JP5672585B1 - Discharge lamp - Google Patents

Abstract

In a discharge lamp in which an emitter other than thorium is added to a cathode, it is possible to prevent the emitter from being excessively evaporated from the tip of the cathode and deplete at an early stage, and to smoothly supply the emitter to the tip of the cathode. Providing such a structure. A main body portion 31 of a cathode 3 is made of a refractory metal material not containing thorium, and a tip portion 32 is made of tungsten containing an emitter (excluding thorium), and the main body portion and / or the tip portion. A sintered body 34 containing an emitter (excluding thorium) with a higher concentration than the emitter concentration at the tip is embedded in a sealed space 33 formed inside, and the grain boundary density of tungsten at the tip: The product of A (mm-1) and the concentration gradient of the emitter from the portion in contact with the sintered body at the tip to the tip surface: B (mol / mm4) is 260 to 10-9 (mol / mm5). ) A? B? 670-10-9 (mol / mm5). [Selection] Figure 2

Description

  The present invention relates to a discharge lamp including an emitter for improving electron emission at a cathode, and particularly to a discharge lamp including an emitter other than thorium.

In general, in a high-input and high-intensity discharge lamp or the like, an emitter is added to the cathode in order to facilitate electron emission, and thorium oxide (ThO ₂ ) is often used as the emitter. It had been.
However, thorium is subject to legal regulations as a radioactive substance, and careful management is required for its management and handling. Therefore, an alternative substance to replace thorium is desired.

Electrodes using rare earth elements or their compounds as emitters have been proposed as substitutes for the thorium oxide.
Rare earth elements are low in work function (generally indicating the amount of energy required when electrons jump out from the surface of the material), are excellent in electron emission, and are expected as substitutes for thorium. .
In Japanese translations of PCT publication No. 2005-519435 (Patent Document 1), tungsten as a cathode material is additionally used as an emitter as lanthanum oxide (La ₂ O ₃ ), hafnium oxide (HfO ₂ ), zirconium oxide (ZrO ₂ ). A discharge lamp containing the above is disclosed.

However, rare earth oxides such as lanthanum oxide (La ₂ O ₃ ) have not been practically used in a high input region where the lamp power exceeds 1 kW.
That is, rare earth oxides are relatively easy to evaporate because they have a higher vapor pressure than thorium oxide (ThO ₂ ). Therefore, when a rare earth oxide is used instead of thorium oxide as an emitter to be contained in the cathode, the rare earth oxide is excessively evaporated and depleted at an early stage. Due to the exhaustion of the emitter, the electron emission function at the cathode is lowered, and there is a problem that flicker occurs and the lamp life is shortened.

In addition, only the emitter that contributes to the electron emission characteristics is present at the tip of the cathode, and it can be said that this is because the transport from the cathode rear end toward the tip is not performed quickly.
Furthermore, the emitter contained in the state of oxide inside the cathode is reduced to a metal state and supplied as an emitter when the temperature rises during the operation of the discharge lamp. In order to reduce the oxide, a certain amount of temperature rise is required. However, when this is done, it takes time to supply the emitter at the start of lighting, which causes the emitter to be depleted.

Japanese Patent Application Laid-Open No. 2005-183068 (Patent Document 2) discloses a structure in which a sealed space is formed inside a cathode and a metal emitter is enclosed therein. This document proposes the possibility of vapor phase diffusion inside the cathode.
However, the relationship between the diffusion of the emitter from the sealed space to the cathode tip in the solid, the diffusion path, and the emitter concentration gradient is not taken into consideration, and the optimum emitter diffusion to the cathode tip is achieved under any conditions. It is unclear.
Furthermore, since no emitter is added to the cathode body, when the lamp is initially turned on, the cathode tip is lit without supply of the emitter, and the lighting startability at the time of the initial lighting is poor. There is also a problem that tungsten evaporates and causes blackening.

As described above, in a discharge lamp using an emitter material other than thorium, there are still problems such as unstable lighting at an early stage. In particular, in a high input discharge lamp of 1 kW or more, it is remarkable that the rare earth element vapor leads the discharge lamp to unstable lighting.
As described above, since thorium used in the past was an excellent emitter material, discharge lamps using rare earth elements as an alternative to it have performance equivalent to that using thorium. The current situation is that it has not reached.

