Metallurgy — Maharashtra (SSC) Class 10 Science Solutions (Free)

Metallurgy is the science of extracting metals from their ores and purifying them. The reactivity series arranges metals in order of decreasing reactivity: K, Na, Ca, Mg, Al, Zn, Fe, Cu, Hg, Ag, Pt, Au. More reactive metals are extracted using electrolysis, while less reactive metals are extracted by heating with carbon or carbon monoxide.

Roasting is the heating of a sulfide ore in the presence of oxygen to convert it to an oxide. For example, 2PbS + 3O2 → 2PbO + 2SO2. Calcination is the heating of a carbonate ore in the absence of air to drive off CO2. For example, CaCO3 → CaO + CO2. Both are concentration and purification steps.

In electrorefining, impure copper is used as the anode and pure copper as the cathode in a solution of copper sulfate. During electrolysis, copper from the anode dissolves and is deposited on the cathode, while impurities either fall to the bottom as anode mud or remain in solution. This produces 99.99% pure copper used in electrical conductors.

Corrosion is the slow degradation of metals by reaction with atmospheric oxygen and moisture. Rusting: 4Fe + 3O2 + 6H2O → 4Fe(OH)3, a reddish-brown hydrated iron(III) oxide. Prevention methods: painting to exclude air and moisture, galvanizing with zinc coating, oiling, and using stainless steel alloys.

The thermite process uses aluminum as a reducing agent to extract metals from their oxides at high temperatures. For example, Fe2O3 + 2Al → 2Fe + Al2O3 + heat (1600°C). This highly exothermic reaction is used to extract metals like Fe, Cr, Mn that cannot be easily reduced by carbon due to their high reactivity.