No abstract

A new glass-ceramic composition containing Si, Mg, Ca, Na, Al, Zr, and B is presented here as sealant for planar SOFCs/SOECs, with the aim of joining the metallic interconnect (Crofer22APU) to the solid oxide cell (YSZ electrolyte or CGO barrier layer). Characteristic temperature, thermo-mechanical properties, and compositional variations are reviewed and discussed by thermal analyses and in situ XRD, in order to design and optimize the sealing profile and reduce the residual porosity. The glass after heat treatment partially devitrifies into augite and nepheline with residual glass phase of around 64.3%; after crystallization the glass-ceramic sealant has a coefficient of thermal expansion of 12.8 9 10 À6 K À1 and it is compliant with the other materials typically used for stack components.This work shows that the developed glass-ceramic can successfully join the ceramic cell with the Crofer22APU (preoxidized and alumina coating), proven by tests on small and large-scale samples. No signs of unwanted reactions at the glass-metal and the glass-cell interface are observed and sufficient gas tightness is achieved. K E Y W O R D Sglass-ceramics, solid oxide fuel cell, synthesis, thermal analysis

Further development and upscaling of the Solid Oxide fuel and electrolysis Cell (SOCs) technologies would significantly benefit from improvement of their mechanical robustness. In this work, microstructure, crystalline phase composition, fracture toughness and susceptibility to lowand high-temperature degradation of six different Ni(O)-Zirconia fuel electrode supports, manufactured from six different stabilized zirconia compounds, are investigated.In the oxidized state, tetragonal zirconia-based supports have higher fracture toughness than cubic zirconia-based substrate, due to the transformation toughening effect and a finer grained microstructure. The NiO-1.5CeO2 4.5YO1.5-SZ support exhibits the highest fracture toughness, showing a 30 and 10 % improvement compared to the state-of-the-art NiO-5.8YO1.5-SZ support at room temperature and 800 °C, respectively. In the reduced state on the other hand, the tetragonal and cubic zirconia-based substrates have comparable fracture toughness. The Ceria-Yttria codoped materials possess superior resistance to hydrothermal degradation due to the stabilizing effect of Ce 3+ formed during reduction.

Ceria-Yttria co-doped tetragonal zirconia is an attractive class of materials having high strength, toughness and thermal stability. In this study, several co-doped zirconia powders with different stabilizers contents were synthesized via continuous hydrothermal flow synthesis (CHFS). The CHFS was concluded as a suitable method in synthesizing ultrafine tetragonal zirconia particles with controlled morphology. The synthesized powders as well as some commercial powders were heat-treated both in the form of powders and pellets between 1150 and 1500°C and their crystalline structure after cooling to room temperature was studied. The results were used to map out the stability range of the tetragonal phase. The developed diagrams are useful tools to select the appropriate amounts of stabilizers applicable for different sintering temperatures and for samples with different target densities.

Thin, porous zirconia-based ceramic components are of high interest in energy application devices where they are used as structural ceramics. Mechanical reliability of such devices is not only dependent on the fracture toughness of the ceramic components, but also on their sensitivity to slow crack growth (SCG). In this work, the fracture toughness and SCG behavior of porous (4.5 to 45.5%) and thin (~ 0.25 mm) 3Y-TZP ceramics are investigated using the Double Torsion method. The analysis of the double torsion data, previously developed for dense materials, was here assessed and adapted. The compliance of the samples was observed to change linearly with crack length and the measured stress intensity factor was dependent on crack length, as for dense materials. This dependency decreased by increasing the sample porosity. For all materials, the ratio of the SCG threshold to fracture toughness was of 0.56 ± 0.06.