US2247755A - Electric contact - Google Patents
Electric contact Download PDFInfo
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- US2247755A US2247755A US317135A US31713540A US2247755A US 2247755 A US2247755 A US 2247755A US 317135 A US317135 A US 317135A US 31713540 A US31713540 A US 31713540A US 2247755 A US2247755 A US 2247755A
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- Prior art keywords
- contact
- rhodium
- metal
- tungsten
- contacts
- Prior art date
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Links
- 229910052703 rhodium Inorganic materials 0.000 description 28
- 239000010948 rhodium Substances 0.000 description 28
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 28
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 22
- 229910052721 tungsten Inorganic materials 0.000 description 22
- 239000010937 tungsten Substances 0.000 description 22
- 229910052751 metal Inorganic materials 0.000 description 18
- 239000002184 metal Substances 0.000 description 18
- 239000003870 refractory metal Substances 0.000 description 17
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 14
- 229910052750 molybdenum Inorganic materials 0.000 description 13
- 239000011733 molybdenum Substances 0.000 description 13
- 238000000034 method Methods 0.000 description 11
- 239000010410 layer Substances 0.000 description 10
- 239000000463 material Substances 0.000 description 9
- 238000009792 diffusion process Methods 0.000 description 8
- 238000010438 heat treatment Methods 0.000 description 7
- 238000007747 plating Methods 0.000 description 4
- 239000002344 surface layer Substances 0.000 description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 2
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical class [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 2
- 239000000853 adhesive Substances 0.000 description 2
- 230000001070 adhesive effect Effects 0.000 description 2
- 239000010953 base metal Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 208000037309 Hypomyelination of early myelinating structures Diseases 0.000 description 1
- 229910001260 Pt alloy Inorganic materials 0.000 description 1
- 239000005864 Sulphur Substances 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 230000001464 adherent effect Effects 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 150000001805 chlorine compounds Chemical class 0.000 description 1
- 239000011247 coating layer Substances 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000001652 electrophoretic deposition Methods 0.000 description 1
- 238000009713 electroplating Methods 0.000 description 1
- 150000004694 iodide salts Chemical class 0.000 description 1
- 229910052741 iridium Inorganic materials 0.000 description 1
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 description 1
- 150000002736 metal compounds Chemical class 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- PXXKQOPKNFECSZ-UHFFFAOYSA-N platinum rhodium Chemical compound [Rh].[Pt] PXXKQOPKNFECSZ-UHFFFAOYSA-N 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 239000001488 sodium phosphate Substances 0.000 description 1
- 238000004901 spalling Methods 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- RYFMWSXOAZQYPI-UHFFFAOYSA-K trisodium phosphate Chemical compound [Na+].[Na+].[Na+].[O-]P([O-])([O-])=O RYFMWSXOAZQYPI-UHFFFAOYSA-K 0.000 description 1
- 229910000406 trisodium phosphate Inorganic materials 0.000 description 1
- 235000019801 trisodium phosphate Nutrition 0.000 description 1
- 239000003039 volatile agent Substances 0.000 description 1
- 239000004636 vulcanized rubber Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Images
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H1/00—Contacts
- H01H1/02—Contacts characterised by the material thereof
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S428/00—Stock material or miscellaneous articles
- Y10S428/922—Static electricity metal bleed-off metallic stock
- Y10S428/9265—Special properties
- Y10S428/929—Electrical contact feature
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S428/00—Stock material or miscellaneous articles
- Y10S428/922—Static electricity metal bleed-off metallic stock
- Y10S428/9335—Product by special process
- Y10S428/934—Electrical process
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S428/00—Stock material or miscellaneous articles
- Y10S428/922—Static electricity metal bleed-off metallic stock
- Y10S428/9335—Product by special process
- Y10S428/937—Sprayed metal
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S428/00—Stock material or miscellaneous articles
- Y10S428/922—Static electricity metal bleed-off metallic stock
- Y10S428/9335—Product by special process
- Y10S428/94—Pressure bonding, e.g. explosive
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S428/00—Stock material or miscellaneous articles
- Y10S428/922—Static electricity metal bleed-off metallic stock
- Y10S428/9335—Product by special process
- Y10S428/941—Solid state alloying, e.g. diffusion, to disappearance of an original layer
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/12—All metal or with adjacent metals
- Y10T428/12458—All metal or with adjacent metals having composition, density, or hardness gradient
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/12—All metal or with adjacent metals
- Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
- Y10T428/12771—Transition metal-base component
- Y10T428/12806—Refractory [Group IVB, VB, or VIB] metal-base component
- Y10T428/12812—Diverse refractory group metal-base components: alternative to or next to each other
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/12—All metal or with adjacent metals
- Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
- Y10T428/12771—Transition metal-base component
- Y10T428/12806—Refractory [Group IVB, VB, or VIB] metal-base component
- Y10T428/12826—Group VIB metal-base component
- Y10T428/12833—Alternative to or next to each other
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/12—All metal or with adjacent metals
- Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
- Y10T428/12771—Transition metal-base component
- Y10T428/12861—Group VIII or IB metal-base component
- Y10T428/12875—Platinum group metal-base component
Definitions
- This invention relates to electric make-andbreak contacts of refractory metals.
