Development of a radon trap device using a corona discharge

Radon is one of the noble gases, which are chemically inert and do not make any reactants under normal conditions. In this experiment we demonstrated an enigmatic reaction between radon and fluorine when a corona discharge is used as a promoter. Distinctive changes in radon concentrations were caused by the discharge and a trap efficiency of >99.5% was estimated. The mass balance between the trapped and the released radon was found to be reasonable. This indicates the existence of chemical reactions with radon. This trap phenomenon has application as a technique for reducing radon concentration in radon-contaminated air. It is possible that this technique will be applicable to other noble gases.     

Synthesis and electrochemical characterization of Pt catalyst supported on Sn0.96Sb0.04O2−δ with a network structure

We synthesized a Pt catalyst supported on Sn_0.96Sb_0.04O_2−δ with a random network structure for the cathode of the polymer electrolyte fuel cell (PEFC). The Sn_0.96Sb_0.04O_2−δ support, synthesized by the flame combustion method, was in the form of nanometer-sized particles with a partially agglomerated structure similar to that of carbon black (CB) and with a high surface area, 125 m² g⁻¹. The structure was considered to be beneficial in reducing the contact resistance between the Sn_0.96Sb_0.04O_2−δ support particles and in dispersing the nanometer-size Pt particles. We applied the nanocapsule method to synthesize the Sn_0.96Sb_0.04O_2−δ-supported Pt catalyst (Pt/Sn_0.96Sb_0.04O_2−δ). The electrochemically active surface area (ECA) of Pt reached a maximum of 60.2 m² g_(Pt)⁻¹, and the high values were maintained during the potential step cycling test (0.9–1.3 V) simulating the start/stop cycling of PEFCs. The oxygen reduction reaction activity of the Pt/Sn_0.96Sb_0.04O_2−δ catalyst exceeded that of Pt supported on carbon black (Pt/CB). We conclude that the random network structured Sn_0.96Sb_0.04O_2−δ might be a good candidate support material for the cathode of PEFCs.     

Effect of stereoregularity and molecular weight on the mechanical properties of poly(vinyl alcohol) hydrogel

The effect of the stereoregularity and molecular weight of poly(vinyl alcohol) (PVA) on the mechanical properties of hydrogel was investigated. Compressive strength, creep behavior, and dynamic viscoelasticity were measured on hydrogels of syndiotacticity‐rich PVA derived from poly(vinyl pivalate) (D_p = 1690 diad‐syndiotacticity = 61%, D_p = 8020 diad‐syndiotacticity = 62%) and atactic PVA (D_p = 1750 diad‐syndiotacticity = 54%, D_p = 7780 diad‐syndiotacticity = 54%). Increasing the molecular weight of molecular chains constituting the gel improved the compressive strength of atactic PVA hydrogel. The stereoregularity of PVA had a greater effect than molecular weight on the strength of the hydrogel. Gel prepared from 8.8 g/dL syndiotacticity‐rich PVA had a high compressive modulus of 10 kPa, and the compressive modulus of the gel prepared from 3.3 g/dL was comparable with that of atactic PVA hydrogel prepared with more than 6 g/dL. The dynamic storage modulus of the gel derived from syndiotacticity‐rich PVA was remarkably higher than that of the atactic PVA gel and remained constant up to 60°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Fabrication and properties of lead-free machinable brass with Ti additive by powder metallurgy

The aim of this paper was to investigate the properties of Cu40Zn2.2Bi + Ti for the development of a new lead-free, high-strength and machinable brass by powder metallurgy. The effect of Ti addition on the mechanical properties and machinability of BS40-2.2Bi (Cu40Zn2.2Bi) brass was studied with respect to different contents of Ti addition. BS40 (Cu40Zn) and BS40-2.2Bi brass powders were prepared by water atomization process, and the β phase was retained in the raw powders predominately. The BS40-2.2Bi powder and Ti powder were elementally mixed to prepare BS40-2.2Bi + xTi (x = 0.3, 0.5 and 1.0 wt.%) premixed powders. The alloy powders and premixed powders were solidified at 1053 K for 600 s by spark plasma sintering (SPS) and extruded subsequently. It was observed that intermetallic compounds (IMCs) such as Ti₂Bi were formed via the reaction between additive Ti and Bi alloying elements, and improved the ductility of BS40-2.2Bi significantly. The yield strength (YS) and ultimate tensile strength (UTS) were increased by increasing the contents of Ti addition, however, the elongation showed a decrease trend and the machinability became worse. The optimal content of Ti addition was 0.3 wt.%, which served excellent mechanical properties and machinability comparing with BS40-2.2Bi. For example, it had a YS of 235 MPa, a UTS of 459 MPa and an elongation of 39%, which showed 4.9%, 4.1% and 18% higher than that of extruded BS40-2.2Bi brass, respectively.     

Elimination of ƞ phase in WC–Co cemented carbides during laser powder bed fusion by powder coating compensation strategy

The formation of ƞ phase induced by the C-loss for the laser powder bed fusion (LPBF) of WC–Co cemented carbides largely deteriorates the fracture toughness. The current approach of mixing C additive into powder cannot mitigate the ƞ phase formation. This study proposed a new carbon compensation strategy of coating carbon resource on powder surface by fluidized bed chemical vapor deposition to address this issue. C nanoparticles and carbon nanotubes (CNTs) were selectively deposited on WC–Co powder to make uniform C- and CNTs-coated powders by tuning the deposition temperature. Compared with CNTs-coated powder and C–WC–Co powder mixtures, the C-coated powder was more effective in impeding the ƞ phase formation because it had higher reactivity and stronger dissolution ability to compensate the C-loss in the Co–W–C liquid. However, the single-carbon compensation was not enough to eliminate the ƞ phase due to the extreme nonequilibrium characteristics of LPBF, which required secondary heat treatment. The conventional heat treatment procedure of 1000°C for 3 h eliminated the ƞ phase for the C-coated powder but failed for the C–WC–12Co powder mixtures. Because of the absence of ƞ phase, the heat-treated sample made from C-coated powder exhibited the highest transverse rupture strength.     

