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Description
An automated corrosion monitoring system using the electrical resistance
technique was applied for assessment of the corrosivity towards carbon steel
and zinc in different phases of a complex accelerated corrosion test recently
introduced by VDA, an association of German car makers. It comprises salt spray,
wet, dry, and freezing phases. The developed small and battery-driven
atmospheric corrosion loggers provided high sensitivity allowing for subangstrom
(<1010 m) measurements of corrosion depth and good accuracy. The
actual corrosion rate was affected by the exposure history due to a limited rate
of wetting/drying and oxygen and ion transport to the reaction interface under a
layer of corrosion products. The hysteresis was particularly strong for carbon
steel. Except the freezing phase, the steel corrosion rate varied in a narrow
range from 0.2 to 0.6 mm/h. For zinc, the corrosion rate varied from 0.001 to
0.1 mm/h in particular phases of the cycle with the maximum in the salt spray
phase. Seventy-five percent of the metal corroded in the salt spray phase and in
the following drying period representing only 13% of the total test time. The
obtained data suggest that the proposed test cycle allowed for rather efficient
drying of the zinc surface, which is believed to be crucial for the formation of
corrosion products with certain protective ability observed also in field
conditions.