Stability and Oxidation Properties of RE-α-Sialon Ceramics (RE = Y, Nd, Sm, Yb) |
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| Authors: | Lars-Olov Nordberg Mats Nygren Per-Olov Käll Zhijian Shen |
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| Affiliation: | Department of Inorganic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden;Department of Physics and Measurements Technology, Linköping University, S-581 83 Linköping, Sweden;Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, People's Republic of China |
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| Abstract: | Oxidation studies of hot-pressed RE-α-sialons, RE x -Si12-4.5 x Al4.5 x O1.5 x N16-1.5 x (with x = 0.40 for RE = Nd, Sm, Yb; and x = 0.48 for RE = Y) were carried out in oxygen in a TG apparatus for ca. 20 h. Very good oxidation resistance was found for the Yb-doped samples, with parabolic rate constants K p similar/congruent 0.09 10-6-3 10-6 mg2cm-4s-1 in the temperature range 1250-1350°C. The promising performance of this material was corroborated by long-term oxidation experiments (5 days) in air at 1350°C. Although the oxidation kinetics can be described by simple equations related to the parabolic rate law (e.g., the arctan equation, Δ W / A 0=α arctan bt + c t ), the oxidation process in these materials is likely to be complex. The significantly lower oxidation resistance of the RE = Nd, Sm doped α-sialons, especially at higher temperatures, is related to the formation of melilite, RE2Si3− y Al y O3+ y N4− y ( y ∼ 1), in these systems. The melilite phase is also responsible for the thermal instability of the Nd- and Sm-α-sialons. |
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