Corrosion - Study Notes

Corrosion Corrosion is the oxidation of a metal. In everyday life, oxidized iron is called rust with the formula Fe2 O3 ·xH2 O. The rusting process includes an electrochemical process, where oxidized Fe metal acts as an anode and oxygen dissolved in water on the iron surface acts as a cathode. Rusting reaction: Anode: Fe Fe2+ + 2 e– Cathode: O2 + 2 H2 O + 4 e 4 OH– The resulting Fe2+ will gradually be oxidized to form Fe3+. Meanwhile, OH– will combine with electrolytes that exist in nature or with H+ ions from dissolved acid oxides (SO2 , NO2 ) resulting from changes with rainwater. From the results of the reaction above, rust will be produced with the compound formula Fe2 O3 ·xH2 O. This rust is a catalyst for the next rusting process which is called autocatalyst. a. Disadvantages Iron that is exposed to corrosion will be brittle and will not have This is very dangerous if the iron is used as a building or bridge foundation. Rust compounds also endanger health, so iron cannot be used as cooking utensils, tools for the food/pharmaceutical/chemical industry. b. Prevention Prevention of iron from rusting can be done in the following way. 1) The coating process. Iron is coated with a substance that is difficult for oxygen to penetrate. This is done by painting or coating with a metal that is difficult to oxidize. The metal used is the metal that is located to the right of iron in the voltaic series (the reduction potential is more negative than iron). For example: silver, gold, platinum, tin and nickel metals. 2) Protective cathode process (cathodic protection) Iron is protected from corrosion by placing iron as a cathode, not as an anode. In this way, iron is connected to other metals that are easily oxidized, namely metals to the left of iron in the voltaic series (metals with a more positive reduction potential than iron). It's just that Al and Zn metals cannot be used because both metals are easily oxidized, but the oxide formed (A12 O3 /ZnO) acts as an inhibitor by tightly sealing the metal inside, so that oxygen cannot enter and it is not oxidized. Alkali metals, such as Na, K also cannot be used because they will react with the presence of water. The most suitable metal for cathodic protection It's just that Al and Zn metals cannot be used because both metals are easily oxidized, but the oxide formed (A12 O3 /ZnO) acts as an inhibitor by tightly sealing the metal inside, so that oxygen cannot enter and it is not oxidized. Alkali metals, such as Na, K also cannot be used because they will react with the presence of water. The most suitable metal for cathodic protection is magnesium metal (Mg). Mg metal here acts as an anode and will be attacked by rust until it runs out, while iron acting as a cathode does not experience corrosion.