Metals and Their Properties

Iron  

- Naturally occurring magnetic material (also nickel & cobalt).  

- Silvery white/greyish, ductile, malleable.  

- Melting point: 1538°C  

- Boiling point: 2862°C  

Forms of Iron (by carbon content):  

- Wrought iron (0.003% C): soft, malleable, weldable → nails, bolts.  

- Low carbon steel (0.3% C): moderate strength → structural pieces.  

- Medium carbon steel (0.3–0.5% C): stronger → i‑beams, frames.  

- High carbon steel (0.55–0.8% C): hard, heat‑treated → drills, chisels.  

- Tool steel (0.8–1.7% C): very hard → saws, files.  

- Cast iron (1.8–4% C): very hard, brittle → machinery, engines.  

Alloys of Iron  

- Stainless steel: iron + 11.5% chromium → corrosion‑resistant, strong, low maintenance.  

  - Uses: architecture, transport, medical equipment, energy, food industry.  

- Carbon steel vs Stainless steel:  

  - Carbon steel → stronger, rusts easily.  

  - Stainless steel → softer, weldable, corrosion‑resistant.  

Structural Steel  

- Used in construction (beams, bridges, factories).  

- High strength‑to‑weight ratio.  

- Common type: carbon‑manganese steels (ASTM A36).  

Famous Structures  

- Eiffel Tower: 7,000 tons of puddling iron, expands/contracts with temperature.  

- Burj Khalifa: 31,400 tons of steel, reinforced concrete core.  

- Empire State Building: 57,000 tons of steel frame, limestone & granite exterior.  

Rusting & Corrosion  

- Rust = hydrated iron oxide (iron + oxygen + water).  

- Factors: temperature, humidity, impurities, pH.  

- Faster near the seaside (salt accelerates rusting).  

- Prevention methods:  

  - Paint, oil/grease, galvanisation (zinc coating), alloys (stainless steel), electroplating, sacrificial protection (zinc plates on ships).  

Zinc  

- Bluish‑white, lustrous, conductor of electricity & heat.  

- Melting point: 419.5°C  

- Boiling point: 907°C  

- Uses: galvanisation, zinc oxide (rubber, UV protection), batteries, alloys (brass).  

- Biological role: essential mineral for immunity, growth, and wound healing.  

- Excess zinc → harmful (loss of smell/taste, toxicity).  

Mining & Environment  

- India: major iron ore & zinc reserves (Rajasthan, Karnataka, Odisha).  

- Issues: illegal mining, ecological damage, battery waste disposal.  

- Recycling zinc/carbon batteries → reduces pollution, recovers valuable metals.