Masao Kohzaki

Synthesis, Cation Distribution, and Electrochemical Properties of Fe-Substituted Li2MnO3 as a Novel 4 V Positive Electrode Material

LiFeO 2 -Li 2 MnO 3 solid solution was synthesized using solid-state reaction and hydrothermal-postannealing methods and characterized as a positive electrode material for rechargeable lithium batteries. Although the maximum Fe content [Fe/(Fe + Mn)] was limited up to 30% by solid-state reaction, the content can extend up to 75% by the hydrothermal-postannealing method. Neutron and X-ray Rietveld analysis reveal that the basic structure of the sample is a layered rock-salt structure isostructural with LiCoO 2 (R3m) in which Fe ions exist on both Li (3a) and Co (3b) sites. Elemental analysis and 57 Fe Mossbauer spectra show Fe ions exist as 3+/4+ mixed-valence state after the samples were postannealed above 650°C. The initial charge capacity of Li/sample cells was above 100 mAh/g when the upper voltage limit was 4.3 V. The plateau around 4 V was observed for all Li/sample cells on first discharge. The maximum of initial discharge capacity was about 100 mAh/g down to 2.5 V for the Li/(50% Fe-substituted sample) cell, when the positive electrode was obtained by postannealing at 650°C in air. The capacity fading of the 4 V plateau could be suppressed by adjusting the Fe content to less than 50%, postannealing temperature between 600 and 700°C, and by 10% Ni substitution.

Tribological characteristics of polycrystalline diamond films produced by chemical vapor deposition

Effects of surface roughness and crystallinity of polycrystalline diamond films on their tribological characteristics, as well as the effects of test environment, have been investigated. Friction and wear characteristics of the diamond films deposited on sintered SiC disks have been examined with a ball-on-disk tester in the absence of any lubricant. The friction coefficients of polished diamond films against SiC and Si 3 N 4 balls were below 0.10 at room temperature while those of as-deposited films were around 0.20. The specific wear of counterparts on the polished film was five orders of magnitude smaller than on the as-deposited film. The friction coefficient between the polished diamond film and a AISI 52100 steel ball was about 0.20. Transfer of a small amount of AISI 52100 material to the diamond film was observed along the wear track of the polished diamond surface. Diamond films of high quality were more resistant to wear than the ones of low quality. On the other hand, the friction coefficients were not affected by the crystallinity of the diamond films in the present study. Tribological characteristics of the diamond films deteriorated with increasing sliding speed and ambient temperature. At 600 °C in dry N 2 , the friction coefficient of diamond films against a SiC ball was about 0.8, which was about ten times higher than that at room temperature in air.

Influence of Deposition Temperatures on Bonding State and Microstructure of Carbon Nitride Thin Films Prepared by Ion-Beam-Assisted Deposition

The influences of the deposition temperature on bonding states and microstructures of carbon nitride films prepared by ion-beam-assisted deposition are analyzed by Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and transmission electron microscopy (TEM). FT-IR absorption spectra exhibit a peak corresponding to the C≡N bond and its population decreases with the deposition temperature. N 1s peaks in XPS spectra indicate the existence of two different N 1s bonding states, one attributed to nitrogen inserted into the graphitic ring structure, and the other attributed to nitrogen surrounded by three carbons in the C–N network. The increase of the deposition temperature leads to the formation of the C–N cluster similar to the highly disordered turbostratic structure. In C–N film growth, however, the sequential phase transformation from sp2-bonded phases to sp3-bonded phase frequently observed in BN film deposition is not found in TEM analyses.

Large-area diamond deposition and brazing of the diamond films on steel substrates for tribological applications

Abstract Diamond films were successfully deposited on molybdenum substrates as large as 100 mm in diameter at a high deposition rate of 30 μm h −1 by the r.f. induction thermal plasma chemical vapour deposition (CVD) method. Besides the uniformity of the film thickness, the surface morphology and the film quality were confirmed to be homogeneous over the deposited area by scanning electron microscopy and Raman spectroscopy. Self-standing diamond films of 30 mm diameter were obtained when the films were deposited on mirror-finished molybdenum substrates by the r.f. thermal plasma CVD method. One of the self-standing diamond film surfaces (originally substrate side) was as smooth as the mirror-finished substrate surface. The self-standing diamond films were brazed in vacuum on steel substrates so that the smooth surface of the film became the top of the brazed materials. The adhesive strength of the brazed diamond film on the steel substrate was found to be rather high, and the as-brazed diamond film with the smooth surface had a low friction coefficient of 0.1 against steel and a high wear resistance without oil lubrication in an ambient atmosphere.

Frictional properties of chemical vapor deposited diamond thin films

Abstract Diamond thin films deposited on sintered SiC by the hot filament CVD method were subjected to ball-on-disk friction and wear test with a SiC ball in an ambient atmosphere. The friction coefficient of the diamond film with smooth surface was about 0.09 and effectively no wear was detected.

Large-Area High-Speed Diamond Deposition by Rf Induction Thermal Plasma Chemical Vapor Deposition Method

By introducing methane as a sheath gas and by reducing the reactor chamber pressure to 150 Torr in an rf induction thermal plasma chemical vapor deposition (CVD) method, a large volume of the thermal plasma was stabilized and elongated to reach far into the reactor chamber where a molybdenum substrate was placed. This made it possible to deposit diamond films uniformly on a substrate as large as 100 mm in diameter at a high deposition rate of 30 µm/h. This deposition area is the largest one of diamond films ever deposited by the rf induction thermal plasma CVD method.

Tribology of niobium-coated SiC ceramics and the effects of high energy ion irradiation

Abstract SiC ceramics, coated with a niobium metal film (Nb-SiC) with and without subsequent Ar + ion irradiation, were subjected to a pin-on-disk friction and wear test in an ambient atmosphere with a diamond pin for 40 h. The friction coefficient between the SiC disk and a diamond pin was about 0.1. Niobium film deposition decreased the friction coefficient to about 0.04 with a normal load of 9.8 N. The wear of SiC was also reduced to one-eighth by the niobium deposition. The Ar + -ion-irradiated Nb-SiC had very high wear resistance; effectively no wear was detected in the samples irradiated to doses over 5 × 10 15 ions cm −2 .

Friction and wear of Nb metal-deposited SiC and the effects of high-energy ion irradiation

Abstract SiC ceramics, with and without niobium metal film (Nb/SiC) and Ar + ion-irradiated Nb/SiC were subjected to a pin-on-disk friction-and-wear test with a diamond pin for 40 h. The metal film deposition reduced the friction coefficient and the wear, and no wear found in the irradiated Nb/SiC.

Structural Analysis of a Carbon Nitride Film Prepared by Ion-Beam-Assisted Deposition

The microstructure of a carbon nitride (CNx) film formed by ion-beam-assisted deposition (IBAD) was investigated by transmission electron microscopy (TEM). This film was formed on the Si (100) substrate by IBAD with an N/C transport ratio of 1. Three different spacings (0.34 nm, 0.21 nm, 0.12 nm) were observed by transmission electron diffraction (TED) and the periodic structure corresponding to the spacing of 0.34 nm was aligned perpendicular to the substrate. The bending of this plane resembled a carbon nanotube; therefore, it seemed reasonable to suppose that the CNx film obtained consisted of numerous carbon-nanotube-like structural elements grown vertically, relative to the substrate, and it also seemed appropriate that these structural elements should be termed nanotube-like carbon nitride.

Tribology of silicon-thin-film-coated SiC ceramics and the effects of high energy ion irradiation

Abstract The sliding friction coefficients and specific wear of SiC ceramics coated with a silicon thin film (Si/SiC) with and without subsequent Ar + irradiation against a diamond pin were measured with a pin-on-disk tester at room temperature in laboratory air of approximately 50% relative humidity without oil lubrication for 40 h. The friction coefficient of Ar + -irradiated Si/SiC was about 0.05 with a normal load of 9.8 N and remained almost unchanged during the 40 h test, while that of SiC increased from 0.04 to 0.12 during the test. The silicon deposition also reduced the specific wear of SiC to less than one tenth of that of the uncoated SiC. Effectively no wear was detected in Si/SiC irradiated to doses of over2×10 16 ions cm −2 .