The density, viscosity, and surface tension of Hastelloy (Ni-Cr-Mo alloy) in the molten state were measured under vacuum conditions. Due to the lack of data in the open literature, the values of these physical properties were compared with those of other compositions of similar nickel-based alloys (CMSX, RENE, Inconel). There was not much difference in viscosity and surface tension when compared with other alloys. The high viscosity of Hastelloy C-276 is considered to be the result of surface oxidation, and the viscosity increases as the surface tension decreases.

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To clarify the effects of oxygen on cool‐flame, hotflame, and two‐stage ignition, n‐decane droplet ignition experiments were conducted at various ambient oxygen volume fractions. The ambient oxygen volume fraction was set to 15%, 21%, or 35%, with nitrogen added as the balance gas. Ambient pressure and temperature were varied from 0.1 to 0.5 MPa and 530 to 890 K, respectively. The results showed that the lower ambient temperature limit for hot‐flame ignition decreased as the oxygen volume fraction increased. In contrast, the effects on the upper ambient temperature limit for coolflame ignition were minimal, likely due to the limited impact on the equilibrium constant of lowtemperature oxidation reactions. Consequently, the no‐ignition region narrowed with the increase of ambient oxygen volume fraction. One of the most significant findings was the observation of two‐stage ignition at 0.2 MPa when the oxygen volume fraction was 35%. This suggests that the two‐stage ignition behavior of hydrocarbon fuel droplets can be evaluated at 0.2 MPa, a condition under which combustion experiments can be conducted on the Kibo module in accordance with safety regulations.

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Since the discovery of a dust crystal by Hayashi et al. (Jpn. J. Appl. Phys., 33 (1994) L804), various interesting phenomena have been observed and actively studied in complex plasmas (also called dusty plasmas) containing 𝜇𝜇m-sized charged microparticles, or dust particles. Although microparticles are macrosopic compared to electrons and ions, the dusty plasmas are treated as fluids when studying their collective behavior. Here we revisit and redescribe one of our representative experimental results on such a complex plasma: the dynamic circulation of microparticles in three dimensions. The experiments were performed under gravity using a glass-tube apparatus whose axis was vertical. Argon gas plasma was generated using radio-frequency (rf) discharge. A neodymium magnet was placed outside the bottom of the glass tube to apply a magnetic field to the complex plasma. Monodisperse acrylic resin spheres of 𝜇𝜇m order were used as microparticles. The microparticles were visualized with the naked eye by irradiating a thin fan-shaped green laser light. Their motions were recorded as still or moving images. A conical cloud of microparticles was formed, and individual particles in the cloud circulated and behaved similarly to tea leaves in a teacup.

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This study aims to establish a simple predicting method for impurity diffusion coefficients of elements, including the effect of atomic weight in liquid Sn based on a hard-sphere model. The impurity diffusion coefficients of Al, Au, and Cu in liquid Sn at 573 K were measured using the shear cell technique and stable density layering. Furthermore, we proposed different prediction methods for impurity diffusion coefficients of elements using a multiple regression analysis based on (σSn/σi)ϕis, where σi and ϕis are atomic diameter and thermodynamic factor of solute element i in solvent element s, respectively. Impurity diffusion coefficients of elements, the value (σSn/σi)ϕis of which is approximately 1.2 or small in liquid Sn near the melting point, were simply proportional to the product of the following three factors with the self-diffusion coefficient of Sn as the slope: (i) the atomic diameter ratio of Sn to the solute element, (ii) 0.182 power of the reduced mass ratio of Sn to the solute element, and (iii) thermodynamic factor. The uncertainty of the impurity diffusion coefficients of reference values and Al was within 6%. However, the impurity diffusion coefficients of elements, the value (σSn/σi)ϕis of which is approximately 1.2 or large, were approximately equal to the self-diffusion coefficient of Sn. This was owing to the inhibited atomic diffusion of Au and Cu in liquid Sn.

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