- An object of the invention is to improve electric contacts.
- the present invention comprises the combination of elements, methods of manufacture, and the product thereof brought out vand exemplied in the disclosure hereinafter set forth, the scope of the invention being indicated in the appended claims.
- FIG. 1 is a side view of an electric contact disc embodying features of the invention.
- Figure 2 is Ia cross-section of the contact.
- the present invention contemplates an electric contact having a. body of refractory metal such as tungsten, molybdenum and thelike and a contacting surface of a hard metal of improved contact characteristics such as rhodium.
- contact surface metal is preferably diffused into the refractory body at the junction
- Tungsten contacts have been extensively used heretofore and have given relatively good service in contact applications where substantial contact pressures are available.
- tungsten contacts have not .been entirely satisfactory for operation at low contact pressures due to objectionable metal transfer and the tendency of the material to become oxidized. This results in high contact resistance at low pressures and often causes erratic operation. For this reason the use of tungsten contacts in sensitive meters and. recording equipment, telephone circuits and similar systems has generally been unsatisfactory due to the-objectionable high resistance and to the production of microphonic noises in the circuits.
- Standard tungsten contacts .capable of operat-v ing at current values of from 1 to 10 milliamperes at from 1/2 to 6 volts and atpressures of from 60 to 150 grams are usually found to havel contact resistance values between the contact pair of from .5 to 3 milliohms under these conditions. Under low contact pressure conditions, however, such as under pressures' from a fraction vof a gram to 5 grams, such contacts will have contact resistance in the magnitude of from 50 to 300 milliohms. Such resistances are often objectionably high in the circuits of sensitive or selective equipment and where low voltages are used.
- contacts of tungsten or molbydenum can be improved greatly and made available for low pressure and low .voltage contact operation by applying a relatively thin surface of rhodium to the contact and preferably by diffusing the rhodium into the contact material a certain amount. The diffusion greatly improves the bond between the two metals and prevents separation or spalling on of the surface material.
- Rhodium may be applied in any one of several ways, the most important of which are described below:
- tungsten -or molybdenum disc may be plated with a. layer of rhodium by a process briefly as follows: v
- the refractory'metal disc is electrochemically cleaned in a solution of sodium hydroxide and tri sodium phosphate, followed by rinsing in 10% aqueous hydrochloric acid, followed by a rinse in hot Water.
- the discs are then plated in a standard acid rhodium plating bath sufficient to give 2 lgrams of rhodium per liter, current densities of approximately 50 amperes persquare foot being used.
- the plated contact may be subjected to a diffusion process to obtain partial diffusion of the rhodium into the underlying tungsten or molybdenum.
- a diffusion process to obtain partial diffusion of the rhodium into the underlying tungsten or molybdenum. 4
- the simplest and preferred method of obtaining such diiusion is by the application of external heat.
- the plated contact disc may be placed in a furnace in a reducing atmosphere.
- the rate above are even moreV and degree of diffusion will, of course, depend on the time, temperature, composition and thickness of the layer to be diffused. 'Ihe temperature can be varied from 750 to 1950" C. depending upon the condition of the surface to which the plate is applied and the extent of diffusion desired.
- the diffusion is preferably carried to a point where the rhodium diffuses into the backing metal a small distance, such as .0005 to .010".
- a thin layer of substantially pure rhodium at the outer surface which layer may have a thickness in the order of .0001 to .0002" although greater thicknesses are also possible by the process.
- the composition gradually changes from substantially pure rhodium at y the surface to pure tungsten or molybdenum at a short depth below the surface, the composition in the intervening region varying with the depth below the surface.
- the refractory metal disc is first plated with an extremely thin layer of rhodium, after which the heat treatment is applied to produce partial or complete diffusion into the refractory metal.
