The structure and mechanical properties of thick rutile–TiO 2 films using different coating treatments

Abstract

The hardness and Young's modulus of thick rutile–TiO 2 films were determined using a continuous stiffness measurement (CSM) technique in this study. Pure rutile–TiO 2 nanopowders ( T H 2 O , T FeSO 4 and T CuSO 4 ) were prepared using a modified homogeneous-precipitation process at low temperature (MHPPLT) method. The TiO 2 films were prepared from sols using 3% (w/w) of the prepared-TiO 2 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 TiO 2 films, and a scanning electron microscopy (SEM) to determine their morphology. Three coatings of T H 2 O , T FeSO 4 and T CuSO 4 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–TiO 2 coatings. The mean hardness and Young's modulus of three coatings increased with preparation temperature. In addition, the T H 2 O coatings demonstrated greater hardness and modulus than those of T FeSO 4 and T CuSO 4 coatings in the natural air-drying condition. Surface cracking observed on the calcinated T FeSO 4 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.