Epitaxial growth of WOx nanorod array on W(001)

Nanorods of substoichiometric tungsten oxide (WO_x) were grown on W(001) substrates. Two methods for the growth of nanorods were used: oxidation of the substrate under appropriate conditions and the deposition of tungsten oxide from a tungsten foil heated in the presence of oxygen. The grown nanorods were observed using a scanning electron microscope and an atomic force microscope. The diameters of the nanorods were 5–20 nm. The nanorods were slightly inclined from the directions parallel or normal to the surface. The inclination of nanorods was explained in terms of the epitaxial relationship between WO₃ crystals and the W(001) substrate. The WO₃ crystals formed at the initial stage of growth act as the nuclei of WO_x nanorods. We observed selective enhancement of the growth in a certain epitaxial direction depending on the method of growth, and an array of WO_x nanorods was produced on the W(001) substrate.     

Effect of grafted polymer species on particle monolayer structure at the air-water interface

We have studied poly(methyl methacrylate)-grafted(PMMA) particle monolayer systems at the air-water interface. In previous papers, we reported that PMMA chains grafted from particles (silica particle and polystyrene latex) were extended on water surfaces. Through observing deposited particle monolayers on substrates using SEM, we have confirmed that PMMA of large molecular weights were either dispersed or arrayed in structure with long inter-particle distances approximately 500 nm. In contrast, low molecular weight PMMA were observed to aggregate upon deposition. We speculated that the difference in morphology in deposited particle monolayers would be attributed to the affinity between the grafted polymer and the substrate. To examine the effect of this affinity three new polymer-grafted silica particles were synthesized with a fairly high graft density of about 0.14 approximately 0.43 nm(-2). As well as PMMA-grafted silica particles (SiO2-PMMA), poly(2-hydroxyethyl methacrylate) and poly(t-butyl methacrylate)--grafted silica particles (SiO2-PHEMA and SiO2-PtBuMA) were also prepared and subjected to pi-A isotherm measurements and SEM observations. These pi-A isotherms indicated that polymer-grafted silica formed monolayer at the air-water interface, and the onset area of increasing surface pressure suggests that the polymer chains are extended on a water surface. However, the morphology of the deposited monolayer is highly dependent on polymer species: SiO2-PHEMA showed that the dispersed particle monolayer structure was independent of grafted molecular weight while SiO2-tBuMA showed an aggregated structure that was also independent of grafted moleculer weight. SiO2-PMMA showed intermediate tendencies: dispersed structure was observed with high grafted molecular weight and aggregated structure was observed with low grafted molecule weight. The morphology on glass substrate would be explaiened by hydrophilic interaction between grafted polymer and hydrophilic glass substrate.     

Catalytic action of metallic salts in autoxidation and polymerization. VI. The inhibitive effects of transition-metal N,N-diethyldiselenocarbamates on the thermal oxidative degradation of isotactic polypropylene

Transition-metal (Zn, Ni, Pd, Cu, Cr, Co) N,N-diethyldiselenocarbamates were prepared, and the inhibitive effects of these compounds on the thermal oxidative degradation of isotactic polypropylene, both in the presence and absence of copper stearate as oxidation accelerator, were examined by conventional oxygen uptake. In both cases, all metal selenocarbamates showed a pronounced inhibitive effect on the degradation of the polymer, especially Zn and Ni selenocarbamates. The inhibitive action of these metal selenocarbamates was discussed from the viewpoint of viscosity change and carbonyl and hydroperoxide contents.     

NMR study of adsorbed water on acrylic acid-grafted and methacrylic acid-grafted cellulose

The water-adsorbing properties of cellulose samples which had been graft copolymerized with hydrophilic vinyl monomers using ceric salt as an initiator were investigated by means of the width of the high-resolution NMR absorption spectrum, water retention, and moisture regain of the samples. In the change of the width at half-value of the spectrum with per cent grafting, a maximum value followed by a minimum value was observed on samples both grafted with acrylic acid and methacrylic acid. Thus, the effect of grafting on the water-adsorbing properties appeared not to be simple. Though no special change in the water retention by grafting was observed, the per cent grafting dependence on the moisture regain in high relative humidity showed a peculiar and definite relation. The per cent grafting giving maximum moisture regain was about 8% and 18% for acrylic acid and methacrylic acid, respectively, and this agreed very well with the minimum widths at half-value. The change in the glass transition temperature of the sample—water system caused by grafting is also described.     

Prediction of temperature and water level in a spent fuel pit during loss of all AC power supplies

A prediction method for water temperature in a spent fuel pit of a pressurized water reactor (PWR) has been developed to calculate the increase in water temperature during the shutdown of cooling systems. In this study, the prediction method was extended to calculate the water level in a spent fuel pit during loss of all AC power supplies, and predicted results were compared with measured values of spent fuel pools in the Fukushima Daiichi Nuclear Power Station. The calculations gave reasonable results, but overestimated the decreasing rate of the water level and the water temperature. This indicated that decay heat was overestimated and evaporation heat transfer from the water surface was underestimated. Results of calculations with 80% decay heat and 155% (Unit 4 pool) or 230% (Unit 2 pool) evaporation heat flux were in good agreement with measured values. The data-fitted evaporation heat fluxes agreed rather well with the evaporation heat transfer correlation proposed by Fujii et al.     

Performance evaluation of eddy current flowmeter in Monju

Measurement of the temperature and flow rate at each fuel subassembly outlet is an effective way for a liquid metal fast breeder reactor to detect a loss of coolant accident or reactivity-initiated accident in the early stage and to understand the reactor’s thermal hydrodynamic performance. Japan Atomic Energy Agency has developed the eddy current flowmeter in practical use and installed 34 of them in the upper core structure of fast breeder reactor, Monju. This report presents data obtained by using the flowmeters in Monju. We observed high linearity between each of the flowmeter’s signal intensity and the primary sodium’s flow rate under 10–100% flow rate condition. High linearity was also observed in a region of low velocity (approx. 0.25 m/s). The fluctuation of flow rate observed by the flowmeters was below 0.2 m/s which is 5% of the time-averaged velocity under a rated condition. These experimental results show that the eddy current flowmeter is an effective tool to detect the changes in relative flow rate.     

Factors affecting vapor phase photografting of vinyl monomers on cellulose

Effects of water contained in the sample, the type of sensitizer, and the nature of vinyl monomer on vapor phase photografting on cellulose were investigated at 60°C. The grafting was enhanced by the water contained in the cellulose sample, resulting in an increased percent grafting with increasing the quantity of water. The use of sensitizers such as ferric chloride, ferrous sulfate, ceric ammonium nitrate, hydrogen peroxide, benzophenone, and sodium anthraquinone-2,7-disulfonate led to accelerated graftings. However, the maximum grafting was observed at an optimum quantity of sensitizer for each sensitized system, and the formation of grafted polymer was restricted by the use of sensitizer beyond the quantity. Ferric chloride and hydrogen peroxide exhibited higher activities among the sensitizers. With respect to the nature of monomer, methyl methacrylate, acrylic acid, methacrylic acid, and acrylonitrile were observed to be introduced into cellulose substrate by the vapor phase photografting, though no initiation was recorded for styrene and N-vinylpyrrolidone. However, the latter monomers were introduced by using monomer mixtures with acrylonitrile, affording a maximum percent grafting at a certain monomer composition.