Ferro Alloys

1. Nickel (Ni):

Nickel is a hard, silvery metal, making up only 0.008% of the earth’s crust, though it is believed to constitute some 10% of the earth’s interior core. Meteorites are also found to contain much nickel. Nickel does not rust and is thus use¬ful for plating purposes. It is one of the hardest, most malleable and least fusible metals known.

It is less mag¬netic than iron and is thus useful for constructing metal parts located near compasses. The main ore of nickel is pentlaudite, a complex mixture of nickel, iron and sulphur. It is also often found in association with copper.

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Uses:

(a) Nearly half the world’s output of nickel is used in steel-making, its use in stainless steel, nickel alloys and plates being the most important. Adding 6% of nickel to steel in¬creases its strength, stiffness and ductility, and this alloy is extensive¬ly used in making constructional machinery and transport equipment.

A higher nickel content up to 35% makes steel highly resistant to heat and acid, qualities essential in such manufactures as turbine blades, marine fittings, tools and machine parts. Stainless steel for cutlery and tableware contains 8% nickel and 18% chromium.

(b) Of the nickel alloys, the most notable is nickel-copper, first made in the nickel-smelting plants of Sud¬bury, Canada where the two min-erals are often found together. This led to the invention of Monel metal (with 67% of nickel and 28% cop¬per), used in kitchenware, laundry fittings, turbine blades, precision in¬struments, and electrical apparatus.

(c) Another nickel alloy made with copper and zinc, is nickel silver, used in making tableware.

(d) An alloy known as Invar, made up of iron and 36% nickel has the property of minimum expansion at high temperatures. This is vital in making accutate measuring tapes, chronometer parts and railway lines that are subject to much heating and expansion.

(e) Nickel and its alloys are used in making coins, armour plates, sub-marine cable sheathing, radio trans¬formers, telegraph relay parts, flame tubes, batteries and in space re¬search.

 

2. Manganese (Mn):

Manganese, the twelfth most common element in the earth’s crust, is a silvery metal. There are two main commercially exploited manganese ores: pyrolusite (MnO2) and psilomelane, an hydrated oxide of manganese. Manganese is ob¬tained from the ores by electrolytic methods. Manganese is also found in nodular deposits on the sea-floor but these are not yet commercially exploitable.

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Uses:

(a) The greatest use of manganese is as a ferro-alloy. Almost all steel contains some manganese from 0.5% to 12%. A little manganese added to iron removes gases, and acts as a ‘cleanser’ in the manufacture of steel. The addition of 2%manganese adds strength and 12% imparts great toughness and resistance to abrasion, as in the making of switches, railway lines, dredge-bucket teeth and jaws of rock crushers used in mining, dredging and heavy constructional work.

(b) Manganese compounds are used in making disinfecting liquids; as a decolorizer in glass-making; and for the manufacture of bleaching pow¬der, used in the textile industry. Manganese is used in making electric batteries, in colouring pottery, tiles and bricks.

(c) It is alloyed with copper to pro¬duce a kind of manganese-bronze, and with a little nickel to make ‘manganin’ which is highly resistant to corrosion.

 

 

3. Chromium (Cr):

Chromium is a hard, silvery metal with a bluish tinge and a metallic lustre. It makes up 0.02% of the earth’s crust occurring in nature in the form of chromate of iron or chromite (FeO. Cr2O3). As it does not rust or tarnish easily, and is capable of taking a high polish, it is widely used in the metallurgical industry where a bright metallic surface is required.

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Uses:

(a) Chromium is essential in making stainless steel (which contains 18% chromium and 8% nickel), for mak¬ing cutlery, kitchenware, household fittings, surgical apparatus and chemical equipment. Chrome steel is a superior steel used for marine and electrical engineering aircraft parts and warship super-structures.

(b) Chromium plating is done by electro-deposition of chromium on nickel or steel plates to improve their durability and resistance to corrosion and rust. It is widely ap¬plied in the automobile industry for plating bumpers, radiator-grills and car-fittings, as well as for cheaper cutlery.

(c) Chromium is also used in making nickel-chromium alloys such as nichrome which is highly resistant to electric current and is thus used as a safety measure in electric wires, toasters and other electrical ap¬pliances.

(d) Chromite or chrome ore (which contains up to 68% of chromic ox¬ide) is used for making refractories for lining furnaces of steel plants where its resistance to very high temperature is highly desirable.

(e) Chromium salts and compounds such as chromates are used in the manufacture of paint pigments, and in the chemicals industry. Chromates are also useful for tanning leather and treating metal and wood to pre¬vent rotting. Chromic acid is a powerful oxidizing agent used in chemical plants.

