999 publications from this institution
The adhesion capabilities of sulfuric acid and tartaric-sulfuric-acid anodic oxide films on cladded AA2024-T3 aluminium substrates have been investigated in a quantitative manner. A relatively simple, versatile and industrially applicable test methodology based on DIN EN ISO 29862 has been used. In addition, the effect of anodising process parameters on the oxide film morphology has been studied and correlated with the adhesion results. The process parameters considered are the chemistry of the acidic pickling pre-treatment step, the addition of tartaric acid to the sulfuric acid electrolyte, the formation voltage, and the electrolyte temperature. The suggested tape peel adhesion test is able to differentiate among pre-treatments and anodising conditions showing a good correlation with the morphological features at the ultimate surface. High peel adhesion strengths are measured when topographies such as pore mouth widening and dissolution-driven roughness take place. These morphologies are typically found in anodic layers formed at elevated electrolyte temperatures. The proposed method can be beneficial for a fast assessment of anodising parameters for good adhesion, which is of special interest for the industrial optimisation of anodising processes.
In this work, thick nanocrystalline mesoporous titania layers are synthesized via chemical solution deposition using a water based citratoperoxo-Ti(IV)-precursor solution. The aqueous citratoperoxo-Ti(IV)-precursor solution is modified by the addition of polyvinyl alcohol (PVA), which acts as a thickener and pore forming agent. Layers are tape casted onto ITO-coated glass substrates and are thermally processed. The influence of process parameters like Ti(IV)-concentration, blade thickness, crystallization temperature and time on the film's phase composition, morphology and thickness are investigated by means of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), variable angle spectroscopic ellipsometry (VASE), atomic force microscopy (AFM) and profilometry. It is shown that the Ti(IV)-concentration and heat treatment influence the size and shape of the grains of which the films are composed, the film morphology (porosity, surface roughness) and the layer thickness, but no influence on the phase formation is observed. In all cases phase pure anatase layers are obtained.
