A rutile TiO 2 single crystal was irradiated by heavy ions with a high energy of the order of several tens of MeV. A good etching selectivity, where only the irradiated surface is well etched by hydrofluoric acid is induced by the irradiation. Through x-ray diffraction and high-resolution electron microscopy, it became clear that the irradiated region lost crystallization. It is considered that this amorphous region and the surrounding region are dissolved in hydrofluoric acid. Through the calculation of the ion energy, it was found that the etching always stopped at the depth where the electronic stopping power of the ion decayed to a critical value of 6.2 keV/nm, regardless of the ion species in the case of I, Br, Cu, and Ti ions. However, in the case of Ca ions with energies higher than about 72 MeV or Cl ions with energies higher than about 77 MeV, the irradiated top surface was not etched with hydrofluoric acid, but the inside surface several m deep from the irradiated surface was etched. A calculation shows that the critical factor which determines whether the irradiated surface can be etched or not is the lateral energy density on the surface deposited by ions. The etched surface observed by atomic force microscopy is very smooth with a roughness of the order of nm. Therefore, a combination of ion irradiation and etching can be used as a novel fabrication method of nanostructures in rutile.

In this study, the sedimentation states of particles in high-concentration slurries were elucidated by monitoring their internal states. We prepared transparent high-concentration silica slurries by adjusting the refractive index of the aqueous glycerol liquid in which the particles were dispersed to match that of the silica particles. In addition, a fluorescent dye was dissolved in the liquid. Then, we directly observed the individual and flocculated particles in the slurries during sedimentation by confocal laser scanning fluorescent microscopy. The particles were found to sediment very slowly while exhibiting fluctuating motion. The particle sedimentation rate in the high-concentration slurry with the aqueous glycerol solution (η=0.068Pa·s) and a particle volume fraction on the order of 0.3 was determined to be 1.58 ± 0.66 μm·min−1 on the basis of the obtained image sequences for 24.9 h. In-situ observation provides a large amount of information about the sedimentation behavior of particles in condensed matter.

The dispersed state of particles in high-concentration slurries has a significant effect on the development of the particle packing structure of the powder compact. We observed individual particle motion directly in highly concentrated ceramic slurries under slow flow through confocal laser scanning fluorescent microscopy using transparent slurries. In particular, we focused on particle motion soon after the application of a constant low shear rate. Measurements of the shear stresses indicated that the stress of a 30 vol% slurry gradually increased from 0.018 Pa over time, whereas the stress of a 40 vol% slurry soon reached 0.03 Pa and remained constant. For direct observation, shear stress was applied to the slurry, which was set between two glass plates, by moving one unilateral glass plate at 0.8 lm/s, to create a shear rate of 0.01 s -1 . The motion of the particles could be observed continuously. In the early stage, particles in the 30 vol% slurry near the moving plate were united as one body and did not alternate positions. Then, a speed incline developed gradually over time. For the 40 vol% case, the particles moved at the same time and together. Increases in the shear stress were caused by increased interaction when the particles were close together.

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