Hiroyuki Ishigaki

Friction and Wear of Hot Pressed Silicon Nitride and Other Ceramics

An investigation was conducted to determine the friction and wear characteristics of hot-pressed silicon nitride. Sliding produced wear debris and a damaged surface. The physical and crystallographic morphology of surfaces was compared with that of diamond ground surfaces. Wear tests were done with pin-on-disk apparatus at a load of 10N with various sliding speeds to 780 mm/s, and in four different environments which included in dry nitrogen, in air at humidities of 50 percent RH and 90 percent RH, and in distilled water. The results of the wear experiments indicated that residual α-silicon nitride was transformed into β-silicon nitride. Adsorbed water appeared to enhance plastic flow of the surface and reduced both the wear rate and friction. A second investigation was conducted to correlate the coefficient of friction with the fracture toughness of silicon nitride, silicon carbide, aluminum oxide and zirconium oxide. The friction experiments were done in reciprocating sliding, using spherical diamonds. Two tip radii, 0.005 mm and 0.1 mm were used over a range of load of 0.1 to 3N and a speed of 0.17 mm/s. The coefficient of friction was found to be inversely correlated with fracture toughness of all four ceramics in several conditions. Frictional anisotropy was also observed in the hot-pressed silicon nitride.

Room Temperature Nanoimprint Technology Using Hydrogen Silsequioxane (HSQ)

Room-temperature nanoimprint lithography (RT-NIL) technology has been developed to overcome critical dimensions and pattern placement error due to thermal expansion in the conventional nanoimprint lithography (NIL) process. We propose RT-NIL using hydrogen silsequioxane (HSQ) instead of PMMA used in conventional NIL, and demonstrate HSQ replicated patterns with 90 nm hole diameter and 50 nm linewidth realized by room-temperature replications. We performed step-and-repeat replications using HSQ on a 1.5 in. wafer and evaluated the uniformity of the imprinted HSQ patterns.

Effect of adsorbed water on friction of hot-pressed silicon nitride and silicon carbide at slow speed sliding

Abstract The effect of adsorbed water on the characteristics of friction of both silicon nitride and silicon carbide was studied experimentally using a pin-on-flat-type friction apparatus at a slow sliding speed of 10 mm min −1 . Silicon nitride and silicon carbide powder were hot pressed under the sintering conditions of pressure, 30 MPa, and temperatures 1800 °C and 2100 °C respectively. A continuous increase in friction during reciprocal sliding was observed for the sliding of silicon nitride in laboratory air with a relative humidity of 50% ± 5%. It was attributed to a decrease in the protective surface layer during reciprocal sliding. The effects of time intervals in reciprocal sliding, environmental humidity and temperature on the formation of the surface layer were examined. Experimental results showed that shorter time intervals, lower humidity and higher surface temperature increased the sliding friction of ceramics. These influences were also attributed to the decrease in the effect of adsorbed water on sliding friction, because the above sliding conditions prevented the formation of a protective surface layer.

Surface modification of fluorocarbon polymers by synchrotron radiation

Fluorocarbon polymers are fluorishingly used as the material for industry from some characteristic advantages - chemical stability, thermal stability, excellent electric property and so on. One of other characteristics of fluorocarbon polymers was hydrophobicity of these surfaces, and fluorocarbon polymers were applicable to various industrial yields by taking advantage of this characteristic. However, in the several yields, such as painting and adhesion, this hydrophobicity has restricted the application of fluorocarbon polymers. In the present study, wettability on the surface of polytetrafluoroethylene (PTFE) chip was modified by exposure to synchrotron radiation (SR). This is the first report on SIR exposure effects about wettability of PTFE.

