Applied Science PDF - Mechanical Properties of Metals

# Applied Science ## (H) Electrorefining - The tough pitch (Blister Copper) containing 99.2 to 99.6% Cu may be further refined to 99.98% pure copper by electrolytic refining. - The tough pitch is cast into thick plates which are made the anodes. The cathodes consist of thin plates of pure copper c...

# Applied Science ## (H) Electrorefining - The tough pitch (Blister Copper) containing 99.2 to 99.6% Cu may be further refined to 99.98% pure copper by electrolytic refining. - The tough pitch is cast into thick plates which are made the anodes. The cathodes consist of thin plates of pure copper coated with graphite to permit easy removal of metal deposited on them, during electrolysis. - The refining tank is a wooden vat lined with lead sheets and placed on glass sheets and the bath contains 15% CuSO4 solution and 5-10% sulphuric acid solution. - The cathodes and anodes are connected either in multiple systems or in series system. - When a current of electricity is passed, copper ions are discharged at the cathode and are deposited as pure copper. - The sulphate ions at the same time travel to anode and on being discharged react with copper from anode to form copper sulphate. ### Fig. 4.3.8: Cell for electrolytic refining of copper - Thus, there is a transfer of pure copper from anode to the cathode while impurities such as Zn, Fe, Ni etc. pass into solution as sulphate as they requires more voltage to discharge. - Impurities like gold and silver are not affected by CuSO4 H₂SO₄ solution and they form insoluble deposit below the anode known as anode mud or slime. Se, Te and Pb also pass into this mud. - The precious metals like Ag, Au, Pt etc. are recovered from this anode mud. ## 4.4 Mechanical Properties of Metals ### Mechanical properties of metals 1. Hardness 2. Ductility 3. Malleability 4. Toughness 5. Brittleness 6. Tensile strength 7. Weldability 8. Machinability 9. Tenacity ### Fig. 4.4.1: Mechanical properties of metals - Metals are possessing different physical and mechanical properties. For an engineer the knowledge of mechanical properties of the metal is most important which includes hardness, ductility, malleability, toughness, elasticity, brittleness etc. - The physical properties are melting point, boiling point, electrical and thermal conductivity etc. ### Following are the mechanical properties of metals 1. **Hardness:** It is defined as the ability of the metal to resist wear (or abrasion), penetration and scratching by other materials is known as hardness. For example Sodium, potassium are soft whereas Iron and tungsten are more hard. 2. **Ductility:** It is defined as property of metal by which it can be stretched in length without breaking and they can be drawn into wires is known as ductility, Metals like gold, silver, platinum are more ductile. 3. **Malleability:** It is defined as the property by virtue of which a metal can be hammered into shapes without cracking or rolled into thin sheet without tearing or breaking is known as malleability For example: Gold, silver, platinum, aluminium, copper are malleable. ## 4.3.5: Reduction in blast furnace - Flux and Slag:Even after the ore dressing gangue still remains with the ore. - The gangue is to be removed during smelting. The lime stone which is used as flux in reduction of haematite decomposes at high temperatures to give lime. This lime reacts with silica to form slag. - CaO + SiO₂ → CaSiO₃ ## 4.3.6: Alumino Thermic Process (Thermite) ### (i) Poling (Oxidation of Impurities) ### Fig. 4.3.7: Poling process - This method is used when the impurities in a metal havemore affinity for oxygen. - In this method, a hot crude molten metal is stirred with green logs of wood. - The wood gases like methane obtained from it, reduce metal oxide impurity to its metallic form. - On the other hand, during stirring large quantity of air is absorbed by molten metal which oxidises the easily oxidisable impurities. - The oxidised impurities escape either in the vapour form or it forms scum over molten metal. - The scum so produced is removed by perforated ladle. - For example: Blister copper is refined by using this method. The impurities like arsenic are oxidised by air absorbed while stirring to As₂O₃ which is escaped away as vapour. ## 4.3.4 Refining ### (i) Poling (Oxidation of Impurities) - **Scum:** Green log of wood - Hydrocarbon of wood reduce metal oxide to metal - Molten metal ## 4.3.5: Reduction in blast furnace - **Flux and Slag:** Even after the ore dressing gangue still remains with the ore. - **The gangue is to be removed during smelting. The lime stone which is used as flux in reduction of haematite decomposes at high temperatures to give lime. This lime reacts with silica to form slag.