Hiroyuki Y. Yasuda

Magnesium-butadiene addition compounds: Isolation, structural analysis and chemical reactivity

Abstract The magnesium-butadiene 1 : 1 (1), 1 : 2 (II) and 1 : 3 addition compounds obtained by the direct metalation of butadiene with metallic magnesium were isolated. These compounds have a polymeric structure. Structural analysis of these compounds by NMR and IR methods was carried out. The process for the formation of II via I and III via II was investigated. The results of protolysis and alkylation of the above magnesium compounds corresponded well to those of crotylmagnesium compounds.

Sulfur-tolerant Pd-Pt/Yb-USY zeolite catalysts used to reformulate diesel oils

Abstract Bimetallic Pd-Pt catalysts supported on ytterbium-modified ultrastable Y (USY) zeolite showed excellent hydrodesulfurization (HDS) and hydrodearomatization (HDA) activity as well as high stability when used to reformulate hydrotreated diesel oils; sulfur decreased from 263 to −1 . Modification of USY zeolite with ytterbium by impregnation decreased the number of strong acidic sites, while it increased the dispersion of the Pd-Pt phases, thus, possibly contributing to the increase in the nitrogen- and sulfur-tolerance and stability of Pd-Pt/Yb-USY zeolite catalysts.

The tensile creep behavior of superplastic tetragonal zirconia doped with small amounts of SiO2

Abstract The constant stress tensile creep behavior is reported of a tetragonal zirconia (3Y-TZP) with a grain size of 0.27 μm as a function of SiO 2 addition up to 2.5 wt%. The effects of SiO 2 addition are classed into two definite regimes. In the first regime, up to 0.3 wt% additions, both stress exponent, n , and apparent activation energy, Q , decrease steeply and strain rate, g3, increases also steeply as the amount of SiO 2 increases. In the second regime, with additions more than 0.3 wt%, n and Q remain almost constant while g3 increases gradually as the amount of SiO 2 increases. The appearance of the respective regimes is closely correlated with grain boundary microstructures modified by the SiO 2 addition.

Effect of Ms Temperature on Residual Stress in Welded Joints of High-Strength Steels

Thermal stress in the weld joints of high-strength steels after welding receives a great influence of dilatation stress during phase transformation, especially martensitic transformation of the low temperature region in weld metal. In order to quantify the amount of residual stress linked with thermal stress, neutron diffraction analyses were carried out in the welded joints having weld metals with very reduced Ms temperatures. In the butt joint of weld metal with an Ms temperature of about 60 °C, compressive residual stresses of about −400 MPa at the weld centre and of about −75 MPa at the toe were observed. The residual stress distributions were quite different from those of conventional weld metals, which have a tensile residual stress of about 400–500 MPa. The formation mechanism of compressive residual stress and the effect of restraint stress and stress-induced transformation on it are discussed, including previous data. It can be concluded that the reduction amount of residual stress induced by low Ms weld metal is about 11–15 MPa per unit length within about 70 mm weld length.

In situ TEM observation of spontaneous alloying in nanometer-sized particles

The alloying behaviour in nanometer (nm)-sized particles was studied by transmission electron microscopy (TEM). When solute atoms are vapour-deposited onto nm-sized particles at room temperature, rapid dissolution of solute atoms into particles occur, and solid solution or compound particles are successfully formed. Such spontaneous alloying occurs even between nm-sized particles of different elements. Our results can be summarized as: (i) spontaneous alloying takes place via a solid-state process, (ii) spontaneous alloying becomes more difficult with increasing particle size, (iii) spontaneous alloying is not an artifact originating from the temperature rise in particles which might be induced by heat of condensation and (iv) remarkable enhancement of solubility is observed in nm-sized compound particles.

Effect of grain boundary on martensite transformation behaviour in Fe–32 at.%Ni bicrystals

