JPH0161216B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an improvement in a method for manufacturing an oxide cathode assembly.

(Technical Background and Problems of the Invention) When a television receiver is turned on, it is desirable to output an image as quickly as possible and to reach a stable screen. For this purpose, so-called directly heated cathodes, in which the base metal is directly heated by electrical current, have been studied. However, directly heated cathodes are prone to wire breakage, peeling of the electron emitting material, etc.
It also has many drawbacks, such as being easily affected by even slight voltage fluctuations. On the other hand, indirectly heated cathodes, which are currently widely used in various picture tubes including television picture tubes, do not have the drawbacks of the directly heated cathodes mentioned above and can provide stable emission. . Currently, an indirectly heated cathode, which is called a fast-acting type, has a cathode at the tip of a cathode sleeve 11 made of, for example, a Ni-Cr alloy, as shown in Fig. 1.
After welding the Ni-Mg-Si alloy base metal 12,
A black oxide film 13 of Cr ₂ O ₃ is formed on the surface of the Ni-Cr alloy cathode sleeve 11 by heating in a hydrogen stream containing water vapor, and then an electron emitting material 14 is applied to the upper surface of the base metal 12. A heater 15 was placed inside the sleeve 11. This cathode has a black oxide film 1 formed on the surface of the cathode sleeve 11.
3, the start-up of the emission becomes faster.

However, the image output time obtained with the above cathode structure is still slow compared to a directly heated cathode.
Further improvements are desired. By the way, if the cathode structure as a whole is made thinner to reduce its heat capacity in order to obtain faster emission rise, the reducing agent in the base metal becomes insufficient, which is not good in terms of emission and life. As a countermeasure against this problem, simply increasing the amount of reducing agent added to the base metal is sufficient. However, although the initial emission is improved by simply increasing the amount added,
After a long period of operation, the effect of increasing the amount of reducing agent cannot be obtained. This is because many of the reducing agents react with the electron-emitting substance more than necessary in the initial stage.

As a result of several detailed studies on oxide cathodes, the present inventors have found that (i) it is possible to separate the sites of the dissociation reaction of oxygen from the electron-emitting substance and the reaction of this oxygen with the reducing agent; and (ii) found that a control layer for the diffusion of oxygen and reducing agent could be formed between both reaction sites, and developed an oxide cathode structure using a base metal having a cross-sectional structure as shown in Figure 2. We fabricated it, installed it in a color cathode ray tube electron gun, and conducted a lifespan test with good results.

In FIG. 2, 24 is an electron emitting material, 22 is a base metal, 26 is an internal oxidation particle of a reducing agent, and 27 is a diffusion control layer. The diffusion control layer 27 is a layer in which the growth of crystal grains is suppressed by the internal oxidation particles 26 of the reducing agent that are dispersed and precipitated, and the oxide of the reducing agent is accumulated and fixed at the grain boundaries. This is what forms the physical layer. A base metal having such a cross-sectional structure was produced, for example, in the following manner. After grinding the surface of a Ni-based alloy containing a small amount of reducing agent and applying processing strain near the surface, CO/
1000℃ in a CO ₂ gas mixture (e.g. partial pressure 1:20),
Internal oxidation treatment is performed by holding for 1 hour. Through this treatment, the internal oxidation of the reducing agent and the recrystallization phenomenon accompanying the release of the processing strain introduced by grinding proceed simultaneously, but the growth of the crystal grains existing in the internal oxidation layer is suppressed as described above, and the desired A base metal having a cross-sectional structure was obtained. In an oxide cathode having such a base metal, the generation of free Ba that contributes to electron emission from an electron emitting substance occurs separately in the following two reactions. Here, reaction 1 occurs at the interface between the base metal and the electron emitting material, while reaction 2 occurs at the diffusion control layer inside the base metal.

Ba0 (electron emitting material) → Ba (in electron emitting material) + O (in base metal) (1) xR (in base metal) + y O (in base metal) → R _x O _y (2) However, R is reduction At this time, the diffusion control layer mainly suppresses the progress of the oxidation reaction of the reducing agent by controlling the diffusion of the reducing agent, and by using a base metal with such a cross-sectional structure, it can be used for a long time. , stable emission can be obtained.

