JP5672569B2 - Discharge lamp - Google Patents

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.

Generally, in a discharge lamp with high input and high brightness, an emitter is added to the cathode to facilitate electron emission. For example, Japanese Unexamined Patent Application Publication No. 2012-15008 (Patent Document 1) discloses a cathode for a discharge lamp containing thorium oxide as an emitter.
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.

As an alternative to the thorium, materials using rare earth elements and their compounds have been proposed. Rare earth elements are materials that have a low work function (generally indicating the amount of energy required when electrons are emitted from the material surface to the outside) and are excellent in electron emission, and are expected as substitutes for thorium.
Japanese Patent Laid-Open No. 2005-519435 (Patent Document 2) additionally discloses lanthanum oxide (La ₂ O ₃ ), hafnium oxide (HfO ₂ ), zirconium oxide (ZrO ₂ ) and the like as an emitter to tungsten which is a cathode material. Disclosed is a discharge lamp.

However, since rare earth oxides such as lanthanum oxide (La ₂ O ₃ ) have a higher vapor pressure than thorium oxide (ThO ₂ ), they are relatively easy to evaporate. 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, there is a problem that the electron emission function at the cathode is lost, 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. For this reason, in discharge lamps using emitter materials other than thorium, there are still problems such as unstable lighting at an early stage. In particular, in a discharge lamp with a high input of 1 kW or more, it is remarkable that the vapor of rare earth elements or barium-based substances leads the discharge lamp to unstable lighting.

JP 2012-15008 A JP-A-2005-519435

  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, An object of the present invention is to prevent the exhaustion, maintain the electron emission function for a long time, extend the life of the flicker of the lamp, and provide a structure excellent in lighting startability at the initial lighting.

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.
The emitter is 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 ), oxide One of neodymium (Nd ₂ O ₃ ) and hafnium oxide (HfO ₂ ), or a combination thereof.
Further, the emitter concentration (CF) at the tip portion is 0.5 wt% ≦ CF ≦ 5 wt%, and the emitter concentration (CB) of the sintered body embedded in the sealed space is 10 wt% ≦ CB ≦ 80 wt%. And CF <CB.
The tip of the sintered body is in contact with the tip.

In the sealed space, a reducing agent for reducing the emitter included in the sintered body is enclosed together with the sintered body.
The reducing agent is foil-shaped and is wound around the sintered body.
Further, the reducing agent is in a powder state and is dispersed and contained in the sintered body.
Further, the reducing agent is arranged along the rear end of the sintered body.
The reducing agent is any one of titanium (Ti), tantalum (Ta), vanadium (V), and niobium (Nb).

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 overheated 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.

1 is an overall view of a discharge lamp having a cathode structure according to the present invention. The cathode structure figure showing the example of the present invention. The manufacturing process figure of the cathode of this invention. The cathode structure figure showing other some examples.

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 contains an appropriate amount of emitter other than thorium (hereinafter, the emitter contained 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 ), hafnium oxide (HfO ₂ ), or the like is used alone or in combination.

Here, the content of the first emitter is set low, for example, 0.5 wt% to 5.0 wt%. This first emitter is for ensuring startability when the lamp is initially turned on, and the concentration is set low to prevent the emitter from being excessively evaporated by being exposed to the discharge arc. Because.
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.

As shown in FIG. 2, a sealed space 33 is formed inside the cathode 3, and a sintered body 34 containing an emitter other than thorium is embedded in the sealed space 33.
In FIG. 2A, the sealed space 33 is formed on the main body 31 side, and the sintered body 34 is substantially embedded in the main body 31.
In FIG. 2B, the sealed space 33 is formed so as to straddle the main body portion 31 and the tip portion 32, and the sintered body 34 is embedded so as to straddle the main body portion 31 and the tip portion 32. .
In FIG. 2C, the sealed space 33 is formed on the distal end portion 32 side, and the sintered body 34 is substantially embedded in the distal end portion 32.
Of course, the dimensions of the tip 32, particularly the thickness, will differ depending on which of these forms, and which one to select depends on the ease of manufacture and the tip 32. It is appropriately selected in consideration of the cost depending on the thickness or the total manufacturing cost.

