LEAD
Lead is a bluish grey metal with a high metallic lusture when freshly cut. It is a very durable and versatile material. The heavy metal obtained from the bottom of the furnace is further oxidized in Bessemer’s converter to remove most of the impurities.
Lead (/lɛd/) is a chemical element in the carbon group with symbol Pb(from Latin: plumbum) and atomic number 82. Lead is a soft, malleable and heavy post-transition metal. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed to air. Lead has a shiny chrome-silver luster when it is melted into a liquid. It is also the heaviest (has the highest atomic number) non-radioactive element (two radioactive elements, namely technetium and promethium, are lighter).
Lead is used in building construction, lead-acid batteries, bullets and shot, weights, as part of solders, pewters, fusible alloys, and as a radiation shield. Lead has the highest atomic number of all of the stable elements, although the next higher element, bismuth, has one isotope with a half-life that is so long (over one billion times the estimated age of the universe) that it can be considered stable. Lead’s four stable isotope shave 82 protons, a magic number in the nuclear shell model of atomic nuclei. The isotope lead-208 also has 126 neutrons, another magic number, and is hence double magic, a property that grants it enhanced stability: lead-208 is the heaviest known stable isotope.
If ingested, lead is poisonous to animals and humans, damaging the nervous system and causing brain disorders. Excessive lead also causes blood disorders in mammals. Lead is a neurotox in that accumulates both in soft tissues and the bones. Lead poisoning has been documented since ancient Rome, ancient Greece, and ancient China.
Properties
Lead has properties of high density and easy work ability. It has very good resistance to corrosion and many acids have no chemical action on it. Its melting point is 327°C and specific gravity is 11.35. It is the softest and heaviest of all the common metals. It is very malleable and may be readily formed into foil. It can readily be scratched with fingernail when pure.
Applications
The lead pipes installed by the Romans in the public baths in Bath, England, nearly 2000 years ago are still in use. Lead is used in safety plug in boilers, fire door releases and fuses. It is also used in various alloys such as brass and bronze. It finds extensive applications as sheaths for electric cables, both overhead and underground. Its sheets are used for making roofs, gutters etc. It is employed for chemical laboratory and plant drains. In the soldering process, an alloy of lead and tin is most widely utilized as a solder material for joining metals in joining processes.
Reference Introduction to basic Manufacturing Processes and Workshop Technology by Rajender Singh.
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