Yasushi Muranaka

Water absorption by coals: effects of pore structure and surface oxygen

Abstract The water-holding capacity of various coals from lignite to anthracite was measured and its relation to their oxygen content and pore structure was investigated. Both factors were found to play important roles in determining the water-holding capacity. Pyrolysis of a lignite at 400 °C decreased its water-holding capacity by more than two-thirds, because of the decrease in the number of hydrophilic sites. This was caused by the decomposition of oxygen-containing groups and the decrease in surface area which resulted from the plugging of small pores by volatile matter condensation, making their surfaces inaccessible to water.

The role of hydrogen in diamond synthesis using a microwave plasma in a CO/H2 system

In order to clarify the role of hydrogen in diamond synthesis using a microwave plasma in a CO/H2 system, carbon films were grown by varying hydrogen mole fractions in a CO/H2/He microwave plasma. The correlation between film properties and plasma species was investigated through film characterization and plasma emission spectroscopy. C and C2 were formed in the gas phase of the CO/He system and only sootlike carbon was deposited. Hydrogen additions to the CO/He system were found to enhance diamond growth by suppressing the formation of C and C2, which inhibited diamond growth by blocking the nucleation sites. The complicated structure of amorphous hydrogenated carbon, diamond microcrystallites having a diameter of 100 A, and graphitic carbon was formed in the CO(5%)/H2 (30%)/He system, while columnar polycrystallites were grown in the CO(5%)/H2 system. Almost the same amount of atomic hydrogen in the ground state was found to exist in both systems, whereas a larger amount of electronically excited atomic...

X-ray photoelectron spectroscopy analyses of lithium intercalation and alloying reactions on graphite electrodes

Abstract Electrochemical lithium intercalation reactions occurring in silver-supported graphite anodes were investigated by X-ray photoelectron spectroscopy (XPS). The binding energy of Li(1s) of intercalating lithium was higher than that of lithium metal, which suggests that lithium exists in the form of a positive ion in the graphite layers. The core level of the C(1s) signal of lithium intercalated graphite was higher than that of graphite, which implies that the carbon in lithium-intercalated graphite has a negative charge. This finding agrees with previous XPS studies indicating that carbon has a negative charge in a graphite-intercalation compound produced by a molten lithium intercalation reaction to graphite. Lithium carbonate, lithium fluoride and organic compounds were produced on the graphite surfaces in charge/discharge reactions in 1 M LiPF 6 /EC—DMC electrolytic solution. It was also confirmed that the initial charge current supplied to the graphite electrode with a potential between 2.8 and 0.6 V did not cause a lithium-intercalation reaction. It caused, however, other reactions such as decomposition of the electrolytic solution and production of passivating films.

Characterization of diamond films synthesized in the microwave plasmas of CO/H2 and CO/O2/H2 systems at low temperatures (403–1023 K)

Diamond films grown in (A)CO/H2 and (B)CO/O2/H2 systems at substrate temperatures (Ts) between 403 and 1023 K were characterized by x‐ray diffraction, Raman spectroscopy, cathodoluminescence, and scanning electron microscopy. A large amount of polyacetylene inclusion occurred in the (A)CO/H2 system on reducing Ts, resulting in worsening of the diamond crystallinity (FWHM of the diamond Raman peak broadened from 6.4 to 19.5 cm−1 when Ts was decreased from 1023 to 403 K). On the contrary, polyacetylene inclusion was significantly suppressed in the (B)CO/O2/H2 system, and high quality diamond films (FWHM=4.0–4.1 cm−1) close to natural diamond (FWHM=2.6–3.0 cm−1) were obtained between 684 and 1023 K. Though there was a little deterioration of crystallinity at 403 K, the obtained film still had good crystallinity (FWHM=10.2 cm−1) compatible with conventional chemical vapor deposition diamond films. The presence of a large amount of atomic hydrogen, atomic oxygen, O2, and OH contributed to suppression of polyac...

Manganese-based lithium batteries for hybrid electric vehicle applications

A manganese-based lithium ion battery was developed for hybrid electric vehicle (HEV) applications. The cell consists of an improved manganese spinel as the positive electrode and hard carbon for the negative electrode. The Mn-based Li ion cell for HEVs was developed by adding a high power density modification to a pure-EV (EV) cell of high energy density specification. It has a power density as high as 2000 W/kg at 50% depth of discharge (DOD) and 25 °C. Storage tests at various temperatures suggest a practical calendar life of more than 5 years. The 48-cell battery module was developed for use in an HEV. It also proved to have an excellent output power density of 1350 W/kg at 50% DOD. Based on the excellent characteristics of the lithium ion battery, it seems very promising to apply this battery not only to EV, HEV and other motor-assisting drive systems but also to other high power applications.

Polymer electrolyte hydrogen-oxygen fuel cell where the polymer electrolyte has a water repellency gradient and a catalytically active component concentration gradiem across oxygen electrode

The polymer electrolyte type hydrogen-oxygen fuel cell of the present invention comprises an oxygen electrode and a hydrogen electrode, a polymer electrolyte membrane provided between the oxygen electrode and hydrogen electrode and electron conductors provided on the side of the electrodes which is opposite to the electrolyte side and the oxygen electrode comprises a catalytically active component, a carrier for the catalytically active component and a binder and has such a gradient in water repellency across the thickness that the water repellency is highest in the area adjacent to the electrolyte and lowest in the area adjacent to the conductor. In this fuel cell, flooding of water at the interface between the oxygen electrode and the electrolyte can be prevented.

