8.1 Alloy and Its Importance
Definition of Alloy
An alloy is a mixture of two or more elements where the main element is a metal.
Comparison Between Pure Metal and Alloy
- Pure Metal: Atoms are uniform in size and arranged in orderly layers. When force is applied, layers of atoms easily slide over one another, making pure metals soft, ductile, and malleable.
- Alloy: Foreign atoms of different sizes are added to the pure metal. These foreign atoms disrupt the orderly arrangement of host atoms and block layers from sliding over each other easily, making alloys harder, stronger, and more resistant to corrosion.
Examples of Alloys and Their Composition
- Bronze: $90\%$ Copper, $10\%$ Tin (Used in monuments, medals, and statues).
- Brass: $70\%$ Copper, $30\%$ Zinc (Used in musical instruments, door knobs, and keys).
- Steel: $99\%$ Iron, $1\%$ Carbon (Used in construction, bridges, and vehicle bodies).
- Stainless Steel: $73\%$ Iron, $18\%$ Chromium, $8\%$ Nickel, $1\%$ Carbon (Used in cutlery, surgical tools, and cookware).
- Duralumin: $95\%$ Aluminium, $4\%$ Copper, $1\%$ Magnesium/Manganese (Used in aircraft bodies and racing bicycles due to its light weight and strength).
- Pewter: $96\%$ Tin, $3\%$ Copper, $1\%$ Antimony (Used in decorative souvenirs and tableware).
8.2 Composition and Uses of Glass and Ceramic
Types of Glass
- Fused Silica Glass: Made of silicon dioxide ($\text{SiO}_2$) without other chemicals. Has a high melting point ($1700^\circ\text{C}$), high thermal resistance, and high optical clarity. (Used in telescope lenses and optical fibers).
- Soda-lime Glass: Made of silica ($\text{SiO}_2$), soda ($\text{Na}_2\text{CO}_3$), and limestone ($\text{CaCO}_3$). Has a lower melting point ($1000^\circ\text{C}$), easy to mold, but cracks under thermal shock. (Used in bottles, window panes, and light bulbs).
- Borosilicate Glass: Made of silica ($\text{SiO}_2$), soda ($\text{Na}_2\text{CO}_3$), limestone ($\text{CaCO}_3$), boron oxide ($\text{B}_2\text{O}_3$), and aluminium oxide ($\text{Al}_2\text{O}_3$). Has high resistance to thermal expansion and chemicals. (Used in laboratory glassware and Pyrex cookware).
- Lead Crystal Glass: Made of silica ($\text{SiO}_2$), soda ($\text{Na}_2\text{CO}_3$), and lead(II) oxide ($\text{PbO}$). Has a high refractive index, heavy density, and high luster. (Used in decorative glassware, crystal decanters, and chandeliers).
Ceramics
Ceramics are inorganic non-metallic solids made from clay (such as kaolin) subjected to high temperatures.
- Traditional Ceramics: Made from natural clay (kaolin). (Used in bricks, pottery, and roof tiles).
- Advanced Ceramics: Made from inorganic compounds like silicon carbide ($\text{SiC}$) and alumina ($\text{Al}_2\text{O}_3$). Excellent heat and wear resistance. (Used in engine blocks, cutting tools, medical implants, and brake discs).
8.3 Composite Materials and Their Importance
Definition of Composite Material
A composite material is a material produced by combining two or more non-homogeneous materials with different physical properties to form a new material with superior properties distinct from its parent components.
Examples of Composite Materials and Their Components
- Reinforced Concrete: Concrete (matrix) + Steel bars/mesh (reinforcement). High compression and tensile strength; used in high-rise buildings and bridges.
- Fiberglass: Plastics (matrix) + Glass fibers (reinforcement). Light, strong, weather-resistant; used in water tanks, helmets, and boat hulls.
- Optical Fiber: Low refractive index glass cladding (matrix) + High refractive index silica core (reinforcement). Enables high-speed data transmission via total internal reflection.
- Photochromic Glass: Glass (matrix) + Silver chloride ($\text{AgCl}$) or Silver bromide ($\text{AgBr}$) crystals (reinforcement). Darkens when exposed to UV light and becomes transparent in dim light.
- Superconductors: Yttrium barium copper oxide ($\text{YBa}_2\text{Cu}_3\text{O}_7$) ceramic matrix. Has zero electrical resistance at very low temperatures; used in MRI machines and Maglev trains.