US1872304A - Copper hemisulphide rectifier - Google Patents

Description

U- 16, 1932 s. B. KRAUT ET A1. 1,872,304

COPPER HEMISULPHIDE RECTIFIER Filed March 2, 1927 z8 1 28kg;1

/ ATTORNEY Patented Aug. 16, 1932 UNITED STATES PATENT 'OFFICE SAMUEL B. KBAUT, F EAST PITTSBURGH, AND CHARLES E. MABGEBUI, OF PITTS- BUBGH, PENNSYLVANIA, ASSIGNORS T0 WESTINGHOUSE ELECTRIC AND IANUFAC- 'f TUBING COMPANY, A CORPORATION OF PENNSYLVANIA corran HEMISULP'HIDE :anc'rrrmn Application med March 2,

Our invention relates to devices for rectifying alternating currents and particularly to devices utilizing the uni-lateral electricalconductivity characteristic of contacts between certain materials.

As an example of such rectifiers, a layer of copper hemi-sulphide, in contact on one face with copper and on the other face with oxidized aluminum, gives a contact series which conducts uni-laterally.

One object of our invention is to produce a rectifier which shall be uniform in performance; which shall, under an invariable impressed voltage, deliver a uniform and invariable continuous current, such as is desired for exciting the cathodes of electron tubes, for example.

Another object of our inventionis to produce a rectifier having an output characteristic which remains substantially constant throughout a long period of service.

Another object of our invention is to produce a rectifier which shall not require frequent adjustment or attendance: which is simple to handle and may be sold as a unit for use by persons who are not specialists in electrical technology.

A further object of our invention is to produce a copper hemi-sulphide unit for such rectifiers of the exact form and size desired which shall be homogeneous and durable and not subject to disintegration while in service.

Other objects of our invention will be clear upon reading the following specification, in which our invention is set forth in detail.

Recti fiers employing uni-laterally conducting contacts between certain materials and plates composed of copper which has been heated in contact with sulphur have been previously employed: but these have been found irregular in performance, yielding a current output subject to rapid and erratic fluctuations and have further been found to deteriorate rapidly in service through disintegration or other changes. They were, therefore, wholly unsuited for use with electron tubes in radio circuits or by persons who were not electrical specialists.

We have found that, by employing, in place 1921; serai 1ro. 172,033.

of such units of sulphuretted copper formed n masse, elements molded from a compound of copper and sulphur which is of homogeneous composition throughout many of the aforesaid defects are avoided. We have found that the performance of such units may be further improved if the copper-sulphur compound is molded under pressure in contact with one or both of its co-operating electrodes.

We have further found that by making one electrode of a metal such as aluminum having an oxide coating on its surface, and, preferably, one formed by electrolytic oxidization, a further great improvement in performance results.

We have likewise found that the difficulties from irregularity of action are obviated by maintaining a spring-pressure upon the contacts so that changes in displacement of the component materials do not result in a decreased contact pressure. The net result of the foregoing improvements is a rectifier of regular electrical behavior, well suited to the requirements of service in radio and other fields.

With the above described features and objects in mind, an understanding of the invention may be had by reference to the accompanying drawing wherein,

Fig. 1 is a sectional view of a uni-laterally conducting unit embodying certain features of our invention.

Fig. 2 is a sectional view of a plurality of units of a somewhat different type from that shown in Fig. 1 assembled in a holder and suitably disposed for service as a half-wave alternating-current rectifier.

Fig. 3 is a sectional view of a plurality of units of still another type assembled in a suitable holder and disposed for full-wave rectification and provided with circuit connections suitable to produce a substantially invariable continuous current.

The preferred methods of making the sulphuretted-copper conducting material and .of oxidizing an aluminum contact plate will first be described; then suitable ways of constructing our rectifier, which are illustrated by the drawing, will be discussed in detail.

011e method of producing a fairly homon geneous copper hemi-sulphide consists in heating a copper sheet in contact w1th sulphur vapor, whereby the sheet is converted 1nto a mass of copper hemi-sulphide. Thls mass may be readily crushed in a mortar and put through a screen, thereby producing a material of uniform fineness of grain.

A method of conglomerating this powder into plates consists in heatingiinely divided hemisulphide of copper, mixed wlth finely divided copper and powdered sulphur to approximately the boiling point of sulphur.

