Superatomic Gallium Clusters in Dendrimers: Unique Rigidity and Reactivity Depending on their Atomicity

Superatoms have been investigated due to their possible substitution for other elements. The solution-phase synthesis of superatoms has attracted attention to realize the availability of superatoms. However, the previous approach is basically limited to the formation of a single cluster. Here, superatoms are investigated and the number of valence electrons in these superatoms is changed by designing the number of gallium atoms present. Based on the dendrimer template method, clusters consisting of 3, 12, 13, and other numbers of atoms have been synthesized. The halogen-like superatomic nature of Ga₁₃ is structurally and electrochemically observed as completely different to the other clusters. The gallium clusters of 13 and 3 atoms, which can fill the 2P and 1P superatomic orbitals, respectively, exhibit different reactivities. The 3-atom gallium cluster is suggested as being reduced to Ga₃H₂⁻ due to the lower shift of energy levels in the unoccupied orbitals. The results for these gallium clusters provide candidates for superatoms.     

XAFS and XRD Analysis of Ceria–Zirconia Oxygen Storage Promoters for Automotive Catalysts

Three types of CeO₂–ZrO₂ (Ce:Zr = 1:1 molar ratio) compounds with different oxygen storage/release capacity (OSC) were characterized by means of the Ce K-edge and Zr K-edge XAFS. In order to investigate the relationship between the OSC and local structure, the quantitative EXAFS curve-fitting analysis was applied. By enhancing the homogeneity of the Ce and Zr atoms in the CeO₂–ZrO₂ solid solution, the OSC performance increased. Additionally, from the XRD analysis, the homogeneous CeO₂–ZrO₂ solid solution has an ordered cation arrangement, and exhibits the highest OSC. The crystal structure of this CeO₂–ZrO₂ solid solution is usually termed as “κ-CeZrO₄ phase”. However, the OSC performance of κ-CeZrO₄ degrades upon a high-temperature treatment under an oxidative atmosphere. The fresh κ-CeZrO₄ was aged at 973, 1,273 and 1,473 K under an oxidative atmosphere, respectively. The OSC performance deteriorated as: the fresh sample ≈973 > 1,273 > 1,473 K-aged samples. We also found that, if the temperature was beyond 1,273 K, the Ce/Zr ordered arrangement would collapse and the local structure around Ce and Zr ions would also changed remarkably. These results indicated that OSC was strongly dependent on its atomic structure.     

Recovery of uranium from seawater V. Preparation and properties of the macroreticular chelating resins containing amidoxime and other functional groups

We have synthesized macroreticular chelating resins containing amidoxime groups from acrylonitrile (AN)-divinylbenzene (DVB)-alkyl acrylate, alkyl methacrylate, or vinylpyridine (VPy) copolymer beads. It was found that the chelating resin (RNMH)-containing amidoxime groups prepared from AN-DVB-methyl acrylate (MA) indicated the highest adsorption ability for uranium in seawater. Hydroxamic acid and carboxylic groups in addition to amidoxime groups were formed during the reaction of the copolymer beads with a methanol solution of hydroxylamine. The adsorption ability for uranium was greatly influenced by the physical pore structure (macropore) and the pore structure formed by the swelling(micropore). RNMH (RNMH10-10) prepared with 10 mol% of DVB and 10 mol% of MA had the highest adsorption ability and physical stability for uranium. On the other hand, improved adsorption ability for uranium was not observed in the case of the macroporous resins (RNPyH) prepared by the copolymerization of VPy as the basic component. After seawater was passed through the column packed with RNMH10-10 at a space velocity (SV) of 180 h^?1 (up-flow) for 10 days, the amount of uranium adsorbed on the resin was about 100 mg/dm³-R and 260 mg/kg-R.     

Preparation of macroreticular chelating resins containing dihydroxyphosphino and/or phosphono groups and their adsorption ability for uranium

The macroreticular chelating resins (RSP, RSPO, RCSP, and RCSPO) containing dihydroxy-phosphino and/or phosphono groups were prepared and their adsorption capacity for UO₂²⁺ and the recovery of uranium from sea water were investigated. RSP and RCSP were prepared by phosphorylation of macroreticular styrene–divinylbenzene copolymer beads and the chloromethylated copolymer beads, respectively. RSPO and RCSPO were prepared by oxidation of RSP and RCSP, respectively. The order of recovery of uranium from sea water with these four resins is as follows: RCSPO ? RCSP > RSPO > RSP. The adsorption of uranium in sea water was not only affected by the chemical structure, but also by physical structure of the resins. Uranium absorbed on the resins was eluted with 0.25 ～ 1 mol·dm^?3 Na₂CO₃ or NaHCO₃ solution by batch and column methods. The average recovery ratios of uranium from sea water with Na-form and H-form RCSP on 10 recycles were 84.9% and 90.5%, respectively, when 20 dm³ of sea water was passed through the column (resin 4 cm³, 10 mm ? × 50 mm) at the space velocity of 60 h^?1. RCSP has a high physical stability and resistance against acid and alkali solution.     

