JPS6343858B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a directly heated oxide cathode.

Conventionally, cathodes used in television picture tubes, such as color picture tubes and black and white picture tubes, have a preheating current flowing through the heater at all times even when no reception is being received, and the heater current value is increased to the rated value during reception. Indirectly heated cathodes, which shorten the time it takes for an image to appear at the start of reception, have been the mainstream. However, in recent years, from the standpoint of energy conservation, there has been a demand for cathodes that do not require preheating and that require a short time from the start of energization to the appearance of an image, that is, fast-acting cathodes. Normally, if a preheating current is not applied to an indirectly heated cathode, it takes about 20 seconds from the start of current application to the appearance of an image, but a directly heated cathode, in which a so-called oxide for electron emission is directly applied to the energized heating element, can be used properly. If designed properly, the time from the start of energization to the appearance of the image can be shortened to 1 to 2 seconds.

FIG. 1 is a sectional view showing an example of a directly heated oxide cathode.

In the figure, 1 is a base metal body (hereinafter referred to as the base) that generates heat when a current is applied, 2 is a terminal for supplying electricity to the base 1, and 3 is a so-called oxide. The base 1 needs to be made of a material with high electrical resistivity so that as much electrical energy as possible is consumed in the shortest possible part in order to improve the speed of movement. In order to keep the temperature within the appropriate range for the object cathode, the substrate should have a shape that increases the length of the circumference relative to the cross-sectional area and increases heat radiation, for example, a thin ribbon shape with a thickness of 100 μm or less, preferably 60 μm or less. This cross-sectional shape requires a material with sufficient high temperature strength to maintain the shape within the cathode operating temperature range. Furthermore, an important property of the base material is the oxides coated on its surface, i.e. alkaline earth oxides such as Ba,
It must be suitable for causing sufficient electron emission from oxides such as Sr and Ca over a long period of time.

Conventionally, it has been empirically and experimentally that Ni is the main component, and high-melting point metals such as W and Mo, which have excellent heat resistance, are used as activators in electron-emitting oxides to meet these conditions. the tiny amount that acts
Zr-added alloys have been proposed as base metals for directly heated oxide cathodes. However, if a metal with such a composition is used as a substrate, W will be formed between the substrate and the oxide layer during the picture tube manufacturing process and subsequent use.
Alternatively, a problem arises in that a large amount of a so-called intermediate layer made of Mo is generated, and as a result, the oxide layer often peels off. In order to eliminate such defects, a method has been used in which a layer of Ni particles is formed between the base metal and the oxide layer to mechanically fix the oxide layer.

FIG. 2 is an enlarged sectional view of a main part of a directly heated oxide cathode having such a structure. In the figure, numeral 4 is Ni particles baked onto the base 1. However, in a directly heated oxide cathode with such a configuration, the shape of the Ni particles changes during operation, making it impossible to fix the oxide layer properly and making it impossible to completely prevent its peeling. There was a problem that occurred.

As a result of repeated experiments and research aimed at improving the reliability and extending the lifespan of direct-heated cathodes, the inventors of the present invention have developed the above-mentioned method using a special combination of previously proposed materials, processing methods, etc. They discovered a solution to these problems and made an excellent directly heated oxide cathode possible.

The present invention will be explained in detail below.

In the present invention, an alloy mainly composed of Ni is used as the base, and the composition is such that it necessarily contains Zr as a reducing agent, and Co powder or Co mainly
It is designed to bake Co-Ni powder.

With this configuration, as will be clear from the specific examples described later, it is possible to use conventional Ni powder or Ni powder.
It has been found that this cathode is extremely effective in preventing oxide peeling and deformation of the substrate compared to a directly heated oxide cathode in which Ni alloy powder, mainly composed of , is directly adhered to the oxide-adhered surface of the substrate.

The present invention will be explained in more detail below.

In the present invention, as described above, the substrate has a composition of a Ni alloy containing Zr as a reducing agent,
This substrate and Co powder or Co mainly composed of Co
-By combining with Ni powder, Zr and Ni
This skillfully takes advantage of the affinity between Zr and Co and the difference in affinity between Zr and Co. This is because in the conventional structure, the Ni particles undergo morphological deformation during cathode operation.
Due to its strong affinity with Ni, Zr in the base metal
This is because Ni particles diffuse into the metal particles and react with so-called oxides there. To prevent this, metal particles with a smaller affinity for Zr than Ni are used to prevent Zr from diffusing into the metal particles. I found out what I should do. As a result of various studies that meet this purpose, we found that Cr, Mn, Fe, Co, Cu, Ag, Mo,
Although W and the like were mentioned, when these were evaluated considering their use in directly heated oxide cathodes, it was found that Co has excellent properties.