- the plating process is then repeated to apply an additional layer of rhodium and further diffusion is produced by heating. This sequence may be repeated several times until the desired thickness is built up.
- a surface layer consisting of an alloy formed predominantly of rhodium and containing relatively lesser amounts of elements such as palladium, platinum and iridium it is also possible to apply a surface layer consisting of an alloy formed predominantly of rhodium and containing relatively lesser amounts of elements such as palladium, platinum and iridium.
- Several ways of accomplishing this have been found feasible. It is possible for instance to provide a surface consisting of a rhodium-platinum alloy by electroplating the refractory metal contact base first with a thin layer of one of the elements and then a thin layer of the other and then applying a heat treatment to cause diusion of the two plated layers into each other and at the same time into the refractory base material.
- a heat treatment to cause diusion of the two plated layers into each other and at the same time into the refractory base material.
- platngs may ⁇ be individually applied interspersed with heat treatments.
- Methodsl other than plating can be used to apply the contact surface metal to the refractory base.
- the surface layer can be applied by cathode sputtering, metal spraying or by condensing evaporated metal onto the surface.
- Other methods involve the deposition of the surface metal in finely divided form onto the refractory metal surface followed by heat treatment to produce a diffused surface layer.
- the metal may be deposited from colloidal suspensions of the finely divided metal either by a settling process or by electrophoretic deposition.
- the refractory metal surface may likewise be coated with a dispersable adhesive and the powder metal dusted or sprayed onto the surface, after which the heat treatment is applied to disperse the adhesive and diffuse the coating layer into the surface.
- the metal may also be applied as a paste containing the metallic powders which is printed onto the contact surface. 'Ihe finely powdered coating metal can also be pressed into the surface in a suitable press.
- a metal compound such as metallic oxide or a volatile compound of rhodium such as the chlorides, borides or iodides may .be used.
- the oxide the compound is reduced by heating in a reducing atmosphere leaving the coating on the surface.
- a reaction with the contact material backing takes place forming a strong adherent bond of the desired thickness.
- a diffused layer of rhodium on a tungsten surface has been found to have an extremely high hardness and high resistance to corrosion.
- the hardness of rhodium matches closely the hardness of tungsten and tungsten ls therefore an ideal base metal.
- the base metal may be in the form of rivets, strip, screws, wire or any other suitable form.
- the diffused rhodium surface layer appears practically unattackable by corrosive atmospheres at ordinary temperatures.
- the contacts are also relatively free from electrolytic disintegration which is often encountered in contacts of the prior art.
- Contacts according to the present invention are particularly useful for microphone switches, relay apparatus for automatic locking of elevator gates, automatic safety signals, voice circuit controls in isolated substations, radio and sound reproducing apparatus especially Where the presence of sulphur in vulcanized rubber is liable to produce tarnish on ordinary contacts, communication receivers, sensitive recording meters and automatic telephone contacts.
- the contacts are also useful for many applications Where tropical climates are encountered.
- the contact base material used is preferably dense non-porous tungsten or molybdenum such as is obtained from swaged and heat treated tungsten or molybdenum rod.
- Figure 1 is a side view of a contact having a tungsten or molybdenum body I0, a rhodium surface H and intervening region l2 wherein the rhodium is diffused into the tungsten or molybdenum.
- Figure 2 is a cross-section of the same contact.
- An electric contact having a body formed of a refractory metal and a contact face thereon formed predominantly of rhodium.
- An electric contact having a ⁇ body formed of a refractory metal and a contact face thereon formed predominantly of rhodium, said contact face being integrally bonded to said refractory metal body.
- An electric contact having a body formed of' a. refractory metal and a contact face thereon formed predominantly of rhodium, said contact face being integrally bonded to said refractory metal body and said facing metal being diffused into said refractory body metal.
- An electric contact having a body of refractory metal selected from the group consisting of tungsten and molybdenum and a. contact face thereon formed predominantly of rhodium.
- An electric contact having a body of refractory metal selected from the group consisting of tungsten and molybdenum and a contact face thereon formed predominantly of rhodium, said contact face metal being integrally bonded to and diused into said refractory body.
- An electric contact having a body of refractory metal selected from the group consisting of tungsten and molybdenum and a rhodium ⁇ contact face thereon.
- An electric contact having a body of refractory metal selected from the group consisting of tungsten and molybdenum and a rhodium contact face thereon, said rhodium being integrally bonded to and diffused into said refractory metal body.