Preparation of Superconducting Y-Ba-Cu-O Thick Film

During sintering, superconducting copper-oxide films commonly have a high chemical activity with substrate materials, which results in poor superconductivity. In this research, the substrate is prepared by coating multiple non-superconducting Y-Ba-Cu-O films on alumina. The superconducting Y-Ba-Cu-O thick films were prepared by mixing powders Y2O3, BaCO3 and CuO, making a paste by mixing this noncalcined mixture with solvent, coating it on to a film-coated substrate using a painting or printing method, and then sintering the specimen. The thick films have positive superconductive characteristics at high temperatures.

Influence of silver on critical current of the Y–Ba–Cu–O superconductor

Electrical properties of Y--Ba--Cu--O superconductors, such as the critical current density and the zero-resistance temperature, are systematically improved by changing the compression pressure during the formation process of the specimens. Also, by changing the silver powder content of the superconducting Y--Ba--Cu--O powder, the critical current density and the zero-resistance temperature are remarkably improved. The resistance-drop temperature is insensitive to changes in the compression pressure, silver content, and magnetic field, whether the field is applied perpendicular to the specimens. The critical current density of the specimens with and without silver decreases exponentially with the perpendicular magnetic field. The critical current densities of specimens without silver showed much lower sensitivity to perpendicularly applied magnetic fields than those of the specimens having a silver content. Along with the above improvements, the present paper also examines several factors that affect the superconducting characteristics. These factors include impurities in the air and strong magnetic fields.

X-Ray Photoelectron Spectroscopy Study of Synchrotron Radiation Irradiation of a Polytetrafluoroethylene Surface.

The effect of synchrotron radiation (SR) irradiation of a polytetrafluoroethylene (PTFE) surface was investigated using X-ray photoelectron spectroscopy (XPS). After the SR irradiation, the relative intensity of the F 1s peak to the C 1s peak decreased markedly. The chemical composition ratio of the F atoms to C atoms was estimated to be 0.29. From the curve fitting analysis of C 1s and F 1s XPS spectra, the chemical components and their intensity ratio were determined. The reason for the chemical composition change by the SR irradiation was discussed.

A simple estimation of the elastic-plastic deformation of contacting asperities

Abstract The elastic-plastic deformation of a contacting asperity was analysed theoretically. The validity of the theory was checked by comparison with the experimental results of an indentation test. The penetration was measured to an accuracy of 0.03 μm using an optical interferometer (Michelson type). The results of the numerical analysis are expressed approximately by a simple formula. As an example of the application of this formula to multiple contact problems, the rolling friction of a ball rolling on a rough plane was estimated theoretically and showed good agreement with experimental results. The elastic recovery of contacting asperities has a significant effect on rolling friction.

Improvement in magnetic shielding by the superposition of a magnetic cylinder over a copper-oxide superconducting cylinder

Magnetic shielding was shown to be improved by superimposing a magnet cylinder over a superconducting cylinder. Examples of such configurations are soft iron and electromagnetic steel cylinders over a copper-oxide superconducting cylinder. The value of the magnetic shielded field for the superimposed cylinder was found to be several times more than that of single superconducting cylinders such as YBCO or a BPSCCO cylinder. Experimental results reveal good characteristics which include the effects of the excitation magnetic field on the inner magnetic field within both the single superconducting and superimposed cylinders, the temporal change of the trapped magnetic field within the superconducting cylinder, the distribution of the magnetic shielded field along the axial direction of the superimposed cylinders, and the relationship between the length of the magnetic cylinder and the shielding effect.<<ETX>>

Influence of Carbon on Critical Temperatures of Superconducting Y-Ba-Cu-O

High Tc copper oxide superconductors, such as Y-Ba-Cu-O, commonly have a high chemical activity during sintering. Y-Ba-Cu-O superconductors are influenced by impurities in air, which cause degradation of the superconducting properties, critical current density (Jc) and temperature of zero resistance (Tczero). XPS analysis of low Jc and Tczero materials shows a presence of carbon in a higher amount compared to high Jc and Tczero materials. This paper shows that Jc and Tczero are very susceptible to impure gases in air.