**4. Developments of new applications**

As stated at the beginning there is the goal to make use of finer grain sizes of feedstock powders to reach denser coatings showing higher cohesion and adherence to the substrate. The lower limit of feeding powders into the process is in the one-digit micrometer range. By dispersing of the feedstock in a liquid outer phase or the formulation of feedstock direct in a suspension by chemical methods, use can be made of nanometer sized feedstock. In the following the efforts are shown in new results regarding the achievement of coatings, which could not be realized by means of thermal spraying before.

Thermal Spraying of Oxide Ceramic and Ceramic Metallic Coatings 181

As chromium exhibits a high steam pressure with rising temperature and therefore may tend to evaporate out of the lattice, the homovalent substitution of the Ti4+-cation in the rutile base lattice was aspired. Several cations where chosen based on the rules for substitution processes stated by V. M. Goldschmidt (Goldschmidt, V. M., 1926), besides Cr3+ primary Ni3+, Co3+ and Zr4+ by considering the ionic radii and coordination given in (Shannon, R.D., 1976). The goal is to reach phases with a similar composition compared to the Andersson-type phases on the one hand and a sufficient stability in temperature ranges up to 800° C on the other, which are commonly used for hot extrusion of aluminum and

The assumption that the applicability of substitution processes may lead to the formation of solid solutions of the desired stoichiometry can be proven by means of the Inorganic Crystal Structure Database. In **Figure 9** for example the structures of the cubic Co(II)-oxide and of tetragonal rutile (i.e. Ti(IV)-oxide) are shown on top, where the oxygen is represented by the

Fig. 9. Structures of Co- and Ti-oxide (top) and of the "mixed" solid solution oxide (bottom)

From the structure it can be inferred, that both cations have similar radii, which is – besides the valence and the coordination by the surrounding ions – the key requirement for the dissolution of the oxides. When both oxides are mixed, a structure of lower symmetry (orthorombic) is formed with a composition of Co2Ti4O10. The difference compared to the aspired composition of Co2Ti4O11 for n = 6 is due to the fact, that the divalent cobalt is incorporated in the structure instead of the trivalent ion. Like the most structures being crystallographic possible solid solution of rutile with the named oxides, the cobalt-titaniumoxide with trivalent Co-ions is not refined yet. Without the feasibility to refine the structures, the full quantitative Rietveld analysis by means of X-ray diffraction of the

copper based alloys.

sprayed coatings is not possible.

larger balls.