The sintered body 34 includes an emitter other than thorium (hereinafter, the emitter contained in the sintered body 34 is also referred to as a second emitter). Similarly, lanthanum oxide, cerium oxide, gadolinium oxide, samarium oxide, praseodymium oxide, neodymium oxide, or a combination of hafnium oxide mixed with a constituent material such as tungsten, and sintered 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.

Since the second emitter contained in the sintered body 34 is embedded in the cathode 3, it is not directly exposed to the discharge arc and is not heated more than necessary, so that it excessively evaporates. There is nothing. Further, the sintered body 34 is appropriately heated as the lamp is turned on, and the second emitter in the sintered body 34 is moved and supplied to the tip 32 side by concentration diffusion. Thereby, the emitter is not depleted at the tip portion 32, and stable lighting performance is maintained.
Therefore, it is desirable that the sintered body 34 is in a state in which the end surface on the cathode tip side is in contact with the tip portion 32. By doing so, the second emitter contained in the sintered body 34 is in contact with the tip 32 while the lamp is lit, so that the emitter moves smoothly and quickly to the tip 32 due to grain boundary diffusion. Will be supplied reliably.

  The first emitter and the second emitter described above may be made of the same material or different materials. For example, the first emitter and the second emitter are both made of the same material as lanthanum oxide, the first emitter is made of lanthanum oxide and zirconium oxide, and the second emitter is made of a material different from cerium oxide. Is optional.

  The function and operation of the tip 32 and the sintered body 34 constituting the cathode 3 of the present invention will be described. The tip 32 is provided with a diffusion path for transporting the emitter to the tip surface that emits electrons. At the time of initial lighting, the first emitter contained in the tip 32 is transported to the tip surface to emit electrons. A reliable initial lighting is performed. The first emitter originally included in the tip portion 32 is consumed by this lighting, but the second emitter in the sintered body 34 embedded in the cathode 3 is consumed by the tip portion 32 until the emitter is depleted. By being supplied to the tip surface through the diffusion path, emitter depletion at the tip surface does not occur.

  As described above, the main body 31 is made of a refractory metal such as tungsten that does not contain thorium, but it does not exclude the inclusion of an emitter other than thorium. In that case, since a high-concentration sintered body 34 is present, there may be no particular advantage in including an emitter other than thorium in the main body 31 in terms of supplying the emitter to the tip 32. Since the main body 31 and the tip 32 are made of the same material, there are other advantages such as easy joining of the two.

An example of the dimensions of the cathode structure of the present invention is as follows.
Cathode outer diameter: φ15 mm, axial length: 60 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 58 mm, material example: zirconium oxide The size of sintered tungsten doped with: φ2 mm, axial length: 5 mm, material example: cerium oxide, tungsten mixed, molded and sintered at a weight ratio of 1: 2.

Next, the manufacturing process of the cathode according to the present invention will be described with reference to FIG.
The sintered body 34 embedded in the sealed space 33 inside the cathode 3 is mixed at a mixing ratio of emitter (CeO ₂ ) and tungsten (W) of 1: 2, and a binder (stearic acid) is added. Then, molding is performed by a pressure press machine. Then, after degreasing and preliminary sintering in hydrogen at a temperature of 1000 ° C., main sintering in vacuum is performed in a tungsten furnace at 1700 to 2000 ° C., preferably 1800 to 1900 ° C. for 1 hour. That ’s it.
The tip 32 of the cathode is La ₂ O ₃ and ZrO ₂ doped tungsten, and the main body 31 is ZrO ₂ doped tungsten. Both are sintered in a vacuum at a temperature of 2300 ° C to 2500 ° C. Thus, when tungsten containing the emitter is sintered at a higher temperature (for example, 3000 ° C.), the emitter is evaporated and disappears, which is not preferable.
In the case where the main body portion 31 does not contain an emitter, sintering can be performed at a higher temperature, for example, 2700 ° C. to 3000 ° C.

First, as shown in FIG. 3 (A), 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 FIG. 3B, 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.
As shown in FIG. 3C, 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, spot welding, or the like.
Next, after joining the tip member 32a and the main body member 31a, the tip of the cathode 3 is cut.
As a result, as shown in FIG. 3D, a final shape of the cathode 3 is obtained in which the tip 32 is joined to the tip of the main body 31 and the sintered body 34 is hermetically embedded in the sealed space 33 inside. It is done.

