JPH04220927A - Cathode for electron tube - Google Patents

Abstract

PURPOSE:To provide possibility of long time operation with high current density by furnishing a metal hybrid layer including a specific reductive metal powder, alkali earth metal oxide, and specific amount of rare earth metal oxide between the substratum and an electron emitting substance layer. CONSTITUTION:A metal hybrid layer 4 is formed on a substratum 1 whose main component is Ni and which includes a reduction agent, and thereover an electron emitting substance layer 5 incl. alkali earth metal oxide is formed. The metal hybrid layer 4 contains a specific reductive metal powder, alkali earth metal oxide, and rare earth metal oxide, wherein the content of the last named substance shall range 0.01 to 25wt.%. Thereby the reduction agent in the substratum 1 and the specific reductive metal powder in the layer 4 promote production of Ba and also contribute to producing rare earth metal, Also the specific reductive metal enhances electroconductivity to cause a reduction of the emission of Joule's heat, which decreases evaporative loss of Ba, and therefore the life characteristic of high current density operation will be enhanced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to cathodes for electron tubes used in cathode ray tubes for televisions and the like.

0002

[Prior Art] FIG. 3 shows, for example, the Japanese Patent Publication No. 64-5417
1 is a cross-sectional view of an electron tube cathode used in a conventional television cathode ray tube disclosed in the above publication. In Figure 3, (1) contains trace amounts of reducing elements such as silicon (Si) and magnesium (Mg), and the main component is nickel (Ni).
), (2) is a sleeve made of nichrome or the like, and (6) is an electron emitting material layer deposited on the upper surface of the base (1). This electron emitting material layer (6) contains at least barium (Ba), and also contains an alkaline earth metal oxide (61) containing strontium (Sr) and/or calcium (Ca) as a main component, such as scandium oxide. The rare earth metal oxide (62) is contained in an amount of 0.1 to 20% (by weight, hereinafter the same). (3) is a heater disposed within the base (1), and by heating this heater (3), thermoelectrons are emitted from the electron emitting material layer (6).

Next, in order to manufacture an electron tube cathode having such a structure, an electron emitting material layer (6) is formed on the base (1).
) will be explained.

First, a suspension is prepared by mixing a ternary carbonate of barium, strontium, and calcium with a predetermined amount of scandium oxide together with a binder and a solvent, and this suspension is sprayed onto the substrate (1). Approximately 80μm
It is applied to a thickness of 100 ml and heated by a heater (3) during the vacuum evacuation process of the cathode ray tube. At this time, the alkaline earth metal carbonate changes to an alkaline earth metal oxide (61). Thereafter, by activation, a part of the alkaline earth metal oxide (61) is reduced and the electron emitting material layer (6) has semiconducting properties, and the base (1)
) An electron emitting material layer (6) made of a mixture of an alkaline earth metal oxide (61) and a rare earth metal oxide (62) is disposed thereon.
) is formed.

In this activation step, a part of the alkaline earth metal oxide (61) reacts as follows. That is, reducing elements such as silicon and magnesium contained in the base (1) move to the interface between the alkaline earth metal oxide (61) and the base (1) by diffusion, and the alkaline earth metal oxide (61) ) reacts. For example, barium oxide (BaO) as the alkaline earth metal oxide (61)
For example, reactions occur as shown in the following formulas (I) and (II).

2BaO+1/2Si → Ba+1/2Ba2SiO
4 (I)BaO + Mg
→ Ba+MgO
(II) As a result of this reaction, a part of the alkaline earth metal oxide (61) deposited on the substrate (1) is reduced and becomes an oxygen-deficient semiconductor, which facilitates electron emission. . Rare earth metal oxide (6) in the electron emitting material layer (6)
If 2) is not included, the cathode temperature is 700 to 800°C.
It is possible to operate at a current density of 0.5 to 0.8 A/cm2 at an operating temperature of be.

