US2441260A - Electrode - Google Patents

Description

R.CORTESE ELECTRODE May 11, 1948.

Filed May 17, 1945 -RALPH CORTESE, INVEN 0R.

%-r f HIS ATTORNEY Patented; it lay 11, 1948 ELECTRODE Ralph Cortese, Eastoraage; N. J; Application Marl-' 1} 1945-;seimfNosssagzze 7 Claims: (01. iit -i'cc l" My invention relates to fluorescenttube light ing, and similar space discharge equipment; and.-

more particularly concerns anelectrodeconstruc tion for the cold cathode operation of fluorescent tubes.

Another object is to provide an electrodeestruc-' ture for space discharge tubes operating under cold cathode conditions, which structure contrib utes appreciably and without detrimentaleffiect thereon, in the preliminary processing of the tubes by the internal bombardment method and-which is capable of satisfactorily operating the tubes with high efiiciencies at elevated current densities without appreciable increase in the electrode size over those heretofore customary in the? art, and with, in the most part, no criticality attaching to the; dimensions thereof, Whichminimizcs cathode drop with substantial avoidance of long dark spots in the tube, so that substantiallythe entire length the associated tube contributes tothe production of useful light, whereir1 =sputtering in large measure is avoided; and'in the use of which electrode bothstriliin-g and operating voltages are minimized.

Other objects andadvantages in'part willbe obvious and in pointed out hereinafter during the course oi-the following description, taken in thelight of the accompanying drawings. 7 My invention accordingly resides in the several combinations of elements, features or con struction, and association of parta aswell as in the relation of each of the same with one or more of the others, the scope of the application of all of which is more particularly pointed-out in the claims at th end of this specification.

In the drawings wherein I 'di'scloseseveral 'ern' bodiments of my invention,

Figure 1 comprises a fragmentary vertical view, partly in section and partly in elevation, disclosing the embodiment of my invention which I prefer at present; 7

Figures 2, 3and t iragmentarily disclose in vertical elevation, transverse section on line '3-'3 of Figure 2 and longitudinal section the details of a second embodiment of my invention; While Figure 5 discloses in schematicillustration certain phenomena attendant upon the practicebf my invention; 7

Figure 6 is a side elevation of a complete tube employing paired electrodesconstructed according to the embodiment disclosed in Figure 1.

Like reference characters denote lik'e'parts in the several views. I

To permit more ready and thorough understanding of my invention, it may bev notedl'at. this point that in comparatively recent'yearssome what revolutionary changes have oecurreaintne 2 illumination art." In large measure. the incandescible filamentary type of lamp-"is beingirapim ly replaced for divide-varietyof'usesby'the'fiuorescent'la-mpr i i Despite the-high *degree of rei lnementto which the incandeseiblelamp had heretofore beer de: veloped; its very nature; whereby" it relies for its entire emission upon the production ;ofintense heat; definitely limi-ted the theoretical maximum efficiencies-which :could be achieved thereby:

The introduction --of :thefluorescent lamp per mittedradica;l broadening of the; possibilities available in -ilhim-inationengineering: The; a l-. most; complete energy conversion into the visible light-spectrumwith the substantial. elimination of; infra-red radiation in;la'rge measure; removes the presenceof sensible heat; N oteWorthy-floodlighting now'is-availablep Batteries 0f 2; 3 or {l or morelampscanbe arrangedfor desired lighting effect st; Mo1'eover,,novclarrangements are available when two ormore batteries; ofltubes are employed in-combination. Effectivecolor combinations can -be--achieved directly by selective: ly employing lamps coated on their-interior walls with'desired'fluorescent salts-or phosphors: Limitations; inv this a respect -arer imposed almost entirely-bythe ingenuityof theoperator.