Description
July l, 1941" F. R. Hl-:NsE-L :TAL 2,247,755
ELECTRIC CONTACT Filed Fqb'. 3, 1940 FP6/rz R. HEMS'EA ATTORNEY Patented July 1, 1941 2,247,755 f ELECTRIC CONTACT Franz E. Hensel andv Kenneth L. Emmett, In-
dianapolis, Ind., assignors to P. R. Mallory i Co., line., Indianapolis, Ind., a corporation of Delaware Application February 3, 1940, Serial No. 317,135
(Cl. 20G- 166) 8 Claims.
This invention relates to electric make-andbreak contacts of refractory metals.
An object of the invention is to improve electric contacts.
Other objects of the invention will be apparent from the following description taken in connection with the appended claims.
The present invention comprises the combination of elements, methods of manufacture, and the product thereof brought out vand exemplied in the disclosure hereinafter set forth, the scope of the invention being indicated in the appended claims.
lWhile a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made inthe method of procedure and the combination of elements without departing from vthe spirit of the invention.
In the drawing Figure 1 is a side view of an electric contact disc embodying features of the invention; and
Figure 2 is Ia cross-section of the contact.
The present invention contemplates an electric contact having a. body of refractory metal such as tungsten, molybdenum and thelike and a contacting surface of a hard metal of improved contact characteristics such as rhodium. The
contact surface metal is preferably diffused into the refractory body at the junction,
Tungsten contacts have been extensively used heretofore and have given relatively good service in contact applications where substantial contact pressures are available. However, up to the present time tungsten contacts have not .been entirely satisfactory for operation at low contact pressures due to objectionable metal transfer and the tendency of the material to become oxidized. This results in high contact resistance at low pressures and often causes erratic operation. For this reason the use of tungsten contacts in sensitive meters and. recording equipment, telephone circuits and similar systems has generally been unsatisfactory due to the-objectionable high resistance and to the production of microphonic noises in the circuits. The provision of a satisfactory contact material for such applications is extremely difficult due to the low contact pressures encountered and Athe require ment that the contacts operate satisfactorily after long periods of use or non-use. Such 'contacts are also often required to stand up satisfactorily in corrosive atmospheres such as in atmospheres where a certain amount of sulphur compounds are present.
Standard tungsten contacts .capable of operat-v ing at current values of from 1 to 10 milliamperes at from 1/2 to 6 volts and atpressures of from 60 to 150 grams are usually found to havel contact resistance values between the contact pair of from .5 to 3 milliohms under these conditions. Under low contact pressure conditions, however, such as under pressures' from a fraction vof a gram to 5 grams, such contacts will have contact resistance in the magnitude of from 50 to 300 milliohms. Such resistances are often objectionably high in the circuits of sensitive or selective equipment and where low voltages are used.
The objections discussed pronounced with molybdenum contacts.
Applicants have now discovered that contacts of tungsten or molbydenum can be improved greatly and made available for low pressure and low .voltage contact operation by applying a relatively thin surface of rhodium to the contact and preferably by diffusing the rhodium into the contact material a certain amount. The diffusion greatly improves the bond between the two metals and prevents separation or spalling on of the surface material.
According to our preferred method of carrying out the invention a contact disc of tungsten or molybdenum cut from rod or punched from a flat strip of the material is given a thin coating of rhodium on its contact surface. Rhodium may be applied in any one of several ways, the most important of which are described below:
vThe cleaned tungsten -or molybdenum disc may be plated with a. layer of rhodium by a process briefly as follows: v
1. The refractory'metal disc is electrochemically cleaned in a solution of sodium hydroxide and tri sodium phosphate, followed by rinsing in 10% aqueous hydrochloric acid, followed by a rinse in hot Water.
2. The discs are then plated in a standard acid rhodium plating bath sufficient to give 2 lgrams of rhodium per liter, current densities of approximately 50 amperes persquare foot being used.