JP 2005-519435 A JP-A-2005-183068

  In view of the above-mentioned problems of the prior art, the present invention provides a discharge lamp in which a cathode and an anode are arranged opposite to each other inside an arc tube, and even if an emitter other than thorium is added to the cathode, Prevents depletion, maintains the electron emission function for a long time, and prolongs the flicker life of the lamp, facilitates the supply of the emitter from the rear of the cathode to the tip surface, and at the time of initial lighting The present invention aims to provide a structure excellent in lighting startability and to realize a discharge lamp using an emitter other than thorium.

In order to solve the above problems, in the present invention, the cathode is composed of a main body portion and a front end portion joined to the front end side thereof, and the main body portion is made of a refractory metal material not containing thorium, The tip portion is made of a refractory metal material containing an emitter (excluding thorium) and contained in the tip portion in a sealed space formed inside the body portion and / or the tip portion. A sintered body containing an emitter (excluding thorium) having a higher concentration than the emitter concentration is embedded, and the grain boundary density of tungsten at the tip portion: A (mm ⁻¹ ) and the firing at the tip portion. The product of the concentration gradient of the emitter from the part in contact with the body to the tip surface: B (mol / mm ⁴ ),
260 × 10 ⁻⁹ (mol / mm ⁵ ) ≦ A × B ≦ 670 × 10 ⁻⁹ (mol / mm ⁵ )
It is characterized by being in the range of
Further, the emitter concentration of the sintered body is 10% by weight to 80% by weight.

According to the present invention, a tip portion containing an emitter other than thorium is joined to a tip of a main body portion that does not contain thorium, and in the sealed space formed in the main body portion and / or the tip portion, Since a sintered body containing an emitter (excluding thorium) with a higher concentration than the emitter concentration contained in the tip is embedded, it was included in the tip when the discharge lamp was initially turned on. The emitter (excluding thorium) covers the tip portion to provide good lighting performance.
Depending on the lighting time, the emitter initially contained in the tip is consumed, but the emitter is diffused and supplied to the tip from the sintered body containing the high-concentration emitter inside the cathode. Thus, good lighting performance is stably maintained for a long time without depletion of the emitter.
Since this sintered body is embedded in the cathode, it is not directly exposed to the discharge arc, and it is suppressed from being heated by the arc. There is no such thing.
In addition, when the cathode is cooled after being turned on for a predetermined time and the cathode is cooled, the emitter diffused from the sintered body at the time of lighting stays in the tip portion. The lighting performance is made good.

Further, the grain boundary density of tungsten at the tip portion: A (mm ⁻¹ ) and the concentration gradient of the emitter from the portion in contact with the sintered body of the tip portion to the tip surface: B (mol / mm ⁴⁾ ) Product (A x B)
260 × 10 ⁻⁹ (mol / mm ⁵ ) ≦ A × B ≦ 670 × 10 ⁻⁹ (mol / mm ⁵ )
Therefore, a stable emitter can be supplied over a long period of time, and a discharge lamp with a long lamp life can be realized.

Overall view of a discharge lamp having a cathode structure according to the present invention Cathode structure diagram showing an embodiment of the present invention Partial enlarged view of FIG. Table 2 showing experimental results of the present invention Chart in Table 2 Other embodiments of the invention Manufacturing process diagram of cathode of the present invention

FIG. 1 shows the overall structure of a discharge lamp having a cathode structure according to the present invention. In a discharge lamp 1, a cathode 3 and an anode 4 are disposed inside an arc tube 2 so as to face each other.
As shown in FIG. 2, the cathode 3 includes a main body portion 31 and a distal end portion 32 joined to the distal end thereof.
The main body 31 is made of a refractory metal material such as tungsten or molybdenum that does not contain thorium.
The distal end portion 32 is joined to the distal end side of the main body portion 31, that is, the surface facing the anode 4 by an appropriate joining means such as solid phase joining or welding. The tip portion 32 is made of tungsten, and contains an emitter other than thorium in an appropriate amount (hereinafter, the emitter included in the tip portion is also referred to as a first emitter).
As the first emitter other than thorium, for example, lanthanum oxide (La ₂ O ₃ ), cerium oxide (CeO ₂ ), gadolinium oxide (Gd ₂ O ₃ ), samarium oxide (Sm ₂ O ₃ ), praseodymium oxide (Pr) ₆ O ₁₁ ), neodymium oxide (Nd ₂ O ₃ ), yttrium oxide (Y ₂ O ₃ ), or the like is used alone or in combination.

