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Publication numberUS2682593 A
Publication typeGrant
Publication dateJun 29, 1954
Filing dateJun 28, 1949
Priority dateJun 28, 1949
Publication numberUS 2682593 A, US 2682593A, US-A-2682593, US2682593 A, US2682593A
InventorsJenny Alfred L
Original AssigneeGen Electric
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electrical contact
US 2682593 A
Abstract  available in
Previous page
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Claims  available in
Description  (OCR text may contain errors)

Patented June 29, 1954 TENT F ICE ELECTRICAL CONTACT Alfred L. Jenny, Pittsfield, Mass., assignor to General" Electric .Company, a corporation. of

New York No *Drawing. Application J une*28, 1949, l

Serial No 101,910

4 Claims. (Cl. 200-166) The present invention'relates to an electrical contact. It is more particularly'concerned with a switch contact which is resistant to corrosion by sulfur when immersed in oil and to a method of making such contact.

Silver is one of themost widely used metals for electrical contact purposes. However, silver contacts are not "wholly satisfactory for oil im-' mersed switching apparatus due .to-the forma-'= tion of silver sulfide scale on the exposed'or nonengaging areas of the'contact surface. As this sulfide is a good conductor of electricity, it is likely to cause electricalfailures when'it drops oifthe contact surface andcollects on insulated or other parts of the oil immersed switchor other electrical equipment. It is important, therefore,

to prevent sulfide formation on all parts of solid silver or silver plate applied for contact purposes and a primary object of the present invention is to provide such an electrical contactwhich is realloys of copper and silver can be used if desired,

the only requirement being that the exposed surface of the electrical contact be composed of a layer of silver amalgam, that is, a silver-mercury alloy, preferably containing from about 5 to percent mercury.

As copper is the most commonly used conductor, the invention will be particularly described,

with reference to a switch contact comprising a copper base or backing. Employing such a base, the copper part is first provided with a coating of silver. The silver suitably may be applied by electroplating employing anysuitable. silver plating bath and allowing the part to remain in the bath until a silver layer of the desired thick ness, usually from about to 5 mils, has been obtained.

The surface layer of silver is next alloyed with mercury to provide a silver amalgam layer of about thersame. thickness containing from 5 to 25 percent by weight of mercury. The mercury preferablyis applied by plating onto thesilvenv surfaced part in order to obtain a uniform"dis= tribution of the mercury and is thereafter causedto diffuse into and alloy with the-silver. natively, the silver-mercury layer may be formed Alter :sponding iodides.

in itself is more resistant to sulfiding than silver by codeposition of :silver and mercury on the metal base.

The invention is not limited to the use of any particular mercury plating bath. The mercury is electro-deposited on the silver'surface in an amount sufficient to provide a silver-amalgam layer of the desired composition. When first plated, the mercury surface has a high lustre with the characteristicappearance of mercury. To obtain the alloy formation the mercury plated part is aged at room or elevated temperature during which time the lustre disappears and is replaced by a dulLmatte surface not unlike the original silver surface. The required amount of diffusion is usually accomplished byimmersion of the part in boiling water for from 2 to minutes, generally about 15.minutes. Aging at room temperature for about one weekproduces about the same degree of alloying .as 15 minutes at C.

When the proper silver-mercury layer has been developed, the surface thereof is passivated by a suitable .treatment designed -to convert the silver and mercury at the surface to the corre-- Although the silver amalgam alone; after longi'periods J of timeithe mercury gradually diffuses through-the entire piece leaving practically free silver on the surface. The immediate formation of an iodide film in accordance with the present invention" captures the proper amounts of silver and: mercury on the surface as iodides, passivating the surface, and removing any concern about the subsequent loss K of the remaining mercury byfurther diffusion.

iodization is preferably accomplished 'anodically in a'suitable'alkali metaliodide solution such as a 10 percent solutionof potassium iodide having a pH- of about 10.- As it is desired to convert as much of the mercury aspossible to mercurous iodide,-the anodic treatment should be carried out at a current density less than 15 amperes per square foot and preferably less than 10 am peres per square foot with the time of treatment being such that the mercury iodide comprises at least 5' percent of the metal iodide content of the surface film. It hasbeen found that the ratio of HgI to AgI in the film varies inversely as the current density and time of treatment. While this ratio also varies directly as the mercury content of the amalgam, it is usually higher than the Hg/Ag ratio of the alloy particularly at low current densities and short treating times and films having very good sulfide resistance have been obtained containing as high as 8085% HgI, balance substantially AgI.

