US1453267A

US1453267A - Electron-emitting cathode and method of making the same

Info

Publication number: US1453267A
Application number: US264504A
Authority: US
Inventors: Bradford James Llewellyn
Original assignee: Forest Radio Telephone & Teleg
Current assignee: De Forest Radio Telephone & Telegraph Co; Forest Radio Telephone & Teleg
Priority date: 1918-11-29
Filing date: 1918-11-29
Publication date: 1923-05-01
Anticipated expiration: 1940-05-01
Also published as: DE467675C

Description

May 1, 1923. 1,453,267

J. L. BRADFORD ELECTRON EMITTING CATHODE AND METHOD OF MAKING THE SAME Filed Nov. 29 1 v Y v I ATTORNEY Patented May I, 1923.

UNITED 4 STATES 1,453,267 PATENT OFFICE.

JAMES LLEWELLYN BRADFORD, OF NEW YORK, N. Y., ASSIGNOR TO DIE FOREST RADIO TELEPHONE & TELEGRAPH COMPANY, OF NEW YORK, Y., A. CORPORATION OF DELAWARE.

EDECTRON-EMITTING CATHODE AND METHOD OF MAKING THE SAME.

Application filed November 29, 1918. Serial No. 264,504.

To all 10770772 it may concern:

Be it known that I, JAMES L. BRADFORD, a citizen of the United States, residing at 'New York, in the county of Bronx, State of 5 New York, have made a certain new and useful Invention in Electron-Emitting (lathode and Method of Making the Same, of which the following is a specification.

This invention relates to the manufacture of the'heated element, such as the filament, or electron-emitting cathode member of an audion or vacuum tube, and particularly to the element referred to, as an article, as well as to the method of making the same.

The object of the invention is to provide a filament or electron-emitting cathode of greatly increased durability and constancy of activity, for use in audions or vacuum tubes.

A further object is to reduce the cost of manufacture of such devices while securing greater length of life thereof, and increased efiiciency.

A further object is to provide an element of the nature. and for the use referred to which requires less current in the use there of, thereby reducing the cost of operation of audions or vacuum tubes in connection with which the element is employed.

Other objects of the invention will appear more fully hereinafter.

The invention consists substantially in the structure and mode of operation hereinafter to be more fully setforth and described, as illustrated in the accompanying drawing, and finally defined in the appended claims. c i

In the construction of audions or vacuum tubes it is customary to emplov one or more cold electrodes and a hot electrode, the latter being called a filament or electron-emitting cathode, and customarily heated by means of an electric current traversing the same. Ordinarily, in the use of the device, the filament or electron-emitting element is heated to a state of incandescence in order to secure the highest degree of activity or electron-emission. This high degree of heat causes rapid deterioration of the heated element and a consequent decrease in its activity. Various expedients have been proposed for increasing the activity in the electron-emission and for heated element of an audion or vacuum tube. This expedient has not .proved to be entirely sat-isfactor and besides is quite expensive because 0 the use of a platinum base for the coating.

I have found that all methods'which involve the application of coatings are undesirable for the reason that filaments or cathodes so made are not sufiiciently stable on permanent and gradually deteriorate, some more rapidly than others, depending somewhat upon the nature of the base employed, the more expensive. bases, such as platinum being the best but open to the objection of greater cost. In carrying out my invention I pro ose to discard the idea of coatings, and, instead, to incorporate the necessary ingredients intothe body of the material out of which the filament or cathode is made. 'I have discovered that by combining certain suitable substances into an homogeneous mass with certain suitable base materials, such mass can be worked into form to produce a filament or electronemitting cathode which is more stable and durable. than any heretofore proposed, which possesses a high degree of activity of electron emission, which possesses longer life in use than any heretofore employed, which reouires only cheap material in its composition, and which requires reduced current for heating the same to the desired degree for the desired extent of activity. I

In carrying out my invention I employ a suitable base material, and I have found that tungsten and molybdenum are well suited for this purpose. I also employ suitable oxides and chlorides, preferably of metals of the alkali earth group, that is including those falling under the second group and including the rare earth class of the eighth group according to Mendelejefis periodic law. I have found that, for illusdients,-base, oxide and chloridein, powdered form, and the best results are secured when the ingredients are employed in the chemically pure state. The base may be whollv tungsten, or molybdenum, or other equivalent material, or a mixture of two or more of these substances. In like manner the oxides and the chlorides may be of separate elements or a mixture of two or more of them of the alkali earth group.

