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

In this paper, the formation and transformation of Magn & eacute;li phases (TinO2n-1) during manufacturing of flame-sprayed coatings from two powders consisting of anatase nanoparticles and submicrometric particles with Magn & eacute;li 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 Magn & eacute;li 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 Magn & eacute;li 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 Magn & eacute;li phases remaining and the TiO produced.