Iron and Carbon Steel - Revision Dec 2005 - Engineering - http://maxpages.com/jpchemical/Iron_and_Carbon

Iron, as per University of Sheffield, http://www.webelements.com/webelements/elements/text/Fe/key.html, Iron as per Wikipedia, http://en.wikipedia.org/wiki/Iron Carbon Steel as per Wikipedia, http://en.wikipedia.org/wiki/Carbon_steel (1) IRON-CHEMICAL REACTION AND PROPERTIES (2) PRESERVATION OF IRON ITEMS (1) IRON. Iron has chemical symbol Fe. Fe has many isotopes but Fe with mass 56 is most abundant. It has 26 protons and 30 neutrons. An atom of Fe is represented as 5626Fe. The symbol of iron is derived from its Latin name ferrum. Fe is one of the transition metals. In transition metals, electrons from few of the outer shells participate in chemical reactions. Iron is placed in the periodic table close to cobalt and nickel, as all of them show similar properties. Since Fe has 26 protons, it also has 26 electrons. The electronic configuration of Fe is K-shell – 2 electrons, L-shell – 8 electrons, M-shell - 14 and N-shell has 2 electrons. Fe shows metallic properties and gives off its 2 electrons in the outermost shell easily to achieve a stable electronic configuration Fe2+. Sometimes Fe gives off 2 electrons from the N-shell and 1 electron from the M-shell to become Fe3+ (variable valance). Fe is a reactive metal and is not found in free state in nature. Fe ores are in the form of compounds of oxides, sulphides and carbonates. The ores found are : Hematite : Fe2O3 Magnetite : Fe3O4 · Limonite : Fe2O3. H2O · Siderite : FeCO3 · Pyrite : FeS2 Physical properties of iron : Fe is a grayish white metal. Its surface may appear brown due to rust. Its density is high (7.86 gm/cc). Its melting point is 1539°C. Fe displays strong magnetic properties. Fe is a very ductile and malleable metal. It is a good conductor of heat and electricity. Chemical properties of iron : 1. Valence : Fe shows variable valance. Since Fe has 2 electrons in its N-shell, it gives them off easily. Fe (II) (ferrous) has valence = 2+. Fe is able to show 3+ valence by emitting one electron from the M-shell. Fe (III) (ferric) has valence = 3 + .2. Action of air : Fe is a reactive metal. But Fe does not react with air at ordinary temperatures. When heated strongly in oxygen, Fe forms Fe3O4.(Iron II and Iron III) . When heated in damp air, Fe forms Fe2O3 along with Fe(OH)3 which is the common rust. . Action of water : Fe does not react with water to form a hydroxide at ordinary temperatures. When steam is passed over red-hot Fe, iron (II, III) oxide Fe3O4 and hydrogen are formed Reaction with acids : Fe reacts with HCl to form Fe (II)-chloride and releases hydrogen. Fe reacts with dilute sulphuric acid to become ferrous sulphate, releasing hydrogen. With concentrated sulphuric acid, Fe reacts by releasing sulphur dioxide and water. (Conc H2SO4 is more oxidizing) When Fe fillings are added to dilute nitric acid, the following reaction occurs. With concentrated nitric acid, Fe forms a passive oxide layer Fe2O3 on the surface. This oxide layer prevents more reaction. Action of alkalis : Pure Fe does not reacts with NaOH and KOH. It is unable to replace Na or K from the hydroxides.6. Reaction with chlorine : Ferric chloride is formed when Fe is heated in chlorine atmosphere. Reducing action : Fe does not show any reducing action. Reaction with sulphur : When iron fillings are heated with sulphur powder, FeS that is ferrous sulphate is formed. Rust and prevention of rust : We have seen that Fe reacts with oxygen in air, in the presence of moisture to form ferric (III) oxide. This is rust. Thus rusting of iron is a slow oxidation process. For prevention of rust the following can be done : iron surface has to be coated with paint or lacquer so that the surface is not exposed to air and moisture. · Iron can be galvanized. A thin layer of Zn is applied on the iron surface. Zn itself gets oxidized and prevents Fe from the oxidation process. · Iron surface can be coated with another metal like Cr, tin, Ni or Al, which are more resistant to oxidation or corrosion. · Iron can be alloyed with Cr and Ni to obtain stainless steel that is completely rust proof. · Iron can be coated with other iron compounds that are already in an oxidized state; these materials can be Fe3O4 or FePO4. 2. PRESERVATION OF IRON ITEMS To preserve the value of metal items, careful cleaning, storage and display are necessary to preserve the original finish and characteristics of the metal. Always test cleaning and care procedures first before use on valued items. Follow safety precautions in using solvents and other chemicals. If in doubt, consult a conservator who specializes in metals. When using commercial cleaners, read and follow the label directions and test first. Hardware stores and lumberyards, grocery stores, and specialty shops and department stores may carry metal cleaners. Remove all residue of the cleaner. Before cleaning iron objects, consider first their original condition. Bright metal finishes; the result of recent polishing, or painting, may affect the value of your iron keepsake. Protect iron objects in good condition from high humidity, fingerprints, salts, and acids. A 40 percent relative humidity level is suggested. Iron is the metal most susceptible to corrosion. Cleaning. Corrosion usually occurs slowly. Unless it is necessary to remove the surface layer of corrosion, the item may be best left alone to retain its value as a keepsake. Over-cleaning cannot be undone. Remove dirt, grease, and moisture from the surface. Vacuum the item to remove dirt. To remove oil or grease stains; wipe the item with acetone (use caution — follow safety procedures and read label). If the condition of the finish is so bad it cannot be saved, fine bronze wool or very fine emery cloth can be used. To remove rust use an abrasive softer than the iron itself. Light rust is removed by rubbing the item with very fine bronze wool and mineral spirits. Strong abrasives are not recommended for historical iron objects. After the outer layer of rust has been removed, the object should be protected, as formation of new rust will result. Some experts recommend avoiding the use of commercial rust removers on valuable items as they can cause pitting or etching of the metal surface. If used, follow directions and remove all residue of the rust remover. Power grinders and wire wheels leave scratches on the surface. If a clean environment and low humidity cannot provide enough protection to prevent rusting, warm the iron piece slightly (e.g. in the sun) and apply microcrystalline wax or beeswax. Waxing is a reversible process. Avoid paraffin. The wax should flow easily when applied to the warmed object without having to melt the wax first. Observe safety precautions. Wipe off excess wax when the item has cooled. Microcrystalline wax is available from conservation supply businesses. Silicone can also be used by spraying or rubbing it on. Avoid application to any wood surface, as silicone may interfere with refinishing the wood and is not easily removed. If your iron keepsakes include old wagons or farm machinery, etc., which were traditionally painted, rust-inhibiting paints may be used. Determine first the original colour and design and whether painting will affect the antique value of the item. If the item can be protected without the addition of paint, the item may be best left alone.

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