CORROSION:Conversion of metals into various compounds bynatural means or agencies is described ascorrosion. Corrosion of ferrous metals appears inthe form of rusting.Corrosion of metals is explained in two ways.One is by the formation of oxides. As in case ofiron, reaction with oxygen, carbon dioxide andwater results in the formation of bicarbonate,which in turn alters into carbonate and finallychanges into hydrated oxide. Continued---
According to other explanation, themetal surface processes areas whichact as cathode and anodes. Thepresence of electrolytes like water ormoisture etc provides a contactbetween such areas which results incorrosion.
Protection against Corrosion:Ferrous metals have tendency forcorrosion. It is maximum for steel and leastfor cast iron. Wrought iron has a moderatetendency to rust. Therefore, all the productsrequire a protective cover to prevent thepossibility of corrosion and thereby addingto its durability. Various methods which arein commonly used include Electroplating,Galvanizing, Tin plating, Metal spraying,Painting, etc.
(1) Electroplating:This method involves the use of electric current togive a coating of chromium or nickel which ishighly resistant to corrosion.(2) Galvanizing:In this method zinc is used to give a coating on theferrous metal products.(3)Tin Plating:This method is similar to the galvanizing process.The iron products are thoroughly cleaned andwashed. Then these are dipped into the hot moltentin and it will give protection against corrosion.
(4) Metal Spraying:This method involves the use of a special sprayerin which fuel gas, oxygen and air are used tomake flame. The wire of metal to be sprayed likezinc, tin, or aluminium is used in these sprayers.The wire metals and a thin layer is sprayed overthe ferrous metal items.(5) Painting:The iron made goods are often coated with paint.Care should be taken to first clean the iron surfacethoroughly and then give a good coating of goodquality paint.