Here, the content of the first emitter is set to a low value, for example, 0.5 wt% to 5.0 wt%, and more desirably 0.5 wt% to 2.5 wt%. This first emitter is for ensuring startability when the lamp is initially turned on, and the concentration is set low so that the emitter is not excessively evaporated by exposure to the discharge arc. It is to do.
That is, when the content of the first emitter is less than 0.5% by weight, the emitter concentration necessary for electron emission cannot be ensured in the initial stage of lighting, and the lamp voltage increases and the fluctuation increases. In addition, if the content exceeds 5.0% by weight, the sintered body becomes brittle during the production of tungsten materials and the like, and breakage due to cracks in the sintering process and the swaging process occurs. Not only is it easy to make it, but even if it can be manufactured, when used at the tip, the evaporation of the emitter becomes noticeable and promotes blackening (white turbidity) of the valve, which is not preferable.
Furthermore, a grain stabilizer for suppressing grain growth due to recrystallization of tungsten grains may be added to the tip 32. Specifically, the grain stabilizer is, for example, zirconium oxide (ZrO ₂ ).

As shown in FIG. 2, a sealed space 33 is formed inside the cathode 3, and an emitter other than thorium (hereinafter referred to as an emitter contained in the sintered body 34) is formed in the sealed space 33. A sintered body 34 containing 2 emitters) is embedded.
The second emitter contained in the sintered body 34 is made of, for example, lanthanum oxide, cerium oxide, gadolinium oxide, samarium oxide, oxidized material, or the like, similar to the one contained in the tip portion 32 described above. Sintered materials containing praseodymium, neodymium oxide, yttrium oxide, or a combination thereof are used.
And the density | concentration of the 2nd emitter contained in this sintered compact 34 is set to the density | concentration higher than the density | concentration of the 1st emitter contained in the said front-end | tip part 32, The density | concentration is 10 weight%, for example ~ 80% by weight.

  If the concentration of the second emitter is less than 10% by weight, it becomes difficult to secure the amount of emitter supplied to the cathode tip 32 due to the size of the sintered body 34 that can be stored inside the cathode 3. . Further, if it exceeds 80% by weight, the proportion of the constituent material such as tungsten in the sintered body 34 is reduced, and the product due to reduction of the oxide is reduced. It will shorten the life.

  In the cathode structure having the above-described configuration, as a result of intensive studies by the inventors, the transfer rate of the emitter diffused from the sintered body 34 containing a high-concentration emitter to the tip surface of the tip portion 32 ( In other words, the amount of emitter diffusion or the amount of emitter supply) is the grain boundary density of the tungsten grains at the tip, and the concentration gradient of the emitter from the portion in contact with the sintered body at the tip to the tip surface. Has found a close relationship.

According to the knowledge obtained by the present inventors regarding the diffusion of the emitter from the sintered body to the tip surface of the tip in such a cathode structure, the diffusion amount of the emitter and the grain boundary density of tungsten which is the structure of the tip are In relation, the amount of emitter diffusion tends to increase in proportion to the increase in grain boundary density. Therefore, if the grain boundary density is too high, the diffusion amount becomes excessive, and if it is too low, the diffusion amount becomes excessively small.
In other words, by setting the grain boundary density in an appropriate range, it is possible to control the evaporation state of the emitter from the tip of the cathode, prevent the exhaustion of the emitter, and maintain an appropriate radiation state for a long time.
In the present invention, the tungsten particles constituting the tip of the cathode have a grain boundary density (A) in the range of 120 to 430 (mm ⁻¹ ).
The grain boundary density of the tungsten particles here is the grain boundary density of the tungsten grains inside the tip of the cathode.

