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thermal properties for materials
Typology: Lecture notes
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- General: The ability of a material to absorb heat.
heat capacity
(J/mol-K)
energy input (J/mol)
temperature change (K)
- Two ways to measure heat capacity:
p
v
p
C
v
kg K
J
Specific heat means heat capacity per unit mass!
- Heat capacity...
Adapted from Fig. 19.2,
Callister 7e.
gas constant
= 8.31 J/mol-K
v
= constant
Debye temperature
(usually less than T room
T (K)
D
0
0
C v
increasing
c
p
- Why is cp significantly
Selected values from Table 19.1, Callister 7e.
- Polymers
Polypropylene
Polyethylene
Polystyrene
Teflon
c p
(J/kg-K)
at room T
- Ceramics
Magnesia (MgO)
Alumina (Al 2
Glass
- Metals
Aluminum
Steel
Tungsten
Gold
c p
: (J/kg-K)
p
: (J/mol-K)
material
Chapter 19 - 7
Adapted from Fig. 19.3,
Callister 7e.
No change!
- Q: Why does
Polypropylene 145-
Polyethylene 106-
Polystyrene 90-
Teflon 126-
at room T
Magnesia (MgO) 13.
Alumina (Al 2
3
Soda-lime glass 9
Silica (cryst. SiO 2
Aluminum 23.
Steel 12
Tungsten 4.
Gold 14.
(
/K) Material
Selected values from Table 19.1, Callister 7e.
Polymers have smaller
because of weak
secondary bonds
gradient
thermal conductivity (J/m-K-s)
heat flux
(J/m
2 -s)
heat flux
dx
dT
q k
STEADY STATE => q, heat flux does NOT change with time
k T
= k l
increasing k
- Polymers
Polypropylene 0.
Polyethylene 0.46-0.
Polystyrene 0.
Teflon 0.
By vibration/
rotation of chain
molecules
- Ceramics
Magnesia (MgO) 38
Alumina (Al 2
3
Soda-lime glass 1.
Silica (cryst. SiO 2
By vibration of
atoms
- Metals
Aluminum 247
Steel 52
Tungsten 178
Gold 315
By vibration of
atoms and
motion of
electrons
Material k (W/m-K) Energy Transfer
Selected values from Table 19.1, Callister 7e.
2
Tension develops at surface
( ) 1 2
E T T
Critical temperature difference
for fracture (set = f)
f
1 2 fracture
set equal
k f
E
k f
for fracture
(quenchrate)
Temperature difference that
can be produced by cooling:
1 2
rapid quench
resists contraction
tries to contract during cooling
2
1
Chapter 19 - 14
Fig. 19.2W, Callister 6e. (Fig. 19.2W adapted from L.J.
Korb, C.A. Morant, R.M. Calland, and C.S. Thatcher, "The
Shuttle Orbiter Thermal Protection System", Ceramic
Bulletin , No. 11, Nov. 1981, p. 1189.)
Fig. 19.3W, Callister 5e. (Fig. 19.3W courtesy the
National Aeronautics and Space Administration.)
Fig. 19.4W, Callister 5e. (Fig. 219.4W courtesy
Lockheed Aerospace Ceramics
Systems, Sunnyvale, CA.)
reinf C-C
(1650°C)
silica tiles
(400-1260°C)
nylon felt, silicon rubber
coating (400°C)
~90% porosity!
Si fibers
bonded to one
another during
heat treatment.
100 m
Chapter-opening photograph, Chapter 23, Callister 5e
(courtesy of the National Aeronautics and Space
Administration.)
