Akio Isogai

The application of CeZr oxide solid solution to oxygen storage promoters in automotive catalysts

The complex oxides in the CeO2ZrO2 system were examined for the improvement of oxygen storage capacity in automotive catalysts. The formation of CeZr oxide solid solution improved the thermal stability and activity of CeO2. The CeZr addition enhanced the removal activity for CO, NOx and hydrocarbons under dynamic air-fuel ratio condition. The automotive catalyst was designed and developed through research on the oxides in the CeO2ZrO2 system.

Thermal stability and characterization of γ-Al2O3 modified with rare earths

Rare earth modification was effective for improving the thermal stability of γ-Al2O3. It inhibited the grain growth of transition Al2O3 and the formation of α-Al2O3. The surface area was 12 m2 g−1 for pure Al2O3, 40 m2 g−1 for ceriummodified Al2O3 and 51–59 m2 g−1 for Al2O3 modified with lanthanum and others, heated at 1200°C for 5 h. The activation energy of α transformation, evaluated by differential thermal analysis, was 581–583 kJ mol−1 for pure and cerium-modified Al2O3 and 635–655 kJ mol−1 for Al2O3 modified with lanthanum, samarium and ytterbium. Lanthanum inserted into the crystal lattice of Al2O3 with spinel structure, whereas cerium existed on the Al2O3 surface as a form of CeO2. The difference in states between La3+ and Ce4+ can explain that the modification of lanthanum is more effective than that of cerium for improving the thermal resistance of γ-Al2O3.

Thermal stability and characterization of γ-Al2O3 modified with lanthanum or cerium

Etude par resonance paramagnetique electronique dans des echantillons contenant 0,5 a 10% mol. de La ou Ce. La stabilite thermique est meilleure par addition de La que par addition de Ce. Les ions de La avec leur large rayon ionique inhibe la diffusion des ions et empeche la transformation de la phase γ a la phase α

Reduction reaction of lanthanum-added cerium dioxide with carbon monoxide

The reaction of lanthanum-added cerium dioxide with carbon monoxide was examined by using a CO pulse reaction method and high-temperature X-ray diffraction (XRD). The lanthanum addition enhanced the activity of cerium dioxide for oxidizing carbon monoxide under moderately reducing conditions. Isothermal XRD observation at 500 and 700 °C indicated that the reduction reaction of CeO2 and La-added CeO2 with CO progressed in CO-N2 flowing gas. The kinetics of the reaction CeO2 + x/2CO → Cex1−x/4+Cex3+O2−x/2 + x/2CO2 + x/2V0 was analysed by Janders model: [1−(1−x)1/3]2=kt.

LEED-AES study of sulfide single crystals

Abstract The clean surfaces obtained by cleaving the sulfide single crystals, PbS, CdS, MoS2 and ZnS were examined by means of low energy electron diffraction and Auger electron spectroscopy. It was found that Auger electron yield of sulfur in sulfide crystals depended strongly on its concentration in the top atomic layer. The δ−η method revealed that the backscattering electrons contributed significantly to Auger electron intensities. Measurements were also made on the energy dependence of the ionization cross section, and the results showed, to a first approximation, a good coincidence with the theoretical model proposed by Gryzinski. An approach to the quantitative analysis of Auger electron spectroscopy was also discussed.

The role of alloying elements in the friction and wear of copper alloys

Abstract The effect of Sn and Al on the wear and frictional properties of Cu-Sn and Cu-Al alloy systems was investigated by electron probe microanalysis and Auger electron spectroscopy. The coefficient of friction and the wear loss in the Cu-Sn alloy increased with increasing Sn content and reached a maximum at about 40% Sn, which corresponds to ϵ - Cu 3 Sn . With the Cu-Al alloy system the coefficient of friction initially decreased with increasing Al content and reached a minimum at about 20% Al corresponding to the composition Cu 9 Al 4 . The wear loss increased initially, reached a maximum at about the solubility limit of Al and then decreased rapidly. The coefficient of friction of a Cu-Sn solid solution showed a maximum at the initial stage in the friction coefficient-sliding time curve, which was not found with Cu-Al and Cu-Zn. This phenomenon is discussed on the basis of surface compositional changes during the friction process.

Observations of Fatigue Deformation by Back Reflection Divergent X-Ray Technique

The structural change of Al crystals due to the cyclic stress in bending was examined by using the back reflection divergent X-ray technique.Al crystals, 99.999% in purity, were made by the strain annealing method. Of crystals thus obtained those of the following three kinds of specimens were used: a bicrystal and two single crystals having the same orientation as those of each part of the bicrystal.The back reflection divergent X-ray photographs of fatigued Al crystals showed the occurrence of polygonization in the early stage of fatigue, but this structure was changed into complicated one with the progress of fatigue process. The fatigue life in the bicrystal was found to be shorter than that in the single crystals, and to form fatigue crack along the crystal boundary.The same experiments were carried out with polycrystalline samples. It was found clear that the degree of deformation varied with the grains, some grains being deformed scarcely even in the later stage of fatigue process. The X-ray photographs obtained from the various stages of fatigue process showed a rapid increase of strain, especially, near the crystal boundary.