After plating the plated contact may be subjected to a diffusion process to obtain partial diffusion of the rhodium into the underlying tungsten or molybdenum. 4The simplest and preferred method of obtaining such diiusion is by the application of external heat. For example, the plated contact disc may be placed in a furnace in a reducing atmosphere. The rate above are even moreV and degree of diffusion will, of course, depend on the time, temperature, composition and thickness of the layer to be diffused. 'Ihe temperature can be varied from 750 to 1950" C. depending upon the condition of the surface to which the plate is applied and the extent of diffusion desired. The diffusion is preferably carried to a point where the rhodium diffuses into the backing metal a small distance, such as .0005 to .010". There should remain a thin layer of substantially pure rhodium at the outer surface, which layer may have a thickness in the order of .0001 to .0002" although greater thicknesses are also possible by the process. The composition gradually changes from substantially pure rhodium at y the surface to pure tungsten or molybdenum at a short depth below the surface, the composition in the intervening region varying with the depth below the surface. i
According to a modified method the refractory metal disc is first plated with an extremely thin layer of rhodium, after which the heat treatment is applied to produce partial or complete diffusion into the refractory metal. The plating process is then repeated to apply an additional layer of rhodium and further diffusion is produced by heating. This sequence may be repeated several times until the desired thickness is built up.
In some instances it is also possible to apply a surface layer consisting of an alloy formed predominantly of rhodium and containing relatively lesser amounts of elements such as palladium, platinum and iridium. Several ways of accomplishing this have been found feasible. It is possible for instance to provide a surface consisting of a rhodium-platinum alloy by electroplating the refractory metal contact base first with a thin layer of one of the elements and then a thin layer of the other and then applying a heat treatment to cause diusion of the two plated layers into each other and at the same time into the refractory base material. Here likewise several platngs may `be individually applied interspersed with heat treatments.
Methodsl other than plating can be used to apply the contact surface metal to the refractory base. For example, the surface layer can be applied by cathode sputtering, metal spraying or by condensing evaporated metal onto the surface. Other methods involve the deposition of the surface metal in finely divided form onto the refractory metal surface followed by heat treatment to produce a diffused surface layer. For example, the metal may be deposited from colloidal suspensions of the finely divided metal either by a settling process or by electrophoretic deposition. The refractory metal surface may likewise be coated with a dispersable adhesive and the powder metal dusted or sprayed onto the surface, after which the heat treatment is applied to disperse the adhesive and diffuse the coating layer into the surface. The metal may also be applied as a paste containing the metallic powders which is printed onto the contact surface. 'Ihe finely powdered coating metal can also be pressed into the surface in a suitable press. In some cases a metal compound such as metallic oxide or a volatile compound of rhodium such as the chlorides, borides or iodides may .be used. In the case of the oxide the compound is reduced by heating in a reducing atmosphere leaving the coating on the surface. In the case of the other materials 'a reaction with the contact material backing takes place forming a strong adherent bond of the desired thickness.
A diffused layer of rhodium on a tungsten surface has been found to have an extremely high hardness and high resistance to corrosion. The hardness of rhodium matches closely the hardness of tungsten and tungsten ls therefore an ideal base metal. In addition to contact discs the base metal may be in the form of rivets, strip, screws, wire or any other suitable form.
Negligible wear was observed after-prolonged periods of operation of the contacts, the operation apparently having a desirable polishing effect upon the contact surfaces.
The diffused rhodium surface layer appears practically unattackable by corrosive atmospheres at ordinary temperatures. The contacts are also relatively free from electrolytic disintegration which is often encountered in contacts of the prior art. Contacts according to the present invention are particularly useful for microphone switches, relay apparatus for automatic locking of elevator gates, automatic safety signals, voice circuit controls in isolated substations, radio and sound reproducing apparatus especially Where the presence of sulphur in vulcanized rubber is liable to produce tarnish on ordinary contacts, communication receivers, sensitive recording meters and automatic telephone contacts. The contacts are also useful for many applications Where tropical climates are encountered.
The contact base material used is preferably dense non-porous tungsten or molybdenum such as is obtained from swaged and heat treated tungsten or molybdenum rod.
Referring to the drawing, Figure 1 is a side view of a contact having a tungsten or molybdenum body I0, a rhodium surface H and intervening region l2 wherein the rhodium is diffused into the tungsten or molybdenum. Figure 2 is a cross-section of the same contact.
While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.
What is claimed is:
1. An electric contact having a body formed of a refractory metal and a contact face thereon formed predominantly of rhodium.
2. An electric contact having a `body formed of a refractory metal and a contact face thereon formed predominantly of rhodium, said contact face being integrally bonded to said refractory metal body.
3. An electric contact having a body formed of' a. refractory metal and a contact face thereon formed predominantly of rhodium, said contact face being integrally bonded to said refractory metal body and said facing metal being diffused into said refractory body metal.
4. An electric contact having a body of refractory metal selected from the group consisting of tungsten and molybdenum and a. contact face thereon formed predominantly of rhodium.
