Categories of Materials

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Categories of Materials

• Organics
• Metals and Alloys
• Polymers or Plastics
• Ceramics
• Composites

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Organics

• Organics are or were living organisms
• Composed of mostly carbon and Hydrogen
• Structure depends on the way cells develop, not
  by human manipulation
• Renewable, sustainable
• Infinite variety
• Genetically alterable

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Organics-Wood

• Hardwood- Deciduous, tend to be harder and more
  expensive
• Softwood- Conifers, tend to be softer and cheaper
• Plywood- Much stronger and dimensionally stable
• Engineered Beams- Construction only
• Oriented Strand Board and MDF- Dimensionally
  stable and cheap

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Metals and Alloys

• Metals are pure elements which comprise about
  three-fourths of the periodic table
• Few are used in their pure form because of
• Hardness too hard or too soft
• Cost scarcity of element
• Engineers need certain characteristics that can
  only be accomplished by a blending of elements
• Metals are malleable, reflective, and
  electrically conductive material
• They are excellent conductors of electricity and
  heat

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Metals

• Possess material properties, including
• high strength and toughness
• high electrical conductance
• high thermal conductance
• luster
• Examples
• aluminum - copper - gold - zinc - iron - lead -
  nickel
• silver - thorium - chromium - tin - beryllium

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Alloys

• Consist of materials composed of two or more
  elements, at least one being a metal
• This combination of elements gives the material a
  combination of properties from each element
• Examples
• Steel- iron, carbon and impurity elements such as
  boron copper or silicon
• Brass - copper, zinc
• Stainless Steel - nickel,iron
• Monel - nickel,copper

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Types of Metallics

• Ferrous Metallics - iron and alloys which contain
  at least 50 iron (e.g. wrought iron, cast iron,
  steel, stainless steel)
• Nonferrous Metallics - Metallic elements other
  than iron (e.g. copper, lead, tin, zinc,
  titanium, beryllium, nickel)
• Powdered (Sintered) Metals (ferrous or
  non-ferrous)
• Sometimes called sintered metal. A process of
  producing small (powdered) particles which are
  compacted in a die and then sintered (applying
  heat below the melting point of the main
  component)
• Examples
  
  trigger on gun, gears, bearings,
  carbide tool inserts

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Polymers

• Polymers
• Chain-like molecule made of many (poly) smaller
  molecular units (monomers)
• Chaining (polymerization) is responsible for the
  formation of natural fibers, wood, lignin,
  rubber, skin, bone and the tissues of animals,
  humans and insects

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Plastics

• Plastics
• Human-made polymers
• Plastics are workable or moldable
• Thermosetting plastics are formable once (e.g.
  epoxy, phonelic (Bakelite), polyurethane)
• Thermoplastics can be heated repeatedly and
• formed into new shapes (e.g. polyethylene,
  nylon, Plexiglas)

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Elastomers

• Elastomer
• amorphous (shapeless) structure consisting of
  long coiled-up chains of entangled polymers
• can be stretched at room temperature to at least
  twice its original length and return to its
  original shape after the force has been removed
• Process to strengthen an elastomer vulcanization
• a chemical process used to form strong bonds
  between adjacent polymers to produce a tough,
  strong, hard rubber (automobile tires)

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Ceramics

• Crystalline compounds combining metallic and non
  metallic elements
• The absence of free electrons make ceramics poor
  electrical conductors.
• Because of the strength of the bonding, ceramics
  have high melting temperatures

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Ceramics(continued)

• Categories
• Clay
• Refractory
• Electrical and Magnetic
• Glasses
• Cermets

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Ceramics(continued)

• Clay Products
• Inorganic material which is shaped, dried and
  fired.
• Examples brick, floor and wall tiles, drainage
  tile, roof tile, sewer pipe, chimney flue, china,
  and porcelain.

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Ceramics(continued)

• Refractory Materials
• Ceramics designed to provide acceptable
  mechanical or chemical properties while at high
  temperatures.
• Most are based on stable oxides such as carbides,
  nitrides, and borides.
• An example of a refractory is the machinable
  all-silica insulating tiles on the U.S. space
  shuttle

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Ceramics(continued)

• Electrical and Magnetic Applications
• Ceramics are used as resistors and heating
  elements for furnaces (silicon carbide)
• Semiconductor properties
• Thermistors- as they heat-up allow current to
  flow.
• Rectifiers- allow current to flow in one
  direction
• Clay based ceramics for high-voltage insulators

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Ceramics(continued)

• Glass
• Based on silica with additives that alter the
  structure or reduce the melting point, optimize
  optical properties, thermal stability and
  resistance to thermal shock

• Cermets
• Combinations of metals and ceramics(oxides,
  nitrides, or carbides) bonded together in the
  same way powdered metallurgy parts are made.
• Examples crucibles, jet engine nozzles

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Composites

• Laminar or Layer Composites - alternate layers of
  materials bonded together. (e.g. plywood, safety
  glass, Formica, bimetallic strips)
• Particulate Composites - discrete particles of
  one material surrounded by a matrix of another
  material. (e.g. concrete, asphalt, powdered
  metals and ceramics)
• Fiber-Reinforced Composites - composed of
  continuous or discontinuous fibers embedded in a
  matrix of another material. (e.g. Kevlar, rayon,
  steel reinforced tires, fiberglass,
  graphite-epoxy)

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Review
Major Categories of Materials

• Organics
• Metals and Alloys
• Polymers
• Ceramics
• Composites