Material Types and Their Applications Study Notes

Course and Document Information

• Course Code: ECE 21112
• Subject: Material Types and Their Applications
• Prepared by: Asst. Prof. Emmanuel C. Guevara

General Classifications of Materials

• There are three basic classifications of materials: metals, ceramics, and polymers.
• The classification system is primarily based on two factors:
  • The chemical make-up of the material.
  • The atomic structure of the material.
• While most materials fall into one of these three distinct groups, there are some intermediate materials.
• Special classifications outside the three basic groups include:
  • Composites
  • Biomaterials
  • Semiconductors

Metals

• Composition: Metals are composed of metallic elements.
• Atomic Characteristics: They contain large numbers of non-localized (free) electrons.
• General Properties:
  • Good conductors of both electricity and heat.
  • Opaque to visible light.
  • Generally reflective when the surface is polished.
  • Strong yet deformable, making them highly versatile.
• Primary Applications: Extensively used in structural applications due to their strength and ductility.
• Specific Examples and Alloys:
  • Bronze
  • Aluminium
  • Brass
  • Cast Iron
  • Steel (used in bridges and cars on assembly lines)
  • Metal Sludge
  • Copper
  • Chrome-Vanadium (used in tools like wrenches)
• Applications and Specific Property Benefits:
  • Copper: Used as electrical conductor wire because of its good electrical conductivity and formability.
  • Alloy steel: Used for tools because of its high impact resistance.

Ceramics

• Composition: Ceramics are compounds formed between metallic and non-metallic elements.
• Chemical Types: Generally consist of oxides, nitrides, and carbides.
• Common Examples:
  • Clay
  • Cement
  • Glass (e.g., wine glasses)
  • Porcelain ("China")
• General Properties:
  • Insulative to both electricity and heat.
  • Highly resistant to high temperatures and harsh environments compared to metals and polymers.
  • Mechanically, they are very hard but brittle.
• Applications and Specific Property Benefits:
  • $Al_2O_3$ (Alumina) and $SiO_2$ (Silica): Used as refractories for containing molten metals due to their high temperature resistance.
  • Silicon Carbide ($SiC$): Used in cutting tools due to its extreme hardness and temperature resistance.
  • Specialized Uses:
    • Ceramic cutting blades.
    • Insulating tiles on the Space Shuttle.

Polymers

• Composition: Generally organic compounds based on carbon, hydrogen, and other non-metallic elements.
• Structure: Characterized by very large molecular structures (macromolecules).
• General Properties:
  • Typically have low densities.
  • May be extremely flexible and easy to form.
• Common Examples:
  • Plastics
  • Rubbers
  • Polyvinyl chloride (PVC) pipes.
  • Rubber tires.
• Applications and Specific Property Benefits:
  • Polyethylene: Used in food packaging because it is easily formed into thin, airtight films.
  • Kevlar: Used in bulletproof vests and helmets due to its high tensile strength.
  • Polyurethane coated polyester: Used in raincoats.

Composites

• Definition: A composite consists of more than one material type (e.g., a combination of metal/ceramic, ceramic/polymer, etc.).
• Design Goal: They are engineered to display a combination of the best characteristics of each component material, achieving properties that no single material could provide alone.
• Specific Examples:
  • Fiberglass: Consists of glass fibers embedded within a polymeric material. It acquires strength from the glass fibers and flexibility from the polymer matrix.
  • Plywood: A common layered composite.
  • Carbon fiber: Used in high-performance applications like bicycle frames.
  • Fiberglass automotive spoilers.
• Trends: Recent developments in material science have heavily involved the creation and refinement of composite materials.

Biomaterials

• Definition: Components intended to be implanted into the human body.
• Purpose: Replacement of diseased or damaged body parts.
• Critical Requirements:
  • Must be inert and not produce toxic substances when in contact with body fluids.
  • Must be biocompatible (compatible with body tissues).
• Material Types: All basic material types (metals, ceramics, polymers, and composites) may be used as biomaterials depending on the application.
• Example: Hip Implant (Components):
  • Acetabular cup
  • Liner
  • Femoral stem (composed of parts like the Taper, Neck, and Stem)
  • Bone tissue (host interface)
  • Cement (fixation agent)
  • Implant assembly

Semiconductors

• Electrical Nature: Semiconductors possess electrical properties that are intermediate between those of electrical conductors (metals) and insulators (ceramics/polymers).
• Sensitivity: Their electrical characteristics are extremely sensitive to minute concentrations of impurity atoms.
• Control: These electrical properties can be controlled over very small regions of the material (via doping).
• Impact: They have revolutionized the electronics and computer industries over the past 20 years.
• Applications and Specific Property Benefits:
  • Silicon ($Si$): Used in integrated circuits due to its unique and controllable electrical properties. Featured in forms like semiconductor wafers and Pin Grid Array (PGA) integrated circuits.
  • Gallium Arsenide ($GaAs$): Used in LEDs (Light Emitting Diodes) because it can convert electrical signals directly into light.