An innovative prototype sensor containing A36 carbon steel as a capacitor was explored to monitor early-stage corrosion. The sensor detected the changes of the surface- rather than the bulk- property and morphology of A36 during corrosion. Thus it was more sensitive than the conventional electrical resistance corrosion sensors. After being soaked in an aerated 0.2 M NaCl solution, the sensor's normalized electrical resistance (R/R₀) decreased continuously from 1.0 to 0.74 with the extent of corrosion. Meanwhile, the sensor's normalized capacitance (C/C₀) increased continuously from 1.0 to 1.46. X-ray diffraction result indicates that the iron rust on A36 had crystals of lepidocrocite and magnetite.
Keywords: X-ray diffraction; carbon steel; chloride; corrosion monitoring; rust.