WO2001035435A1

WO2001035435A1 - Electron tube cathode and method for manufacturing the same

Info

Publication number: WO2001035435A1
Application number: PCT/KR2000/001288
Authority: WO
Inventors: Gi Jin Kwon; Dae Sik Hwang; Young Ho Park
Original assignee: Orion Electric Co., Ltd.
Priority date: 1999-11-12
Filing date: 2000-11-10
Publication date: 2001-05-17

Abstract

An electron tube cathode and a method for manufacturing the same are hereby provided. In the electron tube, the fine uneven portion is formed on one of the surfaces of the base by electrochemical etching in a single electrochemical bath. Reducing metal is coated only on the convex portion of the uneven portion by electro-plating. Then, the sleeve of the cathode is welded to the base. Alternatively, before the sleeve of the cathode is welded to the base, the porous reducing metal layer may be formed on one of the surfaces of the base by electro-plating in a single electrochemical bath. By means of the method, the fine uneven portion and porous reducing metal layer can be easily and uniformly formed on the base.

Description

ELECTRON TUBE CATHODE AND METHOD FOR MANUFACTURING THE SAME

Background of the Invention 1. Technical Field

The present invention relates to an electron tube cathode. In particular, the present invention relates to an electron tube cathode with strengthened adhesion to the electron emissive material layer, and a method for manufacturing the same. The strengthened adhesion to the electron emissive material layer results from a reducing metal layer formed electrochemically upon the base before the sleeve and the base are welded.

2. Background Art

Generally, an electron tube cathode is used as a part emitting thermions as electron source in an electron gun of a cathode-ray tube for TV or a camera tube. The electron tube cathode is manufactured by forming an electron emissive material layer composed of electron emissive material layer upon the base. Fig. 1 illustrates an electron tube cathode in general type. As shown in Fig. 1, a heater 3 is placed in a sleeve 1 , and a base 5 is mounted on the upper aperture of the sleeve 1. The electron emissive material layer 7 is formed on the base 5. The sleeve 1 is made of nichrome.

The base 5 contains reducing materials such as silicon or magnesium (Mg) in the amount of 0.01 to 0.09wt%, and the main ingredient of the base is high-purity nickel

(Ni). The main ingredients of the electron emissive material layer 7 are alkaline earth metal oxides containing at least barium (Ba) and in addition strontium (Sr) or calcium (Ca). The electron emissive material layer 7 also contains rare earth metal oxides such as scandium oxide in the amount of 0.1 to 20wt%. The heater 3 heats electrically the electron emissive material layer 7 so that thermions may be emitted from the electron emissive material layer 7.

The process of forming the electron emissive material layer 7 in the electron tube cathode having the structure described above will now be briefly explained. First, barium carbonate (BaCOs). strontium carbonate (SrCOs), calcium carbonate (CaCOj) and a pre-determined amount of scandium oxide (SC2O3) are combined with a binder and a solvent to make suspension. The suspension is sprayed onto the base 5 to a thickness of about 800 μm thick. Then, the base 5 is heated by the heater 3 during the cathode ray tube's evacuating process. In this process, carbonates of alkaline earth metals are changed into alkaline earth metal oxides such as barium oxide (BaO), strontium oxide (SrO), and calcium oxide (CaO). Thereafter, a portion of alkaline earth metal oxides are reduced and activated in order to have the characteristic of semiconductor. Thus, the electron emissive material layer 7 composed of alkaline earth metal oxides and rare earth metal oxides is formed on the base 5. During the activation process, the reducing materials such as silicon or magnesium, contained in the base 5, move, by diffusion, toward the interface between the alkaline earth metal oxides and the base 5, and react with alkaline earth metal oxides. As a result of such reaction, a portion of the alkaline earth metal oxides formed on the base 5 are reduced to become an oxygen deficient semiconductor. Therefore, electrons may be easily emitted.

Conventionally, the life span of an oxide cathode is approximately 10,000 hours. Most magnesium is consumed within the first 2,000 hours. Thereafter, primarily, silicon is consumed as the reducing material. Among various different theories regarding the life span of cathodes, the representative theory is that the mobility of electrons decreases as the reducing materials are consumed and an intermediate layer is formed to prevent diffusion of the reducing materials and to increase the resistance as a nonconductor.

