US2431947A

US2431947A - Formation of a strong bond between a ferrous metal surface and an electrodeposit of silver

Info

Publication number: US2431947A
Application number: US478294A
Authority: US
Inventors: William M Martz
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1943-03-06
Filing date: 1943-03-06
Publication date: 1947-12-02
Anticipated expiration: 1964-12-02

Description

Patented Dec. 2, 1947 FORMATION OF A STRONG BOND BETWEEN A FERROUS METAL SURFACE AND AN ELECTRODEPOSIT OF SILVER William M. Martz, Indianapolis, Ind., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware No Drawing. Application March 6, 1943, Serial No. 478,294

2 Claims. 1

This invention relates to a process of forming a high strength bond between an iron or steel surface and an electrodeposit of silver.

In the production of a silver plated steel surherent plating of silver.

copper may be dispensed with.

ed steel surface.

silver plated parts are annealed.

ous proportions.

room temperature.

F. or higher.

ties.

portions to the solution.

suitable.

of steel being cleaned.

suitable.

2 results the parts are given a cyanide dip before being silver plated. The cyanide solution may be one containing 100 grams of potassium or sodium cyanide per liter of water, although conface (such as, for example, steel-backed silver 5 siderable variation in the concentration of cyaplated bearings) it has been the practice to first nide may be employed. The work may be imelectrodeposit a plating of a metal such as copmersed or dipped in the cyanide solution for per or nickel onto the steel and then electrodeto seconds. posit the silver onto the copper or nickel. This The steel parts are then given a strike or has been essential in order to form a strong, ad- 10 flash of silver and thereafter silver plated for I have now found it the time necessary to give the desired thickness possible to form a high strength bond directly of silver plate. A suitable procedure for formbetween electrodeposited silver and steel when ing the strike of silver is to provide a silver the steel surface is given a preliminary treatplating bath composed of 1.5-2.5 grams per liter ment, so that the intermediate layer of nickel or 15 of AgCN, and 150 grams per liter of KCN (free). The temperature of the bath is maintained on Broadly stated the invention includes the the order of 75-90 F. The work is struck" in anodic treatment of the iron or steel surface the bath for a period of 10 to seconds using with a phosphoric acid solution, and the subsea current density of 15 to amperes per square quent plating of the silver directly to the treat- 20 foot. The electrical contact must be made prior Wetting agents of various to immersion in the solution for best results. kinds compatible with the phosphoric acid so- The parts are removed and thereafter plated lution may be used with beneficial effect. Best with silver in a silver plating bath which preferresults are obtained when the parts are given a ably contains to grams per liter of AgCN, cyanide dip prior to silver plating and when the -25 to grams per liter of KCN and 10 to 20 grams per liter of KOH. The bath may also con- The phosphoric acid may be employed in varitain any of the known silver brighteners" such It is preferred that equal volas, carbon disulfide, ammonium thiosulfate, poumes of phosphoric acid (l-nPOi) and water be I tassium thiosulfate, etc., if so desired. The bath used and that the treatment be carried out at is operated at a temperature of 100 to 125 F.

However wide variation in The electrical contact should be made prior to the proportions of phosphoric acid and water is the immersion of the piece in the solution. For

permissible and the treatment y e Carried best results suitable agitation is provided and the out at from room temperature or below up to 150 current density permissible depends to a large 35 extent upon this factor.

The cathodes preferably are of stainless steel For b t results t ilver plated part are and should present sufficient surface area so as l d i a m- ,1 or reducing atmosphere t t pe e u Of high arfode fi densitemperature on th order of 400 to 1200 F. for

The Conta m y be of glass 1" rubber about /2 to 2 hours. The annealing may be carlined material and should not expose any metal cied out in an air atmosphere if the temperature of the work is held below 900 F. but a neutral or The current densities at the anode may Vary reducing atmosphere is preferable. The work considerably, current densities on the order of 5 should be allowed t 1 1 1 from the lto 150 amperes per square foot or higher being 7 m temperature higljler currenfi densif'lies result: in 40 Before the steel surface is given the anodic more rapid cleaning and 1n a brlghter fim treatment in the phosphoric acid solution it is The time of the anodic treatment is on the order desirable that the urfac s be cleaned as by of from 30 to 699 seconds depending on the type means of an alkaline cleaning solution. A suitr able solution of this sort is composed as follows:

Direct current in the order of 6 or 12 volts 1s Per cent After the steel parts are thus treated they are Na3PO4 12 thoroughly washed as by the use of warm run- NazSiOa 38 12 ning water and thereafter the silver is eleotro- NagCO; 6 oz'pergal'of H2O deposited directly onto the steel. To secure best 55 NaOH 44 l The temperature of the alkaline cleaning bath should be 180 to 200 F. during operation. Current densities on the order of 75 to 150 amperes per square foot are satisfactory. The work may be either anode or cathode, preferably anodic. After the alkaline cleaning operation the parts are rinsed thoroughly in warm running water.

To secure best results all of the plating and cleaning solutions must be kept well filtered and free from contaminations, especially oil or metaL lic particles from the anode or elsewhere.

I claim:

1. A process of producing a strongly bonded electrodeposit of silver directly onto a steel surface which includes, electrolytically cleaning the said surface in an alkaline solution, washing said cleaned steel surface, anodically treating said washed steel surface in a, solution composed of approximately equal volumes of phosphoric acid and water for from 30 to 600 seconds, the acid solution being operated at a temperature from about room temperature up to 150 F. and at an anode current density of 5 to 150 amperes per square foot, rinsing said anodic treated surface, then dipping said treated surface in an aqueous cyanide solution composed of app o grams per liter of an alkali metal cyanide of the class consisting of sodium cyanide and potassium cyanide for about to 20 seconds, striking a silver plate onto said surface in a bath composed of 1.5-2.5 g./liter, silver cyanide, and 150 g./liter potassium cyanide (free), the bath being maintained at a temperatur of 75-90 F., a current density of -50 amperes per square foot being employed and the time being from 10 to 30 seconds, then electrodepositing a, silver plating of desired thickness in a silver plating bath maintained at IOU-125 F. and containing 130 to 150 g./liter of silver cyanide, 160 to 180 g./liter of potassium cyanide (free) and 10 to g./liter of potassium hydroxide, and thereafter annealing the silver plated steel surface at a temperature of 400 to 1200 F. for 30 to 120 minutes in a nonoxidizing atmosphere.

2. A process of producing a strongly bonded electrodeposit of silver directly onto a steel surface which includes, electrolytically cleaning the said surface in an alkaline solution, washing said cleaned steel surface, anodically treating said washed steel surface in a solution composed of approximately equal volumes of phosphoric acid (B31304) and water for from approximately 30 to 600 seconds, the acid solution being operated at a temperature from about room temperature up to 150 F. and at an anode current density of from 5 to 150 amperes per square foot, rinsing said anodically treated surface, then cyanide dipping said treated surface in an aqueous solution of an alkali metal cyanide of the class consisting of sodium cyanide and potassium cyanide for about 10 to 20 seconds, then striking a silver plate onto said surface in a silver cyanide electroplating strike solution, then electrodepositing a silver plate of desired thickness in a silver cyanide plating bath, and thereafter annealing said silver plated steel surface at a temperature with in the range of approximately 400 to 1200 F. for a time within the approximate range of 30 to minutes in a non-oxidizing atmosphere.

WILLIAM M. MARTZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,104,269 Oplinger Jan. 4, 19381 1,916,503 Wilson July 4, 1933 2,197,653 Wilson Apr. 16, 1940 1,658,222 Burns Feb. 27, 1928 2,277,664 Hull Mar. 31, 1942 1,995,766 Chester Mar. 26, 1935 1,949,713 Gravel] Mar. 6, 1934 1,909,149 Hitner May 16, 1933 OTHER REFERENCES Transactions of the Electrochemical Society, vol. 74 (1938), pages 284 and 287-304.

Transactions of the Electrochemical Society, vol. 82 (1943), page 109 (in the discussion of the paper The Adherence of Thick Silver Plate on Steel, by H. L. Crosby and L. I. Gilbertson, presented at th 82nd General Meeting in Detroit, Michigan, Oct. 8, 1942) American Electro-platers Society Monthly Review, vol. 29, (1942), an article by H. Strow on Metal Cleaning in Wartime, page 996.