By the way, the method for manufacturing a base metal having the cross-sectional structure shown in Fig. 2, an example of which has already been described, consists of a step of applying processing strain to the base metal and a step of subjecting the base metal to internal oxidation treatment. This is done before the electron emitting material is applied. In internal oxidation, the depth of the treatment can be precisely specified by accurately specifying the oxygen partial pressure in the atmosphere, the treatment temperature, and the treatment time, whereas the amount and quality of processing strain imparted to the base metal cannot be precisely determined. It is difficult to control the strain, and the recrystallization situation associated with the release of the strain is also different.
It is not easy to accurately control the position where grain boundary fixation occurs, that is, the position of the diffusion control layer.
Furthermore, the continuity of the formed layer is not necessarily sufficient, and there are disadvantages in that the layer may not be formed in some areas, or the depth may be different in some areas, making it impossible to obtain a uniform layer.

Therefore, it is desired to develop a technique for easily and accurately forming a uniform layer.

(Object of the Invention) The present invention aims to make the precipitated layer uniform and to position the precipitated layer when forming a precipitated layer of internal oxide particles that controls the diffusion of a reducing agent inside the base metal of an oxide cathode structure. An object of the present invention is to provide a method for manufacturing an oxide cathode structure that can easily and accurately control the oxide cathode structure.

(Summary of the Invention) In the course of research on oxide cathodes, the present inventors investigated in detail the internal oxidation characteristics of a Ni-based alloy containing a trace amount of reducing agent. If the oxidation conditions are suddenly changed to high temperature and low oxygen pressure, where the contribution of diffusion of the agent to the alloy surface increases, the progress of internal oxidation into the interior of the alloy becomes stagnant or regressed, resulting in high-density precipitation of internal oxidation particles. We found that (ii) this high-density precipitated layer of internally oxidized particles has the function of controlling the diffusion of the reducing agent.

An example of the processing steps of the present invention will be described below with reference to the drawings.

FIG. 3a shows, as the base metal 32 before treatment,
A cross section of a base metal made of a Ni-based alloy containing 0.1% by weight of Mg is shown, and this base metal 32 is used as a first oxidizing atmosphere in a mixed gas of CO and CO ₂ at a mixing ratio of 1:10. By processing at a temperature of 1000° C. for 20 minutes, a dispersed layer 39 of MgO particles, which are internal oxidation particles 36 of the reducing agent, is formed near the surface of the base metal 32, as shown in FIG. 13b, and then,
In an oxidizing atmosphere in which the amount of CO gas is increased and the partial pressure of oxygen is lower than in the first oxidizing atmosphere, the temperature is higher than the first temperature in a mixed gas of CO and CO ₂ at a mixing ratio of 1:1. By performing the treatment at 1100° C. for 1 minute, the internal oxidation particles 36 of the reducing agent are formed in the vicinity of the surface of the base metal 32, following the dispersion layer 39 of the internal oxidation particles 36 of the reducing agent formed in the first treatment.
A high-density precipitated layer 38 is formed in which MgO particles are precipitated at a high density. This high-density precipitated layer 38, shown in FIG. 3c, acts as a barrier when the reducing agent below this layer diffuses to the surface, suppressing the reducing agent from diffusing to the surface, and as will be described later. act to produce favorable results for electron radiation.

