US 3584253 A
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United States Patent Inventor Manfred Wintzer Munich, Germany Appl, No. 810,743 Filed Mar. 26, 1969 Patented June 8, 197 l Assignee Siemens Aktiengesellschaft Berlin and Munich, Germany Priority Apr. 1, 1968 Germany P 17 64 092.5
GETTER STRUCTURE FOR ELECTRICAL DISCHARGE AND METHOD OF MAKING THE SAME 3 Claims, 1 Drawing Fig.
US. Cl 313/180, 252/18l.6,4l7/51 Int. Cl H0lj 19/10 Field of Search 3 l 3/174,
 References Cited UNITED STATES PATENTS 1,958,967 5/1934 Kniepen 313/178X 2,175,695 10/1939 Kniepen 252/181.6X 2,855,368 10/1958 Perdijk et al... 252/1816 3,102,633 9/1963 Baronetzky 206/0.4 FOREIGN PATENTS 256,105 2/1949 Switzerland 313/178 Primary Examiner-Raymond F. Hossfeld Attorney-Hill, Sherman, Meroni, Gross and Simpson ABSTRACT: A nonevaporating getter, which is optionally heatable in operation within an electron discharge vessel, in whichthe getter material contains at least one metal selected from the group consisting of Zr, Ta, Hf, Nb, Ti, Th and U, and is disposed directly on the insulating layer of the heating means, eliminating the use of an open metal vessel or the like for the getter material.
BACKGROUND OF THE INVENTION The invention is directed to a getter structure for electrical discharge vessels employing a nonevaporable getter material which contains at least one metal selected from a group consisting of Zr, Ta, Hf, Nb, Ti, th and U, which is optionally heatable during operation of the electrical discharge vessel. ln the past getters of this type were constructed in the form of an open metal cup or pot-shaped vessel which was associated with an insulated heating coil of the type of an indirectly heated cathode with such metal vessel consisting of the gettering metal or at least provided with a surface coating of such metal.
Getters constructed of zirconium, particularly correspondingly thick layers thereof produced by pressing and sintering of zirconium powder provide a considerably increased vacuum speed and gas absorption capacity at temperatures above 600 C., but at room temperature the gas absorption capacity is considerably limited by the fact that the gas diffusion into the interior of the zirconium is eliminated whereby only the slight surface absorption of the zirconium layer of the getter remains. However, an increase of the gas absorption capacity of the getter at room temperature is absolutely necessary to insure maintenance of the necessary vacuum of larger electronic tubes under storage conditions.
Exhaustive experiments have revealed that an increase of the gas absorption capacity at room temperature by more than -fold can be achieved with a porous unpressed zirconium body, and in an effort to achieve greater porosity in sintered bodies of zirconium powder for getter purposes, molybdenum or tungsten powder was admixed with the zirconium powder. This arrangement, however, has the disadvantage, among others, that zirconium and molybdenum alloy at l500 C. (2732 F.) as a result of which the sintering and degasification temperatures of such operating electrodes is considerably limited at the upper end.
The present invention therefore has among its objects the elimination of the disadvantages associated with getter structures such as those described and a simple method of producing the same.
BRIEF SUMMARY OF THE INVENTION The present invention proceeds upon the concept of utilizing carbon in conjunction with the getter material in which the sintering of the particles of getter material is partially avoided during the heat treatment by employing carbon particles, which are for example, utilized by mixing carbon powder with the getter material powder and applying the mixture directly to the heating means. By the addition of carbon granules, for example, pressed layers with a higher porosity can be achieved than with ductile molybdenum or tungsten, and at the same time the gas transfer of carbon granules is much lower than that of molybdenum or tungsten powder. Furthermore the porous zirconium-carbon body continues to be readily mechanically machinable, even after application of relatively high heat treatment temperatures, for example, 1300 C. (2372 F.).
Heatable getters of the type described can also be utilized with particular advantage in applications where a definite lack of space exists in a electron tube, replacing the corresponding heating means, but such arrangement has the disadvantage that the temperature range is fixed at a relatively high level.
In accordance with the method of the invention for producing getters of the type described, the heating means, already provided with a sintered-on insulation layer, is suitably coated with a powder mixture of getter metal and carbon and subsequently heat treated in high vacuum at 800l200 C. The powder mixture may be in the form of an alcoholic suspension and applied by a dipping operation or the dry powder mixture may be pressed within a pressing die, at low pressure, and the mo ded material subsequently sub ected to the desired heat treatment.
BRIEF DESCRIPTION OF DRAWING The drawing illustrates a vertical section through a getter structure constructed in accordance with the present invention.
DETAILED DESCRIPTION Referring to the figure of the drawing, the reference 'numeral l designates a heating coil, customarily provided with an insulating coating 2, for example of aluminum oxide, which if desired may be of bifilar design. Disposed on the heating coil is a mass or body 3 of getter metal and carbon which, after heat treatment in a high vacuum, forms a highly porous structure directly on the heating means.
The coating or body 3 may be formed by dipping the heating means in an alcoholic suspension of getter metal and up to 30 percent by weight carbon, particularly electrographite which is thereafter heat treated in a high vacuum at 800- l200 C. until the desired unitary structure results. This construction provides a very large active getter surface which can be selectively heated as desired during operation by control of the heating means to provide appropriate temperatures for the desired application.
The coating may be applied by other conventional methods of application such as atomization or the like. It is also possible to insert the heating means within a die containing a dry powder mixture and by means of a suitable pressure tool press, with low pressure, a sufficiently thick coating upon the surface of the heating means, thereby embedding the latter within the getter material.
A heatable getter structure constructed in accordance with the present invention may be disposed in any suitable location within the electron tube associated therewith, completely exposed and positioned at or in the proximity of the tube electrode system, i.e. wherever there is adequate space to which electrical heating energy can be supplied thereto. An important advantage of an arrangement in accordance with' the present invention resides in the fact that the structure is completely nonmagnetic so that it can be disposed at any suitable location in the tube without in any way creating interference with respect to the electron discharge process of the electron tube involved.
Having thus described my invention it will be obvious that various immaterial modifications may be made without departing from the spirit of my invention, hence I do not wish to be understood as limiting myself to the exact form, construction and arrangement of parts-herein shown and described.
I claim as my invention:
1. The method of making a nonevaporating type of getter, optionally heatable in operation, having heating means provided with a sintered-on layer of insulating material, compris ing the steps of mixing carbon powder with at least one metal powder selected from a group consisting of Zr, Ta, I-If, Nb, Ti, th, and U, with the powder mixture containing'a powder carbon content of up to 30 percent by weight, applying a coating of such mixture directly to the insulating layer of said heating means, subjecting the coated heating means to a high vacuum, and heating the same to a temperature of 800-1200" C. while in such vacuum.
2. A method according to claim 1, comprising applying the getter material to the insulating layer of the heating means by dipping the latter into an alcoholic suspension of getter metal and carbon powders, and thereafter subjecting the same to said heat treatment.
3. A method according to claim 1, wherein a dry powder mixture of getter metal and carbon is pressed within a pressing die at low pressure to form said coating, and thereafter subjecting the same to said heat treatment.