Crystal morphology, or structure, of alumina trihydrate is important in Bayer alumina precipitation. Quantitative work has been hampered by the lack of suitable characterisation techniques. Scanning Electron Microscopy (SEM) is commonly used, but lacks objective parameters.
A fractal analysis technique has been developed and used to quantify alumina trihydrate structure. This technique is based on analysis on light scattering information readily obtainable using existing particle size analysers. A monochromatic beam is directed into a colloidal solution, and is scattered by the colloidal particles. The scattered intensity is measured as a function of angle to the incident beam direction, and analysis yields the fractal dimension.
Alumina trihydrate samples from Australian and European suppliers have been examined. These show a clear relationship between alumina trihydrate strength (attrition index) and the fractal dimension. SEM studies confirmed differences between the samples.
A more definite relationship between the sample history, observed structure, fractal dimension, and strength is being determined in ongoing work.