Characteristic of an AC chopper circuit with LC filters in the input and output side

LC filters are connected to both the input and output side of the AC chopper circuit in order to remove the switching ripple and harmonics. Characteristics of THD and input power factor are examined by simulation and experiments. When the load is resistive, characteristics are minimally influenced by the filters. In the case of an inductive load, since two poles exist owing to the input and output filters, waveform distortion becomes large. This paper shows that THD can be improved by reducing input filter capacitance. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(2): 45–52, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20304     

Elution of sodium caseinate from agar-based gel matrixes in simulated gastric fluids

Elution of sodium caseinate from agar/psyllium composite gels was investigated in simulated gastric fluids to determine predominant mechanical parameters of gels for the elution kinetics and to predict the kinetics using the parameters. When the concentration of agar was fixed at 0.5% in the composite gels, elastic moduli determined by creep tests decreased with increasing concentration of psyllium, while viscosities increased. Compression load upon syringing through an enteral tube increased with increasing concentration of psyllium, whereas the surface-volume diameter d_3,2 of gel particles after syringing decreased. The elution kinetics of sodium caseinate from cylindrical gels was described using two different diffusion coefficients; D₁ and D₂ (D₁ > D₂) and the diameter of gels. Both diffusion coefficients decreased with increasing concentration of psyllium, resulting in 1.9 × 10⁻⁶ (for D₁) and 6.7 × 10⁻⁸ (for D₂) cm²/min by 1.5% addition, which corresponded to approx. 30% and 45% of the control (i.e., 0% psyllium), respectively. The fraction ratio of sodium caseinate having D₁ was not sensitive to psyllium concentration; approx. 80%–85% in the concentration range tested. D₁ was inversely proportional to viscosities determined by creep tests, particularly one from the Voigt body η₁ in the 4-element mechanical model. When cube gels were divided into smaller ones without changing the total volume, elution rates were inversely proportional to the cube length, where the diffusion coefficients did not change. The elution kinetics of sodium caseinate from the gel matrixes was anticipated using η₁ of gels before syringing and d_3,2 of gel particles after syringing when the usage of gels for percutaneous endoscopic gastrostomy is assumed.     

High-temperature properties of extruded titanium composites fabricated from carbon nanotubes coated titanium powder by spark plasma sintering and hot extrusion

Pure titanium matrix composite reinforced with carbon nanotubes (CNTs) was prepared by spark plasma sintering and hot extrusion via powder metallurgy process. Titanium (Ti) powders were coated with CNTs via a wet process using a zwitterionic surfactant solution containing 1.0, 2.0 and 3.0 wt.% of CNTs. In situ TiC formation via reaction of CNTs with titanium occurred during sintering, and TiC particles were uniformly dispersed in the matrix. As-extruded Ti/TiCs composite rods were annealed at 473 K for 3.6 ks to reduce the residual stress during processing. After annealing process, the tensile properties of the composites were evaluated at room temperature, 473, 573 and 673 K, respectively. Hardness test was also performed at room temperature up to 573 K with a step of 50 K. The mechanical properties of extruded Ti/CNTs composites at elevated temperature were remarkably improved by adding a small amount of CNTs, compared to extruded Ti matrix. These were due to the TiC dispersoids originated from CNTs effectively stabilized the microstructure of extruded Ti composites by their pinning effect. Moreover, the coarsening and growth of Ti grain never occurred even though they were annealed at 573, 673 K for 36 ks and 673 K for 360 ks, respectively.     

The combinational or selective usage of the laser SQUID microscope,the non-bias laser terahertz emission microscope,and fault simulations in non-electrical-contact fault localization

Recently, in the field of fault localization of LSI chips, several non-electrical contact techniques have been proposed. The techniques include the laser SQUID microscope (L-SQ) and the non-bias laser terahertz emission microscope (NB-LTEM). Both techniques have pros and cons. The L-SQ, for examples, can localize open defects in some cases, but it requires closed circuit. The NB-LTEM can localize open defects and short defects, and not requires closed circuit. The NB-LTEM, however, cannot localize open defects in some cases. The fault simulation specially designed for the L-SQ or the NB-LTEM makes it precise or efficient to localize defects. The combinational or selective usage of the L-SQ, the NB-LTEM and the related simulations makes it possible to localize defects in many cases. In this paper, we would like to review our results and organize them from the viewpoint of failure mode and defect sites.     

Development of a System for Location Finding of Low-Level Sound Source by Using Human Acoustic System with Stochastic Resonance

The purpose of this study is to develop a system that enables location finding of a small sound. The location finding of a small sound has some difficulties such as high computational costs or disturbances from the ambient noises and reflected waves. The proposed system is composed of a biologically-inspired system which uses a hearing mechanism based on the human ear and a mechanism for perceiving weak signals that uses stochastic resonance. The location finding mechanism in the proposed system is based on the time-lag detecting architecture. On the other hand, the stochastic resonance mechanism can pick up the small sound source in the ambient noises. Using this proposed system, we implemented the location finding of small sounds through numerical simulations and hardware experiments. Good results were obtained for the small sound source location finding.