Deterioration of Crack Growth Resistance Characteristics of a Fine-Grained YSZ–NiO(Ni) Anode Material During Its Degradation in a Hydrogen Sulfide Containing Atmosphere

AbstractThe effect of hydrogen sulfide content in a hydrogenous atmosphere on the microstructure, physical, and mechanical properties of YSZ–NiO(Ni) cermets for solid oxide fuel cell (SOFC) anodes has been studied. To obtain the corresponding YSZ–NiO(Ni) cermet structure, specimens of the YSZ–NiO anode ceramics were reduced in Ar–5 vol% H2 mixture for 4 h at 600 °C under a pressure of 0.15 MPa. A part of reduced specimens was aged in “hydrogen sulfide in Ar–5 vol% H2 mixture” atmosphere for 4 h at 600 °C under a pressure of 0.15 MPa. The atmosphere contained 7 or 18 vol% H2S. After aging, the physical and mechanical behaviors of specimens were studied. The following mechanical tests were performed: strength test under three-point bending, Vickers microhardness test, and fracture toughness test by indentation method. Material microstructure and fracture surface morphology of the specimens were also investigated. It was revealed that the atmosphere containing up to 7 vol% H2S had a slight effect on the strength and electrical conductivity of the YSZ–NiO(Ni) cermet. In contrast to this, an increased content of hydrogen sulfide (18 vol% H2S) caused some changes in the YSZ–NiO(Ni) cermet microstructure. As a result, multiple breaking of the zirconia-nickel bonds occurred. As compared to the preconditioned cermet, strength of the aged cermet decreased by almost 30%. In contrast to this, microhardness and fracture toughness of the aged cermet were only lowered by about 10%. The peculiarities of both strength and fracture toughness tests were explained based on the process zone size and corresponding fracture micromechanisms.