However, the amount of Zr in the substrate and the
Composition of Co powder, Co—Ni powder, deposited Co powder, Co—
It has also been found that the effects of the present invention cannot be expected unless the coating amount of Ni powder is maintained in a certain relationship.

That is, first of all, regarding the amount of Zr in the substrate,
A range of 0.04≦Zr≦5wt% is required. This is Co
When Zr diffuses onto the surface of the substrate, it hinders the reaction between Zr in the substrate and oxide for electron emission (hereinafter referred to as oxide), so if Zr is less than 0.04wt%, the activity will be insufficient; %, a low melting point eutectic is formed as a substrate, which is found to be problematic as a substrate for a directly heated oxide cathode.

Next, regarding the composition of Co powder, there is no problem if it is Co alone, and in a Co-Ni alloy mainly composed of Co, the condition of Ni≦20wt% is required, which is
When Ni exceeds 20wt%, morphological changes begin to occur, which poses a problem. Furthermore, the amount of application
0.1-5mg/ ^cm2 is required. That is, 0.1mg/
If it is less than 5 mg ^/cm2 , the effect of fixing and holding the oxide is insufficient, causing problems with oxide peeling, and
It was found that when the particle size exceeds cm ² , mutual sintering of the particles takes precedence over sintering to the substrate, resulting in insufficient adhesion to the substrate and causing the problem of oxide peeling as described above. Note that this coating amount is also related to the particle size of the particles to be fixed, but for particles with a practical particle size of 1 to 10 μm as a directly heated oxide cathode, it is 0.1 μm as described above.
~5 mg/cm ² was optimal. Furthermore, it goes without saying that the amount of coating may be changed depending on the particle size if necessary. In any case, the amount of application is experimentally
0.3 to 3 mg/cm ² was optimal. In addition, to increase the high-temperature strength of the base and prevent deformation, the base may be coated with W, for example.
It is even more effective to add a high melting point metal such as Mo. These high melting point metals may be added singly or in combination, but in the case of W, 15
It was found that the range of ≦W≦30wt% and Mo is preferably within the range of 10≦Mo≦22wt%. This is W<15wt%, Mo
At <10wt%, the high temperature strength is insufficient, so the particles (Co, Co-Ni) and the substrate [Ni-W (Mo)
-Zr] has the disadvantage that the substrate is easily deformed by the stress generated by the mutual unbalanced diffusion of W.
>30wt% and Mo>22wt%, due to the conflict with the solid solubility limit in Ni in the substrate, as the cathode is repeatedly heated and cooled during operation and non-operation, high melting point metals precipitate and the substrate becomes non-uniform. There is a risk of deformation. In addition, in the case of a combination, various amounts were possible within a range that did not exceed the amount of each individual, but due to the balance with the solid solubility limit mentioned above for the high melting point metal as a whole, it was difficult to keep it within a range where precipitation would not occur. is necessary.

In addition to the above-mentioned W and Mo, for example, Re and the like can be used similarly.

Addition of such a high melting point metal is particularly effective when using Co powder. That is, Co and Ni
This is because the diffusion rate is different from that of the base material, so if the two are fixed together, there is a risk that unbalanced diffusion will occur between them and the substrate will be deformed, and this can be prevented by adding the above-mentioned high melting point metal.

This will be explained in detail below using a specific example.

Specific example 1 Co powder with a particle size of 2 to 3 μm was applied in three types: 0.5 mg, 1.0 mg, and 2 mg per 1 cm ² on a 40 μm thick plate material consisting of 27.5% W, 0.4% Zr, and the rest Ni by weight. death,
Each was baked by heating at 900°C for 30 minutes in a vacuum.
These were further coated with carbonate consisting of three elements of Ba, Sr, and Ca, and heat treated in vacuum at 1000°C for 10 hours.

After that, the oxide was removed and the image was analyzed using a scanning electron microscope.
We investigated Co particles, but no co-shape change occurred in the three types. For comparison, when similar tests were conducted using Ni powder with a particle size of 2 to 3 μm, changes in the shape of the Ni particles occurred. In addition, the Co
As a result of examining the adhesion strength of particles and Ni particles to the alloy plate material, in the case of Co particles, the adhesion strength after baking was rather improved, whereas in the case of Ni particles, on the contrary, it was significantly decreased. and in this example 30%
It had declined to .

