Formation, Transformation, and Electrical Performance of Magnéli Phases Obtained by Flame Spraying from TiO2 Particles

Abstract

In this paper, the formation and transformation of Magnéli phases (TinO2n-1) during manufacturing of flame-sprayed coatings from two powders consisting of anatase nanoparticles and submicrometric particles with Magnéli phases is analyzed, respectively. These powders were thermally sprayed on a ceramic substrate through oxidizing and neutral flame. Crystalline phases in powders and coatings were identified by x-ray diffraction and quantified by the Rietveld method, verifying the presence of identified crystalline phases in coatings by x-ray photoelectron spectroscopy. Finally, the electrical conductance of coatings was measured by the four-point probe method. Results indicate that Magnéli phases are produced from anatase nanoparticles sprayed using both the oxidizing and neutral flames, and when the neutral flame and finest particles are used, a high quantity of Ti4O7 and Ti5O9, recognized thanks to their high electrical conductivity, is obtained. In contrast, when the coatings were fabricated from the powder containing Magnéli phases, they were oxidized as much in oxidizing as in neutral flame, producing a partial transformation from Ti4O7 and Ti5O9 to both the rutile phase and TiO in low quantity. In spite of this partial transformation, the coatings maintain high electrical conductivity thanks to Ti4O7 and Ti5O9 Magnéli phases remaining and the TiO produced.