Michiyuki Yoshida

Unique Chemoselective Hydrogenation using a Palladium Catalyst Immobilized on Ceramic

A heterogeneous palladium catalyst supported on a ceramic (5 % Pd/ceramic) was developed. The catalyst exhibited a specific chemoselectivity for hydrogenation that has never been achieved by other palladium‐catalyzed methods. Either aliphatic or aromatic N‐Cbz groups could be deprotected to the corresponding free‐amines, while the hydrogenolysis of benzyl esters and ethers did not proceed. Furthermore, aryl chlorides and epoxides were tolerant under the Pd/ceramic‐catalyzed hydrogenation conditions. 5 % Pd/ceramic could be reused without any loss of catalyst activity, as no palladium leaching was detected in the reaction media.

Deformation Behavior of SiO2 Doped Nanocrystalline Monoclinic Zirconia at Low Temperatures

The deformation behavior of SiO2 doped nanocrystalline monoclinic zirconia (MZP) was studied at 1323-1223 K in compression tests. The strain rate of SiO2 doped nanocrystalline MZP was slower than that of high-purity MZP by one order of magnitude. SiO2 doped nanocrystalline MZP exhibited a stress exponent n ≈ 2. The apparent activation energy for the deformation of SiO2 doped nanocrystalline MZP was characterized by a higher value than that observed for high-purity MZP. 1wt% SiO2 doped nanocrystalline MZP was deformed at constant flow stress, while the flow stress of high-purity MZP increased significantly with the strain (strain hardening). While no grain growth was observed after the compressive deformation of 1wt % SiO2 doped nanocrystalline MZP, remarkable grain growth was observed after the deformation of high-purity MZP. The addition of SiO2 into nanocrystalline MZP is effective in limiting grain growth at low temperatures

Indentation Size Effect on the Hardness of Zirconia Polycrystals

The hardness of materials is one of the most important mechanical properties from an engineering point of view. The hardening of metals is realized by the inhibition of dislocation glide, which can be managed through microstructural design. The Hall-Petch hardening H ∝ d -1/2 , where H is the hardness and d is the grain size, is a wellknown and useful concept of the design. Conversely, the inverse Hall-Petch relation is recently found out in a metal consisted of very fine grains.1,2 Also, it is revealed that the H-value of metals does not depend on only d but indentation size, i.e. the hardness increases with a decrease in indentation size. The indentation size dependence is described through the building-up of geometrically necessary dislocations under a concentrated stress field.3,4 In terms of ceramics, correlation between hardness and microstructure has not been cleared, although a lot of research has been done.5,6 For example, even the grain size dependence of the hardness has not been generally described. The hardness of ceramic nanopolycrystals, which consists of very fine grains with a diameter less than 1μm, has not been examined in detail. Moreover, indentation size effect on the hardness has been scarcely reported. The experimental and theoretical difficulty to estimate the plasticity of a hard elasticplastic material is one of the reasons for the obscurity in the hardness of ceramics. The development and improvement of the nanoindentation technique helps us to make an accurate evaluation of the plasticity of ceramics.

Influence of pH tuning at the precursor-preparation process on the structural characteristics and catalytic performance of hydrothermally synthesized ZnAl2O4 nanoparticles

ABSTRACT The relationship between the structural characteristics of hydrothermally synthesized ZnAl2O4 nanoparticles and the pH of the source solution used during the precursor preparation process was investigated. A pH of approximately 9 was the turning point between large and small crystallite-sized regimes, and between stoichiometric and nonstoichiometric compositions. This difference can likely be attributed to the formation process of ZnAl2O4, because the stabilities of the Zn2+ and Al3+ hydroxides in the source solution change at pH 9. Additionally, we compared the catalytic performance with regards to the decomposition of methylene blue for the nanoparticles made from source solution with pH 7 (NP7) and 10.5 (NP10.5). The smaller-sized NP7 did not show any catalytic performance; whereas, the larger NP10.5 accelerated the decomposition of methylene blue. The critical difference between NP7 and NP10.5 is the Zn2+ deficiency, rather than the particle size. This result is important for future investigations in order to improve the catalytic properties of ZnAl2O4 nanoparticles.