KR20030078385A - Novel metal cathode - Google Patents

Abstract

PURPOSE: A new metal cathode is provided to achieve improved electron emission capability and useful life of the cathode, while lowering the temperature of generating alkali earth metals. CONSTITUTION: A metal cathode comprises an alloy containing a platinum(Pt) and a barium(Ba); and a metal film layer formed on the alloy and made of one or more refractory metals selected from a group consisting of W, Mo, Nb, lr, Os, Rh and Ta. The metal film layer is formed by sintering a metal powder. Alternatively, the metal cathode comprises an alloy containing a platinum(Pt) and a barium(Ba); a first metal film layer formed on the alloy and made of one or more refractory metals selected from a group consisting of W, Mo, Nb, lr, Os, Rh and Ta; and a second metal film layer formed on the first metal film layer, and which contains a platinum-based metal or a rare earth metal.

Description

New metal cathode

The present invention relates to an electron emission source used in various electronic products, including a CRT, and more particularly, a heat electron emission metal cathode having an excellent electron emission capability and an improved lifetime, which can be used in an electron beam apparatus such as CRT. It is about.

When the electron emission source is classified according to the operating temperature, the heater can be largely divided into a heat electron source equipped with a heater and a cold cathode which emits electrons by an electric field applied without a heater. It provides an improved structure of the emitter, in particular the hot electron emitter for CRTs.

A typical heat dissipation hot cathode has a cylindrical sleeve with a heater and a hot electron emitting layer fixed to the sleeve, and the hot electron emitting material layer has a low work function and electronegativity, is stable, and has electrons in the outermost track. The main ingredient is barium, which is a rich element.

The demand for high current density and long life cathodes is increasing according to the trend of high definition and large size of CRT.The quality of the hot electron emission source based on barium has stable barium supply ability and surface structure that can easily emit electrons. Depends heavily on the securing of.

The oxide cathode, which is mainly used as a hot cathode for CRTs, is thermally decomposed with an electron-emitting material composed of alkaline earth metal carbonate, and is converted into an oxide. It goes through the process of creation. At this time, since the glass barium acts as a donor for giving electrons, the oxide cathode becomes an N-type semiconductor in physical properties during cathode operation. In general, when a large current flows in a semiconductor, Joule heat is generated by self-resistance. If Joule heat generation continues for a long time, it causes cathode self-deterioration by material evaporation or melting due to self heating.

In addition, such an oxide cathode has an intermediate layer as a by-product of the reduction reaction at the interface between the electron-emitting material layer and the sleeve during operation, and the cathode inhibits the reduction reaction and restricts the supply of glass barium while preventing the diffusion of the reducing agent from the sleeve. As a result, the characteristics are lost.

In this case, the solution to the problem is to prevent the formation of an intermediate layer or to prevent the accumulation of materials in the intermediate layer to interfere with the reduction reaction. However, in the case of an oxide cathode, barium is in the form of an oxide so that the barium must be reduced to reduce the barium. In order to prevent the formation of by-products, it is difficult to prevent the formation of by-products and the amount of elements or contents that can be added to the oxides is limited. It is very difficult to do.

As described above, the oxide cathode does not satisfy the requirements due to factors such as the generation of Joule heaters and the growth of the intermediate layer that suppresses the generation of free barium during cathode operation.

Complementing the disadvantages of the oxide cathode as described above, there is an impregnated cathode that realizes high current density and long life. The impregnated cathode solved the above problem by expanding the intermediate layer of the oxide cathode, which was limited to the interface between the electron-emitting material layer and the sleeve, to the entire electron-emitting material layer to prevent local accumulation. In addition, the metal substrate introduced in this process has the effect of improving the conductivity of the electron-emitting material layer and providing the uniform surface at the same time, thereby preventing the problem of generating the joule heat of the oxide cathode as mentioned above, thereby increasing the high current density. It can provide a long lifetime and provide an electron beam with excellent focus characteristics.