Abstract Two types of Fe–32 at.%Ni bicrystals containing a 90°{211} tilt or a 90°<211= twist grain boundary were prepared to investigate the effect of grain boundary character on the martensitic transformation behaviour. The martensite-start temperature (Ms) of bicrystals with the tilt boundary was significantly higher than that of single crystals, while Ms of bicrystals with the twist boundary showed no significant difference from that of single crystals. Near the tilt boundary, the coarse lenticular martensites were symmetrically formed in the neighbouring grains. In contrast, the tiny martensites were homogeneously distributed in bicrystals with the twist boundary, similar to those in single crystals. In the vicinity of the tilt and the twist boundaries, some variants with the habit plane almost parallel to the boundaries were preferentially selected among 24 variants; moreover, the equivalent variants in neighbouring grains were adjoined at the tilt boundary. As a result, the compatibility of shape strains across the boundary was maintained in the case of the tilt boundary, resulting in increasing the Ms. Such characteristic nucleation of martensites can be regarded as an example of self-accommodation across the boundary, which is called cooperative nucleation (C–N). From a crystallographic viewpoint, C–N can occur only at the symmetric tilt boundary. Effects of pre-deformation and applied stress on the heterogeneous nucleation at the boundary were also examined; C–N was always confirmed to occur at the tilt boundary, and the advantage of the boundary for nucleation of martensites did not change even under pre-deformation or applied stress. Furthermore, the martensite-start stress (σM) and the morphology of martensites in the stress-assisted transformation were strongly influenced by C–N.

Selective carbometallation of α,β-unsaturated carbonyl compounds and substituted oxacyclopropanes with zirconium-diene complexes

Abstract The reactions of zirconium-dience complexes, ZrCp 2 (s- cis -diene), with bifunctional electrophiles, i.e. α,β-unsaturated ketones, unsaturated esters and substituted oxacyclopropanes, were investigated. Reaction of ZrCp 2 (s- cis -isoprene) with an equivalent of 3-buten-2-one or alkyl acrylates, selectively gives 1,2-addition products. CC bond formation occured at the C(1) atom of the isoprene moiety whereas 1,3-pentadiene-, 2-methyl-1,3-pentadiene- and 2,4-dimethyl-1,3-pentadiene complexes induced the regioselective 1,2-addition at the C(4) position of the diene moiety. Phenyloxacyclopropane and 2-methyl-3-phenyl-oxacyclopropane also react with ZrCp 2 (isoprene) leading to CC bond formation from the C(1) atom of isoprene to the oxirane carbon bearing the phenyl group. The corresponding reactions of 2-methyl-2-butene-1,4-diylmagnesium with α,β-unsaturated carbonyl compounds were also studied and found to give quite different products.

Magnetic observation of deformation substructure in cyclically deformed Ni3Fe single crystals

The magnetic anisotropy of permeability and high-field susceptibility in Ni3Fe single crystals due to dislocations and antiphase boundary (APB) was theoretically calculated and measured by a vibrating sample magnetometer to determine the cyclic hardening and deformation substructure during cyclic deformation. Two types of anisotropy in magnetic properties were observed due to the atomic rearrangement near APB and the internal stress field around dislocations. In an early stage of fatigue where strong cyclic hardening occurred, the magnetic anisotropy was mainly due to the APB, while in a further stage of fatigue where cyclic softening occurred, the anisotropy was caused by dislocations. The cyclic softening was induced by the disordering in the localized region of coarse slip bands.

Spontaneous atom mixing and unmixing in metallic nanoparticles

The behaviour of atom mixing and unmixing in metallic nanoparticles has been studied in situ by transmission electron microscopy, using particles in the Au2Pb-Sn system. It is confirmed that not only spontaneous mixing but also spontaneous unmixing take place in Au2Pb particles. At room temperature, spontaneous mixing of tin atoms into Au2Pb particles takes place, and this mixing induces unmixing of lead from Au2Pb, resulting in the formation of AuSn particles accompanied by lead precipitates.

Skeletal Ni Catalysts Prepared from Amorphous Ni–Zr Alloys: Enhanced Catalytic Performance for Hydrogen Generation from Ammonia Borane

Skeletal Ni catalysts were prepared from Ni-Zr alloys, which possess different chemical composition and atomic arrangements, by a combination of thermal treatment and treatment with aqueous HF. Hydrogen generation from ammonia borane over the skeletal Ni catalysts proceeded efficiently, whereas the amorphous Ni-Zr alloy was inactive. Skeletal Ni prepared from amorphous Ni30 Zr70 alloy had a higher catalytic activity than that prepared from amorphous Ni40 Zr60 and Ni50 Zr50 alloys. The atomic arrangement of the Ni-Zr alloy also strongly affected the surface structure and catalytic activities. Thermal treatment of the amorphous Ni-Zr alloys at a temperature slightly lower than the crystallization temperature led to an increase of the number of surface-exposed Ni atoms and an enhancement of the catalytic activities for hydrogen generation from ammonia borane. The skeletal Ni catalysts also showed excellent durability and recyclability.