interface by oxidation of ZrC single crystals Original Research Article

A zirconium carbide (ZrC) single crytal was oxidized isothermally at temperatures of 600–1500 °C in a mixed atmosphere of oxygen and argon with an oxygen partial pressure (PO2) of 0.02–2kPa for 1–20 hours. Preferred orientation of tetragonal or monoclincal ZrO2 (t- and m-ZrO2) was occasionally observed on the surface of the oxidized crystal. The oxidized crystal possessed two subscales, outer (white) and inner (black) scales, which could be separated as oxide plates and carbon films, respectively, from the oxidized ZrC by treatment with a concentrated HF solution. The structure and morphology of the carbon films was examined by Raman spectroscopy, scanning electron microscopy and transmission electron microscopy (TEM). The films obtained at low temperatures (700 to 110 °C) were amorphous, as evidenced by TEM observation and Raman spectra. The hexagonal planes of carbon in the films tended to grow; on the electron diffraction pattern, halos changed to arcs or rings at 1500 °C. The t-ZrO2 particles, several to tens of nanometers in size, were dispersed in the carbon films.