JPH01211825A - Indirectly heated cathode for electron tube - Google Patents

Abstract

PURPOSE:To produce a cathode having high reliability by forming a black coat consisting of WC, ZrC or TiC on the internal surface of a metallic sleeve. CONSTITUTION:A heater 2 is placed within a metallic sleeve 1, an emitter 4, within a metallic cup 3, and a black 5 is formed on the internal surface of a metallic sleeve 1. The material of this black coat 5 is produced in form of slurry by dispersing g of the powder of WC, ZrC or TiC with an average particle diameter of 2mum in a solution comprising a mixture of methyl isobutyl ketone and nitrocellulose. It is advisable to mix therein 30-50weight% of the powder of W or Mo, or 50weight% at maximum of the powder of an inorganic binder. This slurry, after being stirred in a bowl mill, is subjected to rolling to be stabilized in the state of its dispersion, and the resultant slurry is injected into the metallic sleeve 1, dried, after allowing the excess to flow out and sintered in an hydrogen atmosphere at 1,600 deg.C for 30min. Then, on the internal surface of the metallic sleeve 1 is formed a heat absorbing membrane of WC with about 5mum in thickness that has such a high heat efficiency that the heater can operate at a lower temperature, thus allowing production of an indirectly heated cathode having high reliability for electron tube.

Description

[Detailed Description of the Invention] [Industrial Application Fields] The present invention has good thermal efficiency, requires low heater temperature,
This invention relates to an indirectly heated cathode for electron tubes that has a long life and is highly reliable.

[Prior Art] Indirectly heated cathodes for electron tubes, despite having various advantages over directly heated cathodes, are inferior in terms of thermal efficiency, and many efforts have been made to improve them. . For example, in Japanese Patent Application Laid-open No. 61-288339, a high melting point metal or its oxide powder and an inorganic binder are coated on the inner surface of a metal sleeve of an indirectly heated cathode and sintered, and the inner surface of the sleeve is coated with black heat absorbing material. The formation of a sexual membrane is disclosed.

[Problems to be Solved by the Invention] However, in the above conventional technology, the degree of blackening of the heat-absorbing film formed on the inner surface of the sleeve is not sufficient, and the electron-emitting material portion that is closely attached to the outside of the cathode sleeve However, there was a problem in that heating could not be achieved sufficiently efficiently by energizing the heater.

SUMMARY OF THE INVENTION An object of the present invention is to provide an indirectly heated cathode for an electron tube in which an electron-emitting material portion closely attached to the outside of a cathode sleeve can be heated more efficiently by a heater.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, a black coating made of WC, ZrC, or TiC is formed on the inner surface of the metal sleeve.

In general, metal carbide powder has a higher degree of blackness than metal powder if the particle size is the same. The inner surface of a metal sleeve blackened with metal carbide powder has a higher degree of blackness and higher heat absorption than the inner surface of a metal sleeve blackened with a high melting point metal or its oxide powder and an inorganic binder, so it is suitable for electron tubes. The thermal efficiency of the indirectly heated cathode can be sufficiently increased.

[Function] As described above, the metal carbide applied to the inner surface of the metal sleeve and sintered can increase the heat absorption rate of the metal sleeve compared to cases where the metal sleeve is blackened by other methods. As a result, an indirectly heated cathode for an electron tube with sufficiently good thermal efficiency can be obtained.

[Embodiment FIG. 1 is a diagram showing an embodiment of the present invention. A heater is inserted into the metal sleeve C, and an impregnated emitter (electron-emitting material portion) is housed in a metal cup closely attached to the top surface of the outer wall of the metal sleeve. This metal sleeve is made by pressing a molybdenum plate.

In Figure 1, 1 is a metal sleeve, 2 is a heater, 3
is a metal cup, 4 is an emitter (impregnated cathode pellet)
, 5 is a black coating according to the present invention.

In this example, WC powder with an average particle size of 2 μI was used, and 15 g of this WC powder was dispersed in a liquid containing 50 cc of methyl isobutyl ketone (MIBK) and 1 g of nitrocellulose to prepare a slurry. This slurry was stirred in a ball mill for about 100 hours and then rolled for about 50 hours to stabilize the dispersion state. This slurry was injected into a metal sleeve, the excess was poured out, and then dried.
Sintering was carried out in hydrogen at 00°C for 30 minutes. A heat-absorbing WC film with a thickness of approximately 5 μm was formed on the inner surface of the metal sleeve.

The heat-absorbing film thus formed could continue to operate stably even when continuously heated at an emitter temperature of 1000°C and a heater temperature of 1200°C in a high vacuum of 10-6 Pa or less. In contrast, in the conventional device, the temperature difference between the heater and the emitter was close to 300°C.

Although the reason is not clear, W or MO powder was added to WC, ZrC, or TiC powder for 30 to 30 minutes.
It was found that when a black film was formed by mixing 50% by weight, the stability after long-term use at high temperatures was improved and the efficiency of the heat-absorbing film was higher. However, whether the mixing amount is greater or less than the above range, the effect is no longer observed.

Furthermore, when a black film was formed by mixing powder of an inorganic binder, such as alumina, up to 50% by weight with any of the above metal carbide powders, a black film with extremely good adhesion was obtained. However, the amount of alumina added was limited to a maximum of 50%; adding more than that resulted in insufficient blackness and decreased thermal efficiency.

[Effects of the Invention] As explained above, according to the present invention, it is possible to obtain an indirectly heated cathode for an electron tube that has good thermal efficiency, requires low heater temperature, and is highly reliable.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention.

Claims (1)

[Claims] 1. In an indirectly heated cathode for an electron tube comprising a heater, a metal sleeve enclosing the heater, and an electron emitting material portion in close contact with the outside of the sleeve, on the inner surface of the metal sleeve, An indirectly heated cathode for an electron tube, characterized in that a black film made of WC, ZrC, or TiC is formed. 2. Indirect heating for an electron tube according to claim 1, wherein a black coating is formed on the inner surface of the metal sleeve by mixing 30 to 50% by weight of W or Mo powder with any of the metal carbide powders. shaped cathode. 3. Indirect heating for an electron tube according to claim 1, wherein a black film is formed on the inner surface of the metal sleeve by mixing up to 50% by weight of an inorganic binder powder with any of the metal carbide powders. shaped cathode.