JPS63310536A - Electron tube cathode - Google Patents

Abstract

PURPOSE:To obtain a stable electron emitting property for a long time by providing an electron emitting substance layer including Sc2O3 which has columnar polyhedron crystal structure including no chlorine atom. CONSTITUTION:This cathode is composed of a cathode base body metal 1 including Ni as the main component and Si, and an electron emitting substance layer 5 consisting of an alkaline earth metal oxide including Ba, and Sc2O3. The Sc2O3 4 has columnar polyhedron crystal structure, including no chlorine atom, and scattered in the electron emitting substance layer 5 at 0.1 to 20wt.%. Since the Sc2O3 scattered in the substance layer 5 includes no impure chlorine, it never extenguishes doners of free atoms such as Ba, and a stable electron emitting current can be obtained. Moreover, an intermediate layer which consists of a complex oxide of the reducing agent is prevented from forming concentrically near the interface 11 between the base body metal 1 and the substance layer 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electron tube cathode used in a picture tube or the like, and is intended to improve the radiation characteristics of electrons emitted from the cathode.

[Prior Art] Conventionally, electron tube cathodes used in picture tubes and the like have a metal base made of nickel (Ni) as a main component and a small amount of a reducing agent such as magnesium (H) or silicon (Si). A so-called oxide cathode in which an oxide layer of an alkaline earth metal containing barium (Ba) is deposited is often used.

This oxide cathode is made by thermally decomposing an alkaline earth metal carbonate to convert it into an oxide.The oxide is then reacted with a reducing agent to generate free atoms from the oxide. is used as an electron emission donor (source) to emit electrons. The carbonates include barium carbonate (BaCO3) units and (Ba, Sr, C
a) Although there are restored ones such as CO3, the basic mechanism of activation and formation of a donor is the same, so for ease of understanding, a detailed explanation will be given using a monocarbonate as an example.

FIG. 4 is a schematic cross-sectional view showing an example of a conventional oxide cathode, and a heater (3) is installed inside the cathode tube, which is composed of a cathode cap body made of a base metal (1) and a tube (2). It has a structure in which the temperature is increased by heating, and the surface of the gold base a (1) is coated with an electron emitting substance El made of barium oxide (Bad).
(55) is formed.

This electron emitting material layer (55) is formed by the following steps. That is, after BaCO3 is mixed with a resin solution such as nitrocellulose dissolved in an organic solvent, a base metal (1
).

The cathode thus formed is then incorporated into an electron tube, heated to approximately 1000°C by a heater (3) during an evacuation process to create a vacuum inside the electron tube, and
aCO3 is thermally decomposed as shown by the following formula, and B
It is converted to aO.

aaco3 →BaO+ CO2 (1) Carbon dioxide gas (CO2) generated by this reaction is discharged outside the electron tube together with the gas generated by thermal decomposition of nitrocellulose.

Figure 5 shows the base gold ff (11 and the electron emitting material layer (55)).
FIG. 2 is a schematic diagram enlarging a portion of a cross section near the interface for explaining the vicinity of the interface in detail. In general, BaO, which constitutes the electron emitting material Im (55), is a rod-shaped microcrystal (8
) aggregates to form crystal grains (9) with a size of several tens of digits. There are moderate gaps between the crystal grains (9) constituting the electron emitting material layer (55), making it porous.

This BaO reacts with the reducing agent 81 and N9 at the interface (Ill) in contact with the base metal (1), and free 88
is generated. These reducing agents diffuse through the grain boundaries (swords) between the N1 crystal grains (6) of the base metal (1), and move through the interfaces (
The following reduction reaction occurs near I+).

2BaO+ St-+ 28a + 5i02
(KIBaO+Hg-*Ba+HgO(
110 This free Ba acts as a donor for electron emission.

Further, at this time, a reaction represented by the formula N: 5i02 + 2BaO-) Ba25in4(N) also occurs simultaneously.

As described above, the free 8a that acts as a donor is generated at the interface between the electron emitting material layer (55) and the base metal (1), moves through the gaps in the electron emitting material layer (55), and comes out to the surface. The donor plays the role of emitting electrons, but the donor evaporates or becomes a gas remaining in the electron tube, such as CO1CO2,02,
Since it reacts with a gas such as 820 and disappears, it is necessary to constantly carry out the above-mentioned reaction to replenish the donor, and this reduction reaction must be carried out at the cathode during operation.

In order to balance this replenishment and depletion, this type of cathode is generally used at high temperatures of about 800°C.

