US2097307A - Apparatus and method for introducing material into electric discharge devices - Google Patents

Description

APPARATUS AND METHOD FOR INTRODUCING M ATERIAL INTO ELECTRIC DISCHARGE DEVICES Filed Feb. 28, 1935 Oct. 26, 1937. WYA. RUGGLES 2,097,307.

VA POR/ ZABL E MA TE R/AL.

\ ELECTRIC HEA TERS Inventor 53 William A.Rugiles, M H/ 7-! W 6 H is. Attorneyatented Oct. 26, 1937 UNITED STATES APPARATUS AND METHOD FOR INTRODUC- ING MATERIAL INTO ELECTRIC DIS- CHARGE DEVICES I William A. Ruggles, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application February 28, 1935, Serial No. 8,631

2 Claims. (Cl. 250-275) The present invention relates to electric discharge devices, more particularly to improved methods for introducing into vacuum tubes materials which are either deleteriously affected by the atmosphere or are difilcult to handle. Another object of the invention is to provide an improved practical method for preparing and storing material which is to be introduced into vacuum tubes for 'gettering 'or for activating purposes.

I have chosen to illustrate and describe my invention in connection with a typical type of electric discharge device and in particular a lamp in which light is produced bygthe passage of electricity through an attenuated gas consisting, at least in part, of vaporized metal'which volatilizes at a relatively low temperature, for example sodium.

Sodium is a very active material and when exposed to the atmosphere, takes up moisture and oxidizes-rapidly. Alkali metals of this sort are very diflicult to obtain in a pure state and even more diflicult to introduce, without sacrificing purity, into an electric discharge device. In certain types of devices, such as glow lamps and other gaseous discharge devices, it is sometimes necessary that the amount and kind of active material introduced therein be accurately controlled in order that the light quality of the lamps and the electrical characteristics of the other devices made in quantity production may not vary but will be of a'predetermined and reproducible character. The present invention provides a practical method of accomplishing these results and in particular, of assuring not only a high degree of freedom from contamination of the active material when introduced into the envelope but also of assuring that the quantity of the material is of a predetermined weight or volume, or at least, falls within narrow permissible ranges of weights or volumes.

The invention will be more fully explained in connection with the accompanying drawing in which Fig. 1 is a elevational view, partly in section, of a vapor lamp in which an active material is to be introduced. Fig. 2 is a diagrammatic view of apparatus useful in carrying out the invention, and Fig. 3 is an elevational view of a structure from which a capsule is formed.

Referring to Fig. 1, the lamp thereillustrated comprises a tubular member I consisting of sodium-resistant glass, or lined with a sodiumresistant glass. In the envelope, there is provided an attenuated gas, ordinarily a rare gas such as neon, and a small quantity ofsodium. While sodium may be introduced in any convenient manner, I prefer to utilize the capsule method so-called, which will be described in detail later. For this purpose, a capsule 2 is provided and containing a few tenths of a gram of metallic sodium. The capsule is preferably formed in the manner described hereinafter out of thin glass which is both heat-resistant and alkali-resistant. A glass sold under the name of Corning 705 AJ has been found to be suitable for this purpose. The sodium is preferably introduced near the center of the lamp so that the sodium escaping from the capsule, as will bepointed out hereinafter. is deposited on the mid-portion of the tube. v

Surrounding the envelope I is a-transparent heat conservator 3 which, as shown in the drawing, consists of a double-walled vessel having substantially th same shape as the lamp envelope and closely surrounding it. The heat conservator preferably is evacuated.

The several electrode structures 4, 5 are provided at opposite ends of the envelope i, each functioning alternatively as cathode and anode during the operation of the lamp on alternating current circuits. The electrode structure 4 consists of a filamentary spiral 6 connected to the leading-in conductors l, 8 and surrounded by a metal member 9 having a flattened cylindrical conflguration'and which as illustrated, is elec-' trically connected to the leading-in conductor 8. When the electrode structure 4 operates as a cathode, electrons are emitted by the spiral member 6 which is heated to an electron-emitting temperature by current supplied through the sealed-in conductors i0, H from any suitable source (not shown). In order to enhance the electron emissivity of the heated member 6, it is preferably coated with alkaline earth material, suchfor example as barium oxide in accordance with well-known practice. During the half-wave period when the electrode structure 4 is operating as a cathode, the cylindrical member 9 which surrounds the heated portion may emit some electrons, particularly so when its interior surface is also coated with emisslve material'such as barium oxide. but in the main it is a function of the member 9 to act as anode during the reverse half-cycle when the electrode 4 is at a positive potential.

