US2194182A - Rectifier - Google Patents

Description

March 19, 940. c. A. KOTTERMAN RECTIFIER Filed July 15, 1959 ATTORNEY Patented Mer. 19, 1940 RECTIFIER Chester A. Kotterman, Indianapolis, Ind., assigner to P.'R. Mallory & Co.. Inc., Indianapolis, Ind., a corporation of Delaware Application July 13, 1939, SerialNo. 284,145

10 Claims.

This invention relates to electric current rectiers of the type comprising asymmetrically conductive couples of the dry surface contact variety.

An object of the invention is to improve such rectiers and the method of making them.v

Other objects of the invention will be apparent from the following description and accompanying drawing taken in connection with the appended claims.

'I'he invention comprises the features of' construction, combination of elements, arrangement of parts, and methods of manufacture and operation referred to above or which will be brought out and exemplified in the disclosure hereinafter set forth, including the illustrations in the drawmg.

In the drawing:

Figure 1 is a cross section through an asymmetrically conductive rectifier couple;

Figure 2 represents the couple after further processing according to one aspect of my invention;

Figure 3 illustrates a further step in forming a finished rectifier;

Figure 4 shows a rectifier element after the process of Figure 3; and

Figure 5 shows a completed rectifier device.

A feature of my invention resides in the method 0f production of a thin rectifier element and the product of such method. Another feature resides in the electrical, chemical and mechanical treatment of the thin element to improve its characteristics. Still other features will be made apparent in the following detailed description.

hWhile a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made in the method of procedure and the construction of parts without departing from the spirit of the invention. In the following description and in' the claims, parts will be identified by specic means for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

My invention has particular application to rectiers of the dry surface contact variety such as are described in Samuel Ruben Patents 1,751,359; 1,751,361; 1,751,469 et al., and may comprise, for example, a layer of magnesium or zinc and a layer of cupric sulfide separated by a thin asymmetrically conductive layer resulting from the reaction of these two layers and comprising a lm of magnesium sulfide.

Figure 1 shows such a rectifier couple produced,

for example, in the following manner; A brass washer is heated in the presence of sulfur in a non-oxidizing atmosphere until the copper inl the brass has been converted into a hard dense body of.sulfides. It appears that during sulflding the zinc migrates to the center of the disc forming a core l2 predominantly of zinc sulfide surrounded by a copper sulfide shell H as shown in Figure l.

A washer l0 of highly electro-positive metals; such as magnesium or zinc is provided with a thin insulating film on its surface by chemical or electro-chemical treatment and is then pressed into intimate contact with the insulated side facing the cupric sulfide washer which has previously been ground to a smooth fiat surface. An

I alternating current of sufficient voltage to breakl down the insulating filmis then applied across the junction. Upon breakdown of the insulating film a chemical reaction takes place resulting in the production of the asymmetrically conducting layer or rectifying lm. The alternating current may be applied for a period suflicient to produce this rectifying film over substantially the entire junction area. The reaction also results in a strong bond being formed between the respective layers welding them strongly together,

According to one feature of my invention after the rectifying junction is produced resulting in the integral assembly shown in Figure 1 the magnesium or zinc washer I0 is peeled or stripped away from the main body of the cupric sulfide washer il. If the electrical formation step has been properly regulated the rectifying film will completely adhere to the electro-positive metal and will carry with it a thin outer layer Ila of cupric sulfide as shown in Figure 2. Thus all the essential parts of the rectifying couple adhere to the magnesium or zinc washer and retain the same rectifying characteristics they possessed before the peeling operation.

The peeled rectifier junctions of my invention present important advantages over ordinary couples, for example;

A. They are flexible to the extent that they can be bent to a degree angle then fiattened out without destroying the rectifier properties. This feature permits them to be unevenly stacked, that is, it is not necessary to go to extreme limits in having all surfaces flat and parallel as in the stacking of 'the ordinary junctions where spacer washers, radiator and terminal plates and other components should have as flat register as is possible in stacking up a plurality of junctions on a common bolt.

' B. By separating the junction from the mother cupric, the possibility of failure due to cracked or fractured cupric sulfide washers is eliminated.

C. In the usual method of manufacturing cupric sulphide, brass washers are sulfided, converting the copper in the brass to cuprous sulfide and cupric sulfide, the zinc being converted into zinc sulfide. A zinc sulfide core is formed surrounded by cuprous and cupric sulfide. Zinc sulfide has a higher electrical resistance than cupric and cuprous sulfide. The peeling operation elimmates the zinc sulfide core and gives a thinner cupric sulfide layer of lower ohmic resistance.

D. Electrical conduction in the ordinary type of cupric sulfide washer having a core of any material other than a copper compound takes place mainly through the cupric sulfide shell. In the peeler type, conduction is through the entire body of the layer and consists of many parallel paths, removing the concentration of current at the edges of the junction and distributing it uniformly over the rectifying area of the junction resulting in an improved current ratio between the A. C. input current to the D. C. output current.

