as a function of pH for the Al-modified samples
can be explained in terms of adsorbed and non-adsorbed aluminium.