US2496721A

US2496721A - Rectifier

Info

Publication number: US2496721A
Application number: US623453A
Authority: US
Inventors: Carl C Hein
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1945-10-19
Filing date: 1945-10-19
Publication date: 1950-02-07
Anticipated expiration: 1967-02-07

Description

r Patented Feb. 7,

UNl'lED STATES PATENT OFFlCE Carl 0. Hein, rorifnna, 1a., asslgnor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania No Drawing.

Claims. 1

Application camber- 19,1945, Serial n0.- 623,453

' My invention relates to copper oxide rectiflers and. in particular relates to methods of forming a contact layer for the oxidized surface.

Copper oxide rectifiers made in accordance with United States Patent 1,640,335, Grondahl, in which an oxidized surface forming on a copper plate is provided with a counter-electrode capable of conducting current into the oxide have come into wide use in recent years.

In accordance with the abovementioned Grondahl patent the counter-electrode was formed by first coating the oxide surface with graphite and then covering it with a thin plate of lead or other impressionable material. A considerable improvement in the method of applying the counter-electrode has been made in recent years through the replacement of the above named described graphite and lead washer counter-electrode by one produced by reducing a portion of the oxide surfaces to metallic copper. For many purposes ithas been found desirable that the reduced copper surface should be provided with a protective plating of nickel applied by deposition from an electrolytic plating bath. However, it has been found that there is a tendency to crack in some deposits of the nickel coating and difficulty frequently has been found in the fact that the plating solution apparently penetrates minute cracks or interfaces between crystals on the oxidized copper surface with resulting deposits of nickel therein. The nickel thus formed in the cracks sometimes is penetrative enough to actually form a bridge or short circuit between the reduced copper on the outside of the copper oxide layer and the mother copper on the inner side thereof. Thus in quantity production it was found that a substantial percentage of the rectifiers subjected to the above mentioned electrolytic process are short circuited and rendered worthless.

It has also been found necessary, where the above mentioned electrical process is used in producing the counter-electrode, to burnish the outer surface of the electrolytic deposition if a low resistance of the rectifier to current flow is to be obtained in its conductive direction. Such a burnishing operation is an additional expense of by no means a negligible amount in rectifier manufacturing.

I have investigated the structure of the electrolytically treated surface of such rectifiers and have discovered that the reduction of the oxide at'various points on the surface appears to be uneven, being largely concentrated on the lines of crystalline division of the oxide surface.

Though reduction occurs almost everywhere at the crystal boundaries it leaves the major portion of the crystal surfaces in its original oxidized condition. This is particularly true during the earlier stages of the reduction, later stages usually resulting in a reduction of all portions of the oxide surface; but the reduction is still most complete along the crystal boundaries. When such surfaces are introduced into the electrolytic plating bath, the nickel deposits largely along the crystal boundaries, penetrating the cracks between crystals and at times short circuiting the oxide crystals themselves as already described.

In accordance with my present invention I have discovered that if the oxide surface is lightly abraded prior to the step of reducing it to copper most of the effects of non-uniformity in reduction is avoided. In particular the selective reduction in the crystal boundaries is greatly reduced. Reduction appears in fact to tend to occur principally along the furrows made by the abrading material; hence by being certain that abrasion covers substantially the entire surface of the oxide layer, an eifective uniformly distributed reduction can be effected. Subsequent deposition of the nickel by electroplating follows the reduced copper in these furrows and very little penetration of depositing nickel into the boundaries between crystals occurs.

One object of my invention accordingly is to provide an improved form of copper oxide rectifler.

. Another object of my invention is to provide an improved form of counter-electrode for copper oxide rectifiers.

Still another object of my invention is to provide an improved method of producing electrical .contacts for copper oxide surfaces.

Still another object of my invention is to provide a method for producing counter-electrodes for copper oxide rectifiers.

