Effect of La Ion-Implantation on High Temperature Oxidation of Ni-40Cr Catalyst Support

Ni-based alloys are widely used in combustion process, and their catalytic activities are strongly influenced by factors such as the nature of support, active phase, metal loading, catalyst preparation method and pretreatment. The isothermal and cyclic oxidizing kinetics of Ni-40Cr alloy and its lanthanum ion-implanted samples were studied at 1000degC in air by thermal- gravimetric analysis (TGA). Scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM) was used to examine the oxide film´s morphology and structure after oxidation. Secondary ion mass spectrum (SIMS) method was used to examine the binding energy change of chromium caused by La-doping and its influence on formation of Cr₂O₃ film. Laser Raman spectrum was used to examine the tress changes within oxide films. It was found that lanthanum implantation remarkably reduced the isothermal oxidizing rate of Ni-40Cr and improved the anti-cracking and anti-spalling properties of Cr₂O₃ oxide film. The reasons for the improvement were mainly that the implanted lanthanum reduced the grain size and internal stress of Cr₂O₃ oxide, increased the high temperature plasticity of oxide film. Lanthanum mainly existed in the outer surface of Cr₂O₃ oxide film in the forms of fine La₂O₃ and LaCrO₃ spinel particles.