Calcination typically increases the aggregation and size of nanoparticles. However, are there any exceptions? I have synthesized NiO/CuO nanoparticles. After calcination at 300 °C the size and aggregation of nanoparticles decreased somewhate (FESEM images). Are there other reasons for this?
As you already stated, calcination generally increases particle size due to aggregation or agglomeration. But, this effect is clear only after 500 °C for most materials and get very intense after 1000 °C.
For calcination at such a low temperature, I don't think any substantial aggregation or agglomeration would happen. And the opposite effect is not that probable. I think, your observation is just a small fluctuation.
To be sure, repeat your experiment. I think, the size would remain almost same. However, crystallinity might improve.
Thanks, Swick. your description makes sense. This experiment was repeated twice: the particle size was somewhat reduced (maybe just a small fluctuation), but the aggregation was clearly reduced. May I please know if it may be related to calcination? Is there any citation for this?
Okay, I understand your point. But, I am doubtful about how calcination at low temperatures can reduce aggregation. Suppose there is an aggregated cluster. If you increase the temperature, then the particles automatically getting unattached from each other is unlikely. The only feasible explanation is some sort of thermal strain is developing, which is diminishing loose agglomerates.
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