| 摘要 |
1,203,275. Electrolytically yttriding and rare earthiding metals. GENERAL ELECTRIC CO. Oct.25, 1967, [NOV.10, 1966], No.48513/67. Heading C7B. A method of forming an yttride or rare earthide coating on a base metal selected from the class consisting of (a) metal compositions having a melting point greater than 500‹ C., at least 50 mole per cent of said metal composition being at least one of the metals selected from the class consisting of metals whose atomic numbers are 4, 13, 21, 22, 25 to 29, 40, 43 to 47, 72 and 75 to 79 and (b) beryllided, borided, aluminided and silicided vanadium, chromium, niobium, molybdenum, tantalum or tungsten, and (c) zirconided niobium, which method comprises (1) forming an electric cell containing said base metal as the cathode, joined through an external electrical circuit to carbon, yttrium or rare earth metal serving as anode and a fused salt electrolyte consisting of (i) one or more of the alkali metal fluorides, or a mixture of one or more of the alkali metal fluorides with strontium fluoride and/or barium fluoride and (ii) an additional fluoride consisting of from 0À01-40 mole per cent of yttrium fluoride or 0À01-40 mole per cent of a rare earth fluoride, said additional fluoride being the fluoride of the anode metal when the anode is other than carbon, said electrolyte being maintained at a temperature of at least 500‹ C. but below the melting point of said base metal in the substantial absence of oxygen, and (2) passing a current between said anode and said cathode sufficient to establish a cathode density of from 0À01 to 30 amperes/dm<2> and a cell voltage below 3À0 volts during the formation of the yttride or rare earthide coating, the cell voltage being from 1 to 3À0 volts when a carbon anode is used. The terms "yttride" and "rare earide" designate any solid solution or alloy or intermetallic compound of Y or a rare earth and the base metal. The cell generates electric current. The deposition rate of the Y or rare earth may be decreased by inserting some resistance in the circuit or may be increased by impressing a voltage, e.g. to obtain constant current densities during the reaction. Specified fluorides that may be used are those of Li, Na, K, Rb and Cs, e.g. a eutectic mixture of NaF and LiF or of NaF, KF and LiF. The process may be carried out under vacuum or an inert atmosphere, e.g. of Ar, He, Ne, Kr or Xe. The electrolyte may be purified, e.g. from carbon by an initial electrolysis. An yttrium or rare earth anode may comprise a rod or be in the form of chips in porous metal baskets, such as Nb or Ta. A carbon anode may be shielded with a tightly woven screen of Nb, Mo, Ta, W or Fe. |
