Direct Energy, 2018a

176 8.3 Bulk Modulus and Related Measures
Material
Bulk
modulus
B in GPa
Thermal
cond. κ
in
m·K
W
Electrical cond. σ
in 1
Ω·m
Ref.
Diamond 539 300 1 · 10 −12 − 1 · 10 −2 [104]
Stainless steel 143 15.5 1.3 · 10 6 − 1.5 · 10 6 [105]
Graphite 18.6 195 1.6 · 10 4 − 2.0 · 10 7 [106]
Silicone rubber 1.75 1.38 1·10 −14 −3.2·10 −12 [107]
Table 8.4: Bulk modulus, thermal conductivity, and electrical conductivity
of some materials. The references list ranges of values for bulk modulus
and thermal conductivity while this table lists their averages.
The Boltzmann constant is
k B =1.381 · 10 −23 K J . (8.5)
These three constants are related by
k B = R . (8.6)
N a
8.3 Bulk Modulus and Related Measures
The bulk modulus B describes how a gas, liquid, or solid changes as it is
compressed [103]. More specically, bulk modulus per unit volume is the
change in pressure required to get a given compression of volume,
B = −V ∂P
∂V
(8.7)
and bulk modulus is specied in the SI units of pascals or N m
2 . The bulk
modulus is greater than zero (B > 0) even though there is a minus sign in
Eq. 8.7 because volume shrinks when pressure is applied. Table 8.4 lists
example bulk modulus values.
Assuming constant temperature, the inverse of the bulk modulus 1 , B
is also called the isothermal compressibility [108]. There is a relationship
between this compressibility and the permittivity ɛ discussed in Chapter
2. If we take an insulating material and apply an external electric eld,
a material polarization is established, and energy is stored in this charge
accumulation. The permittivity is a measure of the charge accumulation