On the other hand, the relationship between the amount of diffusion of the emitter and the concentration gradient of the emitter in the tip portion tends to increase the amount of diffusion of the emitter in proportion to the increase in concentration gradient.
Therefore, if the concentration gradient is too large, the diffusion amount becomes excessive, and if it is too small, the diffusion amount becomes excessive.
A method for calculating the concentration gradient will be described with reference to FIG.
The emitter concentration at the portion 32b in contact with the sintered body 34 at the tip 32 is N ₀ .
The emitter concentration (B) contained in the sintered body 34 is in the range of 10 wt% ≦ B ≦ 80 wt%, and the value of the emitter concentration N ₀ when the emitter concentration (B) of the sintered body 34 is 30 wt%. Is obtained by solving the diffusion equation from the amount of diffusion into tungsten obtained from the analysis result, N ₀ = 3.76 × 10 ⁻⁹ (mol / mm ³ ).

At this time, the emitter concentration N at the distal end surface 32b of the distal end portion 32 is substantially 0, and the concentration gradient is increased when the distance L from the distal end of the sintered body 34 to the distal end surface 32b of the distal end portion 32 is changed. (B) changes. Here, the concentration gradient in which the distance L is 1 to 6 mm is shown in Table 1 below.
<Table 1>

The concentration gradient shown in Table 1 was obtained by changing the distance from the tip of the sintered body to the tip surface of the cathode (tip portion). With this distance constant, the emitter content of the sintered body was changed from 10 wt%. Even if it is changed to 80 wt%, it can be obtained. Range of variation of _{N 0} at that time is ^{approximately, (1.25~10.03) × 10 -9 (} mol / mm 3).

As described above, since the emitter diffusion amount depends on the grain boundary density and the concentration gradient, (grain boundary density × concentration gradient) is used as the index.
A cathode having a grain boundary density (A) in the range of 120 to 430 (mm ⁻¹ ) and a concentration gradient (B) in the range of (0.63 to 3.8) × 10 ⁻⁹ (mol / mm ³ ), respectively. Was built into a lamp and its lamp life was confirmed. Here, the lamp life was evaluated by the time until the illuminance maintenance ratio reached 60% or the time until the voltage fluctuation reached the specified value of 1.2 V or more as an index indicating the occurrence of flicker.
Table 2 in FIG. 4 shows the results. In Table 2, the evaluation ○ indicates that the lamp life is 300 hours or more, and ◎ indicates that 400 hours or more.
FIG. 5 is a graph of this result.

As can be seen from FIG. 4 (Table 2) and FIG. 5 (graph), the value of (grain boundary density A) × (concentration gradient B) is 260 × 10 ^{−9 to} 670 × 10 ⁻⁹ (mol / mm ⁵ ), A good lamp life of 300 hours or more can be obtained.
More desirably, when it is in the range of 400 × 10 ^{−9 to} 560 × 10 ⁻⁹ (mol / mm ⁵ ), a better lamp life of 400 hours or more can be obtained.

An example of the dimensions of the cathode structure of the present invention is as follows.
Cathode outer diameter: φ12 mm, axial length: 21 mm
Dimension of tip part: axial length 2 mm, material example: lanthanum oxide (emitter), tungsten doped with zirconium oxide (tungsten particle coarsening inhibitor) Body part dimension: axial length 19 mm, material example: pure tungsten (Tungsten with an impurity concentration of less than 0.1% by weight)
Sintered body dimensions: φ2 mm, axial length: 6 mm, material example: cerium oxide, tungsten mixed at a mixing ratio of (W: CeO ₂ : ZrO ₂ = 1: 0.45: 0.18), After sintering, degreasing and pre-sintering at 1000 ° C. in hydrogen at a pressure press, the main sintering in vacuum is sintered at 1700-2000 ° C.

