JPS6290819A - Cathode for electron tube - Google Patents

Abstract

PURPOSE:To increase the life of a cathode for an electron tube under the operation at high current density by coating a base principally composed of nickel with an electron-emitting substance layer which is principally composed of the oxides of alkaline earth metals including barium and containing 0.05-15wt% of rare earth metals. CONSTITUTION:A suspension is prepared by adding 0.05-15wt% of scandium or yttrium powder as the powder of a rare earth metal to a ternary carbonic salt of barium, strontium and calcium. This suspension is applied to a base 1 principally composed of nickel by spraying in a thickness of about 80 microns. Next the base 1 is coated with an electron-emitting substance layer 2 through the decomposition process from carbonate to an oxide and an activation process whereby the oxide is reduced partially. Thus, it is possible to increase the life of the cathode under the operation at high current density.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to cathodes for electron tubes used in TV cathode ray tubes and the like, and particularly relates to improvements in electron emissive material layers.

[Conventional technology]

Figure 2 shows a cathode used in conventional TV cathode ray tubes and image pickup tubes. In the figure, (1) is the main component containing small amounts of reducing elements such as silicon (SI) and magnesium (Mg). A cylindrical base with a bottom made of Ni-Nokel,
(2) is deposited on the top surface of the bottom of this substrate and contains at least barium (Ba) and strontium (S).
r) or/and an electron emitting material layer consisting of an alkaline earth metal oxide containing calcium (Ca);
) is a heater (3) disposed within the base (1), which is used to emit thermoelectrons from the electron emitting material layer (2) by heating.

In the cathode for an electron tube constructed in this way, the material layer (2) containing q·1 electrons is deposited on the substrate m in the following manner. First, alkaline earth metals (B a, S
R, Ca) consisting of carbonate/! AM is applied to the base fil and heated by a heater (3) during the evacuation process. At this time, the alkaline earth metal carbonate turns into an alkaline earth metal oxide. Thereafter, a part of the alkaline earth metal oxide is reduced and activated to have semiconducting properties. ). In this activation step,
Some of the alkaline earth metal oxides react as follows. In other words, reducing elements such as silicon and magnesium contained in the substrate +11 move to the interface between the alkaline earth metal oxide and the substrate (1) by diffusion and react with the alkaline earth metal oxide. For example, if the upper alkali oxide is barium oxide (Bad), the following formula fl
l, (2+).

BaO+54SiO*=Ba+H3iO, (11B a
o 10 M g = B a + MgO-121 As a result of this reaction, a part of the fluorine metal oxide deposited on the substrate (1) is reduced to become an oxygen-deficient semiconductor, and the cathode temperature is 700~ 0.5~ at operating temperature of 800℃
Electron emission of 0.8 A/cd will be obtained. However, with the cathode for an electron tube formed in this manner, a current density of electron emission of 0.5 to 0.8 A/cd or more cannot be obtained. The reason for this is as follows. That is, when a part of the alkaline earth metal oxide is subjected to a reduction reaction, as is clear from the above formula 121, at the interface between the substrate (1) and the alkaline earth metal oxide layer, SiO2M or BaOSin, A composite oxide layer (intermediate layer) is formed, and this intermediate layer becomes a high-resistance layer and obstructs the flow of current. It is believed that this prevents barium (Ba) from diffusing to the surface side of layer (2) and not enough barium (Ba) is generated.

In addition, as a conventional cathode for electron tubes, JP-A-59-209
No. 41 discloses a structure similar to that shown in Fig. 2 above, in which the thickness of the substrate (1) is made thinner in order to obtain rapid action of the cathode, and the temperature of the reducing agent during its life is reduced. Prevention and base (1)
In order to prevent the strength from decreasing, a substrate (11) containing lanthanum dispersed in the form of LaNi, La, and O is shown.

[Problem that the invention seeks to solve]

In the electron tube cathode constructed in this way, during operation, the nickel crystal grain boundaries near the substrate fil and the surface, and the nickel crystal grain boundaries near the interface between the substrate (1) and the electron emitting material layer (2), in particular,
) Since the above-mentioned intermediate layer is segregated at a position about 10 μm inside the electron emitting material R (2), the flow of current and the diffusion of reducing elements toward the surface of the electron emitting material layer (2) are impeded, and gT
There was a problem that sufficient electron emission characteristics could not be obtained under i current density.

