COMPARATIVE STUDY OF CORROSION RATE AND EQUIVALENT CIRCUIT MODEL FOR GALVANIZED STEEL IN CHLORIDE SOLUTION TO CARBONATE

• Main Author: WIRA NUGROHO (NIM : 12514016), SATYA
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/30848
• Institution: Institut Teknologi Bandung

Galvanized steel is a regular carbon steel which has been coated with zinc to protect <br /> <br /> steel from corrosion. Zinc on galvanized steel provides protection to steel with two <br /> <br /> mechanisms, as barrier between steel and the environment, and as cathodic <br /> <br /> protection in which zinc will be corroded first when there is imperfection at the <br /> <br /> coating as zinc is more galvanic relatively to steel. Galvanized steel application at <br /> <br /> outdoor environment will create a contact of galvanized steel with corrosive media <br /> <br /> such as rainwater. Rainwater can contain chloride and carbonate ion that can affect <br /> <br /> the corrrosion process on galvanized steel. This research will investigating the <br /> <br /> difference of corrosion process of galvanized steel in chloride and carbonate <br /> <br /> solution from the perspective of corrosion rate and equivalent circuit model. <br /> <br /> A series of electrochemical testing consist of potentiodynamic polarization and <br /> <br /> electrochemical impedance spectroscopy (EIS) were conducted with laboratory <br /> <br /> potentiostat and also immersion test to study the difference of galvanized steel <br /> <br /> corrosion in chloride and carbonate solution. Potentiodynamic test was conducted <br /> <br /> on galvanized steel sample that has been immersed for 15 days in chloride and <br /> <br /> carbonate solution with concentration each of 1 M, 0,5 M, and 0,3 M at room <br /> <br /> temperature. Corrosion potential, corrosion current density, and Tafel slope were <br /> <br /> determined with Tafel extrapolation method from polarization curved acquired <br /> <br /> from potentiodynamic test. Immersion test was also conducted at solution <br /> <br /> concentration of 1 M to calculate corrosion rate that will be compared to corrosion <br /> <br /> rate from Tafel extrapolation. To determine the equivalent circuit model, EIS was <br /> <br /> conducted at day 1, 2, 3, 7, 11, and 15 of immersed sample. <br /> <br /> Highest corrosion rate in chloride solution was 0,22 mm/year at 1 M concentration, <br /> <br /> whereas in carbonate solution was 0,03 mm/year at 0,3 M. Equivalent circuit model <br /> <br /> suitable for galvanized steel corrosion in 1 M chloride solution indicates the <br /> <br /> presence of diffusion process on day 3 to 15. At concentration of 0,5 M, the <br /> <br /> corresponding model indicates no interface diffusion process, and at concentration <br /> <br /> of 0,3 M diffusion occured since day 1 of immersion. On the other hand, in <br /> <br /> carbonate solution of 1 M, the model indicates the presence of oxide layer which <br /> <br /> dissolved on day 11. For concentration of 0,5 M, diffusion process occured on 2 <br /> <br /> days of immersion, with the presence of oxide layer until day 15. At concentration <br /> <br /> of 0,3 M, the model indicates the presence of oxide layer and no diffusion process <br /> <br /> occured.