The fuel cell, a power
source that draws electrical energy from the electrochemical reaction
of fuel and oxygen, is considered a next-generation energy source
because it offers high generation efficiency and low environmental
impact.
Of the several types of fuel cells, the most promising in terms of
generating efficiency is the flat-plate solid electrolytic-type fuel
cell, which can operate at temperatures as high as 900~1,000°C.
The separator material of the solid electrolytic-type fuel cell must
possess
(1) electrical conductivity,
(2) the ability to resist oxidation for a long time at 900~1,000°C
and
(3) a coefficient of thermal expansion close to that of the electrolyte
ZrO2.
One candidate material is ceramics, but metallic materials are more
suitable for reasons of large size and low cost.
Hitachi Metals has developed a metallic material that satisfies these
criteria, the solid electrolytic-type fuel cell separator material
ZMG232. Fe-22Cr is the main component of ZMG232, and it is a ferrite-based
alloy with the addition of microelements. Below are details of its
properties compared with other metallic materials.
Contents
(1) Conductivity
ZMG232 possesses sufficient conductivity as a separator material
to form a Cr2O3 electroconductive
oxide skin, as shown in Figure 1. But Al2O3 alloys
show high electrical resistance.
Figure 1: Electrical resistance
of oxide skin after 1,000 hours of heating at 1,000°C
(2) Coefficient of thermal expansion
Because ZMG232 is ferrite-based, its coefficient of thermal expansion
is close to that of ZrO2, as shown in
Figure 2. At the same time, the coefficient of thermal expansion
of Alloy600, an austenite-type alloy, is considerably higher than
that of ZrO2.
Figure 2: Coefficient of thermal
expansion
(3) Oxidation resistance
General ferrite-based alloys formed from Cr2O3 tend to have lower
oxidation resistance than Al2O3 alloys or nickel-based alloys, but
ZMG232 achieves superior oxidation resistance to that of nickel-based
Alloy600 even after being heated for a long time if microelements
are added (Figure 3).
Figure 3: Oxidation resistance
at 1,000°C
Inquiries
Industrial Materials Bussiness Unit
(Automotive Materials,Industrial Machinery)
Specialty Steel Company
Tel.: +81-3-5765-4396 Inquiry Form
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