YSZ‐Induced Crystallographic Reorientation of Ni Particles in Ni–YSZ Cermets

Abstract

Metal–ceramic interfaces in Ni–YSZ (YSZ, yttria‐stabilized zirconia)‐textured porous cermets prepared by reduction of NiO–YSZ directionally solidified eutectics have been studied by transmission electron microscopy and X‐ray pole figure experiments. Before reduction of NiO, the interfacial plane is but after reduction, the Ni phase does not maintain the same crystallographic orientation as the NiO parent phase. Ni undergoes an interface‐induced crystallographic reorientation to form the lower energy (002)Ni∥(002)YSZ interface. This process has been studied as a function of the reduction temperature, and it seems to be more effective at ∼800°C. Metal–ceramic low‐energy interfaces prevent Ni particle coarsening and impart long‐term stability to the cermet.

The influence of the reducing conditions on the final microstructure and performance of nickel-yttria stabilized zirconia cermets

“…In contrast with the gaps seen in the samples reduced at low temperature, no gap exists in most Ni-YSZ interfaces. At higher temperatures, YSZ becomes a good oxygen ion conductor and NiO reduction could take place through the NiO-YSZ interface [22,31,32]. A lesser amount of nickel coarsening can be seen in the sample reduced in the diluted hydrogen flow when compared to the one reduced with the 800°C dry stream.…”

Orientation relationship and interfaces in Ni and Co-YSZ cermets prepared from directionally solidified eutectics

“…The relationship between metal-ceramic adhesion and metal coarsening can be expressed in terms of thermodynamic considerations. The variation of the interfacial energy during coarsening is lower for higher values of the metal-ceramic work of adhesion, and as a consequence, good metal-ceramic adhesion leads to a lower coarsening driving force [13].…”

“…These reorientation phenomena occur because the Ni atoms re arrange at the interface during the NiO reduction process to replicate the YSZ crystalline order and to reduce the interfacial energy. We have shown that reorientation takes place only if reduction starts at the interface because the oxygen lost by NiO passes through the YSZ lamellae along its way to the reducing atmosphere [13] due to the high ionic conductivity of YSZ at the reduction temperatures. Moreover, we have also shown that the different interfaces correspond exactly to the best possible matches between Ni and YSZ calculated by Dickey et al using the near-coincident site lattice framework several years before our experimental study was accomplished [20].…”

“…The formation of lowenergy oxide-oxide interfaces is thermodynamically driven by the eutectic growth. The subsequent reducing treatment produces porous metal-YSZ cermets where metal and ceramic phases remain crystallographycally aligned, resulting in the formation of metal-ceramic interfaces with high adhesion [13]. Here we review the microstructure of NiO-YSZ and CoO-YSZ directionally solidified eutectic rods, focussing on the crystallographic orientation relationship and interfacial planes before and after reduction of the transition metal oxide.…”

Orientation relationships and interfaces in directionally solidified eutectics for solid oxide fuel cell anodes

“…18,19 For a good understanding of the metal-ceramic interfaces formed after reduction of the eutectic composite, prior understanding of both the oxide-oxide interfaces formed in the eutectic and of the parameters controlling its formation is essential. 20,21,22 This being the main objective of the paper.…”