Mechanical properties of glass-ceramic sealants of the system BaO/SrO-MgO-B2O3-SiO2

Reference Presenter Authors
(Institution)
Abstract
10-022 Francisco Carlos Serbena Moreira Justo, V.(State University of Ponta Grossa); Pascual, M.J.(Instituto de Cerámica y Vidrio); Rodríguez-Lopez, S.(Universidad Autónoma de Madrid); Gallo, L.S.(State University of Ponta Grossa); Serbena, F.C.(State University of Ponta Grossa); Mathias, I.(State University of Ponta Grossa); de Souza Just, L.(State University of Ponta Grossa); Marin, D.(State University of Ponta Grossa); The search for new sources of energy has favored an extensive research on SOFC. Solid Oxide Fuel Cells are devices that transform chemical energy into electricity and are comprised of an anode, an electrolyte and a cathode. In order to make a stack, the cells must be jointed in a way to prevent gas leaking and be electrically insulated. The most common materials to be used as sealants are glass-ceramics due to their good electrical insulation and mechanical properties and the possibility of changing the composition to improve some of these properties. However, cracks can appear during thermal cycles, which may cause leaks leading to a drop of stack performance. Considering these characteristics, a mechanical study was developed for glass-ceramics within the glass systems SiO2-BaO/SrO-MgO-B2O3, and also, another composition of the system SiO2-SrO-MgO-B2O3 with 15% zirconia oxide fiber addition, heat treated at 800°C and 750°C, respectively, for 24h, 100h and 800h. Residual stresses arise due to different thermal expansion coefficients between the glass, the crystallized phases, the anode, the cathode and the steel. The stresses in the anode were measured by Raman spectroscopy. Hardness, elastic modulus and fracture toughness (KIC) of the glass-ceramics of both systems were measured. The mechanical strength of the glass-ceramics was also measured at room and high temperatures. The results of biaxial strength measured by ball-on-three ball test did not vary with heat treatment time when tested at room temperature, being between 104-112 MPa. For the high temperature tests, the mechanical strength was a minimum for the sample treated for 100h. However, for the time treatment of 800h, the mechanical strength was the same as that measured at room temperature. The fracture toughness did not vary significantly with heat treatment time. The fracture toughness of Sr based glass-ceramics was slightly larger than those of the Ba based glass-ceramics.