Flash synthesis of Magnéli phase (TinO2n-1) nanoparticles by thermal plasma treatment of H2TiO3

A flash synthesis method of titanium suboxides (TSO) TinO2n-1 nanoparticles with Magnéli phases by thermal plasma using rutile-phase metatitanic acid (H2TiO3) as the raw material was proposed and investigated, comparing with common sintering hydrogenation process of H2TiO3. TSO powders with diverse colors were prepared and characterized by means of XRD, SEM and TEM. The results showed Magnéli phase nanoparticles with perfect spherical shape and particle size of 20-100 nm were rapidly synthesized by thermal plasma treatment under Ar and Ar/H2 atmospheres. Typical Magnéli phases of Ti5O9 and Ti4O7 with peacock blue color were formed under argon atmosphere. An increase of hydrogen content in the atmosphere made nano-H2TiO3 efficiently reduced to form a different TSO phases with diverse colors of dark blue to blue black. Notably, parts of nanoparticles were of carbon shell/Magnéli phase core structure. The UV-visible absorptivity and electric conductivity of samples were tested and the results indicate that thermal plasma is an efficient way to improve the optical and conductive properties of materials. But the electric resistivity of nano Magnéli phase powders still keep 105-106 Ω.cm.