JPH10302713A - Cathode for discharge tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the evaporation of cathode material, provide a high output, stable light emission, as well as a long life span, and simplify manufacturing process. SOLUTION: For example, a cathode material is formed by mixing metallic power with a high melting point such as tungsten of 45-95 wt.%, hafnium oxide power with a high melting point of 5-30 wt.%, and rhenium power of 0-25 wt.% or chemical compound power containing rhenium and alkali earth metals (101), this cathode material is used to form a cathode body with sharp edge by press mold (102), thereafter making it a cathode by sintering (103). This suppresses sputter and the evaporation of cathode material, as well as prevents the recrystallization of metal with a high melting point and hafnium oxide, so that a high-output emission as well as longer life span can be provided. Further, it eliminates an existing complicated process of the fusion impregnation for barium aluminate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the composition and structure of a discharge tube cathode which is used for a discharge tube cathode, in particular, a rare gas discharge tube, and which is optimal for emitting high-power and stable ultraviolet light.

[0002]

2. Description of the Related Art In general, a cathode used for a rare gas discharge tube is manufactured as follows. First, a high melting point metal powder such as tungsten or molybdenum is press-molded into a cathode shape and then sintered to form a porous substrate having a porosity of 20 to 30%. Next, BaCO _3- was added to the porous cathode molded body.
A barium aluminate made of a powder of CaCO ₃ —Al ₂ O ₃ is melt-impregnated, and a surplus electron-emitting substance attached to the surface is mechanically removed, whereby a cathode is completed.

[0003]

However, since the melting point of the barium aluminate impregnated at the time of manufacture is low in the cathode for a discharge tube, the cathode is particularly liable to be sputtered and evaporated, thereby causing contamination of the tube wall of the discharge tube. However, there is a problem that the light emission amount is limited to a low level. Further, the light emitting state was unstable, and the life was short.

Further, the above barium aluminate process is complicated and the yield is not so good.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to reduce the evaporation of a cathode material, to obtain a stable light emission at a high output, to obtain a long life, and to provide a manufacturing process. To provide a cathode for a discharge tube which can simplify the above.

[0006]

In order to achieve the above object, a cathode for a discharge tube according to the present invention comprises at least a refractory metal powder and a hafnium oxide powder or a mixture of the hafnium oxide and an alkaline earth metal. A cathode material is prepared by mixing the compound powder with the compound powder, a cathode body having a sharp tip is formed from the cathode material, and then the cathode body is sintered. The invention according to claim 2 is characterized in that rhenium powder or a compound powder containing this rhenium and an alkaline earth metal is added as the cathode material in order to prevent recrystallization of the refractory metal and the hafnium oxide. And In the invention of the second aspect, it is preferable to adopt the composition of the following third to fifth aspects. That is, the invention of claim 3 is characterized in that the high melting point metal powder is 45 to 9
5% by weight, 5% to 30% by weight of the hafnium oxide powder, and 0% to 25% by weight of the rhenium powder or the compound powder containing rhenium and an alkaline earth metal. According to a fourth aspect of the present invention, the high melting point metal powder is
5 to 98% by weight, the compound powder containing hafnium and alkaline earth metal is 2 to 10% by weight, and the rhenium powder is 0 to 25% by weight. According to a fifth aspect of the present invention, the high melting point metal powder is 80 to 96% by weight.
The oxide powder containing hafnium is 2 to 10% by weight, and the compound powder containing rhenium and alkaline earth metal is 2 to 10% by weight.

According to the above construction, the cathode material in which the respective powders are mixed is press-molded to form a cathode body, and then the cathode body is sintered, and the electron-emitting substance is replaced with an alkaline earth metal as in the prior art. , But mainly composed of hafnium oxide having a high melting point and a low vapor pressure, it is possible to obtain a cathode which is less susceptible to spatter, and to prevent deterioration due to contamination of the tube wall. Therefore,
It is possible to obtain a stable light emitting state with high output.

Further, by adding rhenium powder or a compound powder containing this rhenium and an alkaline earth metal to the above-mentioned cathode material, recrystallization of the high-melting-point metal and hafnium oxide can be prevented, and high-power and stable power can be obtained. Light emission can be maintained, and a long-life cathode can be obtained.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a manufacturing process of an arc type discharge tube cathode according to an embodiment, FIG. 2 shows a shape of the cathode, and FIGS. The composition weight% of the cathode material in the examples is shown. In FIG. 1, first, in step 101, a cathode material is prepared by mixing a high melting point metal powder and an electron-emitting substance. As the high melting point metal (base metal), tungsten, molybdenum, ruthenium, iridium, osmium, etc. Is used. Also,
Hafnium oxide (HfO) is used as the electron-emitting substance.
₂ ) or a compound containing this hafnium oxide and an alkaline earth metal, for example, Bax HfO ₂ y Oz (x, y, z
: Integer).

