Functional interface of polymer modified graphite anode

Graphite electrodes were modified by polyacrylic acid (PAA), polymethacrylic acid (PMA), and polyvinyl alcohol (PVA). Their electrochemical properties were examined in 1 mol dm⁻³ LiClO₄ ethylene carbonate:dimethyl carbonate (EC:DMC) and propylene carbonate (PC) solutions as an anode of lithium ion batteries. Generally, lithium ions hardly intercalate into graphite in the PC electrolyte due to a decomposition of the PC electrolyte at ca. 0.8 V vs. Li/Li⁺, and it results in the exfoliation of the graphene layers. However, the modified graphite electrodes with PAA, PMA, and PVA demonstrated the stable charge–discharge performance due to the reversible lithium intercalation not only in the EC:DMC but also in the PC electrolytes since the electrolyte decomposition and co-intercalation of solvent were successfully suppressed by the polymer modification. It is thought that these improvements were attributed to the interfacial function of the polymer layer on the graphite which interacted with the solvated lithium ions at the electrode interface.     

Functional binders for reversible lithium intercalation into graphite in propylene carbonate and ionic liquid media

Poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA), and poly(vinyl alcohol) (PVA), which have oxygen species as functional groups, were utilized as a binder for graphite electrodes, and the electrochemical reversibility of lithium intercalation was examined in PC medium and ionic liquid electrolyte, lithium bis(trifluoromethanesulfonyl)amide dissolved in 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide (BMP-TFSA). Columbic efficiency of 75–80% with more than 300 mAh g^?1 was achieved upon first reduction/oxidation cycle in both electrolytes using these binding polymers, which were significantly improved in comparison to a conventional PVdF binder (less than 45% of columbic efficiency for the first cycle). For the graphite-PVdF electrode, co-intercalation and/or decomposition of PC molecules solvating to Li ions were observed by the electrochemical reduction, resulting in the cracking of graphite particles. In contrast, the co-intercalation and decomposition of PC molecules and BMP cations for the first reduction process were completely suppressed for the graphite electrodes prepared with the polymers containing oxygen atoms. It was proposed that the selective permeability of lithium ions was attained by the uniform coating of the graphite particles with PAA, PMA, and PVA polymers, because the electrostatic interaction between the positively charged lithium ions and negatively charged oxygen atom in the polymer should modulate the desolvation process of lithium ions during the lithium intercalation into graphite, showing the similar functions like artificial solid-electrolyte interphase.     

Light absorption and photoluminescence of porous silicon

The results of an experimental study of Raman scattering, photoluminescence, and light absorption and reflection in porous silicon layers obtained by electrochemical etching of single-crystal wafers are presented. It is concluded on the basis of an analysis of the experimental data that the centers responsible for radiative and nonradiative recombination in this material are of a multiple character. The experimental data show that the centers whose maximum of optical excitation lies in the blue-green region of the spectrum have a uniform distribution, in contrast with the centers whose region of efficient excitation lies in the red region of the spectrum. The radiative recombination efficiency of the latter increases in a thin, near-surface layer of a porous-silicon film. Fiz. Tekh. Poluprovodn. 32, 1001–1005 (August 1998)     

Spontaneous Formation of Bonelike Apatite Layer on Chemically Treated Titanium Metals

Generally, artificial materials implanted into bone defects are encapsulated by a fibrous tissue isolating them from the surrounding bone. Only limited kinds of ceramics are known to bond to living bone without forming the fibrous tissue, and already they are being used clinically as important artificial bones. However, they cannot be used under highly loaded conditions, since their fracture toughnesses are not so high as that of human cortical bone. The present study shows that even pure titanium metal and its alloys can bond to living bone, if their surfaces are pre-treated with alkali hydroxide solutions. Thus-treated metals are believed to be useful as artificial bones even under highly loaded conditions because of their high bone-bonding ability as well as high fracture toughness.     

