Form 4 Chemistry Bab 8: Manufactured Substances in Industry
8.1 Alloy and Its Importance
An alloy is a mixture of two or more elements where the main element is a metal (e.g. duralumin, bronze, brass, steel, stainless steel, pewter). (p.254)
Alloys are generally harder and more resistant to corrosion than their pure metal, because foreign atoms of different sizes disrupt the orderly layered atomic arrangement of the pure metal, making it harder for layers to slide over one another. (p.257)
Example compositions/uses: duralumin (Al, Cu, Mg, Mn) for aeroplane bodies; bronze (Cu, Sn) for medals/monuments; brass (Cu, Zn) for keys/instruments; steel (Fe, C) for building structures; stainless steel (Fe, Cr, Ni, C) for cutlery; pewter (Sn, Sb, Cu) for souvenirs. (p.258)
Superconductors are alloys/materials with zero electrical resistance at very low temperature, used e.g. in Maglev train magnets. (p.259)
8.2 Composition of Glass and Its Uses
Basic properties of all glass: transparent, hard but brittle, chemically inert, waterproof, and an electrical and heat insulator. (p.260)
Fused silica glass is made from silica (SiO2) alone; has a very high melting point (~1800°C) and resists thermal expansion/contraction, used for telescope lenses. (p.260)
Soda-lime glass (silica + soda Na2CO3 + limestone CaCO3) has a low melting point (~1000°C), used for bottles/jars. Borosilicate glass (silica + soda + limestone + boron oxide + alumina) resists thermal shock, used for laboratory glassware. Lead crystal glass (silica + soda + lead(II) oxide) is denser with a high refractive index, used for prisms. (p.261)
8.3 Composition of Ceramics and Its Uses
Ceramic is a solid made of inorganic, non-metallic substances (metal, metalloid or non-metal compounds), shaped and hardened by high-temperature heating; basic properties: hard and strong, break easily (brittle), heat and electrical insulator, chemically inert, high thermal resistance. (p.263)
Traditional ceramics are made from clay such as kaolin (Al2O3.2SiO2.2H2O), used for bricks, pottery and crockery. (p.263)
Advanced ceramics (e.g. silicon carbide) are made from inorganic compounds such as oxides, carbides and nitrides; more heat- and abrasion-resistant, used for cutting discs, brake discs and tungsten carbide rings. (p.264)
8.4 Composite Materials and Its Importance
A composite material combines a matrix substance and a strengthening substance to form a material with better properties than either original component alone (e.g. wood = lignin matrix + cellulose fibres). (p.266)
Reinforced concrete (concrete + steel bars/wire mesh) has both high compression and high stretching strength, used for bridges, dams and buildings. (p.266)
Fibre glass (plastic + glass fibres) is used for helmets, car bumpers and printed circuit boards; optical fibre (silica glass fibre core + glass/plastic cladding + plastic jacket) transmits data as light via total internal reflection, replacing copper cables. (p.267)
Photochromic glass (glass + silver chloride/copper(I) chloride) darkens in sunlight (Ag formed) and clears in dim light, used for car windows and camera lenses; YBCO ceramic superconductors are used to make superconductor magnets for MRI/NMR machines and particle accelerators, conducting current with zero resistance at very low temperature. (p.268)