JPH0787070B2 - Electron tube cathode - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cathode for an electron tube used in a cathode ray tube for a TV or the like.

[Conventional technology]

FIG. 2 shows a cathode used in a conventional TV cathode ray tube or image pickup tube. In the figure, 1 is nickel as a main component containing a trace amount of reducing elements such as silicon (Si) and magnesium (Mg). A cylindrical base body 2 having a bottom is attached to the upper surface of the bottom of the base body 1, and at least barium (B
The electron-emitting material layer 3 made of an alkaline earth metal oxide containing a) and additionally containing strontium (Sr) and / or calcium (Ca) is a heater arranged in the substrate 1, and This is for emitting thermoelectrons from the electron emitting material layer 2.

In the cathode for an electron tube thus configured, the electron emitting material layer 2 is deposited on the substrate 1 as follows.
First, a suspension composed of a ternary carbonate of an alkaline earth metal (Ba, Sr, Ca) is applied on the upper surface of the bottom of the substrate 1 and heated by the heater 3 during the vacuum exhaust process. At this time, the alkaline earth metal carbonate is converted into an alkaline earth metal oxide. After that, a part of the alkaline earth metal oxide is reduced and activated so as to have a semiconductor property, so that the electron emitting material layer 2 made of the alkaline earth metal oxide is coated on the substrate 1. It has been formed.

In this activation process, a part of the alkaline earth metal oxide reacts as follows. That is, the reducing elements such as silicon and magnesium contained in the substrate 1 move to the interface between the alkaline earth metal oxide and the substrate 1 by diffusion and react with the alkaline earth metal oxide. For example, if the alkaline earth metal oxide is barium oxide (BaO),
It reacts as in the following equations (1) and (2).

BaO + 1 / 2Si = Ba + 1 / 2SiO ₂ (1) BaO + Mg = Ba + MgO (2) As a result of this reaction, a portion of the alkaline earth metal oxide deposited on the substrate 1 is reduced and oxygen-deficient type Becomes a semiconductor, 0.5-0.8A / cm ² at operating temperature of cathode temperature 700-800 ℃
Will be obtained.

However, in the cathode for the electron tube, the electron emission is 0.5 to 0.8.
Current densities above A / cm ² cannot be extracted.

The reason is that when a part of the alkaline earth metal oxide is subjected to a reduction reaction, as is clear from the above formulas (1) and (2), the interface between the substrate 1 and the alkaline earth metal oxide layer is
A complex oxide layer (intermediate layer) such as SiO ₂ , MgO or BaO · SiO ₂ is formed, and this intermediate layer serves as a high resistance layer to prevent the flow of current, and the intermediate layer reduces reduction in the substrate 1. It is considered that a sufficient amount of barium (Ba) is not generated because the functional elements (Si, Mg) prevent diffusion to the surface side of the electron emitting material layer 2. That is, during operation of the electron tube, the intermediate layer is segregated in the vicinity of the interface between the substrate 1 and the electron-emitting substance layer 2, particularly at the nickel crystal grain boundary in the vicinity of the surface of the substrate 1 and at a position of about 10 μm inside the electron-emitting substance layer 2 from the interface. Therefore, there is a problem that the flow of current and the diffusion of the reducing element to the surface side of the electron emitting material layer 2 are hindered, and sufficient electron emission characteristics under high current density cannot be obtained.

On the other hand, in the application for Japanese Patent Application No. 60-229303,
By including 0.01 to 0.5% by weight of rare earth metal, oxidation occurs when the alkaline earth metal carbonate decomposes during activation when depositing the electron emitting material layer on the substrate or during operation as the cathode. It consists of a complex oxide of reducing elements, which prevents the oxidation of the substrate when barium causes a dissociation reaction and controls the diffusion of the reducing elements contained in the substrate into the electron-emitting material layer. A technique is disclosed in which the intermediate layer is prevented from being intensively formed in the vicinity of the interface between the substrate and the electron-emitting substance layer, and the intermediate layer is dispersed in the electron-emitting substance layer. That is, in the second conventional cathode for an electron tube, since the intermediate layer is dispersed,
It has the excellent characteristics of little emission deterioration at high current density operation of about 3 A / cm ² . However,
Even in this case, there is a problem that emission deterioration is large in high current density operation exceeding 3 A / cm ² , for example, 4 A / cm ² . Further, in the application of Japanese Patent Application No. 60-160851, by containing 0.1 to 20% by weight of a rare earth metal oxide in the electron emitting material layer, oxidation of the substrate can be prevented as in the second conventional example. The technique of dispersing the intermediate layer is shown. Even in this case, 4 A / cm ²
Even in the above high current density operation, the emission deterioration can be reduced. However, in this case, in a high current density operation of 4 A / cm ² or more, although the evaporation of barium becomes remarkable due to Joule heat due to the current flowing through the electron emitting material layer, the electron emitting characteristics may deteriorate.

