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Comparison of Internal Nitridation Reactions in Ammonia and in Nitrogen

机译:氨和氮中内部氮化反应的比较

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Nine commercial high-temperature alloys were reacted with NH_3 and with N_2-5%H_2 at temperatures of 1000-1200℃. In all cases extensive internal nitridation developed according to parabolic kinetics. Reaction with N_2 produced precipitates of Cr_2N plus, at 1000℃, some external CrN, in accordance with thermodynamic prediction. However NH_3 produced an external scale of CrN and a near-surface zone of internal CrN as well as a deeper zone of Cr_2N at 1100 and 1200℃. The CrN phase is metastable, and results from catalytic dissociation of NH_3, which produces a high effective nitrogen activity. This high activity also leads to faster internal-precipitation reactions, whereas reaction rates in nitrogen are in reasonable agreement with Wagner's model of rate control by inwardly diffusing nitrogen at its equilibrium solubility. Precipitate morphologies are complex, reflecting the importance of the energy barrier to homogeneous nucleation.
机译:9种商品高温合金在1000-1200℃的温度下与NH_3和N_2-5%H_2反应。在所有情况下,根据抛物线动力学产生广泛的内部氮化。根据热力学预测,在1000℃下,与N_2的反应产生了Cr_2N +的析出物,还有一些外部的CrN。然而,NH_3在1100和1200℃时产生了CrN的外部水垢和内部CrN的近表面区域以及更深的Cr_2N区域。 CrN相是亚稳态的,是由NH_3催化离解而产生的,NH_3具有很高的有效氮活度。这种高活性还导致更快的内部沉淀反应,而氮气中的反应速率与Wagner的速率控制模型(通过在平衡溶解度下向内扩散氮气)合理地吻合。沉淀物的形貌很复杂,反映了能垒对均匀成核的重要性。

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