US3369145A

US3369145A - Thermionic emissive cathode

Info

Publication number: US3369145A
Application number: US446895A
Authority: US
Inventors: Domotor Lorant
Original assignee: Wagner Electric Corp
Current assignee: Edison International Inc
Priority date: 1965-04-09
Filing date: 1965-04-09
Publication date: 1968-02-13
Anticipated expiration: 1985-02-13

Description

Feb. 13, 1968 DOMOTOR 3,369,145

THERMIONIC EMISSIVE CATHODE Filed April 9, 1965 T'lc i- INVE TOR ATTORNEYS United States Patent 3,369,145 THERMIONIC EMISSIVE CATHODE Lorant Domotor, Newark, N.J., assignor to Wagner Electric Corporation, a corporation of Delaware Filed Apr. 9, 1965, Ser. No. 446,895 Claims. (Cl. 313346) ABSTRACT OF THE DISCLOSURE A thermionic emissive cathode for use in electron discharge devices employs the oxides of barium, strontium, and lithium, resulting in a cathode which starts electron emission at a lower temperature than barium oxide or strontium oxide.

This invention relates to a thermionic emissive cathode for use in electron discharge devices. The cathodes may be used with high vacuum tubes or gas filled tubes such as thyratrons. The invention has particular reference to an emissive coating composition including a mixture of oxides which produce electrons rapidly and efliciently.

The use of barium and strontium oxides is Well known and cathode coatings using these substances have been in use for many years. The mixtures are desopisted by spraying onto the base in the form of carbonates but during the processing of the discharge devive, the carbonates are changed to oxides before the device is sealed. One of the objections to this coating is the inability of the cathode to heat up quickly and assume an emissive temperature in less than about ten seconds. There are many devices and circuits in use today which require a faster action. This is particularly true of television sets which, because of this delayed action, sometimes take thirty seconds before showing a picture.

The present invention eliminates a considerable portion of this waiting time and produces electron emission within a few seconds of the time when current is applied to the heater. This increased action is due entirely to the addition of a small percentage of lithium carbon-ate to the original mixture. After the processing of heating and evacuating, the carbonate changes to the oxide.

One of the objects of this invention is to provide an improved thermionic emissive cathode coating which avoids one or more of the disadvatages and limitations of prior art coatings.

Another object of the invention is to lower the time interval between the application of current to the heater coil and the emission of electrons from the emissive surface.

Another object of the invention is to provide a cathode coating which starts its emissive action at a lower temperature than prior art coatings.

The invention comprises a conductive metallic base "ice d-rical cathode having the emissive coating on the outside surfoce of the cylinder.

FIG. 2 is a cross sectional view of the cathode shown in FIG. 1 and is taken along line 2-2 of that figure.

FIG. 3 is a cross sectional view of a gaseous discharge device having an anode, a firing electrode, and a cathode with its emissive coating on the inside surface of a hollow cylinder.

Referring now to the drawings, the cathode shown in FIGS. 1 and 2 includes a hollowcylinder 10 having a heater wire 11 disposed inside the hollow portion. On the outside surface of the cylinder an emissive coating 12 is deposited, generally by spraying. When the tube is first assembled, the emissive coating contain-s about parts of barium carbonate, 57 parts of strontium carbonate and about 3 parts of lithium carbonate. While these pro portions are considered to be the preferred proportions, small variations (:5 parts of the barium carbonate, :5 parts of the strontium carbonate, :1 part of the lithium carbonate) are permissible and therefore the invention is not limited to the exact proportions listed above. After the parts assembled within an envelope, the air is pumped out and the temperature of the cathode is raised to an emissive temperature. This action changese all the carbonates to oxides, giving off carbon dioxide which is pumped out of the envelope by the vacuum pumps.