E. A peeled junction allows visible inspection of the completeness of formation of the rectifying film. Sensitive electrical tests have been developed for determining the completeness of formation for the ordinary type but they are more complicated and less reliable.

F. 'I'he peeled surface of the mother cupric sulfide washer can be reground at and another rectifying film formed on the new surface. In this way at least four peeled rectifying junctions can be produced from one mother cupric using both sides, thereby effecting considerable economy in manufacture.

According to another aspect of my invention, and illustrating another advantage of the peeled rectifier junctions, I contemplate an additional treatment of the peeled junctions to improve their chemical and electrical properties.

During the original electrical formation of the magnesium or zinc sulfide rectifying film certain by-products are formed at the junction area which are not desired and which reduce the eiilciency and other desirable characteristics of the rectifier. These are `principally excess cuprous sulde, copper oxide and metallic copper. An excess of metallic copper raises the inverse current as well as the conducting current of the junction. This results in a lower DC/AC ratio.

An excess of cuprous sulfide in the rectifying film increases the IR drop in the conducting direction at high current densities. This lowers the DC/AC voltage ratio and hence lowers efflciency. An excess of cuprous sulfide also affects the shelf life of the rectifier causing the rectifier to lose its rectifying ability partially after a pe- Normal rectification can only ffbe restored by a high current treatment.

` Copper oxide is detrimental since it reacts with sulfur producing free copper at the junction.

By additional treatment of the peeled junction it is possible to eliminate these detrimental products. 'I'his treatment comprises subjecting the peeled junction to the action of boiling surfur or sulfur vapor. The sulfur penetrates the thin outer layer of cupric sulfide and reacts with the free copper, cuprous sulfide and copper oxide to convert them to cupric sulfide.

It will readily be apparent that if the junction had not been peeled oii the mother cupric sulfide washer the resuliiding would be almost impossible due to' the thick layer of cupric sulfide which would have to be penetrated.

It is desirable to repeat the rectifier film-forming operation after resulflding by passing an alternating current of suitable value through the junction.

The electrical characteristics of rectifiers made up of peeled junctions are considerably better than those normally obtained with rectifiers of standard construction.

The average inverse or blocking current of a magnesium cupric sulfide junction having a rectifying area of 1.7 sq. in. is 1.0-2.0 amperes when 6 volts D. C. are impressed across the junction with an 0.5 ohm current limiting resistor in series with the 6 volt supply. A junction having an area of 0.7 sq. in. has an inverse current of 0.5-0.75 ampere when 6 volts are impressed across the junction. When junctions, of these areas are peeled, then subjected to the resulfiding process, the blocking current of the larger junction is reduced to between 80 and 100 milliamperes and that of the smaller junction to lessthan 50 milliamperes. This low inverse current greatly improves the peeled type of magnesium or zinc cupric sulfide rectifier for use in the low current field where high inverse currents could not be tolerated.

'I'he usual thick type of magnesium or zinc cupric sulfide junction will stand an A. C. voltage of 3.5 volts RMS on load without junction instability. By peeling, then resulfiding and reforming, it is possible to raise this voltage to 4.0 volts RMS or higher on load retaining stability, a highly desirable advantage.

The current ratio of the peeled type junction Yshows a considerable gain over the conventional type. In three-phase, full-wave bridge operation, the peeled type frequently shows a current ratio of 1.2-1.3 whereas the conventional type in the same circuit lies between 1.1 and 1.15. The increased operating voltage per junction plus the improved current ratio is reected in a higher efiiciency of the peeled type. 'I'he peeled rectier in three-phase, full-wave, 60 cycle operation working into a resistance or battery load will show an efficiency between 55 and 60%. At frequencies higher than 60 cycles, say, 300 to 3000 cycles, Where the conducting cycle is of much shorter duration, the peeled rectifiers can be operated at 4.5-5.0 volts per junction.

In order to make good electric contact with the cupric sulfide layer IIa in the rectifier assembly the layer may be sprayed with a contacting metal, such as tin, nickel or other metal not readily sulfided. The peeled sulfide surface being rough affords an excellent surface for receiving a metal spray. The sprayed metal fills the minute depressions in the sulfide surface and forms a continuous layer over the surface.

Figure 3 shows the method of spraying cupric sulfide surface IIa with contacting metal I3 by use of a metallizing gun I and a suitable mask I 4 to protect the edges of the junction.

Figure 4 illustrates the sprayed disc ready for assembly in a rectifying device.

Figure 5 shows a completed rectifying device made up of the elements of Figure 4 clamped together with heat-radiating and terminal plates I6, two of which are connected to an A. C. source I'I and the other three of which are connected to a D. C. output circuit I 8in the well-known full-wave bridge as shown. The soft contacting metal I3, such as tin, tends to flow slightly under the pressure of the stack and thereby conforms itself to the adjacent surfaces and produces an improved contact.