The effect of time and current density on the composition of the iodide film are shown by the results of a series of tests in which copper contacts surfaced with a layer of 90 percent silverpercent mercury obtained by diffusion for minutes in boiling water were anodically treated in a 10 percent potassium iodide solution as indicated in Table I.

TABLE I Treatment igg Sample (mun) (Amps'l'sq' l6 3. 18. 6 17 and 18 5 9. 2

Each sample contact was weighed after treatment to determine iodine pickup and the film weight determined by rapid solution in sodium cyanide. The composition of the films, i. e., the relative proportion of silver iodide and mercurous iodide was calculated by dividing the film Weight by the iodine pickup to obtain a factor. This factor for pure silver iodide is El I or 1.85 and for pure mercurous iodide is ll l I or 2.58. On the proper assumption that the films contain only iodides, any mixture of silver and mercury iodide has a factor between the two above, and is indicative of film composition by the inverse lever law.

The composition of the iodide films obtained on the above-described samples are set forth in Table II.

TABLE II Per- Perm ms. Milligrams Film s Samples Factor cent cent HgI I plckup Agl HgI formed 1 and 21 29. 85 62. 85 2. 1 65 22. 0 3 and 4- l 48. 85 98. 8 2. 02 77 23 22. 8 5 and. 6- 68. 85 136 1. 975 83 17 23. 0 7 and 8 31.05 61.25 1.975 83 17 10. 5 9 and 10..- 65. 7 126.1 1.92 90. 5 9. 5 12.1 11 and12.. 103. 6 197. 1.90 93 7.0 13. 8 13 30 58,6 1.95 86 14 8.2 1 1 23. 2 49. 4 2. 12 63 37 18. 2 15and16. 123 220 1.79 100 0.0 0.0 17andl8 68.7 130.5 1.9 93 7 9 From the data of Tables I and II, it is apparent that the composition of the iodide film is a function of (a) the current density and (b) the time of treatment and can be controlled by current density or time of treatment or both. The results obtained with samples 15 and 16 show that no I-IgI can be obtained at current densities of 15 amperes per square foot or higher even when the silver amalgam surface contains a substantial amount of mercury.

The high resistance to sulfide formation of two iodized silver amalgams as compared with an untreated silver surface and an iodized silver surface and the desirability of having an iodide film comparatively rich in mercurous iodide is shown by a series of tests on sample contacts treated as shown in Table III.

Samples 1 and 2 were pure silver blanks, 3 and 4 were treated to have a relatively HgI rich film, 5 and 6 were treated to have a relatively AgI rich film, and '7 and 8 were 100% Ag]: films. Each sample was exposed to 125 cc. of oil containing 30 milligrams available sulfur (.03% S), and the test continued for 980 hours at 60 C. After 500 hours, portions of the silver sulfide growing on the surface of the AgI film (7 and 8) were dislodged in degreasing, handling and weighing these samples so the further tests on these samples were meaningless. The increase in weight of the various sample contacts as a result of sulfide formation that is the weight of sulfur picked up out of a total of 30 mg. available sulfur, are given in Table IV.

TABLE IV Sulfur pickup (mg.) after exposure time (hours) samples m 33. 35?. its. $2.

1 and 2 (ave.) "mg" 28. 4 28.8 29. 3 29. 3 29. 3 d 4 0.0 0.0 0. 25 1. 6 1o. 0 0.85 3. 0 3.80 3. 75 12. 6 1. 45 2.85 24. 2 15. 20 14. s

From these results it is seen that the iodide films on the silver mercury alloys afford excellent protection against sulfiding types of corrosion even under the highly accelerated conditions of the test. It is also evident that the best protection is noted with the iodide films comparatively rich in mercurous iodide so that accordingly, it is desirable to employ contacts in which the iodide films comprise at least 15 percent mercurous iodide.

The contact resistances of the iodide coated silver-amalgam contacts are comparatively low as shown by the following test results on various oil-immersed cooperating in. rounded contacts operating at 80 C. and 20 pound contact pressure and a current of amperes A. C.

As compared with the straight silver iodide coated contacts, the contacts of the present invention have surfaces which are much less porous or more dense probably due to the mercury impregnating the silver surface or to the mercury iodide formed upon iodization.