Although the impregnated cathode has such excellent characteristics, it is not as widely used as an oxide cathode, and its adoption is still limited to some high-end models for the following reasons. In other words, the oxide cathode is manufactured by a simple process of coprecipitating alkaline earth metal with carbonate and dispersing it in a solvent to form an electron-emitting material layer on the surface of the gas metal by a suitable method (such as electrodeposition or spraying). Recently used impregnated cathode is a barium source in the pores of the porous metal gas obtained by controlling the porosity of a heat-resistant metal such as tungsten to control the porosity to make a porous pellet having a predetermined pore and high-temperature treatment Impregnation (Barium calcium aluminator, which is produced by mixing barium, calcium carbonate and alumina in a weight ratio of 4: 1: 1 and calcining in a reducing atmosphere at 1100 ° C., is mainly used. Glass barium is produced by thermal decomposition and reaction with tungsten, a gaseous metal, during the process or cathodic operation). It is manufactured through a complicated process of impregnating and enclosing it in a metal container and then fixing it to a sleeve, which is expensive to manufacture and difficult to secure reliability when impregnating electron-emitting materials into the fine pores of porous tungsten gas. This is because a long time aging process is required in order to produce abundantly and stably, resulting in inferior mass productivity and economical efficiency to oxide cathodes.

In addition to the oxide cathode and the impregnated cathode as described above, there are metal cathodes. Unlike the above cathodes using a ceramic material as a barium source, in the metal group of the platinum group-alkaline earth metal system, the barium alloy solid solution is decomposed using an alloy system in which barium and other metals are dissolved as a barium source to generate free barium. Doing. According to this reaction, metals are generated as by-products of the reduction reaction, thereby preventing free barium generation due to accumulation of by-products. Also, since metals are used as electron-emitting materials, generation of joule heat can be prevented. However, since these types of metal cathodes are used as secondary electron emission sources operating at room temperature or low temperature for special purposes in addition to CRTs, they can be used for CRTs and operated at temperatures above 700 ° C. -There are many inappropriate parts such as barium reaction.

Metal cathodes used as electron emission sources such as magnetrons and traveling wave tubes use platinum group metals as their main elements, which are alkaline earth elements such as Ba, Sr, Ca or La rare earths (Ce, Pr). Is used as an electron-emitting material. The metal cathode mainly composed of platinum-alkaline earth metal, which is one of them, has a relatively close property to the cathode for a CRT, but its life characteristics are unstable and its operating temperature is higher than that of an oxide cathode. If the operating temperature is high, errors such as disconnection of the heater mounted to heat the cathode or leakage of current between the heater and the sleeve are increased. Therefore, it is possible to solve the disadvantages of the cathode for cathode ray tube using the barium ceramic mentioned above only by lowering the operating temperature of these cathodes.

In the platinum-alkaline earth metal cathode, an alkaline earth metal formed by decomposition of a solid solution between platinum and alkaline earth metal diffuses to the surface to form a monoatomic layer on the surface of the electron emission layer, and the polarization phenomenon caused by the presence of the monoatomic layer This results in an energy structure where electrons can be easily released into the vacuum. Therefore, in order to lower the operating temperature of the metal cathode, the alkaline earth metal monoatomic layer formed on the surface must be maintained at a low temperature. That is, these alkaline earth metals should be produced at a lower temperature than existing metal cathodes and can be easily diffused to the surface.

Therefore, in order to solve the above problems, by controlling the generation and diffusion of the alkaline earth metal, it is possible to lower the production temperature of the alkaline earth metal layer of the platinum-alkaline earth metal cathode and to easily diffuse the alkaline earth metals to the surface. It is an object of the present invention to provide a new metal cathode for an electron tube.

