KR100393047B1 - Metal cathode and indirectly heated cathode assembly having the same - Google Patents

Abstract

The present invention relates to a metal negative electrode and a heat dissipating negative electrode structure having the same, comprising Sc, Y, La, Ce, Pr, Nd and Sm on the emitter surface of the metal negative electrode made of barium 0.1 to 20% by weight and the remaining amount of platinum. Provided is a hot electron emission metal cathode for an electron beam device, and a heat dissipating cathode structure having the same, wherein a coating layer is formed of at least one rare earth metal selected from the group consisting of:

The metal cathode according to the present invention can lower the operating function to lower the operating temperature, increase the electron emission ability, and can be used for a long time at high current density, so in response to the trend of large size, long life, high resolution, high brightness It can be usefully used as a cathode material of an electron beam device such as a CRT, an imaging tube, and the like.

Description

Metal cathode and heat dissipating cathode structure having same {Metal cathode and indirectly heated cathode assembly having the same}

The present invention relates to a metal cathode of an electron beam device and a heat dissipating cathode structure having the same, and more particularly, can be used in an electron beam device such as a television CRT, an imaging tube, etc. in response to the trend of large size, long life, high definition, and high brightness. The present invention relates to a thermoelectron emitting metal cathode having a low operating temperature, excellent electron emission capability, and a long life at high current density, and a heat dissipating cathode structure having the same.

A conventional alkali metal carbonate layer having barium as a main component on a base metal containing nickel (Ni) as a main component and a trace amount of silicon (Si), magnesium (Mg) as a reducing agent in a conventional electron tube cathode, preferably Preferably, the so-called "oxide cathode" having an electron emitting material layer of oxide converted from a ternary carbonate composed of (Ba, Sr, Ca) CO ₃ , or a binary carbonate composed of (Ba, Sr) CO ₃ is widely used. . These oxide cathodes have the advantage of being able to be used at relatively low temperatures (700-800 ° C.) due to their low work function, but have a limit in electron emission capability, which makes it difficult to emit a current density of 1 A / cm 2 or more. Because the material is a semiconductor and the electrical resistance is high, if the electron emission density is increased, the material is evaporated or melted due to the self heating by Joule heat, thereby deteriorating the cathode, or the intermediate resistance layer is formed between the metal substrate and the oxide layer by long-term use. There is a disadvantage that the life is shortened.

In addition, since the oxide cathode is fragile and has low adhesion to the metal substrate to be mounted, the lifetime of the cathode ray device having this type of cathode is shortened. For example, damage to only one of the three oxide cathodes of a color receiver will cause the entire expensive device to fail.

For this reason, attempts to apply high-performance metal cathodes without the disadvantages of the above-described oxide cathodes to the cathode ray device have been encouraging. Also, in order to meet the recent trends of the enlargement, long life, high resolution, and high brightness of the CRT, There is a need for a cathode that can be used for a long time.

For example, a metal cathode based on lanthanum hexaboride (LaB ₆ ) was developed to meet this demand and is known to have a higher strength and higher electron emission capability than an oxide cathode. A high current density of about / cm 2 can be emitted. However, lanthanum hexaboride cathodes have been used only in some vacuum electronics, which can replace the cathode units because of their short lifetime. The short lifetime of the lanthanum hexaboride cathode is due to its high reactivity with the constituents of the heater, since lanthanum hexaboride forms many fragile compounds in contact with the constituents of the heater, eg tungsten. .

US Pat. No. 4,137,476 discloses a cathode in which another barrier layer is formed between lanthanum hexaboride and the body of the heater to eliminate this possibility of reaction. However, this method significantly increases the cost of producing the negative electrode and makes it difficult to significantly improve the lifetime of the negative electrode. Furthermore, although the negative electrode and the impregnated negative electrode using secondary electron emission have been researched and developed, there are problems such as short lifespan and high cost.

In addition, the conventional metal cathode may cause various problems during operation due to high operating temperature, the high temperature required for the operation of the cathode may cause a leakage current between the heater and the cathode, or the heater may be disconnected. For example, the Russian patent USSR 1975520 discloses a method of adding an alkali metal to reduce the operating temperature of a metal alloy composed of platinum group element and alkaline earth metal and to increase the secondary electron emission coefficient, but the operating temperature is higher than 1200 ℃. Subsequently, there is a problem such as heater disconnection and leakage current when applied to CRT as mentioned above.

Therefore, the technical problem to be achieved by the present invention is to solve the above problems, low operating temperature, excellent electron emission capability, which can be used in electron beam apparatuses such as television CRT, image pickup tube, high-temperature density electron emission that can be used for a long time To provide a metal cathode.

