Andrey O. Zhigachev

The paper reports study of the applicability of calcium-borosilicate glass-ceramics with high boron oxide content as a sealant for solid oxide fuel cells. Chemical composition of the studied materials was 33 mol% CaO, 21 mol% B2O3, 46 mol% SiO2. The material was studied as an alternative to existing sealants on the base of calcium and barium aluminosilicates, because of the limited adhesion of the latter to steel interconnects in fuel cells. The study has shown that the studied sealant has a softening point of about 920–930°C, which allows one to use for sealing of fuel cells at 925°C. Use of relatively low sealing temperature allows one to avoid overheating of the cell during sealing and to avoid accompanying degradation of the service properties. The studied sealant has demonstrated excellent adhesion to surface of interconnect materials (Crofer 22 APU steel). Furthermore, the studied sealant was found to be thermomechanically compatible with Crofer 22 APU steel and ZrO2-based electrolytes.

The applicability of calcium–borosilicate glass-ceramics with high boron oxide content as a sealant for solid oxide fuel cells is studied. Chemical composition of the studied materials is: 33 mol % CaO, 21 mol % B₂O₃, and 46 mol % SiO₂. The material is studied as an alternative to the existing calcium– and barium–aluminosilicate-based sealants because of the latters’ limited adhesion to steel interconnects in fuel cells. The studied sealant is shown to have a softening point of about 920–930°C, which allows using it for sealing of fuel cells at 925°C. Use of relatively low sealing temperature allows avoiding overheating of the cell during the sealing and avoiding the accompanying degradation of the battery operational characteristics. The studied sealant demonstrated excellent adhesion to the surface of interconnect materials (the Crofer 22 APU steel). Furthermore, the studied sealant is found to be thermomechanically compatible with the Crofer 22 APU steel and ZrO₂-based electrolytes.

Solid oxide fuel cells (SOFCs) are promising devices for electrical power generation from hydrogen or hydrocarbon fuels. The paper reports our study of CaO-SiO₂-B₂O₃ material with composition 36 mol.% SiO₂, 26 mol.% B₂O₃, and 38 mol.% CaO as a high-temperature sealant for SOFCs with an operating temperature of 850 °C. The material was studied as an alternative to presently existing commercial glass and glass-ceramics sealants for SOFCs with operating temperature of 850 °C. Many of these sealants have limited adhesion to the surface of Crofer 22APU steel, commonly used in these SOFCs. The present study included X-ray diffraction, dilatometric, thermal, and microstructural analysis The study has shown that the softening point of the CaO-SiO₂-B₂O₃ glass is around 900 °C, allowing sealing of the SOFCs with this glass at convenient temperature of 925 °C. The CaO-SiO₂-B₂O₃ glass sealant has shown excellent adhesion to the surface of Crofer 22APU steel; SEM images demonstrated evidences of chemical reaction and formation of strong interface on sealant–steel contact surface. Furthermore, the glass has shown a coefficient of thermal expansion about 8.4 × 10⁻⁶ 1/K after sealing, making it thermomechanically compatible with the existing SOFC materials.

Wet high-energy milling and uniaxial pressing are used to fabricate CaO-stabilized tetragonal zirconia polycrystalline ceramic (Ca-TZP) with decent mechanical characteristics, i.e., a hardness of 11.5 GPa, Young’s modulus of 230 GPa, and fracture toughness of 13 MPa·m^0.5. The effect of CaO concentration and the sintering temperature on phase composition and mechanical characteristics of CaO-stabilized zirconia ceramic made of baddeleyite is investigated.

The mats of yttria-stabilized tetragonal zirconia nanofibers were prepared using electrospinning. The effect of calcination temperature in the range of 600–1200 °C on their microstructure, phase composition and mechanical properties was investigated. Phase composition of the nanofibers did not change in all ranges of the calcination temperatures, while the average grain size increased from 8 to 39 nm. Nanoindentation testing of the mats showed a decrease in the hysteresis loop energy in samples with higher calcination temperature. Hardness and the elastic modulus measured with the indentation technique were the highest for the mats calcined at 900 °C.