Boron Carbide Fibers from Carbon Fibers

Abstract

There are many properties of boron carbide which make it attractive in a fibrous form. These include high strength, high modulus of elasticity, low density, chemical stability and good oxidation resistance. However, the process of fiberizing such a refractory, hard material by the usual methods, is virtually impossible. Thus, other methods are needed to overcome these problems. Starting with a boron-coated tungsten wire, HIGGINS et al. (1969) deposited B₄C from a mixture of BC1₃, CH₄ and H₂ at 1100–1200°C. HOUGH and GOLF (1966) used organoboranes to deposit B₄C on tungsten and HAMLING (1968) prepared partially converted B₄C fibers by impregnation of rayon with a soluble boron compound followed by heating. GATTI et al. (1966) formed B₄C whiskers by vaporization of B₄C powder followed by condensation in a temperature gradient. None of these methods, however, prepared fibers that were completely B₄C and continuous. It will be shown that multifilament carbon yarn can be totally (or partially) converted to continuous B₄C yarn by reaction with BCl₃ and H₂ under controlled conditions at high temperatures.