However, during operation of the cathode, the reaction products O2 such as Sio2, aa2sho, shown in the formula ([1 or N
is an electron-emitting substance I! (55) and the base metal (1), which is the interface 01), this reaction product 021 accumulates rapidly at the interface 01) and the grain boundaries (7), causing the grain boundaries (force It becomes a barrier for moving 31 (generally referred to as an intermediate layer), and the reaction gradually slows down, making it difficult to generate Ba, which is a donor.In addition, this intermediate layer has a high resistance value, and therefore +31 electrons The problem of blocking current flow also arises.

In order to solve these problems,
9828 and JP-A No. 61-271732, etc., by forming an electron emitting material layer in which scandium oxide (5C203) powder is dispersed, A composite oxide (for example, Ba3 SC409) causes thermal decomposition during operation of the cathode to generate and replenish free Ba, which is a donor.

It has been disclosed that (1) liberated metal scandium (Sc) increases the conductivity of the electron emitting material layer; (2) dissociates reaction products such as Baz SiO+ generated at the interface;

[Problems to be Solved by the Invention] As described above, an electron tube cathode that can be operated at a high current density by providing an electron emitting material layer in which 5c2o3 powder is dispersed has been disclosed. When 5C203 produced by the usual manufacturing method, that is, precipitated with oxalic acid from a hydrochloric acid solution containing Sc to obtain scandium oxalate and then roasted, is used, such 5c2o3 tends to contain chlorine as an impurity, and the formula M : Ba + 2CI-+BaClz
There is a problem in that the reaction shown in (V) occurs and the donor is annihilated. If this donor disappearance is large, a slump phenomenon occurs in which the electron emission current decreases significantly.

The present invention has been made to solve the above-mentioned problems, and by providing an electron emitting material layer containing 5c2o3, which has a columnar polyhedral crystal structure and does not contain chlorine atoms, it can be stabilized for a long time. The purpose of this study is to develop an electron tube cathode that can provide the desired electron emission characteristics.

[Means for Solving the Problems] The present invention comprises a cathode base metal mainly composed of Xi and containing at least Si, and an electron emitting material layer consisting of an alkaline earth metal oxide containing Ba and 5C203. An electron tube cathode constructed of 5C2O, in which the 5C20s has a columnar polyhedral crystal form and does not contain chlorine atoms.
3 relates to an electron tube cathode having 0.1 to 20% by weight dispersed in the electron emitting material layer.

[Function] Since 5C203 having a columnar polyhedral crystal structure dispersed in the electron emitting material layer in the electron tube cathode of the present invention does not contain chlorine as an impurity, it does not annihilate donors such as free atoms of Ba. A stable electron emission current can be obtained. In addition, the intermediate layer made of the composite oxide of the reducing agent is prevented from being concentrated near the interface between the base metal and the electron emitting material layer.

[Example] An embodiment of the present invention will be described based on FIGS. 1 to 3.

FIG. 1 is a schematic cross-sectional view showing an example of an actual flow of the electron tube cathode of the present invention, showing a cathode cap body made of a base metal (1) and a tube (
A heater (3) is provided inside the cathode cylinder composed of (2) and (2), and is configured to heat and raise the temperature. An electron emitting material layer (S) is deposited on the surface of the cathode cap.

The base metal used in the present invention may be any metal as long as it contains Ni as a main component and in particular contains Si, and those conventionally used as cathode base metals may be used. sell.

Specific examples of the cathode base metal include N containing Si and optionally HQ, W, Zr, /V, etc.
Examples include i and nichrome (Ni-Cr). The content of Si in the base metal is preferably 0.01 to 1.0% (interlayer %, hereinafter the same).

There are no particular limitations on the cylinder used in the present invention, and those conventionally used for cathode cylinders can be used, such as those made of nichrome (Ni-Cr).

The electron emitting material layer is a layer mainly composed of alkaline earth gold RM compound containing Ba, has a columnar polyhedral crystal form, and does not contain chlorine atoms, which are impurities.
3 (may contain unavoidably broken crystals, preferably 50% or more columnar polyhedral crystals, more preferably 7
0% or more, particularly preferably 90% or more)
is dispersed in the layer in an amount of 0.1 to 20%, preferably 3 to 10%. The thickness of the layer is preferably from 50 to 200 mm.

In addition, 5C203 which does not contain a chlorine atom as referred to in this specification
may contain chlorine atoms as long as it does not adversely affect the electron emission performance of the electron tube cathode.
0pp- or less.

As the alkaline earth metal oxide, for example, BaC
O3, (8a, Sr) CO3, (Ba, Sr,
Ca) Examples include those obtained by thermally decomposing CO3 and converting it into oxides. Moreover, the content of Ba in the layer is 4
It is preferably 0% or more.