While the invention has been specifically described with reference to the use of a potassium iodide solution for forming the iodide surface film, it is of course not limited thereto. For example, any suitable iodide such as a solution of sodium iodide may be substituted for the potassium iodide. Alternatively, while a longer exposure time will be required, satisfactory iodide films rich in HgI can also be formed merely by immersion of the silver amalgam contact in a solution of iodine, for example, in carbon tetrachloride.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A switch contact comprising a high conductivity metal base, and a coatin of a silverrich silver-mercury alloy containing from 5 to 25 per cent mercury the surface of which is composed of silver and mercury iodide, the mercury iodide comprising at least 5 percent by weight of the combined iodide components of the surface.

2. An oil-immersed switch contact havin a coating of silver containing from 5 to 25 percent mercury, the silver and mercury at the surface of said coating being substantially in the form of silver iodide and mercury iodide.

3. An oil-immersed switch contact having a coating of a silver amalgam containing about percent mercury, the surface of said coating comprising essentially silver iodide and mercury iodide with the mercury iodide comprising about 35 percent of the iodide content of the surface.

4. The method of making an electrical contact resistant to corrosion by sulfur which comprises providing a copper base with a layer of silver having a thickness of from about to 5 mils, electroplating a layer of mercury 0n the silver layer such that on difiusion of the mercury into the silver layer there is obtained a silver-mercury layer containing about 10 percent mercury, making the resultant product the anode in a dilute aqueous solution of an alkali metal iodide and passing current through said solution and anode of a current density less than 10 amps/sq. ft. for a time sufiicient to form on the surface of the silver-mercury layer a film comprisin silver iodide and mercury iodide in which the mercurous iodide comprises from 5 to percent of the total amount of iodides in said film.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 26,978 Edwards Jan. 31, 1860 1,602,595 Sheppard et al. Oct. 12, 1926 1,720,216 Gray et al. July 9, 1926 1,758,293 Murray May 13, 1930 1,860,505 Jones May 31, 1932 2,116,215 Ruben May'3, 1938 2,195,231 Weder Mar. 26, 1940 2,281,446 Laise Apr. 28, 1942 2,430,468 Julich et al. Nov. 11, 1947 2,469,878 Hannon et al May 10, 1949 2,583,581 Lukens Jan, 9, 1952 OTHER REFERENCES Silver in Industry, by Addicks (1940), page 310.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US26978 *Jan 31, 1860 Process for coloring the surface of metals
US1602595 *Feb 27, 1926Oct 12, 1926Eastman Kodak CoElectrolytical process of preparing silver halides from metallic silver
US1720216 *Nov 5, 1923Jul 9, 1929Oneida Community LtdTarnish-resisting silver plate and process for producing same
US1759293 *Sep 25, 1928May 20, 1930Barrett Joseph ODoor or gate operating mechanism
US1860505 *Nov 2, 1928May 31, 1932Parker Rust Proof CoPreparation of surfaces for coating
US2116215 *Jul 23, 1937May 3, 1938Samuel RubenElectrical switch
US2195231 *Sep 22, 1937Mar 26, 1940Gen ElectricArt of coating metals
US2281446 *Jan 7, 1937Apr 28, 1942Callite Tungsten CorpElectrical contact
US2430468 *Nov 8, 1943Nov 11, 1947Bell Telephone Labor IncElectroplating silver on aluminum and its alloys
US2469878 *Jun 23, 1945May 10, 1949Gen ElectricSwitch contact
US2583581 *Jul 1, 1947Jan 29, 1952Lukens Hiram SMetal coating
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2796495 *Dec 23, 1953Jun 18, 1957Baker & Co IncElectrical contact elements
US2917817 *Jan 17, 1956Dec 22, 1959Res Council Of IsraelReceiver for solar energy collectors
US3155804 *Mar 26, 1962Nov 3, 1964Solid States Systems IncMercury amalgam electrical contacts
US3576415 *Oct 26, 1967Apr 27, 1971Textron IncElectrical contact surface plate having a mercury amalgam
US7575665 *Apr 28, 2005Aug 18, 2009Delphi Technologies, Inc.Method of reducing corrosion of silver containing surfaces
US20060246313 *Apr 28, 2005Nov 2, 2006Delphi Technologies, Inc.Method of reducing corrosion of silver containing surfaces
U.S. Classification200/267, 205/171, 205/228, 200/266
International ClassificationH01H1/023, H01H1/02
Cooperative ClassificationH01H1/023
European ClassificationH01H1/023