Transcript Categories of Materials - apolloteched / FrontPage

Forging new generations of engineers
Categories of Materials
• Organics
• Metals and Alloys
• Polymers
• Ceramics
• Composites
Organics
• Organics are or were living organisms
• Composed of mostly carbon and
Hydrogen
• Structure depends on the way cells
developed not by human manipulation
• Renewable, sustainable
• Infinite variety
• Genetically alterable
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 basic
elements
• Metallic materials include alloys, which are
combinations of metals and other elements
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
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
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
Polymers
• Polymers
– Chain-like molecule made of many (poly)
smaller molecular units (mono”mers”)
– Chaining (polymerization) is responsible for
the formation of natural fibers, wood, lignin,
rubber, skin, bone and the tissues of
animals, humans and insects
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)
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)
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
Ceramics(continued)
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Categories:

Clay

Refractory

Electrical and Magnetic

Glasses

Cermets
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.
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
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
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
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)
Review
Major Categories of Materials
• Organics
• Metals and Alloys
• Polymers
• Ceramics
• Composites