In the embodiment of FIG. 2, the sintered body 34 is embedded in the main body 31 of the cathode 3, but is not limited thereto.
FIG. 6 shows another embodiment, and FIG. 6 (A) is an example in which the sintered body 34 is embedded in a sealed space 33 formed across the main end portion 31 and the front end portion 32. FIG. 6B shows an example in which the sintered body 34 is embedded in a sealed space 33 formed in the tip portion 32.
In any of the examples including these examples, the distance between the front end of the sintered body 34 and the tip of the cathode 3 is preferably in the range of 1.0 mm to 6.0 mm.

Next, the manufacturing process of the cathode having the structure of FIG. 2 according to the present invention will be described with reference to FIG.
First, as shown in FIG. 7A, a hole 33a constituting the sealed space 33 is formed on the distal end side of the body member 31a constituting the body portion 31, and the sintered body 34 is inserted into the hole 33a. Next, the tip member 32 a constituting the tip portion 32 is brought into contact with the sintered body 34.
At this time, as shown in (B), the tip of the sintered body 34 protrudes from the surface of the main body 31 by a slight amount of about 0.5 mm.
The tip member 32a is pressed to compress the sintered body 34, and the tip member 32a and the main body member 31a are brought into contact with each other. At this time, since the sintered body 34 is sintered at a temperature lower than the sintering temperature of the main body portion 31 and the tip portion 32, the shrinkage allowance due to pressing is large, and the main body member 31a and the tip member 32a are brought into contact with each other. The sintered body 34 is in a state of being in contact with the tip member 32a.
In this state, the main body member 31a and the tip member 32a are joined by diffusion joining, resistance welding, or the like.
Next, as shown in (C), after joining the tip member 32a and the main body member 31a, the tip of the cathode 3 is cut. In this way, a final-shaped cathode as shown in (D) is obtained.

As described above, according to the present invention, in the discharge lamp in which an emitter other than thorium is added to the cathode, the emitter is contained at the tip portion joined to the main body portion. Assures startability and ensures lighting.
Then, since the sintered body hermetically embedded in the cathode contains the second emitter having a higher concentration than the first emitter at the tip, the second emitter diffuses as the lamp is turned on. Since it is supplied by moving to the tip side, there is no concern that the emitter will be depleted at the tip, and stable lighting is ensured by continuous emitter supply.
Further, the grain boundary density of tungsten at the tip portion: A (mm ⁻¹ ) and the concentration gradient of the emitter from the portion in contact with the sintered body of the tip portion to the tip surface: B (mol / mm ⁴⁾ ) Product (A × B) is in the range of 260 × 10 ⁻⁹ (mol / mm ⁵ ) ≦ A × B ≦ 670 × 10 ⁻⁹ (mol / mm ⁵ ). Is obtained.
Furthermore, since this sintered body is hermetically embedded in the cathode and is not directly exposed to the discharge arc, an emitter with a low vapor pressure other than thorium is excessively evaporated and depleted in a short time. There is nothing.

DESCRIPTION OF SYMBOLS 1 Discharge lamp 2 Light-emitting tube 3 Cathode 31 Body part 32 Tip part 33 Sealed space 34 Sintered body 4 Anode N ₀ Emitter density | concentration in the site | part of the front-end | tip part contact | abutted to a sintered compact N = 0)

Claims (2)

In the discharge lamp in which the cathode and the anode are arranged opposite to each other inside the arc tube,
The cathode comprises a main body part and a tip part joined to the tip side thereof,
The main body is composed of a refractory metal material not containing thorium,
The tip is composed of tungsten containing an emitter (excluding thorium),
A sealed space is formed inside the main body and / or the tip,
In the sealed space, a sintered body containing an emitter (excluding thorium) having a higher concentration than the emitter concentration contained in the tip is embedded,
Grain boundary density of tungsten at the tip portion: A (mm ⁻¹ ), and concentration gradient of emitter from the portion in contact with the sintered body at the tip portion to the tip surface: B (mol / mm ⁴ ) The discharge lamp is characterized in that the product (A × B) is in the following range.
260 × 10 ⁻⁹ (mol / mm ⁵ ) ≦ A × B ≦ 670 × 10 ⁻⁹ (mol / mm ⁵ ) The discharge lamp according to claim 1, wherein the sintered body has an emitter concentration of 10 wt% to 80 wt%.

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