I have a problem when I prepare ZnO or Tio2: it gives a faint yellow after drying. However, it was white through washing. Then, when I grind it, it turns into white. I wonder if real color of oxides appear after or before drying? What is the meaning of the yellow color that appears as it isn't soluble completely in ethanol. Is it complex or what?
After drying i get yellowish green particles which turn into yellowish after exposing to air that mean it`s hygroscopic
i wonder what is this crystals is it salt or what?
Alaa, you may just be observing the thermochromic nature of some metal oxides such as zincite. See http://www.zno.name/zno-chemical-properties.html as one example.
Heating gives a fractionally small loss of oxygen that leads to slight coloration of the solids. Upon cooling and exposure to normal atmosphere it recovers its full stoichiometric amount of oxygen.
Cooling it in a dry (no water) atmosphere, but an atmosphere that still had oxygen in it would probably demonstrate it was not hygroscopic.
Best regards,
Mike
Alaa Abdelaziz
I have similar problem of powder getting yellow. Could you please let me know how to retain its color back into white.
Thanks
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