**4.4 Thermal stability**

Thermal stability and oxidation resistance at high temperatures are important for applications of PDC cutters, especially in hard and abrasive formation drilling in the oil and gas industry. Thermal stability and oxidation resistance tests are performed at different temperatures from room temperature to 1400°C by an in-situ XRD. The in-situ X-ray diffraction (XRD) using Cu kα radiation at a wavelength of 0.15406 nm, a step rate of 0.01°/s, and a scanning range of 2θ = 10°-100°, is used to characterize the phase transition of CFPCD samples from room temperature to up to 1400°C. For comparison, commercial PDC materials were also tested. As can be seen from **Figure 12(a)**, the initial oxidation temperature of commercial PDCs at around 806°C is harsh. On the other hand, the new CFPCD material shows no oxidation until 1400°C (**Figure 12b**) and is found to be even stable at 1200°C – the highest recorded in the industry, well above natural diamond (~800°C), nanoparticle diamond (~680°C), unowned diamond (~1056°C) and commercial PDC (~600°C).
