| 摘要 |
Boron is coated on to an elongated substrate, e.g. a filament or ribbon, by-passing the substrate at a substantially constant speed through an ambient gaseous composition containing a vaporizable compound of boron whilst maintaining the substrate at a temperature effective to cause decomposition of the atmosphere and cause deposition of the boron on the filament. The ambient atmosphere may consist of a mixture of a boron halide e.g. BCl3 + H2, and at least a portion of the substrate is maintained at a temperature in the range 1100 DEG K to 1600 DEG K but below the melting points of both boron and the substrate. Boranes e.g. B2H6 may also be used in the ambient atmosphere, and are particularly suitable when the substrate is of a lower melting point e.g. Al. The speed of the substrate through the deposition zone is adjusted so as to obtain a deposit of the desired thickness. Possible substrates are tungsten, rhenium, tantalum, titanium, molybdenum, iron, copper, nickel, "Nichrome" (Registered Trade Mark) aluminium, magnesium, carbon and graphite. X-ray diffraction data indicate that in the above described method the deposited boron reacts with the substrate to give a boride, e.g. with tungsten WB4 or W2B5. Filaments may be subjected to zone melting to render monocrystalline, and may be treated with HNO3 (see Division C1) to increase the tensile strength of these boron-containing filaments.ALSO:The strength of boron-containing filaments is increased when such filaments are treated with aqueous nitric acid. The filament are preferably treated until 0.5 mil has been removed from the surface of the filament and the preferred acid has a concentration of 40 to 45% by weight and is used at a temperature of approximately 100 DEG C. The tensile strength of the treated filaments is at least 500,000 lb./sq. inch. The filaments are prepared as described in U.K. Specification 1,051,883 by passing an elongated substrate at substantially constant speed through an ambient gaseous atmosphere containing a vaporizable boron compound, e.g. BCl3, B2H6 while maintaining at least part of the substrate at a temperature sufficient to decompose the boron compound and deposit boron on the substrate. The atmosphere may also contain hydrogen. Suitable substrates are given as W, Re, Ta, Ti, Mo, Fe, Cu, Ni, Al, Mg, C and graphite. X-ray diffraction data indicate that when boron is deposited by the stated method it combines with the substrate to form a compound, e.g. tungsten boride WB4 or W2B5.
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