Proton—conducting ceramics as electrode/electrolyte—materials for SOFCs: Preparation, mechanical and thermal-mechanical properties of thermal sprayed coatings, material combination and stacks

Abstract

Abstract This part of investigation includes the synthesis, preparation and examination of the cathode lanthan–strontium–manganite (ULSM) as bulk material, the BCN electrolyte as coating and the cermet anode (BCN/Ni) as coating too. The ULSM powder was made by the conventional solid reaction of carbonates and oxide. The ULSM samples were cold pressed and sintered at temperatures between 1400 and 1600 °C. The measurement of the mechanical properties like bending strength (room and high temperature), Young modulus ( E ), modulus of rigidity ( G ), Poison's ratio, hardness and fracture toughness were done for the ULSM bulk material. The highest values of bending strength, E and G was found to be 85 MPa, 192 GPa and 46 GPa, respectively for the dense material and only 26 MPa bending strength for the porous material (30% pores). The hot bending strength (800 °C) was also in the range of 25 MPa for the porous material. In the case of BCN coatings cold bending strength was determined to 55 MPa for the dense material (99% TD). E - and G -moduli were in the range of 190 and 46 GPa in maximum while Poisons ratio was about 0.35. Vickers hardness was resulted in a maximum value of 5 GPa while Poison's ratio was about 0.35. Finally the cold bending strength of the porous cermet coatings (30% porosity) was measured to 54 MPa with an E -modulus of 15 GPa. The Vickers hardness was about 0.2 GPa and the coefficient of thermal expansion about 11×10 −6 K −1 . Finally, the material combination cathode/electrolyte (ULSM–BCN) and the stacks (ULSM–BCN–BCN/Ni) were prepared and examined. The ULSM samples were cold pressed and sintered at temperature of 1400 °C with a porosity of about 30%. On the surface of ULSM the BCN electrolyte was prepared by plasma spraying. On the surface of the electrolyte the BCN/Ni anode was prepared by flame spraying. The measurement of the mechanical properties like bending strength (room and high temperature), Young modulus ( E ), adhesion strength were done for the material combination and adhesion strength and thermal shock resistance was measured for the stacks too. The values of bending strength and E were found to 35 MPa and 62 GPa, respectively for the material combination. The hot bending strength (800 °C) was in the range of 59 MPa and an E of 51 GPa. The adhesion strength was determined to 0.24 MPa for the material combination and 0.42 MPa for the stacks and the thermal shock resistance of the stacks was greater than 20 cycles.