Despite the strong recent revival of Magnéli phase TiOx as a promising conductive material, synthesis of Magnéli phase TiOx nanoparticles has been a challenge because of the heavy sintering nature of TiO2 at elevated temperatures. We have successfully synthesized chain-structured Magnéli phases TiOx with diameters under 30 nm using a thermal-induced plasma process. The synthesized nanoparticles consisted of a mixture of several Magnéli phases. A post-synthesis heat-treatment was performed to reduce the electrical resistivity without changing the particle morphology. The resistivity of the heat-treated particle was as low as 0.04 Ω.cm, with a specific surface area of 52.9 m2 g−1. The effects of heat-treatment on changes in the crystal structure and their correlation with the electron conductivity are discussed based on transmission electron microscopy images, X-ray diffraction spectra, and X-ray adsorption fine structure spectra. Electrochemical characterization using cyclic voltammetry and potentiodynamic scan shows a remarkable electrochemical stability in a strongly oxidizing environment.

Abstract.A unique large-scale synthesis method for Al-doped TiO 2 nanopowder was developed using 20-kW Ar-O 2 pulse-modulated induction thermal plasmas (PMITP) with time-controlled feedstock feeding (TCFF). This PMITP-TCFF method is characterized by intermittent feedstock powder feeding synchronized with modulated power of the PMITP. The method enables heavy-load feeding of raw material powder to the thermal plasmas for complete evaporation. Synthesized nanopowder was analyzed using different methods including FE-SEM, XRD, BF-TEM, TEM/EDX mapping, XPS, and spectrophotometry. Results showed that Al-doped TiO 2 nanopowder can be synthesized with mean diameters of 50-60 nm. The Al doping in TiO 2 was confirmed from the constituent structure in XRD spectra, the uniform presence of Al on the nanopowder in TEM/EDX mapping, the chemical shift in XPS spectra, and the absorption edge shift in the optical property. The production rate of Al-doped TiO 2 nanopowder was estimated as 400 g h −1 .

Abstract. Nanoparticle synthesis was performed using high-powered pulsemodulated induction thermal plasma (PMITP) technique to study the effect of coil current modulation on synthesized nanoparticles. This is the first paper to present a summary of results of TiO 2 nanoparticle synthesis using high-power Ar-O 2 PMITP at 20 kW. The synthesized particles were analyzed using a field emission scanning electron microscope (FE-SEM), and X-ray diffractometry (XRD). In addition, optical emission spectroscopy (OES) was used during nanoparticle synthesis experiments to measure TiO spectra and to determine the time-averaged vibrational and rotational temperatures of TiO in the reaction chamber. Results showed that the PMITP produced smaller nanoparticles and a narrower size distribution of particles. Moreover, PMITP provided a lower-temperature region in the reaction chamber downstream of the plasma torch than such regions in non-modulated thermal plasmas.

A large amount synthesis method for titanium dioxide (TiO2) nanopowder is proposed by direct evaporation of titanium powders using Ar-O 2 pulse-modulated induction thermal plasma (PMITP). To realize a large amount synthesis of nanopowder, the PMITP method was combined with the intermittent and heavy load feeding of raw material powder, as well as the quenching gas injection. The intermittent powder feeding was synchronized with the modulation of the coil current sustaining the PMITP for complete evaporation of the injected powder. Synthesized particles by the developed method were analyzed by FE-SEM and XRD. Results indicated that the synthesized particles by the 20-kW PMITP with a heavy loading rate of 12.3 g min −1 had a similar particle size distribution with the mean diameter about 40 nm to those with light loading of 4.2 g min −1 .

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