JPS6243298B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a directly heated oxide cathode that is applied to television picture tubes and the like.

In the conventional television picture tubes, indirectly heated cathodes were the mainstream. With this indirectly heated cathode, it takes about 20 seconds from the start of energization to the appearance of an image, so in order to improve this starting characteristic, a method has often been used in which a preheating current is constantly passed through the heater even when no reception is being made.

However, in recent years, from the standpoint of energy conservation, a directly heated cathode has been considered, which can operate from the start of energization to the appearance of an image in a short time without preheating. If a directly heated cathode in which an oxide for direct electron emission is coated on an energized heating element is appropriately designed, the time from the start of energization to the appearance of an image can be shortened to 1 to 2 seconds.

FIG. 1 is a cross-sectional view of a general directly heated oxide cathode. The base 1 is supplied with current from the terminal 2 and generates heat. A layer of oxide 3 is formed on the plane of the substrate 1 . The substrate 1 needs to be made of a material with high electrical resistivity so as to increase the consumption of electrical energy in short parts in order to improve heating speed, and to keep the oxide 3 within an appropriate temperature range, a material with high electrical resistivity is required. A thin plate shape suitable for heat radiation with a large surface area relative to area is preferred. At the same time, sufficient high-temperature strength is required to prevent deformation even when formed into a thin plate. Furthermore, the substrate 1 has an important property that the applied oxide 3, that is, oxides of alkaline earth metals such as barium (Ba), strontium (Sr), and calcium (Ca), has sufficient electron emission over a long period of time. needs to be done.

Conventionally, the main component of the substrate 1 that meets these conditions is nickel (Ni), and tungsten (W) and molybdenum (Mo), which have excellent heat resistance, are used as the main component.
100μ of an alloy containing one or both of the above and a trace amount of reducing agent such as zirconium (Zr).
Considerations have been made to form thin ribbons with a thickness of less than m, preferably less than 60 μm.

However, in such a directly heated oxide cathode, W or
A large amount of Mo intermediate layer is generated. That is, to form the layer of oxide 3 on the substrate 1, for example, when BaCO ₃ is applied as an alkaline earth metal carbonate and this is heat-treated in a vacuum, the following reaction occurs.

BaCO ₃ →BaO→CO ₂ ...(1) Here, as is well known, the reactivity of W, Mo with carbonates is much higher than that with oxides,
Most of the intermediate layer composed of W and Mo is generated during the decomposition of this carbonate. In other words, W and Mo are very well oxidized by the CO ₂ generated in the reaction of equation (1), resulting in the following reaction.

W+3CO ₂ =WO ₃ +3CO (2) 3BaO+WO ₃ =Ba ₃ WO ₆ (3) As a result, a large amount of Ba ₃ WO ₆ is produced as the intermediate layer. In addition to Ba, carbonates of alkaline earth metals containing Sr, Ca, etc. are also used in the substrate 1.
The same applies to cases where . When such a large amount of the intermediate layer is formed on the substrate 1, the oxide 3 layer peels off from the substrate 1, resulting in a significant deterioration in electron emission characteristics.

The present invention was made to eliminate the above-mentioned drawbacks, and its purpose is to provide a method for manufacturing a directly heated oxide cathode in which the oxide does not peel off.

To achieve this objective, the present invention provides a base metal whose main component is Ni and which contains at least one of W and Mo and a reducing agent, carbon (C), magnesium (Mg), zirconium hydride (ZrHx), Formation of a layer of alkaline earth metal carbonate with additives consisting of at least one of titanium hydride (TiHx) and barium nitride (Ba( _N3 ) ₂₎ , with no further additions above this layer. A layer of alkaline earth metal carbonate is formed and heat treated in vacuum to form a layer of alkaline earth metal oxide on the base metal.

That is, by configuring the present invention in this way, the atmosphere on the surface of the base metal during carbonate decomposition can be made reducing, so that W, Mo
This made it possible to suppress the oxidation of oxidation and prevent the formation of an intermediate layer.

Hereinafter, the present invention will be explained in detail based on examples.

[Example 1] 27.5% W and 0.4% reducing agent by weight
Made of an alloy of Zr and the rest Ni, thickness is 40μm
A layer of carbonate consisting of Ba, Sr, and Ca to which 5% of C (graphite) powder was added in a molar ratio was applied to a thickness of 20 μm on a thin ribbon-shaped substrate, and this layer Similarly, Ba, Sr,
Carbonate consisting of Ca3 is applied to a thickness of 50 μm to form a layer. Next, place this base in a vacuum,
Heat treatment at 1000°C for 10 hours turned them into an oxide layer. At this time, CO is released by the following reaction.
is generated.

