We investigated the reaction process in magnetite nanoparticle (MNP) synthesis by glow-discharge electrolysis in atmospheric air combined with iron electrolysis using NaCl aqueous solution as electrolyte. The iron electrolysis supplies Fe2+ in the solution, and electrons from the glow discharge induce liquid-phase reactions. We found experimentally that the concentration of dissolved oxygen (DO) in the solution is a key parameter in MNP synthesis. The excess oxidation of ferrous iron species at a high DO concentration causes the generation of hematite nanoparticles, while MNPs are mainly synthesized at a low DO concentration. Simple rate equations were solved to investigate the liquid-phase reaction process. The calculated results showed that the DO concentration reasonably changed the ratio between ferrous and ferric iron species, which will be important for the chemical composition of synthesized nanoparticles. The solution pH, which is locally increased by the glow discharge, affects the liquid-phase reaction process, especially through the hydroxylation of ferrous iron species.

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Factors that cause nonuniformity in the luminescence lifetime of pressure-sensitive paints (PSPs) were investigated. The lifetime imaging method of PSP does not theoretically require wind-off reference images. Therefore, it can improve measurement accuracy because it can eliminate errors caused by the deformation or movement of the model during the measurement. However, it is reported that the luminescence lifetime of PSP is not uniform on the model, even under uniform conditions of pressure and temperature. Therefore, reference images are used to compensate for the nonuniformity of the luminescence lifetime, which significantly diminishes the advantages of the lifetime imaging method. In particular, fast-responding PSPs show considerable variation in luminescence lifetime compared to conventional polymer-based PSPs. Therefore, this study investigated and discussed the factors causing the nonuniformity of the luminescence lifetime, such as the luminophore solvent, luminophore concentrations, binder thickness, and spraying conditions. The results obtained suggest that the nonuniformity of the luminophore distribution in the binder caused by the various factors mentioned above during the coating process is closely related to the nonuniformity of the luminescence lifetime. For example, when the thickness of the binder became thinner than 8 μm, the fast-responding PSPs showed a tendency to vary significantly in the luminescence lifetime. In addition, it was found that the luminescence lifetime of fast-responding PSP could be changed in the depth direction of the binder depending on the coating conditions. Therefore, it is important to distribute the luminophore uniformly in the binder layer to create PSPs with a more uniform luminescence lifetime distribution.

In this study, sprayable fast-responding pressure-sensitive paint (fast-PSP) with low temperature sensitivity has been investigated. Fast-PSP has a porous binder composed of a polymer and nanoparticles to enhance the oxygen diffusivity. However, it is known that higher mass content of nanoparticles in the porous binder causes an increase in temperature sensitivity of fast-PSP. To develop fast-PSP with a temperature sensitivity of less than 1.0 %/K and a response time of less than 100µs, we employed poly(trimethylsilyl)propyne (poly(TMSP)), which is a glassy polymer with a large free volume and has the highest-oxygen permeability among the existing polymers, as a polymer. Three different nanoparticles of mesoporous silica, boron nitride (BN), and titanium silicon oxide were mixed with poly(TMSP) at various particle mass contents to form porous binder. We investigated the effect of particle type and particle mass content, dye concentration, and binder thickness on the static and dynamic characteristics of PSP. The newly developed fast-PSP successfully achieved a low temperature sensitivity of 0.7 %/K even at a fast response time of less than 100 µs when poly(TMSP) and mesoporous silica were mixed at particle mass contents of 50 to 60 wt%, and the binder thickness was 2-5µm.

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