Titanium oxide (TiO2) nanotubes prepared by anodisation of titanium in an aqueous electrolyte and glycerol have been heat treated in the temperature range 200-600 degrees C to control the conversion of the amorphous structure to nano-crystalline anatase and rutile. The phase changes have been monitored are observed at lower temperatures (100 degrees C or more) than previously reported. The sensitivity of the different techniques, each of which depends on the size of the crystalline phase, can explain the discrepancy with previous results. Transmission electron microscopy (TEM) has shown the phase changes which have occurred and which have been reported in an earlier publication; phenomena such as the collapse of the structures are explained. The TEM results are consistent with the Raman and XRD data, apart from the transformation temperatures, and also shed light on the nature of an amorphous phase found on the surfaces of the nanotubes. (C) 2009 Elsevier B. V. All rights reserved.