In the conventional cathode, the base is manufactured by processing nickel metal plate containing magnesium and silicon into a disk shape. After the sleeve and the base are welded, a carbonate layer, which is the electron emissive material layer, is formed on the base by a spray method. In order to strengthen the adhesion between the base and the electron emissive material layer, the surface of the base may be processed to become uneven through oxidation and reduction after the sleeve and the base are welded.

However, if many half- finished products after the welding of the base and the sleeve are simultaneously processed in one reactor for oxidation and reduction, each base would have a different degree of oxidation and reduction because the effect of heat treatment varies greatly depending on heat-treatment conditions such as flow rate of air or oxygen injected in the reactor during the process and the quantity or location of the half-finished products in the reactor. Also, it is very difficult to form uniform unevenness on the entire surface of the base. Furthermore, the management of the manufacturing process is very difficult. Additionally, because the heat-treatment of the half-finished products is conducted after the sleeve and the base are welded, if the heat-treatment involves any error, the base of the heat-treated half-finished products may not be easily restored to the original state prior to the heat-treatment. Thus, such half-finished products must be discarded, which causes big economic losses and increase of the unit costs. Moreover, because it takes a great amount of time to raise or lower the temperature of the reactor during heat-treatment, efficient management of tact time is difficult and the productivity decreases accordingly.

As an alternative, a reducing material layer may be formed on the base by a sputtering method prior to the coating of the carbonate layer. Additionally, a combination layer composed of carbonates and reducing materials may be formed on the base or a carbonate layer may be formed on the combination layer, which will lower the resistance of the nonconductive intermediate layer, for the purpose of prolonging the life span of the cathode.

However, in the method of forming a reducing material layer on the base by a sputtering method, the reducing material does not react uniformly to the base metal on the entire base metal during the vacuum evacuating and activating process. This renders uniform emission of electrons difficult. Moreover, in the method of forming a combination layer of reducing materials and carbonates on the base and then forming a carbonate layer on the combination layer, the management of such manufacturing process is not easy. Furthermore, if the entire electron emissive material layer is comprised of a combination of carbonates and reducing materials, irregularity in the cathode condition (CC) patterns may occur.

Mitsubishi Electric Corp. of Japan suggested a method of forming a reducing metal layer on the base using a sputtering method. An electron tube cathode according to such method, as illustrated in Fig. 2, is comprised of a heater 3 in a cylindrical sleeve 1 , a base 5 on the upper aperture of the sleeve 1 , a reducing metal layer 9 upon the base 5 formed by the sputtering, and an electron emissive material layer 7 formed on the metal layer 9. The reducing metal layer of a cathode formed by a sputtering method has inferior adhesion compared with the layer formed by electrochemical reaction. Moreover, if the deposition rate of the reducing metal layer is raised for the purpose of forming a porous reducing metal layer, the reducing metal layer becomes loose. This causes serious deterioration in the reducing metal layer. Additionally, because the sputtering process is conducted in vacuum, it takes a long time to form a reducing metal layer through the sputtering method and expensive equipment such as a vacuum system is required.

Japanese Patent Laid-Open No. Hei 11-102636, introduces a method of forming an electron emissive material layer on a base using a spray method and then flattening the electron emissive material layer mechanically using a device such as a press. This method, by improving the flatness of the electron emissive material layer, sharply cuts down moire phenomena. In this method, however, it is difficult to uniformly distribute the electron emissive material on the entire surface of the base because the electron emissive material layer is formed mechanically. Moreover, an adhesive coating material must be injected into the interface between the base and the electron emissive material layer because of the limited adhesion between the base and the electron emissive material layer, which further complicates the manufacturing process.

Disclosure of Invention

It is, therefore, an object of the present invention to provide an electron tube cathode, and a method for manufacturing the same, which can strengthen the adhesion between the base and the electron emissive material layer that the peeling of the electron emissive material layer may not occur.

It is another object of the present invention to provide an electron tube cathode, and a method for manufacturing the same, in which the electron emissive material layer is uniformly distributed on the entire surface of the base so that electrons may be emitted umformly.