Finely divided copper may be obtained by several well-known methods; one of these consists in taking copper oxide which is readily powdered and heating it in an atmosphere of hydrogen, thereby reducing the copper oxide to the metallic form desired. Such powder may be intimately mixed with about one-fourth its weight of flour of sul hur and about twice its Weight of copper emi-sulphide and heated as above described, whereupon the copper and sulphur comblne to cement the mixture to form a uniform and homogeneous compound.

An alternative method of cementing the copper powder and sulphuretted copper consists in heating the above'mentioned proportions of copper and sulphuretted copper, for an extended period, in contact with fumes which rise from molten sulphur.

The compound of copper and sulphur produced in the foregoing manner we believe to be copper heini-sulphide. At any rate, that compound which is formed by heating copper in contact with an excess of sulphur may be employed in a rectifier by simply packing a quantity of it in a proper receptacle and providing oppositesurfaces thereof with a plate vof oxidized aluminum and a plate of copper,

in substantial accordance with the following disclosure. Better results, however, may be obtained if the copper hemi-sulphide is placed in a proper die and compressed therein into a solid cake under a pressure of approxi mately 150,000 pounds per square inch. It will be found, upon removal from the press, that the material has been compacted into a solid and homogeneous plate. This may be placed between an oxidized aluminum terminal plate and a second terminal plate of any suitable inert conductive material to form a rectifying unit.

It is preferable, however, to form one of the contact members in the shape of a cup or ring and to mold the copper hemi-sulphide therein under ';he pressure above specified. When this is done, a strong and uniform layer of the heini-sulphide is produced in the interior of the cup or ring. i

A co-operating terminal member for the unit made as above described may be produced from aluminum, magnesium, zinc, or

other metal upon which an oxidized surface may be formed.

For many purposes it is preferable that the oxide film in the rectifier should reform spon taneously if it is destroyed in any way while in service. Accordingly, it is preferable that the metal used for the oxidized terminal shall be one which is oxidized readily at a low temperature.

Similarly, it is advantageous that the opposing terminal material be one which does not form a high resistance oxide or sulphide spontaneously very readily in air at room temperatures.

It is well-known that the metals may be arranged in a series corresponding to their aliinity for oxygen, those at one end oxidizing readily and those at the opposite end being diiicult to oxidize. A part of that series comprises magnesium, aluminum, chromium, manganese, zinc, cadmium, iron, cobalt, nickel and copper in the order named, the magnesium oxidizing most readily and the copper least readily. The dividing line between those which oxidize readily at room temperature and those which do not may be considered to lie in the neighborhood of iron in this series. Hence, advantages arise from using, for one contact terminal of our rectifier, a metal, such as aluminum, found on the one side of iron in this series and, for the other metal, either iron itself or one of the metals falling on the other side of liron in the series.

We have found, in the case of aluminum, that great practical improvement .results if it is oxidized artificially. This may be done by heating in air, but we prefer to do this by making it the anode of an electrolytic cell, for which a borax solution is one suitable electrolyte. vA film of oxide quickly coats the surface of the aluminum, and current flow thereon virtually stops, as is well-known.

Referring to the drawlng, one convenient form of structural embodiment is shown in Fig. 1. A shallow copper cu 1 is partly filled with copper bami-sulphide 2 produced in the manner above described and placed in a die in a hydraulic or other press and subjected to a pressure of about 175,000 pounds per square inch. The pressure is then removed and an aluminum plate 3, one surface of which has been oxidized in the manner previously described, is placed with the oxide surface adjacent the copper hemi-sulphide.

A suitable insulating ring 4 is placed between the rim of the copper cup 1 and the edge of the aluminum plate 3 and the cup is then replaced in the press; pressure reapplied and the edge 5 of the copper cup crimped down upon the periphery of the aluminum plate, thereby clamping it in position and maintaining a firm contact pressure between the oxide surface and the copper bami-sulphide. The walls of the copper cup are elastic and resilient enough to act like a spring and thereby maintain a uniform pressure between the aluminum disc and the layer of copper hemi-sulphide in spite of changes of volume due to thermal expansion or other cause.

The bottom of the copper cup 1 has three equally spaced bosses 6 so arrangedl that, when it is laced on top. of another emular unit, these osses make contact with the aluminum top plate of the latter.

Instead of molding the copper sulphide in place in the copper cup in one operation and then releasing the pressure before positioning and clampin the aluminum plate 3, the plate 3 may be p aced on top of the copper-sulphide before any, pressure has been applied -to the latter. Pressure may then be applied and the copper-hemi-sulphlde compressed in the copper cup 1 and the edges 5 of the latter crimped down, to clamp the plate, in a single operation.