Specific example 2 Co powder with a particle size of 2 to 3 μm was applied at a rate of 1.0 mg per cm ² to a 40 μm thick plate material consisting of 17.5% Mo by weight, 0.8% Zr, and the rest Ni, and heated at 900°C in a vacuum. I baked it by heating it for 30 minutes.

This was further coated with a carbonate consisting of Ba, Sr, and Ca, and heat treated at 1000°C in vacuum for 10 hours. After that, the oxide was removed and the Co particles were examined using a scanning electron microscope, but no change in shape was found. The adhesion strength of the Co particles to the alloy plate material was investigated using the same sample, and it was found to be better than the adhesion strength after baking, with no significant decrease observed.

Specific example 3 4% W, 15% Mo, and 1.2% Zr by weight
A plate material made of remaining Ni and having a thickness of 30 μm was used, and the other specifications were the same as in Example 1.

Even in this result, there was no change in the shape of the Co particles, and the adhesion strength was also compared to that of Ni of the same specifications prepared for comparison.
It was larger than powder. Furthermore, the deformation of the substrate could be kept within a practical range.

As described above, according to the present invention, the composition of the substrate, in particular, the fact that it always contains Zr as a reducing agent and the amount thereof, and that the oxide for electron emission of the substrate is fixed to the surface to be deposited. Zr
cannot be diffused into the Co particles, so the Co particles do not change their shape and are prevented from peeling off the oxide. Furthermore, it is possible to prevent deformation due to unbalanced diffusion and extend the life of the cathode. It has a great effect.

In addition, when the Zr content of the base metal increases, the Co powder
Compared to Ni powder, it tends to be a little more difficult to bake, but it is possible to use wet hydrogen (wet hydrogen) on the base metal beforehand.
The adhesion strength after baking can also be improved by heat-treating in H ₂ ) or by forming a Ni layer on the surface of the substrate.

Especially the latter, if a Ni layer is formed,
Since the formation of an intermediate layer made of W or Mo is suppressed during the manufacturing process of, for example, a picture tube using the directly heated oxide cathode of the present invention, even more desirable results can be obtained. Also, along with Zr as a reducing agent
Similar effects can be obtained with base metals containing Al, Mg, Si, etc.

Further, the directly heated cathode according to the present invention can be used in any electron tube, such as an image pickup tube, and is of course not limited to the above-mentioned television picture tube.

[Brief explanation of the drawing]

FIGS. 1 and 2 are a side view and an enlarged sectional view of a main part showing an example of a directly heated oxide cathode for explaining the present invention. DESCRIPTION OF SYMBOLS 1...Substrate, 3...Oxide, 4...Metal particle.

Claims (1)

[Claims] 1. A directly heated oxide cathode in which an oxide for electron emission is coated on a base metal made of an alloy mainly composed of Ni and containing Zr as a reducing agent, wherein the base metal A directly heated oxide cathode, characterized in that Co powder or a Co--Ni alloy powder having a weight ratio of Co≧80% and Ni≦20% is baked onto a portion of a metal to which the oxide is deposited. 2 The amount of Zr as the reducing agent is 0.04 to 0.04 by weight.
The directly heated oxide cathode according to claim 1, characterized in that the content is 5%. 3. Direct heat oxidation according to claim 1 or 2, characterized in that the amount of the Co powder or Co--Ni alloy powder deposited on the base metal is 0.1 to 5 mg/ ^cm2 . object cathode. 4 In a directly heated oxide cathode formed by coating an oxide for electron emission on a base metal consisting of an alloy mainly composed of Ni, at least one high-melting point metal, and further containing Zr as a reducing agent. , Co powder or Co-Ni whose weight ratio is Co≧80% and Ni≦20% is applied to the part of the base metal to which the oxide is applied.
A directly heated oxide cathode characterized by being made by baking alloy powder. 5 The amount of Zr as the reducing agent is 0.04 to 0.04 by weight.
Claim 4 characterized in that the percentage is 5%.
Directly heated oxide cathode as described in . 6. The directly heated oxide cathode according to claim 5, wherein W is used as the high melting point metal, and the content of W is 15 to 30% by weight. 7 Mo is used as the high melting point metal, and the
A directly heated oxide cathode according to claim 4 or 5, characterized in that the content of Mo is 10 to 22% by weight. 8 Using W and Mo as the high melting point metal,
And the W is 1 to 8% by weight, and the Mo is 10% by weight.
A directly heated oxide cathode according to claim 4 or 5, characterized in that the content is 22% to 22%. 9. The directly heated oxide cathode according to claim 4, wherein the amount of the Co powder or Co-Ni alloy powder deposited on the base metal is 0.1 to 5 mg/cm ² .