US3505178A - Process of electroplating an article by sequentially passing the same and a platinum coated tungsten anode through a series of different electroplating baths - Google Patents

Description

United States Patent PROCESS OF ELECTROPLATING AN ARTICLE BY SEQUENTIALLY PASSING THE SAME AND A PLATINUM COATED TUNGSTEN ANODE THROUGH A SERIES OF DIFFER- ENT ELECTROPLATING BATHS James E. May, Dorchester, Mass., and Alfred J. Haley,

Jr., Westfield, N.J., assignors to Engelhard Industries,

Inc., Newark, N.J., a corporation of Delaware No Drawing. Filed May 12, 1967, Ser. No. 637,938

Int. Cl. C23b 5/06, 5/72, 5/62 US. Cl. 20432 1 Claim ABSTRACT OF THE DISCLOSURE A method is disclosed for the electroplating of metal objects in copper-nickel-chromium plating cycles, wherin the electroplating steps are preceded by an acidic etching solution containing fluoride ions, by means of a platinum coated tungsten anode.

This invention relates to a method for electroplating copper, chromium and/or nickel from electrolyte solutions in processes in which the electroplating anodes are carried through a pre-treatment bath comprising an acidic etchant solution containing fluoride ions. In particular, this invention concerns methods of electroplating from such electrolytes employing platinum on tungsten anodes.

Platinum-coated titanium anodes are known in the art. Such electrodes have been employed as insoluble anodes in the electroplating of nickel and chromium. It has been found that while these anodes are relatively stable toward dislodgment of the platinum coating when employed in conventional plating baths, the anode suifers from corrosion and platinum dislodgment when carried through pre-treatment immersion baths containing free fluorides.

The extensive usage of plated metal in the automotive industry especially for body appearance is well known. Where strength is required, as in chrome-plated bumpers, the support is generally heavy steel. Other plated parts with more intricate shapes are generally made from castings of relatively low melting metals or alloys. For example, zinc die castings are extensively plated with a Cu-Ni-Cr plating cycle for door handles, grill work and other metallic parts.

In the automotive industry, the Cu-Ni-Cr cycle of plating is carried out automatically. Each plating bath gener ally has main electrodes, which are ordinarily expendable anodes for the copper and nickel plating steps, and nonexpendable anodes for the Cr plating. Generally, in the plating of complex shapes, additional anodes are positioned in the bath for the purpose of controlling the rate of deposition of the plating metal at corners or deep-set recesses of the work, and these are normally designated deep-throw anodes. Such anodes are especially useful in nickel and chromium plating because of the low throwing power of conventional nickel and chromium plating baths and, advantageously, would be of the non-expendable type.

Conventional zinc die-cast plating processes employ deep-throw nickel anodes, which must be replaced in ordinary nickel-chromium plating procedures by non-expendable anodes for the chromium plating steps of the plating cycle. It is seen therefore that non-expendable deep-throw anodes which could remain in place throughout the copper, nickel and chromium plating cycle for plating of die-cast metal shapes would be especially advantageous.

When metallic parts, such as zinc or lead-containing die-cast structural shapes are to be plated in a nickelchromium plating cycle, it is recognized that by far the most difficult step is to clean the surface and it has been found particularly advantageous to first treat the part with an acidic etching solution containing fluoride ions. No electrolysis is performed in this pro-treatment step,

Such solutions may contain hydrogen fluoride, a compound capable of producing fluoride ions in solution, e.g. an acid, or alkali metal or ammonium salt of F, HF2 BF4 SiF and the like. Such treatment activates the support surface for improved adhesion of the plate. It would therefore be of further advantage to provide an electroplating anode capable of passing high current density in a plating bath and substantially inert to fluoridecontaining etchant baths. However, non-expendable deepthrow anodes suitable for such plating procedures are usually attacked by acidic fluoride-containing solutions.

