Thermodynamic equilibrium at a graphite-to-zirconia electrolyte interface

Abstract Two kinds of galvanic cells with yttria-stabilized zirconia as solid electrolyte, used as oxygen sensors for long-term measurements in metallurgical plants, have been studied. Their peculiarity is to adopt graphite as the main component of the reference electrode of the oxygen chemical potential. The cells are Pt|Al 2 O 3 |C|YSZ|Ar {p( O 2 )=np ° }| Pt Pt|Fe+Fe 1−y O|Al 2 O 3 |C|YSZ|Ar {p( O 2 )=np ° }| Pt where p o = 101.325 kPa, n is a factor changing at each step in a procedure which allows modification of the p (O 2 value, and ysz denotes 8 mass per cent of Y 2 O 3 stabilizing ZrO 2 . The e.m.f.s of the galvanic cells were measured against p (O 2 ) from 2.28 to 10.64 kPa at different temperatures. The p (O 2 ) at the ysz -to-C interface, p r , follows, respectively, the equations: l g( p r Pa )= −(4±1)−(19465±1523)/(T/K), 1281 to 1461 K) l g( p r Pa )= (9±2)−(27050±2050)/(T/K), 1125 to 1404 K) Thermodynamic analysis indicates that the chemical equilibria determing the oxygen chemical potential at the ysz -to-C interface are, respectively C(graphite)+O 2 (g)=CO 2 (g) 0.947 Fe(cr)+ 1 2 O 2 (g)=Fe 0.947 O(cr)