JPH01272758A - Hot cathode - Google Patents

Abstract

PURPOSE:To manufacture a hot cathode excellent in thermal stress resistance and increased in the quantity of thermion emission by joining heat-resisting metal chips to both ends of a slender sintered compact of lanthanum hexaboride by a bonding agent composed principally of carbon powder and powdered heat- resisting inorganic matter. CONSTITUTION:A lanthanum hexaboride powder is sintered so as to be formed into a thermion emitter 1 (>= about 0.5mm square section, >= about 10mm length) of zigzag form. Subsequently, heat-resisting metal chips 3A, 3B (tantalum, etc.) of U-shaped sectional form are joined to both ends of the above thermion emitter 1 by using a bonding agent 2 prepared by mixing carbon powder (colloidal carbon, etc.) and a powder of heat-resisting inorganic matter (Ti powder, etc.) in the ratio of about 1:2. Further, linear metal chips 4A, 4B (tantalum, etc.) are welded to the above heat-resisting metal chips 3A, 3B, which is passed through a hole in an insulating supporting stand 5. By this method, the long-life hot cathode having thermal stress resistance and free from the occurrence of breakage during use can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a hot cathode that emits a large amount of thermionic electrons and is used in a thermionic generation source for an electronic shower device built into an ion implantation device.

(Prior Art and Problems) Conventionally, a hot cathode for an electronic shower device uses a high melting point metal such as tungsten as a thermionic emitter. However, a hot cathode made of metal has the disadvantage that the temperature at which it is used is high, so the thermionic emitter is consumed by seven shots, and its lifespan is short.

On the other hand, a hot cathode that uses a single crystal or sintered body of lanthanum hexaboride as the thermionic emitter has a long life and is widely used for electron microscopes, ion sources, etc. (Reference: K.
N. Leung: ' Directly heat
dLaB, cathodes for ton 5o
source operation''.

Vacuu+s/volu+ie 36/number
s 11/12/pages 865 t.

867/1986), for electron shower use, a directly heated hot cathode with a large surface area of the thermionic emitter is required in order to increase the amount of thermionic radiation.

However, such a hot cathode has the problem that it is difficult to fix the thermionic emitter, and the thermionic emitter is likely to chip due to the stress of thermal expansion during use. The object of the present invention is to provide a directly heated hot cathode that uses a thermionic emitter made of lanthanum hexaboride and has a structure that absorbs stress due to thermal expansion.

(Means for Solving the Problems) This invention uses a single elongated lanthanum hexaboride sintered body as a thermionic emitter, and both ends of the thermionic emitter are made of carbon powder and heat-resistant inorganic powder as main components. This is a hot cathode that is bonded to a heat-resistant metal piece via a bonding agent to form a current-carrying terminal.

In this invention, the thermionic emitter is a single elongated lanthanum hexaboride sintered body, and its shape does not matter as long as it has a cross-sectional area that can be used within the range of the current and voltage used.
There are various possibilities such as straight line, wave shape, meandering, etc., but the cross section is 0.5
It is preferable that the length on the m-square side is 10 mm or more.

In the case of a waveform, it is preferable that the waveform has rounded turns, has as many turns as possible, and has a large amplitude. Further, it is preferable that there is a sufficient distance between the turns so that they do not come into contact with each other when thermally expanded.

The carbon powder contained in the bonding agent is preferably colloidal carbon having a particle size of 0.01 to 20 μm. The heat-resistant inorganic powder has a high melting point, and when it is mixed with carbon powder and heated in an inert atmosphere, it reacts with a portion of the hexaboride and a portion of the heat-resistant metal piece that it comes into contact with, forming a dense bonding layer. Preferably, those that form. Such inorganic substances include titanium, zirconium,
These include high-melting point metals such as tantalum, niobium, hafnium, vanadium, rhenium, and rare earth metals, boron carbide, and borides, carbides, silicides, and nitrides of the above metals. Among these inorganic substances, titanium carbide is particularly popular. preferable.

The heat-resistant metal piece is a high-melting point metal such as tantalum, molybdenum, or tungsten. The shape of the heat-resistant metal piece is not particularly limited, but it is preferable to have a U-shaped cross section so as to easily hold the thermionic emitter.

To fix the hot cathode to the device used, heat-resistant metal pieces are bonded to both ends of the thermionic emitter and fixed to an insulating support. The heat-resistant metal piece and the insulating support may be fixed directly by screwing or the like, or a metal piece may be interposed between the heat-resistant metal piece and the insulating support.

In order to conduct electricity to the heat-resistant metal piece, a conducting wire may be connected directly to the heat-resistant metal piece, or when the above-mentioned intervening metal piece is used, a conducting wire may be connected to the metal piece. In the latter case, the shape of the metal piece is preferably a round or flat wire that is as thin as possible within the range that can withstand the current and voltage used, and has as much flexibility as possible. Welding is preferably used to connect the heat-resistant metal pieces to each other.

The insulating support is preferably made of ceramics such as boron nitride or aluminum oxide.

(Example) 1 and 2 show the hot cathode of this invention.

First, a plate obtained by sintering lanthanum hexaboride powder was cut using a wire-cut electric discharge machine to obtain a meandering thermionic emitter l. Its cross-sectional area is 1mm” and its length is 64
He was drunk.

Bonding agent 2 was applied to both ends of the thermionic emitter, and the body was sandwiched between tantalum heat-resistant metal pieces 3A and 3B each having a U-shaped cross section. The bonding agent was produced by mixing colloidal carbon (Nippon Powder Yagyu Co., Ltd. trade name Hitasol) and titanium powder at a volume ratio of 1:2 and kneading the mixture with water.

One end of the tantalum linear metal pieces 4A, 4B is welded to the heat-resistant metal pieces 3A, 3B, and the hot cathode thus obtained is inserted into holes drilled at both ends of the insulating support base 5. It was attached to an electronic shower device, and the electronic shower device was incorporated into an ion implantation device. After evacuating the ion implanter to lXl0-'Torr,
The input voltage to this hot cathode is 12V, and the filament current is 45A.
Electricity was applied under these conditions to operate the electronic shower device. This state was maintained for 300 hours, but there was no abnormality in the thermionic emitter, and there was no abnormality in the joint with the heat-resistant metal piece. Further, when the influence of thermal expansion was examined by turning the power ON and OFF 10 times in a 10-minute cycle, the thermionic emitter was found to be normal with no chipping.

(Effects of the Invention) Although the hot cathode of the present invention is a directly heated type with a relatively large thermionic emitter, it can withstand thermal stress, does not chip during use, and has a long life.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of the hot cathode of the present invention, and FIG. 2 is a perspective view of a part thereof. Code: 1... Thermionic emitter 2... Bonding agent 3A, 3B... Heat resistant metal piece 4A, 4B... Metal piece 5... ...Insulating support stand patent applicant Denki Kagaku Kogyo Co., Ltd. Figure 1 Figure 2

Claims (1)

[Claims] A single elongated lanthanum hexaboride sintered body is used as a thermionic emitter, and both ends of the thermionic emitter are bonded to a heat-resistant metal piece through a bonding agent whose main components are carbon powder and heat-resistant inorganic powder. The hot cathode is used as a current-carrying terminal.