The device shown in :FIG. 3 is a thyrat-ron having an envelope 13 and an anode 14 surrounded by a shield 15. The anode is supported by a rod 16 which is sealed to the envelope and forms a lead-in conductor. The bottom portion of shield 15 contains cut out portions 17 which act as a firing electrode and pass the current between anode and cathode when the tube is conductive. Below the shield 15 is a cathode 18 including a metallic supporting cylinder 20 and an emissive coating 21 on its inside surface. A coil of heating wire 22 is disposed adjacent to the outside surface of cylinder 20 for heating the cylinder and its coating to an emissive temperature. The outside portion of the heater wire 22 may be covered by another cylinder 23'to conserve heat and keep the temperature of the envelope at a lower range. The usual lead-in conductors 24 for the shield, 25 for the heater wires, and 26 for the cathode are sealed in the envelope in conventional manner.

When the heater wire 11 (or 22) receives its normal value of current, the temperature of the base and the portion which may be a hollow cylinder. A heater wire is positioned within the cylinder (or outside of it) for heating it to an emissive temperature. An electron emissive coating is deposited on the outside (or inside) surface of the cylinder, this coating including by weight about 50 parts of barium carbonte, about 47 parts of strontium carbonate and about 3 parts of lithium carbonate. When a cathode is used for heavy duty gaseous discharge devices, the emissive coating may be deposited on the inside surface of the cylinder with the heater wire disposed adjacent to the outside surface.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in conjunction with the accompanying drawings.

FIG. 1 is a side view, with parts cut away, of a cylincoating both heat up in a manner similar to prior art cathodes. However, the lithium oxide starts its electron emission at a much lower temperature than the barium and strontium mixture, cutting down the starting time to about one half the usual time interval. After the cathode has reached its normal temperature, the barium and strontium oxides provide the emissive action.

The foregoing disclosure and drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense. The only limitations are to be determined from the scope of the appended claims.

I claim:

1. A thermionic emissive electrode comprising a conductive metallic hollow member, an electron emissive coating on one surface of the member and a heater for the member for heating it to an emissive temperature, said coating comprising by weight 45 to 55 parts of barium oxide, 42 to 52 parts of strontium oxide and 2 to 4 parts of lithium oxide.

2. A thermionic emissive electrode comprising a conductive metallic hollow member, a heater within the member for heating it to an emissive temperature and an electron emissive coating on the outer surface of the member, said coating prior to heating and exhaust operations comprising by weight 45-55 parts of barium carbonate, 42-52 parts of strontium carbonate and 2 to 4 parts of lithium carbonate.

3. A thermionic emissive electrode comprising a conductive metallic hollow member, a heater disposed on the outside of the member for heating it to an emissive temperature, and an electron emissive coating on the inner surface of the member, said coating prior to heating and exhaust operations comprising by Weight 45 to 55 parts of barium carbonate, 42 to 52 parts of strontium carbonate, and 2 to 4 parts of lithium carbonate.

4. A thermionic emissive electrode within an electron discharge device after heating and exhaust operations comprising a conductive metallic hollow member forming a cathode, a heater within the member for heating it to an emissive temperature, and an electron emissive coating on the outer surface of the member, said coating comprising by weight 45 to 55 parts of barium oxide, 42 to 52 parts of strontium oxide, and 2 to 4 parts of lithium oxide.

5. A gaseous discharge device comprising an envelope, an anode, a firing electrode, and a cathode Within the envelope, said cathode including a conductive metallic References Cited UNITED STATES PATENTS 2,473,358 6/1949 Bright 313345 X 2,840,751 6/1958 Meister et al 313346 X 2,986,671 5/1961 Kersetter et a1. 313-845 X 3,147,362 9/1964 Ramsey et al. 313-346 X FOREIGN PATENTS 1,310,430 10/1962 France.

JOHN W. HUCKERT, Primary Examiner.

A. 1. JAMES, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,369,145 February 13, 1968 Lorant Domotor It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 26, for "desopisted" read deposited line 28, for "devive" read device line 46, for "disadvatages" read disadvantages line 62, for "carbonte" read carbonate column 2, line 15, for "57" read 47 line 22, after "parts" insert are line 24, for "changese" read changes column 4, line 3, for "emisive" read emissive Signed and sealed this 29th day of April 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J BRENNER Attesting Officer Commissioner of Patents