Continuous synthesis of silver nanoparticles based on a polyol process was conducted using a microwave-assisted flow reactor installed in a cylindrical resonance cavity. Silver nitrate (AgNO₃) and poly(N-vinylpyrrolidone) (PVP) dissolved in ethylene glycol were used respectively as a silver metal precursor and as a capping agent of nanoparticles. Ethylene glycol worked as the solvent and simultaneously as the reductant. Silver nanoparticles of narrow size distributions were synthesized steadily for 5 h, maintaining almost constant yield (>93%) and quality. The reaction was achieved within 2.8 s of residence time, although nanoparticles were not formed under this flow rate by conventional heating. A narrower particle size distribution was realized by the increased flow rate of the reaction solution. Nanoparticles of 9.8 nm average size with a standard deviation of 0.9 nm were synthesized at the rate of 100 ml h^−l.

Strong and high purity ${\mathrm{O}}^{-}$ negative ion emission has been observed from a synthesized crystal $12\mathrm{CaO}\text{⋅7}{\mathrm{Al}}_2{\mathrm{O}}_3$ surface. A μA/cm²-level ${\mathrm{O}}^{-}$ emission from this material has been achieved at the surface temperature of 800 °C and the extraction field over 1000 V/cm, which is about three orders of magnitude higher than the current density emitted from the ${\mathrm{Y}}_2{\mathrm{O}}_3$ -stabilized ${\mathrm{ZrO}}_2$ electrolyte surface. The strong emissivity of this material, as well as easy and economical fabrication, may provide a useful tool to generate the ${\mathrm{O}}^{-}$ negative ion, which is expected to be one of the most important radicals for chemical syntheses and material modifications.