C O R R O S I O N PAGE 50 OF 54 Copyright © 2023 – Politeknik Kota Bharu Inhibitors slow corrosion processes by increasing the anodic or cathodic polarization behavior, reducing the movement or diffusion of ions to the metallic surface, and increasing the electrical resistance of the metallic surface. 4.9 Exercises Answer: a. Coating is a process used to created or attached a superficial layer on metals or alloys surfaces to avoid further damages because of corrosive environments. b. Metal coating can be classified into 2 categories: i. Noble coating ii. Non-noble/sacrificial coating c. (i) Question 1 Coating is typical method used for protecting metals and alloys from corrosion. (CLO1 C3) a. Define what is coating? b. List 2 types of metals coating. c. Based on your answer in b, draw a diagram respectively to explain the damages occur to the metal or alloys. Copper noble coating. From sketched diagram, copper used as coating layer to iron. But from electrochemical series, copper is more noble (less anodic) compared to iron (more anodic). Copper will not protect ferrous metals from corrosion. Ferrous metal will experience severe corrosion if not prevented.
C O R R O S I O N PAGE 51 OF 54 Copyright © 2023 – Politeknik Kota Bharu c. (ii) Answer: Zinc acted as non- noble coating to iron From sketched diagram, zinc used as coating layer to iron. From electrochemical series, zinc is less noble (more anodic) compared to iron (less anodic). Zinc will protect ferrous metals from corrosion. Question 2 Passivation is a behavior of certain metal or alloys to protect from corrosion. Sketch a suitable diagram to explain passivation in aluminum. (CLO1 C3) From the sketched diagram: i. An aluminum bar exposed to environment, act to oxygen an create an oxide layer. The bar experience tension caused high train crack to the protective alumina surface layer. ii. The crack exposing the underlaying aluminum metal. iii. Superplastic alumina created and flows to fill the gab caused of the crack. iv. Self-healing, alumina layer preventing further oxidation.
C O R R O S I O N PAGE 52 OF 54 Copyright © 2023 – Politeknik Kota Bharu 5.0 REFERRENCES 1. Callister, W.D. & Rethwisch, D.G. (2018). Material Science and Engineering: An Introduction (10th edition). Asia: John Wiley & Sons 2. Engineering Materials: Properties and Applications of Metals and Alloys. PHI Learning. Smith, W.F. (1996). Principles of Materials Science and Engineering (3rd Edition). USA: McGraw-Hill. 3. Mars G. Fontana, Corrosion Engineering. 3rd Edition. Publisher, McGraw-Hill, 1986. ISBN: 0071003606, 9780071003605 4. Raymond A. Higgin, W. Bolton. Materials For Engineers & Technicians. 4 th. Edition Elsevier. ISBN-13: 978-0-7506-6850-7 5. R. Kesavan, C. Elanchezhian, B. Vijaya Ramnath. Engineering Materials & Metallurgy, 2006 Anuradha Publications. ISBN: 978-81-89638-10-8 6. (Fe,Mn) Zn13 phase and its core-shell structure in novel biodegradable Zn-Mn-Fe alloys Zhang-Zhi Shi , Zi-Lin Li a , Wen-Shan Bai , Ayisulu Tuoliken , Jing Yu , XueFeng Liu. Materials & Designs Volume 162, 15 January 2019, Pages 235-245 7. Corrosion Inhibitors. C. Monticelli, Encyclopedia of Interfacial Chemistry: Surface Science and Electrochemistry, 2018. Elsevier. ISBN 978-0-12-809894-3
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