materials in electrical engineering · 2019-11-04 · syntetic natural classification of...

Reference Sources

The Science and Engineering of Materials, Donald R. Askeland, Springer Science Business Media

Materials Science and Engineering An Introduction, William D. Callister Jr., John Wiley&Sons Inc.

Properties of Materials for Electrical Engineers, K. J. Pascoe

Physics of Semiconductor Devices, J. P. Collinge, C. A. Collinge

Materials in Electrical Engineering

GENERAL VIEWTO MATERIAL SCIENCE

Karadeniz Teknik ÜniversitesiElektrik-Elektronik Mühendisliği

Historical

▪ Early civilizations have been designated by the level of their materials development from stone, bronze, iron (tools and utensils), and then steel (railroads, instruments, and the Industrial Revolution))

▪ Lastly Space Age (materials for stronger and light structures, e.g., composite materials) and Electronic Age (semiconductors, and thus many varieties of electronic gadgets)

▪ Materials constitute foundation of technology.


▪ An engineer, (mechanical, physics, chemical, electrical, electronics, etc.) need to have knowledge of materials

▪ For example: Designing a gear, a superstructure building, an power plant component, an integrated circuit chip, a solar cell.

▪ Selecting the right material for a specific taskThe more familiar an engineer with the properties and structure–property relationship

of materials, also processing techniques of materials, the more effective he or she can be to make appropriate materials choice.

▪ Understanding the limits of materials and the change of their properties for a specific purpose

▪ Developing a new material for a specific task.

Why an engineer should study material science?


• Components for material science: Structure, properties, processing, performance

Materials

Structure Properties Processing

Performance


Metallic Non-metallic

Ferrous Metals

Engineering Materials

Non-ferrous metals

Syntetic Natural

Classification of Engineering Materials


▪ Metals and alloys containing a high proportion of Fe (element iron).▪ Very strong materials, in use for applications where cost-effectiveness

and high strength is required if weight is not of primary importance.For example: bridge building, the structure of large buildings, railway lines, locomotives and rolling stock and the bodies and highly stressed engine parts of road vehicles.

Cast Iron(Grey, White, Malleable,

Alloy, High-duty)

Wrought Iron(Processed iron)

Ferrous Metals

Steel(Carbon steel, Alloy

steel)

Metallic- Ferrous metals


▪ Lack mechanical strength (not used for where strength is needed). Therefore mainly used with other metals to improve their strength

▪ They are used where their special properties such as corrosion resistance, electrical conductivity and thermal conductivity are required.

▪ For example: Copper and aluminum are used as electrical conductors and, together with sheet zinc and sheet lead, are use as roofing materials.

Metals(Al, Cd, Cr, Co, Cu, Au, Pb, Mg, Mn,

Mo, Ni, Pt, Ag, Sn, Ti, W, V, Zn)

Alloys(Brass (Cu-Zn), Tin Bronze (Cu-Sn),

Aluminum bronze (Cu-Al), Cupro-nickel alloys (Cu-Ni alloys), Al alloys, Mg alloys,

Zn based alloys, Sn-Pb alloys)

Non-ferrous Metals

Metallic- Non-ferrous metals


Non-metallic- Synthetic Materials

Plastics Ceramics• Glass• Porcelain• Cemented

carbides

Synthetic Materials

Composites• Carbon fibre• Concrete• Glass

reinforced plastics-GRP

Thermoplastic• Acrylic• Polythene• Polyviny• Chloride-PVC• Nylon• Polystrene, etc.

Thermosetting• Epoxides• Alykids• Bakelide, etc.

▪ Do not exist in nature directly▪ Has advantage of good corrosion with low cost and simple manufacturing▪ Adaptable to use in metallic joints on high stress


Non-metallic- Natural Materials

▪ Exist in nature directly

• Coal• Cotton• Diamond• Wood• Wool• Oil• Quartz• Rubber

Natural Materials

• Clourants• Dyes• Pigments

• Gases• Argon• Nitrogen• Oxygen• Helium

• etc.



General Properties

Mechanical Properties: Strength, response to mechanical forces

Electrical and magnetic properties: response to electrical or magnetic fields, resistance etc.Thermal properties: regarding to transmission of heat , response to thermaleffects

Optical properties: absorption, transmission, reflection of light

Chemical properties: stability response when in environment or in a specific ambient, corrosion resistance

Polymers

Oxides

Metals

Solids

Mechanical properties….

Electrical properties….

Electronic properties of solids→ fulfilled by the behaviour of electrons

Electrical conduction: conducting, semiconducting, insulating, superconducting

Optical properties: absorption, emission, modification of light

Magnetic properties: paramagnetism, ferromagnetism, antiferromagnetism

ATOMIC STRUCTURE and

BONDING


Metals: valence electrons are detached from atoms, and spread in an 'electron sea' that "glues" the ions together. Strong, ductile, conduct electricity and heat well.

Semiconductors: has covalent bonds (electrons are shared between atoms). Their electrical properties can be changed with adding impurities or with external processes. Examples: Si, Ge, GaAs.

Ceramics: atoms behave like either positive or negative ions, and are bound by Coulomb forces. They are usually combinations of metals or semiconductors with oxygen, nitrogen or carbon (oxides, nitrides, and carbides). Hard, brittle, insulators. Examples: glass, porcelain.

Polymers: are bound by covalent forces and also by weak van der Waals forces, and usually based on C and H. They decompose at moderate temperatures (100 – 400 C), and are lightweight. Examples: plastics rubber.

Type of materials according to their atomic bonds?


