US2547536A - Formation of a surface easily - Google Patents

Description

Patented Apr. 3, 1951 FORMATION OF A SURFACE EASILY WETTABLE BY MERCURY Charles E. Pollard, Jr., Hohokus, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York No Drawing. Application June 10, 1948,

Serial No. 32,262

8 Claims. (Cl. 148-635) This invention relates to a method of formin a surface on solid ferrous material to which mercury will readily adhere.

It is well recognized that mercury has certain advantages over solid contacts for opening and closing electric circuits. Being a fluid, it presents a fresh surface for each contact closure and does not become corroded and pitted as a result of successive circuit interruptions. On the other hand, solid contacts have certain advantages. They can be made of materials that are lighter than mercury and can be moved at higher speeds. Also it is possible to apply the forces of a magnetic field more directly to solid contact-operating elements than to a mass of mercury for effecting the desired circuit closures and open- Accordingly it is common practice in the manufacture of switches and relay contacts to employ solid contact-operating elements and to provide means fOr covering the solid elements with a thin liquid coating of mercury.

It is common practice to coat the solid elements with a suitable material, such as platinum, nickel or copper, so as to augment the adhesion of mercury to the solid elements. Ordinarily one or more capillary channels are provided to carry the mercury from a reservoir to the solid elements.

It is an object of this invention to provide an improved method for conditioning a ferrous element so that a thin coating of mercury will readily adhere to the surface of the element. A further object is to provide an improved method of forming capillary channels in the surface of an alloy of iron.

In order to form capillary channels in the surface of an element made of an alloy of iron, large crystals are formed in the alloy by a suitable heat treatment, and then the substance between the crystals which appear on the surface of the member is partially removed by etching or sandblasting.

For 45Ni.55Fe and 52Ni.48Fe Permalloys satisfactory results have been obtained by heating the Permalloy in wet hydrogen at a temperature of about 1000 C. for 90 minutes. The metal is then cooled in the wet hydrogen atmosphere, and the cooling time is not critical. Times of 10 minutes to 2 hours have given satisfactory results. A hydrogen atmosphere is employed so as to minimize oxidation of the metaland keep it clean. The Permalloy is then etched'forabout '7 minutes in a mixture of equal parts of concentrated (38 per cent) hydrochloric acidand a saturated solution of copper sulfate. The solution is agitated during the etching process. The Permalloy is then washed, first in distilled water, then in alcohol, and. then dried in air. On the resulting surface the crystals are easily visible, having dimensions ranging from 0.001 inch to 0.002 inch, and the channels between them are well defined.

Instead of etching, sandblasting may be employed to form channels between the crystals. In this case the Permalloy is subjected to the heat treatment and then sandblasted until the channels become well defined, and then it is washed in distilled water and dried in air.

It should be noted that modifications of the optimum temperature and times indicated above will be required for alloys of iron difiering in chemical composition from those described.

In order to condition the Permalloy elements so that a thin coating of mercury will readily adhere to the surface of the element, the Permallo is subjected to an oxidation-reduction treatment. The surface of the element is oxidized and then the layer of OXide is reduced so that the resulting surface is porous and contains numerous small capillary channels. The surface is oxidized by heating the Permalloy in air to a temperature of about 700 C. and maintaining the Permalloy at this temperature for about 10 minutes. The surface is then reduced by changing the atmosphere from air to wet hydrogen and maintaining the temperature of the Permalloy at about 700 C. for about 30 minutes. The Permalloy is cooled in the wet hydrogen atmosphere, and the coolin time is not critical. A clean porous surface results, and in order to wet the surface for the first time the Permalloy is placed in a chamber containing mercury and a non-oxidizing gas such as hydrogen and then heated to a temperature or" about 400 C. for about minutes. During the latter activation process the substances are subjected to mechanical agitation in order to insure contact between the mercury and the entire surface which it is desired to wet. The Permalloy is cooled and is then in a condition to which mercury will readily adhere. In order to prevent oxidation and keep the Permalloy and mercury clean, the Permalloy element and the mercury should be retained in a non-oxidizing gas atmosphere.

It should be noted that the oxidizing and reducing temperatures are not critical and that a range of from 450 C. to 900 C. will produce satisfactory results on l5Ni.55Fe or 52Ni.l8Fe Permalloy elements of the size ordinarily employed in I small switches such as those employed in telephone systems. If thin Permalloy elements are treated, care must be exercised not to oxidize all of the metal or so much of the metal that it does not retain sufficient strength to perform its function.

The oxidation-reduction process for conditioning the element so that a thin coating of mercury will readily adhere to the surface of the element may be applied to an element made of iron as well as an alloy of iron. Slight modifications of the optimum temperatures and times indicated may be required for alloys of iron differing in chemical composition from those described. The process has been successfully applied to iron by using a temperature of about 600 C. for both the oxidation and reduction treatments.

