Polymorphic and Morphological Transformation during the Transition from a Propagating Band to Static Bands in the Nickel Hydroxide/Ammonia Liesegang System

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 -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.

• Periodical: Defect and Diffusion Forum (Volumes 312-315)
• Pages: 800-805
• DOI: https://doi.org/10.4028/www.scientific.net/DDF.312-315.800
• Online since: April 2011
• Authors: Mazen Al-Ghoul, Manal Ammar
• Keywords: Liesegang Bands, Nickel Hydroxide, Ostwald Ripening, Polymorphic Transitions, Propagating Wave

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