Itmay" be noted at this point that probably the basically l-irniting factorheretofore ;confront-fi ing: the exploitationof fluorescent tube lighting equipment in th'e'sol-utionof illumination-prob lems-- is the -conception-so 'prevaili-ng in '"the' art that "hot cathode operation of the-tubes was es= sential -for the "most -advan-tageous result-si- Under- Cl-audes law; a cold cathode, without emissivecoating can carry "only about 0.94 am: pere of electric;- current per square-"inches sur face area withoutdetrimental-- overheating: Through th'e" simpleexpedient of coatin'g the Workingksurfacer 01" this: electrode with electror-ri emitting -coating;r such:'- as strontium or caesium oxide or the likewelectron emission can boom creased: 'ne'arl terr-fold; to about 0:3 03} am; perepersquare'in'ch? While these-currentdensities aresunieient', in lar e measoreir rnormal operation "ofthetub irr' actual practie eircethe-tun has een rep; erlymanufactured, the i fdualo awbackis s l foondtdexisethati ciwrne tribe electrode tj g g V ua'ress eatmar qui nentisempwyeazrent of the preliminary processing could be effectively carried by the electrode without damage to the latter and without detrimental sputtering and deposition of sputtered metal on the walls of the tube.

And now having reference more particularly to that embodiment of my invention shown in Figures 2 through 4 of the drawings, the vitreous envelope [0, in the form of an elongated cylinder, has a re-entrant portion at each end thereof, terminating in an internal stem or press ll.

Support wire I3 is mounted therein, fast to leadvated temperatures, without, however, any appre- V ciable' increase of the electrode size over that heretofore prevailing, without appreciable damage to the electrode itself, and without sputtering of the electrode material on the wall of the tube, the electrode being fully capable of satisfactory and efficient operation during the subsequent normal use of the tube.

As a first step toward solving the many difficulties hereinbefore recited, I decided upon the expedient of placing an oxide coating on both the internal and external walls of the electrode rather than upon the interior surface alone, as has heretofore been the case. I anticipated a theoretical doubling of the efiective current carrying capacity, with but little increase in temperature and with no increase in the physical dimensions of the electrode. In point of fact, superior results were actually achieved in practice. The current-carrying capacity was by no means doubled, but it was appreciably elevated. However, while satisfactory removal of moisture and occluded gases could be achieved, the temperature of the electrode was raised to such values that highly skilled operators where required in carrying out the manufacturing operation. Moreover, some in wire l1, and carries at its free end a cup-shaped or shell electrode IA, of conventional size and dimension. In the preferred instance, to illustrate,

its length is of the same general order as its diameter, that is, it has no really definite mal'or axis, other than that provided by the shell like contour. I provide an anode concentric with and disposed about the electrode M throughout its length comprised of several turns of wire l5. At

least one turn of this wire projects beyond the outer edge of the electrode in the direction of the opposed electrode. In the preferred embodiment, the free end of this spiral I5 is connected to electrode M at point iii. The other end of the wire i5 is connected at i8 to the lead-in wire [6. Tubulature I2 serves for the evacuation of the tube l0.

To illustrate, it is desired, in order to compete effectively with the known hot cathode fluorescent tubes, to operate with a cup-shaped elec- 7 trode having an internal developed area of apsputtering in the region of the mouth of the electrode was likewise observed. It was apparent that more was required in order to produce entirely satisfactory results,

I thereupon conceived the expedient of providing an electric field in the region of each electrode, auxiliary to that maintaining between the electrodes themselves when the latter were subjected to alternating potentials, and asserting its presence between the electrodes and the adjacent walls of the tube container. Such field, properly designed, will efiectively prevent the deposition of metal on the tube walls and at the same time will channel the electrons from the adjacent electrode, during the negative half-cycle of that electrode, toward the opposed electrode, thus resulting in the greatest possible ionization at maximum energy of the electrons.

1 provided this field, in a first embodiment of the final form of my invention, by encircling the ordinary shell electrode by several turns of wire, which spiral anode was concentric with and spaced from the electrodeby an amount sufficient for the field to assert itself. The number of turns of the anode wire was such, and the spacing therebetween, that is, the pitch distance, so selected, that the electrons could flow freely therebetween. When this spiral element was constructed so that its turns projected slightly beproximately 1.2 square inches and an effective inner diameter of about of an inch. Such an electrode, capable of operating a 25 mm. diameter tube, must function satisfactorily at a curren density of 0.36 ampere.

Ordinarily, it must be effective in carrying temorarily, and without detrimental overheating and without detrimental sputtering, a current ranging from about 2.0 to about 2.5 amperes during the preliminary processing of the tube.

