K. Kamitsuji

Phase transition temperature of γ-Fe2O3 ultrafine particle

The iron oxide ultrafine particles prepared by the gas evaporation method, in which commercial α-Fe 2 O 3 powder is evaporated, are composed of α-Fe 2 O 3 particles covered with a γ-Fe 2 O 3 mantle layer. To study the phase transition temperature of the γ-Fe 2 O 3 mantle layer, the particles were heated and observed in a transmission electron microscope. The present specimen of γ-Fe 2 O 3 transformed completely to α-Fe 2 O 3 at above 700°C, and this phase transition was irreversible. The phase transition temperature was 1.4 times higher than the bulk value. The growth mechanism of the present specimen of α-Fe 2 O 3 particles covered with the γ-Fe 2 O 3 mantle layer has been discussed in terms of the difference in the cooling rates between the inside and the surface of the particle at around the evaporation source.

Au alloy formation with Sn-Pb or Sn-Zn solder nanoparticles

Structures of simultaneously evaporated Sn–Pb and Sn–Zn nanoparticles on amorphous carbon surfaces have been elucidated using a transmission electron microscope. Spontaneous alloy formations by the deposition of Au have been observed at room temperature on a clean particle surface. AuSn2, Au3Zn and AuPb2 ordered alloys have predominantly been produced. It was also shown that the spontaneous formation of oxide film with the thickness of 5.0 nm order upon exposure to air prevents the alloy formation even with heating at 300°C.

Correlations between Crystallite Size, Shape, Surface, and Infrared Spectra Using the Ti-C System

TiC crystallites less than 10 nm in size showed an absorption feature at 14.3 μm. This 14.3 μm absorption was rarely seen in specimens ranging from bulk material to grains of 50 nm in size. The 14.3 μm feature was weakened as a result of the growth of TiC crystallites by heat treatment. When the carbide grains were covered with a carbon layer, the absorption peaks were considerably weakened, i.e., the absorption intensity depended on the grain surface state. A possible explanation is that the effects of size and shape on the spectra depend on the surface anisotropy.

Direct observation of the formation of alumina phase by metallic Al solid-SiO2 solid reaction

The formation of Al2O3 phases by the solid-solid reaction of a metallic Al layer evaporated on a SiO2 amorphous grain has been induced by heating above 600°C in vacuum (1×10−6 Pa). The distortion process of the amorphous SiO2 grains by the formation of Al2O3 have been directly imaged by in-situ TEM observation. A partly deposited Al layer covered the SiO2 grains after heating at 750?C, and ψ -Al2O3 grains of about 25 nm diameters were formed on the SiO2 surface. Upon the growth of Al2O3, the SiO2 grain decomposed into a mixture of metallic Si and SiO2 and disappeared as a result of sublimation due to the formation of SiOx at high temperatures. The present result on dust surface dynamics will become an important field with respect to the metamorphism of grains from the astromineralogical viewpoint.