Thermally sprayed titanium oxide coatings - A truly multifunctional coating solution

Titanium dioxide (TiO2) is the most important oxide in the Ti-O phase diagram, rutile and anatase being its most important modifications. A considerable number of individual phases called titanium suboxides appear in the composition range between Ti2O3 and TiO2. Most of these suboxides are characterized by the presence of planar stacking faults (shear planes) and are related to the so-called Magneli phases (Ti(n)O(2n-1)). Many coating applications are closely connected with the ability of TiO2 to lose oxygen easily. The oxygen content can easily be changed by reduction and oxidation during the spray process, e.g., by use of hydrogen as a plasma gas component. The homogeneity of oxygen distribution in the coatings is determined by the specific spray process used. Generally, the coatings produced by thermal spraying are characterized by dense microstructures and good mechanical properties. Titanium oxide coatings have a high resistance to abrasion and erosion wear. Fluctuations in the O/Ti ratio in the spray powders, the spray process and microstructural effects influence the resistivity of titanium oxide coatings. The presence of anatase appears to be necessary for the preparation of photocatalytic active titanium dioxide coatings.