Fig. 2 shows three somewhat slmilar umts in a supporting frame suitable for malntaining a uniform pressure upon the contact surfaces by spring pressure. Copper hem1sul phide 2 is molded into discs under pressure, in a suitable die. Instead, however, of clamping the aluminum plate 3 permanently 1nside a copper nickel cup, it is merely placed upon the surface of the copper helm-sulphide 2; a copper plate 7 being used for contact to its opposite face. i

Another similar unit is placed in posltion above it and still another on top of the latter. The three are then placed in a frame 8.

-Frame 8 has a top plate 9 in which are fixed three guide rods 10 upon which a plate member 11 is movably mounted. Upon the member 11 is placed an insulating disc 12. Members 11 and 12 are pressed upwardly by a spring 13, the lower end of which rests upon a bottom plate 14, in which the guide rods 10 are fixed.

In the center of the top plate 9 is located a boss 15 having the contour of a portion of a sphere. Between the top plate 9 and the topmost rectifying unit is placed a spacing mem` ber 16 having a socket 17 to receive the boss 15. The ball and socket connection between the members 9 and 16 ensure such adjustment of the latter as to uniformly distribute the pressure exerted by the spring 13 upon the pile of rectifying unit-s. Thus, the pressure of the spring 13 is uniformly distributed over the surface between the aluminum plate and the copper hemi-sulphide of each rectifying unit.

Suitable current terminals 18 and 19 permit the device to be connected to electrical circuits in any of the well-known rectifier connections.

In Fig. 3 arel shown rectifier units of a somewhat different form from those above described. Each plate of copper 20 is provided with an annulardepression 21 in which is molded, under pressure, a layer of copper hemi-sulphide, 2, in a manner suiciently described already. Instead of an oxidized aluminum plate, the co-operating contact member comprises a ring 22 of aluminum, the lower edge of which has been electrolytically coated with oxide in the same manner as has been described for the aluminum plate 3. The ring 22 may be a plane torus, or it may be bent at one or more points around its circumference soy that, if laid upon a plane surface, it touches it at a number of spaced points.

This construction allows contact to be secured between the aluminum andthe copper hemi-sulphide over the adjacent surface of the aluminum ring. Pressure upon the assembled unit causes the soft aluminum to yield locally, if necessary, to take up any inequalities which may have existed in the contact. Each such unit is a uni-lateral electrical conductor, and a plurality thereof may be combined to produce a full-wave rectifier which delivers substantially invariable continuous current by the arrangement disclosed in Fig. 3. t

In -Fig..3, the units yare shown positioned in a supporting frame 23 comprising a base plate 24 in which are fixed three parallel guide rods 10. A rectifying unit is placed upon a contact plate 25, separated from the base plate 24 by insulation 26, with its aluminum ring 22 resting upon plate 25, and a second unit is superposed upon it.'

A contact plate 27 is placed in contact with the copper cup 20 of the upper unit of the two just mentioned, and, on top of the plate 27, are placed two similar units, the copper cup of the lower of the pair resting thereon. Upon the aluminum ring 22 of the uppermost unit rests a plate 16 sufficiently thick to transmit pressure rigidly. The member 16 is provided with a bearing socket to receive a boss with which the plate 11 is provided, substantlally as already described in connection with Fig. 2. The plate 11 slides upon the three guide rods 10 above-mentioned.

A spring 13 transmits pressure to the plate 11 from the cover plate 9 and thereby maintains a substantially constant pressure upon the pile of rectifying units. The pressure of the spring 13 may be adjusted by means of nuts 28 threaded upon the guide rods 10.

The arrangement of Fig. 3 is intended for full-wave rectification. For that purpose, the plates and 11 are connected to opposite ends of a transformer secondary 29` of the desired capacity and voltage, the primary 30 of this transformer being supplied from an alternating-current circuit. A condenser 31 may be connected in shunt across the transformer secondary 29. The plate 27 may be connected to the positive terminal of the direct-current load line through two inductance coils 32 and 33. One terminal of a condenser 34 is connected to the common Azo junction of coils 32 and 33, its other terminal being connected to the negative side of the direct-current circuit. A condenser 1s connected in shunt across the direct-current circuit on the load side of the coils 32 and 33. The negative side of the direct current line is connected to the mid-point of the transformer secondary 29.

