Evolution of multilayered scale structures during high temperature oxidation of ZrSi2

The oxidation behavior of bulk ZrSi2 at 700, 1000, and 1200 degrees C in ambient air has been investigated. Parabolic to cubic oxide layer growth kinetics was confirmed by weight gain measurements and the average oxide layer thickness was 470 nm, 6.7 mu m, and 37 mu m at 700 degrees C, 1000 degrees C, and 1200 degrees C, respectively, after 5 h oxidation tests. Evolution of compositionally modulated nano/micro structures was confirmed in the oxide layer. At 700 degrees C, Si diffusion resulted in discontinuous Si-rich oxide phases in amorphous Zr-Si-O matrix. At 1000 degrees C, complex multilayered structures such as fine and coarse irregular spinodal structures, wavy Si-rich oxide, and Si-rich islands evolved. At 1200 degrees C, additional nucleation of nanoscale ZrO2 particulate phase was observed. The spinodal structures were confirmed to be crystalline ZrO2 and amorphous SiO2, and the thermodynamic driving force for phase evolution has been explained by extension of liquid miscibility gap in the binary ZrO2-SiO2 phase diagram.