Absolutely Shocking
Developer:
Dr. Mary R. Reidmeyer
Project for Grade Level:
High School
Discipline:
Materials, Physics
Topic Area:
Thermal expansion, Thermal shock
Time Required:
Goals:
Demonstrate the behavior of low and high thermal expansion
materials when exposed to extreme temperature changes.
Objectives:
Observe the behavior of materials when they are heated and
rapidly cooled.
Upon completion of this lab, the student will be able t :
Demonstrate a simple thermal shock test.
Explain why some materials fail and others do not.
Relate the behavior to differences in the coefficient of thermal
expansion.
Materials:
Assorted glass and ceramic rods
Bunsen burner
Beaker 400ml
University of Missouri-Rolla – Ceramic Engineering Department
http://campus.umr.edu/ceramics
116106753
Safety Precautions:
Follow the instructions. Wear proper safety equipment such as
goggles and heat resistant gloves. Avoid contact with the heated
rods. Dispose of the fractured glass and ceramics properly.
Procedure:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Set up the Bunsen burner according to the manufacturer’s directions.
Fill the beaker with water and set near the Bunsen burner.
Light the Bunsen burner and adjust your flame so that is medium high and
blue.
Select rod A. To preheat the rod hold it near the flame then pass it through
the flame several times. Place the rod in the flame at mid level in the
center of the flame so that approximately one inch of each rod is being
heated.
Continuously rotate the rod so that it is heated evenly.
After 30 seconds of heating, remove the rod from the flame and
immediately dip the hot end into the beaker of water.
Record the results, indicating whether the rod tip failed and if so how.
Repeat Steps 4-7 with rod B.
Repeat Steps 4-7 with rod C.
Repeat Steps 4-7 with rod D.
Repeat the test with all the rods.
Tabulate the results.
Observations and Questions:
1.
2.
3.
4.
5.
Did the rods behave differently? How?
Look at the table of material properties. What difference in properties
would explain the rods’ behaviors?
Speculate the on the behavior of the rods if they were heated for a longer
period of time.
Did you obtain different results when the test was repeated? Speculate
what might be occurring if you obtained different results on the same rod.
The transparent rods supplied are different compositions of glass and the
opaque rods are polycrystalline ceramics. Did you observe any difference
in fracture behavior?
Teacher’s Note:
University of Missouri-Rolla – Ceramic Engineering Department
http://campus.umr.edu/ceramics
116106753
Supplemental MaterialVocabulary:
Alumina- aluminum oxide; Al2O3; m.p. 2030°C; spgr. 4.0; hardness (Mohs) 9; an
amphoteric material only second to silica in importance in the ceramic industry
Amorphous- having no crystalline structure
Fused silica- a transparent or translucent glass consisting of pure silica with a very low
thermal expansion, a high melting temperature and high chemical resistance.
Glass- an amorphous, ridge, inorganic, nonmetallic material that solidified from the
molten state without crystallization
Hard glass- a glass having a high-temperature softening point and high viscosity at
elevated temperatures
Modulus of rupture (MOR)- the transverse or cross-bending strength of a material
Polycrystalline materials- is composed of many variously oriented crystals
Soft glass- a glass having a relatively low softening temperature or which is easily melted
Thermal conductivity- the rate of heat flow through a body per unit area per unit time per
unit temperature in a direction perpendicular to the surface
Thermal expansion- the reversible or permanent change in the dimensions of body when
heated
Thermal expansion coefficient- also known as the coefficient of expansion (COE)- the
fractional change in the length or volume of a material per degree of temperature change
Thermal shock- exposure of a object to sudden and severe changes in temperature.
Thermal shock resistance- the ability to withstand sudden changes in temperature without
fracture
University of Missouri-Rolla – Ceramic Engineering Department
http://campus.umr.edu/ceramics
116106753
Background Information:
Various materials have different physical and chemical properties such as melting
temperature, strength, density, chemical resistance, optical properties and thermal
properties. A material’s coefficient of thermal expansion, thermal conductivity and
mechanical strength are properties that allow us to understand the behavior of the
material under thermal cycling. When materials are heated, they expand and when they
are cooled, they contract. Materials with a high coefficient of expansion expand and
contract more than materials with a lower coefficient of expansion. When materials are
heated and cooled rapidly, they experience stresses created when they change size. If a
material is not cooled uniformly, enormous stresses can be generated as different portions
of an object try to be different sizes. Cooling an object quickly on the surface forces the
top layer of material to contract will the warmer inner material remains expanded. That
creates tensile stresses on the surface. For brittle materials such as glass and ceramics this
greatly increases the probability of crack formation and subsequent failure. The amount
of stress created is dependent on temperature distribution and this is dependent on the
size and shape of object, its coefficient of thermal expansion and thermal conductivity. If
the stresses that are thermally induced exceed the strength of the material, it will fail.
Materials that have a lower coefficient of thermal expansion, higher thermal conductivity,
high strengths, and objects with less mass and thinner cross sections are more thermal
shock resistant.
The following is a table of properties for several materials:
Material
Composition
Alumina
Fused Silica
Mullite
Soft Glass
Hard GlassPyrex
Al2O3
SiO2
3Al2O3-2SiO2
soda-lime
borosilicate
Coefficient of
Expansion
x 107/C
80
5
50
90
32
Strength,
MOR, ksi
40-80
16
25
10
10
Thermal
Conductivity,
W/m-K
30
1.3
3.9
1.7
1.4
Glass bowls and container used in the kitchen are made from a lower expansion glass to
avoid thermal shock failure. These usually carry the trademark name of Pyrex® and
Kimax® and are a version of borosilicate glass. Even though they are resistant to
reasonable temperature transients such as refrigerator to oven, moving the glass dish from
the freezer to under the broiler would likely result in failure.
University of Missouri-Rolla – Ceramic Engineering Department
http://campus.umr.edu/ceramics
116106753