Figure 1 schematically shows the cross-sectional structure of the negative electrode according to an embodiment of the present invention,

Figure 2 schematically shows the cross-sectional structure of the cathode according to another embodiment of the present invention,

Figure 3 schematically shows a cathode structure during operation of the metal cathode of the present invention,

FIG. 4 is an electron micrograph at 800 times magnification of the changed alloy structure when a heat-resistant metal was added in the preparation of a platinum-barium alloy.

5 is a graph showing a comparison of the current density characteristics of the cathode according to the present invention and the conventional oxide cathode and impregnated cathode,

6 is a graph showing the life characteristics of the anode according to the present invention and the conventional oxide cathode, metal cathode (Pt-Ba-based) and the impregnated cathode.

In order to solve the above problems, the present invention,

Alloys containing platinum and barium; And a metal film layer formed on the alloy and made of at least one high melting point metal selected from the group consisting of W, Mo, Nb, Ir, Os, Rh, and Ta. Provide a cathode.

According to a preferred embodiment of the present invention, the metal film layer of the high melting point metal is preferably in the form of a sintered body formed by sintering a metal powder.

In order to solve the above problems, the present invention also,

Alloys containing platinum and barium; A first metal film layer formed on the alloy and made of at least one high melting point metal selected from the group consisting of W, Mo, Nb, Ir, Os, Rh, and Ta; And a second metal film layer including a platinum group metal or a rare earth metal formed on the high melting point metal film layer.

In the metal cathode as described above, the platinum-barium-based alloy preferably includes 85 to 99% by weight of platinum and 1 to 15% by weight of barium, and the alloy may include Mo, W, It is preferably an alloy formed by further comprising at least one high melting point metal selected from the group consisting of Nb, Ir, and Os. In addition, the content of the third component of the alloy is preferably 0.5 to 5wt% based on the total alloy.

In addition, according to a preferred embodiment of the present invention, the first metal film layer is preferably in the form of a sintered body formed by sintering the metal powder.

Hereinafter, the present invention will be described in more detail.

A cathode structure according to one aspect of the present invention is a structure having a metal alloy containing barium and a high melting point metal layer having pores on the upper surface of the alloy in contact with the vacuum, which can easily move to the surface. The operating aspect of the cathode of this structure is shown in FIG. As can be seen from FIG. 3, the glass barium produced in the barium-containing metal alloy layer moves and diffuses along the pores of the heat resistant metal to the cathode surface to form a stable and flat barium monoatomic layer on the heat resistant metal surface layer. Contributing to the release, a portion of which is evaporated in vacuo, where the amount of evaporation continues to produce and diffuse free barium produced in the barium-containing metal alloy layer.

At this time, the metal alloy containing barium is preferably a platinum-barium alloy, and the high melting point metal of the high melting point metal layer is preferably selected from the group consisting of W, Mo, Nb, Ir, Os, Rh, and Ta. .

According to still another aspect of the present invention, a second metal film layer containing a platinum group or a rare earth element is further formed on the high melting point metal layer.

In the above metal cathodes, the content of barium in the platinum-barium alloy is preferably 1 to 15 wt%. If it is 1wt% or less, Ba is too small and the electron emission characteristic of the cathode is not good. If it is 15wt% or more, the evaporation of Ba becomes too severe, which is not preferable. Conventional magnetron's platinum-barium alloy has a barium content of 1 to 2 wt% and a lifetime of less than 1000 hours, thus making it impossible to apply to a CRT.

In addition, the platinum-barium alloy may further include one or more high melting point metals selected from the group consisting of W, Mo, Nb, Ir, and Os as a third component. The reason why such a high melting point metal is further added as a third component is as follows.

When manufacturing the metal cathode, the metal elements are made of an alloy in a molten liquid state by arc melting or induction melting, and then cooled and cut into a size suitable for the purpose of application, such as welding on a support such as a sleeve. It is fixed by the method.

In the manufacture of such a metal alloy, the alloy has a fine internal structure of the alloy emitter depending on the composition ratio, the temperature, the holding time, the cooling rate, and the like. Tissue size is known to be affected.