Coating both the inside and the outside surface of the electrode with electron-emissive oxides, I found a partial solution of the problem confronting me was obtained in that proper current intensity could be achieved during normal operation at an electrode temperature ranging from about 500 C. to about 600 0. However, as has hereinbefore been stated more generally, such electrodes could not besuccessfully employed in preliminary processing of the tube under bombardment, and some detrimental sputtering was observed to take place.

I thereupon constructed the spiral l5 as hereinbefore referred to. In the instance undergoing description, I imparted a diameter of about 1% of an inch thereto, in that instance where a shell is employed of A; of an inch diameter, leaving a free space of about 3%; of an inch around the shell. Upon coating the wire as well as the shell and thereafter processing several tubes by the glass-heatyond the open end of the adjacent electrode, in

the direction of the opposed spaced electrode, I observed that it fulfilled admirably its function as an anode. By coating this anode with an electron-emissive salt, I found that it participated in the electron-emission function of the mainelectrode. By the use of such anode, I found that for the first time, the substantially increased ouring-by bombardment process, uniform results were achieved. I was able to raise the current in the tube to 2.5 amperes without undue risk Upon shorting leads l6 and H (Figure 2) so that the shell 14 and wire l5 operate in paralleLIfound that the entire shell assembly could be raised to the required temperature of 750 to 800 C., solely by way of internal bombardment without damage to the electrode construction,

I constructed the wire spiral l5 of pure iron, although nickel, molybdenum, or any other heatresisting metal could be effectively employed. In the present instance, the wire has a. diameter r i emanate and the pitch di'stanceis about it of seamen, My observations have disclosed that these-dimensions are not critical and that the dcsignv of the electrode is not limited in the manner as; is true-oi the construction of filamentary electrodes, Thus, a shell of 1.2 square inch internal will operate with a high degree of eflfectiveness in. the preliminary manufacture of thetube. It. will now be described how such an electrode onerates effectively during the normal use or the tube after it has been sold and placed into oporation. Here agaimjust as in the instance here. tofore described, efiective contrasts will be drawn between the prior art cold cathode-tubes on theonchand and my new electrode construction on the other hand.

' Assuming therefore that a shell electrode. prcperly oxide coated, and in a tube which has been properly heat treated, and assuming aninside emitting surface of said electrode of say 1.2 square inches, then assuming the shells to carry their ioadaccording to Claudes law to the maximum rate of 0.043 ampere per square inch, a totalper missible amperage of 0.0516 ampere can; be

achieved. Long tube life will be achieved-b and with a space of about 48 inches between-therop" posed electrodes, there will be about. 326: volts drop across the electrodes when operating at al ternating current after initially striking-at a. volt age in the region of about 550 110600 volts. The energyoutput of such atube is very low-ranginc-from 10 to 12 watts with a tube of 10-25 mm,

diameter. vThat is, brilliancy-is quite low. To obtain ahigh degreeof. illumination over a'wide area. a number of lamps must be strung together in series.

Increase iii-wattage consumption of the tubes is by passinggreater current therethrough, thereby boosting. the surface brilliancy, decreasing the operating voltage, and cutting down the operating costs. Thus, to illustrate, upon increase of the current from the 0.0516 value hereinbefore referred to, to say about 0.150 ampere, the lamp brilliancy will be appreciably greater, the operating voltage will drop toabout 280 volts or thereabouts, and fewer lamps'will be needed to maintain the same level of illumination.

When I surrounded this electrode with a few tums of pure iron wire, all as described heretofore in connection with spiral l5, and spaced thesame from the shell 14 so as to provide enough.

space for the electrons to move ratherfreely around it, I achieved the results which I sought.

My observations were that the spiral I5 served as the anode of a sort of filamentary electrode when the last turn thereof was extended slightly beyond the. end of the shell It. By that, I mean no sputtering occurs on the inside glass wall around the electrode. Moreover, I observed that no cathode glow occurred on the outsidewall, thisadvantageous phenomenon being due in all probability to the electric field set up by the anode in phase with and of the same instantaneous polarity and potential as that of the shell 14. Thirdly, I observed that the anode emits electrons by field emission in appreciable quantity.

