US 2449113 A
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Description (OCR text may contain errors)
Sept. 14, 1948. FRUTH 2,449,113
ELECTRIC DISCHARGE DEVICE Filed July 22, 1944 O/a/ Meder/c/(ghe fiz Patented Sept. 14, 1948 UNITED; STATES PATENT OFFICE"; i
anac'rmc n'rsonsaca navroa ma manic: sna l, Skokie, nt, 'Application July as, 1944, Serial No. 5401120 This invention relates to electrodes. and more particularly to novel electric discharge devices of the general type utilized in gaseous electric discharge tubes or other installationswhere the electrode is to serve as a source of electrons.
The general object of the invention is to pro- 4 Claims; (Cl. 176-128) vide an electrode of the general class indicated which achieves long. life in operation. has unusually good emission characteristics, and is well suited to quantity production. In carrying out the invention, such superior characteristics are obtained by extruding or otherwise fashioning the electrode from a conductive ceramic, such, for example. as a metallic titanate. and firing the same at high temperature.
Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying but disclosing different forms of connections which may be made to the electrode body.
Fig. 5 is a magnified fragmentary view of a portion of the surface of an electrode such as those shown in Fig. 1.
Figs. 6 and 7 are respectively perspectiveand end sectional views of different forms of electrode supports adapted for use with electrodes embodying the present invention.
Fig. 8 is a fragmentary side elevational view of a modified form of electrode body.
While the invention. is susceptible of various modifications and alternative constructions, I have shown in the drawings and will herein describe in detail the preferred embodiment, but it is to be understood that I do not thereby intend to limit the invention to the specific form disclosed, but intend to cover all modifications and alternative constructions falling within the spirit and scope of the inventionfas expressedin the appended claims. 1
Generally considered, electrodes Ill and il, shown in Fig. 1, constitute a preferred embodiment of this invention, and since the two may be substantially identical, a description of one will sufllce for both. These electrodes include a body I! of conductive ceramic material generally cyprovide a large exposed surface area. Connecting and supporting leads ll are secured and electrically connected to one-end of the inner surface of the body I2 and areadapted to be sealed into a glass tube or. closure l1 oi a gaseous electric discharge tube. In some instances auxiliary supports of insulating material such as a mica disk It, shown in Fig. 6, or glass beads l9 extending inwardly from the sides of the 'glass tube or closure, as shown in Fig. 7, are desirable to assist in supporting and steadying the electrode body within the tube. Also, when greater surface area and pointed outer projections aredesired, circumferential grooves may be used to supplement the longitudinal flutes, as illustrated in the modifled disclosure of an electrode 20, shown in Fig. 8.
The material of the electrode body is. generally speaking, a conductive ceramic or refractory which, when emission is desired, has an actinic or electron emitting substance added thereto. The
firing of the electrode body at high temperatures after formation is desirable because it has a tendency to produce a multiplicity of sharp iine points on the electrode surface somewhat as showh in Fig; 5, and also makes the electrode hard and heat resistant.
The material and its characteristics are especially well adapted to the production by simple and inexpensive manufacturing processes of an electrode having particularly desirable electrical and discharge characteristics. That is. the material may not only be suited-to the particular purpose of use by the selection of a desirable actinic or electron emitting substance, but also, the characteristics of the material adapt it to formation by convenient processes, such as extrusion to shapes having sharp or knife edges which are well suited to emcient use in gaseous electric discharge tubes.
Considering the disclosed structure in the drawings in greater detail, an exemplary form of gaseous electric discharge tube is shown in Fig. 1, and has a sealed glass container or closure 11 in which the electrodes l0 and ii are mounted in spaced relation. This gaseous electric discharge tube may be considered to represent any one of a large variety of discharge tubes'some of which utilize electron emitting electrodes, and some of which have non-emitting electrodes and are,dependent upon the ionization of gas to effect a discharge. Still other varieties of such tubes incorporate a vapor or vaporizable substance within the tubeto obtain the desired color or result therefrom. In this instance the electrodes 10 and iindrlcal. in form and having recessed or fluted I I are similar in shape and have similar supporting structures. They may both be electron emitting electrodes, or they may both be non-emitting electrodes. In'some instances also, one may be an emitting electrode and the other a non-emittingelectrode. The emission characteristics of ac-rams electrode and define a series of inner longitudinally extending knife edges 28. The sharp or knife edges on the inner and outer surfaces of the electrode improve the discharge characteristics of the electrode and reduce the potential drop at the surface of the electrode which is often referred to as the cathodedrop. The flutes in the surfaces of the electrode serve to segregate thin sections, and thereby to improve theemission characteristics of an electrode which includes an emitting substance by increasing the heating of the segregated thin sections as a result of the low thermal conductivity of the ceramic.
