Decomposition of the ZrO2 electrolyte in contact with Ni: Structure and chemical composition of the Ni-electrolyte interface

The Ni/(ZrO2 + 9.5 mol% Y2O3) interface was used as a model system to inves tigate decomposition reactions of a yttria-stabilized ZrO2, electrolyte in contact with a metal at elevated temperature. In the present study, the sam ple was a diffusion-bonded symmetrical galvanic cell Ni\ZrO2 + 9.5 mol% Y2O 3\Ni. Various electron microscopy techniques were used to study the morphol ogy and structure of the reaction products at the Ni-ZrO2, electrolyte phas e boundary after current now. Below a critical oxygen partial pressure of a pproximately 10(-27) atm, an intermetallic reaction layer formed at the Ni- electrolyte interface. Between the intermetallic layer and electrolyte a ch in Y2O3 layer was present, which acted as a diffusion barrier for Zr and Ni , slowing down the overall chemical reaction. At several locations at the i nterface the Y2O3 layer brake up, leading to a morphological instability of the interface between electrolyte and Ni5Zr, allowing further reaction. Th e thickness of the total reaction layer varied widely as a consequence of s uch an instability.