Thermal Decomposition of Silver Carbonate: Phenomenology and Physicogeometrical Kinetics

Thermal decomposition of Ag 2 CO 3 to Ag 2 O was investigated to identify the physicochemical events that occur during the reaction and to reveal the interactions that cause the complex kinetic behavior of the reaction. Based on comparative investigation of thermal decomposition behavior of six different commercially available Ag 2 CO 3, a physicogeometrical reaction model of two partially overlapping reaction stages is proposed. The reaction stages involve the formation of a surface product layer and an internal reaction in the as-produced core–shell structure of the reacting particles. Immediately after the formation of the surface product layer, the structural phase transitions of Ag 2 CO 3 to two different high-temperature phases occur. Under these conditions, the thermal decomposition behavior is controlled by the diffusional removal of CO 2 through the surface product layer and/or the increase in internal partial pressure of CO 2 . The growth of Ag 2 O particles in the surface product layer produces possible channels for the diffusion of CO 2 . The relative rates of the formation of the diffusion channels in the surface product layer and the increase in the internal partial pressure determine whether the internal reaction advances at a steady rate or arrests until thermal decomposition of Ag 2 O of the surface product layer occurs at higher temperatures. The sample and reaction conditions influence the kinetic behavior of different component processes, resulting in the complex thermal decomposition behavior.