[Problems to be Solved by the Invention]

It is an object of the present invention to obtain a cathode for an electron tube which has stable emission characteristics for a long time even in a high current density operation of 4 A / cm ² or more.

[Means for Solving the Problems]

The cathode for an electron tube according to the present invention comprises, on a substrate whose main component is nickel, an alkaline earth metal oxide containing at least barium as a main component, and a compound of scandium, neodymium, samarium, gadolinium, dysprosium and lanthanum. , An electron emitting material layer containing a compound of at least one element selected from cerium, europium and ytterbium.

[Action]

In the present invention, the scandium compound contained in the electron-emitting substance layer is used when the alkaline earth metal carbonate decomposes during activation when the electron-emitting substance layer is deposited on the substrate, or as a cathode. This prevents the oxidation of the substrate when the barium oxide undergoes a dissociation reaction during operation, and controls the diffusion of the reducing element contained in the substrate into the electron-emitting material layer appropriately, thereby forming a composite with the reducing element. It is possible to prevent the intermediate layer made of an oxide from being intensively formed in the vicinity of the interface between the substrate and the electron-emitting substance layer, disperse the intermediate layer in the electron-emitting substance layer, and The contained compound of at least one element selected from neodymium, samarium, gadolinium, dysprosium, lanthanum, cerium, europium, and ytterbium,
Suppresses the evaporation of barium.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In this figure, 1 is a substrate whose main component is nickel, and this substrate 1 contains a reducing agent such as Si and Mg. Reference numeral 2a denotes an electron emitting material layer deposited on the upper surface of the bottom of the substrate 1. Specifically, ternary oxide of barium, strontium and calcium contains scandium oxide powder and 0.01 to 20% by weight of neodymium oxide, and nickel. It contains less than 10% by weight of powder. Alkaline earth metal oxides such as barium above are mixed with carbonate first,
As in the conventional case, the decomposition process of carbonate to oxide and the activation process of reducing a part of the oxide are performed.

FIG. 3 shows, as a first specific example, oxides of barium, strontium, and calcium, and scandium oxide (Sc ₂ O ₃ )
4% by weight, neodymium oxide (Nd ₂ O ₃ ) 3% by weight, nickel (Ni) 1% by weight (a), as a second specific example, scandium oxide (Sc ₂ O ₃ ) 4% by weight , A cathode for an electron tube of (b) containing 3% by weight of samarium oxide (Sm ₂ O ₃ ) and 1% by weight of nickel (Ni) was prepared by the above-mentioned method, and a bipolar vacuum tube was formed using the cathode for the electron tube. Create and 4.
This is the result of examining the change in emission current when a life test was performed by operating at a current density of 3 A / cm ² . In addition, in the figure, those containing no scandium oxide (Sc ₂ O ₃ ) (d) and those containing 4% by weight scandium oxide (Sc ₂ O ₃ ) (c) are also shown.

Compared to those containing no Sc ₂ O ₃ (d) and those containing only Sc ₂ O _{3 at} 4 wt% (c), in addition to Sc ₂ O ₃ , Nd ₂ O ₃ or Sm
_The emission deterioration is small in the case of adding ₂ O ₃ and Ni (a, b). Added to _{Sc 2 O 3, Nd 2 O} 3, Sm 2 O 3, and results of various experiments with respect to the amount of Ni, added to rare earth oxides in a total amount from 0.1 to 20% by weight C., among others Nd ₂ O ₃ , Sm ₂ O ₃
Is preferably 0.05 to 10% by weight. Further, Ni may be 10% by weight or less. Furthermore, as rare earth oxides to be added in addition to scandium oxide (Sc ₂ O ₃ ), neodymium oxide (Nd
₂ O ₃ ) and samarium oxide (Sm ₂ O ₃ ), gadolinium oxide (Gd ₂ O ₃ ), dysprosium oxide (Dy ₂ O ₃ ), lanthanum oxide (La ₂ O ₃ ), cerium oxide (Ce ₂ O _3). ), Europium oxide (Eu ₂ O ₃ ) and ytterbium oxide (Yb ₂ O ₃ ) are suitable.