The particular form of the electrode disclosed, which has longitudinally fluted inner and outer surfaces, is well adapted to simple and inexpensive manufacture by processes such as extrusion or molding while the ceramic material of the electrode is in a plastic state. In the extrusion of the electrodes, as is quite evident, the sectional shape is extruded and the electrode bodies are cut to the desired length. After the formation of the electrode body the firing of the ceramic material at a high temperature, for example 2500 F., produces a multiplicity of fine sharp points, such as l l 21 in Fig. 5, on the surface of the electrode.
These points are advantageous in reducing the potential drop at the surface of the electrode and improving the, emission characteristics thereof. In that connection it should be noted'that the provision of points, even microscopic ones, increases the vpltage gradient, as compared to that from a flat surface. thereby resulting in higher acceleration of the electrons away from the points when potential is applied between the electrodes. The fired ceramic material used is capable of operation at high temperatures without deterioration in shape, that is, blunting of the points. Consequently such material is well adapted to withstand the heating of the points on it incident to the high current density in such points and positive ion bombardment of the same. In the event that emissive material is incorporated in the ceramic, as hereinafter more particularly described, the heating of the points materially increases emission by such material. Heating of the non-deforming points is augmented here by reason of the thermal insulating character of the ceramic material of which they, together with the body from which they project, are made. Such material having a low thermal conductivity or, in other words, thermal insulating properties, it follows that the heat imparted to the points is largely trapped in them since it cannot readily flow through the ceramic material. The points are, in effect, thermally isolated from the body from which they project I by reason of the shape of the points, as such,
plus the low thermal conductivity of the ceramic.
In the form shown inFigs. l and 3, the connecting and supporting leads it are connected to the electrodebody i2 through a connector elegreatly increase the inner exposed surface of the ment 28 which includes a tubular portion 2| and a connected tubular portion II. The tubular portion 28 is preferably crlmped onto and soldered to the ends of the leads II. The larger tubular portion 80 fits into the opening 24 at one end of the electrode body. The tubular portion 80 is made secure in the opening 24, and the electrical connection between that portion and the electrode body is improved by filling the spaces between the tubular portion and electrode body with a conductive cement 32.
In the modification shown in Fig. 4, connecting leads 33 are twisted together at 84 and extend into the opening 2} in the electrode body. In this instance, again, the connecting leads are secured in place by filling the space between the twisted portion of the leads and the electrode body with a conductive cement It. In both instances the conductive cement 32 and. I8 is one which not only provides an electrical connection between the connecting leads and the electrode body, but alsohas the property of adhering to the electrode body and solidifying to'form a firm and dependable connection. One example of a cement which is satisfactory is one composed of copper powder, copper titanate and lead borate. Silver paint is a second example of a satisfactory material and has the advantage oi. permitting soldering to the silvered area. A third example is a material made of graphite paste including gelatin or starch and carbonized after the application by heat treatment.
Considering more fully and completely the material of which the electrode body may be made, the conductive ceramic of which the electrode body may be made is desirably a metallic titanate. Examples of the metallic titanates suitable for the purpose of making such electrodes are iron-copper-chromium titanate, iron-copper titanate, iron titanate, copper titanate, and chromium titanate. Examples of other conductive refractories which might be used are those containing silicon carbide, copper oxide, or porcelain heavily loaded with carbon or metal powder or metallic oxides. When conductive refractories such as these are used, magnesium oxide or zirconium oxide may be added to improve the refractory qualities. The magnesium oxide has the additional advantage in some electrodes that it I is an electron emitting substance. When the magnesium oxide is used in the conductive refractory material the quantity may be varied from approximately five per cent mately ten per cent by weight.
to approxi- When it is desired that the electrode shall be one of the electron emitting type, an electron emitting substance or material is added to the metallic titanate or other conductive ceramic material. Examples of such electron emitting substances include both the metals and the oxides of barium, calcium and strontium. This group includes the alkaline earth metals. Actinic or radioactive materials which emit alpha particles, or in some instances also beta and gamma particles or rays,- may also be added to the conductive ceramic material to suit a dc.- sired purpose. Such materials include polonium, thorium, radium and uranium oxide. The addition of an electron emitting substance to the conductive ceramic material, in addition to providing the emission of electrons, also reduces. the potential drop at the surface of the electrode. The electron emitting material which is added to the conductive ceramic in the preferred em bodiment of this invention is thoroughly interport is disclosed in Fig. 7.
