Introduction to Metallurgy

Metallurgy Overview

• Metallurgy is the study of metals and alloys, crucial for various industries.
• Approximately 80 out of 103 elements in the periodic table are classified as metals.
• Non-metals reside on the right side of the periodic table, while metalloids, with properties of both metals and non-metals, form a transitional group (e.g., Carbon, Silicon, Boron).

Properties of Metals

• Metals ionize positively in solution and typically exist as crystalline solids, except mercury and gallium (liquids at room temperature) and hydrogen (a reactive gas).
• Metals are opaque due to valence electrons absorbing light and exhibit metallic luster from the reflection of light by free electrons.
• Excellent conductors of electricity and heat, attributed to mobile free electrons.
• Exhibit high hardness, melting, and boiling points due to strong interatomic bonding within their crystalline structure.
• Ductility and malleability arise from multiple slip planes allowing dislocation movement.
• Emit a characteristic metallic ring when struck.
• Most metals appear white; notable exceptions include gold and copper, which are significant in dental applications.

Pure Metals in Dentistry

• Commonly used pure metals are:
  • Gold foil for posterior restorations.
  • Mercury and gallium in amalgam restorations.
  • Titanium for implants and prosthetic devices.

Shaping of Metals

• Casting: Melting metal or alloy and shaping it in a mold.
• Cold Working: Mechanically forming a solidified block into shapes such as rods or wires by applying stress above the yield strength.
• Powder Metallurgy: Bonding metal particles by pressing and heating below melting temperature, resulting in shrinkage and reduced porosity (e.g., amalgam tablets).

Solidification of Metals

• Cooling molten metal can be plotted; temperature decreases until reaching a constant (freezing point) before further cooling.
• Latent heat of fusion is released during solidification, equal to the heat of fusion for one gram of substance shifting from liquid to solid state.
• Crystals begin to form at freezing point, where temperature remains until complete crystallization.

Mechanism of Solidification

• Occurs through two steps:
  • Nuclear Formation: Atoms aggregate to form crystallization nuclei, occurring via homogeneous (self-nuclei) or heterogeneous (foreign particles) nucleation.
  • Crystallization: Can result in single crystal (rare) or polycrystalline structures with growing nuclei forming trees of crystals.

Factors Affecting Grain Size

• Rate of cooling influences grain size:
  • Rapid cooling yields many nuclei and smaller grains.
  • Addition of nucleating agents produces finer grain structure.

Alloys

• Combinations of two or more metals enhance mechanical properties for dental uses as pure metals are too soft.
• Classification:
  • By number of constituents: binary (2), ternary (3), etc.
  • By miscibility in solid state:
    • Solid Solution Alloy: Completely soluble in liquid and solid states.
    • Eutectic Alloy: Soluble in liquid but not in solid state.
    • Intermetallic Compound: Forms when metals have a strong chemical affinity.

Types of Solid Solutions

• Substitutional Solid Solutions: Different atoms occupy equivalent lattice positions; conditions include similar lattices, same valence, atomic size differences under 15%.
• Interstitial Solid Solutions: Smaller atoms fit between larger atom spaces (e.g., carbon in iron).
• Properties: Homogeneous, exhibiting increased strength and hardness but typically reduced ductility.

Eutectic Alloys

• Completely soluble in liquid but differing solubility in solid states.
• Characterized by a distinct melting point, low corrosion resistance, and brittleness due to a heterogeneous structure.

Intermetallic Compounds

• Formed from metals with chemical affinities, characterized by hardness and brittleness and often possessing unique properties distinct from the constituent metals.

This quiz explores the fundamental concepts of metallurgy, focusing on the properties of metals, nonmetals, and metalloids. It delves into the classification of elements based on their chemical properties and their placement in the periodic table. Brush up on your understanding of how these elements behave and interact in various applications.