(Ba, Sr, Ca) CO ₃ + C = (Ba, Sr, Ca) O
+2CO (4) The CO generated in this way makes the atmosphere on the surface of the substrate reducible, and thus acts to suppress the oxidation of W by CO ₂ as shown in the above formula (2). Therefore, the reaction of the above formula (3) is not performed and no intermediate layer is produced.

The oxide layer on the substrate obtained in this example was scratched with an insect pin in a vacuum to examine its adhesion strength, but no peeling occurred. For comparison, when a test similar to the above was conducted on a sample prepared by a conventional method in which a layer was formed by coating 70 .mu.m of the carbonate without adding anything on the substrate, the oxide layer peeled off. After taking these samples out into the air and removing the oxide layer, we analyzed the intermediate layer by X-ray diffraction, and found that a large amount of W oxide intermediate layer was detected in the samples prepared using the conventional method. , was hardly detected in the samples of this example.
Furthermore, when we analyzed the gas released after carbonate decomposition was completed, we found no difference in CO between the two. This confirmed that C was completely consumed when the decomposition of carbonate was completed.

Note that similar results can be obtained even if Mg is used as an additive.

[Example 2] On the same substrate as in Example 1, a layer was formed by coating a carbonate consisting of three elements of Ba, Sr, and Ca to which 5% of ZrHx powder was added in a molar ratio to a thickness of 20 μm, and then On top of this layer, add 50 μm of the above carbonate without adding anything.
to form a layer. The substrates were then heat treated in vacuum at 1000°C for 10 hours to form an oxide layer. The adhesion strength of the thus obtained substrate was examined in vacuum in the same manner as above, but no peeling occurred.Also, the oxide layer was removed in air and the intermediate layer was analyzed by X-ray diffraction. No intermediate layer was detected. Furthermore, the oxide layer was analyzed by X-ray diffraction, and ZrHx and Zr
was also not detected.

In this example, ZrHx becomes Zr and _H2 through thermal decomposition, and these react as follows to generate CO.

(Ba, Sr, Ca) CO ₃ + H ₂ → (Ba, Sr, Ca) O
+H ₂ O + CO ……(5) 2 (Ba, Sr, Ca) CO ₃ +Zr→ (Ba, Sr, Ca)
ZrO ₃ + (Ba, Sr, Ca) O + 2CO (6) Note that similar results can be obtained even if TiHx is used as an additive.

[Example 3] On the same substrate as in Example 1, a carbonate consisting of three elements of Ba, Sr, and Ca to which Ba(N ₃ ) ₂ powder was added at a molar ratio of 2% was applied to a thickness of 20 μm to form a layer. 50 of the above carbonate without adding anything further on top of that layer.
The layers were coated to a μm thickness and heated in vacuum for 10 hours to convert them into oxide layers. The substrate thus obtained was subjected to the same measurements as in each of the examples above, but no peeling of the oxide layer occurred.
The middle layer was also almost undetectable.

In this example, Ba(N ₃ ) ₂ becomes Ba and N ₂ through thermal decomposition, but Ba undergoes the same reaction as in equation (4) above to generate CO.

In each of the above embodiments, a base metal containing W was used, but similar results can be obtained even if Mo is included instead of W or both W and Mo are included.

In addition, C, Mg, ZrHx, TiHx and Ba(N ₃ ) ₂
If the amount of addition exceeds 10% in molar ratio, the electron emission characteristics will deteriorate, so the addition amount of these is preferably 10% or less.

Also, the thickness of the carbonate layer without any addition is 10 μm.
If it is less than that, the electron emission characteristics will deteriorate.
This layer is preferably formed to have a thickness of 10 μm or more.
However, the compositions of the carbonate to which the additive is added and the carbonate to which no additive is added do not necessarily have to be the same.

As described above, according to the method for producing a directly heated oxide cathode according to the present invention, the alkaline earth metal oxide having electron emissive properties does not peel off from the base metal, and when used in television picture tubes etc., it will last for a long time. This has the effect of maintaining stable quality.

[Brief explanation of the drawing]

The figure is a cross-sectional view of a general directly heated oxide cathode. 1...Substrate, 2...Terminal, 3...Oxide.

Claims (1)

[Claims] 1 A base metal whose main component is nickel and contains at least one of tungsten and molybdenum and a reducing agent, carbon, magnesium, zirconium hydride,
A layer of alkaline earth metal carbonate containing an additive consisting of at least one of titanium hydride and barium nitride in a molar ratio of 10% or less (excluding zero) is formed, and nothing is further added on top of this layer. A method for producing a directly heated oxide cathode, which comprises forming a layer of alkaline earth metal carbonate and heat-treating it in vacuum to form a layer of alkaline earth metal oxide on the base metal.