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4. Tungsten (W):

Tungsten is a heavy metal, with a melting point higher than any other metal at 3,370°C (6,098°F). Its extreme ductility and resistance to abrasion and electricity makes it indispensable in the metallurgical industry.

Tools made of tungsten carbide are second in hardness only to industrial diamonds and will last many times longer than the best steel. The chief source of tungsten is wolfram or wolframite, often found in association with tin cassiterites in quartz veins. It is also ob-tained from scheelite, and from hubnerite.

Uses:

(a) Tungsten is used widely in steel alloys (containing 15-20% of tung¬sten) for the manufacture of high¬speed cutting tools, which are cap¬able of retaining their hardness and high tensile strength even at ex¬tremely high temperatures. Tung¬sten carbide is even harder and is employed in the cutting edges of machine tools, razor blades, armour plates, jet engines and the construc¬tion of rockets and missiles.

(b) Pure tungsten is one of the few metals that can be used to make the filaments of electric light bulbs be¬cause of its very high electrical re¬sistance. Most other metals would melt at such high temperatures.

5. Cobalt (Co):

Cobalt is a hard, blue metal and has many properties similar to those of iron. It was first discovered by George Brandt in 1735. It is often found together with nickel, as in the Sudbury region of Canada, or with many other minerals. Cobalt is usually derived as a by-product from the working of complex metal¬lic ores.

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Uses:

(a) The original use of cobalt was for the making of blue pigments for staining window glass, pottery and bottles; as finely ground ‘smalt’ for making coloured papers; and in paints for artists as ‘cobalt blue’. Cobalt compounds are also used as invisible ink, which when heated or dried appears as visible blue.

(b) Modern uses of cobalt, depend on its hardness and electrical properties. It is used in the manufacture of cobalt steel and in other alloys. Al Ni Co is a cobalt steel comprising aluminium, nickel and cobalt which is used for making very strong permanent magnets, as in magnetos and dynamos.

Another cobalt alloy is satellites made up of 62% cobalt, 28% chromium and a little tungsten, molybdenum or nickel, which is used in making cutting tools, jet engines, gas turbines and in the generation of atomic energy.

(c) Radioactive cobalt isotopes have medical applications, especially in connection with radiotherapy.

6. Vanadium (V):

Vanadium is a hard silvery metal named after a Scandinavian goddess of beauty by its discoverer Sefstrom in 1830. Its ores are carnotite, patronite, descloisite and rescoelite. It is also derived as a by-product from boilers that burn oil drilled in the Caribbean region as traces of vana¬dium are found in this oil. It is also produced as a by-product of uran¬ium. Difficult extraction makes its price high.

Uses:

(a) The principal use of vanadium is in making steel. In smelting it acts as a ‘scavenging agent’ removing the non-metallic impurities, and at the same time improving the grain of the steel, and increasing its ductility and resilience. Steel that contains 1% of vanadium is highly resistant to impact and to abrasion. It is thus used in tools, springs and machine parts in constructional engineering.

(b) Vanadium compounds and salts are used in making paints and dyes, coloured glasses and glazes, and in the chemicals industry, e.g. as a ca¬talyst in the manufacture of sul¬phuric acid. It is highly poisonous and is employed in making insecti¬cides and fungicides.

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7. Molybdenum (Mo):

Molybdenum is a silvery metal with many properties similar to those of chromium, and may re¬place tungsten in steel alloys be¬cause of its great resistance to shock and heat, and partly because of the low availability of tungsten whose production has always been domi¬nated by China.

Another advantage of molybdenum in steel manufacture is that suitable qualities can be ob¬tained with the use of only half as much molybdenum as tungsten. The two main ores of molybdenum are molybdenite and wulfenite which occur in quartz veins in granitic rocks. The former is more readily available and yields a high metallic concentrate of 48% or more. Some molybdenum is also derived as a by-product of copper smelting.

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Uses:

(a) The greatest use of molybdenum is in making alloyed steel for the manufacture of high-speed tools and machine parts, including parts of gas turbines and jet engines, be¬cause it imparts toughness and ten-sile strength. It can be used at high working temperatures. Some of the best steels are made with the addi¬tion of nickel-chromium-molyb¬denum combinations.

(b) Pure molybdenum is highly re¬sistant to electric current and, like tungsten, is used in the manufacture of electric lamps, valves, X-ray tubes, permanent magnets, electrical con¬tact points and in other electrical apparatus. In space engineering many missile and rocket parts use molybdenum. It is also employed in making armour plating, vaults and pigments in paints and dyes.