Kei Demizu

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.

The Effect of Trialkyl Phosphites and Other Oil Additives on the Boundary Lubrication of Ceramics: Friction of Silicon-Based Ceramics

In order to examine the fundamental boundary lubrication properties of ceramics, reciprocating friction experiments of silicon based ceramics such as silicon carbide and silicon nitride were conducted with trialkyl phosphites and other oil additives. When ceramics were slid against ceramics, trialkyl phosphites with long carbon chains reduced the friction of silicon nitride markedly; the friction coefficients decreased with an increase in the carbon chain length. Other oil additives, however, did not greatly affect the friction

The effect of trialkyl phosphites and other oil additives on the boundary friction of oxide ceramics against themselves and metals

In order to examine the fundamental boundary friction properties of ceramics, reciprocating friction experiments of oxide ceramics such as zirconium oxide and aluminum oxide were conducted with trialkyl phosphites and other oil additives. When ceramics were slid against ceramics, no additives used in this study reduced friction markedly. Trialkyl phosphites with short carbon chains appreciably increase the friction coefficients compared with base oil. Several kinds of pure metals were slid against oxide ceramics with a trialkyl phosphite which gave the lowest friction in the case of ceramic to ceramic contacts, and the friction coefficients were compared with those of base oil. The trialkyl phosphite reduces the friction of ceramics slid against each metal except for Cu. Reaction products between Cu and phosphorus had adhesive characteristics against oxide ceramics and increased friction.

The effects of an electric current on the sliding wear of cast iron

Dry sliding wear tests were carried out to clarify the influence of an electric current on friction and wear of cast iron. Some carbon steels were also examined for comparison. A ball-on-plate type tribotester was used with a high-carbon chromium bearing steel as a fixed ball. It was found that changes in the friction coefficient, due to an increase in electric current, were completely different for cast irons than for carbon steels. The friction coefficient of cast iron is lower than that of carbon steel under zero current conditions, but with an increase in applied current the coefficient increases. In contrast, the friction of steels decreases under a high electric current. A further increase in current produced an inversion of the friction coefficient between cast irons and steels. The direction of the current affects the amount of wear: the anode of the couple always experiences heavier wear than the cathode, in the case of both cast irons and carbon steels. The wear of cast iron increased with an increase in electric current under all tested contact loads. However, the wear of the carbon steel showed little increase (with increasing electric current) under high contact load. These differences in the tribological behavior under electric current of both cast iron and carbon steel are attributed to the difference in melting point of the materials, which changes the transition of wear mode from adhesion to fusion.

The Tribological Properties of Ion-implanted JIS SUS304 Stainless Steel

Experiments using unimplanted JIS SUS304 as well as N + -, B + -, N + +B + - and Ar + -implanted JIS SUS304 were performed with a self-manufactured tribology testing apparatus. From the experimental results, the coefficient of friction was significantly dependent on the kind of the opposite component in the tribological tests. It has also be observed that the magnitude of the wear damage on JIS SUS304 is dependent upon the kind of the ions implanted.