US 3650825 A
Contact elements are made by amalgamating copper or silver contact pieces through thermal treatment with mercury. Subsequently a different amalgam, e.g., lead, thallium, or preferably, indium amalgam is deposited thereon, rubbed in and thinned.
Description (OCR text may contain errors)
United States Patent Lihl 5] Mar. 21, 1972  METHOD FOR MANUFACTURE OF AN 3,007,994 11/1961 Urry ..117/227 x ELECTRICAL CONTACT 3,179,575 4/1965 Dippel et al.... ..117/217 x  Inventor: Franz Um, Vienna, Austria 3,497,377 2/1970 Allmgham ..117/107 X  Assignee: Schaltbau GmbH, Munich, Germany P i E i -Ral h S, Kendall 2 Filed: June 9 1969 Assistant ExaminerC. K. Weiffenbach Attorney-Smyth, Roston & Pavitt  Appl. No.: 834,839
 ABSTRACT  U.S.Cl ..117/217, 29/199,29/589,
1 17] M 117/227, 1 17030 317/234 L Contact elements are made by amalgamatmg copper or silver  Int Cl 844d 1/14 844d 1/18 contact pieces through thermal treatment w1th mercury. Sub- 581 Field of Search ..148/6.14; 1 17/217, 213, 227, Sequemly dlfferem amalgam, '8 lead thalllum 117/230, 71 M; 317/234 L; 29/289, 590, 199 preferably, indium amalgam is deposited thereon, rubbed in and thinned.
 References Cited 18 Claims, 1 Drawlng F rgure UNITED STATES PATENTS 5 I Saller et al 1 l7/71 X METHOD FOR MANUFACTURE OF AN ELECTRICAL CONTACT The present invention relates to electrical contact elements, and more particularly the invention relates to an improved electrical contact element and method for making such element by layering known contact material, such as silver or copper, and using mercury so that the silver or copper surface obtains particular electrical properties which are of particular advantage if such a surface is used for contact making.
It is known generally to make contact elements from particular alloys or intermetallic compounds. The known materials, however, are often rather expensive, or they are usable only for contacts employed in a particular manner, or they have insufficient life. No known solid contact has electric properties which are as advantageous as those of mercury. Of course, mercury has the very important disadvantage that it is normally in the liquid state, particularly for temperatures as they occur usually in electrical equipment, or inthe environment thereof. Therefore, mercury can be used only in enclosed containers which must have a particular orientation in order to operate normally.
The present invention has as a particular object, the providing of a solid electric contact which combines useful properties of conventional solid contact material with useful properties of mercury. In particular, as stated above, a contact layer is to be provided on the surface of a copper or silver element to be used as contact piece, and the method is characterized by the following features. The copper or silver surfaces are prepared at first in that, for example, atleast the particular surface portion to be treated subsequently is cleaned. Next, the cleaned surface is brought into contact with mercury for a considerable period of time, up to 100 hours, and at an elevated temperature such as 60l00 C.; preferably 70 C. The mercury employed for this treatment has been cleaned previously, preferably, it has been distilled. Subsequently, preferably after an extensive period of storage, the thus treated surfaces are cleaned again, and a mercury alloy is deposited thereon, using thallium'amalgam or lead amalgam, but preferably indium amalgam is employed.
Therefore, the inventive method is comprised of essentially two basic steps; in the first step, the copper, or better, the silver contact element, is amalgamated on its surface, as respectively a copper or silver amalgam layer is formed as a result of extensive thermal treatment in contact with clean mercury. The strength and uniformity of that layer depends on the duration of the treatment and the temperature which is maintained. Tests have shown that, for example, copper, when treated thermally over 400 hours at 18 C. in contact with mercury, forms an amalgam of 0.1 mm. thickness. However, a layer of similar thickness may be produced in 100 hours if a temperature of 70 C. is used. Additionally it has been observed that for a higher temperature the initial amalgam layer forms more uniformly and is, therefore, better. Silver, when treated with mercury, over 400 hours at 18 C., as described, will form a layer of 0.02 through 0.03 mm. thickness. However, if treated for 100 hours only at 70 C., again a more uniform layer of slightly less than 0.01 mm. thickness is obtained.
