JP2619106B2 - Oxide cathode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to an oxide cathode used for a thermoelectron tube, and more particularly to an improvement in an electron emitting layer.

(Prior Art) In general, an oxide cathode formed by activating an electron emitter layer of an alkaline earth metal carbonate on a cathode substrate has a lower electron emission temperature than other types of cathodes. It is widely used for various electron tubes because it has many advantages such as a large ratio, easy to obtain an arbitrary shape, low cost, and the like.

On the other hand, it has problems such as being weak against gas ion bombardment in the tube and difficult to obtain a high current density. In particular, recently, a high current density of a cathode ray tube has been required, and further improvement is desired.

In a conventional oxide cathode, an alkaline earth metal carbonate powder composed of barium (Ba), strontium (Sr), and calcium (Ca) is applied to a cathode substrate formed in a predetermined shape by a spraying method or the like, and the inside of an electron tube. And heat decomposition of the carbonate in the exhaust process to form an alkaline earth metal oxide.

This alkaline earth metal carbonate is a double salt or a mixed salt with another alkaline earth metal containing barium as a main component. Generally, barium contains 57% by weight and strontium contains strontium.
Ternary carbonate, which is a double salt of 39% by weight and 4% by weight of calcium, is widely used.

The alkaline earth metal carbonate requires high purity, and is usually produced by reacting an aqueous solution of high purity alkaline earth nitrate with a high purity aqueous solution of sodium carbonate or ammonium carbonate. The crystal shape and particle size of the generated alkaline earth metal carbonate depend on the reaction conditions, particularly the temperature, concentration, and the like.

Also, since the suspension needs to be uniform and stable,
The alkaline earth metal carbonate is suspended in an organic solvent, and if necessary, a binding dispersant such as nitrocellulose is added, and the mixture is dispersed and homogenized by a ball mill for about 50 hours. Then, a suspension of an alkaline earth metal carbonate is prepared and applied to the surface of the cathode substrate by a method such as dipping, spraying, or electrodeposition. The cathode is assembled in an electron tube, and a required evacuation operation is performed to form an alkaline earth metal oxide. Further, sufficient electron emission can be obtained by the activation treatment.

This activation treatment is performed by using a reducing agent such as magnesium, silicon, or chromium contained in the cathode substrate. The reducing agent reacts with barium oxide to increase the excess barium concentration.

JP-A-63-110521 proposes an oxide cathode in which a small amount of scandium carbonate is coprecipitated with an alkaline earth metal carbonate.

However, according to the oxide cathode, although the electron emission ability in a short time is excellent, the electron emission ability sharply decreases when operated for a long time. Although the reason has not been elucidated yet, when observing the cathode surface with reduced electron emission capability over a long period of time (6000 hours), a fine coating peeling phenomenon and a coating surface Cracks are observed.

Probably, it is considered that the electron radioactivity causes local composition segregation due to the inclusion of scandium, and the above phenomenon occurs due to shrinkage stress. The degree of this phenomenon depends on the amount of scandium contained, and the scandium in the central part of the coating surface becomes higher in concentration with the operation time than in the initial stage.

As a result, it is considered that the peeling of the coating impairs the reduction of the temperature of the electron emitting surface and the reduction reaction with the base metal, and the crack reduces the effective electron emitting surface, so that the electron emitting ability sharply decreases.

(Problems to be Solved by the Invention) The electron emission capability of the conventional oxide cathode as described above is maintained by excess barium in the electron emitter layer, which is usually caused by the reaction between the reducing agent and barium oxide in the cathode substrate. Done by

Therefore, to operate the oxide cathode well for a long time,
Although it is necessary to maintain the reaction at the interface between the cathode substrate and the electron emitting layer for a long time, the oxide cathode to which a small amount of scandium carbonate is added as described above, the operating time of the electron emitting layer, especially Local composition segregation is caused in the portion of the first grid from which the electron beam is taken out, and the reduction reaction with the base metal is hindered by coating peeling caused by shrinkage stress, and sufficient electron emission capability is obtained. Can not be.

In addition, the effective electron emission area decreases due to cracks,
As in the case of coating peeling, the electron emission capability deteriorates.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned disadvantages of the conventional oxide cathode and to provide an oxide cathode in which the electron emission characteristics are not deteriorated even after long-term operation.

[Constitution of the Invention] (Means for Solving the Problems) The present invention provides an electron emission layer formed by activating a cathode substrate to which a small amount of a reducing agent has been added, so that the alkaline earth metal does not contain scandium carbonate. An oxide cathode comprising a first layer made of a carbonate and a second layer made of an alkaline earth metal carbonate containing scandium carbonate formed on the first layer.

(Action) According to the present invention, since the first layer made of the alkaline earth metal carbonate not containing scandium carbonate is formed on the cathode substrate by the activation treatment, the alkali containing scandium carbonate in the long-time operation is formed. Although the earth metal carbonate is activated, it is possible to prevent a peeling phenomenon and a crack from occurring due to a specific local composition segregation.