auxiliary support l8 fits into the tube or closure i1 and has a central opening 31 which fits .over the outer surface of the electrode body If. This auxiliary support is made of an insulating material such as sheet mica. It is disposed between the ends of the electrode body and serves to support that electrode body from thewall of the tube. A plurality of openings 38 are provided in the support for the passage of the discharge within the tubeto the exposed surfaces of the electrode. p
A modified form of auxiliary electrode sup- In this auxiliary support a plurality of radially extending and circumferentially spaced glass beads I 9 extend inwardly from the wall of the tube l1 and engage the outer surface of the electrode body at circumfcrentially spaced points. Additional support for the beads I9 may be provided by dimples 39 in the wall of the tube. With this type of auxiliary support the discharge may pass between the spaced bead to the exposed surfaces of the electrode body.
r In some instances, and particularly where high emission and low surface potential drop are desired, the electrode 29, shown in Fig. 8, is grooved circumferentially in addition to the longitudinal 2; A radiation emitting cold cathode type discharge tube comprising, in combination, first and second electrodes having means for supplying current thereto, a radiation transparent envelope mounting said electrodes therein in spaced apart relation, at least one of said electrodes being constructed of refractory ceramic material having the property of conducting electricity through the body thereof even at low temperatures, said ceramic electrode having a surfa-ce'which includes a multiplicity of sharp outward protrusions formed thereon and giving rise 'to a high potential gradient in the region thereof upon application' of voltage to said electrodes, said one electrode comprising a metallic titanate as its 7 major constituent and with magnesium oxide flutes to provide a large number of projecting points on the electrodev surface. Onesatisfactory method of obtaining or making an electrode having the projecting points is to make the electrode body as-previously explained, with the longitudinal flutes, and then thread the outer surface with a V-groove thread while the ceramic material is still in a plastic state but sufficiently solid to withstand the operation.
In the claims which follow, the term cold cathode" will be understood to refer to electrodes not having a filament or similar auxiliary source of heat. As is well known to those skilled in the art cathodes of this general type become heated only by reason of-the current in the dis-"- charge path.
Iclaimasmy invention: 1, A radiation emittingcold cathode type discharge tube comprising, in combination, first and second electrodes having means for supplying current thereto, a radiation transparent envelope mounting said electrodes therein in spaced apart relation, at least one of said electrodes consisting of a homogeneous refractory ceramic material, said material being comprised predominately of a titanate having the property of conducting electricity through the body thereof even at low temperatures, said ceramic electrode having a surface which is covered by a'mul-' tiplicity of microscopically fine points resulting from high temperature firing, said points giving rise to an intense potential gradient in the region' thereof upon application of voltage to said electrodes to facilitate the passage of electrons therefrom at a magnitude sumcient to produce localized heating at said points.
unrran s'ramsm'rsurs Number Name a Date 1,291,441 Donle Jan. 14, 1910 1,619,318 Summers Mar. 1, 1927 1,661,589 Winninghoi! Mar. 8. 1928 1,832,009 Foulke (a) Nov. 17, 1831 1,851,706 Hull .1..... Mar. 29, 1932 1,922,244 Hunter Aug. 15, 1933' 1,932,025 Thomas (a) Oct. 24, 1938 to 2,001,509' Uyterhoeven May 14, 1985 2,129,357 Marden Sept; 6, 1938 2,162,414 Abbott- June 18, 1939 2,305,327 Thurnauer (a) Dec; 15, 1942 2,311,917 Wainer ,(a) Feb. 23, 1943 to 2,311,918 Wainer (b) Fen-23, 1943 2,328,410 Berge Aug. 31,1943 2,369,266 Thurnauer (1)) .Feb. 13, 1945 FOREIGN PATENTS Number Country Date 520,128 Great Britain Apr, 18, 1940 added in minorproportion.
3. A radiation emitting cold cathode type discharge tube comprising, in combination, first and second electrodes having means for supplying current thereto, a supporting envelope mounting said electrodes therein in spaced apart relation, at least one of said electrodes beingconstructed of refractory ceramic material having the property of conducting current through the body' current thereto, a supporting envelope mounting of the oxides ofbarium, calcium and strontium.
, HAL FREDERICK mum.
an-reassess .orran The following references are'of record in the file of this patent: