US2057908A - Luminous tube - Google Patents

Description

Oct. 20, 1936.

- Smaentor RAYMOND NAUTH (Ittomeg Patented Oct. 20, 1936 UNITED STATES PATENT OFFICE LUMINOUS TUBE Application January 8, 1935, Serial No. 862

9 Claims.

This invention relates to luminous or glow tubes suitable for advertising purposes, and it has particular reference to a durable and permanent tube which is stable and operative at low atmospheric temperatures.

When a small quantity of gas at a low pressure is enclosed in a glass tube and subjected to the influence of a high potential electric discharge passing therethrough, a luminous glow in the gas is produced. This efiect is usually attributed to the bombardment of the gaseous molecules by electrons emanating from the cathode, with a resulting ionization of the gas, and its corresponding phenomenon of luminescence. The color produced is more or less specific for the gas so ionized,thus, neon invariably produces a red color, while argon, or mixtures of argon and neon, produce a blue. If a small quantity of mercury vapor be included in the tube, the blue color is more pronounced.

While a blue color may be obtained by electronic ionization of argon, a number of difficulties are encountered in utilizing this eflect in a practical way. Some are due to the high ionizing potential of argon, in comparison with other gases, such as neon. The higher the potential, the greater the prospects of cathodic disintegration, which leads to the early failure of the tube. If, as just suggested, mercury be included in the system (to provide a certain quantum of ions for secondary ionization of the argon or other gas), there is a strong possibility of amalgamation between mercury and the cathode; which effect again increases the potential drop.

One particular deleterious efiect arising from mercury addition, in a haphazard manner, to a low pressure gas tube, is that of fading", or the failure of the tube at low temperatures. What has been suggested in the preceding paragraphs applies to operation at normal atmospheric temperatures, such as those obtaining in the summer months in the north temperature zone. When, however, winter temperatures prevail, such as from say plus fifteen to minus thirty degrees Fahrenheit, the glow light which might otherwise obtain cannot be produced, or, if instituted, it diminishes in brilliance, and ultimately goes out altogether. Or, in a glow tube containing no mercury, there is the possibility of failure at low temperatures, due to the low temperature of the tube wall, rendering it more capable of adsorbing the contained gas. This is the effect which is herein denominated as fading.

Critical study of the ultimate cause of fading, or its underlying philosophical explanation, in-

volves further considerations of molecular and atomic physics which are too abstruse for detailed presentation here, it being the primary purpose of this specification to describe useful ways in which the effect may be circumvented. Suffice it to say, therefore, that such explanation may proceed on some one or more of these premises. (1) That by virtue of the high temperature gradient between the electrode and the exterior wall of the glow tube, which exists at winter temperal0 tures, the mercury ions are discharged before they can enter the electron stream in sufiicient quantity to produce any useful result, with the consequent raising of the potential drop through the gas to an unattainable value. (2) That vaporiza- 15 tion of the mercury is confined to the electrode region, and such mercury attacks the electrode with the formation of a high boiling point surface amalgam, attractive -to vaporized atomic mercury, which in turn increases the potential drop. (3) That such mercury as is vaporized by the heat of the electrode forms a shield therearound, in which only a small percentage of the atoms or molecules are in an ionized state, thus locally exhausting the electron discharge from the oathode before it can appreciably affect the gaseous medium.

Whatever may be the soundness or acceptability of the foregoing or other views is, of course, a matter of opinion, but the fact on which the foregoing hypotheses are based, namely, that tubes fade with reduction of temperature, is demonstrable by simple experiment.

With these general considerations in mind, it may be stated that the present invention contemplates improvements in luminous tubes, to the end that the light produced therein shall be of good color, and permanent at normal and low temperatures, and such tubes shall have a long life.

These general objects may be achieved by the conjoint or separate use of the hereinafter described expecliencies. According to one of them, it is proposed to contain mercury in a small still which may be provided with a reflux condenser, and which is heated by the electrode to provide an aliquot, but not excessive, quantity of mercury vapor to augment the desired operation.

According to another phase of the invention, it is proposed to protect the electrode from ex- 50 cess amounts of mercury, so that amalgamation will not take place.

Viewed from a different aspect, the invention contemplates the association with the electrode and ionized gas of the heavy isotopes of mer- 55 be made with the elements gallium and indium.

