The use of the box-counting dimension for characterization of the aggregation of colloidal hematite

Studying properties of natural colloidal systems, one major issue is the question, whether the shape of the associations formed can be described morphometrically. Therefore, X-ray microscopy experiments have been performed with hematite particles, which have been forced to coagulate by adding increasing amounts of sodium sulfate as a coagulation agent. An important figure is the critical coagulation concentration c.c.c., where the repulsive potential around these colloidal particles is matched in its range with the attractive van der Waals potential. To calculate the fractal dimension of the associations in the X-ray micrographs is one way to characterize the structures formed. The method used here is the box-counting algorithm. The calculated box-counting dimensions show that the associations have an increasingly denser shape when crossing the c.c.c