Statistical Analysis of Mechanical‐Shock Fragility Test Results

The mechanical‐shock fragility testing methods applied to packaging and product designs according to Japan Industrial Standards Z 0119:2002 incur some problems related to statistical analysis. One such problem is that the applied shock levels are increased in steps. We cannot determine the true fragility values for each sample. This is called interval‐censored data. If the maximum level of non‐damaging shock is selected for each sample, the calculated average will be too small. Another problem is that the number of shocks is limited to a maximum of 5 or 6, so as to minimize the effect of the accumulated fatigue. Therefore, if we determine the considerably high first shock level, initial‐censored data are obtained by the failure of the product when subjected to the planned first shock. If we determine the considerably low final shock level, final‐censored data are obtained when the product has not been damaged by the application of the planned final shock. These problems make statistical analysis difficult. We therefore propose an improved analysis method for data including interval‐censored, initial‐censored, and final‐censored data, and provide examples in which the method is applied to the results of a drop test. The results of the examples show that the proposed method is practical and that the censored data yields errors and loss of accuracy for the statistics. Finally, by means of a comparison between the staircase method of ISO 7765‐1:1988 and the method of JIS Z 0119:2002, we analyse the advantages and disadvantages of the respective methods. Copyright © 2017 John Wiley & Sons, Ltd.     

Effect of medium condition change on green body density during casting and drying

The present study examined whether the optimum slurry conditions in which the green body with the highest packing fraction was fabricated were the same regardless of whether tape or slip casting methods were used. Additionally, we investigated the optimum slurry evaluation method to predict the packing fraction of each green body. Specifically, aqueous dense alumina slurries, whose particle dispersion state was changed by varying pH and the amount of dispersant additive, were prepared. After changing the pH, the optimum slurry conditions were achieved regardless of the casting method. The most suitable amount of additive dispersant differed due to the changing solution conditions during the casting and drying process; the medium of the slurry permeated into the plaster during slip casting and dried on the substrate during tape casting. Thus, in slip casting, non-adsorbed polymers could also be permeated. Hence, it is crucial for slurry evaluation to predict the packing fraction of the slip cast body. A sedimentation test, which involved particle condensation as well as casting, was valid for the green sheet. Conversely, it was experimentally shown that the constant pressure filtration test, which involved the permeation of the medium in addition to particle condensation, was suitable for slip casting.     

Mo5Si3-Boron Composites Fabricated by Induction Plasma Deposition and Their High-Temperature Oxidation Resistance

Induction plasma spraying was used to produce freestanding parts of Mo₅Si₃-boron (Mo₅Si₃-B) composite materials. Four different Mo₅Si₃-B compositions were prepared and oxidized isothermally at 1210°C in air at atmospheric pressure. The high-temperature oxidation performance of these materials was dependent strongly on the boron content in the specimens. The composite that contained 2.0 wt% boron exhibited excellent resistance to oxidation, as indicated by the almost-zero change in specimen mass after oxidation for 24 h.     

Solidification mechanism of the sediment formed by particle settling – Analysis of the formation of the solidified layer

In various industrial processes, it is important to prevent the solidification in order to maintain the slurry properties. In order to predict the formation of the sediment and solidified layer, the gravitational sedimentation behavior of the slurries obtained by changing the slurry pH and the time change in the formation of sediment were observed. As a result, we can predict the solidification time and precisely predict the formation of the solidified layer and determine suitable conditions for the storage of slurries.     

Synthesis of azobenzene‐functionalized two‐arm,three‐arm and four‐arm telomers using polyfunctional chain transfer agents

BACKGROUND: Star‐shaped polymers are very attractive because of their interesting properties such as reduced viscosity, good solubility, low glass transition temperature and fast response to external stimuli. The incorporation of azobenzene moieties in star‐shaped polymers could significantly widen their potential applications in various optical devices. One of the most important properties of the azobenzene chromophore is its reversible trans–cis photoisomerization induced by UV or visible light. Photoisomerization induces conformational changes in azopolymer chains, which in turn lead to macroscopic variations in chemical and physical properties of the surroundings and media. RESULTS: This study reports the synthesis of azobenzene‐functionalized two‐, three‐ and four‐arm telomers via free radical telomerization using the di‐, tri‐ and tetrafunctional chain transfer agents 1,2‐ and 1,4‐benzenedimethanethiol, trimethylolpropane‐tris(2‐mercaptoacetate) and pentaerythritol‐tetrakis(3‐mercaptopropionate), respectively, in the presence of azobisisobutyronitrile. Azotelomers were characterized using gel permeation chromatography and ¹H NMR and Fourier transform infrared spectroscopy. Thermal phase transition behaviors were investigated using differential scanning calorimetry and polarized optical microscopy. Azotelomers synthesized in this study showed reversible photoisomerization and a fast generation of birefringence. CONCLUSION: Considering the photoisomerization behavior and birefringence of the two‐, three‐ and four‐arm azotelomers, it can be concluded that they could be potential candidates for use in various optical devices. Copyright © 2009 Society of Chemical Industry