Further, in the embodiment, in order to prevent the above-mentioned refractory metal and hafnium oxide from recrystallizing after production, rhenium powder or a compound powder containing this rhenium and alkaline earth metal is used as a cathode material. Mixed. That is, the refractory metal and the hafnium oxide tend to recrystallize at high temperatures, and the change in the crystalline state causes a disadvantage that the output is reduced, the emission becomes unstable, or the life is short. Therefore, in this example, rhenium or a rhenium compound is added to solve the above-mentioned disadvantage.

FIG. 3 shows a first embodiment of the cathode material. In the first embodiment, a powder of the high melting point metal M (M: tungsten, molybdenum, ruthenium, iridium, osnium, etc.) is used for 45 minutes. To 95% by weight, the hafnium oxide powder to 5 to 30% by weight, the rhenium (Re) powder to 0 to 25% by weight, and mixing these powders to form a cathode material. The composition ratio of this powder is obtained by using the point at which the resistance value of the refractory metal of the manufactured cathode rises as a critical point.

That is, since the above-mentioned hafnium oxide is an insulating material, it is necessary to consider not only the weight ratio but also the volume ratio in the design stage. In other words, it is important to consider the particle size and number of high melting point metal or hafnium oxide. On the other hand, instead of selecting each of these factors, if each powder is uniformly distributed, the state where the particles of the refractory metal are continuous without being isolated has a low resistance value and is isolated. In such a case, the resistance value increases. Therefore, paying attention to this, the point at which the resistance value increases can be set as the critical point of the weight ratio.

Next, in step 102, a cathode body having a sharp tip as shown in FIG. 2 is formed by a mechanical press, hydrostatic pressure or the like using the mixed and prepared cathode material. The cathode body 10 in the case of FIG. 2A has a trapezoidal conical shape having an apex 10T, and is formed so as to embed the electrode rod 12 on the bottom surface side. In this case, the apex 10T Is the discharge point.

The cathode body 14 in the case of FIG.
It has a truncated conical shape having 4T, and is similarly formed by embedding the electrode rod 12 on the bottom side. This cathode body 14
Compared with the cathode body 10 shown in FIG. 2A, a high emission output can be obtained because of having a wide top surface 14T. The cathode body 16 in the case of FIG. 2 (C) has a truncated conical shape with a trapezoid, has a cylindrical concave portion 16S formed on the top surface, and the electrode rod 12 is embedded on the bottom surface side. In the cathode body 16, the upper circumferential edge 16T serves as a discharge portion, and has a linear discharge portion instead of a dot, so that a similarly high light emission output is obtained.

In the next step 103, the cathode bodies 10, 14, 16 formed of the above-mentioned cathode material are sintered. This sintering is performed in a vacuum or reducing atmosphere at about 2000-260.
In this temperature range, appropriate mechanical strength can be obtained, and the porosity of the porous body can be adjusted in the range of 5 to 40%, depending on the particle size distribution and the like of the raw material powder. It is possible. According to the sintering step 103, a porous sintered body (cathode bodies 10, 1) in which particles of hafnium oxide, which is an electron-emitting substance, are scattered and distributed in the high-melting-point metal particles.
4, 16) were obtained.

In the last step 104, the cathode bodies 10, 14, 16 which are sintered bodies are subjected to a surface treatment such as plasma cleaning, and the surplus electron-emitting substance adhering to the surfaces of the cathode bodies 10, 14, 16 is physically removed. And mechanically removed.

According to the cathode (10, 14, 16) of the first embodiment manufactured as described above, hafnium oxide having a high melting point and a low work function is used as the electron-emitting material, and the sintered porous material is used. Rather than impregnating the body with barium aluminate or the like, the respective material powders are mixed in advance and then press-formed, and the formed cathode body is sintered, so that evaporation by sputtering is less likely to occur. That is, the cathode used in the rare gas discharge tube is evaporated by thermal action or by sputtering (ion bombardment), and the main components of evaporation are barium and barium oxide. However, in this example, since these substances are not contained and hafnium oxide having a high melting point and a low vapor pressure is contained, no evaporation problem occurs.

The addition of rhenium raises the recrystallization temperature of the refractory metal and hafnium oxide, so that a higher output, more stable and longer life cathode for a discharge tube can be obtained. Furthermore, there is an advantage that the conventional melt impregnation step of barium aluminate or the like can be omitted in the production process.

FIG. 4 shows a second embodiment of the composition of the cathode material. This second embodiment uses Bax Rey O, a compound containing barium and rhenium, instead of rhenium.
z (x, y, z: integer). That is, the powder of the high melting point metal M is 45 to 93% by weight, the powder of hafnium oxide is 5 to 30% by weight, and the powder of Bax Rey Oz is 2%.
To 10% by weight. This weight percent, as described above,
The point at which the resistance value of the refractory metal M becomes high (isolated) is set as a critical point.

