JP2017111996A - Short arc type discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure capable of keeping an operating temperature in a tip of a cathode low and improving the service life of the cathode by suppressing the deformation of the tip in a short arc type discharge lamp.SOLUTION: A cathode 1 and an anode are arranged facing each other inside a luminous tube. The cathode 1 is composed of a body part 2 not containing an emitter material, and a tip part 3 joined to the body part 2 and containing thorium oxide. A second emitter material 5 having electron emission characteristics superior to thorium oxide is embedded inside the body part 2. The second emitter member 5 contains at least one of lanthanum oxide, cerium oxide, gadolinium oxide, samarium oxide, praseodymium oxide, and neodymium oxide.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a short arc type discharge lamp including an emitter for improving electron emission at a cathode, and particularly to a short arc type discharge lamp including thorium as an emitter. is there.

2. Description of the Related Art Conventionally, high-input and high-intensity short arc type discharge lamps are often used in which an emitter is contained in a cathode to enhance electron emission characteristics.
For example, Japanese Unexamined Patent Application Publication No. 2012-15008 (Patent Document 1) discloses a cathode for a short arc type discharge lamp containing thorium oxide as an emitter.

The tip of the cathode in such a short arc type discharge lamp is in a very high temperature state of about 3400 K due to ion collision during lighting.
Under such a high temperature, thorium evaporates violently from the tip of the cathode, so that thorium in the cathode is exhausted in a long time. In particular, from the viewpoint of thorium saving, when adopting a cathode structure in which thorium oxide is contained only at the cathode tip portion, the tendency of the thorium is limited because the amount of thorium retained is limited.
Due to such depletion of thorium oxide, there has been a problem that it becomes difficult to maintain a stable discharge state due to a decrease in electron emission characteristics of the cathode.

JP 2012-15008 A

  In view of the above-mentioned problems of the prior art, the present invention provides a short arc type discharge lamp in which a cathode and an anode are opposed to each other inside an arc tube, and at least a tip portion of the cathode contains thorium oxide. It is intended to provide a structure capable of suppressing the consumption of thorium oxide by suppressing the operating temperature of the cathode tip at the time, and suppressing the deformation of the tip to improve its life.

In order to solve the above problems, in the present invention, the cathode contains thorium oxide at least at a part on the tip side, and the cathode has a second electron emission characteristic superior to thorium oxide. Emitter material is embedded.
The second emitter material 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 ) and at least one of neodymium oxide (Nd ₂ O ₃ ).
The cathode includes a main body portion not including an emitter material and a tip portion containing thorium oxide joined to the main body portion, and the second emitter material includes the main body portion and / or the tip end. It is embedded in the department.

According to the present invention, since the second emitter material having electron emission characteristics superior to that of thorium oxide is embedded in the cathode containing thorium oxide on the tip side, the tip portion is oxidized by lighting. Thorium is reduced and supplied as thorium to the tip surface, and the emitter is also diffused and supplied from the second emitter material to the tip surface of the cathode.
In this way, the cathode front end surface is formed so that the monoatomic layer of thorium by thorium oxide and the monoatomic layer of the emitter of the second emitter material coexist, and the electron emission characteristics are improved as compared with the case of using only thorium. At the same time, the operating temperature of the cathode tip surface can be kept low.
This decrease in operating temperature can suppress thorium consumption, suppress deformation of the cathode tip, and improve the life of the cathode.

Sectional drawing of the cathode structure of the discharge lamp of this invention. FIG. Comparison of electron emission characteristics of two types of emitters.

FIG. 1 shows a cathode structure used in a short arc type discharge lamp according to the present invention. A cathode 1 includes a main body portion 2 made of pure tungsten, and triated tungsten (so-called thorium oxide (ThO ₂ ) contained in tungsten). , Tritan), and the main body 2 and the tip 3 are joined by means such as diffusion bonding.
A sealed space 4 is formed inside the cathode 1, and a second emitter material 5 having an electron emission characteristic superior to that of thorium oxide is enclosed in the sealed space 4.
In this embodiment, the sealed space 4 is formed by forming a bottomed hole that opens at the upper end of the main body 2 and joining the front end 3 to the main body 2.

The second emitter material 5 enclosed in the sealed space 4 includes lanthanum oxide (La ₂ O ₃ ), cerium oxide (CeO ₂ ), gadolinium oxide (Gd ₂ O ₃ ), and samarium oxide (Sm ₂ O _3). ), Praseodymium oxide (Pr ₆ O ₁₁ ), neodymium oxide (Nd ₂ O ₃ ), etc., all of which are materials that have better electron emission characteristics than thorium oxide contained in the tip 3.
One or two or more of these emitter materials are enclosed in the sealed space 4.
The second emitter material 5 can be formed, for example, as a sintered body of tungsten and one or more of the oxides and enclosed in the sealed space 4.