The process of forming the high-density precipitated layer 38 of internally oxidized particles 36 of the reducing agent will be described in more detail with reference to FIGS. 3d to 3f. Figure 3d shows the initial state in the process at a first temperature in a first atmosphere.
Oxygen dissolved in the base metal 32 in equilibrium with the first oxidizing atmosphere diffuses toward the lower part of the base metal 32 at a diffusion rate v ₀ (T ₁ ) determined by the first temperature T ₁ . . On the other hand, the reducing agent added to the base metal 32 has a diffusion rate v _act determined by the first temperature T ₁
(T ₁ ) and diffuses toward the surface of the base metal 32, but in the first oxidizing atmosphere, the amount of oxygen supplied is sufficient, and v ₀ (T ₁ )≫v _act (T ₁ ) Therefore, oxygen and the reducing agent collide and react to form oxide particles 3.
The position where 6 is formed progresses toward the bottom as shown in Figure 3e. Next, when the processing conditions are suddenly changed to a second oxidizing atmosphere with a lower oxygen partial pressure than the first oxidizing atmosphere and a second temperature T ₂ higher than the first processing temperature, the oxygen , the diffusion rate of both reducing agents becomes faster than at T ₁ , but v ₀ (T ₁ )≫v _act (T ₁ )
However, v ₀ (T ₂ )>v _act (T ₂ ), and
The atmosphere has shifted to the low oxygen partial pressure side, and the base metal 3
The amount of solid solution of oxygen in 2 rapidly decreases, and the amounts of oxygen and reducing agent required for the reaction, v ₀ (T ₂ ) and v _act (T ₂ ), and the diffusion rates v ₀ (T ₂ ) and v _act ( T ₂ ) product, v ₀ (T ₂ )×v ₀
(T ₂ ) and v _act (T ₂ )×v _act (T ₂ ) become balanced, and as shown in FIG. 3f, the reducing agent oxide particles 36 formed by the first treatment are Dispersion layer 3
Oxygen and the reducing agent react with each other one after another at the bottom of 9, and a high-density precipitated layer 38 of oxide particles is formed there. Note that if the second treatment is performed immediately without the first treatment, a surface oxide layer will be formed on the surface of the base metal 32, which will conversely impede electron emission.
Further, the first treatment alone does not provide a layer that suppresses the diffusion of the reducing agent, and the object of the present invention cannot be achieved.
In other words, the treatment in the first oxidizing atmosphere and at the first temperature allows the reducing agent in the vicinity of the surface of the base metal 32 to be dispersed in advance as oxide particles, and at the same time, the high density precipitation layer 38 of the oxide particles 36 is deep. Furthermore, the treatment in the second oxidizing atmosphere and at the second temperature affects the lowermost position of the dispersed layer 39 of the internal oxide particles 36 formed by the first treatment. This is to precipitate internal oxidation particles at high density.

Next, a method for controlling the depth H of the high-density precipitated layer 38 of internal oxide particles 36 will be described.

Figure 4 shows the depth H of a high-density precipitated layer formed by changing the time under the first processing conditions (temperature, atmosphere, time) while keeping the second processing conditions (temperature, atmosphere, time) constant. This shows the measurement results. That is, the base metal is a Ni-based alloy containing 0.1% by weight of Mg, and the first atmosphere is a mixture ratio of 1:20.
In a mixed gas of CO and _CO2 , as the first temperature
After processing at 1000℃ for t1 hour, the amount of CO gas was increased and the second treatment temperature was 1100℃ in a second atmosphere consisting of a mixed gas of CO and CO ₂ at a mixing ratio of 1:1.
The depth H of the high-density precipitated layer 38 of internal oxidation particles was measured after heating for 1 minute. The results shown in FIG. 4 show that if the oxygen partial pressure of the first treatment atmosphere and the first treatment temperature are constant, the difference between the depth H of the high-density precipitated layer 38 and the treatment time t ₁ of the first treatment is The parabolic law holds, that is, H=K ₁ √ K ₁ indicates that the depth H of the high-density precipitated layer 38 can be easily controlled according to the constant relationship.

