Principles of Metallurgy — Telangana (SSC) Class 10 Science Solutions (Free)

Ore: A naturally occurring mineral deposit from which a metal can be extracted economically. Examples: 1. Bauxite (Al₂O₃·2H₂O) - ore of aluminum 2. Hematite (Fe₂O₃) - ore of iron 3. Chalcopyrite (CuFeS₂) - ore of copper Concentration of ore: Process of removing unwanted impurities (gangue) from ore to increase metal content. Methods: 1. Gravity separation (different densities) 2. Magnetic separation (magnetic property difference) 3. Froth flotation (wetting properties difference)

Roasting: • Ore heated strongly in presence of air/oxygen • Converts ore to oxide • Example: 2ZnS + 3O₂ → 2ZnO + 2SO₂ • Used for sulfide ores (galena, chalcopyrite, sphalerite) Calcination: • Ore heated strongly in absence of air/limited oxygen • Decomposes ore by heat • Example: CaCO₃ → CaO + CO₂ • Used for carbonate ores (limestone, dolomite) and hydroxide ores (bauxite) Key difference: Roasting requires oxygen; calcination requires absence of oxygen

Blast Furnace has three zones: 1. Combustion Zone (bottom, 1500°C): Coke burns in air → C + O₂ → CO₂ + heat 2. Reduction Zone (middle, 800-1200°C): Iron oxide reduced → Fe₂O₃ + 3CO → 2Fe + 3CO₂ 3. Fusion Zone (upper): Limestone (CaCO₃) decomposes → CaO + CO₂. CaO combines with impurities (silica) → slag (CaSiO₃) separates from molten iron Output: Molten iron (pig iron) at bottom; slag floats on top Overall: Fe₂O₃ + 3CO → 2Fe + 3CO₂

Reactivity series: An arrangement of metals in decreasing order of their reactivity (tendency to lose electrons). Order (most to least reactive): K > Na > Ca > Mg > Al > Zn > Fe > Ni > Sn > Pb > Cu > Hg > Ag > Au Application in metal extraction: 1. Highly reactive metals (K, Na): Extracted by electrolysis of molten compounds 2. Moderately reactive metals (Al, Mg, Zn): Extracted by electrolysis or carbon reduction 3. Less reactive metals (Fe, Cu): Extracted by carbon/CO reduction 4. Least reactive metals (Ag, Au): Found free in nature; simple purification needed Rule: Metal higher in series can displace metal lower in series from its salt

Refining crude iron (pig iron) into steel: Process (Bessemer or Open Hearth method): Step 1: Molten pig iron heated in furnace Step 2: Air blown through molten iron → oxygen reacts with impurities Step 3: Carbon oxidized: C + O₂ → CO₂ (removes excess carbon) Step 4: Phosphorus oxidized: 4P + 5O₂ → 2P₂O₅ Step 5: Silicon oxidized: Si + O₂ → SiO₂ Step 6: Lime (CaO) added → forms slag with oxides Step 7: Slag removed; refined steel remains Main impurities removed: Carbon, phosphorus, silicon, sulfur Result: Steel (iron + 0.1-1.5% carbon) with desired properties

Alloy: A homogeneous mixture of two or more metals, or a metal with non-metal. Examples: 1. Steel (Fe + C, 0.1-1.5%): Uses: Tools, machines, structures, vehicles 2. Brass (Cu + Zn, 60% Cu + 40% Zn): Uses: Decorative items, pipes, cartridge cases 3. Bronze (Cu + Sn, 88% Cu + 12% Sn): Uses: Sculptures, coins, bells, bearings Advantages of alloys over pure metals: • Greater hardness and strength • Better corrosion resistance • Lower melting point • Enhanced appearance

Electroplating: Coating one metal with another using electrical current. Setup: • Anode: Metal to be deposited (e.g., zinc) • Cathode: Object to be plated (e.g., iron) • Electrolyte: Salt solution of plating metal (ZnSO₄) • Power source: Battery/DC source Process: • Positive terminal → Anode (zinc) → electrons removed → Zn → Zn²⁺ • Zn²⁺ migrate to cathode through electrolyte • Cathode (iron): Zn²⁺ + 2e⁻ → Zn deposited on iron surface Why zinc on iron: 1. Zinc is more reactive than iron 2. Zinc oxidizes preferentially → protects iron from rusting (sacrificial protection) 3. Zinc coating is hard, attractive, resistant to corrosion