The solid-state reaction, ½Y2O3 + ½Cr2O3 YCrO3, was carried out at temperatures of between 1458 and 1719K under an O partial pressure of 0.21atm. It was found that the reaction obeyed a parabolic rate law, and that the diffusion of Y ions controlled the reaction. The diffusion coefficient of Y3+ ions was deduced from the Gibbs free energy change of the reaction and the parabolic rate constant. The diffusivity of the Y ion could be described by:
D(m2/s) = 8.36 x 10-9exp[-272(kJ/mol)/RT]P3/16a1/8
where a was the Cr2O3 activity and P was the O partial pressure.
K.Kawamura, A.Saiki, T.Maruyama, K.Nagata: Journal of the Electrochemical Society, 1995, 142[9], 3073-7
Table 73
Grain Boundary Diffusivity of S in Cr2O3
Temperature (K) | Method | Dd (cm3/s) |
1173 | Whipple | 7.10 x 10-16 |
1173 | Fisher | 3.00 x 10-16 |
1223 | Whipple | 1.73 x 10-15 |
1223 | Fisher | 9.30 x 10-16 |
1273 | Whipple | 3.40 x 10-15 |
1273 | Fisher | 1.53 x 10-15 |
1323 | Whipple | 5.53 x 10-15 |
1323 | Fisher | 2.56 x 10-15 |
1373 | Whipple | 7.92 x 10-15 |
1373 | Fisher | 4.10 x 10-15 |
Table 74
Bulk Diffusivity of Y in Cr2O3
Temperature (C) | D (cm2/s) |
800 | 2.0 x 10-18 |
850 | 1.7 x 10-18 |
900 | 3.2 x 10-18 |
950 | 7.9 x 10-18 |
1000 | 2.4 x 10-17 |