Electrical Properties of Nonconventional Bi-Ba-Cu-O Glasses

Electrical properties of Bi-Ba-Cu-O glasses have been systematically investigated, and possible conduction mechanisms are discussed. Conductivity behavior is described by a small-polaron hopping mechanism. log σ_o, the slope of the log σ- W straight line, and the magnitude of the polaron bandwidth reveal that adiabatic hopping is dominant in the glasses. The Seebeck coefficient, S , of the Bi₁₆BaCu₃O_y glass is positive, indicating that the glass is a p -type hole conductor. The positive deviation of the observed S value from the theoretical S value is explained by assuming that the only oxygens bonded to both Cu²⁺ and Cu⁺ ions mediate indirect Cu⁺-O-Cu²⁺ hopping.     

Reduction of temperature fluctuation within low temperature region using a cryocooler

Modeling and experiments are performed to decrease temperature fluctuation generated by the periodic motion of the displacer in a Gifford-McMahon (GM) type cryocooler within the low-temperature region. The one-dimensional heat equation allows us to show that thermal diffusivity is an essential factor to achieve much smaller temperature fluctuation, and fiber-reinforced plastic (FRP) with low thermal diffusivity makes it possible to reduce the temperature fluctuation dramatically. Based on the model, experiments are performed to vary the thickness of two FRP dampers, on the cryohead of the cryocooler and on the sample stage. As a result, the FRP dampers enable us to achieve the temperature fluctuations of only 0.7 mK, corresponding to a standard deviation of 0.25 mK, when the sample stage is maintained at 4.2000 K, even if a GM cryocooler is utilized for cooling the temperature, which introduces an initial temperature fluctuation of 282 mK at the cryohead.     

Photoconductive Emission and Detection of Terahertz Pulsed Radiation Using Semiconductors and Semiconductor Devices

Recent studies on the techniques and development of photoconductive (PC) semiconductor devices for efficient generation and detection of terahertz (THz) pulsed radiation are reported. Firstly, the optimization of PC antenna design is discussed. The PC detection of THz pulsed radiation using low-temperature grown GaAs with 1.55-μm wavelength probe is then described. Finally, the enhancement of THz radiation from InSb by using a coupling lens and magnetic field is investigated. These results reveal valuable insights on the design of an efficient, compact, and cost-effective THz time-domain spectroscopy system based on 1.55-μm fs laser sources.     

Experimental and numerical investigation of the gas‐phase effectiveness of phosphorus compounds

The effectiveness of phosphorus‐containing compounds as gas‐phase combustion inhibitors varies widely with flame type. To understand this behavior, experiments are performed with dimethyl methylphosphonate (DMMP) added to the oxidizer stream of methane–air co‐flow diffusion flames (cup‐burner configuration). At low volume fraction, phosphorus (via DMMP addition) is shown to be about four times as effective as bromine (via Br₂ addition) at reducing the amount of CO₂ required for extinguishment; however, above about 3000 μL/L to 6000 μL/L, the marginal effectiveness of DMMP is approximately zero. In contrast, the diminished effectiveness does not occur for Br₂ addition. To explore the role of condensation of active phosphorus‐containing compounds to the particles, laser‐scattering measurements are performed. Finally, to examine the behavior of the flame stabilization region (which is responsible for extinguishment), premixed burning velocity simulations with detailed kinetics are performed for DMMP addition to methane–air flames. Analyses of the numerical results are performed to understand the variation in the inhibition mechanism with temperature, agent loading, and stoichiometry, to interpret the loss of effectiveness for DMMP in the present experiments. Copyright © 2015 John Wiley & Sons, Ltd.     

Highly Active Titania Photocatalyst Particles of Controlled Crystal Phase, Size, and Polyhedral Shapes

Mesoscopic crystalline anatase particles of titanium(IV) oxide (titania) with decahedral morphology and with octahedral morphology were synthesized by gas-phase reaction of titanium(IV) chloride with oxygen and hydrothermal reaction of titanate nanowires in an alkaline medium, respectively, and their photocatalytic activities in relation with their crystal morphology were investigated.