It is still another object of the present invention to provide an electron tube cathode, and a method for manufacturing the same, by which, the management of the manufacturing process is facilitated, resulting in the raised processing stability and productivity.

To achieve the above object, the method for manufacturing electron tube cathode according to a preferred embodiment of the present invention comprises the steps of: forming a fine uneven portion on one of surfaces of a base by an electrochemical method; forming a reducing metal layer on the fine uneven portion by an electrochemical method; welding a sleeve to other surface of the base after said reducing metal layer is formed; and forming an electron emissive material layer on the reducing metal layer after the sleeve and the base are welded.

Preferably, the fine uneven portion is formed by an electrochemical etching and the reducing metal layer is formed by an electroplating. In order to further the fine uneven portion, electrochemical etching is conducted without stirring the electrolyte. It is also preferred to form the reducing metal layer by electroplating without stirring the electrolyte. Furthermore, it is preferable to form the fine uneven portion and the reducing metal layer in a single electrochemical bath. As the electrolyte in the electrochemical bath, at least one reducing materials such as tungsten, tantalum, molybdenum, titanium, magnesium or silicon may be used.

The electron tube cathode according to a preferred embodiment of the present invention comprises: a base having one of surfaces of which a fine uneven portion has been formed by electrochemical etching; a reducing metal layer formed on the fine uneven portion by electroplating; a sleeve welded to the other surface of the base after the reducing metal layer has been formed; and an electron emissive material layer formed on the reducing metal layer. The method for manufacturing the electron tube cathode according to another preferred embodiment of the present invention comprises the steps of: forming a porous reducing metal layer on one of surfaces of a base by an electrochemical method; welding a sleeve to other surface of the base; and forming an electron emissive material layer on the reducing metal layer.

Preferably, the reducing metal layer is formed by an electroplating.

It is preferred to conduct the electroplating without stirring the electrolyte in order to further the porosity of the reducing metal layer. Also, it is preferred to conduct the electroplating in the electrolyte of the pH not greater than 7 and at a voltage level higher than the conventional electroplating voltage by ImV to 5N. The electrolyte containing at lest one reducing materials such as tungsten, tantalum, molybdenum, titanium, magnesium or silicon may be used for the said reducing metal layer.

The electron tube cathode according to another preferred embodiment of the present invention comprises: a base having a plurality of surfaces; a porous reducing metal layer formed on one of the surfaces of the base by electroplating; a sleeve welded to other surface of the base after the reducing metal layer has been formed; and an electron emissive material layer formed on the reducing metal layer.

The present invention, using an electrochemical method, forms the fine uneven portion of one of the surfaces of the base before the base and the sleeve are welded, forms a reducing metal layer upon the fine uneven portion, or forms a porous reducing metal layer on the base. Consequently, the adhesion between the base and the electron emissive material layer is strengthened, preventing the peeling of the electron emissive material layer. Furthermore, the manufacturing process becomes stable and the unit cost may be lowered. Additionally, the time consumed for processing may be shortened and the productivity may be improved.

Brief Description of Drawings Fig. 1 is a cross-sectional view illustrating an electron tube cathode in general type.

Fig. 2 is a cross-sectional view illustrating a conventional electron tube cathode. Fig. 3 is a cross-sectional view illustrating an electron tube cathode according to a preferred embodiment of the present invention.

Fig. 4 is a process flow diagram illustrating the method for manufacturing an electron tube cathode according to a preferred embodiment of the present invention.

Fig. 5 is a structure diagram of a device for consecutive conducting of electrochemical etching and electroplating, applied to the method for manufacturing an electron tube cathode according to a preferred embodiment of the present invention.

Fig. 6 is a partial magnified diagram illustrating forming of the fine uneven portion and electro-deposition of the reducing metal particles in the method for manufacturing an electron tube cathode according to a preferred embodiment of the present invention.

Fig. 7 is a partial magnified diagram illustrating forming of fine uneven portion and electro-deposition of reducing metal particles further in the manufacturing process in the method for manufacturing an electron tube cathode according to a preferred embodiment of the present invention. Fig. 8 is a cross-sectional structure diagram illustrating an electron tube cathode according to another preferred embodiment of the present invention.