The reason why the operable current density is low when the rare earth metal oxide (62) is not included is that, in general, in the case of an oxide cathode, the electron emission ability depends on the amount of excess Ba present in the oxide. This is because sufficient excess Ba necessary for high current density operation cannot be supplied. That is, barium silicate (Ba2SiO4) and magnesium oxide (MgO), which are by-products produced during the reaction and are called intermediate layers, form the nickel grain boundaries of the base (1) and between the base (1) and the electron emitting material layer ( 6), the reactions of formulas (I) and (II) are rate-limited by the diffusion rate of magnesium and silicon in this intermediate layer, resulting in insufficient supply of excess Ba. . On the other hand, when the electron emitting material layer (6) contains a rare earth metal oxide (62), taking the case of scandium oxide (Sc2O3) as an example, when the electron emitting material layer (6) is used as a cathode, the substrate (1) and the electron emitting material At the interface with the layer (6), a part of the reducing agent that has diffused in the substrate (1) reacts with scandium oxide as shown in the following formula (III) to generate a small amount of metallic scandium (Sc). A part of the metallic scandium is dissolved in the nickel of the substrate (1), and a part is present at the interface.

1/2Sc2O3 + 3/2Mg →
Sc+3/2MgO
(III) This metallic scandium is deposited on the substrate (1) or on the substrate (
The intermediate layer formed at the grain boundaries of nickel in 1) is expressed by the following formula (
It is thought that since it has the decomposition effect as shown in IV), the supply of excess Ba is improved and higher current density operation is possible than when the rare earth metal oxide (62) is not included.

1/2Ba2SiO4 + 4/3Sc
→ Ba+1/2Si+2/3Sc2O3
(IV)

0010

[Problems to be Solved by the Invention] In the cathode for an electron tube constructed as described above, the rare earth metal oxide contains excess Ba.
However, the supply rate of excess Ba is limited by the diffusion rate of the reducing agent present in the nickel base, and
In operation at a high current density of A/cm2 or more, Ba is evaporated and lost due to the local generation of Joule heat in the electron passing region of the electron emitting material, resulting in a problem that the lifetime characteristics are significantly reduced.

The present invention has been made to solve the above-mentioned problems, and its object is to obtain good life characteristics even in high current density operation of 2 A/cm 2 or more.

0012

[Means for Solving the Problems] The present invention involves forming a metal mixed layer on a substrate whose main component is nickel and containing at least one type of reducing agent, and forming an alkaline earth metal oxide layer containing at least barium thereon. A cathode for an electron tube, comprising an electron-emitting material layer deposited thereon, the metal mixed layer having a reducing property lower than or equal to at least one kind of reducing agent in the substrate, and having a reducing property more than nickel. (hereinafter referred to as a specific reducing metal) powder, an alkaline earth metal oxide containing at least barium, and a rare earth metal oxide, and the content of the rare earth metal oxide is 0.
．． 01 to 25% layer.

[0013]

[Function] In the present invention, in addition to the reducing agent in the substrate, a specific reducing metal in the metal mixed layer contributes to the supply of Ba and also to the production of rare earth metals that have a decomposition effect in the intermediate layer. In addition, since the specific reducing metal in the metal mixed layer improves conductivity, the evaporation loss of Ba is also reduced along with the reduction of Joule heat, which improves the life characteristics especially at high current density operation of 2A/cm2 or more. Significantly improved.

[0014]

EXAMPLES In the present invention, a base metal is used which has nickel as its main component and contains at least one, usually 2 to 4 types of reducing agents.

[0015] Examples of the reducing agent include silicon,
Examples include magnesium, zirconium, and tungsten.

[0016] The proportion of reducing agent in the substrate is 0.01 to 3%.
It is preferable that

[0017] On the substrate, a metal (specific reducing metal) whose reducibility is lower than or equal to at least one of the reducing agents in the substrate and whose reducibility is higher than nickel is disposed.
A metal mixed layer is provided that contains powder, an alkaline earth metal oxide containing at least barium, and a rare earth metal oxide, and the content of the rare earth metal oxide is 0.01 to 25%.

