Design And Performance Of Sealing Material For It-SOFC

Solid Oxide Fuel Cell （SOFC） is an all solid state energy conversiondevice that can transform chemical energy of fuels directly into electricalenergy by electrochemical reaction. As a research focus in new energyfield, SOFC has the advantages of high energy conversion efficiency, fuelflexibility, environmentally friendly, non-noble-metal catalysts, etc. Afterabout three decades of rapid development, SOFC single cell manufacturingtechnology has become mature enough for marketization andindustrialization. However, one of the most significant challenges for theplanar SOFC design is to realize the effective high temperature sealing.Therefore, it has attracted many people’s attention and research to developsealants with high hermetic reliability, long term stability and good thermalcycling property. During the prevailing sealing techniques，Reactive AirBrazing（RAB）and Metal-base composite sealants are promising solution.This thesis aims at lowering the CTE of braze by adding low thermalexpansion ceramic. The main research lies in design and manufacturing ofcomposite solder, brazing process design, performance characterization ofthe joints. The specific tasks are as follows:Chapter1reviews fuel cells, and gives a brief introduction of theSOFC working principle,:research and developments, as well as the planarSOFC sealant materials research status and trends. After that, innovativepoints and research background are proposed. Finally, this chapter lists outthe main research contents of this paper.Chapter2describes composite solder design. Reactive Air Brazing was chosen after analyzing different sealing techniques. Ag-CuO was usedas solder matrix on the basis of RAB. Low thermal expansion ceramic wasdesigned to add to Ag-CuO as to produce a composite braze. A briefintroduction of working principle and development of composite braze isgiven, which proved by example and theory that composite solder canproduce a joint with lower CTE. Al₂TiO₅particles were used asreinforcements, after taking Ag-CuO wetting ability, SOFC workingrequirements and manufacturing cost into consideration.Chapter2sets the process of composite solder preparation andbrazing. Al₂TiO₅particles were prepared by sol-gel method andcharacterized by XRD. Ag-CuO-Al₂TiO₅solder paste was preparedthrough ball milling and hand lapping. After that we designed a series ofprocess, including joint type selection, surface treatment, weldmentassembling, metallographic specimen preparation. SeveralNi-YSZ/SUS430joints were brazed using the composite solder paste. Theresult showed that Ag-CuO-Al₂TiO₅solder can produce strong andcompact joints, and brazing temperature is980℃while soaking time is10min. On above basis, an effective brazing process was set.Chapter4conducts joint performance characterization and evaluation.Leakage rate test、100h aging test and thermal cycle test were conducted,and SEM and EDX were made to evaluate its hermeticity，oxidationresistance， thermal cycling stability. SEM micrograph showed thatAl₂TiO₅particles were well-distributed within the braze，improving itshermetical and mechanical properties. The particle promoted CuOmigration towards surfaces. It may improve the oxidation resistance of thebraze by using more Al₂TiO₅and less CuO. Leakage rate was below0.001mL/（min cm）. Open circuit voltage（OCV） exhibited no decrease after100haging or8thermal cycles（400～800℃）.The results demonstrated thatAg-8CuO-2Al₂TiO₅is an effective sealant for planer solid oxide fuelcell（pSOFC） components. Chapter5summarizes research achievements and experimentaldeficiencies，puts forward improving measures, proposes the directionfor further research.