In the titanium industry, chlorination of ilmenite (FeOTiO₂) at elevated temperatures in the presence of a reducing agent promotes formation of TiCl₄ in gaseous form, which can be subsequently selective condensed and then reduced to titanium metal or oxidized to producing TiO₂ [1]. Alternatively, in the absence of the reducing agent, the process becomes selective, favoring the formation of iron chlorides and promoting enrichment in content of TiO₂ obtained in the solid product of the reaction [2].  Therefore, the present study reports the observations by Analytical Electron microscopy (AEM) of principals characteristics of the TiO₂ polymorphs, anatase and rutile, obtained by chlorination with and without reducing agent respectively.  The experimental analysis involved the as-received material, the intermediate and final products, all sequentially characterized by means of X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and Transmission Electron Microscopy (TEM).

Fig. 1a., shows a low mag SEM image of the as-received material constituted essentially by Ilmenita particles rich on Ti and Fe.  Fig. 1b and 1c., are secondary electrons (SE) SEM images of the products after chlorination process for 60 minutes.  While Fig 1b., corresponds to direct chlorination product shows faceted TiO₂ crystals, Fig 1b., corresponds to the product resulting from chlorination in the presence of carbon showing spheroidal TiO₂ anatase aggregates.  The XR-Difractograms shown in Fig 2., corroborated the crystal identification on each mentioned products.  Fig 3.a and 3b., is TEM bright field (BF) -dark field (DF) pair of a robust single crystal of TiO₂ rutile and corresponding diffraction patron pointing in red the diffracted bean use for the DF image.  Fig 4a., and 4b, is also BF and DF pair however of an anatase aggregates and the correspond diffraction patron in the Fig 4c., showing, namely in the DF imagen shaped nanocrystals about 10 nm in sizes.  Interested to note in this aggregated nucleation rate of nanocrystals in a still shapeless aggregated.  The same anatase product has been captured in the BF-DF pair of Fig 5a and 5b and corresponding diffraction patron of Fig. 5c. These images correspond to a later state of nucleation and growth processes, configurating well-defined spherical nanocrystalline aggregates of TiO₂ anatase in order to minimized of surface energy.  After calcination of this product under N₂ atmosphere, it can seen the TiO₂ nanoparticles of about 10 nm in size have been more homogeneity distributed, mostly spheroidal and some exhibiting facets thereby implying in a thermodynamics states closer to the equilibrium.[2]

[1]. MOODLEY S, et.al. Chlorination of titania feedstocks, 3^rd International Symposium on High-Temperature Metallurgical Processing, 2012.

[2]. L.M. Cáceres, I.G. Solorzano, E. Brocchi.  Electron Microscopy observations over the processes yielding to obtaining TiO₂ from Natural Ilmenite Mineral.

The authors are grateful to LaBNano /CBPF for the access of TEM and XRD, the financial support of CAPES, CNPq and FAPERJ (Brazil).

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EMC Abstracts - https://emc-proceedings.com/abstract/aem-characterization-of-the-products-yielding-from-chlorination-process-to-obtain-tio2-from-natural-ilmenite/