I accidentally produced gray-Tio2 and I am not sure what reaction conditions lead me to this. Tio2 appears as a white powder, and under reducing atmosphere Tio2-x, appears blue.
I have heard about different colors for TiO2 (black, purple) What are the specific conditions that I can achieve them? And what are their implications?
Deposited thin films will have different colors depending on the substrate refractive index and the thickness of the TiN thin film
These thin films are colored due to the interference between the light rays reflected from the outer and inner faces of the film, and their color changes with sample thickness, as said by Shahid Aslam.
You are right Tsvetanka. Obviously, Ralph interests are TiO2 films. So, my first answer has been changed.
I absolutely agree with you, Mohamed, that different colors for the thin films are due to different thicknesses. But from the question I got the impresion that Ralph is working with the powder samples. If this is the case the different colors could be related to different sizes because the color will be mainly determined by the scattering.
Thank you for the prompt responses everyone! But my question would be for bulk (powder) samples!
Thank you, Tsevetanka. Thank you, Ralph. Now, the topic is much more clear.
Therefore, due to anisotropy of growth phenomenon, when a polycrystalline (or bulk ) sample is oxidized, different colors appear on the different metal grains in the area of the interference film and are delimited by the contours thereof.
So how could we explain the difference between the BLUE powder and the GRAY powder?
You may have formed secondary Magneli phases of reduced TiO2. These are known to exhibit such coloration.
Conference Paper Ti4O7 Used as Electrode in Biomedicine...
Chapter Pathways for the Production of Non-stoichiometric Titanium Oxides
Conference Paper Fabrication and Thermoelectric Properties of Magneli Phases ...
We obtained colours between very dark blue and black, in powders, depending of Magneli phase obtained. But we have not obtained grey powders in the conditions which we use (T>1000C in N2:H2 atmosphere)
Thank you very much Dorian! These magneli phases are of great interest due to their high conductivity! Have you worked with magneli tio2 before?
Certain changes in the material can effect the color of the material.
I would suggest to read about the structural, chemical changes in TiO2 under different synthesis methods.
The color is what we perceive from the reflected part of the radiation, rest all is absorbed by the material eg white titania is the purest form possessing a bandgap of 3.2 eV, which cannot absorb visible light. On the other hand, black TiO2 is basically a core-shell structure, where TiO2 at the core consisting disordered Ti2O3 at the shell. The disordered Ti2O3 at the shell is responsible for turning TiO2 black.
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