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Chapter 19 – Thermal Properties of Materials
MURPHY
Objective
This chapter delves into how heat and temperature could affect materials and its properties. After
going through these notes, the reader should understand these topics:
Heat Capacity: how materials store heat as energy and how much energy is required for
raising temperature on a material
Thermal Expansion: the change in length in material as temperature increases and
decreases
Thermal Conductivity: how heat transfers to regions with lower temperatures
Thermal Stresses: how increasing/decreasing temperature can cause stresses onto a
material which can then lead to deformation/fracture
Heat Capacity
How well a material can hold heat from its environment indicates what it’s
_______________________ is. Given with this equation:
C=
___ = heat capacity
___ = change in temperature
___ = change in time
𝑑𝑄
𝑑𝑇
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Vibrational Heat Capacity
The amount of a materials heat capacity energy stored in vibrations.
A _________ is a quantum of vibrational energy.
Thermal Expansion
As we know, materials can expand or shrink depending on the temperature. Just like how
in bridges you want small gaps inbetween the concrete so that when the
temperature__________, it doesn’t crack.
We can find out how much a material expands by using the following expression:
∆𝑙
𝑙𝑜
= α1 ∆𝑇
___ = change in length
___ = initial length
___ = linear coefficient of thermal expansion
___ = change in temperature
Example: Bridge Expansion
In a regular fall day with a temperature of 4°C, a concrete bridge in question is 50 m long, if in
the winter the temperature drops to -3°C, how much did the bridge expand in this time if the
linear coefficient of thermal expansion is 10 x 10−6 ?
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Thermal Conductivity
When heat is transferred throughout a material it is called ________________.
Heat travels through ________ and free __________.
Thermal conductivity can be expressed as:
q=-k
𝑑𝑇
𝑑𝑋
___ = heat flux
___ = thermal conductivity
___ = temperature gradient
Table 1: Graph of thermal conductivity against copper-zinc alloys
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Thermal Stresses
When a material goes through a change in temperature, it sees a stress called _______
_______________.
If the thermal stresses get excessive, fractures and deformation can occur.
The gradient of temperature depends on a materials__________, the change in
________________ over time and how ___________ the material is.
Image 1: Glass breakage
(Taken from Glass Technology services, News Article by Daniel Capon, what is a thermal
stress glass breakage pattern?)
References:
All information and Table 1 are taken off Materials Science and Engineering - An
Introduction, 10th Edition, W.D. Callister Jr. and D.G. Rethwisch, John Wiley & Sons
Image 1 is taken off: https://www.glass-ts.com/news/what-is-a-thermal-stress-glassbreakage-pattern/
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