Diffusion macroscopique dans un tuffeau et un alginate, mesure IRMMacroscopic diffusion in a limestone and in an alginate as measured by MRI.

Although Pulsed Field Gradient experiments allow measuring a diffusion coefficient at different time and length scales, it may be of some interest to use macroscopic methods. The result of a macroscopic diffusion is viewed here by proton MRI. For water in a limestone, analysing a concentration profile following a superficial coating gives a precise measure. For a divalent ion diffusing in an alginate gel or in the initial alginate solution, the reaction front position allows a tortuosity comparison. The originality of the last part is to visualize the syneresis phenomenon. Moreover, it makes it possible to estimate the maximum reaction time for the chelation (1 ms).