US1845067A - Solid rectifier - Google Patents

Description

Feb. 16, 1932. E. A, WEAVER 1,845,067

SOLID RECTIFIER Original Filed March 10. 192'? 71H56 Mr/Z695.

Patented Feb.A 16, 1932 UNITED STATES PATENT oFFlcE EASTMAN A. WEAVER, 0F CAMBRIDGE, MASSACHUSETTS, ASSIGNOR TO RAYTHEON INC., 0F CAMBRIDGE, MASSACHUSETTS, A CORPORATION 0F MASSACHUSETTS `soLIn :taormina Application led March 10, 1927, Serial No. 174,198. Renewed March 14, 1931.

The present invention relates to electrical apparatus and in particular to alternating current rectifiers in which two metals of different character are employed as electrodes, the metals fulfilling alternately the function of cathode and anode. scribed hereinafter is designed to carry current of an order sufficient to energize the flamentary cathodes of the largest radio sets in use and employs a product of oxidation on one or both electrodes to eect a portion of the unilateral conducting .characteristic. Heretofore in the art, it hasbeen proposed to derive the product by subjecting the electrodes to a liquid oxidizing agent,

` usually an acid. However, this form of defrom a container otherwise carefully sealed.l

vice presents many disadvantages, one of which is\.the fact that the liquid is apt to spill and, in the case of concentrated acid, to attack the metallic or other surfaces over which it spreads. Moreover, under continued operation, considerable gas may be formed due to violent electrolysis throughout the, entire fluid, necessitating ayent or opening that offers to the liquid ready escape The vent, if large, also has the undesirable feature of varying the specific gravity of the oxidizer. by promoting evaporation or condensation of moisture in the same manner as a leaky container. Some of these defects are accentuated when the rectifier is under normal load and in a heated condition. Furthermore, in the rectifiers evolved by prior art, the voltage drop, as measured in the direction of current fiow, is often of such magnitude as to cause considerable' loss of energy by heat with resulting reduced efficiency.

In order to eliminate the disadvantages of a liquid rectifier, some of which have been .pointed out, I propose to provide a strucoxidizing agent.

ture that employs a solid substance for the Moreover, by a special form of electrode I am enabled to minimize the loss in voltage referred to and toprocure an oxidation product without destructive gas formation, permitting the container to be sealed. j.

. Objects of the invention are, to improve The rectifier de generally on the structure and operation of a rectifier, the efficacy of which depends in part on the phenomenon of oxidation; to dispense with the liquid electrolyte, particularly an acid; to provide an oxidizing agent in solid form; to devise apparatus that will efficiently pass considerable current; to provide a sealed container .of rugged construction; and to reduce the cost of manufacture of the unit by simplifying the design and materials. Other objects and features Will'be apparent asthe specification is perused.

Referring to the drawing, numeral l designates a container preferably of metal, as iron, that is resistant to various salts; the container may conveniently take the form of tubing closed at one end in any suitable manner. Secured to the bottom of the receptacle is the anode 2, preferably of silver, and in juxtaposed relation thereto, I place cathode 3 shaped as a rod and preferably of a nickelsilicon alloy having a content of silicon approximating Q9. per cent'um. The specific erably neutral in reaction and preferably in-4 cluding the nitrates and salts of ammonium and of silver, the latter substance appearing to facilitate ion travel upon the rcapplication of potential to the cold rectifier. Excellent results have been obtained by mixing with either or both of silver and ammonium nitrates certain other substances; in particular, thallium nitrate. It has been found that generally speaking, constituents such as thallium nitrate which reduce the melting temperature of the salt mass also decrease the losses in the device ensuring long life for the rectifier. For the purpose of removing any tendency to short circuit, I may include a small amount of potassium or lithium salt as a nitrate.

may incorporate in the mixture a quantity of silver in powder form preferably equal to about one-third the weight of the salts. This powdered silver may be considered as an extension of the anode 2 of silver. In fact the anode 2 is really more of a conductor to make good contact with the salt and silver mixture and also furnish a supply of silver. Thus the device will rectify even without button 2.

tential tends to force current from the alloy to the silver, the surface molecules of the alloy are forced into chemical combination with oxygen or other material obtained from the oxidizing agent; this forms an insulating layer and stopsl the passage of substantial current. On the other half-wave, the opposite potential tends to set this oxygen free, perhaps to combine with silver atoms in close contact with it, forming conducting silver .oxide and permitting current to pass freely without electrolysis. This phase may take place only at certain points of the cathode surface, since when a free path for the current becomes available, there is no further tendency to decompose the protecting film.

In the manufacture of my rectifier, 313-' Occasionally, when this reciprocal transfer proximately two grams of the powdered lsalt mixture is placed in bottom of the container followed by the cathode which is preferably held in a position defining the central axis of the tube. In case a nickel-silicon alloy is employed for the cathode material,-I find itadvantageous to heat the member 1n an oxidizing flame. While the precise nature of the reaction is uncertain, whether the treatment affects the metallic structure throughoutor merely thesurface, a cathode treated in this manner exhibits a tenacious lm when subjected to the salt mixture. The salt may be moistened with a minimum quantity of water, then more powder firmly packed around the cathode by aid of the water and preferably by moderate warming. If the water is omitted, the device 1s heated in any suitable manner tothe fusion point'of the salt, at which time connection is made to a source of'alternating potential and electro- Alytic conduction sets in. During this forming period, so-called, the device is preferably allowed to rectify considerable current, approximately as much as it can stand without Y excessive heating which would decompose the ammonium nitrate. After forming, the rectifier works equally well in solid or fused state, hence may be started when cold and dry; moreover, the solid state is considered preferable on account of increased stability and less attack on the electrodes.

