Chemical Bonds
• Alloys are metallic, homogeneous mixtures composed of two or more elements. • These mixtures include both pure metals and alloys. • Pure metals serve as the baseline for understanding metal properties (e.g., malleability, conductivity).
Types of Alloys:
Substitutional Alloys:
• In these alloys, some of the atoms of the base metal are replaced by atoms of a different element that have a similar size. • Example: Brass (Copper and Zinc) and Bronze (Copper and Tin) are common substitutional alloys. • These alloys are generally malleable and maintain properties such as lower electrical conductivity than pure metals. • They have similar densities to the base metal, offering a blend of properties between the elements involved.
Interstitial Alloys:
• Occurs when smaller atoms fit into the spaces (interstices) between the larger atoms in a crystal lattice. • Example: Steel, where small carbon atoms fit into the interstices of iron’s crystal lattice. • These alloys are harder and less malleable than substitutional alloys. • Due to the restricted movement of atoms, interstitial alloys tend to have higher melting points. • The hardness and strength come from the atoms’ interference with each other, making bending more difficult.
Combination of Substitutional and Interstitial Alloys:
• Example: Stainless Steel, a hybrid alloy, where chromium substitutes some of the iron atoms (substitutional), and carbon atoms occupy interstitial spaces. • Stainless steel exhibits both the hardness and toughness of interstitial alloys and the corrosion resistance and sheen from chromium substitution.
Properties
• Substitutional Alloys (e.g., brass and bronze): - Tend to be malleable (easy to shape). • Lower electrical conductivity compared to pure metals. • Density is similar to the pure metal from which they are derived. • Interstitial Alloys (e.g., steel): • Generally harder and less malleable due to atoms interfering with each other’s movements. • Have a higher melting point due to restricted atomic movement. • Combination Alloys (e.g., stainless steel): • Exhibit unique properties like corrosion resistance, shine, and hardness.
These three types of alloys highlight how combining different elements can drastically alter the properties of metals to make them suitable for various industrial and practical applications.