As described above, the specific reducing metal in the metal mixed layer contributes to the supply of Ba, the production of rare earth metals, and the improvement of electrical conductivity. The requirement that the reducibility of the particular reducing metal be less than or equal to at least one of the reducing agents in the substrate and greater than nickel is that the reducing nature of the particular reducing metal is less than nickel. If the supply effect of excess Ba is small, and if it is larger than all the reducing agents in the substrate, the main supply reaction of excess Ba will occur at the interface between the specific reducing metal and alkaline earth metal oxide in the metal mixed layer. This is because the effect of excessive Ba supply of the reducing agent in the substrate becomes smaller, and the contribution of the interlayer decomposition effect of the rare earth metal oxide to the characteristics becomes smaller.

Specific examples of the specific reducing metal include:
Although it depends on the composition of the reducing agent in the substrate, for example, W, Mo,
Examples include Ta, Cr, Si, Mg, etc., and at least 1
All you have to do is choose the type of metal.

The particle size of the specific reducing metal is preferably 10 μm or less, more preferably 2 to 7 μm, although it depends on the particle size of the alkaline earth metal oxide used. If the particle size exceeds 10 μm, even if the additive concentration is the same, the total surface area of the specific reducing metal will be smaller than when it is 10 μm or less, and a sufficient conductivity improvement effect will not be obtained, and the reduction reaction will be difficult to occur. Because it will be.

The proportion of the specific reducing metal in the metal mixed layer is preferably 10 to 50%, more preferably 20 to 40%. If the proportion is less than 10%, the above-mentioned sufficient effect cannot be obtained, and if it exceeds 50%, the electron emission characteristics tend to decrease.

[0022] Examples of the alkaline earth metal oxide include oxides of strontium, calcium, etc. in addition to barium, and those having a particle size of 3 to 10 μm are preferable.

The proportion of the alkaline earth metal oxide in the metal mixed layer is preferably 50 to 90%, more preferably 60 to 70%. If the ratio is less than 50%, sufficient electron emission characteristics cannot be obtained, and if it exceeds 90%, the concentration of specific reducing metals and rare earth metal oxides decreases, and the effect of improving life characteristics in high current density operation appears. It becomes difficult.

Examples of the rare earth metal oxide include scandium oxide and yttrium oxide.

The proportion of the rare earth metal oxide in the metal mixed layer is 0.01 to 25%, preferably 0.1 to 10%. If the proportion is less than 0.01%, the effect of interlayer decomposition expressed by reaction formula (IV) is small, and if it exceeds 25%, sufficient initial electron emission characteristics cannot be obtained.

The thickness of the metal mixed layer is preferably 10 to 40 μm, more preferably 20 to 30 μm. This is because if the thickness is less than 10 μm, the conductivity of the electron emitting material layer tends to be insufficiently improved, and if it exceeds 40 μm, it becomes difficult to obtain sufficient electron emission characteristics during initial and lifetime characteristics.

An electron emitting material layer containing an alkaline earth metal oxide containing at least barium is deposited on the metal mixed layer in order to impart sufficient electron emitting ability to the cathode. In this way, the electron-emitting material layer is provided on the metal mixed layer to create a two-layer structure.In the case of only the metal mixed layer, alkaline earth metal oxidation is performed by the specific reducing metal and rare earth metal oxide contained in the metal mixed layer. This is because the occupancy of the material on the upper surface of the metal mixed layer decreases, and sufficient electron emission cannot be obtained.

[0028] Examples of the alkaline earth metal oxides include oxides of strontium, calcium, etc. in addition to barium.

[0029] The thickness of the electron emitting material layer is 50 to 100μ.
It is preferable that it is about m.

Next, an example of the method for manufacturing the electron tube cathode of the present invention will be explained.

[0031] First, after welding the base metal to the sleeve,
Heat treatment such as cleaning and hydrogen treatment is performed to remove surface dirt and oxidized layers.

Next, a suspension is prepared by mixing a specific reducing metal powder, an alkaline earth metal carbonate powder, and a rare earth metal oxide powder in a binder such as nitrocellulose with an organic solvent such as butyl acetate. The metal mixed layer is provided by coating on the substrate by a method such as a spray method. There are no particular limitations on the proportions of the binder and organic solvent used.

[0033] Next, a suspension prepared by mixing alkaline earth metal carbonate powder with nitrocellulose, butyl acetate, etc. is applied onto the metal mixed layer by a spray method or the like. An electron tube cathode of the invention is manufactured.