The electrode structure 5 at the opposite end of the lamp has a construction similar to the electrode structure 4. It is supported by a pair of parallel conductors which extend throughout the length of the lamp envelope and are surrounded by suitable insulating jackets it, as,

consisting, for example, of alumina or beryllia. Current for heating the filamentary spiral member H of the electrode structure 5 is supplied through the .external conductors II, I! from some suitable source (not shown). The electrode structure 5 is surrounded by a metal cyl lnder 2| preferably of flattened configuration which acts as anode during the half-cycle when the electrode 5 is at positive potential. This structure is prevented from vibrating by an anchor 22 which is secured to the insulating coatin gs l3, H by the supports 23, 2.

In operation, when alternating voltage is impressed between the electrodes 4, 5 and the filaments 6 and I! are suitably energized, the lamp gives off an intense but soft yellow light, assuming the material 2 to be sodium. In order to start the lamp at reasonably low voltages, a starting anode 25 may be provided to which connection is made from the exterior by means of a leading-in conductor 28. This electrode may consist of a metal sleeve surrounding one of the insulating Jackets i3, I4 and in operation, takes the .function of auxiliary anode positioned fairly close to the spiral 8 which serves as a cathode during the starting period.

A lamp structure such as described has been disclosed and claimed in a patent application filed July 7, 1934, in the name of Gorton R. Fonda and Andrew H. Young, Serial No. 734,090, entitled Method of operating .vapor electric lamps" and assigned to the same assignee as the present invention.

It is apparent that in a lamp of this type it is essential that the sodium or other luminosityproducing material be absolutely pure because the slightest amount of impurity, for example the oxide or hydroxide, may have a deleterious effect on the activity of the cathode, even to the extent of de-activating the same and thereby reducing the light intensity of the lamp'as well as materially shortening its life. Furthermore, in certain types of tubes,,the amount of active material introduced therein may also have a profound efiect on theelectrical characteristics of the tube. The present invention, therefore, is directed to an improved method for introducing sodium or similar material into devices in which the introduced material must be of the highest degree of purity. and of a definite and predetermined quantity.

In general, the improved method contemplates the use of a capsule constituted of a readily frangible material or having a frangible portion, and filling the capsule with sodium or other material in such a manner as to remove all foreign substances and also to prevent any adulteration and contamination of pure material. Thereafter the capsule is mounted in an electric discharge device and the material released at the proper time during or after the manufacturing schedule of the tube simply by breaking the capsule and permitting the material to leave the capsule bodily and practically instantaneously.

Inthe practice of my invention, I prefer employ a multi-distillation process in which sodium is successively transported either in the liquid or vapor phase, or both, through several compartments and finally is forced into one or more capsules. As shown in Fig. 2, apparatus which may be successfully used for this purpose constitutes a closed system having only two openings, one of which may be connected to a pump for evacuating the system and the other to a gas supply for providing the necessary pressure communicating with a bulbous receptacle 2|;

This receptacle is joined to another bulbous receptacle 29 through a piece of tubing 30, and fused to the receptacle 28 there is an angular pieceof glass tubing 3| which is joined to a manifold member 32 also of glass. A tubulation 33 is taken from the upper left-hand corner (as shown) of the manifold 32 and this tubing terminates in two smaller tubuiations 34 and 35, each of which is provided with a stopcock 35 or 11 respectively. The lower end of the manifold 32 terminates in a plurality of outwardly and downwardly extending tubulations ll to which the capsules 39 may be fused in any suitable and well-known manner. As shown, three such capsules are secured to each of the tubulatlons 38.

Fig. 3shows an enlarged view of one of these capsules. The capsules preferably take the form of a spherical or bulbous member made of suit able glass such as Corning 705 AJ and having a diameter of approximately 96". From this member, there extends a glass capillary tubing 40 of about 5 millimeters diameter and long. This tubing has a central bore of about 4% millimeters diameter. The capsules are fabricated separately from the remainder of the apparatus and thereafter fused in any suitable and wellknown manner tothe tubulations 38. While these capsules may be made in any suitable and wellknown manner, I have found it preferable to form the bulbous portion in a mold, and this may be conveniently done by first sealing one end of a capillary tubing of the same size as the extension 40 and after heating the closed end of the tubing, the latter is placed in a mold of suitable shape. The glass-blower then blows into the open end of the tubing until the other end conforms to the shape of the mold which in the illustrative case is spherical. The excess length of capillary may be cutofi, leaving an extension of suitable length secured to the spherical portion. Before the capsule is fused to the tubulation fl, it should preferably be given a test to determine the thickness of the wall of the sphere. For this purpose, the so-called bump test has been found to be satisfactory. These tests are conducted within a yer-- tically mounted glass tube (not shown) resting on a heavy glass plate (not shown). tube has an interior diameter or bore somewhat larger than the capsuleso as not to introduce any cushioning effects. The capsule is suspended within the glass tube, at the upper end thereof and released, thereby failing the length of the tube and striking the glass plate at the bottom. If the glass of the capsuleis of the proper thickness the necessity for which will appear hereinafter, the capsule will bounce a-"certain height within the tube. The proper height may be determlned by experiment; The preferred thickness of a capsule containing a few tenths of a gram of sodium is of the order of .007", although it will be understood that when greater amounts of sodium are employed, the thickness may be increased correspondingly. The thickness of glass will usually be less than .010". If the glass is less than the predetermined thickness found to be necessary, the distance through which the capsule falls may be so regulated as'to cause the capsule to break, whereas if the glass wall is too thick, the capsule will bounce too high.

The glass arm 34 may communicate with a The vertical pump (not shown) and the arm 33 is preferably secured to a receptacle containing a gas such as neon which is inert with respect to the material being driven through the system into the capsules. 7

As shown in Fig. 2, under each of the bulbous members28, 23, there is an electric heater M of any suitable and well-known design which is preferably enclosed in a heavy metal plate 42 presenting a fiat surface to the spherical members 28 and 29.

The sodium or other active material isillustrated as taking the form of chunks 43 contained within the glass tube 2! and indicated generically by the clause "vaporizable material. In the case of sodium, which is extremely diflicult to handle, it has been found convenient to employ a stocking 43 made of metal gauze of fairly fine mesh, this stocking having a configuration as to fit snugly within the tube 21. In order to introduce the active material, the stocking is filled with the material while positioned away from the remainder of the apparatus, and the tube 21 is temporarily open at the top to allow insertion of the stocking member therein, after which the tube 21 is closed by a flame. In the case of sodium, it is necessary to work with the greatest dispatch in placing the active material 'within the stocking so that the material will not be exposed to the atmosphere any longer than is necessary.

Assuming that all of the capsules 39, after being tested in the manner described hereinbefore, have been secured to the tubulations 38 so that the lower end of the manifold member 32 is closed to the atmosphere, the stopcock 3! is closed and the stopcock 33 is opened to the pump. The latter may be of any convenient type and provided with the usual pressure gages so that the entire glass system is eventually evacuated to as high a degree as desired. When the necessary vac.- uum has been obtained, the sodium or other vaporizable material 63 is subjected to heat, externally applied through the glass tube 21, preferably by means of an oven surrounding the tube. In the case of sodium, the material 43 melts at about 250 C. and falls as a liquid into the bottom of the bulbous receptacle 28. The heaters M maintain the receptacles 28 and 29 at an elevated temperature, sufficiently high to cause the melted sodium 65 in the receptacle 23 to be distilled first into the receptacle 29 and then redistilled into the tubulation 3!, then through the manifold 32, finally becoming lodged in the tubulations 38. The latter are maintained at a relatively low temperature, e. g. of the order of the room temperature during the time that the sodium is passing through the melting and the distillation stages, consequently, the sodium 'tends to condense over the interior surface of the tubulations 38. When all of the sodium has collected at the places mentioned, the pump is cut oil by turning the stopcock 36, and the stopcock 31 is turned to its on position, permitting inert gas such as neon to pass through the tubes 35, 33 into the manifold 32 and the tribulations 38. At the same time, the tubulations 38 are heated, preferably by means of a Bunsen flame, which causes the sodium to be converted into vapor and under the pressure exerted by the gas, to be forced through the capillaries 40 into the capsules 39. The sodium immediately condenses and solidifies in the capsules, and the torching and gas-admitting operations are maintained until the proper amount of sodium has collected in each of the capsules. It is desirable that the capsules shall not be filled up completely with sodium. The height of the material in each capsule may be visually determined whereby the volume of the material in the respective capsules is accurately controlled because the capsules are of substantially the same volume content. This visual method of determining the amount of sodium in each capsule is so accurate that errors of only less than a fewper cent in volume are made. For the size of capsule given hereinbefore, approximately from 1.3 to 1.5 grams of sodium are contained therein. The exact amount of sodium per capsule depends upon the use to which the capsule is to be put and whether or'not the sodium is to be used for producing luminosity in'a tube or for serving a strictly gettering purpose.

After the capsules have been filled to the proper level, as determined initially by experiment and later by observation, the cock 31 is turned to its 05 position, thus cutting oil the gas supply and the cook 36 turned on, connecting the system again to the pump. The capsules may then be disconnected from the system by means of a Bunsen flame or torch played upon the respective capillaries 4B in such a manner as notto reduce or destroy the vacuum within the system.

In view of the foregoing, it is apparent that the glass system shown in Fig. 2 first permits the vaporizable material 43 to be melted and to pass into the distillation chambers 28' and 29 where, after successive distillation and causing the sodium to pass into successive vapor phases, the sodium finally reaches the capsules 39 in a highly distilled and pure state. The impurities originally present in the sodium are of course collected at the various receiving points and do not enter into a vapor phase, at least not at the temperatures employed, consequently, are not transported through the system into the capsules. 'It has been found in practice that the mesh stocking member 44 collects the largest bulk of the slag or other impurity and that additional impurities are successively 29, also in the manifold 32. In addition to collecting foreign matter contained within the sodium, the stocking member 44 also serves the purpose of holding the chunks of sodium within the tube 29 so that only material in melted form is permitted to drop into the chamber 28. For this purpose, the stocking member 44 is par tially closed at the bottom by a transverse mesh member through which sodium in liquid form may pass. When the openings in this transverse member become clogged by the impurities, the stocking member is replaced.

For the closed system shown in Fig. 2, it is necessary that the glass shall be of the alkaliresistant type in case sodium or similar material is being melted and distilled. Such a glass is well known in the art and lends itself to all of the ordinary glass-blowing operations.

If des red, the capsules may be used simply as convenient receptacles for storing the alkali or similar metal because the atmosphere is positively precluded from reaching the purified material. However, in the present illustrative case, the confinement of the sodium in a glass sheath or capsule is for the purpose of introducing the sodium in a pure state within an electric discharge device, typified by the lamp shown in Fig. 1. As stated hereinbefore, the loaded capthe lamp. The latter may then be disconnected from the pump, assuming that all of the electrodes have been mounted in place and the lamp has been given the usual bake-out at a temperature of approximately 500 C. in order to remove occluded gases, etc. The necessary inert gas is then admitted to the envelope. If the wall thickness of the capsule 2 is suiilicientv to withstand the vapor pressure of the alkali metal within the capsule, the latter will remain intact during this heat treatment and will not allow the sodium to escape. v

Assuming the improved capsule 2 to be in proper position, the lamp is energized or otherwise heated to a temperature suiilciently high to cause the sodium in the capsule to liquefy. The envelope is then given a violent shaking, sufficient to break the capsule by causing it to strike against the envelope. The capsule immediately shatters if the glass is of the proper thickness, permitting the sodium to escape instantaneously and in bulk and to flow over the mid-portion of the envelope. As the envelope cools down, the sodium immediately condenses on this portion where it would normally collect after each operation of the lamp, due to theiact that the mid-portion of the envelope is cooler than the end portions. The glass content of the capsule is so small that all that remains of it after shattering is simply a flne glass powder which does not aflect, even in the slightest degree, either the quality or the quantity of light given of! by the lamp.

While I have described my invention more especially in connection with a condition in which the sodium serves the purpose of a luminosity-producing material, it will be understood that the sodium or other alkali metal may be used for other purposes, for example, as a getter. The improved capsule method in which the wall of the capsule is shattered and the contained material instantaneously released is particularly advantageous in cases where it is desired that the full effect of the active material shall be immediately available at the proper time for consponsor trolling or otherwise modifying the character of the discharge between two or more electrodes within a sealed envelope. It will also be understood that the present invention is not limited to sodium or any other alkali metal but con-- templates the use of any material which must be provided in an ultra-pure state or one which is diiiicult to handle or which may readily combine with the gases of the atmosphere. Indeed, the frangible capsule may enclose a body of gas and after being introduced into a tube, the gas may be' released by shattering the capsule at any time during the manufacture of the tube or afterwards. Liquid materials such as mercury may also be introduced into a tube'in this manner and the mercury purified by one or more distillation steps before being placed in glass capsules.

As stated hereinbefore, the glass capsule provides a most convenient and effective manner of storing active materials, solid, liquid or gas, over long periods of time, at the end of which the capsule is quite as adaptable to use as a means for introducing the material into an electric discharge device as it was when the capsule was originally made and filled. I The apparatus employed in carrying out this process is extremely simple and inexpensive, calling for the services only of a skilled glass-blower and yet the quality of the capsule and contained material is uniformly of a high standard.

What I claim as new and desire to secure by Letters Patent of the United States, is:

a 1. A lamp comprising a sealed envelope containing an inert gas, a plurality of cooperating electrodes and a quantity of sodium contained within a glass capsule having a wall thickness less than .010" so as to be completely shattered when struck against the envelope and thereby permitting the sodium to escape instantaneously and completely. p

2. A capsule containing alkali metal and composed of glass having a wall thickness less than WILLIAM A. RUGGLES.

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