A subsequent period of storage, for, example, of 2,000 hours, serves primarily for permitting the previously produced amalgam layer to harden. It has been observed, and this is the reason for preferring silver as contact material, that a silver amalgam layer is less coarse by a factor of 10 than a copper amalgam layer. In the second principal step succeeding the storage period, additionalamalgam is deposited onto the initial amalgam layer using, as has been stated above, a mercury alloy of indium, thallium, or lead. The second step can include several depositing steps using different amalgams.
It has been observed that a contact element made in accordance with the method of the invention has the advantage that excellent electric characteristics and properties are maintained in use for a long period of time. The initial amalgamation of a silver or copper surface already establishes good electric properties which, however, decay as time passes, because progressive diffusion of the mercury into the contact carrier depletes the surface layer. The mercury is dissolved progressively in the interior of. the contact carrier, so that for all practicalpurposes the mercury simply vanishes from the contact making surface. However, the subsequently deposited amalgam inaccordance with the second step establishes a kind of barrier layer within the initialsilver or copper amalgam which, in turn, preventsa reaction of the initial amalgam, i.e., a reaction of the mercury of the initial layer or at least migration of mercury into the interior of the contact carrier material and reaction therewith. is at least considerably delayed. The effect of the barrier can be enhanced in accordance with an additional feature of the invention, in that the mercury treated surface of the contact carrier material, after the first principal step, is thermally treated additionally prior to depositing the second amalgam thereon, using temperature within the range of 60 to 100 C.
The concentration of mercury in the mercury alloy deposited in accordance with the second step is selected in accordance with. the expected operating temperature of the completed contact, the. selection following the rule that for an expected higher operating temperature the mercury content in the mercury alloy deposited in accordance with the second step is lower than for a lower operating temperature.
The two essential steps in accordance with the invention are preceded by more elaborate preparations in that the yet untreated surface of the carrier material is polished and/or abraded first. Subsequently that surface is cleaned with the mixture of different alcohols, for example, a mixture of acetone and n-pentane. The last two mentioned chemicals can also be used for cleaning required subsequent to the first and prior to the second step. However, other organic solvents can be used likewise for cleaning.
in accordance with an additional feature of the invention, it is suggested to provide the second amalgam layer with a higher mercury content than desired finally. A solid piece of the metal which is part of the amalgam is employed for rubbing the second layer into the surface of the carrier. The second step thus includes a depositing step and a subsequent particular working in of the deposit. It was found that the relative content of that metal in the amalgam layer is, in fact, increased so that there is a relative reduction in the mercury concentration. This has the advantage of working the layer into the carrier without concurrently forcing impurities from a tool into the material. The tool employed for rubbing is made of that alloy metal. The amalgam layer provided in accordance with the second step may additionally be reduced in thickness by a polishing, abrading, or any other suitable thinning process so that its total thickness is just sufficient to as sure presence of an uninterrupted, contiguous layer.
In the following an example for practicing the invention shall be disclosed using more specific data. A silver body of extreme purity is chosen as carrier which is first ground and polished and then cleaned in a mixture of alcohols. lndependently therefrom a quantity of mercury is cleaned by distillation. In accordance with the first step the polished and cleaned silver surface is brought into contact with the cleaned mercury. Mercury and silver are heated to C. and maintained at that temperature and in intimate contact with each other for 100 hours. A thin silver amalgam layer forms during that period in the surface of the silver body as exposed to mercury.
Subsequently, the silver body is stored and exposed to air for curing, for example, for a period of about 500 hours. This means that for that period of time the initial silver mercury layer is exposed for hardening. Subsequently, the layer is cleaned very carefully by means of organic solvents. Thereafter, an indium mercury alloy, i.e., an indium amalgam is deposited upon the initial silver amalgam layer using 60 percent indium. After depositing the layer, a piece of metallic indium is used to rub the indium amalgam into the surface of the silver amalgam. As a consequence, the relative percentage of indium is increased up to percent. The layer produced in the second layering step, even after rubbing, has a pasty consistency. However, a cut glass edge is used to polish this amalgam surface, i.e., that surface layer is thinned so that in effect the indium amalgam is largely disposed in indentations in the silver amalgam.
lt was found now that the contact resistance of a contact piece made in accordance with that example was 11.76 milliohms mm. independent from contact pressure up to 0.02 kilograms (weight) per square millimeter. These values have been determined experimentally, 10 hours after the manufacturing of such a contact element and at a temperature of 20 C. The thus completed contact surface was then exposed to air for 1,000 hours, and it was observed that the critical contact pressure increased up to 0.04 milliohm mm. A further reduction in the critical contact pressure and of the contact resistance was obtained by depositing upon the carrier additionally a liquid indium amalgam at 0.05 to 0.1 mm. layer thickness. The mercury content of that additional layer was particularly high and the critical contact pressure was found to drop below 0.01 kilogram (weight) per square millimeter and the resistance dropped to 1 1.6 milliohm mmf".
