Introduction of Engineering Materials

Materials are the substances from which things are composed. The fundamental science of materials looks at their structure and properties. Materials engineering is the processing and selection of materials. Processing → Structure → Properties → Application. (Read arrow as determines)

A material’s structure determines its properties which in turn determine the applications for which it can be used. However, with knowledge of the structure and some creativity, the engineer can formulate a process that will change the structure and enhance the properties, thereby enabling it to be used for a sophisticated application.

Classification of Materials

One way to classify materials is in these six categories:

1. Metals/Alloys
2. Ceramics
3. Glasses
4. Polymers
5. Composites
6. Semiconductors

An alternate classification of materials uses categories based on their properties:

1. Structural materials
2. Electronic materials
3. Magnetic materials
4. Semiconducting materials
5. Optical materials

Metals/Alloys

• Structure:
  • any metallic element /alloy (see periodic table)
  • simple crystalline structure
  • metallic atomic bonding
  • delocalized electrons
• Properties:
  • high conductivity
  • not transparent to visible light (i.e. opaque)
  • lustrous
  • strong
  • ductile
• Examples:
  • iron (Fe)
  • steel (Fe+C)
  • aluminum (Al)
  • copper (Cu)
  • brass (Cu+Zn)
  • magnesium (Mg)
  • titanium (Ti)
  • nickel (Ni)
  • zinc (Zn)

Ceramics/ Glasses/ & Glass-Ceramics

• Structure:
  • compounds of metals and non-metals (see periodic table)
  • primarily ionic atomic bonding (however, these bonds might have some covalent character)
  • ceramics are crystalline (crystalline structure can be relatively simple to relatively complex)
  • glasses are amorphous (primarily made of SiO₂)
  • glass-ceramics are devitrified glasses
• Properties:
  • insulative
  • refractory
  • wear resistant
  • brittle
  • strong
  • hard
  • chemically stable
  • high melting temps
  • glasses are transparent
  • gl-cer can have low thermal expansion (good for thermal stresses)
• Examples:
  • oxides (Al₂O₃, MgO, SiO₂)
  • nitrides (Si₃N₄)
  • carbides
  • silicates
  • lithium-alumino-silicates
  • clay
  • cement

Polymers (aka Plastics)

• Structure:
  • organic compounds primarily based on C and H.
  • large molecular structures in a chain or network configuration
  • atomic bonding is covalent on the chains or network and additionally there is secondary bonds acting between the chains or network.
  • 5-95% crystalline in relatively simple structures to very complex
• Properties:
  • very ductile (elastic and plastic)
  • low density
  • low strength
  • low melting temp
  • high chemical reactivity
  • insulative
• Examples:
  • polyethylene
  • PVC
  • rubber
  • acrylics - O
  • nylons - N
  • fluoroplastics - F
  • silicones - Si

Composites

• Structure:
  • Engineered materials of more than one type, usually a matrix material with fibers or particulates
• Properties:
  • Could be anything, depending on constituents, relative amounts and geometry.
  • Examples:
  • fiberglass
  • concrete
  • asphalt
  • wood

Semiconductors

• Structure:
  • elemental (Group IVA)
  • compound (Groups IIIA/VA or IIB/VIA)
  • covalent/ionic bonding
  • similar to ceramics
• Properties:
  • intermediate conductivity which is extremely sensitive to minute concentrations of impurities
  • precise control of chemical purity allows precise control of electrical properties
  • techniques exist to produce variations in chemical purity over very small spatial regions
  • hence, sophisticated and minute circuitry can be produced in exceptionally small areas (This is what makes micro-circuitry possible in ICs)
• Examples:
  • Si, Ge, Sn
  • CaS
  • GaAs