In fact, at the initial stage of bombardment, the anode is made to supply the current that: the cathode cannot supply. Thus, with ionic bombardment taking place inside the shell, I believe it; to be ,a'iair assumption that the (L36 ampere current passing through thetubes is made up, of

about 0.3'ampere from the interior of the shell ode shell atasubstantially higher temperature than has heretofore been suggested according to Claude'slaw, this value nevertheless falls far short of thehot cathode operating temperature of from 1000 C, to 1200 C. This operating temperature, while sufiicient to give rise to an appreciable field emission, isynotrsufiiciently elevated to result in dangerous softening of I the metal of the electrode. The fieldemission could be increased by winding'the anode I 5 with more turns of wires I prefer, however, to provide sufficient space ,.:.sayl the approximately of an inch pitch distance already referred to between adverseitm'ns'of the wire, I having observed that in practice this distance is sufficient to prevent sputtering of the electrode material on the glass walls 'of'the tube.

I have further observed that during the normal operation of the tube, the interior of the vitreous wall It) becomes constantly charged to a negative potential, as. indicated schematically in Figure 5. Now, shell I5 is alternately positive and negative during each. half-cycle of the energizing current; when positive, the electric field created thereby attracts the electrons emitted by the electrode. During the negative half-cycle of the charging current, however, all the parts coming under the influence of the electric field of spiral i5 are attracted thereby, as are many ions created by the electron bombardment and thereupon coming into the influence of the field of electrode M. It is the extreme mass of these ions which in large measure accounts for the sputtering which has heretofore been so detrimental.

Referring now to Figures 3 and i, annular spaces 11-!) and c--d are established between shell 14 and wire l5, and between wire l5 and tube l0,-.respectively. When elements. 14 and [5 are positive, then the region ab carries a positive charge. As a. result thereof, it, not only attracts electrons thereto, but at thesame time either repulses the positive ions or at least serves as a brake therefor. This lowered momentum results in their being-less destructive when they impact on the shell Hi; Space c-cZ is likewise charged positively at this time, and thus to a certain extentv at least, attracts the negative charge from the glass wall 10. This has the efiect of establishing what may be termed a screen or shield preventing ln large part the positive ions from reaching the glass envelope and perhaps resulting in failure at local points.

Because of the positive field which is thus established around electrode l4 during the positive part of the energizing cycle, many of the migratory positiveions do not reach this electrode, while those which do bombard thereagainst have much less disruptive effect, due to their lowered velocity and hence diminished momentum.

Now whenv the elements It and l 5 are negatively charged, a profusion of electrons escape from the interior of shell l4, while lesser quantities escape from both the exterior surface of shell l4 and iron; wire anode l5. It should be noted that eleagar-poo merits I 4 and 15 are simultaneously'at;the. same negative charge. Accordingly,'field a-b becomes negatively charged :so that .a strong electric field of negative potential is formed around electrode 14. Those electrons which escapefrom'region ab progress to a large extent towards the ope posed electrode, which normally is positive. These electrons carrying over from the field w-b form a negative shield around the column of electrons escaping from the open end of electrode [4, this screen contracting the pencil of electrons and shielding the outeredge of thiselectrodd'so that no sputtering can occur at that point. Simultaneously, the region cd becomes negatively charged so that most of the migratory positive ions are attracted and as well, a strong tendency exists to neutralize the charge on the-glass surrounding the electrodes. I have just described themanner in'which the presence of the anode -participates in -the establishment of electric fields which during the posi-- tive half-cycle of currentflowshields-both the electrode and the adjoining region ofgthe glass envelope from ionic bombardment, and which during the negative half-cycle of current flow efiectively dissipates the negative charge from: the tube walls and directs the pencil. of electrons towards the opposed, positive electrode.

It will now be in order to discuss briefly the advantageous results attendant upon the opera-. tion of the shell electrode at comparatively high: temperatures during the normal service of the tube. By operating the electrodes Id and mat elevated temperatures which while substantially higher than those heretofore customary, being in the neighborhood of 500 to 600 (3., it is insured that the metal will not be softened to a dangerous extent. Nevertheless, these temperatures are sufficiently high to reduce the worlc'barrier or function of the emitting surface of the electrode so that a much larger quantity of electrons can be emitted from .the electrode surface than has heretofore been possible under cold cathode operation. I accomplish this simply by bombarding the electrode by a combination of electrons and positive ions until electrode temperature is reached where the work barrier is substantially lowered and an electron emission is achieved with substantially less cathode drop than has heretofore been possible.