The magnesium or zinc cupric suliide rectifier requires a certain reservoir of cupricsulde for maximum operating life. When the junction is peeled from the mother cupric washer only a thin layer of cupric suliide adheres to the junctionl usually a layer about .002 to .005 inch thick. While this will be suiiicient in many cases it will be desirable for heavy current uses to build up the cupric sulfide layer of the peeled unit by spraying the layer lla with metallic copper and then resuliiding the sprayed junctions to produce additional supric sulfide. The cupric suliide layer may thus be built up to a thickness in the order of 0.02-0.03 inch or greater, such as to v0.5 inch. 'I'he spraying operation is similar to that illustrated in Figure 3, using copper as the sprayed metal. Spraying with copper and resulding is, of course, accomplished before spraying with a contacting metal such as tin.

It is also possible to spray or otherwise apply a solution of cupric suliide. such as cupric suliide in alcohol, to the surface and then drying and resulflding.

Whilethe 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 current rectier comprising a layer of metal selected from the group consisting of magnesium and zinc, a layer of cupric sulfide and an interposed rectifying iilm produced by reaction therebetween, said layer of cupric suliide having a thickness not substantially greater than 0.05 inch.

2. The method of making a rectifying element which comprises placing a layer of a highly electropositive metal against a layer of cupric suliide, passing an electric current through the junction of said layers to form a rectifying iilm thereat resulting from the reaction of said layers, and then peeling said electropositive metal layer together with said rectifying film and a thin layer of cupric sulfide from the main body of said cupric sulde layer. A

3. The method of making a rectifying element which comprises placing a layer of a highly electropositive metal against a layer of cupric sulfide, passing an electric current through the junction of said layers to form a rectifying iilm thereat resulting from the reaction of said layers, and then peeling said electropositive metal layer together with said rectifying iilm and a thin layer of cupric sulfide from the main body of said cupric sulfide layer and then bringing the thin cupric sulfide layer into contact with sulfur at an elevated temperature.

4. The method of making a rectifying element which comprises placing a layer of a highly electropositive metal against a layer of cupric sulfide, passing an electric current through the junction of said layers to forma rectifying film thereat resulting from the reaction of said layers, and then peeling said electropositive metal layer together with said rectifying film and a thin layer of cupric sulfide from the main body of said cupric suliide layer and then depositing additional cupric sulfide on said thin layer of cupric sulfide.

5. The method of making a rectifying element which comprisesv placing a layer of a highly electo reform the rectifying film thereat.

6. The method of making a rectifying element which comprises placing a layer of a highly electropositive metal against a layer of cupric sulfide, passing an electric current through the `iunction of said layers to form a rectifying iilm thereat resulting from the reaction of said layers, and then peeling said electropositive metal layer together with said rectifying film and a thin layer of cupric sulfide from the main body of said cupric sulfide layer, depositing metallic copper on said thin layer of cupric sulfide and then sulfiding said deposited copper to produce additional cupric suliide.

7. The methodof making a rectiiying element which comprises placing a layer of a highly electropositive metal against a layer of cupric sulfide, passing an electric current through the junction of said layers to forml a rectifying film thereat resulting from the reaction of said layers, and then peeling said electropositive metal layer t0- gether with said rectifyin'g lm and a thin layer of cupric sulfide from the main body oi. said cupric sulfide layer and then depositing an adhering metallic layer on said thin layer of cupric sulfide.

8. The method oi' making a rectifying" element which comprises placing a layer of a highly electropositive metal against a layer of cupric sulfide, passing an electric current through the junction of said layers to form a rectifying iilm thereat resulting from the reaction of said layers, and then peeling said electropositive metal layer together with said rectifying film and a thin layer of cupric sulfide from the main body of said cupric sulde layer and then depositing an adhering layer of contacting metal on said thin layer of cupric sulfide.

9. The method of making a rectifying element which comprises placing a layer of a highly electropositive metal against a layer of cupric sulfide, passing an electric current through the junction of said layers to form a rectifying iilm thereat resulting from the reaction of said layers, and then peeling said electropositive metal layer together with said rectifying lm and a thin layer of cupric sulfide from the main body of said cupric sulfide layer and then bringing the thin cupric sulfide layer into contact with sulfur at an elevated temperature and then depositing an adhering layer of contacting metal on said layer of cupric sulflde.

10. The method of making a rectifying element which comprises placing a layer oi metal selected from the group consisting of magnesium and zinc, against a layer of cupric sulfide, passing an electric current through the junction of said layers to form a rectifying film thereat resulting from the reaction of said layers, and then peeling said magnesium or zinc layer together with said rectifying film and a thin layer of cupric sulde from the main body of said cupric sulfide layer.

CHESTER A. KOTI'ERMAN.

. CERTIFICATE OF CORRECTION.

Patent No. 2,19Lh182. f -March 19, 19m.

` CHESTER A. KOTTERMAN.

It is hereby'certified that error appears in the printed specification of. the above numbered patent requiring correction as follows: Page 5, first column, line 1b., for "supric'read cupric.; line 16, for "0.5" read 0.05; and that the said Letters Patent should be readwith this correction therein l that the 4same may conform to the record -of the case inthe Patent Office.

signed and sealed this 9th day gf April, A. D. 19m.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

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