While any suitable method of closing the container may be employed, I prefer the structural arrangement shown. This compr1ses a layer 5 of sand, insulating washer 6 of mica,

glass spacer 7, asbestos washer 8 and a poured lseal 9, preferably not air-tight, which may be of a fused salt, as potassium nitrate.

The completed rectifier may be lconnected f by usual circuits to the alternating current source from which the direct current is to be derived. Moreover, by obvious change, it is apparent that the structure may be modified torectify both half waves.

Whiie the operation of my device is rather obscure at present, the indications seem to point to the following theory: When the poof oxygen takes place imperfectly at a point, the passage of considerable back current at that point ma fuse or vaporize a few nearby molecules of t e oxidizing agent, which furnish additional oxygen to reform the protecting film. The current in the conducting direction is vcarried electrolytically at the very first application of potential, as evidenced by v the formation of a little gas. The stoppage of gas evolution indicates the prompt formation of metallically conduct-ing paths, composed atleast in part presumably of silver electrolyzed out of the salt mixture and con- 'ductively' united with the powdered silver and the anode; this of course means also the saving of the energy necessary for the electrolysis. It will be apparent that the subdivided, filamentary, comminuted or other porous character of the totality of conducting paths thus formed allows access of the oxidizing agent to the cathode surface. Whatever may be the correct theory, it is a fact born of `experience that a unilateral conductor made in the manner stated is capable of passing current having an order of several amperes without undesirable heating.

I claim:

1. Electrical apparatus comprising two conductors of dissimilar material, at least one of the conductors being metallic and having a thin surface stratum converted into an oxidation compound which permits flow of current from one conductor to the other while obstructing flow of reverse current, and a solid oxidizing agent active during operation to maintain said stratum, the other conductor being of 'a nonfilm-forming material in porous forml to permit access of said agent to said stratum. Y

2. In combination, a film-forming electrode and a porous nonfilm-forming electrode incorporated in a solid electrolyte.

3. In combination, a plurality of electrodes, one being film-forming and another of a nonfilm-formi'ng material in subdivided form, said electrodes being embedded in a solid oxidizing agent.

one of said, electrodes being of non ilmform ing material in porous form, means including a solid electrolyte for deriving a unilaterally conducting characteristic between said electrodes, another of the electrodes being film-forming.

5. Electrical apparatus y comprising two conductors of dissimilar material, a thin surface stratum of one electrode bein converted into a. compound which permits gow of current from one conductor'to the Iother while obstructing flow of reverse current and a solid substance active during operation to maintain said stratum, one of the conductors being non film-forming and in finely divided form to permit access of said substance to said stratum, and another of the said conductors being of hlm-forming material.

6. A rectilier comprising electrodes separated by a solid salt mixture, one of said electrodes consisting of silver, and another of the said electrodes being formed of film-forming metal. i

7 .f In a rectifier, a plurality of electrodes and means including `a silver salt in solid form for deriving a uni-laterally conducting characteristic between said electrodes, one of the said electrodes containing silver and another being formed of film-forming metal. 30

8. Electrical apparatus comprising ,two electrodes of different composition, one of which is of a nonilm-forming material in porous form, and means including a solid electrolyte which penetrates the porous material for coverin one ofthe electrodes with a self-healing sur ace film giving rise in conjunction with the other materials toa uni- A.

directionally conducting system.

9. Apparatus for rectifying alternating current comprising in combination a filmforming electrode adapted to serve as a cathode, a layer of oxidation product in contact with said cathode and serving to separate the electrode fromA adjacent portions of the apparatus, ,a finely divided nonilm- `forming material in proximity to said oxide adapted to serve as an anode, a solid electrolyte in contact with said metallic material adapted to regenerate said layer, and means for passing an alternating current to said electrodes.

10. A rectifier comprising the combination within a casing of a plurality of electrodes within said casing, at least one of which electrodes contains silver and the other electrode is film-forming, and a separating mediumv comprising a non-acid mixture ofsolid oxidizing compounds, one of the said compounds containing silver.

11. Electrical apparatus comprising two v electrodes, onefof which serves as an anode YW'uind the other as a cathode, the said anode 'comprising silver in finely divided form, and

the said cathode being of a film-forming ma.-A

t'eriyl, and-.a solid oxidizing mixture between and substantially surrounding the said electrodes, the said mixture permitting the ow of current from one electrode to the other, while obstructing flow of reverse current, the said mixture acting through the formatim of lilm upon the said film-forming catho e.

v Signed by me at Cambridge, Massachusetts, this 24th day of February, 1927.

EASTMAN A. WEAVER.

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