US1716149A - Evacuating electric discharge device - Google Patents

Description

June 4, 1929. H. c. RENTSCHLER 1,716,149

EVACUA'I'ING ELECTRIC DISCHARGE DEVICE Filed Feb. 1, 1927 WWW.

ATTORNEY if atented June 4,- 1929.

PATENT OFFICE.

UNITED S'I'ATES HARVEY CLAYTON RENTSCHLER, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTINGHOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA.

EVACUATING ELECTRIC DISCHARGE DEVICE.

Application filed February 1, 1927. Serial No. 165,092.

This invention relates to the removal of gases from solids and to the creation of high vacua in discharge devices. More particularly the invention relates to the removal of gas from conductive bodies, such as electrodes, lead wires, supports and other metal bodies in electrical discharge devices and to the method of expediting the exhaust thereof.

In the manufacture of electrical discharge devices it is the usual practice to sub ect the mount before sealing-in to the envelope, to a heat treatment in vacuum or in a reducing gas, such as hydrogen, to liberate the gases therefrom as completely as posslble and after the electrodes have been incorporated into the envelope, to heat the electrodes bv bombardment or high frequency induction currents to drive off the gases therefrom. In spite of this careful treatment, however, serious difficulty is BXPGII- enced, due to further release of gas during operation from such of the metal parts of the device which it was impossible to heat treat in this manner, thus causing an impairment of the vacuum and changing the characteristics of the device, often rendering the same inoperative. This is particularly troublesome in high vacuum devices employing high plate voltages. The same difficulty is observed, however, in the manufacture of gaseous discharge devices, such as discharge lamps, rectifier-s, etc., employ ng a rare gas filling as argon, neon or helium. In such devices the gas becomes contan'iinated with common gases and impurities given off by the metal parts of the device during operation, causing the starting and operating characteristics thereof to be changed often to such a. degree, as to render the device in capable of operation or operable only at materially higher volta es.

It is one of the ob ects of the present 1nvention, therefore, to provide a new method of effectively removing the gases from the electrodes, lead wires, supports and other metal and glass parts of an electric discharge device and to produce a device, the characteristics of which will not be altered by gas evolution during operation thereof. A further object is to provide a method of removing gases from such metal parts which are closely adjacent the glass without subjecting the same to heat treatment or creating cracks or strains in the adjacent glass.

Another object is to provide a discharge device which may be operated throughout a long commercial life without appreciable change in the vacuous condition thereof.

A still further object is to provide an improved method of exhausting a discharge device which is simple and effective and which materially reduces the time required for obtaining a high vacuum therein.

Other objects and advantages will hereinafter appear.

It has been found that the metal parts of the device, after the baking out thereof and prior to mounting in the discharge device, become coated on the surface with an appreciable amount of gas and impurities and that such gas and impurities adhere very tenaciously so that they are not removed by the pumping operation. In the case of the electrodes, the gas and other impurities may be driven off by the bombardment or high frequency treatment thereof but the portions of the device lying adjacent the glass are difiicult to treat, due to the fact that heat radiated from the electrodes to the lead wires and supports is insufficient to effect a removal of gas therefrom and moreover, even if it were possible to heat the metal adjacent the glass sufficiently to drive the gases therefrom, the heat would cause the glass to crack, rendering the device defective. It will be understood therefore, that with the methods in vogue for removing the gases from the electrodes of discharge devices that the leading-in wires and other metal parts, in the vicinity of the glass, are not sufficiently treated and when the apparatus is later operated, gases or vapors are given off which impair the operation of the apparatus. In accordance with the present invention a discharge device is exhausted by the usual pumping methods and during such exhaust the bulb is baked in the usual manner at a sufiiciently high temperature to drive the gases and water vapors from the surface of the glass and in the case of devices employing incandescent cathodes, the cathode is heated by a passage of current to drive off the gases on the surface or occluded therein. After the removal of the major portion'of the gas in this manner a high potential, high frequency electrical discharge is passed between the electrodes to create a strong electrostatic field in the device. This high voltage discharge causes a vigorous sparking directly between the metal parts and particu larly those parts adjacent the glass, since as is well understood, such a discharge tends to take the longest path possible through the residual gas. By virtue of the high vacuum which was produced prior to the high frequency discharge, there is very little heat produced by the discharge and the removal of the gas from the surface of the metal is effected without danger of causing the glass to become cracked or having strains set up therein.

The action of the discharge appears to be to create an electrostatic field which pulls the occluded or closely adherent gases or vapors and other impurities from the leading-in wires and from the electrodes and permits them to be removed by the pump which is operated continuously during this operation. The high frequency, high voltage operation should be continued until further ionization and sparking within the bulb ceases. The voltage employed when using high frequency current may be very high Without danger to the envelope or other parts of the device and preferably should be several times the voltage to which the device is to be later subjected in operation, thus, for instance, if the device being exhausted is designed to operate at 10,000 volts it is preferable to employ a high frequency, high voltage discharge having a potential of 25,000 to 50,000 volts or higher. If the operating voltage is around 100,000 volts,

' such as employed in X-ray tubes and similar devices, the metal parts should be treated out with a high frequency discharge of 150,- 000 to 200,000 volts. The frequency of the current should be sufiiciently high to render the operation safe and may range from 20,000 to 500,000 or more cycles per second.

After the denuding of the metal parts in this manner the electrodes are heated to a high temperature, either by electron bombardment or by high frequency induction currents to drive out the gases contained in the interior thereof and at the same time, these gases are cleaned up by a metallic clean-up agent having a high aflinity for such gases as hydrogen. Preferably, aluminum is employed as the clean-up agent since aluminum may be applied directly to the electrode and by virtue of its high vaporization temperature, it is possible to practically completely degasify the electrode before the aluminum is vaporized. Upon vaporization of the aluminum the gases liberated by the electrodes during heating are cleaned-up and the aluminum deposited on the walls of the envelope where it serves throughout the life of the device to maintain the vacuum therein in a first class condition. By cleaning up the gases liberated almost instantaneously in this manner, the danger of the gases redepositing on other parts of the device is very much reduced and the time of exhaust considerably decreased.

However'gdn order to insure the complete cleaning of the metal parts of gases I prefor to again subject these parts to another high frequency, high voltage discharge prior to scaling off of the device. It is to be understood, of course, that throughout the entire operation of exhausting and removing the gases from the interior parts, that the pumps are maintained continuously in operation and the gases are removed from the device as they are detached from the metal to which they so tenaciously adhere.

In order that the invention may be more fully understood reference may be had to the accompanying drawing in which the single figure illustrates a high voltage electron discharge device and circuit arrangements for subjecting the same to my improved exhaust treatment.

The discharge device illustrated consists of a glass envelope 1 containing an anode or plate electrode 2 and a filamentary cathode 3. The anode consists of a cylindrical plate supported from a reentrant stem 4 of the device by a pair of metal supports 5 secured to a metal collar 6 clamped about the reentrant portion 4 in any desired manner. Current is conducted to the anode 2 by a. leading-in wire 7 joined to the supports 5 by a cross bar 8. The leading-in conductor 7 is in electrical connection with the terminal 9.

The cathode 3 is in the form of a looped or hair pin shaped filament having its ends supported by and secured to the leading-in conductors 10 and 11 sealed through the press 12 at the opposite end from the reentrant portion 4. The bight of the filament is supported by a metal rod 13 also sealed in the press. A. quantity of aluminum 14 is secured to the plate in any suitable manner, such as welding, or may be retained thereon by striking out a strap from the plate material and inserting the aluminum strip thereunder. The envelope 1 is connected to an exhaust system in any suitable manner as by the exhaust tube 15. l a

Any desired apparatus may be employed for supplying the high voltage, high frequency current to the device and as shown, the secondary 16 of a high frequency or Tesla coil 17 is connected by current conductors 18 and 19 to the terminals of the device. A switch 20 is provided for controlling the high frequency, high voltage discharge.

A source of current, such as battery 21 is provided for heating the cathode to an electron-emitting temperature and a suitable source of direct current, such as a generator 22, having a voltage in excess of the voltage Ill well known in the exhaustin for which the device is designed to operate is joined to the respective terminals of the device through a switch 23. A SW1t0h 24 is also provided for controlling the filament heating current.

In carrying out the exhaust treatment b means of the apparatus illustrated, the bul is first connected to the exhaust tube 15 and the pumps operated until a high vacuum is obtained. The switch 24 is then closed and the filament 3 heated to cause the ases contained therein to be liberated, the pum meantime being operated to I remove suc gases from the envelope. During th1s treatment and the succeeding treatments, the bulb is heated from the exterior, in the manner of such devices, to drive ofi the gases an vapors therefrom and to prevent the same from recondensing or collecting on the surface thereof. After the preliminary vacuum has been obtained in this manner the high frequency, high voltage discharge is passed through the device by closing the switch 20, thus energizing the Tesla coil 17. This discharge 1s continued as long as signs of gases are shown but it is to be understood that, due to the degree of vacuum in the device, that'the electrodes and metal .parts, particularly those parts adjacent the glass, remain comparatively cool. At the completion of this treatment the switch 20 is opened and the switch 23 is closed to pass a direct current .or low frequency discharge between the electrodes 2 and 3. This discharge should be of sufiiciently high potential to heat up theelectrode 2 to a high. incandescence, by electron bombardment, thus driving oif the gases therefrom and permitting them to be removed from the device by the pumps. A voltage somewhat in excess of the normal operating voltage of the device should be employed. After the degasificatlon of the anode, the discharge is increased to further raise the temperature of the plate sufliciently high to effect a vaporization of the aluminum 14 on the plate. The aluminum, upon vaporization, immediately cleans up all gases given off by the plate or residual gas in the envelope, thereby greatlyj facilitating the exhaust process. It then'deposits upon the wall of the envelope where it serves throughout the life of the device to clean-up any gas which may be liberated as from the plate, during operation. Aluminum is particularly effective in cleaning up hydrogen and since hydrogen is a troublesome gas in devices of this nature and is very diflicult to remove by the usual clean-up material, such as magnesium, I am enabled to obtain and maintain better vacua with devices employing very high voltages than has heretofore been possible. After the flashing of the aluminum, the switch 23 is opened to discontinue the bombardment as is also the switch 24 and preferably the high frequency, high voltage treatment is a ain. given to the device for a short time to msure the removal of any gas which may have de osited on the metal adjacent the glass durm the degasification of the plate electrode. uring this entire criod, the pumps are maintained in operation and the'gases are removed from the device as fast as they are detached. The tubulature 15 may then be sealed oil".

It will be noted that a process has been devised which is effective first for ridding both the glass and metal parts of adherent gases which might be liberated during the operation of the device and that in cooperation therewith a substance is provided within the envelope for assisting in maintaining the high vacuum so originally created. By virtue of the cooperation of these two features 1 am enabled to produce discharge devices which may be operated at several hundred thousand volts without signs of ionization and which have a long life without impairment of the vacuous condition therein.

It is, of course, obvious that many changes may be made in the exact details of the process from that described and I do not desire to be limited to the precise order of steps given herein except as defined in the appended claims.

What is claimed is:

1. The method of removing adherent gases and vapors from the metal parts of a discharge device, closely adjacent the glass, consisting in creating a high voltage electrostatic field between the metal parts, in a vacuum to detach the gases therefrom and removing the gases from the device as they are detached.

2. The method of creating and maintaining high vacua in discharge devices comprising detaching the gases from the metal parts of the device ad acent the glass by a high voltage, high frequency discharge therebetween, removing the gases so detached from the device and vaporizing a metallic clean-up agent in the device which serves during operation of the device to assist in maintaining the vacuuous condition.

3. The method of creatin and maintaining a high vacuum in an el ectric discharge device, comprising establishing a hi h voltage electrostatic field in the device between the parts to be degasified to detach gases therefrom, removing the gases from the device, and vaporizing a metallic clean-up agent therein.

4. The method of creating and maintaining a high vacuum in an electric discharge device comprising creating an initial vacuum passing a high voltage, hi h frequency discharge throu h the device etween the parts to be degasi ed to detach the surface gases therefrom, heatin the electrodes to a high temperature to rive the occluded gases high frequency discharge therethrough to detach the surface gases from the metal parts adjacent the glass, passing a high voltage, direct current or low frequency discharge through the device to drive the occluded as from the electrode, said discharges oth having a potential in excess of the operating potential of the device, and vaporizing a uantity of aluminum in the device to faci itate the exhaust and maintain the vacuous condition during the operation of the device.

In testimony whereof, I have hereunto subscribed my name this 31st day of J anuary 1927.

HARVEY CLAYTON RENTSCHLER.

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