| 摘要 |
1,206,140. Zirconiding and hafniding metals. GENERAL ELECTRIC CO. Oct. 27, 1967 [Nov. 10, 1966], No.48886/67. Headings C7B and C7F. A zirconide or hafnide layer is formed on a metal composition, the metal composition having a melting point of more than 800‹C and at least 50 mole percent of said metal composition being at least one of the metals selected from the class consisting of metals whose atomic numbers are 13, 22-29, 41-47 and 73-79 inclusive, The method of forming the layer comprises (1) providing a fused salt electrolyte, (2) providing an electric cell containing said electrolyte, (3) providing said cell metal composition as the cathode, and joining said cathode through an external electrical circuit to zirconium or hafnium as anode, (4) maintaining said electrolyte at a temperature of at least 800‹C. but below the melting point of said metal composition and (5) controlling the current flowing in said electric cell so that the current density of the cathode is in the range from 0À01 to 10 amperes/ dm<2> during the formation of the zirconide or hafnide layer; said electrolyte consisting of (a) lithium and/or sodium fluoride, or a mixture of lithium and/or sodium fluoride,with one or more of the fluorides of strontium, barium, magnesium and calcium and (b) from 0À01 - 5 mole percent of zirconium fluoride (when zirconium serves as anode) or 0À01 - 5 mole percent of hafnium fluoride (when hafnium serves as anode) substantially all traces of oxygen and oxides being absent from the electrolyte and from above the electrolyte and an inert atmosphere or vacuum being maintained over the electrolyte at all times; the electrolyte being free from carbon and carbon compounds at least when the said metal composition includes a metal of atomic numbers 23, 24, 41, 42, 73, or 74 during formation of the zirconide and hafnide layers. When the metal composition is Ti, the method may be modified in that no external electrical connection need be provided between the anode and the Ti. The terms "Zirconide" and "hafnide" designate any solid solution or alloy of Zr or Hf and the metal composition whether or not the metal composition forms an intermetallic compound with either metal. Prior to zirconiding or hafniding, impurities such as oxygen and carbon can be removed from the fused electrolyte by an initial electrolysis. Oxygen can also be removed by contacting the fused electrolyte with Zr or Hf. During the "iding" the cell generates electric current. The deposition rate of the Zr or Hf may be increased by impressing a voltage, e.g. to obtain constant current densities during the reaction. The electrolyte may comprise a eutectic mixture of NaF and LiF. The process may be carried out under an atmosphere of Ar, He, Ne, Kr, or Xe. The zirconide and hafnide have hard wear - and corrosion-resistant surfaces. |
