Electric lamp and discharge devices – Electrode and shield structures – Cathodes containing and/or coated with electron emissive...
Reexamination Certificate
1998-11-12
2001-01-30
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Electrode and shield structures
Cathodes containing and/or coated with electron emissive...
C313S3460DC
Reexamination Certificate
active
06181058
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron tube, such as a cathode ray tube for a TV receiver, and more particularly, to a cathode in an electron tube, of which electron emission performance is improved.
2. Background of the Related Art
To keep pace with recent development of large sized, highly defined, and multimedia images, a cathode with an improved electron emission concentration is required for use in a cathode ray tube.
Referring to
FIG. 1
, a related art cathode is provided with a thermion emission material layer
3
of an oxide of an alkaline earth metal containing at least barium Ba formed on a base metal
1
of nickel as a main composition added with a small amount of reducing element, such as silicon Si or Mg. And, there is a heater
4
is fitted in a cylindrical sleeve
2
, for heating the thermion emission material layer
3
, to emit thermions.
The aforementioned related art cathode is fabricated by the following process.
A suspension of an alkaline earth metal carbonate is coated on the base metal
1
and heated by the heater
4
in a vacuum, to convert the alkaline earth metal carbonate into the alkaline earth metal oxide. Then, a portion of the alkaline earth metal oxide is reduced at 900~1000° C. so that the alkaline earth metal oxide is activated to have a semiconductor property, forming the thermion emission material layer
3
on the base metal
1
. In above activation, the reducing element, such as silicon or magnesium contained in the base metal
1
is diffused to an interface of the alkaline earth metal oxide and the base metal
1
and makes a chemical reaction with the alkaline earth metal oxide. This alters the thermion emission material layer
3
into an oxygen depleted type semiconductor in which a portion of the alkaline earth metal oxide is reduced, which has an emission current of 0.5~0.8 A/cm
2
under a regular operation temperature.
However, a high current can not be obtained from the related art cathode during a lifetime of the related art cathode because of a highly resistant layer of an interface layer formed of a reaction oxide between the thermion emission material layer
3
and the base metal
1
, which impedes current flow and diffusion of the reducing element in the base metal into the thermion emission material layer
3
that suppresses emission of adequate amount of barium Ba. Japanese laid open patent No. 59-20941 discloses a cathode provided with a thin base metal for obtaining a quick action of the cathode and a base metal containing lanthanum La in forms of LaNi
5
and La
2
O
3
in purposes for preventing dry up of reducing elements and preventing weakening of the base metal during the lifetime of the cathode. A. van Oostrom discloses a cathode formed by press molding a mixed powder of tungsten W and Ba
3
Sc
4
O
9
in the Application of Surface Science 2(1979), p173-186 of the USA. German laid open patent No. 2626700 discloses a thermion emission material for use in a high pressure discharge lamp, of alkaline earth metal oxide, such as a mixture of BaO and tungsten oxide, or molybdenum and a rare earth metal oxide. U.K. patent No. 1592520 discloses a thermion emission material layer for use in a discharge lamp, of BeO and Y
2
O
3
added with Ba
2−x
Sr
x
CaWO
v
(
x
=0-0.5). For an improvement of a thermion emission characteristic, Korea patent application No. 86-5652 discloses, as a first embodiment, a cathode having a base metal
1
of nickel as a main composition, and a thermion emission material layer
3
of an alkaline earth metal oxide containing at least barium Ba as a main composition added with 0.1-20 wt % of a rare earth metal oxide or 0.05-15 wt % of rare earth metal, formed on the base metal
1
, as a second embodiment, a cathode having a base metal
1
of nickel as a main composition, an intermediate layer of a rare earth metal oxide of a thickness below 10 &mgr;m or of a rare earth metal of a thickness below 6 &mgr;m formed on a base metal
1
, and a thermion emission material layer of an alkaline earth metal oxide containing at least barium Ba formed on the intermediate layer, and, as a third embodiment, a cathode having a base metal
1
of nickel as a main composition added with 0.01-0.5 wt % rare earth metal, and a thermion emission material layer of an alkaline earth metal oxide containing at least barium Ba formed on the base metal
1
. In the cathode disclosed in the Korea patent application No. 86-5652, powder of the rare earth metal oxide in the thermion emission material layer
3
makes reaction with the alkaline earth metal oxide, for example BaO, to produce a composite oxide of Ba
3
Sc
4
O
9
or Ba
3
Y
4
O
4
. It is supposed that the composite oxide scattered in the thermion emission material layer
3
decomposes at a working temperature of the cathode and makes production of free barium easy, allowing presence of adequate barium, and a portion of the rare earth metal in the composite oxide, freed and scattered in the thermion emission material layer
3
, increases a conductivity of the thermion emission material layer
3
, that compensates for the resistance of the interface layer. It is described that the cathode in the Korea patent application No. 86-5652 has an advantage in that an electron emission concentration approx. 2-3 times is obtainable compared to a related art cathode of an alkaline earth metal oxide due to less degradation during the lifetime under a high current concentration.
However, the cathode in the Korea patent application No. 86-5652 has problems in that the electron emission current concentration can not be improved any further and has difficulty in fabrication due to complicate process coming from a high temperature heat treatment of the rare earth metal oxide at a temperature over 800° C. in a reducing ambient before the rare earth metal oxide is mixed with the alkaline earth metal oxide.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a cathode in an electron tube that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a cathode in an electron tube, which can improve electron emission performance, significantly.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the cathode in an electron tube includes an actinoid metal or actinoid metal compound added to either a thermion emission material layer or a base metal, or formed between the thermion emission material layer and the base metal, whereby improving an electron emission characteristic of the cathode, significantly.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
REFERENCES:
Patent Abstract of Japan, A 59020941, Feb. 02, 1984.
Patent Abstract of Japan, A 62088240, Apr. 22, 1987.
Patent Abstract of Japan, A 62090819, Apr. 25, 1987.
Patent Abstract of Japan, A 62088239, Apr. 22, 1987.
Patent Abstract of Japan, A 62022347, Jan. 30, 1987.
Birch & Stewart Kolasch & Birch, LLP
LG Electronics Inc.
Patel Nimeshkumar D.
Quarterman Kevin
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