Fig. 9 is a process flow diagram illustrating the method for manufacturing an electron tube cathode according to another preferred embodiment of the present invention. Fig. 10 is a structure diagram of a device for consecutive conducting of electrochemical etching and electroplating, applied to the method for manufacturing an electron tube cathode according to another preferred embodiment of the present invention.

Fig. 11 is a partial magnified diagram illustrating a porous reducing metal layer in the method for manufacturing an electron tube cathode according to another preferred embodiment of the present invention.

Fig. 12 is a partial magnified diagram illustrating a porous reducing metal layer further in the manufacturing process in the method for manufacturing an electron tube cathode according to another preferred embodiment of the present invention.

Best Mode for Carrying Out the Invention

Reference will now be made in detail to preferred embodiments of the present invention's electron tube cathode and the method for manufacturing the same as illustrated in the accompanying drawings. Same numerals shall be given to the parts of the same structure and function as the conventional parts of the electron tube cathode.

Fig. 3 is a cross-sectional view illustrating an electron tube cathode according to a preferred embodiment of the present invention. As shown in Fig. 3, a heater 3 is placed in a cylindrical sleeve 1. A base 15 is mounted on the upper aperture of the sleeve 1. A reducing metal layer 17 is formed on the base 15 and an electron emissive material layer 19 is formed on the reducing metal layer 17.

Here, on the surface 16 of the base 15 at the electron emissive material layer 19's side, the fine uneven portion is formed. The fine uneven portion is formed by a electrochemical method such as electrochemical etching before the sleeve 1 and the base 15 are welded. The fine uneven portion is formed uniformly throughout the entire surface 16 and there are convex portion 115 and concave portion 125 in the fine uneven portion. The fine uneven portion strengthens adhesion between the base 15 and the electron emissive material layer 19, preventing peeling of the electron emissive material layer 19.

Metal particles 117 of the reducing metal layer 17 are deposited only to the convex portion 115, not to the concave portion 125 by electroplating. The reducing metal layer 17 may be composed of at least one group selected from the materials such as tungsten, molybdenum, tantalum, magnesium and silicon. The electron emissive material layer 19 is formed by a conventional method such as a spray method. The main ingredient of the electron emissive material layer is an alkaline earth metal oxide containing at least barium and in addition strontium and calcium. The electron emissive material layer also contains rare earth metal oxides such as scandium oxide in the amount of 0.1 to 20wt%. The base 15 contains reducing materials such as silicon or magnesium in the amount of 0.01 to 0.09wt% and the main ingredient of the base is high-purity nickel.

The method for manufacturing the electron tube cathode will now be explained with references to Fig. 4, Fig. 5 and Fig. 7 will also be referenced to for the convenience of explanation.

As shown in Fig. 4, before the sleeve and the base of an electron tube cathode are welded, the fine uneven portion is formed and the reducing metal layer is formed on the base in a single electrochemical bath in step S10. More specifically, as shown in Fig. 5, in step SI 1, the electrochemical bath 20 is filled with the electrolyte 21, and the opposing electrode 23 and a base 25 to be used as the base 15 illustrated in Fig. 3 are located vertically with a constant separation gap therebetween. The opposing electrode 23 and the base 25 are completely immersed in the electrolyte 21. As illustrated by the solid lines in Fig. 5, the base 25 is electrically connected to + terminal the first terminal of the power supply unit 30 and the opposing electrode 23 is electrically connected to - terminal the second terminal of the power supply unit 30.

An Electrolyte containing at least one reducing materials such as tungsten, tantalum, molybdenum, titanium, magnesium or silicon may be used as the electrolyte 21. As the opposing electrode 23, platinum electrode or carbon electrode, or an electrode containing at least one reducing material such as tungsten, tantalum, molybdenum, titanium, magnesium, or silicon may be used. The base 25 in this step is in the condition before it is welded to the sleeve. The surface 27 of the base 25 which should not be subject to electrochemical etching is protected by a contact prevention part 29 of insulating material, which prevents the surface from being exposed to the electrolyte 21 using a coating or packing method.

At this state, if the power supply switch of the power supply unit 30 is turned on and a voltage less than the hydrogen generation level is applied between the base 25 and the opposing electrode 23, the fine uneven portion begins to be formed on the surface 26 of the base 25 exposed to the electrolyte 21 by an electrochemical method such as electrochemical etching. In contrast, the other surface 27 of the base 25 does not form any fine uneven portion because the surface 27 is isolated from the electrolyte 21 by the contact prevention part 29.