The rectifying units conduct current readily with the copper cups negative. Hence, current flows from that partlcular terminal of the transformer secondary 29 which happens to be positive at any particular instant, through the adjacent rectifying units to the plate 27 and thence out, through coils 32 and 33, to the direct-current load. Current returns through the negative conductor of the direct-current-load line to the mid-point of transformer 29, thus completing its circuit. Upon the reversal of the alternating E. M. F., current flows through the opposite set of rectifying units to the plate 27 and through the direct-current load in the same manner. The coils 32 and 33 and condensers 34 and 35 tend to take up the instantaneous fluctuations of the pulsating uni-directional voltage which exists between the plate 27 and the mid-point of transformer 29. In consequence, an invariable continuous current is supplied to the direct-current load. The condenser 31 permits the flow in the secondary of transformer 31 of the current harmonies which are necessarily present where invariable continuous current is supplied by the rectifier. The alternating supply circuit is thereby relieved of the necessity of carrying such undesirable harmonics.

It will be evident that a higher D. C. voltage may be obtained if a number of rectifier units each comprising an assembly 23 and transformer winding 29 are connected in series, in a manner well-known in the rectifier art, ahead of the inductances 32., 33 and their associated load circuit.

The rectifier produced by the foregoing combination of elements exhibits great uniformity in performance and delivers toA its load circuit an invariable continuous current, substantially free from disturbing fiuctuations.

It is obvious that oxidized plates of other metals than those here recommended as preferable may be employed as contact members in our rectifier, and, similarly, that other unoxidized metal terminals than those here recommended may be employed for the co-operating terminals.

It will be clear that the mechanical arrangements above described for obtaining uniform contact pressure on the rectifying units are in no way limited to units embodying copper sulphide or the other particular contact materials here described, but maybe found useful in units employing, for example, lead sulphide or silver sulphide as their intermediate contact material.

In the foregoing description we have referred to the intermediate contact material as copper hemi-sulphide. That, we believe to be its chemical composition but we do not wish thereby to imply that it is a pure compound of precisely that atomic composition. Other compounds of sulphur and copper may be components of the mixture actually produced by the methods of manufacture which We have described.

It is characteristic of the metals which we have named as available for use in the oxidized terminal that their oxidization proceeds by the formation of a relatively thin surface coating which is stable and impervious so that it protects the underlying metal from subsequent progression of the oxidation process. Such films may be termed glazes, and it is found to be a characteristic of these glazes on the metals named that they are of high electrical resistivity.

If the conduction of current through our rectifier junctions were electrolytic, it is evidently possible for a high-resistance film to form very rapidly when current starts to flow into 'the aluminum, thereby sealing the interior metal off from further current infiux. The high resistence'of our rectifier to current flow into the oxidized metal may be explained on this basis. We do not, however, wish our invention to be in any way dependent upon the correctness of, or otherwise limited in scope by, the hypotheses that we here advance.

Although we have shown and described our process and apparatus in a preferred embodiment thereof it is to be understood that it is not limited thereto, as many changes and modifications will readily suggest themselves to skilled workers in the art. We desire. therefore, that the appended claims shall be accorded the broadest interpretation consistent with their wording and with the state of the art.

We claim as our invention:

1. A device possessing uni-lateral electrical conductivity comprising a member of sulphuretted copper in contact, at one face, with a conducting material and, at the other face, with the oxidized surface of an aluminum contact member.

2. A device possessing uni-lateral electrical conductivity comprising a layer of sulphuretted copper in contact, on one face, with a metallic contact member and, on the other face, with the oxidized face of an aluminum contact member.

3. A device possessing uni-lateral electrical conductivity comprising a layer of sulphuretted copper in contact, under pressure, at one face, with a conducting material and` at the other face. with the oxidized face of an aluminum contact member.

4. A device possessing uni-lateral electrical conductivity comprising a homogeneous composite of sulphur and co per in contact, on onefface, with an oxidize aluminum contact member and, on the other face, with an unoxidizedmetal having a less ainty for .oxygen than aluminum.

der pressure, between said compound and the member last specified.

7. A device possessing uni-lateral electrical conductivity comprising -a cup-shaped metal member, a homogeneous compound of sulphur and copper molded in said cup, under ressure, a contact member comprising oxid1zed aluminum, and means for maintaining spring pressure contact between said compound and the member last specified.

8. In a rectifying device, an asymmetric couple comprising an electronegative electrode element of a sulphur compound with copper, and electropositive electrode element of aluminum, said electropositive electrode element having a relativel thin oxide thereof overlying its active sur ace and disposed in o rative contact with said electrone ative e ectrode element.

testimony whereof, we have hereunto subscribed our names this 23rd day of February, 1927.

SA`MUEL B. KRAUT. CHARLES E. MARGERUM.

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