The unique chemical affinity between the
oxides of
silicon and
aluminium has been cited as a potential route for the amelioration of the detrimental effects of
aluminium in the environment and in
biological systems. A greater understanding of
silicon-
aluminium interactions may assist in this endeavour and also provide a means of overcoming
silica fouling problems encountered by industry which are exacerbated by the presence of
aluminium. It is also conceivable that this increased knowledge may demonstrate a positive use for
aluminium in the processing of the
silicon dioxide phase. In this study we report the effect of
aluminium ions, derived from
aluminium chloride, on
silicic acid species obtained from
potassium catecholato complexes of
silicon at circumneutral pH at the molar ratios 1000Si:Al, 100Si:Al and 50Si:Al.
Silica and low levels of
aluminium-rich
silica materials were formed with Si:Al ratios of about 3.5:1 comparable with the
element ratios detected in
senile plaques and
aluminium-rich scale. A kinetic study showed that
aluminium in the reaction medium slowed down the rate of formation of one of the
silica species formed early in the condensation process, e.g. trimers, but increased the rate at which
silicic acid was removed from sub 1 nm diameter particles. The materials precipitated in the presence of
aluminium were composed of smaller particles and aggregates with smaller pores (Si100:Al and Si50:Al systems) or larger pores (Si1000:Al) compared to the control. The nature of the interactions responsible for these differences is discussed. The effects described here demonstrate the ability of
silica and
aluminium to interact under conditions such as those found in
biological systems. That
silica reacts with
aluminium in the presence of
catechol supports the protective role assigned to
silicon.