Electric lamp and discharge devices – Discharge devices having a thermionic or emissive cathode
Reexamination Certificate
2002-04-19
2004-05-11
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Discharge devices having a thermionic or emissive cathode
C313S446000, C313S3460DC
Reexamination Certificate
active
06734609
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to a cathode in a cathode ray tube (CRT).
2. Background of the Related Art
Referring to
FIG. 1
, in general, the CRT is provided with a panel
1
having a coat of fluorescent film, a shadow mask
4
fitted to an inside of the panel, and a funnel
2
having a neck tube
3
of a funnel form in rear. There is an electron gun
5
built in the neck tube
3
having a cathode
10
therein. Thermal electrons from the cathode
10
are focused to form an electron beam, which is controlled by a magnetic field from a deflection yoke
7
around an outer part of the neck part. The color for the CRT is then selected at the shadow mask
4
for illumination by the electron beam, which lands on a preset location of the fluorescent film screen and causes the fluorescent film to emit a light and display a picture.
Referring to
FIG. 2
, the cathode
10
is provided with an emission layer
12
, a base metal
14
, a heater
16
, a sleeve
20
, and a holder
18
. The emission layer
12
is primarily made of an alkali earth metal carbonate, such as barium carbonate BaCO
3
, strontium carbonate SrCO
3
or calcium carbonate CaCO
3
The emission layer
12
is usually in an acicular form of fine powder with a long axis of approximately 8 &mgr;m, and a short axis of approximately 0.5 &mgr;m which can be spray coated on the base metal
14
. The base metal
14
is primarily made of nickel with a small amount of a reducing agent, such as magnesium or silicon, for promoting reduction of the emission layer
12
and supporting the emission layer
12
.
The heater
16
has a resistance wire primarily composed of tungsten (W) with a coat of alumina (Al
2
O
3
) thereon as an insulating layer. For generating heat, the sleeve
20
is primarily composed of Ni—Cr. The holder
18
, which supports the base metal
14
and transmits heat from the heater
16
to the base metal
14
, is primarily composed of an alloy of nickel for holding the sleeve
20
.
The cathode in the CRT emits thermal electrons to form an electron beam. Meanwhile, the heat from the heater
16
is transmitted to the emission layer
12
by conduction and radiation through the sleeve
20
.
The picture presentation time lag is the amount of time required from the application of power to the heater
16
to the eventual presentation of a picture on the screen. This lag depends upon the heater power consumption and thus the heater power required for regular operation of the CRT. It is important that the picture presentation time lag is made shorter while the heater power consumption is reduced in order to optimize the efficiency of the display. In other words, minimizing the picture presentation time lag can be achieved by transmitting the heat from the heater to the emission layer within a minimal time period to therefore minimize the heat loss at the heater
16
.
Therefore, in order to minimize the heat loss, a reductive heat treated sleeve
20
for reducing a heat loss from radiation is often employed. However, the use of such a sleeve
20
has often led to a long picture presentation time lag as the sleeve has a long time period of heat storage during the heat conduction.
FIG. 2A
illustrates a related art method for reducing heat loss, which includes blackening only an inside surface
20
a
of the sleeve
20
, as described in JP laid open patent No. 07182965 JP A, and No. 09139171 JP A. This method employs a nickel alloy containing approximately 18-20 wt % of chrome, and a reductive material, for blackening a cathode sleeve at approximately 1050° C. for 1 to 2 minutes in a moisturized hydrogen atmosphere to form chrome oxide. Then, the blackened cathode sleeve is heat treated in a dried hydrogen atmosphere to reduce an outer wall of the oxidized cathode sleeve. These blackening/reducing treatments, as illustrated in
FIG. 2B
, provide the inside surface
20
a
of the sleeve with little surface porosity and approximately 32 wt % chrome and a radiation ratio of approximately 0.65 to shorten the picture presentation time lag. The outside surface
20
b
has approximately 26 wt % of chrome and an approximate 0.32 radiation ratio, thereby serving to reduce the heat loss of the heater.
However, the foregoing method is expensive as the fabrication process is complicated due to the two blackening/reducing heat treatments. Additionally, second reduction heat treatment of this related art fabrication process causes the heat radiation ratio of the inside surface
20
a
of the sleeve of the cathode to possibly be reduced. The fabrication method also has difficulty in controlling degrees of the blackening/reducing the inside and outside surfaces of the cathode sleeve in the blackening/reducing heat treatments.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
SUMMARY OF THE INVENTION
An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
Accordingly, the present invention is directed to a cathode in a CRT 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 a CRT which can reduce a heater power consumption and shorten a picture presentation time lag.
Another object of the present invention is to provide a cathode in a cathode ray tube which includes an emission layer at an upper part of the cathode, and a sleeve for inserting a heater therein, wherein the sleeve contains a blackened material that has a porous surface.
Another object of the present invention is to provide a cathode in a CRT including, an emission layer at an upper part of the cathode, a sleeve on side portions of the cathode, and a heater within the cathode, wherein the sleeve has a porous surface formed by heat treating a metal alloy in a moisturized hydrogen atmosphere to blacken the metal alloy, and vaporizing the blackened metal alloy to form the porous surface.
Another object of the present invention is to provide a method of forming a cathode in a cathode ray tube including forming a cathode which include an emission layer, a heater and a sleeve, then heat treating the sleeve, and vaporizing the sleeve to form pores in the surface of the sleeve.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.
REFERENCES:
patent: 4370588 (1983-01-01), Takahashi et al.
Fleshner & Kim LLP
Leurig Sharlene
LG Electronics Inc.
Patel Nimeshkumar D.
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