Question: Classification of Engineering Materials
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Mumbai University > Mechanical Engineering > Sem 4 > Material Technology

Marks: 5M

Year: May 2014

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modified 2.4 years ago  • written 2.4 years ago by gravatar for Juilee Juilee ♦♦ 2.1k
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Materials Science and Engineering (MSE) is a field of engineering that encompasses the spectrum of materials types and how to use them in manufacturing. Materials span the range: metals, ceramics, polymers (plastics), semiconductors, and combinations of materials called composites. We live in a world that is both dependent upon and limited by materials. Everything we see and use is made of materials. All of these require materials specifically tailored for their application. Specific properties are required that result from carefully selecting the materials and from controlling the manufacturing processes used to convert the basic materials into the final engineered product. Exciting new product developments frequently are possible only through new materials and/or processing.

Engineers deal with the science and technology of producing materials that have properties and shapes suitable for practical use. Activities of these engineers range from primary materials production, including recycling, through the design and development of new materials to the reliable and economical manufacturing for the final product.

Metals

Metals are materials that are normally combinations of "metallic elements". These elements, when combined, usually have electrons that are non-localized and as a consequence have generic types of properties. Metals usually are good conductors of heat and electricity. They are also quite strong but deformable and tend to have a lustrous look when polished.

Ceramics

Ceramics are generally compounds between metallic and nonmetallic elements and include such compounds as oxides, nitrides, and carbides. Typically they are insulating and resistant to high temperatures and harsh environments.

Plastics

Plastics, also known as polymers, are generally organic compounds based upon carbon and hydrogen. They are very large molecular structures. Usually they are low density and are not stable at high temperatures.

Semiconductors

Semiconductors have electrical properties intermediate between metallic conductors and ceramic insulators. Electrical properties are strongly dependent upon small amounts of impurities.

Composites

Composites consist of more than one material type. Fiberglass, a combination of glass and a polymer, is an example. Concrete and plywood are other familiar composites. Many new combinations include ceramic fibers in metal or polymer matrix.

Note:-Table below is given for additional information.

  STRUCTURE PROPERTIES EXAMPLES
Metals/ Alloys ▪,any metallic element /alloy
▪ simple crystalline structure
▪metallic atomic bonding,delocalized electrons
▪ high conductivity
▪ not transparent to visible light,(i.e. opaque)
▪ lustrous
▪ strong,ductile
▪ iron (Fe)
▪ steel (Fe+C)
▪ aluminum (Al)
▪ copper (Cu)
▪ brass(Cu+Zn)
Ceramics/,Glasses/,& Glass-Ceramics ▪ compounds of metals and non-metals
▪ 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
▪ insulative
▪ refractory
▪ wear resistant
▪ brittle
▪ strong
▪ hard
▪ chemically stable
▪ high melting temps
glasses are transparent
▪ oxides,(Al2O3, MgO, SiO2)
▪ nitrides (Si3N4)
▪ carbides
▪ silicates
▪ lithium-alumino-silicates
▪ clay
cement
Polymers and plastics ▪ organic compounds primarily based on C and H.,(see periodic table)
▪ 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
▪ very ductile (elastic and plastic)
▪ low density
▪ low strength
▪ low melting temp
▪ high chemical reactivity
▪ polyethylene
▪ PVC
▪ rubber
▪ acrylics - O
▪ nylons - N
▪ silicones - Si
Composites ▪ Engineered materials of more than one type, usually a matrix material with fibers or particulates. Could be anything, depending on constituents, relative amounts and geometry ▪ fiberglass
▪ concrete
▪ asphalt
▪ wood
Semi-conductors ▪ elemental (Group IVA)
▪ compound
▪ covalent/ionic bonding,similar to ceramics
▪ 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
▪ Si, Ge, Sn
▪ CaS
GaAs
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written 2.4 years ago by gravatar for Juilee Juilee ♦♦ 2.1k
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