However, the disadvantage of arc melting or induction melting is that it is difficult to obtain an alloy of uniform structure and composition due to differences in specific gravity or cooling rate of the components, and thus it is difficult to control the size of the structure.

In the present invention, when a heat-resistant metal element (eg, tungsten, molybdenum, niobium, and platinum group metals) is added as a third component to the platinum-alkaline earth metal alloy system, the alloy has a stable structure structure, thereby resulting in the dispersion of the alloy manufacturing process. It has been found that by reducing the non-uniformity of the tissue and forming a fine tissue structure, it is possible to promote alkaline earth metal dissociation to obtain a metal cathode having excellent initial properties.

In this case, the preferred amount of the third component is 0.5 to 5 wt% based on the total alloy. In this range, the metal alloy exhibited the most uniform structure, whereby the internal diffusion of barium was most promoted.

FIG. 4 is a micrograph showing an 800 times magnification of an alloy structure when a tungsten is added in an amount of 2 at% of platinum atoms to a platinum alloy containing 8 wt% of barium according to the method of the present invention. to be. As can be seen from this photograph, the alloy in which tungsten was added as a third component showed a very fine and uniform structure.

Hereinafter, the manufacturing method of the metal negative electrode of this invention is demonstrated in detail.

First, an alloy is prepared by alloying a certain amount of Pt-Ba in an inert atmosphere furnace, and the detailed process is as follows. A metal material (Pt, Ba) weighed at a constant composition ratio is prepared. At this time, the composition ratio of the alloy is preferably such that the Ba content is 1 to 15wt%.

The form of the metal material is not particularly limited, and mainly uses a powder form, a block form may also be used. The metal material (Pt, Ba) is charged to the arc furnace, and the vacuum is extracted, followed by injecting high-purity Ar gas to the atmospheric pressure to start melting. Platinum-barium alloy solid solution has a large difference in specific gravity and melting point property, and melting is performed by using an arc furnace which can melt metal instantaneously to prevent the composition change during alloying process and to make a uniform alloy. In addition, since there is a high density difference between metals, it is very unlikely that homogeneous alloying will occur during solidification after melting. Therefore, the dissolution and solidification process should be repeated several times or more while changing positions to have a uniform metal body. In this process, Ba having a low melting point is easy to evaporate. Therefore, a certain amount of Ba metal should be added at the time of initial blending in consideration of the evaporated amount. As addition amount, it is preferable to add 10-15%. Repeated dissolution and solidification several times yields a very uniform metal body. Samples of different parts of the electron-emitting material can be taken and analyzed to confirm a uniform phase.

According to a preferred aspect of the present invention, in order to further facilitate the diffusion of Ba in the alloy, it is also possible to add 0.5 to 5 wt% of a third component made of a high melting point metal in the production of the Pt-Ba alloy. In the case of manufacturing such a ternary alloy, in order to reduce evaporation loss during metal material melting and to make the composition of the alloy more uniform, the alloy is first formed by obtaining a binary alloy between metals having similar melting temperatures and then adding the remaining elements. do.

As described above, after preparing a binary alloy of Pt-Ba or a ternary alloy further comprising a high melting point metal therein, cutting or molding to match the cathode structure of the CRT and a high melting point metal on the prepared electron emitting material. The metal film layer is formed.

The role of the metal film layer is as follows. That is, in the case of the ternary alloy, since the third component facilitates Ba diffusion to the surface, the initial characteristics of the electron emission may be very good, but when used for a long time, it may affect the life characteristics due to excessive evaporation of Ba. Can be. This phenomenon is the same as in the case of the binary alloy, the phenomenon occurs that the life characteristics are degraded when used for a long time. Therefore, a means for controlling this is required, and for this purpose, the evaporation of Ba can be controlled by forming a metal film layer of a high melting point metal on the surface. Specific control can be controlled by the particle size of tungsten, the thickness of the metal film layer and the like. Furthermore, such a metal film layer also lowers the work function of the surface so that the monoatomic layer of Ba is easily formed, and thus has a high electron emission characteristic at a low temperature.