At this time, as shown in Fig. 6, concave portion 115 and convex portion 125 of the fine uneven portion are created uniformly throughout the entire surface 26 of the base 25. If a voltage equal to or greater than the hydrogen generation level is applied between the base 25 and the opposing electrode 23, the surface 26 of the base 25 will have the furthered fine uneven portion compared with the case where a voltage less than the hydrogen generation level is applied.

Furthermore, while the electrochemical etching is in progress, if the electrolyte 21 is not stirred, materials in the electrolyte 21 are not easily transferred to the concave portion 125 in contrast to the convex portion 115. Therefore, furthered fine uneven portion with more developed convex portion 135 and concave portion 145 may be formed on the surface 26 of the base 25 as illustrated in Fig. 7. This makes it easy to deposit the reducing metal only to the convex portion 145 selectively in the following process of deposition of the reducing metal.

When the fine uneven portion is sufficiently formed on the surface 26 of the base 25, the power supply switch of the power supply unit 30 is turned off.

After the power supply switch of the power supply unit 30 is turned off, in step SI 3, the base 25 remains in the electrolyte 21 of the electrochemical bath. As shown as the dotted line in Fig. 5, the base 25 is electrically connected to - terminal the first terminal of the power supply unit 30 and the opposing electrode 23 is electrically connected to + terminal the second terminal, which is the contrary to the connection during the electrochemical etching.

Thereafter, when the power supply switch of the power supply unit 30 is turned on, at least one reducing metal among tungsten, tantalum, molybdenum, titanium, magnesium and silicon in the electrolyte 21 begins to be electrically deposited, by electroplating, to the surface 26 where the fine uneven portion has been formed. The reducing metal is deposited more quickly to the convex portion 115 on the surface 25 of the base 25 than to the concave portion 125. This is due to the much higher current density in the convex portion 115 than that in the concave portion 125. Thus, as illustrated in Fig. 6, for example, one reducing metal particle 117 is deposited selectively to each convex portion 115.

Moreover, if the formation of the fine uneven portion and the deposition of reducing metal is continued without stirring the electrolyte 21, the reducing metal material is not transmitted easily to the concave portion 145. Thus, the reducing metal materials are formed more easily on the convex portion 135. As a result, as illustrated in Fig. 7, six reducing metal materials 117 may be deposited selectively to the convex portion 135.

The thickness and density of the reducing metal layer 17 may be adjusted by controlling the quantity of the reducing material contained in the electrolyte 21 and the level of voltage and period of voltage application to the power supply unit 30. The reducing metal layer 17 may, thus, have a strong adhesion. It is difficult to suggest a definite number for the level of voltage and period of voltage application because the ideal level of voltage and period of voltage application differs depending on the type of electrode and electrolyte. Generally, however, it is preferred to have the applied voltage as high as a few volts above the standard voltage, and it is preferred to have the voltage applied approximately 10 seconds.

When the reducing metal materials are sufficiently deposited to the surface 26 of the base 25 to form the reducing metal layer 17 of the desired thickness shown in Fig. 3, the power supply switch of the power supply portion 30 is turned off and the base 25 is taken out of the electrolyte 21 in the electrochemical bath 20. Then, the electrolyte 21 remaining on the base 25 must be completed eliminated and the contact prevention part 29 must be separated from the base 25. If the base 25 is not in the shape of cap such as the base 13 shown in Fig. 3, it is necessary to process the base 25 in the shape of cap.

Thereafter, in step S20, the base 15 is welded to the upper aperture of the sleeve 1 shown in Fig 3 through a conventional method. In step S30, the electron emissive material layer 19 is formed on the base 15 through a spray method, for example. Thus, the electron tube cathode according to the present invention is completely manufactured.

Consequently, the preferred embodiment of the present invention, by forming a fine uneven portion on one of the surfaces of the base through the electrochemical etching prior to the welding of the base and the sleeve, strengthens the adhesion between the base and the electron emissive material layer and, by using the electroplating, forms the reducing metal layer selectively on the convex portion of the fine uneven portion only. Moreover, according to the preferred embodiment of the present invention, it is easy to form the fine uneven portion uniformly throughout the surface of the base resulting in the high stability in the manufacturing process.

