Impact of the TiO2 polymorphic modifications and сitric acid amount on the particle size and crystallite formation of lithium-containing titanium oxides under the melting route

The presented work aimed to synthesize and melt lithium- containing titanium oxides in the citric acid media, and to determine the impact of the ratio of TiO2 polymorphic modifications and сitric acid amount on the particle size and crystallite formation. New approaches for changing particle and crystallite size were performed based on the post-synthetic melting treatment in the solid citric acid of the Li- containing TiO2 powders. The X-ray powder diffraction analysis detected the main TiO2 polymorphs phases (anatase, rutile, Ti6O11, Ti3O5, Li0.026TiO2, and lithium titanium oxide (2.7/1.3/4) in all samples prepared via orthotitanic acid alkaline hydrolysis and under the melting route in citric acid media. There was a correlation between the ratio of citric acid in the melting mixture and crystallite size in ending products. The maximum anatase crystallite size (10372 nm) was detected in the samples prepared in media with a large surplus of citric acid. The total pore volume (Vtotal) was calculated from the volume of nitrogen adsorbed converted to liquid at a pressure close to P/P0 = 1. All samples were found to involve two kinds of pores: micropores with approx. 1÷2 nm radius, and mesopores with approx. 10÷29 nm radius. The samples’ SEM analysis also detected the size of the two kinds of particles in all samples. Increasing amounts of citric acid lead to increasing amounts of particles with size < 100 nm in the presence of small amounts of large-scale (> 900 nm) particles. The maximum pore and particle size were detected after melting treatment TiO2 polymorphs in media with a large surplus of citric acid. It was proposed a scheme of crystallite formation in the presence of Magnéli phases and reductants from the thermal decomposition of citric acid.