The cathode for electron tubes of the present invention as described above can be applied to cathode ray tubes for television tubes and image pickup tubes, and in particular, high current density operation is possible, so high brightness of projection type or large-sized televisions can be realized. .

Next, one embodiment of the present invention will be explained in more detail based on FIG. In FIG. 1, (1) is a base, (2) is a sleeve, (3) is a heater, (4) is a metal mixed layer, and (5) is an electron emitting material layer. Heater (3
), thermionic electrons are emitted from the electron emitting material layer (5). Example 1 and Comparative Example 1 First, the main component nickel was mixed with a trace amount of magnesium (0.05
%) and silicon (0.05%) was welded to the sleeve (2) and then heat treated in a reducing atmosphere. Next, tungsten powder with a particle size of 5 μm, scandium oxide powder with a particle size of 10 μm, and powder with a particle size of 5 μm.
100 g of ternary carbonate powder (carbonate of barium, strontium, and calcium) weighed in proportions of 30%, 5%, and 65%, 10 g of nitrocellulose as a binder, and acetic acid as an organic solvent. A suspension was prepared by mixing with 200 ml of butyl. The obtained suspension was applied onto the substrate (1) by a spray method to form a metal mixed layer (4) with a thickness of 25 μm.

Next, barium, strontium, and calcium carbonates, nitrocellulose as a binder, and butyl acetate as an organic solvent were mixed to prepare a suspension. The obtained suspension was applied by a spray method to form an electron emitting material layer (5) having a thickness of 60 μm, thereby producing a cathode as shown in FIG. 1.

The obtained cathode for an electron tube was attached to a CRT for a normal television device, and the completed CRT was subjected to a normal evacuation process, and a life test was conducted by operating the CRT at a current density of 2 A/cm 2 . The results are shown in Figure 2.

As a comparative example, an electron emitting material layer made of an alkaline earth metal oxide containing 7% scandium oxide was used instead of the metal mixed layer (4) and electron emitting material layer (5) in the electron tube cathode. The formed conventional cathode for an electron tube was similarly evaluated.

It can be seen from FIG. 2 that the deterioration of the emission current of the electron tube cathode of the present invention is significantly less than that of the conventional cathode.

The reason why the electron tube cathode of the present invention has such good life characteristics is presumed to be as follows.

That is, the base body (1) and the metal mixed layer (4)
Excess Ba is supplied at the interface based on the reactions shown in formulas (I) and (II). In addition, W in the metal mixed layer also has the formula (V): 2BaO + 1/3W → Ba
+ 1/3Ba3W06
(V) It reacts as shown below and contributes to the production of excess Ba. Furthermore, since W and Sc2O3 coexist in the metal mixed layer (4), they also contribute to the generation of Sc, which has an interlayer decomposition effect. Further, the W powder, which is a conductive material, suppresses the local generation of Joule heat in the high current density operating region, which causes the disappearance of the generated excess Ba, thereby contributing to an increase in the concentration of excess Ba.

[0042]

As described above, the electron tube cathode of the present invention enables high current density operation of 2 A/cm2 or more, which was difficult with conventional oxide cathodes.

[Brief explanation of the drawing]

FIG. 1 is a partially enlarged sectional view of a cathode for an electron tube according to the present invention.

FIG. 2 is a graph showing changes in emission current over time.

FIG. 3 is a partially enlarged sectional view of a conventional cathode for an electron tube.

[Explanation of symbols]

1 Base 4 Metal mixed layer 5. Electron emitting material

Claims (1)

[Claims] Claim 1: A metal mixed layer is formed on a substrate whose main component is nickel and contains at least one reducing agent, and an electron emitting material layer containing an alkaline earth metal oxide containing at least barium thereon. A cathode for an electron tube, the metal mixed layer comprising a metal powder having a reducing property lower than or equal to at least one of the reducing agents in the substrate and having a reducing property higher than nickel, and at least barium. and a rare earth metal oxide, the content of the rare earth metal oxide being 0.01.
-25% by weight layer of electron tube cathode.