Accordingly, it produces less base that should be discarded and saves the basic costs.

Furthermore, because the electrochemical etching and electroplating are conducted consecutively in the same device, the inconvenience accompanying to the moving of the base from the device for electrochemical etching to the device for electroplating is eliminated and the management of the manufacturing process becomes simple.

Additionally, the productivity improves because the time necessary for the process to form the fine unevenness is shortened.

The electron tube cathode and the method for manufacturing the same according to another preferred embodiment of the present invention will be explained hereinafter. Same numerals shall be given to the portions of the same structure and function as the electron tube cathode according to the above-described preferred embodiment of the present invention.

Fig. 8 is a cross-sectional structure diagram illustrating the electron tube cathode according to another preferred embodiment of the present invention. As shown in Fig. 8, a heater 3 is placed in a cylindrical sleeve 1. A base 45 is mounted on the upper aperture of the sleeve 1. A reducing metal layer 47 is formed on the base 45 and an electron emissive material layer 49 is formed on the reducing metal layer 47. According to the said another preferred embodiment of the present invention, the reducing metal layer is formed through an electrochemical method such as electroplating before the sleeve 1 and the base 45 are welded. During the electroplating, a large quantity of hydrogen is generated, forming the porous reducing metal layer. This porous reducing metal layer is formed uniformly throughout the surface 46 of the base 45 and provides the fine uneven portion to the surface 48 adjoining the electron emissive material layer 47. The fine uneven portion strengthens adhesion of the electron emissive material layer 49, effectively reducing the peeling of the electron emissive material layer 49.

The reducing metal layer 47 may be constituted by at least one reducing material selected from materials such as of tungsten, molybdenum, tantalum, magnesium and silicon. The electron emissive material layer 49 is formed by a conventional method such as the spray method. The main ingredient of the electron emissive material layer is an alkaline earth metal oxide containing at least barium and in addition strontium and calcium. The electron emissive material layer also contains rare earth metal oxides such as scandium oxide in the amount of 0.1 to 20wt%. The base 45 contains reducing materials such as silicon or magnesium in the amount of 0.01 to 0.09wt% and the main ingredient of the base is high-purity nickel.

The method for manufacturing the electron tube cathode will now be explained with references to Fig. 9. Same numerals shall be given to the portions of the same structure and function as the electron tube cathode according to the above-described preferred embodiment of the present invention. Fig. 10 and Fig. 11 will also be referenced to for the convenience of explanation.

As sown in Fig. 9, in step SI 10, before the sleeve and the base of an electron tube cathode are welded, the porous reducing metal layer is formed on the base in a single electrochemical bath, providing the fine uneven portion on one of the surfaces of the reducing metal layer.

More specifically, as shown in Fig. 10, in step SI 10, the electrochemical bath 20 is filled with the electrolyte 21 and the opposing electrode 23 and a base 55 to be used as the base 45 illustrated in Fig. 8 are located vertically with a constant separation gap therebetween. The opposing electrode 23and the base 25 are completely immersed in the electrolyte 21. The base 55 is electrically connected to - terminal the first terminal of the power supply unit 30 and the opposing electrode 23 is electrically connected to + terminal the second terminal of the power supply unit 30.

As electrolyte 21, any electrolyte containing at least one reducing material such as tungsten, tantalum, molybdenum, titanium, magnesium, or silicon may be used. Also, the electrolyte 21 is preferred to be of the pH not greater than 7.

As the opposing electrode 23, platinum electrode or carbon electrode, or an electrode containing at least one reducing material selected from reducing materials such as tungsten, tantalum, molybdenum, titanium, magnesium or silicon may be used. The base 55 in this step is in the condition before it is welded to the sleeve. The surface 57 of the base 55 which should not be subject to electroplating is protected by the contact prevention part 29 of insulating material, which prevents the surface from being exposed to the electrolyte 21 using a coating or packing method.

