Physico-chemical nanomaterials science

Application of crack growth resistance characteristics for assessing the degradation of fine-grained YSZ–NiO(Ni) anode materials in a hydrogen sulfide containing atmosphere
Vasyliv B.D.1, Kulyk V.V.2, Duriagina Z.A.2,3, Kovbasiuk T.M.2, Lemishka I.A.2
1 Department of Hydrogen Technologies and Alternative Energy Materials, Karpenko Physico-Mechanical Institute of the NAS of Ukraine, 5 Naukova str., Lviv 79060, Ukraine.
E-mail: mechengin1111@gmail.com
2 Department of Materials Science and Engineering, Lviv Polytechnic National University, 12 S.Bandera str., Lviv 79000, Ukraine.
3 Department of Materials Engineering, The John Paul II Catholic University of Lublin, 14 Racławickie Al., Lublin 20-950, Poland.

One of the main areas of improvement of existing solid oxide fuel cell (SOFC) models is the formation of anode, cathode and electrolyte structures resistible against degradation in operating environments. The aim of this work is to study the effect of hydrogen sulfide content in a hydrogenous atmosphere on the microstructure, physical, and mechanical properties of YSZ–Ni cermets for SOFC anodes. To obtain the corresponding YSZ–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 0.1 MPa. The atmosphere contained 7 or 18 vol% Н2S. After aging, the physical and mechanical behaviours of specimens were studied. Two different mechanical tests were performed: strength test under three-point bending 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% Н2S had a slight effect on the strength and electrical conductivity of the YSZ–Ni cermet. In contrast to this, an increased content of hydrogen sulfide (18 vol% Н2S) caused some changes in the YSZ–Ni cermet microstructure. As a result, multiple breaking of the zirconia-nickel bonds occurred. As compared to the one-time reduced ceramics, microhardness and fracture toughness of the cermet remained at the same level whereas its strength decreased by almost 30%.