Polymorphic and Morphological Transformation during the Transition from a Propagating Band to Static Bands in the Nickel Hydroxide/Ammonia Liesegang System
We present an experimental study of the Ni+2/Ni(OH)2/NH3 reaction-diffusion system in a gel (agar). The system, which consists of a gel containing an inner electrolyte Ni+2 and a diffusing outer electrolyte (NH3/OH-), exhibits pulse propagation due to the concomitant precipitation reaction between Ni+2 and hydroxide ions and re-dissolution due to ammonia. During the propagation of the pulse, a transition to Liesegang banding is shown to take place. The bands are characterized by IR and XRD and are shown to consist of the polymorph -Ni(OH)2 whereas the pulse contains the other polymorph -Ni(OH)2. SEM measurements also reveal a morphological change accompanying the polymorphic transition between the pulse and the bands and uncovering an Ostwald ripening mechanism.
Andreas Öchsner, Graeme E. Murch and João M.P.Q. Delgado
M. Al-Ghoul and M. Ammar, "Polymorphic and Morphological Transformation during the Transition from a Propagating Band to Static Bands in the Nickel Hydroxide/Ammonia Liesegang System", Defect and Diffusion Forum, Vols. 312-315, pp. 800-805, 2011