At this state, if the power supply switch not shown in the diagram of the power supply unit 30 is turned on and a voltage not less than the hydrogen generation level is applied between the base 55 and the opposing electrode 23, the reducing metal 147 selected among materials such as tungsten, tantalum, molybdenum, titanium, magnesium and silicon existing in the electrolyte 21 is electrically deposited uniformly to the surface 56 of the base 55 exposed to the electrolyte 21, as illustrated in Fig. 11. On the other hand, during the electrode reaction, when a large quantity of hydrogen is generated, the generated hydrogen edges into the reducing metal 157 on the surface 56 of the base 55 under the process of electroplating, forming the pinholes as illustrated in Fig. 12. In this manner, Fig. 8's porous reducing metal layer 47 is formed, offering a strengthened adhesion with the resulting fine uneven portion on the surface 48 of the reducing metal layer 47. The porous reducing metal layer 47 also prominently reduces the peeling of the completed electron tube cathode.

The quantity of hydrogen is determined by the pH of the electrolyte 21. The lower the pH is, the more hydrogen is generated.

Generally, hydrogen is generated at the anode and the standard electric potential for hydrogen generation reaction is 0 V in the reaction of 2H⁺ + 2e <-» H₂, or - 0.8277 V in the reaction of 2H₂O + 2e <- H₂ + 2OH^".

It is preferred, during the electroplating, that the voltage applied between the anode and the cathode is higher than the voltage used for the ordinary electroplating in order to expedite the deposition of the reducing metal.

Conventionally, if the applied voltage is high, the dendrite structure is formed. The electric field is concentrated to the convex portion generally and the reducing metal is transmitted more easily to the peak portion than to the concave portion. Thus, once the reducing metal is deposited to the convex portion, the reducing metal is deposited to the same portion at a high speed.

The thickness and density of Fig. 8's reducing metal layer 47 formed by the electroplating may be adjusted by controlling the quantity of the reducing material contained in the electrolyte 21 and the level of voltage and period of voltage application to the power supply unit 30. The reducing metal layer 47 may, thus, have a strong adhesion.

The applied voltage differs depending on the anode, the cathode and the electrolyte, but generally the voltage lower than 5V is applied for the electroplating. In the present invention, the voltage of 3 to 8V (which is higher than the conventional electroplating voltage of ImV to 5V) is applied for 1 to 20 seconds.

The standard electric potential for the metal used as reducing material is - 2.38V in the reaction of Mg²⁺ + 2e <-» Mg, or -1.75V in the reaction of Ti²⁺ + 2e <-» Ti.

On the other hand, the base metal, which comprises silicon together with magnesium, may be used for electroplating as well. For the silicon electroplating, nonaqueous electrolyte must be used because silicon has a very high (-) reducing electric potential. As the electrolyte, SiHCl₃, dissolved in the organic solvent such as tetrahydrofuran, is frequently used.

Thereafter, when the reducing metal material is deposited on the surface 56 of the base 55 sufficiently to have the thickness required for the porous reducing metal layer 47 of Fig. 8, the power supply switch of the power supply unit 30 is turned off and the base 55 is taken out of the electrolyte 21 in the electrochemical bath 20. Then, the electrolyte 21 remaining on the base 55 is completely removed and the contact prevention portion 29 is separated from the base 55.

If the base 55 is not in the form of cap, as illustrated by the base 45 in Fig. 8, but is in the plate form, it is necessary to have an additional step to process the base 45 in the form of cap as shown in Fig. 8.

In step SI 20, the base 45 is welded to the upper aperture of the sleeve 1 shown in Fig. 8, using a conventional method. In step SI 30, the electron emissive material layer 49 is formed on the base 45 through a spray method, for instance, completing the manufacturing process for electron tube cathode of the present invention. Consequently, according to the another preferred embodiment of the present invention, the porous reducing metal layer is formed on one of the surfaces of the base using the electroplating before the welding of the base and the sleeve, strengthening the adhesion between the base and the electron emissive material layer. Moreover, it is made easy to form the fine uneven portion on the surface of the reducing metal layer, which results in the high stability in the manufacturing process. Accordingly, it produces less base that should be discarded and thus saves the basic costs. Furthermore, because the reducing metal layer is formed quickly through the electroplating, the time required for the processing is shortened and the productivity is improved. Additionally, it is easy to manage the manufacturing process. The present invention is not limited to the drawings deposited hereto and the detailed description of the present invention. It shall be apparent to persons with conventional knowledge in the relevant field that the present invention may be modified or changed in various forms within the extent not exceeding the gist of the present invention claimed in the following claims.

