10 - Lecture 04.pdf

MatE 10: Lecture 04 MRSPoblete

Materials Engineering 10:

Engineering Materials

Lecture 04Material Properties:

Thermal, Electrical, Magnetic, Optical and Chemical


MUST WITHSTAND THE EXTREMEST OF TEMPERATURES


Thermal Property

maximum service

temperatures

response to increase/decrease in temperature

dictated by chemical bonds present

coefficient of

thermal expansion thermal

conductivity

thermal

diffusivity

heat capacity


maximum service temperature

Thermal Properties

limiting temperature at which the material starts to creep

measure of the rate at which a

temperature disturbance at one point

in a body travels to another point

thermal diffusivity


Thermal Properties

coefficient of thermal expansion

measure of the amount by which a length of material expands when

temperature is increased

=

l = change in lengthl = original lengthT = change in T

Unit: C-1


thermal conductivity

Thermal Properties

measure of the rate at which heat flows through the materialmeasure of the ability of a material to conduct heat

=

Q = amount of heat, Joulest = time, secT = change in temperature

higher , better conductorUnit: J s-1 K-1


specific heat capacity

Thermal Properties

amount of heat needed to raise one kilogram of material by 1C

=

Q = amount of heat, Joulesm = mass, kgT = change in temperature

higher c, slower to heatUnit: J kg-1 C-1


Example:

By how much will a 10cm strip of a) Cu and b) PVC expand when the temp changes from 200C to 300C?

Cu = 18 x 10-6/K

PVC = 75 x 10-6/K


Electrical Property

electrical

resistance

response to electron flow

electrical

conductance dielectric

strength

resistivity

conductivity


electrical resistanceopposition to the passage of an

electric current through that conductor

Electrical Properties

=

R = resistance, ohm

= resistivity(measure of the electrical resistance of a material)

A = x-sectional area, m2

L = length, m


electrical conductanceopposite of resistance


=

G = conductance, ohm

= conductivity

A = x-sectional area, m2

L = length, m


Paper Circuit


superconductivitymaterials with zero resistivity (no electrical losses)

strong repulsive interaction with magnetic field



dielectric strength

measure of the highest voltage an insulating material can

withstand without material breakdown


=


Magnetic Property

ferromagnetism

response to magnetic field

paramagnetismdiamagnetism


Magnetic Property

ferromagnetism

attracted to magnets have some unpaired

electrons so their atoms have a net magnetic moment

Fe, Ni, Co

paramagnetism

Slightly attracted to magnets

due to the presence of some unpaired electrons, and from the realignment of the electron paths caused by the external magnetic field

magnesium, molybdenum, lithium, and tantalum

diamagnetism

little or not attracted at all all the electron are paired

so there is no permanent net magnetic moment per atom

Most elements in the periodic table, including copper, silver, and gold, are diamagnetic.


Ferrofluids


Optical Propertyresponse to electromagnetic radiation,

particularly to visible light

opacity

transluscency

transparency


Optical Properties

more

crystalline,

more opaque


Optical Properties


Chemical Propertyresponse to chemical changes brought

about by reactions

heat of

combustioncorrosivity

toxicity

flammabilitychemical

stability

measurement usually requires destroying the material


Chemical Property

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