Other objects of my invention will; become apparent upon reading the following description:

Rectifiers in accordance with my invention may be made by first oxidizing clean copper plates or discs by heating them in an oxygen atmosphere at a temperature not far below the melting point of copper. The plates may then be subjected to heat treatment such as is described in the application of Charles S. Duncan, Serial No.'625,452, filed Oct. 29, 1945, now Patent No. 2,459,630, issued January 18, 1949, assigned to the assignee of this application. After the cupric oxide formed on the outer surface of the units has been removed by pickling in acid solusteel. A current density of 80 milliamperes per square inch at 50 to 60 volts direct current may be applied for two and one half to three minutes.

The units are then removed from the bath,

thoroughly rinsed in distilled water and then put into an electrolytic plating bath comprising nickel sulphate at 200 grams to the liter and boric acid 30 grams to the liter. The units should constitute the cathode of this electrolytic bath which ma subject them to a current density of 100 milliamperes per square inch for about three and one half minutes. The units may be removed then from the plating bath, rinsed thoroughly in both hot and cold water and dried.

Investigation has shown that rectifiers produced as above described have a lower resistance to current flow in their conductive direction than rectiiiers produced by the prior art processes. Furthermore, a sumeient reduction of the oxide layer to provide acceptable electrical contact can be produced in about one-half minute as against a treatment of something like three minutes by the prior art methods. This reduction in the time required for the electrolytic treatment is of course extremely important in quantity production of copper oxide rectifiers.

I claim as my invention:

1. The method of providing contact surfaces for copper oxide rectiflers which comprises forming a uniform coating of cuprous oxide on the rectifier, subjecting the surface of the cuprous oxide to abrasion, and subjecting the abraded surface to chemical reduction.

2. The method of providing contact surfaces for copper oxide rectifiers which comprises forming a uniform coating of cuprous oxide on the rectifier, subjecting the surface of the cuprous oxide to abrasion, and subjecting the abraded surface to chemical reduction and electroplating the surface resulting from such reduction.

3. The method of providing contact surfaces for copperoxide rectifiers which comprises forming a uniform coating of cuprous oxide on the rectifier, subjecting the surface of the cuprous oxide to abrasion, and subjecting the surface of the cuprous oxide to an electrolytic bath.

4. The method of providing contact surfaces for copper oxide rectifiers which comprises forming a uniform coating of cuprous oxide on the rectifier, subjecting the surface of the cuprous oxide to abrasion, and subjecting the surface of the cuprous oxide to an electrolytic bath, and

electroplating the surface produced by such treatment.

5. The method of providing electrical contacts for metallic oxide surfaces which comprises abrading said surfaces, subjecting them to a chemical reducing action.

6. The method of providing electrical contacts for metallic oxide surfaces which comprises abrading said surfaces and subjecting them thereafter to an electro-chemical reducing action.

7. The method of providing electrical contacts for metals having surface layers consisting of compounds of said metals which comprises abrading said surfaces, and subjecting them thereafter to an electro-chemical action.

8. The method of providing electrical contacts for metallic oxide surfaces which comprises abrading said surfaces, subjecting them thereafter to an electro-chemical reducing action and electroplating them thereafter.

9. A copper oxide rectifier comprising mother copper having an oxidized surface, said surface being traversed by abrasion marks which have been subjected to electrolytic reduction.

10. A copper oxide rectifier comprising mother copper having an oxidized surface, said surface being traversed by abrasion marks which have been subjected to electrolytic reduction and subsequently electro-plated with metal.

CARL C. HEIN.

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

UNITED STATES PATENTS Number Name Date 1,892,832 Geiger Jan. 3, 1933 1,926,132 .Ackerly Sept. 12, 1933 2,239,770 Becker Apr. 29, 1941 2,383,311 Hein Aug. 21, 1945

Claims

1. THE METHOD OF PROVIDING CONTACT SURFACES FOR COPPER OXIDE RECTIFIERS WHICH COMPRISES FORMING A UNIFORM COATING OF CUPROUS OXIDE ON THE RECTIFIER, SUBJECTING THE SURFACE OF THE CUPROUS OXIDE TO ABRASION, AND SUBJECTING THE ABRADED SURFACE TO CHEMICAL REDUCTION.