SC203, which has a columnar polyhedral crystal form, is a crystal as shown in FIG. 2 (electron micrograph at 800x magnification). The average particle size of the 5c2o3 is preferably 5 to 50 particles. If the average particle size is less than 5p, it becomes easier to fill the gaps in the electron emitting material layer, and if it exceeds 50p, the electron emitting material layer is formed by spraying. It tends to precipitate, and the dispersion state within the layer tends to deteriorate.

Furthermore, if the 5C203 contains m chlorine atoms to the extent that it adversely affects the electron emission performance of the electron tube cathode, donors are likely to disappear, causing a slump phenomenon.

5C)03, which has a columnar polyhedral crystal shape and does not contain chlorine atoms, is a nitrate containing Sc! ! It can be produced by precipitation from a solution of (8H03) with oxalic acid (C204)+2). It has been found that 5C203, which has been commonly used in the past, tends to contain chlorine as an impurity and requires special treatment such as washing and firing to remove this impurity.

If the content of 5c2o3 in the electron emitting material is less than 0.1%, the effect of preventing deterioration of electron emission under high current operation is insufficient, and if it exceeds 20%, the electron tube cathode may be activated. It is not practical because a sufficient electron emission current cannot be obtained at the stage where the process is completed (initial characteristics).

There are no particular limitations on the method of forming the electron emitting material layer, and methods such as electrodeposition, coating, and spraying may be used, but in order to obtain good electron emitting performance, it is important to form the layer into a porous layer. Therefore, it is preferable to use the method of spraying. For example, in a solution of nitrocellulose dissolved in an organic solvent, 8aCO3
It is preferable to mix 5c2o3 and 5c2o3 in a desired ratio to form a suspension, and to form a coating by spraying.

The electron tube cathode manufactured as described above through the evacuation process and activation process becomes an electron tube cathode through the conventional evacuation process and activation process to generate donors, which are electron emission sources. .

The effects of the electron tube cathode manufactured in this way will be explained using BaCO3 as an example of the starting material of the donor.

The electron tube cathode produced as described above is assembled into the electron tube through the evacuation process and activation process, and is heated to approximately 1000°C by the heater (3) during the evacuation process to create a vacuum inside the electron tube. BaCO3 is thermally decomposed as shown in the following equation.

BaC03-) aao+ CO2 (1) The CO2 generated during this reaction is discharged outside the electron tube. When a suspension of nitrocellulose is used to form the electron emitting material layer, the nitrocellulose is simultaneously thermally decomposed and becomes a gas.
It is discharged outside the tube along with CO2. By this reaction,
BaCO3 is BaO forming electron emitting material m1(5)
Convert to

FIG. 3 is a schematic enlarged view of a part of the cross section near the interface between the base metal (1) and the electron emitting material layer (5), for explaining the area near the interface in detail. In the BaO constituting the electron emitting material layer (5), minute rod-shaped crystals (8) aggregate to form crystal grains (9) with a size of several to several quarts.

From the viewpoint of electron emission performance, it is desirable that the electron emitting material layer (5) be porous with appropriate gap color between crystal grains.

These characteristics are almost determined when BaC0 is deposited. 5C203[41 having a columnar polyhedral crystal form is dispersed in the electron emitting material 11[5].

The reducing agent Si and particles diffuse and move through the grain boundaries (7) between the crystal grains (6) mainly composed of Ni of the base metal (1).
BaO generated by the reaction shown in formula (11) is mixed with oxidative aftereffects diffusing from the base metal (1) at the interface 01 during the activation step to reduce this BaO, for example, formula (■). : 2BaO+ Si→2Ba+5i02
The reaction shown in (I) is carried out. This free Ba emits electrons as a donor for electron M radiation.

Moreover, this separation N: 5f02+ 2BaO-+ Baz 5iOi
The reaction represented by (IV) also occurs.

As described above, Ba, which becomes a donor, is used in the electron emitting material layer (5
) is generated at the interface (II) between the base metal (1), moves through the gaps □□□ of the crystal grains (9) of the electron emitting material layer (5), emerges on its surface, and plays the role of electron emission. However, it evaporates or disappears by reacting with gases such as CO1CO2,0, which remain in the electron tube, so it is necessary to constantly perform the above reaction to replenish the supply. is being carried out. To balance this replenishment and depletion, it is desirable to maintain the cathode at about 800° C. during operation.

In the electron tube cathode of the present invention, the dispersed 5C203 has a columnar polyhedral crystal shape, which is similar to the crystal shape of BaO, so it has the characteristic that it is easily dispersed in the electron emitting material layer (5). . Therefore, Baz 5i04, which is the reaction product represented by the above formula (1), has the formula @J: 5c203 +1ONi-+ 2ScNi, +30
ScN produced by the reaction shown in [
i 5 and formula ■: 98a2 5i04 + 16ScNi
s 44Ba3 SC40g+EiBa +9Si
+8ONi (reacts as shown by 17ID,
Since it is decomposed by 5c203 and old, it becomes difficult to accumulate at the interface 0η between the electron emitting material layer (S and base metal (1)).