5. An electric contact having a body of refractory metal selected from the group consisting of tungsten and molybdenum and a contact face thereon formed predominantly of rhodium, said contact face metal being integrally bonded to and diused into said refractory body.
t 6. An electric contact having a body of refractory metal selected from the group consisting of tungsten and molybdenum and a rhodium` contact face thereon.
7. An electric contact having a body of refractory metal selected from the group consisting of tungsten and molybdenum and a rhodium contact face thereon, said rhodium being integrally bonded to and diffused into said refractory metal body.
tungsten body.
FRANZ R. HENSEL.
KENNETH L. EMLIERT.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US317135A US2247755A (en) | 1940-02-03 | 1940-02-03 | Electric contact |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US317135A US2247755A (en) | 1940-02-03 | 1940-02-03 | Electric contact |
Publications (1)
Publication Number | Publication Date |
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US2247755A true US2247755A (en) | 1941-07-01 |
Family
ID=23232269
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US317135A Expired - Lifetime US2247755A (en) | 1940-02-03 | 1940-02-03 | Electric contact |
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US (1) | US2247755A (en) |
Cited By (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2449078A (en) * | 1943-03-15 | 1948-09-14 | Rca Corp | Commutator apparatus |
US2456761A (en) * | 1947-04-19 | 1948-12-21 | Eitel Mccullough Inc | Rugged cathode |
US2547658A (en) * | 1947-02-24 | 1951-04-03 | Gen Electric | Electric switch contact |
US2874453A (en) * | 1956-11-02 | 1959-02-24 | Westinghouse Electric Corp | Applying metal coatings to molybdenum |
US2952904A (en) * | 1957-01-15 | 1960-09-20 | Westinghouse Electric Corp | Applying protective metal coatings on molybdenum |
US2993678A (en) * | 1955-07-21 | 1961-07-25 | Gen Electric | Coated molybdenum article |
US3063835A (en) * | 1959-06-18 | 1962-11-13 | Union Carbide Corp | Corrosion-resistant alloys |
US3066393A (en) * | 1958-02-17 | 1962-12-04 | Allegheny Ludlum Steel | Metal clad molybdenum article |
US3246980A (en) * | 1964-03-23 | 1966-04-19 | Union Carbide Corp | Corrosion-resistant alloys |
US3522974A (en) * | 1968-06-20 | 1970-08-04 | Stephanois Rech Mec | Friction pair adapted to operate without lubrication |
US3713901A (en) * | 1970-04-20 | 1973-01-30 | Trw Inc | Oxidation resistant refractory alloys |
US20080274372A1 (en) * | 2005-06-15 | 2008-11-06 | Danfoss A/S | Corrosion Resistant Object Having an Outer Layer of a Precious Metal |
-
1940
- 1940-02-03 US US317135A patent/US2247755A/en not_active Expired - Lifetime
Cited By (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2449078A (en) * | 1943-03-15 | 1948-09-14 | Rca Corp | Commutator apparatus |
US2547658A (en) * | 1947-02-24 | 1951-04-03 | Gen Electric | Electric switch contact |
US2456761A (en) * | 1947-04-19 | 1948-12-21 | Eitel Mccullough Inc | Rugged cathode |
US2993678A (en) * | 1955-07-21 | 1961-07-25 | Gen Electric | Coated molybdenum article |
US2874453A (en) * | 1956-11-02 | 1959-02-24 | Westinghouse Electric Corp | Applying metal coatings to molybdenum |
US2952904A (en) * | 1957-01-15 | 1960-09-20 | Westinghouse Electric Corp | Applying protective metal coatings on molybdenum |
US3066393A (en) * | 1958-02-17 | 1962-12-04 | Allegheny Ludlum Steel | Metal clad molybdenum article |
US3063835A (en) * | 1959-06-18 | 1962-11-13 | Union Carbide Corp | Corrosion-resistant alloys |
US3246980A (en) * | 1964-03-23 | 1966-04-19 | Union Carbide Corp | Corrosion-resistant alloys |
US3522974A (en) * | 1968-06-20 | 1970-08-04 | Stephanois Rech Mec | Friction pair adapted to operate without lubrication |
US3713901A (en) * | 1970-04-20 | 1973-01-30 | Trw Inc | Oxidation resistant refractory alloys |
US20080274372A1 (en) * | 2005-06-15 | 2008-11-06 | Danfoss A/S | Corrosion Resistant Object Having an Outer Layer of a Precious Metal |
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