Periodic formation of FeSi bands in diffusion couples Fe (15 wt.% Si) - Zn

During the reaction in Fe(15 wt.% Si)-Zn diffusion couples at temperatures between 623 and 723 K thin regularly spaced parallel bands containing very small FeSi precipitates are observed throughout the 6 and ~ reaction layers. The periodic nature of this effect is strongly reminiscent of the well-known Liesegang phenomenon. A detailed analysis of our results with respect to the principles underlying the Liesegang mechanism, however, shows that such a mechanism cannot explain the observed phenomenon in our case. A more probable explanation is found in the action of shear and tenSile stresses in the diffusion couple which lead to a periodic release ofthe continuously formed FeSi precipitates from the Fe(15 wt.% Si) substrate. Preliminary results obtained with substrates of varying thicknesses are strongly in favour of the latter explanation.