Demonstration of the Common History Behaviour using Growth of Bimodal Crystals
Growth Rate Dispersion of crystals has been observed for many materials. One of the strongest techniques used in the analysis of this phenomenon is Common History (CH) seed. These are crystals whose growth rate is proportional to their size. Thus these seeds maintain the same size distribution shape (e.g. as measured by the Coefficient of Variation) as the mean size of the population increases. As yet there has been little direct evidence to demonstrate that crystal seeds nucleated at the same time show this behaviour.
This work demonstrates CH crystal behaviour by showing that each crystal fraction in a bimodal distribution of Common History Seed maintains its CV over growth and that the growth rate of each distribution is proportional to its mean size. Two differently sized (38-63 µm and 180-212 µm) seed fractions were separated by sieving from a batch of ultrasound generated sugar seed crystals. These two fractions were mixed and then grown in a laboratory batch crystalliser. Within the accuracy of sampling and analysing, the results indicated the growth rate was proportional to the size of the crystals and each fraction maintained its CV. This supports the assumed common history (CH) crystal behaviour.