Worldwide status of low temperature growth of diamond

Abstract Recent trends in low temperature growth of diamond films (LTGD) are reviewed. LTGD can be classified into non-substrate-heating processes and substrate-heating processes. In non-substrate-heating processes, room temperature growth of diamond has been demonstrated by sputtering, r.f. plasma, and laser excitation methods. However, the film quality has still not been analyzed quantitatively. In substrate-heating processes, polycrystalline diamond growth has been confirmed at substrate temperatures between 80 and 135 °C by microwave plasma of both CO H 2 and CO O 2 H 2 systems, electron cyclotron resonance plasma of C 2 H 5 OH (H 2 , Ar, He) systems, and tantalum filament decomposition of the CH 4 H 2 system. Source gases providing oxygen and excess atomic hydrogen in the gas phase were found to be suitable for LTGD because these species suppress the inclusion of amorphous components and the degradation of crystallinity which are likely to occur at low substrate temperature. The lowest substrate temperature for synthesis of diamond films with the same crystallinity as natural diamond is about 400 °C. The film quality deteriorates near 130 °C, which may be due to the incorporation of H, O, and OH from the gas phase into the diamond films. Growth rates are between 0.01 and 0.2 μm h −1 near 400 °C, and 0.035 and 0.3 μm h −1 at 130 °C. Growth rates can be accelerated by the addition of Ar or He to the source gas, but inert gases may cause the film quality to deteriorate.

Low temperature (∼400 °C) growth of polycrystalline diamond films in the microwave plasma of CO/H2 and CO/H2/Ar systems

In order to elucidate the growth conditions for pure diamond of good crystallinity, the correlation of the properties of deposited films and gas phase species in microwave plasma of CO/H2 and CO/H2/Ar systems was investigated through film characterization and optical emission spectroscopic measurements. It was found that the increase of gas phase atomic hydrogen and the suppression of gas phase acetylene were effective for the growth of pure diamond of good crystallinity. Low temperature growth was proposed to realize these growth conditions. It was confirmed that diamond films with good crystallinity and optical transparency could be synthesized at 410 °C (diamond film growth was possible even at 365 °C). The growth rate was accelerated in a CO/H2/Ar system (0.33 μm/h at 410 °C), which was several times faster than that obtained in a CO/H2 system (0.14 μm/h at 450 °C).

SUITABLE GAS COMBINATIONS FOR PURE DIAMOND FILM DEPOSITION

Abstract In order to identify the appropriate gas combinations that realize diamond film growth in an excess atomic hydrogen environment, the relative atomic hydrogen concentrations C [H] of various source gas systems (CH 4 /H 2 , CO/H 2 , CO 2 /H 2 , CH 4 O 2 (or CO 2 )/H 2 and CO/O 2 (or CO 2 )/H 2 ) were compared using plasma emission spectroscopy. C [H] was ranked in the following order: CO/O 2 /H 2 > CO 2 /H 2 CH 4 /O 2 /H 2 > CO/CO 2 /H 2 , CH 4 /CO 2 /H 2 > CO/H 2 > CH 4 /H 2 When oxygen-containing molecules (CO, CO 2 and O 2 ) were present in the plasma, there was also an increase in the amounts of atomic oxygen, O 2 and OH. These species had the same effect of eliminating non-diamond components and reproducting diamond-growing sites as atomic hydrogen. Thus enhancement of diamond-selective growth can be expected in the above-ordered gas systems. Diamond films synthesis was attempted using the CH 4 /H 2 , CO 2 /H 2 plasmas of these systems were correlated with the properties of the deposited films. Polycrystalline films could be synthesized at a growth rate of 0.93–1.2 microm h −1 in the CO(7%–10%)/H 2 system. However, no deposits were confirmed within 2 h in the CH 4 (1%)H 2 system and only amorphous phases were deposited in the system is considered to be due to the larger amounts of atomic oxygen, O 2 , OH and atomic hydrogen than in the CH 4 /H 2 system, which was due to the high concentration of oxygen in the plasma removing both diamond and amorphous deposits faster than they grew. The CO/O 2 /H 2 system was found to be promising for pure diamond synthesis because inclusion of the amorphous components was greatly suppressed with the addition of O 2 (the optimized concentration was about 2%). Diamond film with good qualities was synthesized in the CO/O 2 (2.2%)/H 2 system. The full width at half-maximum of the diamond Raman peak was 4.1 cm − , which is extremely close to that of natural diamond.

Design and performance of 10 Wh rechargeable lithium batteries

Abstract New metal—carbon composite anodes were developed by a chemical deposition method of metal particles onto graphite powder. Silver—graphite composites consisted of ultrafine silver particles on a graphite surface, exhibiting a large specific volume capacity of 468–505 Ah/l which may be due to Li Ag alloy formation. The Ag—graphite anodes also showed excellent cycleability over 700 charge/discharge cycles with only 3% capacity loss. 10 Wh class rechargeable lithium batteries with energy densities of 270–300 Wh/l were manufactured using Ag—graphite anodes and cathodes of LiNiO 2 or LiCoO 2 . Little capacity loss in these batteries was found even after 250 cycles because of the highly durable Ag—graphite anodes.