Metal Foams: A Design Guide

Chapter 14
Electrical properties of metal foams
The electrical conductivity of a metal foam is less than that of the metal from
which it is made for the obvious reason that the cell interiors, if gas-filled, are
non-conducting. One might guess that the conductivity should vary linearly
with the relative density, but the real dependence is stronger than linear, for
reasons explained below. Though reduced, the conductivity of metal foams
is more than adequate to provide good electrical grounding and shielding of
electromagnetic radiation.
The large, accessible surface area of open cell metal foams makes them
attractive as electrodes for batteries (see Case Study 17.6). Nickel foams are
extensively used in this application.
14.1 Measuring electrical conductivity or resistivity
The electrical resistivity of a thick metal foam sheet can be measured using a
four-point probe technique sketched in Figure 14.1. Two probes (P1 and P4)
are used to introduce a current, I, into the sample while a pair of different
probes (P2 and P3) are used to measure the potential drop, V, between them.
If the plate is sufficiently thick, the electrical resistivity, 2, of the foam
(commonly measured in units of µ . cm) is given by:
2 D 2
where
� �
V
IS
⊲14.1⊳
S D 1
C
s1
1
s3
1
s1 C s2
1
s2 C s3
⊲14.2⊳
and s1, s2 and s3, are the probe spacings shown in the figure.
The electrical conductivity, (units, 1 1 . m ), is the reciprocal of the
resistivity. The resistance, R, of a piece of foam of length ℓ and a crosssectional
area A normal to the direction of current flow is given by:
R D 2 ℓ ℓ
D
A A
⊲14.3⊳