** - CaO + SiO₂ → CaSiO₃ ## 4.3.6: Alumino Thermic Process (Thermite) - **Carbon + feldspar** - **Mg wire** - **Fe₂O₃ + Al Powder** - **Broken rail** - **Slag** - **Alumino-Thermic Process (Thermite)** ## 4.6 Metals and Alloys - **Reduction** is carried out in a blast furnace. The other type of furnace is used for heating purpose named as muffle furnace. ### (1) Smelting - The oxide of metal is reduced to a metal by carhon and the process is called carbon reduction process. - A reducing agent is used for reduction must he powerful and cheap. - Carbon in the form of coke is a satisfactory reducing agent. - The other reducing agents like carbon monoxide also can be used. - The carbon reduction process is extensively used for reduction of oxides of metals whose atomic weights are higher than that of manganese (55). Therefore iron oxide, zinc oxide, lead oxide, tin oxide, etc. are reduced by carbon. - In the process of smelting the calcined oxide ore is mixed with coke and flux (lime stone) and the mixture is strongly heated to high temperature. - The reducing agent, coke converts oxide of metal (ore) into molten metal, while the flux removes the gangue in the form of fusible mass known as slag. This process is called smelting. Smelting means to melt the ore. Smelting is carried out in (i) blast furnace or (ii) reverberatory furnace at higher temperature. - The iron oxide ore, Haematite (Fe₂O₃) is reduced by using coke as a reducing agent in a blast furnace. - In a blast furnace, the hot blast of dry air is blown into the furnace just above the hearth through a number of pipes called twyers. - In the well (hearth) of the furnace there are two tap holes. The upper tap hole is used to remove the slag being a lighter and lower tap hole is used to remove molten metal. - Fe₂O₃ + 3C → 2Fe + 3CO ## 4.7 Metals and Alloys ### B. Chemical Processes ### (1) Calcination - It is the process of heating the ore in absence of air or limited supply of air. - Calcination consists of the thermal decomposition of calcium ores. - Carbon dioxide is given out as by-product. - During calcinations moisture is removed from the ore. The process is carried out in reverberatory Furnace. - CACO₃ - CaO +CO₂↑ - Calcium Carbonate Calcium Oxide #### Example: Carbonate (CaCO₃) and hydroxide (Fe₂O₃.311₂O)type of ore ### (ii) Roasting - The process of heating the ore in presence of air is known as roasting. - The process is used for sulphide ores. The purpose of roasting is to oxidize the ore into suitable form which can be reduced to metal, also to remove the moisture. - During roasting volatile impurities like Sulphur, arsenic antimony are removed in the form of their oxides. #### Example :Sulphide ores like Zinc blende (Zns), Galena (Pbs), Cinnabar (HgS), Copper pyrite (CuFeS₂). - 2Zns +3O₂→2ZnO+2SO₂↑ - CuS+2O₂ CuSO₄ ### 4.3.3 Reduction - This is the important part of metallurgy in which the concentrated ore is reduced to a metal by the following process of reduction: - Smelting - Aluminothermic process and, - Electrolysis. ### 4.7.2 Non-Ferrous Alloys #### Brass - Due to high electrical conductivity, pure copper has been used in the manufacture of electric transmission cables and many electrical appliances. - In addition, copper has also been used in the manufacture of large number of useful alloys. Alloys of copper are mainly classified as: - Brasses (Copper and Zinc alloys) - Bronzes (Copper - Tin alloys) #### (a) Brasses - Brasses are the most important alloys of copper in which percentage of zinc goes upto 45% and other metals such as Sn, Mn, Al, Fe, Pb etc are added to give special properties to alloy. | Alloys | Composition | Properties | Uses | |---|---|---|---| | a. Brasses: | Cu=60-90% <br> Zn40-10% | These alloy possess greater strength, durability and machinability than copper and low m.p. than Cu and Zn. They are corrosion resistant and water resistant. | Making sheets, utensils, condenser tubes etc. | | Main brasses are: | | | | | (i) Commercial brass | Cu = 90% <br> Zn = 10% | It is golden in colour and stronger as well as harder than copper. | It is used for architectural metal work, jewellery, forging rivets, hardware, screws etc. | #### 4.13 Metals and Alloys | Alloys | Composition | Properties | Uses | |---|---|---|---| | (0) Dutch metal or low brass | Cu = HO% <br> Zn 20% | It has golden colour. It is suitable for all drawing and forming operations. | Used in making cheap jewellery, musical instruments, battery caps, flexible hoses, name plates etc. | | (Cartridge brass or spinningbrass | Cu = 70% <br> Zn = 30% | It is strong, highly ductile in the