SECM and EIS Studies of Galvanic Corrosion of Copper/Iron Connected to Automotive Parts in Seawater
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SECM and EIS Studies of Galvanic Corrosion of Copper/Iron Connected to Automotive Parts in Seawater Joseph Raj Xavier1 Received: 13 April 2019 / Accepted: 26 September 2019 © The Korean Institute of Metals and Materials 2019
Abstract The electrochemical behavior of galvanic coupling between copper and iron was investigated in natural seawater by SECM and EIS. The accumulation of metal complexes on the sample prevents the steep decrease in the resistance of film ( Rf) and charge transfer (Rct). It was shown that the film resistance, Rf of sample is decreased from 1.37 × 104 Ω cm2 at 1 day to ct from 2.95 × 104 Ω cm2 at 1 day to 1.57 × 104 Ω cm2 at 15 7.51 × 103 Ω cm2 at 15 days. Similarly, there is a decrease in R days with increase in test time. On the other hand, the double layer capacitance is increased from 157.4 µF at 1day to 977.8 µF at 15 days. Similarly, the film capacitance is also increased from 40.4 µF at 1 day to 123.7 µF at 15 days. The Fe2+ ions at + 0.60 V Cu+ ions + 0.34 V are detected. The tip current at iron is 14.8 nA at 1 day (light pink) and reached 6.0 nA at 15 days (greenish yellow). This indicates that the deposition of metal complexes at the sample slows down the iron oxidation further. After corrosion testing, the enrichment of corrosion products of Cu and Fe at the sample was analyzed by SEM/ EDX. FIB-TEM analysis confirms the rust layer containing Cu and Fe in the rust. The corrosion protection performance has been enhanced by nanoscale corrosion products deposition on the sample. Keywords SECM · SEM · Corrosion · Copper · Iron · TEM
1 Introduction Corrosion failures in automotive industry are one of the major problems [1]. Pipeline systems of oil and gas are another major source of corrosion that created the largest environmental disaster in pipeline industry. Metals and their alloys are prone to corrosion generally. Therefore, corrosion is inevitable in various industries such as automobile, petroleum and chemical industries, bridge, and drainage systems. Automobile manufacturers normally use a variety of metals to build a product that meets numerous functional demands. Copper alloys are used in automobile parts, heat exchangers and oil transportation due to their good durability and low cost [2]. Pure copper material must be coupled with aluminium, titanium, zinc, magnesium and steel in order to design industrial products [3, 4]. When two metals or alloys are immersed in the seawater due to free corrosion potentials, * Joseph Raj Xavier [email protected] 1
Department of Chemistry, Vel Tech Rangarajan Dr. Sagunthala R&D Institute of Science and Technology, Avadi, Chennai, Tamil Nadu 600 062, India
galvanic corrosion occurs [5–7]. The rate of corrosion of the anodic metal will be higher than that of the cathodic alloy. The potential of the less noble (more reactive metal) is raised by virtue of the potential difference that exists between the two metals (Cu/Fe). This stimulates corrosion of more reactive metal (Fe), simultaneously reducing the corrosion rate of
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