US1366452A - Vapor rectifier for high-potential currents - Google Patents

Description

G. W. HEIMROD.

VAPOR RECTIFIER FOR HIGH POTENTIAL CURRENTS.

APPLICATION FILED sun: 3.1914.

1,366,452, Patented Jan. 25; 1921.

Inter 307;

GEORGE WILLIAM HEIMROID, OF HANOVER, GERMANY.

VAPOR RECTIFIER FOR HIGH-POTENTIAL OURREN'IS.

Specification of Letters Patent.

Patented Jan. 25, 1921.

Application filed June 3, 1914. Serial No. 842,795..

To all whom it may concern:

Be it known that I, Dr. GEORGE WILLIAM HEIMROD, chemist, a citizen of the United States, residing at Hanover, Germany, No. 8 Bodenstedtstrasse, have invented certain new and useful Im rovements in Vapor Rectifiers for Highotential Currents, of which the following is a specification.

This invention relates broadly to vapor electric devices and more particularly to vapor rectifiers for use on high potential circuits, such as employed for instance in operating Roentgen ray tubes.

Mercury rectifiers as in use at present contain generally solid anodes of iron or graphite. Alternatingcurrents of comparatively low potential are satisfactorily rectified by an apparatus of this sort. With currents of higher potential, however, difliculties invariably result inasmuch as the anode material is disintegrated under the influence of hi 'her electric charges. Moreover these anode materialswill liberate dissolved gases more or less readily, which deteriorates the vacuum of the rectifier. Since complete rectification in mercury rectifiers depends on complete absence of gases in the discharge space these defects necessarily lead to discharges in the undesired direction, whereby complete rectification is made impossible. In case the rectifier is provided with several anodes a discharge may. take place between the anodes directly thus causing arcing or striking-back. These defects increase with increase of potential and v the practical limit of the rectifier now in use is generally considered to beat less than 10,000 volts. None of the anodematerials now in use satisfiesthe demands to be made upon them for completerectification particularly under the influence of electrical discharges of .high potential.

In the following it will be shown that by replacement of the anode materials now in use bymetals possessing qualities more fully in accord with the demands to be made upon such material, .not onl more complete rectification may be attalned at voltages already employed, but that currents at potentials far above these present limits may be rectified completely.

Rectification in mercury rectifiers is the result of the ease with which electrons are emitted from a hot mercury surface, as compared to the difliculty withwhich they meet in leaving the surface of a cold solid metal;

"be emitted from the solid anode.

that is to say, while under the influence of cathodic charge negative electricity will flow readily from the hot cathode spot of a mercury cathode to a cold metallic anode, no current can flow at even much higher potentials 1n the opposite direction. The higher the potential applied to the rectifier, the greater is the tendency for electrons to To prevent this undesirable discharge it has been found necessary to free the mercury rectifier completely from gaseous impurities. With the anode material used so far this was impossible because the electrodes contained too large quantities of gases which were given off slowly but continuously as soon as the anode material became disintegrated under the influence of electrical discharges.

In order to avoid these difficulties the anode material should therefore have the following "properties 1. It must show little tendency toward amal amation.

2. t must possess high heat and electrical conductivity. 4

3. Even at relatively high temperatures, its vapor pressure must be low which corresponds to a high melting point.

4. It must resist the disintegrating effects of electrical discharges.

5. It must have small tendency to dissolve gases or to retain them; that is, it must be possible to free the material readily from gaseous impurities.

6. Even at high cathodic potentials it must not permit the emission of electrons. Since this seems to depend on'the purity of the surface it must'be possible to free the rectification, at any potential practically obtainable.

Obviously, it is not suflicient in order to realize the conditions of this invention merely to employ suitable materials for the anodes of the rectifier such as above mentioned, but at the same time care must be taken that no other source of gas development is present in the discharge space of the rectifier. In this regard the invention is distinguished from known forms of mercury lamps and rectifiers where a starting cathode covered with a layer of oxid of alkaline earths is provided within the discharge space; such starting device necessarily 'leading to development of gas and therefore preventing the maintenance of the very high vacuum necessary for the rectification of currents of high tension, even ifanodes of tungsten, etc.. are used, as has been proposed in connection with such lamps and rectifiers. As a further consequence of the necessity of avoiding the presence of even traces of ionizable gases within the rectifier space, all available means for eliminating traces of gas which may adhere to the inner walls of the container vessel must be used in order to secure the effect aimed at. It is well known in the manufacture of incandescent electric lamps to free the inner walls of the bulbs from adsorbed air by heating them to temperatures of say 350, and more in extreme vacuum. It is important in connection with this invention to make use of this method also in the manufacture of rectifiers in accordance therewith.