Industrial Applicability

As explained above in detail, the electron tube cathode and the method for manufacturing the same according to the present invention forms the fine uneven portion on one of the surfaces of the base through electrochemical etching and then forms the reducing metal layer selectively on the convex portion of the fine uneven portion through electroplating in a single electrochemical bath. Thereafter, the sleeve and the base are welded. Alternatively, a porous reducing metal layer may be formed on the base by electroplating in an electrochemical bath and then the sleeve and the base ma\ be welded.

Therefore, according to the present invention, it is easy to form the fine uneven portion on the surface of the base or to form the porous reducing metal layer uniformh on the surface of the base. Resultantly, the stability in the manufacturing process is improved and the strengthened adhesion between the base and the electron emissive material layer prevents the peeling of the electron emissive material layer. Furthermore, the defective processing rate is reduced, producing less base to be discarded and saving the basic costs. Additionally, because the electrochemical etching and the electroplating are conducted consecutively in a same device, the manufacturing process may be easily managed. Moreover, the time required for the manufacturing process is shortened and the productivity is improved accordingly.

Claims

What is claimed is:

1 . A method for manufacturing an electron tube cathode, comprising the steps of: forming a fine uneven portion on one of surfaces of a base by an electrochemical method; forming a reducing metal layer on the fine uneven portion by an electrochemical method; welding a sleeve to other surface of the base after the reducing metal layer is formed; and forming the electron emissive material layer on the reducing metal layer after the base and the sleeve are welded.

2. The method for manufacturing the electron tube cathode according to claim 1 , wherein the line uneven potion is formed by an electrochemical etching.

3. The method for manufacturing the electron tube cathode according to claim 1 . wherein the reducing metal layer is formed by an electroplating.

4. The method for manufacturing the electron tube cathode according to claim 1 . wherein the fine uneven portion and the reducing metal layer are formed in a single electrochemical bath.

5. The method for manufacturing the electron tube cathode according to claim 4. wherein an electrolyte containing at least one reducing material selected from the materials of tungsten, tantalum, molybdenum, titanium, magnesium and silicon is used as an electrolyte in the electrochemical bath.

6. An electron tube cathode, comprising: a base having one of surfaces of which a fine uneven portion is formed by an electrochemical method; a reducing metal layer formed on the fine uneven portion by an electrochemical method: 5 a sleeve welded to other surface of the base after the reducing metal layer has been formed; and an electron emissive material layer formed on the reducing metal layer.

7. The electron tube cathode according to claim 6, wherein the fine uneven l () portion has been formed by an electrochemical etching.

8. The electron tube cathode according to claim 6, wherein the reducing metal layer has been formed by an electroplating.

15 9. A method for manufacturing an electron tube cathode, comprising the steps of: forming a porous reducing metal layer on one of surfaces of a base by an electrochemical method: welding a sleeve to other surface of the base; and forming an electron emissive material layer on the reducing metal layer.

20

10. The method for manufacturing the electron tube cathode according to claim 9. wherein the porous reducing metal layer is formed by an electroplating.

11. The method for manufacturing the electron tube cathode according to claim 10. 25 wherein the electroplating is conducted in an electrolyte of pH not more than 7.

12. The method for manufacturing the electron tube cathode according to claim 10. wherein the electroplating is conducted in the voltage level of 3 to 8 V.

13. The method for manufacturing the electron tube cathode according to claim 10. wherein the reducing metal layer is formed with an electrolyte containing at least one reducing material selected among materials such as tungsten, tantalum, molybdenum,

5 titanium, magnesium and silicon.

14. An electron tube cathode, comprising: a base having a plurality of surfaces; a porous reducing metal layer formed on one of the surfaces of the base by an l ϋ electrochemical method: a sleeve welded to other surface of the base after the reducing metal layer is formed; and an electron emissive material layer formed on the reducing metal layer.

15 15. The electron tube cathode according to claim 14, wherein the porous reducing metal layer has been formed by an electroplating.