Diffusion of insoluble carbon in zirconium oxides

Theoretical and Experimental Investigations on the Mechanism of Carbothermal Reduction of Zirconia (Preprint)

“…15 is less than 20 μm on bottom faces of all the pellets. This is in agreement with results and analysis from Vykhodets et al 13 where carbon can diffuse only to depths of ~25 μm at 1800 o C, shown in Fig. 9.…”

“…Based on previous research [6][7][8][9]14 where CO is thought to be the reaction driver for ZrC conversion, the bottom face of the MP2 top half should produce more ZrC formation than P3. However, it was determined that P3 bottom face exhibits significantly more ZrC conversion (70%) than MP2 (23% Moreover, diffusion measurements 13 show that kinetics of carbon diffusion in zirconia is rather slow. Thus, any YSZ to ZrC conversion occurring because of carbon will be highly localized.…”

“…The carbon diffusion coefficient in zirconia has been reported to be six orders of magnitude smaller than oxygen self-diffusion 13 . This would indicate several orders of magnitude difference in diffusivity between C and CO through YSZ due to the gaseous nature of CO. Based on the recent work of Vykhodets et al 13 and utilizing their data, the diffusion coefficient of C in YSZ at 1800 ºC is calculated to be 3×10 -14 m 2 /sec. Using Fick's second law and this diffusion coefficient, the effective diffusion length of C in YSZ can be approximated to 25 μm for 0.5 hour at 1800ºC (calculated plots shown in Fig.…”

Growth and thermal oxidation of Ru and ZrO2 thin films as oxidation protective layers

“…However, apart from the size, the charge is also important, which gives an extra driving force for diffusion. For instance, diffusion of carbon 243 is ~10 5 times slower than of oxygen (O 2-) 244 in sintered ZrO2 powder at 900°C. Although C is much smaller than O 2-, the charge was absent in the implanted C in that study, 243 leading to slower diffusion, and showing the lower diffusivity of insoluble C in ZrO2, compared to O 2-.…”

“…For instance, diffusion of carbon 243 is ~10 5 times slower than of oxygen (O 2-) 244 in sintered ZrO2 powder at 900°C. Although C is much smaller than O 2-, the charge was absent in the implanted C in that study, 243 leading to slower diffusion, and showing the lower diffusivity of insoluble C in ZrO2, compared to O 2-. It should be noted that cations are usually smaller than anions (from the ionic radius), leading to faster diffusion rates depending on their charge.…”