Oxidation behaviour of TaxTi1-xC and TaxTi1-xCyN1-y whiskers

TaxTi1-xC and TaxTi1-xCyN1-y (0 less than or equal to x less than or equal to 1, 0 less than or equal to y less than or equal to 1) whiskers have been oxidised under non-isothermal as well as isothermal conditions. The non-isothermal oxidation experiments were carried out in a combined thermogravimetric differential thermal analysis set-up (TG-DTA), using oxygen atmosphere, with a heating rate of 5 degrees C/min. It was found that the oxidation onset temperature (T-on) increased with increasing x-value within the temperature range 375-550 degrees C for both TaxTi1-xC and TaxTi1-xCyN1-y whiskers and also that T-on is higher for carbonitrides compared to carbides. Scanning and transmission electron microscopy studies (SEM and TEM) showed that whiskers with a diameter exceeding 0.3 mu m were split into two halves along the length of the whisker when oxidised, whereas whiskers with a diameter less than 0.3 mu m retained their morphology after oxidation. Isothermal oxidation experiments were performed with TaxTi1-xC whiskers in the temperature range 400-1200 degrees C, and it was found that the size of TiO2 particles formed from mixed transition-metal carbide precursors was substantially smaller compared to the particle size resulting from oxidation of TiC. However, the size of Ta2O5 particles were found to be small and of the same size independently if TaC or TaxTi1-xC were oxidised. (C) 1999 Elsevier Science B.V. All rights reserved.