And in another phase, the invention proposes an oxidized metal electrode having thereon a surface coating of or derived from a salt such as ruthenium chloride.

A typical form of electrode and tube assembly embodying the principles of the invention is i1- lustrated in the drawing, in which Fig. 1 is a longitudinal section and. Fig. 2 is a transverse section.

The numeral I0 designates what may be termed the end of the visible or glow portion of the luminous tube, which, as it is here supposed for exemplary purposes, is of considerable length and takes the form of one or more letters or symbols used for advertising purposes. To the end, or other point, but preferably a low point, of the visible tube It is affixed an electrode tube portion or case II, of slightly greater diameter, the purpose of which is to receive an electrode and to seal oif the visible tube so that gas contained therein cannot escape. Disposed within the electrode portion H is another tube l3, also of glass, which may be termed the electrode sheath, and containing a suitable electrode M. As herein illustrated, the electrode id is in the form of a coiled cylinder, of a nature hereinafter described, but it will be understood that other forms of electrodes may be used.

A lead wire I 5, secured to the electrode M, extends through the sheath l3 and electrode portion H, to provide a means for connecting the usual electric circuit to the tube. The glass tube I3 is flattened down and blocked in the rear of the mesh id, as indicated by the numeral l6, and tube H has its end turned over and integrated with the blocked end of the tube l3, as indicated by the numeral l7, thereby sealing the tubes from leakage.

The forward end of the sheath I3 is drawn down to provide a relatively small aperture 2|, thus forming a type of guide through which the electrons must flow, and a restriction resisting the counter-flow of excess quantities of material contained in the remaining portions of the entire tube. The walls of the aperture 2| are then flared downwardly with a reverse bend to a point adjacent the wall of the tube ll, thus forming an annular pocket 22, which may be further defined by drawing the glass inward, as indicated by the numeral 23, and then outward to form a joint with the tube ll, adjacent its junction with the tube l0.

The pocket 22 is filled with as much clean mercury as it will comfortably hold, and by the term mercury, when used generically, it is meant to embrace not only the element commonly regarded as mercury, but also such amalgams or isotopic concentrates as are useful in the same relationship. When the sign is formed to include the foregoing principles, it is then evacuated and filled with a suitable quantity of inert gas. For the purpose of producing a blue light, argon may be used, or mixtures of argon and neon, or other suitable mixtures.

It will be observed that when current is applied to the electrodes, the generated heat is concentrated at the pocket 22, thereby forming a still for the contained mercury. Hence, whatever the external temperature may be, the mercury will be caused to vaporize, and the parts should be so proportioned, for best operation, as to produce such vaporization at the lowest temperatures to which the sign is apt to be subjected.

At the same time, however, it is not advantageous to distill the mercury at such rate as to exhaust the still, or to eject the vapors entirely into the visible portion in of the tube. There fore, the flared portion 23 is included, with a relatively large radiating surface, to provide a reflux condenser for a major portion of the vapors, thereby not only protecting the visible portion I0, but also insuring the presence of some mercury in the pocket 22, since the condensate flows back into the still. It will thus be seen that the present invention provides for the production of, or what might be termed the priming of the sign with, mercury vapors, a part of which are in the ionic state, regardless of atmospheric temperatures. On' the basis of the theory that such ions facilitate the conduction of the current, it follows that the sign may be operated from a normal electric potential without regard to the existing atmospheric temperatures.

Having thus described means for insuring the institution of the luminous glow, attention'is now invited to a further consideration of the mode of protecting the electrode M from excesses of mercury vapor. As stated in the forepart of this specification, it is well known that electrodes are subject to the phenomenon known as disintegration, which, generally speaking, means that particles of the electrode actually depart from the solid mass. Such disintegration alters the electrode surface, and tends to induce gas adsorption and occlusion, all of which efiects increase the potential drop, and so lead to operating failure for an initially satisfactory voltage. It has also been reported in the literature that sodium amalgam, when used as an electrode, disintegrates to such an extent as to coat the walls of. the visible tube portion with a substance rapidly adsorbing the contained gas. From these considerations, as well as others, and from practical observations, it appears that if. too much mercury is allowed to contact the electrode, even if it be of some reputedly non-amalgamating substance such as iron, the electrode material is damaged and ineificient I operation results.