The oxide and chloride constituents, whether consisting of single oxide and chloride elements, or mixtures of oxides and of chlorides or their equivalents, in powder form, are thoroughly mixed together, and the mixture is then added to the base material and the whole composition is then thoroughly mixed. Care should be taken in the mixing operation to avoid as much as possible abrasion or breaking up of the particles of the base material as that would tend to prevent the composition, in the subsequent operations, from being drawn or formed into wire or filament dimensions.

Without intending to be limited or restricted thereto the following relative proportions of the ingredients is given as illustrative of a composition which I have found sufficient and satisfactory for the purpose:

Example: Oxides and chlorides are mixed together in powdered form in about the proportions as follows,--

60% of strontium oxide,

30% of barium peroxide,

, 10% ofpalladium chloride.

This mixture is then added to the base material in about the proportion as follows,-

5% by weight of the mixture of oxides'and chlorides,

95% by weight of the base material.

For convenience, I will call the mixture of the oxid-s and chlorids diluents, or the rad io-active element.

the mass or pressed bar seem to amalgamate and form into an homogeneous body, the time required in the heating operation varying somewhat according to the nature and composition of the base material employed.

The homogeneous bar is then suitably swaged or drawn into the proper dimensions to form a filament or cathode element for the purpose set forth.

The use of the chloride constituent increases the activity of the filament or cathode as to its electron-emission properties.

I have found that when a filament or cathode, constructed in accordance with my invention, is heated only to a dull red condition, an electron emission is secured to a degree of efficiency comparable with the best filaments heretofore employed in audions or vacuum tubes which are heated to incandescence to secure maximum activity. This means that less heating current is required, and consequently there is less deterioration of the filament or cathode through oxidation or otherwise, thereby greatly prolonging the life of the filament or cathode without decrease of its activity. I have also found that the electron-emission activity of the filament or cathode embodying my invention is more constant and uniform, and that the physical structure of the filament or cathode is more stable and stronger than those heretofore employed.

It will be observed that I avoid the use of platinum which is very expensive and adds materially to the cost of manufacture of filaments or cathodes, and, instead, I employ comparatively cheap materials and still secure greater longevity as well as advantageous results in the way of more stable and uniform emission, greater strength of filament or cathode, therefore less liability to become injured or broken in handling or transporting the audions or vacuum tubes, less current for heating the element in use, and consequently securing economy not only in manufacture and upkeep, but also in operation of the audions or vacuum tubes employing the filament or cathode.

In the drawing I have shown a form of audion or vacuum tube as illustrative of the manner of use of an electrode, filament or cathode embodying my invention, and wherein 1 is an evacuated vessel, 2 the base thereof, 3, 3 the plate or wing, and 4 the grid electrodes or elements, and 5 the hot member 0r element produced in accordance with my in- Ill mating the mixture into an homogeneous body.

2. The process of manufacturing electronemitting cathodes, which consists in mixing together, a tungsten containing a base ma terial, with a diluent including oxides and a chlorid of metals of the alkali earth group, and then amalgamating the mixture into an homogeneous body. I

' 3. The proces of manufacturing electronemitting cathodes, which consists 1n mixing together in powdered form a base material and a diluent including metallic oxides of the second group, and chlorids of therare earth class of the eighth group of the periodic law, and then amalgamating the 111mture into an homogeneous body.

' 4. The process of manufacturing electronemitting cathodes, which consists in mixing together tungsten and a diluent including metallic oxides and a chloride of the al- I I kali earth group, and then amalgamating the mixture into an homogeneous body.

5. The process of manufacturing electronemitting cathodes, which consists in mixing together powdered tungsten and a diluent including metallic oxides and a 'chlorid of the alkali earth group, and then amalgamating the mixture into an homogeneous body.

