Naoto Kodama

A method for large-scale synthesis of Al-doped TiO2 nanopowder using pulse-modulated induction thermal plasmas with time-controlled feedstock feeding

A unique method of large-scale synthesis of Al-doped TiO2 nanopowder was developed, using 20 kW Ar–O2 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 modulation of the power of the PMITP. The method enables heavy-load feeding of raw material powder to the thermal plasmas for complete evaporation. The nanopowder synthesized was analysed using different methods including field emission scanning electron microscopy, x-ray diffraction (XRD) spectroscopy, bright-field transmission electron microscopy (TEM), TEM/energy dispersive x-ray (EDX) mapping, x-ray photoelectron spectroscopy, and spectrophotometry. The results showed that Al-doped TiO2 nanopowder can be synthesized with mean diameters of 50–60 nm. The Al doping in TiO2 was confirmed from the constituent structure in the XRD spectra, the uniform presence of Al in the nanopowder in the TEM/EDX mapping, the chemical shift in the x-ray photoelectron spectra, and the absorption edge shift in the optical properties. The rate of production of the Al-doped TiO2 nanopowder was estimated as 400 g h−1.

Fundamental study of Ti feedstock evaporation and the precursor formation process in inductively coupled thermal plasmas during TiO2 nanopowder synthesis

Two-dimensional spectroscopic observations were conducted for an inductively coupled thermal plasma (ICTP) torch during TiO2 nanopowder synthesis. The feedstock was injected intermittently into the ICTP torch to investigate the Ti feedstock evaporation process clearly and to elucidate the formation process of precursor species. Spatiotemporal distributions of Ti atomic lines and TiO spectra were observed simultaneously inside the plasma torch with the observation system developed. The observation results showed that the injected Ti feedstock was evaporated to form high-density Ti atomic vapour in the torch, and that the generated Ti atomic vapour is transported and diffused by gas flow and the density gradient. In addition, TiO molecular vapour was generated almost simultaneously around the on-axis region in the torch.

Two-dimensional spectroscopic observation of a pulse-modulated induction thermal plasma torch for nanopowder synthesis

The two-dimensional distributions of spectral radiation intensities in the plasma torch were observed for the pulse modulated induction thermal plasmas (PMITP) with continuous or intermittent feedstock feeding for TiO2 nanopowder synthesis. For this observation, an imaging spectrophotometer with a high speed video camera were adopted. The evaporation of feedstock Ti powder, the formation of TiO and TiO transportation were investigated from the observation results of a Ti atomic spectral line and TiO molecule spectra as well as those of Ar and O atomic lines. An interpretation was suggested from the observation results for Ti feedstock evaporation and TiO formation in nanoparticle synthesis using a PMITP with intermittent feedstock feeding.