Abstract:
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 β-Ni(OH)2 whereas the pulse contains the other polymorph α-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. © (2011) Trans Tech Publications.