On account of the excellent valve action of mercury rectifiers equipped with these new anodes not only voltages far above those rectified so far c rn' be completely rectified. but also far better efficiencies may be obtained at normal potentials. This leads to entirely.

new and important applications of the recti fiers as for instance in Roentgen ray work. Roentgen tubes require a unidirectional current of from 20,000 to 150,000 volts which could notbe obtained satisfactorily before, except by a mechanical synchronous make and break apparatus such as the Snook converter.

With the improvement in the mercury rec tifier herein described currents of potentials higher than those above mentioned may be rectified completely and automatically. It is advantageous to provide the rectifier in this case with a second anode preferably of mercury from which by means of a directcurrent source a constant mercury arc is produced. The cathode spot of this are will insure a regular and constant passage of the high tension current in the proper direction.

Another application of the new rectifier is suggested by the problem of generation of electric oscillations. In search of a solution of this problem attention has often been called to the excellent qualties of mercury vapor and the rapidity with which mercury ions disappear. The attempts to utilize these properties for the production of high frequency oscillations have failed on account of the before mentioned inadequacies of the known types of mercury vapor valves. Under the influence of the relatively high current densities of condenser discharges the anode material became highly heated, disintegrated and evolved its gaseous impurities. \Vith the replacement of such anode materials by the metals like tungsten, ete., these difiiculties have been overcome. A mercury valve by itself or in conjunction with spark gaps when properly connected to an oscillatory system may be used to generate oscillations at any frequency used in wireless telegraphy. -By proper regulation of the energy charging the oscillatory system, it is possible to produce discharges of almost any desired sequence up to continuous waves, since the mercury valve permits the discharge to take place in only one direction. The primary'oscillatory system is thus disconnected from the secondary system with which it is coupled and this permits not only a very firm coupling of the two systems but also a wide divergence of the frequency of the two systems.

It is evident that these rectifiers may be used for the rectification of multiphase currents analogous to the methods now in use with the ordinary mercury rectifier. If necessary two or more may be used in parallel or in series and the resulting wave crests may be smoothed out by proper self-induction. They may be used in any arrangement in which the rectifiers known at present have proved useful, but they may also be employed for the rectification of currents at potentials at which the present rectifiers have failed completely.

A mercury rectifier in accordance with the invention is shown on the drawing.

The vessel of the rectifier is designated with the numeral 1, and contains a tungsten anode 2, a mercury cathode'3 and a further mercury electrode 4 adjacent the mercury cathode 3. The conductor 5 is for transmitting current from the source of electric power 6 and for connecting electrodes 3 and 4. A conductor 7 connects anode 2 and mercury cathode 3 and contains the direct current consumer 8. A coil'9, in the alternating current circuit 10 and the transformer coil '11, in connection with conductor 7 forms a rectifier 1 be under very high vacuum and that it does not contain any material which is adapted to give oti' gas under operative conditions.

What I claimis:

1. In a mercury rectifier. the combination of a tungsten anode actually freed from gases, a mercury cathode and a further electrode adjacent said mercury cathode and freed from gases and gas evolving elements.

2. A mercury rectifier provided with anodes comprising as active material, metals capable of being freed and actually freed from gaseous and gas-evolving impurities. inclosed within a receptacle free alsofrom any other gas-evolving elements and likewise freed from any gas contained therein or absorbed by its inner walls and by any elements inclosed thereby.

3. A mercury rectifier provided with 20 from any gas contained therein or adsorbed 26 by its inner walls and by any elements inclosed thereby.

In testimony whereof I afiix my signature in presence of two witnesses.

Dr. GEORGE WILLIAM HEIMROD.

Witnesses I T. HENELBY REED, ERNEST HENDERSON, Jr.

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