6. The process of manufacturing electronemitting cathodes, which consists in mixing together a base material and a mixtureof oxides and a chloride of the alkali earth group, and finally amalgamating the mixture Into an homogeneous body.

7. The process of manufacturing electronemitting cathodes, which consists in mixing together a mixture of base materials including tungsten, an oxide and a. chloride ofthe alkali earth group, and then amalgamating the mixture into an homogeneous body.

-8. The process of manufacturing electronemitting cathodes, which consists in mixing together tungsten and molybdenum as a base material, and an oxide and a chloride of metals of the alkali earth group, and then amalgamating the mixture into an homogeneous body.

9. The process of manufacturing electronemitting cathodes, which consists in mixing together tungsten, and a diluent including strontium oxide, barium peroxide and palladium chloride, and then amalgamating the mixture into an homogeneous body.

10. The process of manufacturing electron-emitting cathodes, which consists in mixing to ether a base material, and a dilu-' ent includii ng oxides and a chloride of metals falling under the second and eighth groups respectively of the periodic law, and heatin the mixture to cause the ingredients thereo to form an homogeneous 'body. t

11. The process of manufacturing electron-emitting cathodes which consists in mixing together a base material, including tungsten, and a diluent including an oxide and a chloride of metals falling under the second and eighth groups respectively of the periodic law, and then compressing the mixture and subjecting the compressed mass to heat to amalgamate the same into an homogeneous body. 7 I

12. The process of manufacturing ,electron-emitting cathodes which consists in mixing together a base material, and a diluent including oxides and a chloride of metals falling under the second and eighth groups respectively of the periodic law,- and heating the mixture to a degree below the melting point of the base material to amalgamate the mass into anhomogeneous body.

13. The process of manufacturing electron-emitting cathodes which consists in mixing together a base material, and a diluentincluding an oxide and a chloride of metals falling under the second and eighth groups respectively of the periodic'law, and

then compressing the mixture and subjecting the compressed mass to heat to a degree below that of the melting point of the base material to amalgamate the mass into an homogeneous body.

14. The process of manufacturing electron-emittin cathodes which consists in mixing toget er a base material, and a diluent including an oxide and a chloride of metals falling under the second and eighth group respectively of the periodic law, and then compressing the mixture and subjecting the compressed mass to heat to amalgamate the same into an homogeneous body, and finally drawing the heated body into the dimenslons to formthe cathode.

15. The process of manufacturing electron-emitting cathodes, which consists in mixing together a base material, and a diluent including an oxide and a chloride of metals falling under the second and eighth groups respectively of the periodiclaw, andearths and palladium chloride, and then amalgamating the mixture into an homogeneous body.

17. The process of manufacturing electron-emitting: cathodes which consists. in

mixing together a base material, a diluent including an oxide of a metal of'the alkali tron-emitting cathodes -which' consists in mixing together a base material, a diluent including an oxide of a metal of the alkali earths and palladium chloride, and then compressing the mixture and heating the compressed mass.

19. An electron-emitting cathode consisting of an homogeneous body containing a base material, an oxide, and a chloride.

20. An electron-emitting cathode consisting of an homogeneous body containing a base material, and a diluent including an oxide and a chloride of metals of the alkali earth group.

21. An electron-emitting cathode consisting of an homogeneous body containing tungsten as a base material, and a diluent including oxids and a chloride of metals falling under the second and eighth respectively roups of the periodic law.

22. n electron-emitting cathode consisttungsten and-molybdenum-as a base material, and a. diluent including oxids and a chloride of metals falling under-the second and eighth respectively. groups of the periodic law. I

23. Anelectron-emitting cathode consisting of an homogeneous body containing a base material, a metallic oxide and palladium chloride.

24. An electron-emitting cathode consisting of an homogeneous body containing a base material, strontium oxide and a metallic chloride.

25. An electron-emitting cathode consisting of an homogeneous body containing tungsten, and a diluent including strontium ogiiide, barium peroxide and palladium chlon e.

26. An electron-emitting cathode consistving of an homogeneous body containing a base material, strontium oxide, barium peroxide and a metallic chloride.

In testimony whereof I have hereunto set my hand on this 23rd day of November JAMES LLEWELLYN BRADI'URD.