The diffusional transport of Mn through MnO scales was studied at 900 to 1200C by using a novel diffusion/evaporation method and the two-stage oxidation (Rosenburg) method. In the phase field of Mn1-xO near to the Mn3O4 phase boundary the Mn self-diffusion coefficient (table 140) and the concentration of defects was deduced to be proportional to PO2½. The concentration of defects increased with decreasing temperature at constant O partial pressure. Within this non-stoichiometry range, Mn1-xO had properties which were similar to those of wüstite. It was concluded that the important cation defects were defect clusters. The results could be explained by assuming that the defect clusters consisted of 4 vacancies on octahedral sites and one interstitial on a tetrahedral site. For the phase field near to the Mn/MnO phase boundary, it was concluded that Mn-interstitials predominated.
Defects and Diffusion in MnO. P.Kofstad: Journal of Physics and Chemistry of Solids, 1983, 44[9], 879-89
Table 140
Diffusion of Mn in MnO at the MnO/Mn3O4 Boundary
Temperature (C ) | PO2 (atm) | D (cm2/s) |
900 | 5.8 x 10-9 | 2.7 x 10-9 |
1000 | 2.3 x 10-7 | 1.45 x 10-7 |
1050 | 1.2 x 10-6 | 3.40 x 10-6 |
1100 | 5.4 x 10-6 | 7.20 x 10-6 |
1150 | 2.2 x 10-5 | 1.55 x 10-5 |
1200 | 8.2 x 10-5 | 3.03 x 10-5 |