FIG. 5 shows a high-density precipitated layer 38 of oxide particles formed by changing the atmosphere from the first processing conditions (temperature, atmosphere, time) while keeping the second processing conditions (temperature, atmosphere, time) constant. This figure shows the measurement results of the depth H of . That is, 0.1 as in the case of Figure 4.
Using a Ni-based alloy containing % Mg by weight, the first temperature was 1000°C, the first treatment time was 10 minutes (curve a) and 20 minutes (curve b), and the first treatment atmosphere was mixed. Changed the ratio from 1:10 to 1:25
After processing in a mixed gas of CO and CO ₂ , the temperature rapidly changes to a second processing temperature of 1100°C in a mixed gas of CO and CO ₂ with an increased amount of CO gas and a mixing ratio of 1:1. The depth H of the high-density precipitated layer of internal oxidation particles was measured after heating for 1 minute. The results shown in FIG. 5 show that if the first treatment temperature and treatment time are constant, there is a constant difference between the depth H of the high-density precipitated layer 38 and the mixing ratio of CO and CO ₂ in the first treatment atmosphere. It turns out that there is a relationship between In order to examine this situation in detail, FIG. 6 is a diagram redrawing the relationship between the solid solution oxygen concentration N _p in the base metal and the depth H of the high-density precipitated layer 38 from each processing atmosphere. A constant relationship holds between N _p and H: H=K ₂ √ _p K ₂ . Therefore, by defining the atmosphere and determining the solid solution oxygen concentration, the depth of the high-density precipitated layer 38 can be easily determined.

As can be seen from Figures 4, 5, and 6, the position H of the high-density precipitated layer of internal oxidation particles can be controlled according to a certain law, so it can be adjusted accurately and with good reproducibility. be able to.

The processing time of the second processing for depositing internal oxide particles at a high density at the lowest position of the oxide particle dispersion layer 39 formed by the first processing is several minutes, preferably 1 minute. ~2 minutes. In other words, if the concentration is less than this, precipitation with the density necessary to suppress the diffusion of the reducing agent cannot be obtained, resulting in a discontinuous layer. The treatment oxidizes the reducing agent more than necessary, and the reducing agent level decreases, making it impossible to maintain the characteristics of the emission.

This dense precipitated layer of oxide particles also interacts favorably with the electron-emitting material. In other words, among the electron emitting materials, BaO, which contributes the most to electron emission, generates free Ba in the above-mentioned dissociation reaction near the interface between the electron emitting material and the base metal 32, and oxygen in Ni, which is the base metal 32. It dissolves into solid solution and diffuses towards the inside of the base metal. On the other hand, the reducing agent added to the base metal 32 diffuses toward the base metal surface, but since the high-density precipitated layer 38 of internal oxidized particles acts as a barrier to the diffusion of the reducing agent, for example, the reducing agent is reduced at this position. When the agent is Mg, the following reaction proceeds.

Mg (in the base metal) + O (in the base metal) → MgO (3) At this time, the high-density precipitated layer of internal oxidation particles suppresses the progress of the oxidation reaction of the reducing agent mainly by controlling the diffusion of the reducing agent. This prevents unnecessary consumption of the reducing agent and allows for long-term use.
Stable emissions can be maintained.

Furthermore, as an advantage of the present invention, the oxidation reaction of the reducing agent occurs inside the base metal, and the constituent components of the electron emitting material do not enter through the vertical grain boundaries near the surface, so that contact between the generated oxide and the electron emitting material is prevented. At the same time, the formation of a so-called intermediate layer is prevented, and the range of selection of reducing agents is greatly expanded in terms of types and amounts.

(Example of the invention) Examples will be described below.

Example 1 A Ni-based alloy with a thickness of 70 μm containing 0.1% by weight of Mg was heated at 1000°C for 10 minutes in a stream of dry hydrogen in order to release the strain that had been accumulated, and then heated to a mixed gas of CO/CO ₂ . By applying heat treatment at 1000℃ for 20 minutes in an atmosphere where the oxygen partial pressure was specified using (mixing partial pressure ratio 1:20), the mixing partial pressure ratio was adjusted at the point where internal oxidation had progressed to a position approximately 10 μm from the surface. The ratio was changed from 1:20 to 1:1, and the temperature was rapidly increased from 1000°C to 1100°C. At this time, a high-density precipitated layer of internal oxidation particles was formed with a width of about 2 μm. This layer was seamless and uniform. After this, it was punched out into a disk with a diameter of 1.3 mm, welded to the tip of the cathode sleeve, and the surface coated with an electron emitting material, which was then incorporated into the electron gun of a color cathode ray tube. Thereafter, a color cathode ray tube was fabricated through the usual steps such as evacuation, sealing, carbonate decomposition, getter flash, etc., and a lifespan test was conducted.

