JPS60177528A - Tantalum filament excellent in durability and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the captioned filament in which deterioration due to ion impact and heating is reduced by forming a carbonized layer mainly composed of carbonized tantalum on the surface of metal tantalum for a filament while coating it. CONSTITUTION:Under the condition that metal tantalum is used for a filament 2' and hydrocarbon gas is introduced for gas G, arc discharge is performed between a chamber 4 and metal tantalum for fixed hours while current IF is made to flow to metal tantalum for forming a carbonized layer efficiently on the surface for coating it. Or by irradiating carbon ions, especially carbon ions generated from methane or ethane on the metal tantalum for the filament, the carbonized layer mainly composed of carbonized tatnalum is formed on its surface. The thickness of the carbonized layer can be changed according to the conditions of arc discharge and ion irradiation while the range 5-10mum is commonly sufficient.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tantalum filament and a method for manufacturing the same, and more particularly to a tantalum filament with excellent durability that is improved in deterioration due to ion bombardment and heating, and a method for manufacturing the same.

BACKGROUND ART Filaments made of tungsten, tantalum, niobium, etc. have been proposed as filaments for thermionic emission used in ion sources such as ion irradiation devices. Among these, tantalum filaments have a low work function (excellent electron emission ability), but are inferior to tungsten filaments in terms of melting point, lifespan, cost, etc., so they are rarely used in practice.

For example, taking a PIG type ion source as an example, the problems with conventional methods will be explained below. Figures 1 and 2 of the attached drawings show a PI in which a round rod-shaped filament (29) is arranged in an arc chamber (4) made of graphite or molybdenum, and an ion extraction TIl pole (6) is attached to the outside. This shows a G-type ion source.As shown in Fig. 3, the filament (29) is heated by passing a direct current through the power source vy to emit thermionic electrons, and the gas is injected from the gas injection port (51). gas G (for example, N
! , Ar, BFs.

H2, etc.] are ionized by the emitted thermionic electrons e under arc discharge (arc discharge TfL voltage is applied between chamber (4) and filament (2') by power source E), and the ionized gas G+ The structure is such that it can be accelerated and extracted as appropriate by an extraction electrode.

In this case, the arc current IA flows from the arc chamber (4) to the filament (2') as shown by the arrow, but the filament current IP also flows from the a end to the b end of the filament. M and Ko! This is a trivial matter, and together with the 1 unevenness of the external radiation, the current density in the filament becomes the maximum and the temperature becomes the highest.

In this case, if a tantalum filament is used as the filament (29), since it has a low melting point, it will be easily consumed by evaporation and ion bombardment near the b end in a short period of time, and will eventually melt. Tungsten filaments have been applied to such PIG type ion sources, but tantalum filaments, which have better electron emission characteristics than tungsten filaments, have not actually been used. At present, there is little consideration given to prolonging the service life through improvements in surface treatment and structure.

The present invention was made in view of this situation, and it is an object of the present invention to provide an improved tank/I/filament that can be used as a practical filament of the above-mentioned PIG type.

Thus, according to the present invention, there is provided a tankle filament with excellent durability, which is formed by coating the surface of tantalum metal for filament with a carbonized layer mainly composed of tantalum carbide, and a method for manufacturing the same.

As the tantalum metal for the filament of the present invention, tantalum metal in the shape of a straight round bar, which is usually available for filaments, is suitable.

A tantalum filament (1) of the present invention as shown in FIG. 4 can be obtained by coating the surface of such tantalum metal with a carbonized layer mainly consisting of tantalum carbide (Tag). In the figure, (2) shows a metal tantalum in the shape of a straight round rod, and (3) shows a carbonized layer mainly made of tantalum carbide coated on the outer peripheral surface of the tantalum.

Such tantalum filaments can be formed efficiently by using hydrocarbons, but the methods can be broadly divided into methods using arc discharge and methods using ion accelerators. The former is a method in which tantalum metal for filament is subjected to arc discharge in a hydrocarbon gas atmosphere to form a carbonized layer on its surface. As the hydrocarbon gas at this time, it is preferable to use methane gas or ethane gas.

The suitable processing time is usually about 0.3 to 0.5 hours. This method using arc discharge is based on the above-mentioned PI
Preferably, this is carried out in a G-type ion source.

That is, under conditions in which tantalum metal is used as the filament (29) and hydrocarbon gas is introduced as gas G, arc discharge is performed between the chamber (4) and the tantalum metal for a predetermined period of time while flowing the metal tantalum through the metal tantalum. At this time, a carbonized layer consisting of tantalum carbide is formed on the surface of the metal tantalum that comes into contact with the hydrocarbon gas, but in particular, the b-end in Fig. 3 is more dense than the central part and the a-end. Due to the high temperature, the tantalum carbide density of the carbonized layer in this part is denser, and a preferable tantalum filament is obtained.On the other hand, in the latter case, carbon ions, especially carbon ions generated from methane or ethane, are added to the tantalum metal for the filament. This is a method of forming a carbonized layer mainly made of tantalum carbide on the surface by irradiation.The carbon ions at this time can be supplied by any ion source known in the field of accelerated ion irradiation, not just the PIG type ion source mentioned above. can.

