Mechanochemical preparation of nanocrystalline TiO2 powders and their behavior at high temperatures

The mechanochemical stability of hydrogen titanate nanostructures

“…The occurrence of the high-pressure TiO 2 II phase during the milling of crystalline H 2 Ti 3 O 7 or titanate nanotubes was not observed by the experimental techniques employed in this work, although this phase normally occurs during the milling of anatase [40,[49][50][51][52][53]. This is surprising, since in this work we employed exactly the same milling conditions as in our earlier ball-milling experiments performed with anatase TiO 2 [40], in which the appearance of the TiO 2 II phase was already clearly observed. We suppose that during the milling experiments described in this work, a sufficiently high pressure (2.56 GPa [59]), necessary for the formation of the TiO 2 II phase, was not reached because a part of the energy released in the impact between the balls and the sample particles was consumed for the dehydration of the H 2 Ti 3 O 7 crystallites and nanotubes.…”

“…However, the rutile phase was observed by Raman spectroscopy after 60 and 120 minutes in the crystalline powder and the nanotubes, respectively. These differences between the results obtained by XRD and Raman spectroscopy can be readily explained if we take into account the fact that the XRD responds to changes in the whole volume of the particle, while the Raman spectroscopy is influenced primarily by the changes on the particle surface [40]. Taking this into account it can be assumed that the transition from anatase to rutile starts inside the particles, induced by a local heating of the whole particle volume during milling, and then proceeds toward the surface of particles.…”

“…2b for the case of the lines at positions 24.46675° (•) and 36.147° (■) , indicating a decrease in the crystallite size and an increase in the lattice strain. It is reasonable to assume that the strain was induced mainly in the outer parts of the particles [40]. The diffraction-line broadening due to the crystallite size is T3 T3 T3 T3 T3 T3 T3 T3 T3 T3 T3 T3 T3 T3 T3 T3 T3 T3 T3 T3 T3 proportional to 1/cosθ, while the broadening due to the lattice strain is proportional to tanθ (θ being the Bragg angle) [66,67].…”

“…The simplest method of doping or alloying the material is mechanochemical processing [39,40]. This process is usually employed for the synthesis of advanced ceramics [41][42][43][44][45] and in the preparation of catalytic materials [46][47][48].…”

“…The high-energy mechanochemical treatment of TiO 2 , for example, has been investigated in detail [40,[49][50][51][52][53], where it was shown that high-energy ball milling can be used to induce a phase transition from anatase TiO 2 to the high-pressure TiO 2 II phase. Prolonged ball milling then transformed the TiO 2 II to rutile TiO 2 .…”