In addition, as a whole structure of the cathode 1, a joining structure of a pure tungsten main body 2 and a tritium tungsten tip 3 is shown. However, the main body 2 is also made of triated tungsten, and thorium oxide is formed on the entire cathode 1. It may have a structure containing
Furthermore, although the sealed space 4 formed in the cathode 1 has been shown to be formed in the main body 2, it is not limited thereto, and may be formed in the tip 3, or It may be formed across the main body 2 and the tip 3.
That is, what is necessary is just to form in the inside of a main-body part and / or a front-end | tip part.
Furthermore, it is also possible to form a bottomed hole that opens on the rear end side of the cathode (main body part) and insert and fix the cathode core wire into the bottomed hole.

The electron emission characteristics of the cathode can be compared by the relationship between the cathode tip temperature and the emission electron current density. That is, the lower the cathode tip temperature for obtaining the same emission electron current density, the better the electron emission characteristics.
FIG. 3 shows a comparative view of electron emission characteristics of emitters Th (thorium) and Ce (cerium). As shown in the figure, Ce requires a lower temperature than Th to obtain an equivalent electron current density. That is, by using Ce (cerium) as an emitter, a desired electron current density can be achieved at a temperature lower than that of thorium.
In the present invention, the cathode tip portion contains thorium, and the cathode is provided with a second emitter material (for example, a rare earth emitter material) having electron emission characteristics superior to that of thorium.

As shown in FIG. 2, at the time of lighting, thorium oxide (ThO ₂ ) contained in the tip portion 3 of the cathode 1 is reduced to generate thorium (Th), which is transferred to the cathode tip surface by a diffusion action and is transferred to the tip surface. Then, a monoatomic layer (Th on W) of thorium is formed.
At the same time, cerium oxide (CeO ₂ ), which is a second emitter material with excellent electron emission characteristics, is reduced to produce cerium (Ce), which is diffused and transported within the tip portion 3, and the cerium single substance on the tip surface. An atomic layer (Ce on W) is formed.
As described above, the cerium, which is the second emitter material having high electron emission characteristics, is supplied to the tip surface of the cathode, so that the operating temperature of the cathode becomes lower than that of the case of using only thorium.
Therefore, while cerium is acting as an emitter, the temperature at the tip of the electrode is kept low, so that thorium consumption is suppressed during that time. Also, since the thorium that has been preserved starts to operate mainly when cerium begins to be depleted, a stable discharge state can be obtained for a longer time.

One numerical example of the cathode structure based on the embodiment of FIGS. 1 and 2 is as follows.
<Whole cathode>
Total length: 17mm
Body diameter: φ10mm
<Tip>
Material: 2 wt% tria (ThO ₂ ) doped tungsten, density 18.8 g / cm ³
Tip diameter: φ0.6mm
Tip taper angle: 40 °
Total length of tip: 3 mm
<Main body>
Material: Potassium (K) doped tungsten, density 19.2 g / cm ³ ,
Total length of main body: 14mm
<Second emitter material>
Material: A sintered body obtained by mixing, molding, and sintering cerium oxide (CeO ₂ ) and tungsten (W) at a weight ratio of 1: 2, density: 9.5 g / cm ³
Dimensions: φ1.4mm, axial length 2mm,
<Sealed space>
Formation area: The distance from the cathode tip is 3 mm to 5 mm. Dimensions: φ1.4 mm, axial length 2 mm
<Lamp configuration>
Lamp: 4kW, Xe short arc lamp (light source for digital projector)
Electrical characteristics: 115A-35V-4kW

As described above, according to the present invention, the second emitter material having an electron emission characteristic higher than that of thorium oxide is embedded in the cathode containing at least the thorium oxide at the tip portion, so that the electron emission characteristics are different. By using the emitter of the seed, the cathode operating temperature can be kept low by the second emitter material functioning and being supplied to the cathode tip surface, and thorium consumption can be suppressed.
The thorium consumption suppression effect continues until the second emitter is consumed, and then thorium functions as an emitter, so that the depletion period can be delayed, and for a longer time. There is an effect that a stable discharge state can be obtained.
In addition, since the operating temperature is kept low, there is an advantage that the thermal stability of the tip of the cathode is suppressed and the stability of the arc is achieved.

1 Cathode 2 Body 3 Tip (containing thorium oxide)
4 Sealed space 5 Second emitter material

Claims (3)

In the short arc type short arc type discharge lamp in which the cathode and the anode are arranged opposite to each other inside the arc tube,
A short arc type discharge characterized in that thorium oxide is contained at least at the tip of the cathode, and a second emitter material having electron emission characteristics superior to that of thorium oxide is embedded in the cathode. lamp. The second emitter material 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 ). _2. The short arc discharge lamp according to claim 1, comprising at least one of neodymium oxide (Nd ₂ O ₃ ). The cathode comprises a main body portion that does not include an emitter material, and a tip portion that contains thorium oxide bonded to the main body portion,
2. The short arc discharge lamp according to claim 1, wherein the second emitter material is embedded in the main body part and / or the tip part. 3.

Images