Abstract
Single planar fuel cell elements consisting of metallic interconnectors that are bonded and sealed by a thin glass solder layer form the core of a solid oxide fuel cell. For reliable operation, the bonding layer has to adhere well and must be without voids or foreign material inclusions, which might cause gas leakage, electrical shorts or mechanical weakening and structural failure. Nondestructive testing (NDT) by the high-frequency ultrasound in immersion technique and by air-coupled ultrasound was optimized to find such defects. Another technique was flash light excited thermography for detection of voids. The NDT techniques used are complementary to each other, as they are based on different physical principles. Voids and small steel platelets of different sizes were prepared in the glass solder layer before the high-temperature bonding process and then monitored by the NDT techniques through the interconnector plates. Two selected NDT techniques were then validated in a probability of detection (POD) study. The study resulted in detection limits for the two main types of defects. As a step towards production testing, a demonstrator was built combining testing by air-coupled ultrasound and that by flash thermography. During the testing steps, the cell elements were handled by a collaborative robot.
Highlights
We focus on nondestructive testing (NDT) of solid oxide fuel cells (SOFC)
Photos were taken of the interconnector covered with the glass solder before the cell elements were joined at high temperature (Figure 4)
It was found that the latter option is less accurate, as the two sheets of the cathode interconnector are not always tightly coupled thermally. They often generate artifacts that might be misinterpreted as defects in the glass solder layer. Another testing task that could be fulfilled by active thermography is the localization of electrical shorts in the cell element
Summary
Ships and mobile homes, fuel cells are in development or already in operation for cars (Figure 1). We focus on nondestructive testing (NDT) of solid oxide fuel cells (SOFC). Within a research consortium consisting of three research institutes and an industrial company, some of the material-related questions, concerning the development of suitable glass solders, were investigated [1]. The task described here was the development and evaluation of nondestructive techniques for 100% testing of the joints between the metal and glass solder. The sealant between the metallic interconnectors must have good adhesion to the steel It should be electrically insulating and prevent uncontrolled mixing of the gases involved. Another requirement is stability in the presence of temperature cycles. Single cell elements of this type are later stacked to form the SOFC device
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