As mentioned above, in addition to Sc ₂ O ₃ , other rare earth oxides and Ni
It is considered that the reason why excellent characteristics are obtained in the case of adding is compared with the conventional one is as follows. A part of Sc ₂ O ₃ dissociates and diffuses from the surface of the substrate 1 to a depth of about 20 μm as the cathode of the electron tube operates. On the other hand, the reducing agents Si and Mg in the substrate 1 diffuse to the surface contrary to Sc and react with BaO on the surface to form free Ba, but also produce BaSiO ₃ . this
BaSiO ₃ is called the intermediate layer and inhibits the reaction of the reducing agent with BaO. However, in the present invention, it exists in the surface layer of the substrate 1.
Since the intermediate layer is decomposed by Sc, the reducing agent Si can further move into the electron emitting material layer 2a and contribute to electron emission. It is considered that the added rare earth oxides such as Nd ₂ O ₃ and Sm ₂ O ₃ suppress the evaporation of Ba. The surface of this cathode for electron tubes was observed with an Auger spectroscopic analyzer, which showed that Nd ₂ O ₃ and S
It was found that Ba was sufficiently present on the m ₂ O ₃ particles. That is, when a high current flows through the electron-emitting substance layer 2a,
The Joule heat causes the temperature of the electron emitting material layer 2a to rise, and as a result, the evaporation of Ba increases. Increased evaporation of Ba inevitably leads to a short life and must be avoided. In this example, it is considered that rare earth oxides such as Nd ₂ O ₃ and Sm ₂ O ₃ have a function of adsorbing Ba. The Ni powder is added to improve the conductivity of the oxide of the electron emitting material layer 2a, and enters between or inside the oxide particles to make a current easily flow. Other than nickel (Ni), cobalt (Co), iron (Fe), aluminum (Al), titanium (Ti), zirconium (Zr), hafnium (Hf), niobium (Nb), tantalum (Ta), molybdenum (Mo). ), Tungsten (W), magnesium (Mg), silicon (Si),
Rhenium (Re), Osmium (Os), Iridium (I
r), platinum (Pt), palladium (Pd), rhodium (R
h), gold (Au), vanadium (V), chromium (Cr), manganese (Mn), copper (Cu), zinc (Zn), bismuth (Bi)
Is effective.

When the total amount of rare earth oxides exceeds 20% by weight, the initial electron emission amount is low, and when this amount is 0.1% or less, it is not effective for suppressing the formation of the intermediate layer and Ba evaporation.

Moreover, the amount of the metal powder such as Ni added is preferably 10% by weight or less. If this amount exceeds 10% by weight, the state of sintering of the electron-emitting material layer proceeds, and the electron emission characteristics deteriorate. Although this amount is effective even in a small amount, it is preferably 0.01% by weight or more.

〔The invention's effect〕

As described above, the cathode for an electron tube according to the present invention has, as a main component, an alkaline earth metal oxide containing at least barium on a substrate made of nickel, and a compound of scandium, neodymium, samarium, gadolinium, Since an electron emitting material layer containing a compound of at least one element selected from dysprosium, lanthanum, cerium, europium, and ytterbium was deposited, a high current of 4 A / cm ² or more was obtained only by a normal activation process. It has an effect that a long life can be surely realized under the operation based on the density.

[Brief description of drawings]

1 is a sectional view showing a cathode for an electron tube according to an embodiment of the present invention, FIG. 2 is a sectional view showing a conventional cathode for an electron tube, and FIG. 3 is a life test time of a bipolar vacuum tube using the cathode for an electron tube. It is a figure which shows the relationship between and emission current. In the figure, 1 is a substrate and 2a is an electron emitting material layer. In each drawing, the same reference numerals indicate the same or corresponding parts.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Suzuki 2-14-40 Ofuna, Kamakura-shi, Kanagawa Product Research Laboratory, Mitsubishi Electric Corporation (72) Masato Saito 2-14-40 Ofuna, Kamakura-shi, Kanagawa (56) References JP 62-193032 (JP, A)

Claims (1)

[Claims] 1. A substrate whose main component is nickel, which contains an alkaline earth metal oxide containing at least barium as a main component and a compound of scandium and neodymium, samarium, gadolinium, dysprosium, lanthanum, cerium, europium, ytterbium. A cathode for an electron tube, wherein an electron emitting material layer containing a compound of at least one element selected from the above is deposited.