boron fibres otherwise boron filaments (rus. волокна, борные) — structural fibre, obtained by deposition of boron on a continuous thin filament or wire.

Description

Boron fibre is produced by chemical vapour deposition (CVD): a mixture of BCl3 + H2 is fed into a sealed reactor, where a filament (substrate with a diameter of about 12 microns, usually tungsten) is supplied through the mercury seals; the filament is heated by direct electric current. Under certain conditions (substrate temperature of 1,000-1,300°C) the resulting fibre, 100 to 200 microns in diameter (usually 140 microns), has a polycrystalline structure with a grain size of 2-4 nm. Increased substrate temperature accelerates the deposition process, but leads to larger crystals in the structure of the fibre, which significantly reduces its strength. The average strength of fibres obtained in optimal conditions is up to 4 GPa at a length of 25 mm, the elastic modulus in the direction of the axis is about 480 GPa, and the density depends on the substrate and the fibre diameter and is usually in the range from 2.3 to 2.6 g/cm3. Boron fibre rapidly recrystallises at temperatures above 600°C, which limits process temperatures in production of the corresponding composites and temperatures of their operation. Boron fibres are used as reinforcing fillers in polymer and aluminium matrices. Due to high cost of such fibres their applications are limited. The boron-aluminium composite is most efficiently used in spacecraft structures.

Author

  • Mileiko Sergey T.

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