A Predictive Model for Zinc Runoff Rates from Zinc Sheet and Galvanized Steel in Outdoor Constructions

Abstract

A survey of the most important findings related to atmospheric corrosion of zinc and zinc-based alloys in atmospheric environments is currently undertaken by the authors. The survey also includes the concomitant zinc dispersion (also named runoff) from the same materials. This survey includes the corrosion product formation in different environments, influence of the most important parameters on the atmospheric corrosion process and also the influence of the most important parameters on the runoff process. The whole effort is motivated both because of recent progress made in the mechanistic understanding of the corrosion and runoff processes and also because of environmental concerns and initiatives, e.g., as formulated by the White Paper Strategy for a Future Chemicals Policy from the Commission of the European Communities in Brussels (2001) and in the Brundland report Our Common Future (1987). This presentation shows some highlights from the compilation of zinc runoff rates from zinc and zinc-containing materials exposed to different urban, rural, marine and tropic atmospheric exposure sites. Based on the extensive amount of generated data (see, e.g., 1-16) an effort has been made to formulate a general model which is able to predict the annual runoff rates of zinc from zinc-containing materials. The aim has been to formulate the model with help of parameters that all have a physical meaning. They include the annual rain amount, the annual average rain acidity, and surface inclination. To provide better experimental support for developing the runoff model, the field exposures have been complemented with laboratory exposures with artificial rain water allowing the individual parameters to be better controlled and varied one by one. The zinc runoff rates have been used, among others, for environmental risk assessments, legislation and restrictions (e.g. 17-18). In this case it was also necessary to include the chemical speciation and dilution effects upon entry of zinc into the environment.