Such The high melting point metal forming the metal film layer is preferably at least one selected from the group consisting of W, Mo, Nb, Ir, Os, Rh, and Ta. In the method of forming the metal film layer, the powder of the metal is mixed with a binder to form a paste, and then applied by various methods including a printing method, and the thus applied is sintered to form a high melting point metal film. The metal film layer is preferably in the form of a sintered body, and such a high melting point metal Powder Upon sintering, pores are secured, allowing barium atoms to diffuse more easily onto the surface, and also helping to form a barium monoatomic layer on the surface in a stable structure.

In addition, when the heat treatment is performed at too high a temperature, there is a fear that Ba inside the alloy may evaporate, so that a sintering aid may be added in order to sinter even at a low temperature. The thickness of the metal layer is suitably between 5 and 40um.

The negative electrode thus prepared is welded to the top of the container as shown in FIGS. 1 and 2 to complete the metal negative electrode.

Conventional oxide cathodes have a low current density of 2A / cm ² and have a very short lifetime when used continuously at high currents. On the other hand, the cathode can be used in the high current region with a current density of 6A / cm ² at an operating temperature of 950-1000 ℃ and guarantees a long life of more than 10,000 hours. Its use as a cathode is very high. In addition, it is compatible with the existing cathode structure, and the long-term exhaust aging required for the oxide cathode is very short. In particular, the aging process can be performed in less than 30 minutes, which is very efficient.

Hereinafter, the negative electrode of the present invention will be described in detail with reference to Examples.

Example 1

First, 10 g of platinum and 1.3 g of barium were placed in an arc induction copper pot. After the vacuum was drawn and the inside of the furnace was very clean, and the vacuum was maintained, high purity Ar gas was injected at atmospheric pressure, and then melting was started. After melting, the solidified metal was turned upside down and repeatedly melted and alloyed several times to obtain an alloy ingot. Samples were taken from different parts of the obtained alloy ingot and analyzed to confirm a uniform phase to obtain an alloy body. The alloy body thus obtained was cut by a diamond wire cutter and processed into an alloy plate having a constant thickness.

On the surface of the alloy plate obtained as described above, a tungsten spherical powder (average particle diameter of 5 micrometers), which is a heat-resistant metal, was added to iso amyl acetate in which 0.2 wt% of nitrocellulose was added as a binder. The mixed paste was printed to form a tungsten metal layer having a thickness of 10 micrometers, and heat-treated at 1,700 ° C. for 30 minutes in a reducing atmosphere.

The platinum-barium alloy with the heat resistant metal surface layer obtained as described above was cut into squares of 1 square millimeter size, and then laser welded to the sleeve to complete the metal cathode.

Example 2

A metal negative electrode was prepared in the same manner as in Example 1 except that 10 g of platinum, 1.3 g of barium, and 0.05 g of molybdenum were used as the alloying material.

The characteristics of each negative electrode prepared in Examples 1 and 2 were confirmed as follows.

In order to investigate the changed alloy structure when the heat-resistant metal was added to the platinum-barium alloy, samples were taken from each part of the ternary alloy prepared during the process of Example 2 of the present invention, and their uniformity was investigated. The results are shown in FIG. Figure 4 shows an enlarged 800 times the surface of the ternary alloy, it can be seen that the uniformity of the structure structure and the particle size distribution in the structure significantly improved.

In addition, the metal cathode prepared by using the alloy prepared as an electron-emitting material has better electron emission characteristics than other cathodes. In particular, as a result of investigating the electron-emitting characteristics of the tertiary alloy, the platinum element, barium, It was found that when the tungsten atoms were added at a ratio of about 2% of the number of platinum atoms as the third element and contained about 10% by weight, it showed the best electron emission ability. A layered structure is formed, which is believed to show excellent properties because it readily dissociates barium from the alloy.

