چكيده به لاتين
Long thought to be inexhaustible, fossil fuels are being used at an unsustainable rate. This and their significant environmental degrading impacts, are attracting researcher’s attention to cleaner and more efficient ways of generating electrical power. Solid Oxide Fuel Cells (SOFCs) as one of such alternatives, have many advantages to other fuel cell types. However, SOFCs come with their own set of challenges caused by their high operational temperatures, among which one can point to high oxidation rate of interconnects, Spallation and cracks in oxide scale due to the mismatch of Thermal Expansion Coefficient (TEC), Cathodic Poisoning and high Area Specific Resistance (ASR) of oxide scale. Manganese-containing coatings, with their unique properties, have overcome these challenges successfully. In this project, we aim to coat AISI-430 ferritic stainless steel with Cu-Mn Spinel to be utilized as SOFCs interconnects and evaluate its performance in operational environments. Our novel contribution lies in how the coating is done unconventionally, applying Electrophoretic codeposition of CuO and MnO2 followed by an oxidating thermal treatment for spinel synthesis. Simplicity and lower fabrication cost are the main advantages of this procedure. Among Electrophoretic deposition parameters effecting quality and quantity of the green body, the following ranges were studied for each parameter: applied voltage 10-100 volts, deposition time 1-10 minutes, solid concentration 2-40 g.l-1 and dispersant to powder ratio 0- 1/4. 100 volts, 10 minutes, 10 g.l-1 and 1/16 were selected as the optimum values for these parameters in Ethanol and Acetone media (1:1 volume ratio) with PVP as dispersant. Thermal treatment for spinel synthesis was studied in two stages, constant time (5 hours) at 700, 750, 800, 850, 900 and 950°C, and constant temperature (800 and 850°C) for 3, 5 and 7 hours. Phase analysis and microscopic evaluation of coatings suggested that 3 hours of oxidating thermal treatment in 800 and 850°C was the best conditions for spinel synthesis. These two samples, in addition to an uncoated and a green coating, were undergone 10 cycles of 10 hours cyclic oxidation at 750°C for performance evaluation. All of coated samples showed significant improvement in oxidation behavior, and were effective barriers for Chromium migration and Cathodic Poisoning. Parabolic Rate Constant of oxidation was reduced from 5.93×10-13g2.cm-4.s-1 in uncoated sample, to 5.76×10-14g2.cm-4.s-1 in coated sample with 3 hours of oxidating thermal treatment in 850°C.