FIG. 4 shows a plurality of other embodiments. In these embodiments, the reducing agent 5 for promoting the reduction reaction of the emitter is enclosed in the sealed space 33 together with the sintered body 34. .
FIG. 4A shows a reducing agent foil 51 wound around a sintered body 34 and enclosed in a sealed space 33. Specifically, a Ta foil having a thickness of 5 to 40 μm is wound around the sintered body 34.
FIG. 4B shows a case where a powder of a reducing agent, for example, Ta powder 52 having a particle diameter of 1 to 10 μm is mixed in the sintered body 34, and the tungsten powder and Ta powder, which are sintered body constituting materials, Are mixed and sintered.
FIG. 4C shows a case where a reducing agent powder 53 such as Ta powder is disposed below the sintered body 34 in the sealed space 33.
Other than these, the reducing agent is encapsulated in such a manner that a reducing agent paste is applied to the outer peripheral surface of the sintered body 34.

The reducing agent used here is preferably titanium (Ti), tantalum (Ta), vanadium (V), or niobium (Nb). The amount of encapsulation is 1 wt% to 30 wt% with respect to the total amount of second emitters included in the sintered body 34.
Carbon (C) is also considered as a reducing agent, but carbon reacts with tungsten oxide produced by the reaction between the emitter and tungsten (W) to produce CO, and this CO diffuses from the sintered body 34. Then, it reaches the inside of the tip 32, where it is decomposed into C and O to be dissolved and diffused to the cathode tip. Here, it is finally released into the discharge vessel as O2 or CO. And when they reach the anode, tungsten oxide and tungsten carbide are generated, which causes a disadvantage that the discharge vessel is blackened and the anode is deformed, which is not preferable.
Therefore, it is preferable to use Ti, Ta, V, Nb, etc. other than carbon (C).

  Although the cathode structure of the present invention is applied to a short arc type discharge lamp such as a mercury lamp or a xenon lamp in FIG. 1, it can also be applied to a long arc type discharge lamp.

As described above, in the present invention, in the discharge lamp in which an emitter other than thorium is added to the cathode, the emitter is contained in the tip portion joined to the main body portion. Secure start-up ensures reliable 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.
Since this sintered body is hermetically embedded in the cathode and is not directly exposed to the discharge arc, emitters with low vapor pressures other than thorium may be excessively evaporated and depleted in a short time. Absent.
Moreover, since the reducing agent is sealed in the sealed space, the reduction reaction of the emitter is promoted, and the supply of the emitter to the tip portion is not delayed.

DESCRIPTION OF SYMBOLS 1 Discharge lamp 2 Arc tube 3 Cathode 31 Body part 32 Tip part 4 Anode 5 Reducing agent 51 Foil-like reducing agent 52 Powdery reducing agent 53 Powdery reducing agent

Claims (9)

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 portion and a tip portion joined to the tip surface thereof,
The main body is composed of a refractory metal material not containing thorium,
The tip is composed of a refractory metal material containing an emitter (excluding thorium),
A sintered body containing an emitter (excluding thorium) having a higher concentration than the emitter concentration contained in the tip is embedded in a sealed space formed inside the main body and / or the tip. Yes,
A discharge lamp characterized by that.
The emitter includes 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 ( _2. The discharge lamp according to claim 1, wherein the discharge lamp is one of Nd ₂ O ₃ ), hafnium oxide (HfO ₂ ), or a combination thereof. The emitter concentration (CF) at the tip is 0.5 wt% ≦ CF ≦ 5 wt%,
The emitter concentration (CB) of the sintered body embedded in the sealed space is 10 wt% ≦ CB ≦ 80 wt%, and CF <CB.
The discharge lamp according to claim 1.   The discharge lamp according to claim 1, wherein a tip of the sintered body is in contact with the tip.   2. The discharge lamp according to claim 1, wherein a reducing agent for reducing an emitter contained in the sintered body is sealed together with the sintered body in the sealed space.   The discharge lamp according to claim 5, wherein the reducing agent has a foil shape and is wound around the sintered body.   6. The cathode for a discharge lamp according to claim 5, wherein the reducing agent is in a powder state and is dispersed and contained in the sintered body.   The discharge lamp according to claim 5, wherein the reducing agent is disposed along a rear end of the sintered body. 6. The discharge lamp according to claim 5, wherein the reducing agent is any one of titanium (Ti), tantalum (Ta), vanadium (V), and niobium (Nb).

Images