I have prepared some TiO2 monodisperse particles through controlled hydrolysis of precursor Titanium (IV) n-butoxide, dissolved in ethanol. The particles formed are spherical and amorphous (confirmed using XRD). However, when attempting to determine the wt.% water through DSC/TGA I observed that all the batches turned black.
Despite changing the gas between Ar, N2 and He (among different batches even) the end product is the same: a black powder. Can anybody tell me why this is the case ? and what could be the possible explanation. Any help, suggestion and advice in this regards is welcome.
Reduction of titania e.g.
http://pubs.rsc.org/en/Content/ArticleLanding/2014/TA/c4ta00685b#!divAbstract
Dear Aditya Chauhan,
1) as Claudio Imparato: it is essential to say the temperatures (TDSC , TTGA) that you reached in DSC / TGA ?
2a) at what (maybe estimated) temperature Tblack your TiO2-x are turning black ?
2b) say (if possible) : if Tblack (TDSC or TTGA) is about the same (for argon, nitrogen and helium cases) ?
3) are there any XRD infos for the black product : is it somewhat Anatase or Rutile ? (as Kenneth M Towe)
4) what (material) are the crucibles used for thermal analysis ?
A stupid question: because you start from organic precusors that you calcine in neutral or reducing atmosphere, is it possible that the black color comes from organic traces that transform into pure C (graphite) as you would have in active carbon production ?
Dear all,
Thank you for your valuable inputs. I don't think impurities from organic precursor should be an issue as the particles were subjected to repeated washing procedures (distilled water) and overnight drying at 60oC. Further, all the reagents used were ultra pure (>99.99%). Further, the DSC curves show a similar phase change peak (at 400oC) which corresponds well to the reported literature in the area. I am attaching my DSC and TGA graphs for reference. The crucible used in all the cases was recrystallized alumina.
But yes, I do believe that XRD will reveal a lot more information. I was just curious as majority of the literature reported in the area indicates a clear lack of color change.
There is indeed an analogy to magnetite. Titanium forms a whole series of oxygen-deficient oxides known as Magneli phases, with the general formula Ti(n)O(2n-1), where n can be as high as 10. These compounds are dark, and for large n values the powder pattern is superficially similar to that of rutile. See Andersson & al., Acta Chem. Scand. 11 (1957) 1641, freely available on the web.
I think you need an oxidizing atmosphere to prevent this from happening. If you have a small amount of organic residue adsorbed on the surface of the particles, they may coat them with carbonaceous material AND/OR cause reduction of a surface film of the titania to a dark Magneli phase. Oxygen should prevent this from happening.
Most probably your TiO2 sample was carbonated by left over ethanol and n-butoxide during heat treatment and as well as partial reduction of TiO2 by carbon may contribute to gray to black coloration. Your sample should be visible light active ( see Science, 297 (2002) 2243.
Dear Aditya Chauhan,
maybe you can try an available spectroscopy[1,2] technique (in the lab.), just in case that your sample(s) might not behave as an ... ideal black body.
1 . Reflectance spectroscopy from TiO2 particles embedded in polyurethane http://orbit.dtu.dk/files/58334668/Reflectance_spectroscopy.pdf
2 . MULTIPLE SCATTERING FROM RUTILE TiO2 PARTICLES http://engineering.case.edu/centers/sdle/sites/engineering.case.edu.centers.sdle/files/multiple_scattering_from_rutile_tio2_particles.pdf
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