| T/℃ | a | b | c |
| 25 | 29.553 | 311.514 | 36.205 |
| 100 | 37.303 | 269.921 | 37.601 |
| 300 | −756.826 | 896.207 | 5.567 |
| 500 | −287.229 | 477.846 | 44.651 |
| 700 | −268.579 | 549.094 | 15.876 |