Spatio-temporal dynamics of corrosion and precipitation systems

Self-organization of coherent spatio-temporal patterns occurs in numerous physical, chemical, and biological systems. In particular, electrochemical reactions generate a wealth of examples for this intriguing phenomenon. Patterns arise from the interplay of temporal reaction instabilities and transport processes such as fluid convection, electro-migration, and diffusion. In this work, we study the propagation of electro-dissolution waves, the self-motion of localized corrosion cells and a related reaction-precipitation system.; The iron/nitric acid system has been the subject of numerous studies and shows spontaneous, periodic transitions between an active dissolution and a passive inert state. For a pseudo-one-dimensional system, we report the existence of three distinct regions (continuously active, oscillatory and continuously passive) along a cathodic wire under potentiostatic conditions as well as sporadic long-range pulses for lower acid concentrations. Under pseudo-two-dimensional and open-circuit conditions, rotating spiral waves of electro-dissolution can form on the surface of low-carbon steel. Self-adhesive polymer masks are employed to determine the critical size of a defect that initiates a global corrosion event.; We also investigate the propagation of corrosion trails or “filiform corrosion” on low-carbon steel samples protected by a layer of commercial grade acrylic lacquer. From optical data and computer analyses, we determine that filament growth responds to variations in the thickness of the acrylic film. To control the direction of the growth, we develop a technique to pattern the organic coating using polydimethylsiloxane molds created by soft-lithography. We successfully direct the filiforms along linear and curved paths. Finally, we also report the formation of corrosion tubes from blisters that nucleate in a higher relative humidity environment.; To understand the growth mechanism of corrosion tubes, we examine a simpler reaction-precipitation model, commonly known as “chemical gardens”. A novel injection technique provides control over parameters that are not accessible in the classic system. For the example of cupric sulfate injection into waterglass solution, we identify three distinct growth regimes (jetting, popping and budding) and study their concentration-dependent transitions. These data enabled us to derive an equation that relates the period of the popping events to flow rate and cupric ion concentration.