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Classification of Engineering Materials

Basic Classification of Engineering Materials

Basically Engineering Materials Can be classified into two categories-
  1. Metals
  2. Non-Metals

Metals

Metals are polycrystalline bodies which are having number of differentially oriented fine crystals. Normally major metals are in solid states at normal temperature. However, some metals such as mercury are also in liquid state at normal temperature. All metals are having high thermal and electrical conductivity. All metals are having positive temperature coefficient of resistance. Means resistance of metals increase with increase of temperature.
Examples of metals – Silver, Copper, Gold, Aluminum, Iron, Zinc, Lead, Tin etc.

Metals can be further divided into two groups-

  1. Ferrous Metals –
    All ferrous metals are having iron as common element. All ferrous materials are having very high permeability which makes these materials suitable for construction of core of electrical machines. Examples: Cast Iron, Wrought Iron, Steel, Silicon Steel, High Speed Steel, Spring Steel etc.
  2. Non-Ferrous Metals -
    All non-ferrous metals are having very low permeability. Example: Silver, Copper, Gold, Aluminum etc.

Non-Metals

Non-Metal materials are non-crystalline in nature. These exists in amorphic or mesomorphic forms. These are in both solid & gases forms at normal temperature.
Normally all non-metals are bad conductor of heat and electricity.
Examples: Plastics, Rubber, Leathers, Asbestos etc.
As these non-metals are having very high resistivity which makes them suitable for insulation purpose in electrical machines.

Difference between Metals and Non Metals

Sl. No.PropertyMetalsNon-Metals
1.StructureAll metals are having crystalline structureAll Non-metals are having amorphic & mesomorphic structure
2.StateGenerally metals are slid normal temperatureState varies material to material. Some are gas state and some are in solid state at normal temperature.
3.Valance electrons and conductivityValance electrons are free to move with in metals which makes them good conductor of heat & electricityValence electrons are tightly bound with nucleus which are not free to move. This makes them bad conductor of heat & electricity
4.DensityHigh densityLow density
5.StrengthHigh strengthLow strength
6.HardnessGenerally hardHardness is generally varies
7.MalleabilityMalleable Non malleable
8.DuctilityDuctileNon ductile
9.BrittlenessGenerally non brittle in natureBrittleness varies material to material
10.LustreMetals possess metallic lustreGenerally do not possess metallic lustre (Except graphite & iodine)

Other classification of engineering materials:

Engineering materials can also be classified as below-
  1. Metals and Alloys
  2. Ceramic Materials
  3. Organic Materials

Metals and Alloys

Metals are polycrystalline bodies which are have number of differentially oriented fine crystals. Normally major metals are in solid states at normal temperature. However, some metals such as mercury are also in liquid state at normal temperature.
Pure metals are having very low mechanical strength, which sometimes does not match with the mechanical strength required for certain applications. To overcome this draw back alloys are used.
Alloys are the composition of two or more metals or metal and non-metals together. Alloys are having good mechanical strength, low temperature coefficient of resistance.
Example: Steels, Brass, Bronze, Gunmetal, Invar. Super Alloys etc.

Ceramic Materials

Ceramic materials are non-metallic solids. These are made of inorganic compounds such as Oxides, Nitrides, Silicides and Carbides. Ceramic materials possess exceptional Structural, Electrical, Magnetic, Chemical and Thermal properties. These ceramic materials are now extensively used in different engineering fields.
Examples: Silica, glass, cement, concrete, garnet, Mgo, Cds, Zno, SiC etc.

Organic Materials

All organic material are having carbon as a common element. In organic materials carbon is chemically combined with oxygen, hydrogen and other non-metallic substances. Generally organic materials are having complex chemical bonding.
Example: Plastics, PVC, Synthetic Rubbers etc.



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