GB1253858A - Electrolytic treatment employing hydrofluoric acid electrolytes - Google Patents

Abstract

1,253,858. Electrolytic pickling and plating of semi-conductors. SIEMENS A. G. Dec. 9, 1968 [Dec.8, 1967], No.58476/68. Heading C7B. The surface of a body of niobium or niobiumzirconium alloy is cleaned by anodic etching in an aqueous solution of hydrofluoric acid containing ammonium ions. A similar electrolyte may be employed in coating a super-conductor material such as niobium-zirconium alloys with a metal that is electrically normally conductive at the temperature at which the super-conductor is super-conductive by first anodically etching the super-conductor to clean it and subsequently electro-depositing on it the coating metal from a similar electrolyte containing additionally ions of the coating metal while preventing inactivation of the super-conductor surface between cleaning and electro-plating. The electro-deposited metal may be Cu, Au, Zn, In, Sn or Ni and may be included in the electrolyte as the fluoride salt. As described the super-conductor material is a wire of either NbZr25 or NbZr33 and is subjected to an initial HF/HNO 3 pickling treatment, and the counter electrode is of the plating metal or graphite. In the case of nickel plating, subsequent electro-plating with copper first from a cyanide strike bath and then from a sulphate bath may be effected. The electrolytic etching and plating may be effected in the same vessel 4 through which the wire is fed intermittently by a conveying head V, the wire being stationary in the bath during progress of the head to the right and polarity change being effected during this movement of the head; and being wound up from off roller 7, rollers 2, 3, 5, 6 being stationary, the wire being fed rapidly through the bath during return movement of the head when rollers 2, 3, 5, 6 rotate. Reference is made also to feeding the wire continuously through the bath resulting in the wire having successive differently coated portions. Alternatively the wire may be continuously fed as a bipolar-electrode through a bath divided by a plastics screen so as to effect first etching and then plating Fig. 4 (not shown). In another arrangement, Fig. 2 the wire is continuously fed and is alternately made positive and negative while the counter electrode 18 in chamber 13 in which etching and plating is effected is repeatedly synchronously changed in polarity so as to provide repeated etching and plating treatments of the wire, an etching ante-chamber 15 divided from chamber 13 by an insulating screen containing an electrode 17 which similarly is alternately negative and disconnected. By choosing the length of the ante-chamber so that the wire residence time is equal to a single plating period in compartment 13 only pre-etched wire is plated. In a further arrangement Fig.3 (not shown) using a separate permanent pre-etching tank the wire is permanently connected to a positive voltage, and passes from this tank into a tank in which the counter electrode is repeatedly alternately negative and positive with respect to the wire. The Specification discloses suitable electric circuits, Figs.5 to 8 (not shown) for the various electrolysis current patterns required, the circuits providing relay-operated current reversal Fig.5, (not shown), an over-riding voltage instead of current reversal Fig. 6, (not shown), a high cathodic pulse by capacitor discharge on current reversal Fig. 7 (not shown) and a high cathodic capacitor discharge pulse on application of an over-riding reverse voltage Fig. 8 (not shown).