The relationship between reaction and diffusion during ultrafine NiO reduction by H₂ in a fluidized bed reactor were investigated. The result illuminates that the reduction reaction proceeding in the unreduced NiO powders is according to the nucleation model. A modified force balance model between cohesive and collision forces incorporating grain‐boundary diffusion and reaction is proposed to predict the agglomeration behavior of ultrafine Ni during the reduction of NiO in a fluidized bed. The modified force balance model shows more precise predictions than the model without consideration of grain‐boundary diffusion. Based on the model, it is found that the core of the two‐step reduction is to decouple grain growth from reduction for achieving full conversion while retaining nanosized grain sizes.

中文翻译：

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NiO超细还原过程中反应与扩散的关系

研究了流化床反应器中H ₂在超细NiO还原过程中反应与扩散之间的关系。结果表明，未还原的NiO粉末中的还原反应是根据成核模型进行的。提出了一种结合晶粒边界扩散和反应的内聚力和碰撞力之间的修正力平衡模型，用于预测流化床中NiO还原过程中超细Ni的团聚行为。与不考虑晶界扩散的模型相比，改进的力平衡模型显示出更精确的预测。根据该模型，发现两步还原的核心是使晶粒生长与还原脱钩，以在保持纳米级晶粒尺寸的同时实现完全转化。