Toshio Nagasawa

High-strength alkali-resistant sintered SiC fibre stable to 2,200 °C

The high-temperature stability of SiC-based ceramics has led to their use in high-temperature structural materials and composites. In particular, silicon carbide fibres are used in tough fibre-reinforced composites. Here we describe a type of silicon carbide fibre obtained by sintering an amorphous Si–Al–C–O fibre precursor at 1,800 °C. The fibres, which have a very small aluminium content, have a high tensile strength and modulus, and show no degradation in strength or change in composition on heating to 1,900 °C in an inert atmosphere and 1,000 °C in air — a performance markedly superior to that of existing commercial SiC-based fibres such as Hi-Nicalon. Moreover, our fibres show better high-temperature creep resistance than commercial counterparts. We also find that the mechanical properties of the fibres are retained on heating in air after exposure to a salt solution, whereas both a representative commercial SiC fibre and a SiC-based fibre containing a small amount of boron were severely degraded under these conditions. This suggests that our material is well suited to use in environments exposed to salts — for example, in structures in a marine setting or in the presence of combustion gases containing alkali elements.

A general process for in situ formation of functional surface layers on ceramics

Ceramics are often prepared with surface layers of different composition from the bulk, in order to impart a specific functionality to the surface or to act as a protective layer for the bulk material. Here we describe a general process by which functional surface layers with a nanometre-scale compositional gradient can be readily formed during the production of bulk ceramic components. The basis of our approach is to incorporate selected low-molecular-mass additives into either the precursor polymer from which the ceramic forms, or the binder polymer used to prepare bulk components from ceramic powders. Thermal treatment of the resulting bodies leads to controlled phase separation (‘bleed out’) of the additives, analogous to the normally undesirable outward loss of low-molecular-mass components from some plastics; subsequent calcination stabilizes the compositionally changed surface region, generating a functional surface layer. This approach is applicable to a wide range of materials and morphologies, and should find use in catalysts, composites and environmental barrier coatings.

Some problems on the insulating polyethylene in the manufacturing process of a submarine coaxial cable

On the manufacturing process of a submarine coaxial cable, a multitroughs water cooling system is adapting to avoid the voids forming and to strengthen the gripping force between the insulating polyethylene and a center conductor.

On the use of Polyethylene Insulation in the Manufacture of Submarine Cables

In the manufacturing process of a submarine coaxial cable, a multitrough water cooling system is used to avoid formation of voids and to strengthen the gripping force between the insulation polyethylene and the metallic center conductor. In submarine coaxial cable systems, the standards for dielectric properties of the insulation, polyethylene, are very strict. The adverse effect of small amounts of water in the polyethylene can not be neglected. In the cable manufacturing process quench cooling is favorable to the decrease of the water content in polyethylene. On the other hand, gradual cooling is better to avoid formation of voids. To find the optimum manufacturing process under these two conflicting conditions, computor simulations of the diffusion mechanism of water in polyethylene and the void forming mechanism have been made using available experimental data.