Zeta potential, also known as electrokinetic potential, is
one of the most relevant parameters controlling the rheological behavior of
ceramic suspensions. It is the potential difference across phase boundaries
between solids and liquids. Its measurement is frequently used in coagulation
(aggregation) and dispersion processes in several applications, such as
colloidal processing of ceramic pastes and slurries, water purification, paints
and cosmetics.
In this paper, the authors discussed the behavior of zeta potential
versus pH, in the vicinity and away from the isoelectric point (IEP), presented
by suspensions of several silica raw materials of different crystal structures
and specific surface area. The chosen silica powdered raw materials for this
study were two crystalline polymorphs of silica (α-quartz and α-cristobalite),
as well as vitreous silica. And it was observed that for pH values below the
isoelectric point (IEP), the positive value of zeta potential of water
suspensions of α-quartz and α-cristobalite, experienced a sudden
steep increase with the increase in specific surface area of the powders. For
pH values above the IEP, the zeta potential values of crystalline forms of
silica (α-quartz and α-cristobalite) got gradually more
negative with the increase in pH. Conversely in the case of vitreous silica,
for pH values above 6, there was a steep change towards more negative values of
zeta potential than those presented by quartz and cristobalite.
In conclusion, through this work, it was possible to identify
different behaviors of the zeta potential versus pH for silica samples,
crystalline or vitreous, which was found remarkably different from pH values
below and above the IEP. And understanding how the zeta potential varies with
crystalline and vitreous character and its dependence on powder surface area of
silica raw materials would help to predict and control the rheological behavior
of the silica slips. In this manner, the stabilization and destabilization of
these ceramic materials under colloidal processing can be considerably
facilitated.
Article by José Antonio Alves Júnior
and João Baptista Baldo, from Universidade Federal de
São Carlos, São Carlos, Brazil.
Full access: http://mrw.so/vja34
Image by Geoff Whiteway, from
Flickr-cc.
评论
发表评论