annealed state, harder and stronger than copper, can be cold deformed by drawing, pressing and extruction, and which hardens quickly. | Used for making tubes, sheets and cold press work locomotive, condenser tubes, household articles and cartridge cases etc. | | (iv) Muntz metal | Cu = 60% <br> Zn = 40% | It is stronger than 70/30 brass and suitable only for hot work. | It is used for hot stampings, sheets, etc, in making hot rolled products, marine fittings; condenser tubes, springs, chains. | #### Special brasses: Contain metals other than Cu and Zn. | Alloys | Composition | Properties | Uses | |---|---|---|---| | (1) Admiraltybrass | Cu = 70% <br> Zn = 29% <br> Sn = 1% | It possesseshigh corrosion and abrasion resistance, resistant to corrosion by seawater. | It is used for propellers and marine works. | | (ii) Naval brass | Cu = 59% <br> Zn = 40% <br> Sn = 1% | It possesseshigh abrasion resistance and corrosion resistance to seawater. | Used for marine castings and condenser tubes. | | (ui) German silver or Nickel silver | Cu = 62% <br> Zn = 18% <br> Ni = 20% | It is very resistant to corrosion by seawater, strong, ductile, malleable, appears like silver. | In decorative articles, utensils, table wares, ornaments, cutlery, coinage, screw, bolts. | | b. Bronzes: | Cu=80-95% <br> Sn = 20-5% | They are tough, strong, hard alloys, resistant to corrosion and wear can be easily casted and machined. | In making bells, coins, statues, utensils etc. | #### Main bronzes are | Alloys | Composition | Properties | Uses | |---|---|---|---| | (i) Gun metal | Cu = 85% <br> Sn = 5% <br> Zn = 5% <br> Pb = 5% | It is hard, tough and so strong that it can resist the force of explosion, resist corrosion by water and atmosphere. | Used for making gun barrels, In hydraulic and boiler fittings, foundryworks, heavy load bearing. | | (ii) Aluminium bronze | Cu = 90-93% <br> Al = 10-7% | It is quite strong, readily fusible, gives good castings resistant to corrosion, good abrasion resistance, beautiful: golden colour. | For all casting operations, bushes and bearings, jewellery, utensils, coins, photo frames, forged rods etc. | | (iii) Phosphor bronze | Cu = 96% <br> Sn = 3.75% <br> P = 0.25% | It is hard, tough, ductile, having low coefficient of friction, good casting property, resistant to sea water corrosion. | For making bearings, springs gears, bushes, taps, turbine blades, spindles for valves, pumps, electric switches, radio aerial wires, suspension wires for moving coil galvanometersetc. | ## 4.14 Metals and Alloys | Alloys | Composition | Properties | Uses | |---|---|---|---| | (iv) Nickelbronze |Cu-90% <br> NI-9% <br> Fe1% | They are hard, have high tensile strength, and resistant to corrosion even than copper. | Used for rolling purposes, shafts, valves and general purpose, semi-hard bearings. | | (v) Bell Metal | Cu 80% <br> Sn = 20% | They are hard, good resistant to surface water, produces sound etc. | in making bells and gangs, utensils etc. | ## 4.7.3 Duralumin - It is most useful alloy of aluminium. - Composition: Al95%, Cu = 4%, Mg = 0.5%, Mn = 0.5% ### Properties 1. Duralumin is light, tough, ductile, easily castable. 2. It is corrosion resistant alloy. 3. It is good conductor of heat and electricity. 4. Its tensile strength can be increased by heat treatment up to 2000 kg/cm². 5. It is as strong as mild steel, though its density is 1/3rd that of steel. 6. It can be easily worked and they have high machinability. ### Application 1. Duralumin is extensively used in making aeroplanes, automobiles and locomotive parts from the 'alclad' sheets. 2. It is used for all kinds of structural work. 3. It is used in making rivets, bars, body of vehicles, housing cases, sheets, tubes etc. 4. It is used in making cables, fluorescent tube caps, surgical instruments etc. 5. It is also used for ship building, pressings etc. ## 4.7.4 Wood's Metal - This is a fusible alloy of lead, bismuth, tin, and cadmium. - It is known as solders. - **Composition:** Bi = 50%. Pb = 25% Sn 12.5%, Cd=12.5%. - **Properties** 1. The most important property of wood's metal is that it is easily fusible. 2. It has low melting point i.em.p. = 71°C. ### Applications 1. Wood's metal is employed form making safety plugs of pressure cookers, boilers, fire alarms, automatic water sprinklers etc. 2. It is used for taking impressions of coins and medals. 3. It is used as soft solder for joining two metallic parts. 4. It is used for die mountings and fillers for tube bendings. 5. It is used in electric fuses (or fuse wires) because it is easily fusible. 6. It is used as casting for dental work. 7. It is also employed for making seals and gas tight joints in glass apparatus.