While the form of tube shown in Figures 2 through 4 proves initially satisfactory, I have found that somediiiiculty was encountered from time to time in connecting the shell 16 and the spiral [5 together at It. To illustrate, 'upon undertaking to install my new electrode construction into a tube of 38 mm. diameter, than the space c-d (Figures 3 and i) becomes much larger than in the case of tubes of 25 mm. diameter. The desirable field action is diminished greatly in such instance, due probably to the negative charge on tube Hl'being too remote from spiral iii. In such instance, electron emission appears not only around spiral l5, but also'around the interior and exterior of the shell I l. Inasmuch as the weld l6 serves only to support spiral l5 and to keep it in properly spaced relation to electrode it, I find it convenient in certain instances to replace the wire shield !5 with a cylindrical anode it closely encircling shell electrode l4,

being spaced therefrom to a slight extent. I

- I prefer to construct this ring anode 18 of thin sheet metal having a-thiclmess of say 0.005 inch. It may, however, conveniently be madeof' closely wound wire or with closely woven metal sheeting: The plain sheet rmetal I find, however, to, befquite'cheap to manufactureand to entirely satisfactory results. 1

A'support wire l9 carries ring [8.while. wire 13 carries electrode l4; Thesesupport wires 13 and I8, extend through press. it and arecon nected' with eXternallead-in'wires l6, H.

In experimenting with this new construction, I

B,? between the open end I4 of shell l4 andthe...

inward edge l 8' ofcylinder l 8 was critical at least to a=certain extent. I found that this distance should vary between 0.2 'toabout '0.4..times;;the; diameter of the ring lSitself; :2 When so constr'uctd'all thedesirable. results heretofore sought I found to be;.:.admirably achieved. To satisfy-myselfthat s'uchwasthe case, I took" occasion to measure the current 'e'sez tablished between lead-in it, 11 when lead-inv 1:1; was connected to the source of power. Ifoundthat when a total of 350 milliamperes current: flowed through the electrode M, .then about'lSto l2o-milliamperes current was flowing through these two leadins. Inasmuch as this current was. measurable with a direct current 'meter, thisestablishedv that a uni-directional alternating current flow had been achieved through rectification in the mercuryarc. Moreover, since at; all times the leaclain llwas'positive with respect to lead-in I6, it'is reasonable to assume that elec-; tronsflow from anode 18 through lead-in Hi to lead-in ll. -Upon disconnecting lead-in 16 from: lead-in ll, and thereupon measuring the potential difference therebetween, this was found to attain a value of from 25'to 60 volts, direct current. It? appears to be a reasonable conclusion that this potential exists between the gas column and the anode Hi. It may thus logically be concluded'that the higher the operating current, the lower the voltage across the'discharge gap, a phenomenon which is found to take place in actual practice.

Upon contrasting the operation of the con-- struction according to Figure l with that accord-- ing to Figures 2 through 4, inclusive, I concluded internal ionic bombardment, properly heat a tube of fi-foot length and of 25 mm. diameter in very? easy and rapid'rnanner, with sensible reduction in. manufacturing costs andwith the production of: a clean and long-lasting lamp.

" The practice of my invention makes it readily;

possible, for the first time, to employ a shell type cathode of minimum dimensions with-increased current carryingcapacity under coldcathodebp eration. "My new technique makes 1 it entirely possible forthe electrode to have an initial .cur-" rent-carrying capacity sufficientto heat both the surrounding glass envelope itself and the electrode: by internal bombardment to a temperature suffi: ciently high to drive off retained moisture-and occluded gases, while avoiding'abnornial -sputter-.--

ing of the cathode material. I find that the heat imparted to the shell surface by ionic bombardment increases'the kinetic energy of the electrons in the cathode metal, thus freeing more electrons through a weakened potential energy barrier. Moreover, the cathode drop across the electrodes is appreciably diminished, while both the striking voltage and the operating voltage of the arc itself are substantially lowered. All these, along with many other highly practical advantages, attend upon the practice of my invention.

