Growth and Characteristics of Liesegang Rings in Cu–Cr System: Optical and XRF Study

Liesegang rings were first discovered more than 100 years ago by German chemists R. E. Liesegang and they attracted much attention since then. Liesegang rings are observed as spontaneous evolution of precipitate ring structure during diffusion of certain electrolyte into medium containing other electrolyte. One such example is diffusion of CuSO4 into gelatin containing K2CrO4 that is subject of our study. We present first results using X–Ray fluorescence technique for Cu–Cr system obtained at beam line BL4A, Photon Factory, KEK, Japan. Cu and Cr concentration profiles are in phase except the green ring at the boarder of the ring system with higher Cu concentration. Cu diffusion path is short, but in the case of 2 sources of CuSO4 the diffusion path is enhanced between them due to interference. Conditions for ring growth and time evolution of the 2 sources experiment are described as well.