At the same time, as I have discovered, it is advantageous to admit a limited quantity of mercury vapor to the cathode, and the line of demarcation between too much vapor, and a suitable quantity, as I have determined it for practical purposes, is that which distinguishes from deposition of mercury, and its immediate re-boiling or ionization. I may here suggest, in an endeavor to explain, rather than to limit my invention, that the observation made heretofore by others, to the eifect that secondary ionization with mercury is highly inefl'icient, may be because such observation was made under conditions permitting an excess of mercury to contact the electrode. Therefore; what is desired by the present invention, in this phase, is to limit the quantum of mercury coming into contact with the electrode to that value which can either be readily ionized by the available current, or immediately redistilled by the available heat.

Referring again to the drawing, it will be seen that any mercury coming into contact with the electrode it must pass through the small aperture 2 l, and, in so doing, it is subjected to the full intensity of the electrons flowing from the electrode. While a certain quantity of vapors will so pass the aperture 2!, the total quantum is relatively small, and insufiicient to form an adherent deposit on the cathode. My experience with the invention further indicates that the ionized mercury is incapable of dislodging particles from the electrode. Hence, while some secondary ionization is obtained, thereby facilitating the conduction of current through the gas, there is small likelihood of the formation of a surface film or amalgam of mercury with the electrode material. In practice, it will be found advantageous to space the sheath l3 from the electrode I4, and to dimension the aperture 2 l, in such manner that the maximum amount of mercury may surround the electrode in a highly vaporized form, without concurrently forming any adherent deposit.

If a concentrate of the heavier isotopes of 'nercury be employed, in lieu of the ordinary mercury of the chemists, the foregoing effects are not only obtained to better advantage, but the intensity of blue light is also appreciably increased. With regard to isotopes, it is believed sufficient here to recall that mercury, which has an assigned atomic weight of 200.6, is assumed to be composed of a mixture of. chemically indistinguishable 'atoms, whose several atomic weights lie in the range of 197 to 204. The atoms so mixed together can be separated or concentrated after a fashion into two portions, a light portion containing a higher percentage of the atoms in the range 197 to 200, and a heavy portion containing a higher concentrate of the atoms having weights of 202 to 204. While any desired method may be employed for effecting such concentration, as outlined or referred to by Aston in his work, Isotopes, 2nd ed., 1924, I have found it sufficient for the purposes here intended to distill a large quantity, of. say five kilograms, at the critical boiling point of ordinary pure mercury referred to normal barometric pressure. The vaporization proceeds slowly, and the temperature should be held as close to the established value as possible, until the original mass is concentrated to about 20 grams. While such method is theoretically-inefficient, I find it best for economic reasons, since more theoretically eiiicient methods are too expensive for commercial work.

Analysis of the residue shows that it contains more than a normal amount of the heavier isotopes of mercury, which, either through their greater ionizing ability, or the greater intensity of their emitted blue wave lengths, impart to the glow a durable blue color of greater depth than that obtained with ordinary mercury. Another desirable feature of such concentrate is its passivity toward oxidized metal electrodes.

When ordinary mercury is employed, for example, against an electrode of oxidized nickel, there is a tendency towards too rapid disintegration. The heavy isotopic concentrate, however, may be used with oxidized metal electrodes which are not protected with any further coating, thereby permitting economies in tube construction which otherwise could not be tolerated.

Another form of mercury which may be used is an amalgam with such metals as gallium and indium. These light metals form with mercury low boiling point amalgams, which are readily vaporized by the heat of the electrode. Unlike sodium amalgam electrodes, however, they do not coat the visible tube walls, or adsorb the contained gas. Hence, the use of these low boiling point amalgams protects the electrode from any tendency to disintegrate by contact with mercury. If the amalgam is prepared with the heavy isotope concentrate, then the advantages of. such isotopes may also be concurrently obtained.

