Alignment mechanisms between particles in crystalline aggregates

This paper examines the effect of mechanisms leading to alignment between the individual particles which make up aggregated crystal systems. It is postulated that when crystals collide in a suspension, their relative orientations have an effect on the probability that the crystals will stick together. Scanning and transmission electron microscopes have been used to study aggregates produced during the precipitation of calcite, and the relative orientations of crystallites within the aggregates have been measured. In a calcite sample produced at low solution ionic strength, it is found that more than half of the crystallite pairs measured show some special alignment between the crystallites. Aggregates taken from moderate ionic strength experiments do not show any noticeable degree of alignment. It is proposed that this alignment in the aggregates made at low ionic strength is caused by an ability of the crystallites to re-align themselves into a more favourable energy state before they are fixed into place.