The thickness of the carbonized layer varies depending on the arc discharge conditions and ion irradiation conditions, but is usually sufficient in the range of 5 to 10 μm.

The carbonized layer mainly composed of tantalum carbide formed in this way is about 100% thicker than the base material, that is, tantalum.
It has a high melting point and high hardness even at 0°C.

Therefore, such a tantalum filament has excellent heat resistance and ion bombardment resistance, so even when used in a PIG type ion source, it does not wear out or melt, and its durability is significantly improved. The tantalum filament, which is manufactured on-site in the arc chamber intended for use in this field, has ideally improved durability due to the increased density of the carbonized layer corresponding to its high-temperature areas.

Therefore, the tantalum filament of the present invention has durability comparable to that of a tungsten filament.

Both tantalum and tantalum carbide have a lower work function than tungsten and superior electron emission ability.
Efficiency (electrons can be extracted, and power consumption can be reduced compared to tungsten filaments.

Although filaments using niobium metal also have the same problems as tantalum filaments, it has also been found that durability can be improved by carbonizing the surface.

Example 1 Tantalum rods with a diameter of 2111% and a length of 145 mm were
As shown in Figure 3, it is installed as a filament in a PIG type ion source, approximately 100 μm, 6.5 V (xy and Vν
2 x 10-” torr inside the chamber.
(The vacuum was about 10-' torr before introduction), and under these conditions, an average arc current of 1.5 A and 80 V (corresponding to I and V) was passed between the chamber and the filament, and the vacuum was about 30 torr. Arc discharge was performed for a minute. As a result, a carbide layer was formed on the surface of the tantalum filament, and the tantalum filament of the present invention as shown in FIG. 4 was obtained. The thickness of this carbonized layer is 5 μm on average (ma
x, 10 μm), and surface analysis was performed using X-ray diffraction, and the results are shown in the table below, which almost matches the characteristic values of tantalum carbide (Tag) on the A8TM card, indicating that this carbonized layer is formed from tantalum carbide. It was confirmed that Note that the measurement conditions were as follows.

A comparison will be made below between the case where the tantalum filament of the present invention obtained in this manner is used as it is as a filament of a 210 m ion source, and the case where a conventional tungsten filament and tantalum filament are used instead.

Table 1 (Required voltage, current and power) Thus, the power consumption of the tantalum filament of the present invention is reduced by about 20% compared to the tungsten filament under the same arc current, and the efficiency is increased. It can be seen that Furthermore, although the power consumption is slightly higher than that of conventional tantalum filaments, the arc current is about three times as high, indicating good efficiency.

On the other hand, when the conventional tantalum filament and the tantalum filament of the present invention were used for one hour, the weight loss of each filament was as follows.

As shown in Table 2, the decrease in the amount of M was reduced by about 40%, and it can be seen that the durability was significantly improved.

For reference, the melting point, hardness, sputtering rate, and work function of each material are shown in the table below.

As shown in FIG. 3, tantalum carbide has a higher melting point and hardness than tantalum, has a lower sputtering rate, and has a lower work function, so it has excellent electron emission characteristics. Therefore, the filament of the present invention has a filament of about 3
It is thought that the electron emission ability is twice as good, and therefore it can be operated at a lower temperature with less filament current to extract the same amount of electrons. The life of the filament is determined by the amount of sputtering and evaporation, but tantalum carbide has a better sputtering rate than tantalum metal and can be operated at lower temperatures, resulting in less evaporation.
It is thought that it will be possible to extend the service life to some extent. In addition,
When using the tantalum filament of the present invention for a long period of time, it is possible to further extend the life by changing the polarity midway through the use.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view illustrating a PIG type ion source in which the tantalum filament of the present invention can be used, FIG. 2 is a cross-sectional view of the same, FIG. FIG. 1 is a cross-sectional view illustrating a tantalum filament of the present invention. (1)... Tantalum filament, (21... Tantalum metal for filament, (3)...
・Carbonized layer. Figure 1 Figure 3F Figure 2 Figure 4

Claims (5)

[Claims] (1) A highly durable tantalum filament made by coating the surface of the filament metal tantalum with a carbonized layer mainly made of tantalum carbide. (2) A method for producing a highly durable tantalum filament, which is characterized by forming a carbonized layer containing tantalum carbide as a living body on the surface of tantalum metal by subjecting it to arc discharge in a hydrocarbon gas atmosphere. (3) The production method according to claim 2, wherein the hydrocarbon is methane or ethane. (4) A method for producing tantalum filaments with excellent durability, which comprises forming a carbonized layer mainly made of tantalum carbide on the surface of tantalum metal for filament by irradiating it with accelerated carbon ions. (5) The production method according to claim 4, wherein the accelerated carbon ions are carbon ions generated from methane or ethane.