In addition, in what was shown to the actor, 1aNis and La20.
Therefore, variations in the content of aNiS and La2O5 were likely to occur in the substrate (11).

This invention has been made in view of the above-mentioned points, and prevents the formation of an intermediate layer made of a composite oxide in a concentrated manner near the interface between the substrate and the electron emitting material layer under high current density. The object of the present invention is to obtain a cathode for an electron tube that has stable Eminence characteristics over a long period of time and has high productivity and reliability.

[Means for solving problems]

The cathode for an electron tube according to the present invention has an alkaline earth metal oxide containing at least barium as a main component, and has 0.05
An electron-emitting material layer containing ~15% by weight of a rare earth metal is deposited on a nickel-based substrate.

[For production]

In this invention, 0 contained in the electron emitting material layer
, 05 to 15% by weight of rare earth metals are added to barium oxide during activation when depositing an electron emissive material layer on a substrate, when carbonates of alkaline earth metals are decomposed, or during operation as a cathode. It prevents the oxidation of the substrate when a dissociation reaction occurs, and moderately controls the diffusion of the reducing element contained in the substrate into the electron emitting material layer. This prevents the intermediate layer from being formed intensively near the interface between the substrate and the electron emitting material layer,
The intermediate layer is dispersed within the electron emissive material layer.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. In the figure, (2) is deposited on the upper surface of the bottom of the substrate +11, and contains at least barium, and also contains strontium or/and calcium as a main component, and has an alkaline earth metal oxide (11) of 0.05 to 15 This is an electron emitting material layer containing a significant amount of rare earth metals (12) such as scandium and yttrium.

Next, in the electron tube cathode configured in this way, the base (
To explain the method of depositing the electron emitting material layer (2) on 1), first, scandium powder or lithium powder is added to a ternary carbonate of barium or strontium-calcium in a desired weight percent (the above ternary carbonate). % by weight assuming that all the salts become oxides) are added and mixed to create a suspension.

This suspension was applied to a thickness of about 80 microns by spraying onto the substrate (1) whose main component was nickel, and then
Similar to the conventional method, the electron-emitting substance H (2) is deposited on the substrate (1) through a decomposition process from carbonate to oxide and an activation process to reduce a portion of the oxide. .

Various cathodes for electron tubes were created with various amounts of rare earth metals contained in the electron emitting material layer (2) deposited by this method, and diode vacuum tubes were created using these cathodes for electron tubes. However, as a result of conducting life tests at various current densities and observing changes in the emission current, the results shown in Figures 3 and 4 were 11J. Figure 3 shows a current density of 3.1 times (2,05A/cj) the current density of the conventional TV cathode, which is 0.66A/cj.
A cathode for an electron tube having an electron emitting material layer (2) containing 3% by weight of Sc when operated at cII+), having an electron emitting material layer (2) containing 7% by weight of Y. The graph shows the relationship between the lifetime characteristics of the cathode for an electron tube and the lifetime characteristics of a conventional example having an electron emitting material layer (2) containing no rare earth metal. As is clear from FIG. 3, the device of this embodiment containing rare earth metals exhibits less emission deterioration during high current density operation than the conventional device.

Furthermore, Fig. 4 shows the current density at a current density of 0.66 A/ci (assumed to be 1) in an electron tube cathode having an electron emitting material layer (2) with various addition ratios of Sc, a rare earth metal. A life test was conducted under the conditions of 2 times #3.1 times and 4 times, and the relationship between the current density and the ratio of the emission current at 6000 hours to the initial working current is shown. As can be seen from FIG. 4, when the rare earth metal Se is added at a rate of 0.05% by weight or more, it has the effect of preventing a decrease in emissions under high current density operation, and although it is not shown in the figure, Sc This effect was confirmed up to an addition rate of 15 wt%. However, if the addition rate of Sc, which is a rare earth metal, exceeds 15% by weight, it becomes difficult to stably extract the emission current unless immersion through the manufacturing process or aging for a long time is performed, making it impractical. . Therefore, the content of rare earth metal oxide in the electron emitting material layer (2) needs to be in the range of 0.1 to 15% by weight. Particularly in the range of 0.2 to 7% by weight, the effect of improving air content was remarkable.

