Kenichi Gomi

Diamond synthesis from CO-H2 mixed gas plasma

Particulate or film-like diamond was prepared on silicon substrates from CO-H2 mixed gas using a microwave plasma technique. The growth rate of diamond without graphite and amorphous carbon, as measured by Raman spectroscopy, was 9Μm h−1 for particles and 4Μmh−1 for flims. These values were larger than those in other source gas systems, such as CH4-H2, CH4-H2-H2O and CH3OH-H2. The good formation rate and high quality of diamond in the CO-H2 system was attributed to acceleration of methyl radical formation by the reaction of excited CO and H2 molecules and removal of by-product graphite by OH radicals in the plasma.

Tribological behavior of thin film rigid disks with regular dot array texture on carbon overcoats

Frictional behavior and contact start/stop (CSS) performance are described for thin film rigid disks with regular dot array texture on carbon overcoats formed by a photo-lithography technique. Both initial friction and friction buildup in CSS tests become smaller with a decrease in apparent area of contact between the slider and disk, while wear depth of carbon overcoats in tests increases. These phenomena agree well with those of concentric circular texture formed by similar process. These results show that the apparent area of contact is the dominant factor for friction and wear, nearly independent of texture arrangement. When the hill height is insufficient, a sudden increase in friction may occur during a CSS test due to wear of the hills. To improve tribological durability, the optimum texture profile should be designed by taking account of the wear rate of overcoats during the operating conditions of magnetic disk drives. >

Micro-tribology of carbon-coated thin-film media with well-defined surface texture

Contact start/stop (CSS) performance is described for thin film media with well-defined surface texture on carbon overcoats. Using a photolithography technique, concentric circular hills with uniform height (ca. 20 nm) are formed on the carbon overcoat to control the apparent area of contact with a slider. This texturing process provides the medium with a flat magnetic layer independent of the texture profile, which would be suitable for high density recording. A decrease in the apparent area of contact results in lower friction buildup during the CSS test, while it causes large wear of the carbon overcoat over the test. Take off velocity of the slider also becomes higher with a decrease in the apparent area of contact, which increases sliding distance prior to take off. Although the smaller apparent area of contact causes greater wear due to an increase in contact pressure and sliding distance between the medium and slider, it effectively limits the increase in the real area of contact, keeping friction low. >

Comparative Combustion Studies of Ultrafine Coal/Water Slurries and Pulverized Coal

The effects of the physical properties of slurried and pulverised fuels (specifically particle size, density, and phase composition) on combustion are described in this paper, For solid fuels there is considerable flexibility for controlling the particle size, which in turn has a significant impact on ignition, char burnout, and emissions. In contrast, the chemical properties and reaction temperature range of a given fuel are narrowly constrained in most applications. In this work we use a laminar flow reactor to study the initial stages of combustion of coal/water slurries and pulverized coal. In conjunction with the flow reactor, a laser-based in situ particle counter has been used to determine the size distributions of pulverized coal and various slurry mixtures prior to and during combustion. Initial size distributions and subsequent evolution of these distributions vary markedly depending on the fuel preparation, emphasizing the importance of the physical properties of the fuel in determining subsequ...

Wear Characteristics of Carbon-Coated Magnetic Rigid Disks With Well-Defined Surface Texture

Wear characteristics are described for carbon-coated magnetic rigid dirks with well-defined surface textures. Concentric circular hills with uniform height (ca. 80 nm) are produced on a dirk surface using a photo-lithography technique, to control the apparent area of contact with a slider. Wear depth on the order of nanometers of the carbon overcoat is evaluated from the decrease in hill height after a drag test. Wear depth increases proportionally with the increase in average contact pressure, which is calculated from the load and apparent area of contact between the disk and slider

Effect of pre-oxidation on reactivity of chars in steam

Abstract The effects of pre-oxidation of char from Taiheiyo coal, a non-caking bituminous coal, in the 400–550 °C temperature range on its gasification reactivity with N 2 -H 2 O at 0.1 MPa (steam partial pressure of 13.2 kPa) have been investigated. The pre-oxidation of char markedly enhances gasification rates at temperatures between 800 and 900 °C. Reactivity is found to parallel the burn-off level during preoxidation at low temperatures (400–430 °C), whereas at relatively high temperatures (480–550 °C), the burn-off level only affects the reactivity slightly. The amount of CO and CO 2 evolved from the preoxidized char by heat treatment is proportional to the burn-off level at low temperatures (400–430 °C), being closely related to the enhancement of the gasification reactivity in steam.