Thermoanalytical study on oxidation of TixTa1−xCyN1−y whiskers with formation of carbon

The oxidation of whiskers with the compositions of TixTa1−xCyN1−y (x=0 to 0.95; y=0.35–0.66 for x≤0.5 and y≤0.18 for x>0.67) was followed in an O2/Ar mixture (PO2=20 kPa) at 20–1000 °C by simultaneous thermogravimetry (TG), differential thermal analysis (DTA), and mass spectrometry analysis (MS). The weight and thermal changes and the gas evolution of CO2, N2, and NO were monitored with identification and microstructural observation of oxidized whiskers by X-ray analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with electron diffraction (ED). The onset oxidation temperature was found to increase with increasing Ta content, while the temperature for completion was not much changed. The oxidation of the whiskers was divided into two stages at ∼600 °C, irrespective of the whisker composition. The two-stage oxidation was discussed on the basis of the results of the experimental results. It was revealed that some amount of carbon is retained without oxidation for the whiskers with x=0.05 to 0.95 and then oxidized above ∼750 °C.