• Materials are composed of atoms which are indestructible

• All atoms of an element are identical

• Different elements have atoms have different weights and different chemical properties

• Atoms of different elements combine in simple whole number ratios to form compounds and by decomposing the compound you get the elements back

An atom (Dalton model)


Structural Properties - Atom

Positively chargedEqual amount as electrons

Chargeless

Negatively chargedOrbits around nucleus

Particle Charge (C) Mass (g)

Electron (e-) -1.6x10-19 9.11x10-28

Proton (p+) 1.6x10-19 1.67x10-24

Neutron (n0) 0 1.65x10-24

Table: Particles of an atom


• In order to understand the materials and how they behave like they are, we need to look at atomistic understanding that first explained atoms and then solids starting in the 1930s.

http://resources.schoolscience.co.uk/ici/periodictable/downloads/periodictable.pdf

Why to call it “periodic”?

Mendeleyev’s Law: Properties of elements vary periodically with atomic mass (not totally periodic but you can see the a rough repetitions)


Refer to the lectures notes for the rest of the topic

✓Mole: A mole is the amount of matter that has a mass in grams equal to the atomic mass in amu of the atoms (A mole of carbon has a mass of 12 grams)

❑ The atomic mass unit (amu), is often used to express atomic weight. ❑ 1 amu is defined as 1/12 of the atomic mass of the most common isotope of carbon that has 6 protons and 6 neutrons. ❑Mass of proton is almost equal to mass of neutron = 1.66x10-24 g= 1 amuThe atomic mass of the 12C atom is 12 amu

Atomic weight of an element: The atomic weight is often specified in mass per mole

The number of atoms in a mole is called the Avogadro number.Navogadro = NAV = 6.023 x 1023

Example: Atomic weight of iron = 55.85 g/mol

Atomic Mass Unit and Atomic Weight

n: Number of atoms per cm3

: Material of density (g/cm3)A: Atomic mass (g/mol)

n = (NAV x ) / A

BONDS


Ionic Bonding

Primary Interatomic Bonds

• Always found in metallic – nonmetallic compounds • Atoms of metallic element give up their valance electrons to the

nonmetallic atoms.• All the atoms want to become inert gas configuration, and an

electrical charge that they become ions. In order to have stable outermost orbit.

• NaCl (Sodium Chloride) is a common example for ionic material.• A Na atom can assume the electron structure of Ne with a single

positive charge (by giving away its one valence 3s electron to a chlorine atom.)

• After this transfer Cl ion has a net negative charge and an electron configuration that is identical to that of Ar.


Ionic Bonding

• High hardness and low conductivity are typical properties of ionic bond.

• Insulators are in this group.



Cl- Na+ Cl- Na+Na+

Cl- Na+ Cl- Na+ Cl-

Cl- Na+ Cl- Na+Na+

Cl- Na+ Cl- Na+ Cl-

• Sticks together with colombic bonding forces; positive and negative ions attract one another

Covalent Bonding• Stable electron configurations are achieved by sharing of electrons

between adjacent atoms.• Each of covalently bonded two atoms contribute at least one

electron to the bond, shared electrons are considered to belong to both atoms.

• The covalent bond is directional. Because it is between specific two atoms and may exist only in the direction between one atom to another that shares the electrons.

• Nonmetallic element molecules including H2, Cl2, F2, etc. or molecules containing dissimilar atoms like CH4, H2O, HNO3 and HF are covalently bonded.

• Diamond (carbon), silicon, germanium, GaAs (Gallium Arsenide), InSb(Indium antominide) or SiC (Silicon carbide) elemental solids are also has covalent bonding



Covalent Bonding• With covalent bond the atoms behave as they have full

outer orbits. • Therefore, full strength to the material and low

electrical conductivity (because there is no electrons are free to move)

• Some specific materials allow valency electrons to become free by thermal energy (semiconductors)

• The wider the separation from the lower left to the upper-right corner the more ionic the bond (because of the greater the difference in electronegativity)

• The closer the atoms the greater the degree of covalency (because of the smaller difference of electronegativity)



Refer to the lecture notes for further information

Metallic Bonding

• Metallic bonding is in metals and their alloys.• The atoms of the elements which have 1, 2 or the most 3 valance

electrons . These electrons are loose and free to drift throughout to whole metal.

• They form an “electron cloud (sea of electrons)”, and become positive ions.

(the remaining non valence electrons and atomic nuclei form “ion cores” that posses a net positive charge equal to the magnitude of valence electrons of an atom)• The material held together with electrostatic force between positive

ions and the cloud. (otherwise they would exert upon one another). Therefore, metallic bond is non directional.



• The elements having small number of valency electrons are formed by this type of bonding, become good in electrical conduction.

• Conductors are in this group.

Metallic Bonding



+ + + +

+ + + +

+ + + +

+ + + +

Delocalized electrons(electron sea)

Schematic illustration of metallic bonding

Some properties of the materials can be suggested by the bonding types:

• Metals are good conductors of temperature and heat due to their free electrons.

• Ionically or covalently bonded materials are typically thermally and electrically insulator because of the absence of large number of free electrons.


Secondary Bonding (Van-der Waals Bonding)

• These type of bonding occurs between molecules in which atoms are covalent bonded.

• Inert gases that have stable electron structure has this type of bonding.

• H2O, CO2, O2, N2 can be some examples• Van-der Waals bonds are not so strong, has very low

melting temperatures as low as 50oC.

• Hydrogen bonding is a special type of secondary bonding, exist between some of molecules which have H as one of the constituents.


Dipole

Electric dipole occurs when there is a separated positive and negative charges.

• Secondary bonding forces arise from atomic or molecular dipoles.

• The bonding results from the colombic attraction between the positive and negative endings of two dipoles.


REFER TO THE LECTURE NOTES FOR FURTHER EXPLANATION

materials in electrical engineering · 2019-11-04 · syntetic natural classification of...

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