JPS60202633A - Thermal cathode and its manufacture - Google Patents

Abstract

PURPOSE:To prevent deformation of a thermal cathode during its life by forming said thermal cathode with a filament which is a molybdenum alloy wire rod containing lanthanum oxide and platinum, and its crystal grain being immensely extended in the filament drawing direction in the aspect ratio not less than 3. CONSTITUTION:A sintered material of Mo containing La2O3 is made into a wire rod by a drawing process for making a V-shaped filament 1 or a filament coil 3 while being given heat treatment in the temperature range from 1,700-2,200 deg.C in a hydrogen gas flow followed by platinum plating and heat cementing in a benzene-hydrogen mixed gas flow for forming a thermal cathode. Accordingly, the crystal grain of a wire rod can be immensely extended in the drawing direction in the aspect ratio substantially not less than 3 when being drawn in the vertical direction, thus being able to suppress crystal grain growth during its life while removing life deterioration due to deformation, thus obtaining the thermal cathode having a stable emission property.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a hot cathode and a method for manufacturing the same.

[Technical background of the invention and its problems]

A high melting point hot cathode made of a tungsten alloy containing lanthanum oxide, which is similar to the so-called tricune cathode, has been proposed in Japanese Patent Application Laid-Open No. 50-39868. There is.

According to this publication, 120% more than the conventional tritan cathode
It is said that it is possible to obtain thermionic emission current (hereinafter referred to as emission) equivalent to that of a tritanium cathode at a temperature about 250°C lower.

In addition, another Japanese Patent Application Publication No. 51-91659 discloses an improvement in which a plating layer of platinum, palladium, rhodium, ruthenium, etc. is applied to the filament surface in order to promote the diffusion of lanthanum to the filament surface and improve emission characteristics. The technique is shown.

Furthermore, another Japanese Unexamined Patent Publication No. 54-146951 discloses a technique for prolonging the life of the hot cathode by separately providing a layer made of rhenium or the like, which can be called a diffusion suppression layer, inside the above-mentioned plated layer of platinum or the like. has also been proposed.

However, among the technologies disclosed in these publications, when we experimented with the hot cathode disclosed in Japanese Patent Application Laid-Open No. 50-39868, we found that the emission characteristics were not stable compared to the conventional tritanium cathode. It turned out to have points. In addition, in order to improve this emission characteristic, a plating layer such as platinum was provided on the surface of the JP-A No. 51-
When we experimented with the hot cathode disclosed in Publication No. 91659, we found that during a life test using a filament as a hot cathode, it sagged significantly due to its own weight (referred to as sag).
When we experimented with the hot cathode shown in No. 1-91659, we found that it had a large sag and large deformation, making it difficult to apply it to a hot cathode in the form of a thin wire coil.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a hot cathode that does not suffer from deterioration in life due to deformation and exhibits stable emission characteristics, and a method for manufacturing the same.

[Summary of the invention]

That is, the present invention provides a hot cathode comprising a filament in which crystal grains of a molybdenum alloy containing lanthanum oxide and platinum metal are elongated in the drawing direction of the filament with an aspect ratio of substantially 3 or more, and a molybdenum alloy. After molding the filament made of the alloy into a predetermined shape,
This is a method for producing a hot cathode, which is characterized in that the hot cathode is produced by heating at 2200° C. or lower.

[Embodiments of the invention]

The present invention is based on the knowledge that the deformation of a hot cathode during its life is closely related to the recrystallization of the filament material and the elongation of its crystal grains during its life. Later, before using it as a hot cathode, it is heated to a sufficiently high temperature to recrystallize and lengthen the crystal grains in advance, thereby suppressing crystal grain growth during its life and preventing deformation of the hot cathode during operation. It is done for the purpose of

Next, a detailed explanation will be given using examples.