As a result, it has been found that the emission characteristics of this color cathode ray tube are superior to conventional cathode tubes having no layer for controlling the diffusion of reducing agents, especially during long-term operation. A typical example of this embodiment is shown in FIG. A curve 41 shown in FIG. 7 is for a conventional oxide cathode structure, and a curve 42 is for a diffusion control layer formed by the method of Example 1. It was confirmed by EPMA measurements of the cross section of the base metal before and after the life test that the high-density precipitated layer of internal oxidation particles formed by the above-mentioned treatment acts as an interface for the reaction between the reducing agent and oxygen.

Example 2 A Ni-based alloy with a thickness of 50 μm containing 0.15% by weight of Zr was annealed in a dry hydrogen stream at 1200°C for 10 minutes, and then subjected to CO/
After internal oxidation treatment at 1000℃ for 10 minutes in a mixed gas of CO ₂ (mixing ratio 1:15), internal oxidation particles were dispersed and precipitated to a depth of approximately 7 μm, and then the mixing ratio was changed to 1:1. , the temperature was rapidly increased from 1000℃ to 1150℃. At this time, a high-density precipitated layer of internal oxidation particles was formed with a width of about 2 μm. This layer was seamless and uniform. After that, a color cathode ray tube was manufactured in the same manner as in Example 1, and a life test was conducted.
Emission characteristics almost equivalent to curve 42 shown in FIG. 6 were obtained.

In each example, an example was shown in which internal oxidation was performed by suppressing the oxygen partial pressure in the atmosphere with a mixed gas of CO/ _{CO 2 ,} H ₂ O/H ₂ , O ₂
-If you are in an atmosphere where you can control the oxygen partial pressure, such as Ar,
The same can be achieved.

The above-described structure can be confirmed by using an optical microscope or a scanning electron microscope after polishing and etching the cross section of the base metal.

As described above, according to the present invention, a highly concentrated precipitated layer of internally oxidized particles can be easily formed inside the base metal. As a result, we mainly control the diffusion of the reducing agent, suppress the progress of the oxidation reaction of the reducing agent, prevent unnecessary consumption of the reducing agent, and use thin-walled base metals containing a high concentration of the reducing agent. It is possible.

[Brief explanation of drawings]

FIG. 1 is an enlarged cross-sectional view of a main part showing a fast-acting cathode, FIG. 2 is an enlarged cross-sectional view of a main part showing a base metal having a conventional diffusion control layer, and FIG. 3 a to f are oxides according to the present invention. Figure 4 is an enlarged cross-sectional view of the main parts showing the treatment process of the base metal of the cathode structure. Figure 4 is a diagram showing the relationship between heating time in an oxidizing atmosphere and the depth of the layer formed. Figure 5 is
A diagram showing the relationship between the gas mixture ratio of CO and CO ₂ and the depth at which a layer is formed. Figure 6 is a diagram showing the relationship between the solid solution oxygen concentration in the first treatment and the depth at which a layer is formed. FIG. 3 is a diagram showing the results of a life test of a color cathode ray tube using the cathode structure according to the invention. 11... Cathode sleeve, 12, 22, 32...
Base metal, 13... Black oxide film, 14, 24...
Electron emitting material, 15... Heater, 26, 36...
Internal oxidation particles of reducing agent.

Claims (1)

[Scope of Claims] 1. An electron-emitting substance is applied to one surface of a base metal made of a nickel-based alloy containing a trace amount of a reducing agent, and a dispersed layer of oxide particles is formed on this surface to control the diffusion of the reducing agent. In the method for manufacturing an oxide cathode assembly, the base metal is formed in an oxidizing atmosphere at a first temperature for forming a dispersed layer of oxide particles near the surface of the base metal. and a step of heat treating the base metal at a second temperature higher than the first temperature in an atmosphere with an oxygen partial pressure lower than the oxygen partial pressure in the oxidizing atmosphere. A method for manufacturing an oxide cathode structure.