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首页> 外文期刊>Journal of Materials Engineering and Performance >Local Dynamics of Chemical Kinetics at Different Phases of Nitriding Process
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Local Dynamics of Chemical Kinetics at Different Phases of Nitriding Process

机译：渗氮过程不同阶段化学动力学的局部动力学

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摘要

The local dynamics of chemical kinetics at different phases of the nitriding process have been studied. The calculations are performed under the conditions where the temperature and composition data are provided experimentally from an in-service furnace. Results are presented in temporal variations of gas concentrations and the nitrogen coverage on the surface. It is shown that if it is available in the furnace, the adsorption of the N-2 gas can seemingly start at temperatures as low as 200 A degrees C. However, at such low temperatures, as the diffusion into the material is very unlikely, this results in the surface poisoning. It becomes clear that, contrary to common knowledge, the nitriding heat treatment with ammonia as a nitrogen-providing medium is possible at temperatures like 400 A degrees C. Under these conditions, however, the presence of excess amounts of product gas N-2 in the furnace atmosphere suppresses the forward kinetics in the nitriding process. It seems that the best operating point in the nitriding heat treatment is achieved with a mixture of 6% N-2. When the major nitriding species NH3 is substituted by N-2 and the N-2 fraction increases above 30%, the rate of the forward reaction decreases drastically, so that there is no point to continue the furnace operation any further. Hence, during the initial heating phase, the N-2 gas must be purged from the furnace to keep its fraction less than 30% before the furnace reaches the temperature where the reaction starts.
机译：研究了氮化过程不同阶段的化学动力学局部动力学。该计算是在从使用中的炉中通过实验提供温度和成分数据的条件下进行的。结果显示了气体浓度和表面氮覆盖率随时间的变化。结果表明，如果在炉中可以使用，则N-2气体的吸附似乎可以在低至200 A的温度下开始。但是，在如此低的温度下，由于极不可能扩散到材料中，这会导致表面中毒。显然，与常识相反，可以在约400 A的温度下使用氨作为提供氮的介质进行氮化热处理。但是，在这些条件下，会存在过量的产物气N-2炉内气氛抑制了氮化过程中的正向动力学。看起来，氮化热处理的最佳工作点是使用6％N-2的混合物达到的。当主要的氮化物NH3被N-2取代并且N-2的分数增加到30％以上时，正向反应的速率会大大降低，因此没有必要再继续进行炉子操作了。因此，在初始加热阶段，必须在炉子达到反应开始的温度之前从炉子中清除N-2气体，以使其含量小于30％。

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