Therefore, as in a conventional cathode, reaction products such as Ba2SiO4 accumulate at the interface between the base metal and the electron emitting material layer and act as a barrier for reducing agents such as Si to pass through, gradually slowing down the reduction reaction and releasing free materials that become donors. There is no difficulty in producing 8a. Moreover, since there is no intermediate layer with high resistance, the electron tube cathode can be operated at high current density without interfering with the electron emission current. In addition, 5c2, which can be obtained by precipitating with oxalic acid from a hydrochloric acid solution,
Unlike the case where 5C303 is dispersed, free atoms in the electron emitting material JI[5] are not annihilated by the halogen contained in the 5C303, so a sufficient electron emission current can be obtained. Furthermore, in the electron tube cathode of the present invention, the step of decomposing and activating the electron emitting substance may be the same as that of conventional ones.
This has the advantage that the manufacturing process for the electron tube can be the same as the conventional method.

Example 1 Scandium hydroxide was dissolved in nitrate 11 (HNO3),
5C303 is precipitated with oxalic acid (C204H2), and 90% or more of the 5C303 has a columnar polyhedral crystal form that does not contain chlorine atoms and has an average particle size of 10-5C2.
I got 03.

Ba was added to a solution of nitrocellulose dissolved in an organic solvent so that the content of 5C203 in the electron emitting material layer was 5%.
C0, and 5C203 were mixed to form a suspension.

This suspension contains 0.03% Si, and 8g is 0.05% Si.
A layer that will become an electron discharge material layer is formed by spraying on the surface of the cathode base metal made of Ni containing 100% Ni to a thickness of approximately 100AII11, and is then subjected to an evacuation process and an activation process to form a layer that will become an electron discharge material layer (Fig. 1). An electron tube cathode as shown in Figure 1 was fabricated.

The resulting electron tube cathode was used as a conventional electron tube cathode (Comparative Example 1: An electron emitting material that did not contain 20 g of SC was installed in the three cathodes of a color cathode ray tube having three primary colors). (Other than that, the same as in Example 1) was assembled, and an electron tube was manufactured through the usual evacuation process and activation process.

The yield of color cathode ray tubes that reached a predetermined flow rate of emitted electrons during the inspection process was 98% or more. In addition, in order to investigate the deterioration state of the electron emission current during use of color cathode ray tubes, we conducted a 6000 fI f
As a result of the IT life test, the conventional cathode without dispersing 5C20,3 was 50% of the initial value at 600G@
The deterioration characteristics are shown below, but the electron tube cathode of the present invention was maintained at 70% of its initial value after 6000 hours, and in terms of life time, it had a lifespan approximately 2.5 times longer.

[Effects of the Invention] As described above, the electron tube cathode of the present invention has 5C203, which has a columnar polyhedral crystal form and does not contain chlorine atoms, on the surface of the base metal containing at least Si as a reducing agent.
An electron emitting material layer made of an alkaline earth metal oxide dispersed therein is formed, and the effect is that stable electron emitting characteristics can be obtained over a period of time. In addition, the electron tube cathode can be used to constantly obtain a stable electron t1i emission current.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an embodiment of the electron tube cathode of the present invention;
Figure 2 is an electron micrograph (magnification: 800x) showing the crystal structure of scandium oxide used in the electron tube cathode of the present invention.
FIG. 3 is a schematic diagram showing the vicinity of the interface between the substrate typhoon and the electron emitting material layer in the electron tube cathode of the present invention, in which a part of the cross section near the interface is enlarged; FIG. 4 is a schematic sectional view of a conventional electron tube cathode; FIG. 5 is a schematic diagram showing the vicinity of the interface between the base metal and the electron emitting material layer in a conventional electron tube cathode, enlarging a part of the cross section near the interface. (Main symbols in the drawings) (1) Bisubstrate metal (4): Scandium oxide crystal with a columnar polyhedral crystal structure (S: Electron emissive material layer No. 2 Oki 30

Claims (2)

[Claims] (1) An electron tube cathode comprising a cathode base metal mainly composed of nickel and containing at least silicon, and an electron emitting material layer consisting of an alkaline earth metal oxide containing barium and scandium oxide, which An electron tube cathode in which scandium oxide has a columnar polyhedral crystal form and does not contain chlorine atoms, and is dispersed in an electron emitting material layer in an amount of 0.1 to 20% by weight. (2) Scandium oxide having a columnar polyhedral crystal form is synthesized by dissolving scandium hydroxide in nitric acid and precipitating it with oxalic acid.
The electron tube cathode described in section 1).