[Example 1] A wire rod with a diameter of 9.5 am was formed by drawing a Mo sintered material containing 2 wt% of La2O3, and then a V-shaped filament with a side of 50 am as shown in Fig. 1 was made using this wire rod. (1) was produced. Then 1000 in a hydrogen stream
Heat treatment was performed for 10 minutes each in a temperature range of .degree. C. to 2000.degree. Next, the filament (1) pretreated at each temperature was plated with platinum to a thickness of 5 μm, and then heated and carburized in a benzene-hydrogen mixed gas flow. Next, both ends of this filament were attached to a pair of horizontally arranged electrodes, and electrical heating was performed in vacuum to reach the vacuum operating temperature of the hot cathode. The broken line (2) in FIG. 2 shows the results of measuring the relationship between the drooping characteristics (sag characteristics) due to the weight obtained at this time and the heat treatment temperature.

Note that the drooping characteristic is evaluated as follows.

That is, a current of 60% of the fusing current is applied to the wire to form the ■-shaped filament (1) shown in Figure 1, and then a current of 80% of the fusing current is applied for a certain period of time to form the top (1□).
Measure the difference between the two and compare it with the case where there is no deformation.1
It is shown as a sag value by 00 minutes display.

[Example 2] A wire with a diameter Q and 8 tnw produced in the same manner as in Example 1 was fabricated into a filament coil (3) with a coil diameter of 12 mm and a coil length of 57 mm as shown in FIG. Next, heat treatment was performed in a hydrogen stream at a temperature range of 1000°C to 2000°C for 10 minutes each. Next, the filament coil (3) pretreated at each temperature was coated with platinum to a thickness of 5 μm, and then heated and carburized in a benzene-hydrogen mixed gas flow. Next, both ends of this filament coil (3) were attached to a pair of electrodes, and they were heated under vacuum for 3 minutes to reach 1800℃, which is the vacuum operating temperature of the hot cathode.
Electrical heating was performed with N and OFF for 3 minutes. This 0N-OF
The amount of radial deformation of the filament coil (3) with respect to the number of times of energization heating is shown by the curve group (4) and (5) in Fig. 4.
, (6) and (7). However, the curve (4
) is 1300℃, curve (5) is 1500℃, curve (6)
The pretreatment temperature was 1700°C, and the curve (7) was 1900°C.

As is clear from FIG. 4, it can be seen that the amount of deformation can be extremely suppressed by performing pretreatment heating at 1700° C. or higher, and this is found to be in good agreement with the sag amount test results of Example 1.

When the cross-sectional structure of the wire was observed using an optical microscope based on the results of Examples 1 and 2, it was found that 1700'
It has been found that the crystal grains of the wire pre-heated at C or above consist of crystal grains that are elongated in the drawing direction and have an aspect ratio of substantially 3 or more when the drawing direction is the longitudinal direction.

As clarified in the examples above, if heat treatment is performed at 1700°C or higher as a pretreatment on a molybdenum alloy filament containing lanthanum oxide and platinum metal, a hot cathode with less deformation during operation can be obtained. can. The upper limit of the heat treatment temperature as pre-treatment was 2200°C. This is because if the temperature is increased beyond this level, the lanthanum temperature on the filament surface will drop, making it impossible to obtain sufficient emissions even after the operation starts. Furthermore, although platinum was used in the above-described embodiments, it is needless to say that other platinum metals may also be used.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a hot cathode that has a long life, exhibits stable emission characteristics, and has extremely little deformation in shape.

[Brief explanation of drawings]

Figure 1 is a side view showing the filament shape for the sag test.
Figure 2 is a graph showing the relationship between the sag value and the pretreatment temperature, Figure 3 is a side view showing the shape of the filament coil for repeated heating, and Figure 4 shows the amount of deformation of the filament coil shape with respect to the pretreatment temperature for repeated heating. It is a group of curves. 1 - V-shaped filament 3... Fi 1' Lament coil Agent Patent attorney Inoue -Male

Claims (2)

[Claims] (1) A hot cathode comprising a filament in which crystal grains of a molybdenum alloy wire containing lanthanum oxide and platinum metal are elongated crystal grains that are elongated in the drawing direction of the wire with an aspect ratio of substantially 3 or more. (2) After forming a filament made of a molybdenum alloy containing lanthanum oxide and platinum metal into a predetermined shape, heat treatment is performed at a temperature of 1700°C or higher and 2200°C or lower, so that the crystal grains of the molybdenum alloy are substantially reduced in aspect ratio. target 3
A method for producing a hot cathode characterized by forming long crystal grains that are elongated in the direction in which the filament is drawn.