Densification of SOFC Yttria-Stabilized Zirconia Electrolytes Through Addition of Sintering Additives

Abstract

The use of sintering additives for fully yttria-stabilized zirconia (8YSZ) was investigated in order to reduce the sintering temperature. Both state-of-the-art SOFC systems, i.e. the tubular Siemens Westinghouse design and the planar anode-supported system, were electrolyte-coated by wet chemical methods (e.g. vacuum slip casting and wet powder spraying) with different sintering aids. For the planar system, alumina was used while in the tubular system boron nitride was investigated. The addition of low amounts of alumina (< 2%) resulted in either better gas tightness of the electrolyte sintered at 1400°C or in comparable gas tightness (in comparison to the normally used 8YSZ without additions) at lower sintering temperatures. The performance of single cells is enhanced by addition of alumina for all temperatures measured (750-900°C). For the tubular system low amounts of boron nitride (< 2.5%) led to a strong decrease in the sintering temperature necessary to reach gas tightness (<1300°C). The reaction mechanism for enhanced densification of both sintering experiments was examined.