As hereinabove stated, the electrodes may be of any suitable form and composition, even oxide coated electrodes being serviceable when used under suitable precautions. For very good results, in conjunction with the foregoing proposals,

or for use in ordinary tubes, however, I havefound that an electrode may be made according to the following plan. A coil of metal, such as steel containing chromium, is cleaned and is given a surface oxide coating by passing it through an oxidizing flame, or by heating in air to a coloring temperature. The coating so formed should not be so heavy as to flake or scale off, however. After heating, the .metal is quenched in a solution'of ruthenium chloride, removed, and dried. As a result of this treatment, there is formed on the electrode a firm coating of the ruthenium salt, and the electrode is conditioned for use in luminous tubes.

In the device illustrated in the drawing, it may therefore be supposed that the electrode I4 is provided with a ruthenium coating, and the material marked Hg, in the still 22, is an amalgam .containing a concentrate of the heavy isotopes of mercury, thus utilizing all of the foregoing features in combination, to produce a luminous tube of good brilliance under all weather conditions, having a deep blue spectrum, and in which relatively low voltages may be employed. Or, it may be supposed that some of the foregoing features are not utilized, but others are, as it will be readily understood that marked advantages may be obtained by using the various apparent sub-combinations. It will therefore be understood that the scope of the invention should be ascertained in the light of the following claims,

I claim:

1. A luminous tube comprising a visible tube portion and electrode portions aflixed thereto and in communication therewith, one of said electrode portions containing an'electrode, a glass sheath around said electrode, said sheath being formed with a restricted aperture at its end adjacent said visible tube, said apertured portion merging into a pocket portion and an outwardly flared portion, said pocket portion containing mercury, and said visible tube portion containing an ionized inert gas at a low pressure.

2. A luminous tube comprising a length of visible tubing, electrode portions affixed to and in communication with said length, one of said electrode portions containing an electrode, a glass sheath for said electrode, said sheath being secured to said electrode portion at one end and being drawn down to provide a restricted aperture at the opposite end of said electrode, said tubing being formed with a pocket adapted to receive mercury beyond said restricted portion and being outwardly flared into contact with said electrode portion beyond said pocket portion, said Visible tube lengthcontaining a gas at low pressure which when ionized under suitable potential produces a blue light.

3. The method of preventing fading in glow tubeswhich comprises subjecting an isolated inert gas at low pressure to an electric discharge between a pair of electrodes, and simultaneously subjecting the electrodes and gas to the influence of a limited quantity of mercury vapor distilled by the heat of said electrodes.

4. A luminous tube comprising a visible tube portion and an electrode portion afiixed thereto and in communication therewith, said electrode portion containing an electrode, inert gas in said tube adapted to be ionized by an electron discharge from said electrode, and a concentrate of the heavier isotopes of mercury in said tube and adapted to be vaporized therein. q

5. A luminous tube comprising a visible tube portion and electrode portions affixed thereto and in communication therewith, said electrode portions containing electrodes for the discharge of a, high electric potential through said gas, and a quantity of mercury in said tube adapted o e v porized during such discharge, said mercury being in the form of an amalgam with a metal of the class composed of gallium and indium.

6. A luminous tube comprising a visible tube portion and electrode portions aifixed thereto and in communication therewith, said electrode portions containing electrodes for the discharge of a high electric potential through said visible tube portion, and inert gas in said tube adapted to be ionized by said discharge, a quantity of mercury in said tube adapted to be vaporized by the heat of said discharge, said mercury containing a, concentrate of its heavy isotopes, at least one of said electrodes consisting of a metal having a surface coating of its own oxide thereon.

7. In a luminous sign having a visible tube portion and an electrode portion, an electrode in said electrode portion, said electrode being formed of metal having a coating of a ruthenium compound thereon.

8. A luminous sign having a visible tube portion and electrode portions amxed thereto and in communication therewith, one of said electrode portions containing an electrode, said electrode being formed of metal having a coating of a ruthenium compound thereon, an inert gas in said tube portion, and a quantity of mercury in said sign adapted to be vaporized by the heat of said electrode.

9. A luminous sign having a visible tube portion and electrode portions afiixed thereto and in communication therewith, one of said electrode portions/containing an electrode, said e1ectrode being formed of metal having a coating of a ruthenium compound thereon, an inert gas in said tube portion, and a quantity of mercury in said sign adapted to be vaporized in said tube, said mercury containing a high percentage of the heavy isotopes thereof.

RAYMOND N AUTH

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