Another object of the present invention is to provide a heat radiation type negative electrode structure having the metal cathode.

1A is a photograph showing a state in which Pt ₅ Ba is dissolved in a conventional metal anode;

Figure 1b is a photograph showing the diffusion of Ba on the emitter surface of the conventional metal cathode,

1C is a schematic cross-sectional view illustrating a state in which a Ba monoatomic layer is formed on an emitter surface of a conventional metal cathode.

2 is a graph showing the electron emission capability of the alloy according to an embodiment of the present invention.

Figure 3 is a schematic cross-sectional view showing the structure of a heat radiation type negative electrode structure having a metal cathode according to the present invention.

The present invention to achieve the above technical problem is any one or more selected from the group consisting of Sc, Y, La, Ce, Pr, Nd and Sm on the emitter surface of the metal cathode consisting of 0.1 to 20% by weight of barium and the remaining amount of platinum Provided is a hot electron emitting metal cathode for an electron beam device, characterized in that a coating layer made of rare earth metal is formed.

In the metal cathode according to the present invention, the coating layer preferably has a thickness of 500 kPa to 30000 kPa.

In order to achieve the above another technical problem, the present invention provides a heat radiation type negative electrode structure comprising the metal negative electrode.

Hereinafter, a metal negative electrode and a method of manufacturing the same according to the present invention will be described in detail.

The present invention is directed to the emitter surface of the binary alloy metal cathode in order to lower the work function of the binary alloy metal anode made of platinum group-alkaline earth metal, thereby increasing the current density of the metal anode emitter and reducing the operating temperature. It is characteristic to provide a coating layer made of rare earth metals.

1A, 1B, and 1C are views schematically showing states at each step in the electron emission mechanism of the Pt-Ba alloy system.

In the case of pure Pt metal, the work function is very high as 5.3eV, but when Ba is added thereto, the work function is reduced to 2.2eV, which can be used as a hot cathode. It is known that the work function is reduced by the addition of Ba because a monoatomic layer of Ba is formed on the surface of the Pt-Ba alloy during cathode operation to reduce the surface work function.

Accordingly, the electron emission mechanism of the Pt-Ba alloy can be divided into three stages as follows.

The first step is to decompose Pt ₅ Ba inside the alloy, as shown in FIG. In the Pt-Ba alloy system having a Ba content of 16.66 wt% or less, Ba is present in the form of a Pt ₅ Ba intermetallic compound, which decomposes during cathode operation to provide Ba atoms.

In the second step, as shown in FIG. 1B, the decomposed Ba atoms are diffused onto the emitter surface. This diffusion must be continued quickly to improve the characteristics and life of the cathode.

In the third step, as shown in FIG. 1C, an optimal Ba monoatomic layer is formed on the emitter surface.

Through these three steps, the work function of the emitter surface is reduced, and electron emission is possible even at a relatively low temperature.

However, as mentioned above, the hot electron emission cathode made of a binary alloy composed only of Pt-Ba has excellent electron emission characteristics compared to the conventional oxide cathode, but the heater is disconnected because the operating temperature of the metal cathode is about 1200 ° C. Problems such as the occurrence of leakage currents occur, and the crystal growth of the emitter is excessive, resulting in a limitation in the life characteristics.

Therefore, the present inventors have studied a method of reducing the work function based on the electron emission mechanism, and by forming a coating layer made of rare earth metal on the emitter surface of the binary alloy-based metal anode made of platinum group-alkaline earth metal, The work function could be reduced, and as a result, a low-temperature operating temperature, excellent electron emission capability, and a long-term use at high current density could be manufactured.

The metal anode of the present invention contains 0.1 to 20% by weight of barium. If the content of the barium metal is less than 0.1% by weight, the lifetime of the negative electrode is shortened due to the lack of the active barium metal. If the content of the barium metal exceeds 20% by weight, the brittleness of the ingot is greatly increased, making it difficult to manufacture an emitter. In addition to the quality, there is a problem in that a compound such as Pt ₂ Ba having low electron emission characteristics is formed on the surface of the cathode.

By adding a metal of any one or more of the remaining amount of platinum and palladium to the barium can be prepared a metal anode consisting of a binary alloy.

Subsequently, the metal anode according to the present invention may be manufactured by forming a coating layer made of rare earth metal on the emitter surface of the metal anode made of the binary alloy.

The thickness of the coating layer made of the rare earth metal is preferably 500 kPa to 30000 kPa, more preferably 1000 kPa to 10000 kPa. Within this range, the work function of the cathode can be effectively reduced without lowering the electron-emitting ability.