In addition, in order to compare the life characteristics of the negative electrode and the oxide negative electrode prepared in Example 1, the result of the accelerated life test to enhance the 120% condition for the normal driving conditions is shown in FIG. In the graph of FIG. 6, the oxide cathode is about 60% after 2500 hours, but the metal cathode of the present invention is maintained at 90%, indicating that the life characteristics of the metal anode of the present invention are superior to that of the oxide cathode. .

That is, the negative electrode of the present invention is very excellent in the initial characteristics and the change is very small even over time. This is the basis of the efficient evaporation of barium, it can be seen that the operating temperature is reduced due to the platinum group coating on the double layer, it has a high current and a long life. On the other hand, the conventional metal cathode shows a tendency that the initial characteristics do not continue due to the continuous evaporation of barium, and similar characteristics to the impregnation type.

In addition, the performance of the cathode can be compared by numerical values such as the size of a work function, an electrical characteristic (electron emission ability), an operating temperature, etc., which is a limit energy capable of emitting electrons in a vacuum. The operating temperature is about 950 ℃, as shown in Figure 5 can be seen that the current density is 5-10A / cm ² level or higher than the impregnated cathode characteristics can be used for fixed tubular large CRT. In addition, as can be seen from Figure 5, the saturation current density is 7 ~ 10A / cm ² level at least three times higher current density than the oxide cathode is possible, so it can be used as an electron emission source, such as fixed tubules, large CRTs.

At the same time, the process applicability is also excellent, and in the case of the conventional oxide cathode, the activation process takes more than 500 minutes, but the cathode of the present invention is possible within 30 minutes, so the process was easy and reliable. Furthermore, because of the excellent stability due to external factors such as vacuum degree, gas, etc. in the CRT, the lifespan characteristics are further improved.

According to the metal negative electrode of the present invention, the alloy composition of the negative electrode is made uniform and a stable structure is maintained on the surface of the negative electrode to promote the diffusion and formation of barium, thereby lowering the operating temperature of the negative electrode and at the same time increasing electron emission characteristics of high current density. It enables the cathode for electron tubes which have.

In addition, since the operating temperature is similar to the impregnated cathode, it can be applied without changing the existing cathode manufacturing process, and thus the process compatibility is excellent, and it is more stable in the air than the conventional oxide cathode, so it is easy to handle and process, and the electron emission ability is higher than that of the oxide cathode. There is an advantage that the life characteristics are remarkably excellent.

Claims (7)

Alloys containing platinum and barium; And A metal cathode formed on top of the alloy, the metal film layer comprising at least one high melting point metal selected from the group consisting of W, Mo, Nb, Ir, Os, Rh, and Ta; . 2. The metal cathode for an electron tube according to claim 1, wherein the metal film layer made of the high melting point metal is in the form of a sintered body formed by sintering a metal powder. Alloys containing platinum and barium; A first metal film layer formed on the alloy and made of at least one high melting point metal selected from the group consisting of W, Mo, Nb, Ir, Os, Rh, and Ta; And And a second metal film layer including a platinum group metal or a rare earth metal formed on the high melting point metal film layer. The metal cathode for an electron tube according to claim 1 or 3, wherein the platinum-barium-based alloy comprises 85 to 99% by weight of platinum and 1 to 15% by weight of barium. The metal for electron tube according to claim 1 or 3, wherein the third component is an alloy formed by further comprising at least one high melting point metal selected from the group consisting of Mo, W, Nb, Ir, and Os. cathode. 6. The metal cathode for an electron tube according to claim 5, wherein the content of the third component in the alloy is 0.5 to 5 wt% based on the total alloy. 4. The metal cathode for an electron tube according to claim 3, wherein the first metal film layer is in the form of a sintered body formed by sintering a metal powder.