In the formation of Zno nano particles process, after drying at 120 degree C, my zno nano particles are completely white but when i calcine it for 450 degree C it converts into grey colour. i changed calcination degree and time also but it does not affect.
i am making Zno from zinc acetate and NaOH with Distilled water as a solvent.
help me if any one knows
Dear all, I think you are not applying good ventilation during calcination step. My Regards
This effect in oxides, generaly were correlated for suboxides formation, mediated by oxigen vacancies and metal valence changing (reduction). But i unknow this effect for ZnO. Following a Ellingham diagram, you can determine the effect of temperature and atmosphere during a calcination.
You are not observing a change in "colour". You are just observing a change in reflected intensity of the whole visible spectrum, and this is possibly due to a change in the size (and perhaps also og shape) of the nanoparticles after calcination. Remind that ZnO is not resonantly absorbing visible light at specific wavelenghts. Instead it absorbs in the UV range.
I suggest you to evaluate the average size of your particles before and after calcionation and take into account the possibility that the diffuse reflectans (hence the visible appearance) of your particulate changes from Raileigh to Mie regimes after calcination.
See also an aearlier discussion on RG about a similar case: https://www.researchgate.net/post/Why_does_aluminium_oxide_powder_have_different_color_with_aluminite_powder
Dear all, I think you are not applying good ventilation during calcination step. My Regards
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