Refractory metal coatings deposited in bore of metal tubes - by chemical vapour deposition e.g. of niobium, tantalum or tungsten, where coating has exact length in tube bore

摘要

Adherent and uniform coating is obtd. by the redn. of a metal halide with H2 in a tube heated by induction. The induction coil consists of a row of turns mounted on holders so the spaces between the turns can be varied, and the tube is joined via a gas tight seal to an evaporator contg. a boat which can be driven at a controlled speed into the evaporator. Boat contains the metal halide, and H2 is fed into the evaporator to obtain the desired gaseous reaction mixt. A slight positive gas pressure is maintained in the tube, and the gas mixt. can escape into the outer atmos. Pref. the outside of the tube is exposed to a stream of H2 or inert gas, and the induction coil produced an exact temp. gradient along the tube. Wear-, heat- and/or corrosion resistant coatings are applied to tubes used in the chemical industry or nuclear technology.