As part of the invention, an electric contact is illustrated in the appended drawing.
1n the drawing there is a contact 10 having copper or preferably silver as carrier metal 11; a contact surface region 12 is provided which includes a copper or silver amalgam layer 13 and carrying one or several layers 14 of an indium and/or thallium and/or lead amalgam with indium amalgam being preferred.
The invention is not limited to the embodiments described above, but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be included.
1. Method of making an electrical contact using copper or silver as a carrier comprising the steps of:
first, cleaning the surface or a portion of the surface of the carrier;
second, exposing the surface or a portion thereof to mercury for a period of time and at a temperature sufficient, to obtain a copper or silver amalgam surface layer;
third, storing for a period of time the thus treated carrier sufficient to harden said amalgam surface layer;
fourth, cleaning the surface or the portion of the surface of carrier which was exposed to mercury in accordance with the second step; and
fifth, depositing on the surface layer an amalgam, the nonmercury component of said amalgam selected from the group which consists ofindium, thallium or lead.
2. Method as set forth in claim 1 including the step subsequent to the second step but preceding the fifth step oftreating the carrier thermally at a temperature of 60-100C.
3. Method as set forth in claim 1 wherein the carrier is silver and the amalgam of the fifth step is an indium amalgam, the method including the additional step, subsequent to the fifth step of depositing a liquid indium amalgam layer upon the layer formed during the fifth step.
4. Method as set forth in claim 1, the first step including abrading or polishing of the surface and cleaning up treatment of the surface with a mixture of acetone and n-pentane.
5. Method as set forth in claim 1, the fourth step including cleaning with an organic solvent.
6. Method as set forth in claim 1, the fifth step including working the amalgam into the carrier using a piece of the same metal of which the alloy is formed, thereby reducing the mercury content in the resulting layer.
7. Method as set forth in claim 1 including the step, succeeding the fifth step, of removing part of the amalgam deposited by polishing or abrading.
8. The method as set forth in claim 1, the second step lasting for about hours, the temperature for the second step being chosen from within the range of 60 to 100 C.
9. The method as set forth in claim 8, the temperature for the second step being 70 C. I
10. Method as in claim 8, the storing step including exposure of the thus treated carrier to air for up to about 2,000 hours.
11. Method of making an electrical contact element comprising the steps of forming a first copper or silver amalgam layer in the surface of a copper or silver carrier integral therewith;
and depositing at least one second layer of an amalgam on the first layer, the non-mercury component of the amalgam of said second layer selected from the group consisting of indium, thallium and lead.
12. The method as set forth in claim 11, a first amalgam layer being formed by treating copper or silver with mercury at a temperature of 60 to 100 C., the steps providing the second layer comprising depositing of at least one of indium, thallium and lead amalgam onto the first formed layer, rubbing the deposited amalgam into the first formed layer, using a piece of non-mercury metal of the same type as the non-mercury component in the deposited amalgam, to increase the content of that metal in the deposited amalgam, and further including abrading part of the deposited amalgam.
13. The method as in claim 12, there being a period of storage between the first layer forming and the second layer depositing step sufficient to obtain hardening of the first layer.
14. The method as in claim 13, each of the first layer forming and of the second layer depositing step being preceded by cleaning the surface subjected to layer forming or depositing, by an organic solvent.
15. The method as in claim 14, including the subsequent depositing of a third layer of a liquid indium amalgam on said second layer with a mercury content higher than used for the providing of the second layer.
16. The method as in claim 15, the third layer provided at a thickness of about 0.05 to 0.1 mm.
17. Method of making an electrical contact element comprising the steps of:
exposing a copper or silver contact to mercury for a period of time and at a temperature so that a first amalgam layer results from the exposure having thickness in the order of one-hundredths ofa millimeter;
causing the first amalgam layer to harden for a period of time up to 2,000 hours; and
depositing at least one second layer of an amalgam on the first copper or silver amalgam layer with indium, thallium or lead as the non-mercury component of said second layer.
18. Method as in claim 17, the exposure of the copper or silver contact to mercury carried out at temperatures between 60 to 100 C. for a period up to about 100 hours.