The effect of dry heating of synthetic 2-line and 6-line ferrihydrite: II. Surface area, porosity and fractal dimension

Abstract

AbstractNitrogen adsorption isotherms were measured on synthetic 2-line and 6-line ferrihydrites heated to 400 K, 500 K, and 600 K under dry conditions for different times ranging from 4 to 3000 h. Evaluation of specific surface area, microporosity and fractal dimension revealed that 2-line and 6-line ferrihydrites are highly microporous powders consisting of aggregates with corrugated interior and exterior surfaces. Furthermore, the surfaces of the single particles forming the aggregates have a smaller fractal dimension, i.e. a smoother appearance, than those of the entire aggregate. The diffusion of water lost during the heating process is influenced by the size of the micropores. The initial stage of the dehydration of the ferrihydrites can be described as similar to the process of Ostwald ripening.