In the second embodiment as well, each material powder is mixed, molded and then sintered, and barium is contained in Bax Rey Oz. , And rhenium, it has a large binding energy. Therefore, the evaporation of barium hardly occurs, and the same effect as in the first embodiment can be obtained.

FIG. 5 shows a third embodiment of the composition of the cathode material, which is a compound containing barium and hafnium oxide instead of hafnium oxide instead of hafnium oxide.
axHfO ₂ y Oz (x, y, z: integer). That is, the high melting point metal M powder is 65 to 98% by weight, the Bax HfO ₂ y Oz powder is 2 to 10% by weight, and the rhenium powder is 0 to 25% by weight. Also in the third embodiment, each material powder was sintered after being mixed and molded, and barium was not Bax HfO ₂
Since y Oz is contained in the compound, the binding energy is large, and the same effect as in the above embodiment can be obtained.

FIG. 6 shows a fourth embodiment of the composition of the cathode material. In the fourth embodiment, both hafnium oxide and rhenium are compounds containing barium. That is, 80 to 96% by weight of the powder of the high melting point metal M, ₂ to 10% by weight of the powder of Bax HfO ₂ y Oz which is an oxide powder containing hafnium, and B is an oxide powder containing rhenium.
ax Rey Oz powder is 2 to 10% by weight. Also in the fourth embodiment, it is difficult to receive spatter for the above-mentioned reason, and the problem of evaporation does not occur.

[0023]

As described above, according to the present invention,
At least, a high melting point metal powder, a high melting point hafnium oxide powder or a compound powder containing this hafnium oxide and an alkaline earth metal is mixed to produce a cathode material, and a cathode body is press-molded using the cathode material, After that, since this was sintered, spatter hardly occurred, evaporation of the cathode material was reduced, and stable light emission with high output can be obtained.
In addition, there is an effect that the life is extended.

Further, a complicated step of melting and impregnating barium aluminate, which is a conventional step, can be eliminated, and the manufacturing process can be simplified, the yield can be improved, and a highly reliable cathode can be obtained. It becomes possible.

According to the invention of claim 2, rhenium powder or a compound powder containing this rhenium and an alkaline earth metal is added as the cathode material, so that recrystallization of the high melting point metal and hafnium oxide is prevented. Therefore, there is an advantage that stable light emission at a high output and a longer life can be further promoted.

[Brief description of the drawings]

FIG. 1 is a view showing a manufacturing process of a cathode for a discharge tube according to an embodiment of the present invention.

FIG. 2 is a view showing various shapes of a cathode shape in the embodiment.

FIG. 3 is an assembly weight percentage of the cathode material of the first example of the embodiment.
FIG.

FIG. 4 is an assembly weight percentage of the cathode material of Example 2 of the embodiment.
FIG.

FIG. 5 is an assembly weight percentage of the cathode material of Example 3 of the embodiment.
FIG.

FIG. 6 is an assembly weight percentage of a cathode material of Example 4 of the embodiment.
FIG.

[Explanation of symbols]

 10, 14, 16: Cathode, 12: Electrode, M: High melting point metal powder.

Claims (5)

[Claims] 1. A cathode material is prepared by mixing at least a refractory metal powder and a hafnium oxide powder or a compound powder containing the hafnium oxide and an alkaline earth metal, and a cathode body having a sharp tip is formed using the cathode material. A cathode for a discharge tube, which is molded and then sintered. 2. A method according to claim 1, wherein said cathode material comprises rhenium powder or a compound powder containing said rhenium and an alkaline earth metal in order to prevent recrystallization of said refractory metal and said hafnium oxide. The cathode for a discharge tube according to claim 1. 3. The method according to claim 1, wherein the refractory metal powder is 45 to 95% by weight
And the hafnium oxide powder is 5 to 30% by weight,
3. The cathode for a discharge tube according to claim 2, wherein said rhenium powder or a compound powder containing rhenium and an alkaline earth metal is 0 to 25% by weight. 4. The high melting point metal powder is 65 to 98% by weight.
The compound powder containing hafnium and an alkaline earth metal is set to 2 to 10% by weight, and the rhenium powder is set to 0 to 2% by weight.
3. The cathode for a discharge tube according to claim 2, wherein the content is 5% by weight. 5. The high melting point metal powder is 80 to 96% by weight.
The cathode for a discharge tube according to claim 2, wherein the oxide powder containing hafnium is 2 to 10% by weight, and the compound powder containing rhenium and an alkaline earth metal is 2 to 10% by weight. .