Transcript Nonmetallic Materials - Central Piedmont Community College

Nonmetallic Materials
MEC 180
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Introduction
• The non-metallic family of materials
– Expands with each new discovery
• In the 80’s and 90’s material science field was a
hot commodity
• Substitution of metals with non metals will
continue at a rapid pace
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Plastics
• We use more plastics than steel, aluminum or copper
combined
• Structure of Plastic
– Covalent bonds form saturated molecules
• Strong bond but weak forces between adjacent molecules
– Unsaturated molecules are ideal for plastics
• Allow small molecules to link together around the atom
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• Isomers
– Same atoms unite different structurally to form different
compounds
• Polymerization
– Linking of molecules by either addition or condensation
mechanisms
– Monomers link together to form polymer (large molecule)
• Monomer with activators initiate/terminate the chain of molecules
• Mer = repeated unit
– Copolymer – two different types of mers are combined
– Terpolymer- three different monomers
– Condensation polymerization – reactive molecules combine to
form a polymer and water
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• Thermosetting & Thermoplastic materials
– Refer to materials response to elevated temp
– Thermoplastics
• Contain molecules at various lengths
• Do not have a definite melting temperature (soften)
• Can be poured, cast or injected molded
– Thermosetting
• Contain a three dimensional molecular framework
• Produced by condensation process
• Stronger and rigid with poor impact properties
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• Properties and Applications of Plastics
– Light weight
• Specific gravities 1.1 to 1.6 verses magnesium 1.75
– Corrosion resistance
• Many perform well in environments such as acid
– Electrical resistance -Low thermal conductivity
• Superb insulator
– Formability
• Usually convert raw material to final product in one operation
– Surface finish
• Any variety of finish desired
– Low cost
– Low energy content
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• Common Types of Plastics
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ABS
Acrylics
Cellulose acetate
Cellulose acetate butyrate
Ethyl cellulose
Fluorocarbons
Nylon (polymides)
Polycarbonates
Polyethylenes
PMMA
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- PVC
- Polypropylene
- Polystyrenes
- Vinyls
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• Thermo sets
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Epoxies
Melamines
Phenolics
Polyester
Silicones
Urea-formaldehyde
• Additive agents in plastics
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Improve properties
Reduce cost
Improve mold ability
Impart colors
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Elastomers
• Special class of linear polymer take large amount of
elastic deformation and return to original shape
• Rubber
– Oldest natural commercial elastomer
– Vulcanized process by Mr. Goodyear
• Cross linked by heating and using sulfur
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Ceramics
• Increased role as engineered material in recent years
• Characteristics
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High electrical resistively
Withstands high heat
Resist to wear
Usually hard and brittle
• Refractory materials
– Acidic type – silica or alumina
– Basic type – Magnesium oxide
– Neutral type - Chromite
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• Ceramic uses:
– Abrasives
• Aluminum oxide
– Glass
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– Glass Ceramic
• White pyroceram like corningware
– Cermets
• Combination of metals and ceramics used as cutting tools
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Composite Materials
• A non uniform solid consisting of several
different materials that are bonded together
• Classified into three distinct families
– Laminar or layered, Particulate & Fiber reinforced
• Laminar
– Having distinct layers of material bonded together
• Plywood is common example
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• Particulate
– Consist of discrete particles of one material surrounded by matrix
of another
• Concrete is an example, also grinding wheels
• Fiber reinforced
– Thin fibers of one material are embedded in
a matrix of another
• Fiberglass
• Kevlar flak vest
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Summary
• Discussed non-metallic
materials
• Questions
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