THE EVOLUTION OF THE ADSORBED SOLUTION LAYER DURING ATMOSPHERIC CORROSION AND ITS EFFECTS ON THE CORROSION RATE OF COPPER

A better understanding of the atmospheric corrosion of materials requi res an improved knowledge of the adsorbed electrolyte layer. Such insi ghts include the ionic constituents present and their concentrations a s well as how these depend on experimental variables such as time, pol lutant gas, and relative humidity. The present work describes experime nts which combine quartz crystal microbalance measurements with ion ch romatography to study the evolution of the adsorbed electrolyte layer during the exposure of Au and Cu to low levels of NO2. These measureme nts show that it takes up to 20 h for the electrolyte layer to approac h a steady-state composition in which the nitrate concentration is on the order of 1M. The dominant nitrogen specie is nitrate, though both nitrate and nitrite are detectable. The results support the idea that metal surfaces preferentially catalyze one of the NO2/water reaction p athways. The corrosion rate of copper was shown to increase only alter a sufficiently aggressive solution chemistry was developed in the ads orbed electrolyte.