Hereinafter, the manufacturing method of the metal negative electrode which concerns on this invention is demonstrated in detail, for example.

First, Pt and Ba are put into an arc furnace. Since Pt and Ba have a large melting point difference, it is preferable to use an arc furnace that can melt the metal instantaneously. Since Ba is easy to evaporate, the content of Ba is controlled by adding 1 to 10% more than the content of the final alloy. Do it. Subsequently, the inside of the arc furnace is kept in a vacuum state and then an inert gas such as Ar gas is injected. Then, a voltage is applied to the arc furnace to melt the two metals in a short time. Since Pt and Ba have a large density difference, it is difficult to obtain a uniform alloy composed of these metals. Therefore, by repeatedly performing the melting process and the solidification process, it is possible to manufacture a metal anode made of a binary alloy with improved chemical and microstructure uniformity.

Subsequently, the rare earth metal is coated on the emitter surface of the metal anode made of the binary alloy using a vacuum deposition method, etc. to prepare a metal cathode according to the present invention, and the cathode structure after cutting or molding to suit the cathode structure of the electron tube. Mount on.

The metal cathode for an electron tube according to the present invention may be used in a direct type cathode structure, but is preferably used in a heat radiation type cathode structure as shown in FIG. 3.

That is, referring to Figure 3, the metal cathode 33 of the present invention made of a binary alloy 31 having the rare earth metal coating layer 32 is welded to the upper portion of the sleeve 35, the heater 34 is embedded Therefore, it is preferable to use it as a hot electron emission material of the heat radiation type cathode structure.

The present invention will be described in detail with reference to the following examples, but the present invention is not limited to the following examples.

<Example 1>

First, 4.6 g of ingot form Pt and 0.5 g of Ba are placed in an arc furnace. Subsequently, Ar gas was injected after the inside of the arc furnace was kept in a vacuum state. Then, a voltage was applied to the arc furnace to melt the Pt and Ba metals and to alloy the two metals well. The ingot thus obtained was repeated three times to melt the chemical and microstructure uniformity of the alloy. Finally, a binary alloy composed of 92 wt% Pt and 8 wt% Ba was prepared.

After forming a Sc coating layer having a thickness of 3000 kPa on the metal cathode made of a binary alloy by using a vacuum deposition method, and heat treatment at about 1,000 ℃ in hydrogen or nitrogen atmosphere to prepare a cathode according to the present invention.

The metal cathode was cut and welded to the upper portion of the heat dissipating cathode structure shown in FIG. 3, and then the operating temperature was measured. The results of the measurement are shown in Table 1 below. It was.

<Example 2>

A metal cathode was prepared in the same manner as in Example 1 except that the coating layer was formed using Y instead of Sc. The metal cathode thus obtained was cut and welded to the upper portion of the heat dissipating cathode structure shown in FIG. 3, and then the operating temperature was measured, and the measurement results are shown in Table 1 below. Indicated.

Comparative Example 1

A metal anode was manufactured in the same manner as in Example 1 except that the coating layer was not formed on the metal anode made of a binary alloy. The metal cathode thus obtained was cut and welded to the upper portion of the heat dissipating cathode structure shown in FIG. 3, and then the operating temperature was measured, and the measurement results are shown in Table 1 below. Indicated.

Alloy type Operating temperature (℃) Example 1 Pt-Ba-Sc Coating Layer 1150 Example 2 Pt-Ba-Y coating layer 1180 Comparative Example 1 Pt-Ba 1220

Referring to Table 1 and the accompanying FIG. 2, the metal cathodes (Examples 1 and 2) according to the present invention in which a rare earth metal coating layer is formed on the emitter surface of the metal anode made of a binary alloy are conventional binary alloys. It can be seen that the operating temperature is about 40 to 70 ° C. lower than the metal cathode (Comparative Example 1), and the current density is also improved by 50% or more at the same temperature.

The metal cathode according to the present invention can lower the operating function to lower the operating temperature, increase the electron emission ability, and can be used for a long time at high current density, so in response to the trend of large size, long life, high resolution, high brightness It can be usefully used as a cathode material of an electron beam device such as a CRT, an imaging tube, and the like.

Claims (3)

A coating layer made of at least one rare earth metal selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, and Sm is formed on the emitter surface of the metal cathode composed of 0.1 to 20% by weight of barium and the balance of platinum. A hot electron emission metal cathode for an electron beam device. The hot electron emission metal cathode for an electron beam apparatus according to claim 1, wherein the coating layer has a thickness of 500 kPa to 30000 kPa. A heat radiation type negative electrode structure comprising the metal negative electrode according to claim 1.