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TiO2 sol was prepared hydrothermally in an autoclave from aqueous TiOCl2 solutions as a starting precursor. Titanate nanotubes were obtained when the sol–gel-derived TiO2 sol was treated chemically with a 10 M NaOH solution and subsequently heated in the autoclave at 150 °C for 48 h. The samples were characterized using XRD, TEM, SEM, EDX, Raman spectroscopy, and a BET surface area analyser. The effect of post treatments, such as washing with and without hydrochloric acid and calcination, on the phase structure, shape and morphology, pore structures, and BET surface area of the titanate nanotubes was investigated. When a sample containing 7.08 wt% Na (after washing only with water) was calcined at different temperatures from 300 to 900 °C, it showed the formation of a mixture of sodium trititanates and sodium hexatitanates and was found to preserve the tubular morphology at higher temperatures. However, a sample containing 0.06 wt% Na obtained after prolonged washing with hydrochloric acid followed by heat treatment showed the formation of TiO2 anatase involving TiO2 (B) as an intermediate at lower temperatures and anatase was further transformed to the rutile phase when the temperature was raised. On the basis of different observations, a general formula NaxH2−xTi3O7·nH2O has been proposed for the trititanate nanotubes.

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This letter reports on the successful synthesis of hydrogen titanate nanotubes (H-Ti-NT) and TiO 2 (anatase) nanotubes and their thermal solid-state transformational chemistry and clarifies some of the confusion surrounding their literature Raman vibrational assignments. Hydrothermally prepared titanate nanotube powders with negligible (<0.1 wt % Na, H-Ti-NT) and high (∼7.0 wt % Na, Na/H-Ti-NT) Na content, that underwent freeze-drying and thermal treatments, were prepared and characterized with ambient and in situ Raman spectroscopy. The H-Ti-NT phase gives rise to Raman bands at ∼195, 285, 458, ∼700, 830, and 926 cm -1 . The Raman bands above 650 cm -1 were found to be sensitive to the presence of moisture, which indicates that they are related to surface vibrational modes. The titanate nanotube Raman band at ∼926 cm -1 was shown not be related to a Na-O-Ti vibration, which was previously assigned in the literature, since its intensity does not vary with Na content, which varied by a factor of >70. The nanotubular H-Ti-NT phase was found to be thermally stabilized, <700 °C, by Na that had been entrapped during synthesis. The Na-free H-Ti-NT phase, however, transformed to TiO 2 (anatase) nanotubes upon heating above 200 °C and was stable up to 700 °C. SECTION Nanoparticles and Nanostructures

The functional silica/polyamide-imide composite films were prepared via simple ultrasonic blending, after the silica nanoparticles were modified by cationic surfactant—cetyltrimethyl ammonium bromide (CTAB). The composite films were characterized by scanning electron microscope (SEM), thermo gravimetric analysis (TGA) and thermomechanical analysis (TMA). CTAB-modified silica nanoparticles were well dispersed in the polyamide-imide matrix, and the amount of silica nanoparticles to PAI was investigated to be from 2 to 10 wt%. Especially, the coefficients of thermal expansion (CET) continuously decreased with the amount of silica particles increasing. The high thermal stability and low coefficient of thermal expansion showed that the nanocomposite films can be widely used in the enamel wire industry.