I have synthesized TiO2 powder through sol gel method. I tried to do calcination of this white TiO2 powder under vacuum at 500 deg C. No change in colour was observed. Is this normal? because I have seen in literature that calcination under inert atmosphere and under vacuum leads to oxygen deficiencies and thus causes dark colouration of the sample powder. Am I doing something wrong?
Dear Dr. Rajaraman Ts,
regarding this specific subject, I suggest you to have a look at the interesting discussion available on RG at:
https://www.researchgate.net/post/What_is_the_ideal_ramp_rate_for_calcination_step_of_TiO2_nanocatalyst
Best regards, Pierluigi Traverso.
TiO2 has two important types which are rutile titanium dioxide and anatase titanium dioxide. The key difference among them is in their appearance. Anatase Titanium Dioxide is colorless, whereas Rutile Titanium Dioxide is usually found in dark red appearance. The nanoparticles of Anatase titanium dioxide are found in colorless , white or yellow color. The natural form of Anatase titanium dioxide contains a lot of impurities which makes it dark.
As you calcined your sample at 500 deg C under vacuum condition, your sample will be mainly consists of anatase phase. but if you increase the temperature from 600 to 800 deg C,the anatase phase will be gradually decreases and rutile phase will be increases and the colour change from white to dark will be take place. At 800 deg C the anatse phase will be totally vanished.
just analyse your sample with XRD and confirm the phase of your sample.
Regard Zia Ullah Khan
normally, when you will treat Titanium Dioxide mineral, you can get dark colour always
As explained above, in fact the TiO2 has three phases ( anatase brookite and rutile). thus, raising temperature above 600°C led to phase change ( to rutile ) and gave dark color.
Use X-ray to confirm which phase you have
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