In order to investigate in detail the effect of containing a rare earth metal oxide in the electron emitting material M(2), in the experimental results shown in Figure 3, after measuring the emission current for 6000 hours,
Conventional product and electron emitting material layer containing 3% by weight of Se (
As a result of analyzing the cross section of the cathode for electron tubes with 2) using an electron beam X-ray microanalyzer (EPMA), it was found that the cathode for electron tubes had a conventional electron emitting material layer (2) that did not contain any rare earth metals. In this case, Si and Mg, which are the reducing agents contained in the substrate (1), are segregated near the interface between the nickel that is the substrate (1) and the electron emitting material layer (2), and this segregation state is caused by the fact that the substrate fi+ A position at a depth of approximately 5 μ from the interface between the electron emitting material layer (2) and the substrate (11 side) and approximately 3 to 5 μ from the interface to the electron emitting material layer (2) side.
The peaks of Sl and Mg, which are reducing agents, were confirmed at the same time at the position of the electron emitting material layer (2).
) The maximum peak was observed at a position of about lθμ toward the side.

Since the peaks of these Si and Mg almost coincide with the peak of oxygen, it is assumed that these metals exist as oxides or composite oxides. In this way, in the conventional product under high current density operation, 5i02. It can be seen that O and a composite oxide layer of these are formed on M, and further a composite oxide layer of BaO, MgO, and Sio□ is formed at the position of the electron emitting material layer (2) from the above interface. be. -S iO as described above
zMgo 511 and B ao Si OJf! J suppresses the diffusion rate of Si and Mg, which are reducing agents, from the substrate (1) into the electron emitting material layer (2), and is highly insulating, thus inhibiting the flow of current, and eventually the electron emitting material This will lead to wear and tear due to dielectric breakdown inside.

On the other hand, in the electron tube cathode of this embodiment, which has an electron emitting material layer (2) containing Se, which is a rare earth metal, Si, which is a reducing agent contained in the base film,
, M are evenly dispersed, and as in the conventional example, near the interface between the substrate (11 and the electron emitting material layer (2)),
These reducing agent peaks are completely absent. This is considered to be due to the following reasons. Si and Mg, which are reducing elements, form an electron emitting material 1 at the interface 11.
Even if SiO□, MgO, or a composite oxide of these and BaO is formed near the interface by reacting with i (21), Sc contained in the electron emitting material layer (2) reacts with these oxides, and This generates Si or Mg and facilitates the movement of reducing elements within the electron emitting material layer (2).

Finally, the rare earth metal in the electron emitting material layer (2) moderately controls the rate of diffusion of the reducing element into the electron emitting material, so it is stable and good even after long-term operation under high current density. Emission current can be maintained.

Therefore, when less than 0.05% by weight of rare earth metal is added, the effect of suppressing the formation of sio, Mgo oxide layers near the interface of the substrate (1) is insufficient, resulting in a decrease in the emission current. start. Furthermore, if the addition exceeds 15%, a reaction between barium oxide and other rare earth metals in the electron emitting material will occur, resulting in a decrease in the emission current.

In addition, in the above embodiment, Se is used as the rare earth metal material.
Although a similar effect was obtained using other rare earth metals, the effect was particularly remarkable for Se, Y, and Ce.

As described above, according to the present invention, a cathode can be manufactured under almost the same manufacturing conditions as conventional methods, and the state of dispersion of the rare earth metal can be controlled relatively easily.

〔Effect of the invention〕

As described above, the present invention includes an electron emitting material layer which is deposited on a substrate and whose main component is an alkaline earth metal oxide containing at least barium, which contains 0.05 to 15% by weight of a rare earth metal. Since the electron emitting material layer does not contain rare earth metals, it is
This has the effect of providing a cathode for electron tubes that has a long life under operation at a current density four times as high, is inexpensive, and has fewer manufacturing constraints (high ffl properties).

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an embodiment of the present invention, Fig. 2 is a sectional view showing a conventional electron tube cathode, Fig. 3 is a graph showing the relationship between life test time and emission current, and Fig. 4 is a sectional view showing an example of the present invention. FIG. 3 is a diagram showing the relationship between current density and emission current ratio. In the figure, (1) is a base body, and (2) ζ is an electron emitting material layer. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] The main component is nickel, the main component is an alkaline earth metal oxide containing at least barium, and the main component is 0.05
A cathode for an electron tube, characterized in that an electron emitting material layer containing ~15% by weight of a rare earth metal is deposited.