It may be noted that the phenomenon is observed that the working area, that is, the electron-emissive area, of my electrode is large during the initial bombardment process, but is thereupon decreased during the normal operation of the electrode. This phenomenon is attendant upon the practice of my invention according to Figure 1, simply by coating only the interior surface of the shell it. With such construction, then at the very outset of the preliminary bombardment the combination of the three factors comprising the excess of bombarding current, the high work function of the surface of the shell, and the elevated air pressure or gas pressure maintaining in the tube serve to spread the bombarding are over the entire electrode assembly.

tube, by exhausting it through a suitable vacuum reduced to highly emissive oxides, the shell l4,

progressively takes the current load until it attains a light cherry red temperature corresponding to about 850 C., and thereupon carries substantially the entire tube current, amounting to about 2.50 amperes. When this current levels off at a steady value, then the tube is ready to be cooled, filled and sealed off.

While, in general, the character of the salts employed are sufii-ciently oxidizable to assume excellent elimination of moisture and occluded gases I nevertheless find it advantageous in some instances to subject the electrodes, with their electron-emissive salt coatings, to a reducing treatment prior to assembly in the lamp. In this way I assure complete elimination of moisture and 0ccluded gases in the subsequent operations wherein the electrodes are brought to a light cherry red heat.

Since many embodiments of my invention will readily occur to those skilled in the art, once the broad aspects thereof are disclosed,.it will be understood that all matter described herein, or shown in the accompanying drawings, is to be as illustrative and not in a limiting sense.

I claim as my invention:

1. As a new article of manufacture, a space discharge tube comprising, in combination, a vitreous envelope, an oxide-coated shell electrode at one end thereof, and an anode comprising several turns of wire encircling said electrode in spaced relation thereto and electrically connected thereto.

2. As a new article of manufacture, a space discharge tube comprising, in combination, a vitreous envelope, an oxide-coated shell electrode at one end thereof, and an anode comprising several turns of Wire encircling said electrode throughout its length and electrically connected thereto, the spacing of both the anode from the electrode and the turns of the anode amongst themselves being sufficient to provide room for the eifect of the electric field established between the anode and the electrode to assert itself.

3. As a new article of manufacture, a space discharge tube comprising, in combination, a. vitreous envelope, an oxide-coated shell electrode at one end thereof, and an anode comprising several turns of wire encircling said electrode and electrically connected thereto with a free space of about /32 of an inch therebetween, the wire having a thickness of approximately 0.03 inch and the turns being spaced about A; of an inch apart.

4. As a new article of manufacture, a space discharge tube comprising, in combination, a vitreous envelope, an oxide-coated shell electrode at one ei'idthereof, and an anode comprising several turns of wire encircling said electrode in spaced relation thereto and electrically connected thereto, both the interior and exterior of the shell electrode and the turns of the wire being coated with an electron-emissive oxide.

5. As a new article of manufacture, in combination, an oxide-coated shell electrode, and an anode comprising several turns of wire encircling said electrode in spaced relation thereto and electrically connected therewith.

6. As a new article of manufacture, in combination, a shell electrode, and an anode comprising several turns of wire encircling said electrode in spaced relation thereto and electrically connected therewith, both the interior and exterior of said shell electrode and the turns of wire being coated with an electron-emissive oxide.

7. As a new article of manufacture, a space discharge tube comprising in combination, an elongated vitreous envelope, oxide-coated shell electrodes at opposite ends thereof, and corresponding anodes associated with said electrodes, each of said anodes comprising several turns of wire encircling its corresponding electrode in spaced relation thereto and in electrical connection therewith.

RALPH CORTESE.

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

UNITED STATES PATENTS Number Name Date 1,582,720 Zworykin Apr. 27, 1926 1,756,889 Thompson Apr. 29, 1930 1,845,777 Alexander et a1 Feb. 16, 1932 1,971,907 Found Aug. 28, 1934 2,008,066 Ende July 16, 1935 2,020,393 Woolrich Nov. 12, 1935 FOREIGN PATENTS Number Country Date 315,387 Great Britain Jan. 9, 1930 Patent No; 2,441,260.

r the Patent Office.

Certificate of Correction May 11, 1948.

the paragraph reading Figure igure I. in line 51, same col beginning with 6 is a side elevation strike out all t with this correction therein th umn; and that the said Letters Patent should be read at the same may confer Signed and sealed this 21st day of September, A. D. 1948.

THOMAS F. MURPHY,

Assistant Uommz'ssz'oner of Patents.

m to the record of the case in

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