High Durability Electrodeposition Painting for SOFC Metal Interconnector

Osaka Gas Co., Ltd. has been developing electrodeposition painting method for SOFC metal interconnector coating since 2010. Although the general electrodeposition painting was mainly consisted of resin with small amount of ceramics as a pigment, we have successfully increased the amount of ceramics in the coating and this method was adopted to SOFC metal interconnector coating. Generally, SOFC interconnector had the complex structure with the gas flow path. This method had the advantage of coating thickness uniformity regardless of the interconnector structure and mass productivity.

We have investigated to enhance the durability of the SOFC interconnector with this method.In addition, we aimed to reduce the cost of the metal interconnector by using the normal stainless steel, not stainless steel specially designed for the SOFC component.

The composition of Co-Mn spinel-type oxide widely used in this field was selected as the coating ceramics.

As is often the case with interconnector, the protective coating needed to be partially coated. The wet coating method like electrodeposition painting needed to be fired after coating to remove the resin and sinter the spinel-type oxide.

From the standpoint of processing cost, it was desirable to be fired in air, but non coated area was severely oxidized and Cr2O3 layer showing high ASR was formed on the surface of the stainless steel.

In order to prevent the oxidation of non-coated area and sinter the spinel powder enough, two steps of firing have been normally taken: the resin was removed in air first, then the Co-Mn spinel powder was sintered in the reduction atmosphere. This process cost tends to be high due to changing atmosphere.

However, our electrodeposition painting method did not need to be fired in two steps because its resin was acrylate resin which was removed completely even in the reduction atmosphere.

Cross section images of the post anneal coating showed the dense structure and the uniform layer thickness.

ASR test over 10,000hr showed excellent durability at the both of the continuous condition and thermal cycle condition.

The Cr diffusion from the stainless steel was also evaluated, it showed the high prevention of Cr diffusion.

The variability of coating weight were quite small, it was concluded that this electrodeposition painting method is suitable for mass production.