As a result, it is possible to maintain stable electron activity for a long time.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

The cathode structure provided with the oxide cathode according to the present invention has a first structure.
A cathode base 3 mainly composed of nickel to which a small amount of a reducing agent is added is fixed to one end of a cathode support sleeve 2 which is configured as shown in the drawing and in which a heater 1 is accommodated.

On the cathode base 3, an electron emitting layer 4 is formed. In this case, the electron emitter layer 4 is composed of a first layer 4a made of an alkaline earth metal carbonate not containing scandium carbonate.
And a second layer 4b made of an alkaline earth metal carbonate containing scandium carbonate formed on the first layer 4a and formed by activating the second layer 4b. It has become.

Next, a method for manufacturing the above-described oxide cathode will be described.

First, scandium carbonate-free alkaline earth metal carbonate to be applied as the first layer 4a is suspended in an organic solvent, for example, butyl acetate, aluminum acetate, ethanol, or the like, and a necessary amount of a binder, for example, nitrocellulose is added thereto. Perform a ball mill for about an hour to produce a uniform suspension.

Also, a suspension of alkaline earth metal quaternary carbonate obtained by coprecipitation containing scandium carbonate to be applied as the second layer 4b is prepared in the same manner as the suspension of the first layer 4a.
The two suspensions thus produced are applied on a cathode base 3 mainly composed of nickel to which a small amount of a reducing agent is added.

That is, first, a suspension containing no scandium carbonate to be applied as the first layer 4a is applied to the cathode base 3 by a spray method to a thickness of 10 μm.

Thereafter, the suspension of the second layer 4b is similarly applied to the first layer 4a by a spray method to a thickness of 60 μm.

 Except for the above, the oxide cathode is completed by a known method.

Now, a first layer made of an alkaline earth metal carbonate not containing scandium carbonate is formed on the above-described cathode substrate, and a first layer made of an alkaline earth metal carbonate containing scandium carbonate is formed on the first layer. What formed two layers,
It was incorporated in a cathode ray tube and subjected to a usual exhaust gas activation treatment to obtain an oxide cathode. When the initial values of the emission characteristics of the oxide cathode of the present invention were compared with those of the conventional oxide cathode, there was no difference. Here, the conventional oxide cathode is an oxide cathode obtained by subjecting an electron emission layer of an alkaline earth metal carbonate containing scandium carbonate to an exhaust activation treatment on a cathode substrate.

In addition, the release of the decomposition gas in the exhaust gas did not change as compared with the conventional case, and no problem occurred in the conventional exhaust operation.

Next, with respect to the electron tube using the oxide cathode of the present invention, emission characteristics associated with long-term operation were measured.

Figure 2 shows a pulse emission (A / cm ²⁾ maintaining values for each time when allowed to prolonged operation at a current density of 0.8 A / cm ^2. A curve S shown in the figure is a case of the oxide cathode of the present invention, and a curve R is a case of a conventional oxide cathode (an oxide cathode in which only an alkaline earth metal carbonate containing scandium carbonate is coated on all layers). is there.

As is apparent from this comparison of characteristics, the oxide cathode of the present invention has much less deterioration of emission due to long-term operation than the conventional one, and the effect is more remarkable as the time becomes longer.

Further, the cathode operated for a long time was taken out from the electron tube, and the surface of the cathode was observed. As a result, the fine coating peeling phenomenon and cracks observed in the conventional product did not occur.

(Modification) In the above embodiment, the application thickness of the first layer 4a was described as 10 μm, but according to the experimental results, the application thickness of the first layer 4a was 5 μm.
Even in the range of 5050 μm, the same effect as in the above example was obtained.

The total thickness of the first layer 4a and the second layer 4b is 70-80.
It is desirable that the thickness be smaller than the range of μm.

Further, in the above embodiment, an example in which the present invention is used for a cathode ray tube has been described. However, similar effects can be obtained by using the oxide cathode of the present invention for an image pickup tube, a transmission tube, or the like.

[Effects of the Invention] As described above, according to the present invention, it is possible to obtain a stable and highly reliable oxide cathode which has particularly excellent emission characteristics associated with long-term operation.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a cathode structure provided with an oxide cathode according to one embodiment of the present invention, and FIG. 2 shows the relationship between life test time and emission characteristics in each of the present invention and conventional oxide cathodes. It is a characteristic curve figure. 3 ... Cathode base, 4 ... Emitting material layer, 4a ... First layer,
4b: Second layer.

Claims (1)

(57) [Claims] 1. An oxide cathode formed by activating an electron emission layer of an alkaline earth metal carbonate on a cathode substrate to which a small amount of a reducing agent is added, wherein the electron emission layer is A first layer of scandium carbonate-free alkaline earth metal carbonate formed on the substrate, and a second layer of scandium carbonate-containing alkaline earth metal carbonate formed on the first layer; An oxide cathode, comprising: