The structure and mechanical properties of thick rutile-TiO2 films using different coating treatments

The hardness and Young's modulus of thick rutile-TiO2 films were determined using a continuous stiffness measurement (CSM) technique in this study. Pure rutile-TiO2 nanopowders (TH2O, T-FeSO4 and T-CuSO4) were prepared using a modified homogeneous-precipitation process at low temperature (MHPPLT) method. The TiO2 films were prepared from sols using 3% (w/w) of the prepared-TiO2 suspension solution coated onto silicon wafers. After dip-coating was completed, the coatings were further treated by natural air-drying, water-vapor exposure, and calcination, respectively. An ellipsometry with a monochromator was used to measure the thickness and refractive index of the TiO2 films, and a scanning electron microscopy (SEM) to determine their morphology. Three coatings of T-H2O, T-FeSO4 and T-CuSO4 demonstrated their refractive indexes of around 1.60 under three treatments. Volumetric expansion and thickness of the coatings should influence their refractive index. Furthermore, the continuous stiffness measurement (CSM) technique was used to perform nanoindentation testing on the hardness and Young's modulus of prepared rutile-TiO2 coatings. The mean hardness and Young's modulus of three coatings increased with preparation temperature. In addition, the T-H2O coatings demonstrated greater hardness and modulus than those of T-FeSO4 and T-CuSO4 coatings in the natural air-drying condition. Surface cracking observed on the calcinated T-FeSO4 should be the reason why an obvious decrease of the mean hardness and Young's modulus appeared. Finally, two mechanical properties and related nanoindentation depth of the coatings were discussed in detail. (C) 2011 Elsevier B.V. All rights reserved.