In the manufacture of mercury contact switches it is necessary to insure that substantially all the metal surfaces in the switch be wet with mercury. This result may be achieved by making all the metal surfaces of ferrous materials which have been subjected to the oxidation-reduction process described above. If it is desired to provide for a substantial capillary fiow of mercury in some or all the metal surfaces, the surfaces in which the capillary flow is desired should be subjected to the heat treatment and etching or sandblasting process described above and then subjected tothe oxidation-reduction process.

In employing the above-described processes in the manufacture of a switch, the metal parts are first cut and tumbled for three or four hours in sand to clean them and remove the burrs. The parts are then welded where welding is required. The surfaces in which capillary flow is desired are then subjected to the heat treatment and etching or sandblasting treatment described above. In the final assembly of a mercury contact switch, the metal members are ordinarily placed in a glass envelope. An opening for the introduction of mercury and gas is left in the envelope. This assembly is then subjected to the oxidation-reduction treatment described above. The glass envelope is then filled with mercury and a non-oxidizing gas and sealed, and the activation treatment described above is applied. The switch is then in condition to be used.

This method of manufacturing switches. is simpler and cheaper than ordinary methods. The product produced is superior to those disclosed in the prior art since the many channels scattered over the surface of each member form a hydraulic flow path of very low impedance. A further improvement results from the avoidance of the formation of amalgam which is common in switches in which the ferrous members are coated with a metal such as nickel or copper which amalgamates with mercury.

Although specific details of this process have been described, it will be understood that modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. The. method of treating the surface of a solid ferrous material, comprising oxidizing said surface by heating the material in the presence of oxygen, reducing said surface by heating the material in the presence of hydrogen thereby causing said surface to become easily wettable by mercury, and applying mercury to said. surface.

2. The method of treating the surface of an alloy of iron comprising forming a layer of oxide of the constituents of said alloy on said surface, reducing said layer of oxide to cause said surface to become easily wettable by mercury, and applying mercury to said surface.

3. The methodof forming a surface on an alloy of iron comprisingv the steps of oxidizing said surface, reducing said surface, placing the surface in a chamber containing mercury having a non-oxidizing atmosphere, and mechanically agitating said surface with respect to said mercury to insure good contact between the mercury and the said surface.

4. The method of forming a mercury surface on an iron alloy comprising the steps of heating the iron alloy in the presence of oxygen for a sufficient time and a sufficiently high temperature to form a layer of oxide on said surface, heating the iron alloy in the presence of hydrogen for a sufficient time and a sufiiciently high temperature to reduce said layer of oxide thereby causing said surface to become easily wettable by mercury, placing said surface in a chamber containing mercury and a non-oxidizing gas, and agitating said surface with respect to said mercury so as to Wet said surface thoroughly with said mercury.

5. The method of forming a mercury surface on an alloy of iron and nickel comprising the steps of heating the alloy in the presence of oxygen for a sufiicient time and a sufi'iciently high temperature to form a layer of oxide onsaid surface, heating the alloy in the presence of hydrogen for a sufficient time and a sufiiciently high temperature to reduce said layer of oxide to cause said surface to become easily wettable by mercury, placing said surface in a chamber containing mercury and a non-oxidizing gas, and agitating said surface With respect to said mercury so as to Wet said surface thoroughly with said mercury.

6. The method of forming a surface on an alloy of iron and nickel which is easily wettable by mercury, comprising recrystallizing said; alloy by means of heat treatment to form large crystals, etching said alloy to form channels between said large crystals, forming a layer of oxide of the constituents of said alloy on the resulting surface by oxidizing said, etched alloy surface, and reducing said layer of oxide.

7. The method of forming a surface on an alloy of iron and nickel which is easily wettable by mercury, comprising recrystallizing said alloy by means of heat treatment to form large crystals therein, sandblasting said alloy surface to form channels between saidv large crystals, forming a layer of oxide of the constituents of the said alloy on the resulting sandblasted surface by oxidizing said alloy, and reducing said layer of oxide.

8. The method of forming a surface on an alloy of iron which is easily wettable by mercury, comprising recrystallizing said alloy by means of a heat treatment to form large crystals therein,.removing the surface boundary matter between the crystals of the alloy to form channels between said crystals, forming a layer of oxide of the constituents of said alloy on the resulting surface, reducing said layer of oxide, and applying a layer of mercury to said surface.

CHARLES E. POLLARD, JR.

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

UNITED STATES PATENTS Number Name Date 1,156,170 Page Oct. 12, 1915 1,669,648 Bandur May 15, 1928 1,958,338 Gwyn May 8, 1934 2,110,893 Sendzimir Mar. 15, 1938 2,283,109 Von Ende May 12, 1942 2,340,461 Gage et al Feb. 1, 1944 2,442,223 Uhlig May 25, 1948 FOREIGN PATENTS Number Country Date 453,543 Germany Dec. 10, 1927