In accordance with the present invention, non-expendable anodes of tungsten having platinum coatings thereon are employed in electroplating processes to deposit electroplates of copper, nickel and/or chromium where immersion of the rack in an acidic fluoride containing etchant solution precedes the electrodeposition. The anode which is used in the practice of the present inven tion, consists of a tungsten base of suitable shape for the work to be performed, partly or completely coated with a conducting layer of platinum. Such anodes can be prepared by electroplating platinum on tungsten by means of conventional platinum plating solutions, e.g. P salt platinum baths as disclosed in US. Patents No. 1,779,436 and No. 1,779,457. In general, the platinum coating may cover all or a portion of the anode sutficient to carry the electric current applied during use as an anode. The electroplated platinum coating will not ordinarily be imporous and need not be of substantial thickness, a coating of microinches platinum Ibeing usually suificient for use as an anode. While platinum is preferred as a coating, other platinum group metals such as rhodium and iridium as well as alloys thereof with platinum, are also suitable.

EXAMPLE I A coupon of commercially pure tungsten was coated with 100 microinches platinum by electrodeposition from a P salt platinum bath. The coating was fired in an inert atmosphere at a temperature of 800C. for one hour.

The platinized tungsten coupon so prepared was immersed in 52% by volume hydrofluoric acid for 19 hours. No attack was visible on either the tungsten or the platinum coating.

A similar coupon was employed as anode in a commercial chromium-plating bath (M & T Cr chromium plating bath). Electrolysis was carried out at 1.5 amperes per square inch for five hours. No attack was evident on the coating or the tungsten substrate.

EXAMPLE II (A) Three coupons were prepared by the procedure of Example I, one of platinized-tantalum, one of platinized tungsten and one of platinized molybdenum. Each of the coupons was immersed in a 52% by volume HF solution. The platinized tantalum coupon showed immediate gasing, and was removed within three minutes of immersion; attack was severe. The platinized-tungsten and platinized molybdenum were removed after 66 hours. Neither of these coupons showed any evidence of attack.

(B) A similar test of three coupons was conducted by immersing each in a solution of a commercially available fluoride-containing etchant (Actisalt-l, Northwest Chemical Co.) containing 4 oz./ gallon of salt for a period of 66 hours. At the end of this time, the coupons were examined visually with the following results:

Platinized tantalum-slight attack Platinized tungsten-no change Platinized molybdenum-no change Platinized titanium-moderate corrosion -Platinized molybdenum-severe corrosion Platinized tungstenno change Platinized tantalumno change From the above tests, it is apparent that platinized tungsten resists attack in highly-concentrated HF solution, in etchant salts containing fluoride conventionally employed in pre-treatment of metal objects to be subjected to nickel plating, and to anodic attack in conventional nickel and chromium plating baths. It will be seen therefore that the so-called valve metals, which are employed as substrate for platinized electrodes are not all equivalent, and where pre-treatment in solutions containing free fluoride is required, platinized tungsten is an outstandingly useful electrode. Such electrodes can be employed as the main anodes for the electrodeposition process, or as auxiliary deep-throw anodes, and may be used in both nickel and chromium plating baths, thus obviating any need for anode replacement in plating processes which employ a nickel-chromium plating cycle.

What is claimed is:

1. In a process for electroplating zinc or lead-containing die castings wherein the casting and associated anodes are immersed in an acidic etchant containing fluoride ions and subsequently and consecutively immersed in nickel plating and chrome plating baths for electrodeposition of nickel and chromium electrodeposits on the castings, the improvement of employing platinum-coated tungsten as the anode.

References Cited UNITED STATES PATENTS 1,835,679 12/1931 Van Derau 20441XR 1,970,804 8/ 1934 Kerk.

2,128,550 8/1938 Ford 20441XR 2,979,553 4/1961 McCallum et al. 20429O 3,287,250 11/1966 Broun et a1. 204-290 3,336,658 8/1967 Husni 29492 3,410,785 11/1968 Clough et al 20429O 3,412,000 11/1968 Bedi 204147 JOHN H. MACK, Primary Examiner W. VAN SISE, Assistant Examiner US. Cl. X.R. 204--41, 290